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Title: Specifications for street roadway pavements: with instructions to inspectors on street paving work
Author: Whinery, Samuel
Language: English
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ROADWAY PAVEMENTS ***
SPECIFICATIONS FOR
STREET ROADWAY PAVEMENTS
McGraw-Hill Book Company
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SPECIFICATIONS FOR STREET ROADWAY PAVEMENTS
WITH INSTRUCTIONS TO
INSPECTORS ON STREET PAVING WORK
BY
S. WHINERY
MEMBER AMERICAN SOCIETY OF CIVIL ENGINEERS
SECOND EDITION
REVISED, ENLARGED AND ENTIRELY RESET
McGRAW-HILL BOOK COMPANY
239 WEST 39TH STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E. C.
1913
COPYRIGHT, 1913, BY THE
MCGRAW-HILL BOOK COMPANY
THE·MAPLE·PRESS·YORK·PA
PREFACE TO SECOND EDITION
In offering to the public a new edition of “Specifications for Street
Roadway Pavements” the author has taken advantage of the opportunity to
revise and expand somewhat the matter in the original edition and to add
thereto Instructions for Inspectors on pavement work.
Since the publication of the original pamphlet in 1907 no little advance
has been made in the design and construction of street pavements and the
framing of specifications for that work. Aside from the personal study
and efforts of individual engineers, the Association for Standardizing
Paving Specifications, organized in the latter part of 1909, has held
four important conventions, devoted to the improvement and
standardization of specifications for street pavements, and its able
standing Committees have devoted much time and thought to the subject.
The American Society of Municipal Improvements has also devoted much
attention to the subject and has adopted standard specifications for
most of the common kinds of pavement. Other organizations have been
working along the same lines.
Under these circumstances it might be thought that there is no longer
any pressing need for the continuance of individual efforts in this
field, and it has been with some hesitation that the author has returned
to it. Without venturing to criticise the work done by these public
organizations it has seemed to the author that there is yet room for
individual work in this field, if for no other reason than that there
still remain quite divergent views not only as to the substance, but as
to the form, scope and phraseology of specifications, and contributions
based upon some knowledge and experience in street pavement may not be
without value in reaching final conclusions.
As might be expected experience and observation during the past five
years have, in a number of particulars, modified the author’s opinions
and shown where the original specifications offered might be improved
and enlarged, so that while, in the main, those now offered follow the
original text, the reader will find not a few changes. There has also
been added specifications for two comparatively new kinds of roadway
pavement that have merited attention, and for concrete sidewalk and
concrete combined curb and gutter.
So far as the author is aware there has not been printed, in America at
least, any complete and comprehensive code of instructions for pavement
inspectors, though there appears to be a demand, as there certainly is a
need, for something of the kind.
Having been asked about a year since to prepare such a set of
instructions for the use of one American city, the author has rewritten
parts of them in a more general form, and they are printed (with the
permission of the engineer for whom they were written) as Part II of
this edition. While they would need some revision and modification to
meet the conditions and special specification provisions in any
particular city, it is thought they may be useful in at least suggesting
the points to be covered.
CONTENTS
PART I
SPECIFICATIONS
=Introductory= PAGE
Value of general specifications 1
Theory of specifications 1
Street paving work 2
Specifications should be fair and just to contractor 4
Relations of contractor to municipality 6
Advertisements for proposals 7
Instructions to bidders 9
Relation between specifications and contract 9
Specifications 9
Preparation of specifications 9
Engineer as arbiter 11
Itemized unit prices 12
SPECIFICATIONS
=General= PAGE SECTION
General description of work 13
Definitions 14 1
Changes in plans and specifications 15 3
Quality of material and work 15 4
Inspection 15 5
Injury to persons and property 16 6
Sanitary and public convenience 16 7–9
Disorderly employees 17 10
Order and progress of work 17 11
Pavement datum 18 12
City monuments and stakes 18 13
Old and new material 18 14–15
Adjusting street structures 18 16
Connection with existing pavements 19 18
Measurements and computations 20 21
Incidental and extra work 20 23–24
Guaranty 21 25
Preparing the sub-grade 22 26
=Foundations=
Concrete foundations—Portland cement 24 28–29
Sand 26 30
Stone 26 31
Care of materials 27 33
Ratios 27 34
Mixing Concrete 28 35
Placing concrete 29 36
Setting of concrete 29 37
Foundation of old paving stone 30 39
Foundation of broken stone 31 40–41
=Sheet asphalt pavement=
General note 33
Crude and refined asphalts 36 43–46
Tempering agent 38 47
Sand 38 48
Pulverized stone 39 49
Asphaltic paving cement 39 50
Composition, surface mixture 40 51
Base course 42 52–54
Laying asphalt pavement 42 55–58
Plant 45 59
=Asphalt block pavement=
Sub-grade and foundation 46 60–61
Asphalt block 46 62
Composition and quality 46 63–64
Laying blocks 48 66
=Granite block pavement=
Granite blocks 50 71
Sand cushion 51 72
Setting blocks 51 73–74
Filling joints 52 75
Bridge and crossing stone 55 79
=Brick pavement=
Sub-grade and foundation 56 80–81
Paving brick 56 82–84
Delivering brick 58 85
Sand cushion 58 86
Setting the brick 59 87–89
Filling the joints 60 90
=Wood-block pavement=
Sub-grade and foundation 62 92–93
Wood-blocks 63 94
Creosote oil 65 95
Preservative treatment 65 96
Laying wood-blocks 66 97
Filling joints 68 98
Inspection 68 99
Expansion joints 68 101
=Bituminous concrete pavement=
General note 69
Sub-grade and foundation 70 103–109
Bituminous concrete 71 110
Mixing and laying 73 111–112
=Hydraulic concrete pavement=
Sub-grade and foundation 73 113
Bottom course 74 115
Top, or surface, course 74 116–120
Expansion joints 76 121
Bituminous surface 77 122
=Experimental or Untried Pavements= 78 123–126
=Concrete Curb and Gutter=
General 80 127
Excavation and drainage 81 128–129
Concrete 81 130
Weather 82 132
Expansion joints 82 133
Circular corners 83 134
Steel protection 83 135
Finishing, forms, etc. 83 136–138
Payment for 84 139
=Concrete Sidewalks=
General note 84
General dimensions 84 140
Grading 85 141
Drainage 85 142–143
Bottom course 86 144
Surface course 86 145
Expansion joints 87 147
Weather 88 149
Regrading 88 150
Repairing defects 88 151
Measurement and payment 88 152
PART II
INSTRUCTIONS TO INSPECTORS
Introductory note 91
General remarks, inspection and inspectors 91
General instructions 94 1–13
Sub-foundation work general 96 14
curbing 97 15
rough grading 98 16
fine grading 98 17
incidental work 98 18
concrete foundation 98 19
quality of materials 98 20
storing materials 99 21
proportioning 99 22
mixing concrete 100 23
placing concrete 100 24–25
Old paving stone foundation 101 26
Broken stone foundation 101 27
Sheet asphalt pavement 101 28
inspecting at paving plant 102 29–30
sand 102 31–33
refined asphalt and flux 103 34–36
asphaltic cement 103 37
ratio, sand and cement 104 38
mixing 104 39
records 104 40
Inspecting on the street 105 41–42
temperature of mixture 105 43
preparing street surface 105 44
laying binder-course 106 45
laying surface-course 106 46–50
Asphalt block pavement 107 51–52
Granite block pavement 108 53
blocks 108 54
sand cushion 108 55
setting the block 108 56
ramming the blocks 109 57
filling joints 110 58
Brick pavement 110
inspecting the brick 110 60
sand cushion 111 61
setting brick 111 62
rolling 111 63
filling the joints 112 64–65
Wood-block pavement 112
inspection of blocks 112 67
mortar bed 112 68
setting blocks 113 69
filling the joints 113 70
Bituminous concrete pavement 113 71–72
Hydraulic concrete pavement 113 73
foundation 113 74
surface-course 114 75–77
expansion joints 114 78
care of work 114 79
Concrete combined curb and gutter 114
concrete 115 81
removing forms 115 82
corner protection 115 83
patching 116 84
Hydraulic concrete sidewalk 116
materials 116 86
drainage 116 87
two-course work 116 88
finishing surface 116 89–90
PART I
SPECIFICATIONS FOR STREET ROADWAY PAVEMENTS
INTRODUCTORY
In addition to their value as memoranda and aids in preparing
specifications for a particular project, carefully prepared general
specifications, embodying the latest approved practice, sometimes supply
the most useful and acceptable brief treatises upon any particular
branch of engineering work. It has been partly with this thought in mind
that the following set of specifications for standard street pavements
has been prepared and is now offered to city engineers and municipal
authorities.
To widen their range and increase their usefulness, copious foot notes
have been added, referring to alternative requirements and methods of
construction, and giving some of the reasons for the preference or
adoption of the construction called for in the specifications. It is
recognized that in a good many matters of detail embraced in these
specifications there is difference of opinion among able engineers, many
of whom are at least as competent as the writer to determine what is
best. They are not offered in a dogmatic spirit, or with the hope that
all the provisions found therein will be accepted. If they shall be of
some assistance in bringing about correct standards for such
specifications, their preparation will have been justified.
Theoretically, three general classes of engineering specifications may
be noted. In the first, the aim of the engineer is to specify the end or
result that it is desired to secure, leaving the contractor free to
originate and follow the methods by which these results are to be
attained. In the second the engineer aims to secure the desired end by
specifying in detail the materials and the methods which in his opinion
will accomplish the purpose, he himself assuming responsibility for the
results. Either of these two classes of specifications is permissible,
and the engineer may choose the one which in his opinion seems best
adapted to the character of the work to be done, and the conditions
under which it must be prosecuted.
In the third class of specifications, met with more frequently than they
should be, the engineer undertakes to prescribe not only the character
of the materials to be used and the methods to be pursued, but also the
results to be attained. The position thus assumed is illogical, and
often unreasonable, and may lead to complications between the engineer
and the contractor. If a contractor be required to turn out a product
which shall conform to certain standards, he may properly be given much,
if not full latitude, as to how the stipulated results shall be secured,
and may be held fully responsible for the outcome; if on the other hand
the engineer chooses to specify with more or less minuteness the
character of the materials to be used and the methods of construction to
be followed, and enforces compliance therewith, it seems fair and just
that he should assume responsibility for the results produced, and
therefore unfair to hold the contractor to responsibility for
consequences arising from the use of materials and methods which he was
allowed no choice or latitude in selecting.
In street paving work, of well-known and standard character, the second
class of specifications seems preferable for a number of reasons, the
leading one being that the time required to develop the good or bad
quality of the work must usually extend over a considerable number of
years, and the conditions to which the pavement may be subjected in the
meantime are likely to vary so widely that it may be very difficult, if
not impossible, to prescribe a satisfactory standard of service and
endurance. Disputes are therefore liable to arise between the
municipality and the contractor as to the latter’s liability, or
conditions may make it difficult or impossible to hold the contractor to
strict account for that liability.
It is believed that in the present state of the art it is entirely
practicable to so frame specifications for the materials to be used and
the methods to be followed in the construction of standard street
pavements, and to so enforce compliance therewith, that the engineer and
the municipality may safely assume responsibility for the quality of the
work produced. While it may be true that local conditions sometimes make
it very difficult to enforce compliance with specifications, the same
conditions are likely to make it at least equally difficult to secure
effective responsibility on the part of the contractor for any
long-period guarantee of the work done by him; and the contractor who
negligently or purposely violates the specifications during construction
is not likely to be more faithful or scrupulous in living up to any
guarantees he may make with regard to the future, even where the terms
and conditions of such guarantees may be clearly defined and
indisputable. The writer has discussed the subject of time guarantees as
applied to street pavements pretty fully in his book, “Municipal Public
Works,” and the above brief statement seems all that is necessary here.
In conformity with this view of the matter, the following specifications
aim to set out as definitely and clearly as practicable the requirements
for the construction of good pavements of the several standard kinds,
and it is assumed that the engineer will be able to, and will enforce
them.
It is, however, not infrequently the case that the engineer will be
called upon to prepare specifications for new, or patented, or
proprietary pavements advocated by their promoters, the value or
usefulness of which have not been sufficiently established by
experience, and for which the data for detailed, definite specifications
are not yet available.
In such cases the wisest course to follow is to confine the precise
specifications to the general or standard parts of the work, while
stipulating only the _results to be attained_ with regard to those
features of the work that are proprietary or questionable, thus placing
upon the promoter or his contractors full responsibility for such
results as are promised or guaranteed. This applies to new or
comparatively untried materials or processes, whether patented or not.
A proposed form of general specifications to cover such cases is offered
herein.
It is usually unwise to adopt or to incorporate in the municipal
specifications those prepared or offered by the promoter or patentee,
which are often brief, incomplete, and indefinite, and are sometimes
carefully, and even cunningly, drawn to evade final responsibility.
No attempt has been made to submit specifications for proprietary or
patented pavements, or those composed wholly or in part of materials
which are patented or protected by trade-marks. The owners or
contractors engaged in constructing these pavements, often, if not
usually, claim the right to dictate the material parts of the
specifications under which such work shall be done, and the municipal
engineer who is called upon to construct such pavements, must, in each
case, determine whether the specifications offered are adequate and
satisfactory, and the extent to which he feels justified in accepting
responsibility for the results. Naturally, the contractor or promoter,
even if competent to prepare specifications, cannot be expected to bind
himself within closer limits than he thinks necessary to secure the
work. In many such cases the form of general specifications for “untried
or experimental pavements” given herein might appropriately be used.
The engineer is, in common with all men, fallible, and he can hardly
hope, in the preparation of specifications, to make them perfect; to
cover every item and particular; or to escape some ambiguities of
expression, and some degree of indefiniteness. The writer can only claim
that he has aimed, in the light of a considerable experience, to set out
as fully and definitely as practicable the requirements for the proper
construction of high-class street pavements, and has endeavored to avoid
loose or obscure terms and expressions. The ideal specification is one
that furnishes a wholly sufficient guide to the accomplishment of the
desired purpose; that provides for every possible contingency which may
arise, and is couched in language which not only means exactly what it
was intended to mean, but is incapable of any other interpretation. It
is needless to say that no example of such a perfect specification can
be instanced as a model.
It has been the aim to make these specifications fair and just to the
contractor; that is, to require of him no impracticable or indefinite
service, or the assumption by him of risks other than those fairly
involved in the business conduct of the work.
If the plans and specifications for any work which a contractor bids
upon are so full, specific, and clear, that he may know exactly what he
will be expected to do, and if they do not require him to assume unusual
chances and risks, he may intelligently name prices which he believes
will compensate him for the service. Having done so, his proposal having
been accepted, and a contract entered into accordingly, the engineer and
the municipality have a right both in law and equity to demand that he
will do exactly and fully what he has contracted to do. No excuses on
his part can be valid and none should be accepted. He may in all
fairness and justness be required to “toe the mark” strictly. To the
neglect to recognize and enforce these principles is chargeable the
greater part of the poor and unsatisfactory work so common in street
pavement work in our cities. Unexpected contingencies may, of course,
arise where some changes and concessions may be proper and just, but
these should be, and usually are, very rare. On the other hand, sweeping
general clauses in contracts and specifications intended to catch the
contractor “goin’ or comin’,” unnecessarily stringent stipulations which
were never intended to be strictly enforced, but were put into the
specifications with the idea that they would help hold the contractor up
to a high standard, and “one-sided” contracts intended to give the
municipality an unfair advantage over the contractor, are as inadvisable
in policy as they are wrong in principle. Nothing should be put in a
specification that is not clearly essential to secure the results aimed
at, and, this having been done, every requirement should be enforced.
The existence in specifications of requirements that are not intended to
be enforced, gives the contractor a pretext for neglecting others that
may be important.
In these specifications will be found a number of details that are often
not regarded as important and which, when found in paving
specifications, the contractor is frequently allowed to ignore. In the
writer’s opinion, based upon his experience in street paving, every one
of these requirements is essential to the production of high-class work,
which, it is hardly necessary to argue, is, in the end, the most
economical work from the standpoint of the municipality.
It may be argued that the adoption and enforcement of these
specifications would have the effect of raising prices. In many cases
this would doubtless prove true. Contractors are entitled to a fair and
reasonable compensation for their services. It is admitted that in some
cities the prevailing prices for some kinds of pavements are below the
actual cost of the work if it were done in a proper manner, conforming
strictly to the specifications. Illogical as it undoubtedly is, the low
price at which work is taken is sometimes considered a sufficient reason
for accepting work below standard. The consequence is that bidders not
only count upon concessions and lax enforcement of the specifications,
but bid lower and lower, expecting that further concessions will enable
them to get out with an undeserved profit. This is one of the most
serious evils in the paving business to-day, and the highest public
interests demand a thorough reform. Low first cost, desirable as it may
be, is the poorest economy if it be secured at the sacrifice of the
quality of the work. If one pavement costs twenty per cent. more than
another, but renders forty per cent. more service, it is obviously the
cheaper of the two.
Contractors are prone to contend that this or that provision in a
specification is unusual, unnecessary or unfair. In dealing with them
the engineer should bear in mind that no requirement of a specification
that is clearly and definitely stated, so that the bidder may understand
exactly what it means and what he will be expected to do, and may frame
his prices accordingly, can be unreasonable or unfair to the contractor.
Unusual or unnecessary requirements may result in unwarrantably
increasing the cost of the work, and this may raise a question between
the engineer and the municipality employing him, but it can furnish no
occasion for questions of fairness or unfairness between the contractor
and the engineer.
The relations that should exist between the contractee and the
contractor, and the attitude of the engineer toward the contractor have
been widely discussed and are quite well understood from both the
ethical and legal standpoint.
It is well to bear in mind that when a contract is duly entered into,
both the parties thereto are equal before the law. Neither can impose
upon the other terms or conditions that are not clearly included in or
to be fairly inferred from the contract itself. The assumption that
either party has superior or extra rights not expressed or to be fairly
inferred from the written agreement, or in accordance with the
established rulings of the courts, is wholly without warrant. The
smallest contractor is, in this respect, upon an equal footing with the
largest city government for which he may undertake to do contract work.
It is not infrequently the case that the city assumes a superior and
dictatorial attitude not in harmony with these principles, and it is too
common for the contractor to seek to evade or to escape from clear
contractural obligations. In neither case is the action warranted by
fairness, justice, or law.
It should be needless to say that the attitude of the engineer toward
the contractor should be one of unyielding and uncompromising
requirement that the contract and specifications shall be fully and
faithfully complied with, but at the same time one of absolute fairness
and even helpfulness to the contractor. The ideal relation, which should
be more commonly attainable than it appears to be, is that of helpful
cooperation to bring about the results the contract and specifications
were intended to secure.
In line with the principles here outlined some observations upon the
preparation of contracts and specifications are appropriate.
It is the general practice to include in and make a part of “The
Contract” (herein for convenience called The General Contract) all the
various documents that are supposed to relate directly to the
transaction as a whole. The separate parts of such a general contract
may vary in number or character, but the principal ones are the
following:
1. The advertisement for proposals.
2. Instructions to bidders.
3. The proposal submitted.
4. The contract proper.
5. The specifications.
Each of these should be drawn to cover fully and clearly its appropriate
purpose or function but _nothing more_. It is not unusual to find, even
in the instructions to bidders, stipulations that properly belong in the
contract or specifications, and it is quite common to find in the
contract proper a lot of matter that properly belongs in the
specifications only. In such cases there is liable to be more or less
confusion as to the actual meaning or requirements of the general
contract as a whole, which may lead to serious misunderstandings and
complications between the parties thereto. The several documents
composing the general contract are likely to be prepared by different
persons, looking at the transaction from different points of view, and
often not wholly familiar with the scope, intent and language of the
other documents. There is therefore a possibility, at least, of
indefinite, if not of conflicting expressions which are open to
different interpretations, particularly in the light of special or
unexpected conditions that may arise during the progress of the work or
the settlement therefor. It would tend to eliminate or avoid the
possibility of such complications if each of the several documents
confined itself strictly to its appropriate function in the general
contract.
Advertisements for proposals may be divided into two general classes.
The one is brief in form and substance, simply stating that proposals
for a certain named work will be received at a stated place and time,
and referring those interested to documents on file at a stated place
for all further information. This is the general form adopted by the
United States War Department for the many projects carried out by
contract under its direction. A sample advertisement taken from a
current technical journal is as follows;
TREASURY DEPARTMENT, OFFICE OF the Supervising Architect, Washington,
D. C., October 10, 1912. Sealed Proposals will be received at this
office until 3 o’clock p. m. on the 1st day of November, 1912, and
then opened, for an electric passenger elevator in the United States
post office, Bellingham, Wash., in accordance with the drawing and
specification, copies of which may be had at this office at the
discretion of the Supervising Architect. OSCAR WENDEROTH, Supervising
Architect.
The other general class of advertisement, very commonly used by
municipal corporations, is much longer and more elaborate, giving a
condensed statement of the character of the work to be done, the
conditions under which proposals are invited and will be received, and a
schedule of the quantities of work involved, together with other
particulars. A typical example of such an advertisement, taken from the
same periodical, is here given:
PUMPING MACHINERY—ROSELAND PUMPING STATION
DEPARTMENT OF PUBLIC WORKS
CHICAGO, ILL., October 2, 1912.
Sealed proposals will be received by the City of Chicago until 11 A.
M. Wednesday, October 30, 1912, at Room 406, City Hall, for furnishing
and erecting at Roseland Pumping Station one vertical triple expansion
crank and fly wheel pumping engine of a capacity of twenty-five
million (25,000,000) gallons per day against a normal head of one
hundred and forty feet (140′). This proposal also includes the
dismantling of a similar engine now at Lake View Pumping Station,
transporting and erecting it at Roseland Pumping Station, together
with the furnishing and erection of certain auxiliaries and
appurtenances, according to plans and specifications on file in the
office of the Department of Public Works of said city, Room 406, City
Hall.
Proposals must be made out upon blanks furnished at said office, and
be addressed to said Department, indorsed “Proposals for Pumping
Machinery, Roseland Pumping Station,” and be accompanied with Five
Thousand ($5,000) Dollars in money or a certified check for the same
amount on some responsible bank located and doing business in the City
of Chicago and made payable to the order of the Commissioner of Public
Works.
The Commissioner of Public Works reserves the right to reject any or
all bids. A deposit of One Hundred Dollars ($100) will be required to
insure safe return of the plans.
No proposal will be considered unless the party offering it shall
furnish evidence satisfactory to the Commissioner of Public Works of
his ability, and that he has the necessary facilities together with
sufficient pecuniary resources to fulfill the conditions of the
Contract and Specifications, provided such Contract should be awarded
to him.
Companies or firms bidding will give the individual names as well as
the name of the firm with their address.
L. E. McGANN,
_Commissioner of Public Works_.
Such advertisements as this may be required by statutes or ordinances,
and in that case are, of course, proper and necessary. Even where not so
required they may be considered advantageous, because they give
prospective bidders more complete information as to the character and
magnitude of the work, and may enable them to decide at once whether
they care to pursue the matter further. But on the whole, the shorter
form of advertisement, if permissible, seems preferable, because it
refers the enquirer directly to the original and official sources of
information, the forms to be used, the contract, specifications and
estimated quantities of work, exactly as they will and must be presented
to all bidders, and as they will appear in the subsequent stages of the
transaction, and leaves, therefore, no room for possible confusion of
statements between the advertisement and the other documents.
Furthermore, the cost of the shorter form of advertisement is much less,
and this is often a matter of some importance.
Instructions to bidders should be confined strictly to such information
and directions as the bidder may need to properly and intelligently make
up and submit his proposal in accordance with the requirements relating
thereto. This should include primarily, a reference to the contract and
specifications for all general and detailed information about the work
to be done, but should carefully avoid any statements or language that
might be construed to add to, take from, limit or modify the contract or
specifications. Perhaps the briefest and best statement of what this
document should or should not contain is that it should be so framed
that, except as a matter of record, its office and usefulness should
absolutely end with the award and signing of the contract.
No one who is not a lawyer can presume to say just what the contract
proper should contain or cover, particularly as this may vary with the
requirements of statutes and ordinances in force in a given city. It
would seem logical and proper, however, to separate the special
functions of contracts and specifications in such a way that each should
cover a distinct field of its own, and be free from encroachment upon
the proper domain of the other. With such a conception of the proper
domain of each, one might safely say that the contract should undertake
to set out only the legal and contractural relations of the parties
thereto, and should refer to the plans and specifications for all
detailed instructions as to the actual performance of the work and the
results to be secured.
In the preparation of specifications for any public work the main points
to be kept in mind are fulness, definiteness, and exact expression.
While brevity and conciseness are desirable qualities in any document,
they should not be secured at the expense of completeness and precision
of statement. Even the frequent repetition of words, phrases and
sentences throughout a document, where it is necessary to avoid the
possibility of misunderstanding or ambiguity, should be resorted to
freely. Exact description and definition are more important than
literary style, though they may often be successfully combined. Of
course, it is not possible or necessary to go into minute detail with
regard to every part of the work. Certain things may be safely assumed
to be required by established practice or trade usage. If, for instance,
it is specified that certain lumber shall be “dressed” this word has a
well-understood meaning in the trade and it is unnecessary to stipulate
how the dressing shall be done or its character or quality, though it
may be necessary to say whether it is to be dressed on one or more
sides.
The proper preparation of specifications for any work involves a clear,
distinct and complete conception, determination and design of what is to
be done; of the conditions that are likely to be met with in carrying it
out; and of alternate plans that these conditions may necessitate. This
may not always be possible, for the engineer is not omniscient. But
careful study and maturity of design will enable him to avoid the great
majority of such indefinite expressions as “or in such other manner as
the engineer may direct,” “in accordance with the instructions of the
engineer,” etc. A great many of the items to which such expressions are
intended to and do apply in practice, could be definitely settled before
the specifications are prepared and thus all uncertainty on the part of
both engineer and contractor be avoided. To illustrate: specifications
for block pavement commonly stipulate that the blocks shall be set in
rows running at right angles to the axis of the street, except at street
intersections, where the engineer may direct them to be laid at a
different angle. There is usually no good reason why the engineer should
not determine beforehand at which, if any, street intersections the
general rule should be changed and so state in the specifications. These
may be and usually are unimportant matters which may not much affect one
way or the other the cost to the contractor. But they often prove
otherwise, and the contractor is entitled to know when he submits his
proposal just what he will be required to do. Of course it may develop
during the progress of the work that changes from the original plan will
become necessary, but these should be provided for in some such definite
and previously stipulated manner as outlined in Sect. 3 of the following
specifications.
The practice of inserting, either in the specifications or the contract,
a clause making the engineer judge and arbiter in any differences that
may arise between the city and the contractor, and providing that his
decision in all such cases shall be final, is as unwise as it is often
illegal. Such clauses are based on the assumption that the engineer is a
competent as well as a disinterested party in the transaction, an
assumption that is usually wholly wrong, though to their honor it may be
said that the confidence thus reposed in engineers is seldom abused. But
the fact is that the engineer is never actually a disinterested party.
He is employed and paid by the city to look after its interests, and is
under no obligations to the contractor other than those named in the
contract and specifications and his sense of justice, propriety and
professional honor. He would be recreant to his duty if in all nicely
balanced matters of doubt he did not espouse the side of his employer.
Moreover, his personal interests are often involved. Having prepared the
plans, specifications and estimates for the work, he is naturally and
properly anxious that it shall be successful and that the cost shall not
exceed that estimated. Under all these conditions it is hardly possible
for any human being to be a wholly disinterested and unprejudiced judge.
No broad-minded and conscientious engineer desires to be placed in such
a difficult position, and it is as unfair as it is unwise and improper
to require him to assume it.
There are, however, a number of matters of fact in reference to which it
is proper and necessary to make the judgment and decision of the
engineer controlling and final, unless it may be shown that his decision
is clearly erroneous or affected by improper motives, or by fraud. Some
one must necessarily be made the immediate and final judge as to whether
the quality of materials and workmanship is in accordance with the
requirements of the plans and specifications, and as to the quantity of
work actually performed, and these duties and responsibilities are very
properly placed upon the engineer.
It not infrequently occurs that specifications are not drawn as clearly
as they should be in the matters of methods of measuring the work and of
applying contract unit prices, and indefiniteness and carelessness in
this regard are often a source of misunderstanding and dispute between
the engineer and the contractor. It is a good practice, followed by many
able engineers, after specifying how a certain part of the work shall be
done, to state how it shall be measured and paid for at the contract
unit prices.
In many respects it is desirable that all the work to be done under
contract should be quite fully itemized, and a unit price named for each
kind of work. It is the custom in many cities to name only certain
leading items of the work to be done under a paving contract, as for the
pavement complete, furnishing and setting new curbing, redressing and
resetting old curbing, and possibly a few other leading items, and to
require that all necessary incidental work shall be done by the
contractor without cost to the city; or, in other words, he must take
this possible extra work into consideration in naming his unit prices
for the leading items of the work. As the quantity of this incidental
work is often not stated, and the contractor has no means of
ascertaining it, he must guess, as intelligently as he may be able, how
much he should add to his unit prices to cover its cost. If he is a
prudent contractor he will be sure to add enough to prevent any possible
loss on this account. In most cases the quantities of this incidental
work can be determined and scheduled by the engineer with the more
important items, and the contractor may be required to name unit prices
for it. True, there are likely to develop during the progress of the
work some items that could not be foreseen or that were overlooked. In
some cities such contingencies are provided for by a clause in the
contract or specifications scheduling, by name, all the incidental minor
items of work that experience has shown are likely to be met with in
street paving contracts, and naming fair unit prices which the
contractor will be paid for each, should it occur. The contractor may
then feel assured that however much the quantity of such incidental work
may vary, he will receive compensation proportionate thereto, and he may
name his prices for the main items with more confidence. Under such
conditions it is reasonable to expect closer figures than he would be
willing to name if an unknown quantity of incidental work for which no
separate pay is provided had to be taken into consideration.
Sub-division of unit prices is also desirable in order that the engineer
may be able to analyze and record the elements that make up the
aggregate cost of the work. Thus, in the case of the construction of a
new sheet asphalt pavement it is common to ask for a single price for
the pavement complete, including a five year guarantee. Now the work
will consist of several distinct operations or kinds of work for each of
which a separate price might be named:
1. The grading of the street and preparation of the sub-grade. The
quantity of this work will vary on different streets and is best
reckoned by the cubic yard of material excavated.
2. A price, either per cubic yard or per square yard for the concrete
foundation.
3. A price per square yard for the asphalt pavement proper. This might,
if desired, be sub-divided into separate prices for the base-course and
the surface-course.
4. A price per square yard for guaranteeing the pavement for five years.
Such sub-division would, it is true, increase the work of final
computation but if of no other value, the detailed costs would be a
great aid to the engineer in estimating the reasonable cost of future
work where the relative quantity of these detailed parts varied.
SPECIFICATIONS
For Grading and Paving, or Repaving
with.. ........ ........ .............. .... Pavement
on a... ......... .......... ...... Foundation, the Roadway
of..... ........ ........... ............ . ............
Street, from...... .......... ............. .............
to. ....... ....... ........... ............ ........
together with work incidental thereto.
GENERAL DESCRIPTION OF WORK
The work embraced in and to be done under this contract consists of
grading the entire street from curb to curb between the limits named,
including the removal or readjustment of the pavement now on the
roadway, setting and resetting curbing, laying or relaying sidewalks
where required, furnishing all new material and performing all the labor
required for paving the roadway, together with all incidental work
necessary to complete the whole in a proper manner, in accordance with
the contract, the plans on file in the office of the City Engineer,
these Specifications and the instructions of the City Engineer, herein
referred to as the Engineer, or his authorized agents.
REFERENCES
The numbered divisions of these specifications are herein designated as
“sections,” each being referred to by the number standing at its
beginning. Where reference is herein made to any such section number it
shall be considered equivalent to a quotation of that section.
The plans and drawings relating to this work, on file in the office of
the City Engineer are designated as ...
=1. Authority.=—Wherever, in these specifications, the words, the City,
are used, they shall be understood to refer to the duly constituted
municipal government of the city of ... or its authorized agents, acting
within the authority specifically conferred upon them by the said
municipal government.[1]
Wherever, in these specifications, the words, the Engineer, shall be
used, they shall be understood to refer to the City Engineer of said
city, or his deputies or assistants, acting within the authority
conferred upon them by the City Engineer.
But no agent of the city shall have power to revoke, alter, enlarge or
relax the stipulations or requirements of these specifications, except
in so far as such authority may be specifically conferred in or by the
specifications themselves, without the formal authorization so to do,
conferred by the contract of which these specifications are a part, or
by ordinance, resolution or other usual official action of the city.[2]
=2. Interpretation.=—In case of any actual or alleged disagreement or
discrepancy between the contract, these specifications, and the plans
for the work on file in the office of the Engineer, the language and
provisions of the contract shall take precedence and prevail; and the
Engineer shall determine in each case whether the specifications or the
plans shall be followed.
=3.= The Engineer shall have the right to make such changes in the plans
and specifications of the work as he may deem necessary or desirable or
to provide for unexpected conditions or contingencies that may develop
at any time after the signing of the contract, or during the progress,
or before the final acceptance of the work; provided that all such
changes do not involve an aggregate increase or decrease in the cost of
the work, as shown by his estimates, of more than ten (10) per cent. The
contractor shall accept such changes when made, as a part of the
original contract and specifications, subject to all the provisions and
conditions thereof. But before any such changes shall become valid and
before the contractor shall begin the particular work involved in such
changes, the increased or decreased cost of the work by reason of such
changes, above or below what it would have been under the original plans
and specifications, shall be agreed upon in writing between the engineer
and the contractor. And when the whole work, including such changes,
shall have been completed and accepted by the engineer, the sum or sums
so agreed upon shall be added to or deducted from the sum that would
have been due the contractor if no such changes had been made.
=4. Quality of Material and Work.=—The judgment and decision of the
Engineer as to whether the materials supplied and the work done under
this contract comply with the requirements of these specifications,
shall be conclusive and final. No material shall be used in the work
until it has been examined and approved by the Engineer, or his
authorized agents. All rejected material must be promptly removed from
the work and replaced with that which is acceptable to the Engineer, and
all improper or defective work must be corrected, and, if necessary,
removed and reconstructed so as to comply with these specifications and
the instructions of the Engineer.
In all matters of detail not specifically covered by the specifications
the work shall be well and skillfully done in accordance with the best
trade or art customs and standards for work of like character and
purpose.
=5. Inspection.=—The Engineer may provide for the inspection, by
assistants and inspectors under his direction, of all materials used and
all work done under this contract. Such inspection may extend to all or
any part of the work, and to the preparation or manufacture of materials
to be used, whether within the limits of the work on the street, or at
any other place. The Engineer and his inspectors shall have free access
to all parts of the work, including mines, quarries, manufactories, or
other places where any part of the materials to be used is procured,
manufactured or prepared. The Contractor shall furnish the Engineer all
information relating to the work and the material therefor which the
Engineer may deem necessary or pertinent, and with such samples of
materials as may be required. The Contractor shall, at his expense,
supply inspectors with such labor and assistance as may be necessary in
the handling of materials for proper inspection. Inspectors shall have
authority to reject defective material and to suspend any work that is
being improperly done, subject to the final decision of the Engineer.
Inspectors shall have no authority to permit deviations from, or to
relax any of the provisions of these specifications without the written
permission or instruction of the Engineer; nor to delay the Contractor
by failure to inspect materials and work with reasonable promptness.
The payment of any compensation, whatever may be its character or form,
or the giving of any gratuity, or the granting of any valuable favor, by
the Contractor to any inspector, directly or indirectly, is strictly
prohibited, and any such act on the part of the Contractor will
constitute a violation of these specifications.[3]
=6. Injuries to Persons and Property.=—The Contractor shall be held
alone responsible for all injuries to persons, and for all damages to
the property of the city or others, caused by or resulting from the
negligence of himself, his employees or agents, during the progress of,
or connected with the prosecution of the work, whether within the limits
of the work, or elsewhere. He must restore all injured property,
including sidewalks, curbing, sodding, pipes, conduits, sewers and other
public or private property to a condition as good as it was when he
entered upon the work.
=7. Sanitary Conveniences; Nuisances.=—The Contractor shall provide all
necessary privy accommodations for the use of his employees on the
street, and shall maintain the same in a clean and sanitary condition.
He shall not create nor permit any nuisance to the public or to
residents in the vicinity of the work.
=8. Public Convenience.=—No material, or other obstruction shall be
placed within five feet of fire hydrants, which must be at all times
readily accessible to the Fire Department.
During the progress of the work the convenience of the public and of the
residents along the street must be provided for as far as practicable.
Convenient access to driveways, houses and buildings along the street
must be maintained wherever possible. Temporary approaches to and
crossings of intersecting streets and sidewalks must be provided and
kept in good condition, wherever practicable.
=9. Barriers, Lights, Watchmen.=—The Contractor shall provide and
maintain such fences, barriers, “street closed” signs, red lights, and
watchmen as may be necessary to prevent avoidable accidents to residents
and to the public.
=10. Disorderly Employees.=—Disorderly, intemperate, or incompetent
persons must not be employed, retained, or allowed upon the work.
Foremen or workmen who neglect or refuse to comply with the instructions
of the Engineer, shall, at his request, be promptly discharged, and
shall not thereafter be re-employed without his consent.
=11. Order and Progress of Doing Work.=—The work under this contract
shall be prosecuted at as many different points, at such times, and in
such sections along the line of the work, and with such forces as the
Engineer may from time to time deem necessary, and direct, to secure its
completion within the contract time. Not more than one thousand (1,000)
linear feet of the street shall be torn up, obstructed or closed to
travel at any one time without the written permission of the Engineer.
Completed portions of the pavement shall be opened to travel as directed
by the Engineer, but such opening shall not be construed as an
acceptance by the City of the work done. Where thus opened to public
travel by the direction of the Engineer, the Contractor will not be held
responsible for injuries to the work caused by such travel or public
use, pending the final completion and acceptance of the whole work.
=12. Grade and Contour of Pavement.=—Roadway pavements shall be laid to
such grades, crown and contour of surface as the plans may show or the
Engineer may direct, and the surface of the completed pavement shall
conform accurately to such grades, crown and contour. The designed
surface of the completed pavement shall be considered as the datum or
plane of reference in fixing the location or level of the sub-grade, of
the pavement foundation, and of structures connected therewith. It will
be hereafter referred to in these specifications as “The pavement
datum.”
=13. City Monuments or Stakes.=—The Contractor must carefully protect
from disturbance or injury all city monuments, stakes and benchmarks,
and shall not excavate nearer than five feet to any of them without the
permission of the Engineer; or until they have been removed, witnessed,
or otherwise disposed of by the Engineer.
=14. Old Material.=—All material or structures removed from the street
and not required for the new construction, but which the city may desire
to reserve, shall be delivered and neatly piled up in a corporation yard
or elsewhere, by the Contractor, as the Engineer may direct. Such
reserved material shall be considered in the custody of the Contractor
until delivered at the place designated, and he will be held responsible
for its care and protection, and must make good any losses occasioned by
damage, theft, or misappropriation while it is on the street or en route
to the place of storage. If the Contractor shall be required to haul
such reserved material more than one-half mile, he shall be paid a
reasonable price, to be agreed upon in advance, for the haul exceeding
that distance.
Material taken from the work which is to be used in the new construction
shall be compactly piled where it will least obstruct the sidewalks or
adjoining sections of the street, and properly protected by the
Contractor until it is required for use.
All old material removed from the work, including the material excavated
in preparing the sub-grade, not reserved by the City nor to be used
again in the work, shall belong to the Contractor and must be removed by
him from the street as promptly as possible. It must not be placed on
the sidewalks or adjacent streets, nor on any other street or property
belonging to the City, nor on the property of private owners, without
the written consent of the Engineer, or the owner of the property.
=15. Storage of New Material.=—The material for construction when
brought upon the street shall be neatly piled so as to cause as little
obstruction to travel as possible, and so that it may be conveniently
inspected.
=16. Rebuilding and Adjusting Street Structures.=—Catch basins, manhole,
sewer and water frames and covers, sewer inlets, water pipes and other
conduits, belonging to the City and within the limits of the work,
shall, if necessary, be reset to the new lines and grades of the street
and for this purpose good brick masonry of the original thickness, laid
in Portland cement mortar shall be used. Great care must be taken to set
all such structures as project through the pavement exactly to the grade
and contour of the new street surface, and any defects in the conformity
of such structures to the pavement datum, discovered at the time, or
during the progress of the work, or during the guaranty period,
stipulated in Sec. 25 shall be promptly remedied by the Contractor.
=17. Clean Sidewalks.=—During the progress of the work, the sidewalks
and portions of the street adjoining the work, or in its vicinity, must
not be obstructed or littered more than may be absolutely necessary, and
the adjacent sidewalks must be kept clean.
=18. Connection With Existing Pavements or Streets.=—Wherever a new
pavement joins or abuts against an existing pavement of a different
kind, or an unpaved street, either at the end of the new pavement or at
cross or intersecting streets, a line of stone headers shall be provided
and set. The stone shall be of sound, hard limestone, sandstone, granite
or bluestone, free from injurious imperfections. The separate stones
shall be not less than three (3) feet long, at least eighteen (18)
inches deep, not less than four and one-half (4½) inches wide at the
top, nor less than three (3) inches wide at the bottom. The top shall be
of uniform width for each line of headers, and shall be dressed square
and even. The ends shall be dressed to secure a joint not wider than
one-half (½) inch for a depth of six inches from the top, and the sides
dressed so as to secure good contact and close jointing with the
pavement. The stones shall be set accurately with their tops at the
pavement datum, on a bed of concrete nine (9) inches wide and six (6)
inches deep, and after being set the trench shall be filled and rammed
full of gravel or crushed stone.
All existing pavements adjoining or abutting against the new pavement,
with their crosswalks, curbs, and gutters, shall be adjusted, or taken
up and relaid, to conform to and connect with the pavement datum, to
such an extent as the Engineer may direct.
Where the new and adjoining pavement are of the same kind, and headers
are not used, the new and the old pavement must be properly joined and
connected, as the Engineer may direct.
Stone headers will be paid for by the linear foot at the contract price
for that item, and the other work embraced in this section will be paid
for at the contract prices for the several items, where such contract
prices are provided; otherwise the work shall be considered as
incidental work and shall be done at the expense of the Contractor.
=19. Curbing to be Completed in Advance.=—The setting of all new curbing
and guttering and the redressing, resetting or readjustment of all old
curbing must be completed at least 100 feet in advance of the
construction of the street foundation.
=20. Final Cleaning Up.=—Immediately after the completion of the work or
any consecutive portion of it, the Contractor shall remove from it all
unused material, refuse and dirt placed by him on, or in the vicinity of
the work, or resulting from its prosecution, and restore the street to a
condition as clean as before the work was begun; and the new pavement
shall be properly cleaned.
=21. Measurements and Computations.=—Unless otherwise distinctly
provided in the contract and specifications, measurements, computations
and payments will be based upon the actual quantities of completed work,
customary or conventional methods of measurement and computation to the
contrary notwithstanding.
The area of street pavement shall be reckoned in square yards of
completed pavement surface, deducting manholes, inlets and other
openings in the surface of the pavement having an area of over three (3)
square feet. Unless separately paid for under the contract, stone
headers and crosswalks will be measured as a part of the pavement
surface.
=22.= The price for the pavement per square yard shall, unless otherwise
stated herein, include the preparation of the sub-foundation, the
construction of the foundation, the cushion course, and the pavement
complete, including all the materials and labor required therefor.
=23. Incidental Work at Contractor’s Expense.=—All the work to be done
by the Contractor for which specific unit prices are not named in the
contract, specified and enumerated in Sections 4, 5, 6, 7, 8, 9, 12, 13,
14, 15, 16, 17, 18, 19, and 20, as well as any minor details of work not
specifically mentioned in the specifications, but obviously necessary
for the proper completion of the work, shall be considered as
incidental, and as being a part of and included with the work for which
prices are named in the contract. The Contractor will not be entitled to
any extra or additional compensation therefor.
=24. Extra Work.=—The City may require the Contractor to furnish such
additional materials and to do such additional work, not provided for in
the contract and these specifications, but which may be found necessary
or pertinent to the proper prosecution and completion of the work
embraced in the contract, at prices to be agreed upon in writing, in
advance. But no work other than that included in the contract and these
specifications and which is covered by and to be paid for at the prices
named in the contract, shall be done by the Contractor except upon a
written order from the Engineer, which order shall describe the work to
be done and name the compensation agreed upon therefor. In the absence
of such written order from the Engineer the Contractor will not be
entitled to payment for any such additional or extra work.
In the same manner the city may omit or dispense with items or parts of
the work, by previous agreement with the contractor, and a like written
order by the engineer. But such additions, omissions or alterations
shall not together increase or decrease the aggregate cost of the whole
work more than fifteen per cent. (15%). Any changes in the plans,
specifications, character of material used or method of doing the work
that may increase or decrease the aggregate cost of the work more than
fifteen per cent. (15%) may be authorized and validated only by a
formal, supplemental contract, regularly executed by all the parties to
the original contract.[4]
=25. Guaranty.=[5]—The Contractor shall guarantee that all the materials
used and all the work done under this contract shall fully comply with
the requirements of these specifications, the plans herein before
referred to and the instructions of the Engineer. Any defects in the
completed work, or any part of it, or any failure of the work to fully
perform or endure the service for which it was intended, which, in the
opinion of the Engineer, are attributable to the use of materials,
skill, or workmanship not in compliance with the said specifications,
plans and instructions, within a period of ... years after the date of
the certificate of completion and acceptance, shall be regarded as prima
facie and conclusive evidence that the Contractor has failed to comply
with the said specifications, plans and instructions. And the Contractor
shall, at his own expense, at such time and in such manner as the
Engineer may direct, repair or take up and reconstruct any such
defective work, in full compliance with the original specifications,
plans and instructions. And as surety for the performance of this
guaranty the Contractor’s bond, required by the contract, shall remain
in full force until the expiration of the period of ... years above
stipulated in this section.
PREPARING THE SUB-GRADE
=26. Grading.=—The whole area to be occupied by the pavement and its
foundation shall be excavated or filled up to a sub-grade at such an
elevation that after being compacted by the roller, the surface will
be ... inches below the pavement datum, and truly parallel thereto. In
excavating, the earth must not be disturbed below the sub-grade. Plowing
will not be permitted where the depth of earth to be removed is less
than five (5) inches, and in no case must the plow be allowed to
penetrate to within less than one inch of the sub-grade. Places that are
found to be loose, or soft, or composed of unsuitable material, below
sub-grade, must be dug out and refilled with sand, or other material as
good as the average of that found on the street.
Where the natural surface of the ground shall be below the sub-grade, or
shall become so by the removal of old pavement or other structures, it
must be filled to the sub-grade in layers not exceeding five inches in
depth, and each layer shall be thoroughly rolled or rammed before the
next layer is placed upon it, and when the filling is completed the
filled area must be properly trimmed and compacted by rolling or ramming
to the true sub-grade, as in excavation. The material excavated from the
street may be used for such filling, provided it be of suitable quality.
Where it cannot be thus procured from the street it must be obtained by
the Contractor elsewhere, in which case the actual quantity so obtained,
measured after it is compacted in the street, will be paid for at the
contract price for “earth filling.” The price bid for “earth excavation”
will be paid for all material excavated above the sub-grade, measured in
place on the street, which price includes the cost of disposing of the
excavated material, whether as waste or filling, and of trimming and
rolling or ramming the sub-grade, and of making it ready for the
pavement foundation.
After the excavation is completed and the surface neatly trimmed, the
whole area shall be well compacted by rolling with a roller weighing not
less than five tons. Areas inaccessible to the roller shall be rammed
until they are as well compacted as the rolled surface. When the rolling
is completed the surface must be nowhere more than three-fourths inch
below, nor more than three-eighths inch above the true sub-grade. If,
after the rolling is completed and before the pavement foundation is
laid, the surface shall become disturbed in any way, it must be replaced
and properly compacted.
Where the soil composing the sub-foundation is found to be wet or
“springy,” a system of soft tile drains, discharging into the street
drainage system, shall be constructed by the Contractor, as directed by
the Engineer. The tile shall be laid in trenches about one foot wide and
from one to two feet deep. After the tile is in place the trenches shall
be filled with crushed stone or gravel, well compacted by tamping. The
tile will be paid for per linear foot at the contract price for the
same, which price shall include the cost of excavating and refilling the
trenches with crushed stone.
PAVEMENT FOUNDATION
=27.= Pavement foundation shall consist of hydraulic concrete, or of old
pavement stone relaid, or of broken stone or gravel, as may be herein
specified, constructed upon the sub-grade.[6]
HYDRAULIC CONCRETE FOUNDATION
=28. Concrete.=—Concrete shall be composed of Portland cement, sand,
broken stone and water.
=29. Portland Cement.=[7]—Portland cement shall be defined as the
pulverized product resulting from the calcination to incipient fusion of
an intimate mixture of properly proportioned argillaceous and calcareous
materials, and to which no addition greater than three per cent. has
been made subsequent to calcination.
=Specific Gravity.=—The specific gravity of the dry cement at a
temperature of two hundred and twelve (212) degrees F. shall not be less
than 3.10.
=Fineness.=—It shall be pulverized to such fineness that not more than
eight (8) per cent. shall fail to pass a number one hundred (100) sieve
and not more than twenty-five (25) per cent. shall fail to pass a number
two hundred (200) sieve.
=Time of Setting.=—At the temperature of sixty (60) degrees F. mortar
made of neat cement shall not begin to set in less than thirty (30)
minutes, nor set hard in less than one hour, but must set hard within
ten (10) hours.
=Strength.=—When thoroughly mixed dry with clean, sharp, moderately
coarse sand, in the ratio by weight of one part cement to three parts of
sand, and then made into stiff mortar, briquets made from this mortar
and exposed for one day to moist air and immersed in water for the
balance of the periods named below, shall develop a tensile strength per
square inch not less than the following:
In seven days 175 pounds.
In twenty-eight days 250 pounds.
=Constancy of Volume.=—When subjected to standard tests for constancy of
volume, the cement shall show no tendency to swell or crack.
=Composition.=—The cement shall not contain more than one and
three-fourths (1.75) per cent. of anhydrous sulphuric acid, nor more
than four (4) per cent. of magnesia.
=Tests.=—Cement tests shall be conducted in accordance with the methods
recommended by the “Committee on Uniform Tests of Cement” of the
American Society of Civil Engineers.
=Conditions.=—All cement shall be supplied in original packages with the
brand of the manufacturer marked on each package. It shall be protected
during transportation from rain and moisture. It shall be delivered upon
the work at least ten (10) days (exclusive of Sundays and holidays)
before it is to be used, in order to allow of proper inspection, and the
contractor shall furnish all necessary facilities for such inspection.
Brands of cement without established good reputation, or not heretofore
used in the City of ... may be rejected; or they will be accepted only
after they satisfactorily pass the 28–day test. Rejected cement must be
at once removed from the street.
=30. Sand.=—Sand for concrete shall be composed of grains not softer
than hard limestone. It shall be moderately coarse and preferably made
up of grains of varying size producing a mass with low percentage of
voids. It shall not contain, in all, more than seven (7) per cent. by
volume of clay, loam, mica scales, silt, or other objectionable
inorganic matter, nor more than one (1) per cent. of organic matter.
=31. Broken Stone.=—Broken stone for concrete shall be of hard and sound
limestone or other stone equally hard and durable, broken to a roughly
cubical form. It shall be screened through efficient revolving screens,
and only such fragments as have passed through circular screen openings
two and one-half (2½) inches in diameter, shall be used. If the crushed
dust and fine fragments be not screened out, the stone must be so
handled that the fine material will be evenly distributed through the
mass when it reaches the concrete platform or mixer.[8]
=32. Water.=—Water used for concrete shall be fresh, and reasonably
clean.
=33. Care and Handling of Concrete Material.=—Cement must not be allowed
to become wet or damp. It shall be stored until used, whether in
storehouses or on the street, so that no part of the packages shall be
nearer than four (4) inches to the ground or pavement, and shall be
effectually covered so that rain cannot reach it. Sand and stone, if
stored on the street, shall be on lumber floors.[9] The stone shall be
thoroughly wetted a sufficient time before being placed in the concrete
to allow any surplus water to drain away, but shall remain moist where
it reaches the concrete platform or mixer.
=34. Ratio of Concrete Materials.=—Concrete will be composed of one part
Portland cement, ... parts of sand and ... parts of broken stone, and
the proper quantity of water, all measured by volume.[10] The unit of
measurement shall be the barrel of cement which shall be considered as
containing four (4) cubic feet. The materials shall each be measured in
such manner and with such accuracy that the quantities used will not
vary more than seven (7) per cent. from the quantities required in the
ratio named above for each batch of concrete.
=35. Mixing Concrete.=—If mixed by hand, concrete shall be mixed on
platforms of iron or wood of sufficient size to admit of proper
manipulation of the concrete. The sand shall be first spread evenly over
the platform and the cement evenly distributed over the sand. These two
materials shall then be mixed dry until a uniform and homogeneous
mixture is secured. Sufficient water shall then be added and the mixing
resumed and continued until a mortar of uniform consistency and texture
is produced and distributed in an even layer over the platform. The
stone shall then be distributed over the mortar and mixed therewith
until the mortar is evenly distributed through the mass and every
fragment of stone is well coated with mortar, sufficient additional
water being added as the mixing progresses to produce a rather wet, but
not sloppy, concrete.[11] Machine mixing of concrete will be preferred,
provided the machine used secures equal accuracy in the ratios of
materials and equally as good mixing as prescribed above for
hand-mixing. Machine-mixed concrete must be delivered from the machine
upon a wood or metal platform, or directly into barrows.
=36. Placing the Concrete.=—Concrete shall be placed on the sub-grade in
such a manner as to prevent as far as possible the separation of the
mortar from the stone. It shall be evenly distributed in a single
horizontal layer of such depth that, after ramming, it will be not less
than ... inches thick. Immediately after being so placed it shall be
well rammed until a compact mass is produced with its upper surface
parallel to and ... inches below the pavement datum. Depressions that
may appear during the ramming may be filled with concrete of the same
composition as used for the foundation, except that smaller-sized stone
shall be used; mortar alone must not be used for this purpose, nor shall
the upper surface of the concrete be plastered with mortar. The surface
of the concrete shall not be broomed or troweled.[12]
=37. Setting of Concrete.=—After the concrete is completed it shall
remain undisturbed until it be firmly set. The time allowed for setting
shall not be less than five days, and as much longer as, in the judgment
of the Engineer, may be necessary, depending upon the temperature of the
weather and the setting qualities of the cement. During this period no
hauling or traveling over the concrete must be permitted unless its
surface be first protected by a covering of plank. The Contractor shall,
if necessary, keep the concrete moist by wetting it, with hose, or
otherwise, until twenty-four (24) hours before it is to be covered with
the pavement surface.
=38. Measurement of Concrete.=—Concrete will be measured and computed in
cubic yards as found completed on the street, the thickness being taken
as ... inches. The contract price for concrete foundation covers the
cost of providing all the materials required, making, placing and
ramming the concrete, and keeping it moist for the necessary period.
FOUNDATION OF OLD PAVING STONE
=39.= Foundations made of old stone paving blocks shall be constructed
as follows:
Upon the sub-grade prepared as specified in Section 26, shall be spread
a layer of good sand to an even depth of one and one-half (1½) inches.
The paving blocks, whether taken up from the street to be paved, or
brought from other streets or storage yards, shall be cleaned of all
adhering earth, dirt and street refuse. The blocks shall then be set on
the bed of sand, on edge, perpendicular to the grade, with their long
dimension at right angles to the line of the street, in courses composed
of stones of the same width, extending entirely across and at right
angles to the axis of the street. Stones in adjoining courses shall
break joint at least two inches. Joints between courses or stones, or
along the curbstones, shall not exceed one inch in width. The stone
shall be fitted closely around manholes or other structures in the
street. The stones shall be so set in the bed of sand that after being
rammed as hereafter specified, their tops shall be at the proper grade.
After being thus set in place the stone shall be rammed with paving
rammers having wooden faces and weighing not less than thirty (30)
pounds, so as to force each stone to a good bearing in the sand below,
and to bring its top to a uniform grade, parallel to and ... inches
below the pavement datum. No stone shall project more than one-fourth
(¼) inch above the proper grade, and stones whose tops, after ramming,
are more than one-half (½) inch below such grade, shall be raised,
additional sand placed under them, and reset and re-rammed to the proper
grade and bearing. After the ramming shall have been completed, the
joints between the stones shall be filled with mortar. The mortar shall
be composed of Portland cement and sand, complying with the
specifications for these materials in Sections 29 and 30. One part of
cement and three parts of sand, by volume, shall be thoroughly mixed
dry, and then made into mortar with sufficient quantity of water to
produce a mortar of such consistency that it will just flow freely into
the joints between the stones. All the joints between the stones must be
completely filled with this mortar before it has begun to set. The
mortar filling shall be brought even with, but not above, the tops of
the stones. After the filling is thus completed, the foundation must
stand undisturbed until the mortar shall have set firmly, in no case
less than five days. The mortar must be kept moist during the period
allowed for setting.[13]
Old stone foundation will be measured in square yards, in place after
completion. The contract price includes the cost of handling and
cleaning the stone, supplying and placing the bed of sand, setting and
ramming the stone, supplying the materials for, making and placing the
mortar in the joints and watering the street while the mortar is
setting. Where stone is procured from other streets, or from storage
yards, the Contractor will be required to load, haul and unload them,
and will be allowed for this service a price of ... cents per cubic yard
for loading and unloading, plus ... cents per cubic yard for each
one-half mile, or fraction thereof, over which they are hauled by the
nearest practicable route, the measurement to be made after the stone is
set in the street, without deduction for joints.
=40. Broken Stone Foundation.=—The sub-grade for broken stone foundation
shall be prepared as specified in Section 26, except that the rolling
may be omitted at the option of the Contractor. The broken or crushed
stone shall be of hard, durable stone. The foundation shall have an
aggregate thickness of ... inches and shall be constructed in two
courses, as follows:
The broken stone used in the first course shall be of such size that it
will all pass through a screen having openings three (3) inches in
diameter, and will all be retained on a screen having openings one (1)
inch in diameter. This stone shall be evenly spread over the sub-grade
to such a thickness that after being thoroughly consolidated by rolling,
its upper surface shall be three-fourths inch below, and parallel to the
surface of the foundation when completed. It shall then be rolled with a
road-roller weighing not less than ten (10) tons until the stone is
thoroughly compacted.
The second course, composed of screenings, all of which shall have
passed through a screen with openings one inch in diameter, shall then
be spread over the first course and well raked into the voids of the
first course. It shall then be thoroughly wetted, and shall be rolled
with the ten-ton roller until the fine stone is driven into the
interstices of the first course and the whole thoroughly consolidated,
the wetting being repeated while the rolling continues. Additional
screenings shall be added and rolled in where necessary to bring the
surface to the proper elevation. When completed, the top surface of the
foundation shall be ... inches below, and parallel to the pavement
datum. No part of the upper surface of the completed foundation shall
project more than one-fourth (¼) inch above, nor shall it be more than
one-half (½) inch below the grade and contour above specified.
Gravel of a quality satisfactory to the Engineer may with his written
consent be substituted for broken stone. If of assorted sizes, such as
will compress into a mass having not more than thirty (30) per cent. of
voids, the foundation may be constructed in a single layer, graded,
watered and rolled, as prescribed above for broken stone.[14]
=41. Measurement.=—Broken stone and gravel foundation will be measured
and computed by the cubic yard in the street as completed, without any
allowance for consolidation by the roller or for settlement into the
sub-grade, the thickness being taken as ... inches. The contract price
for it shall cover the cost of supplying the material, placing it on the
street, and grading, watering and rolling it.
SHEET ASPHALT PAVEMENT
_Note._—A number of distinct varieties of asphalt are now used for
asphalt pavements, either alone or mixed. These different varieties
differ from each other quite widely in their physical and chemical
properties. Thus, in the form called “refined asphalt” some of their
properties are shown by the following table, the data for which is taken
from the second edition of Richardson’s “The Modern Asphalt Pavement.”
COMPARATIVE PROPERTIES OF DIFFERENT REFINED ASPHALTS
───────────────────────────────────────────────────────────────────────
Trinidad, Bermudez, Maracaibo, Calif. Gilsonite,
average average average of “D” average of
of two six grade, two
samples samples average samples
of two
samples
───────────────────────────────────────────────────────────────────────
Softens, degrees F. 180 165 225 132 280
Flows, degrees F. 190 175 236 151 300
Penetration at 78° F. 7 24 21 48 0
Loss, heated to 325° 1.1 3.7 3.2 1.7 1.6
for 7 hours, %.
Loss, heated to 400° 4.0 8.8 5.5 7.1 2.6
for 7 hours, %.
Bitumen soluble in 56.5 95.5 93.9 99.3 99.4
CS_{2}.
Inorganic, other than 36.5 2.2 2.9 0.3 0.5
bitumen.
Bitumen soluble in 35.6 65.6 51.1 69.6 47.2
naphtha.
Bitumen sol. in 98.7 99.0 93.2 95.7 99.8
carbon
tetra-chloride.
Fixed carbon. 10.8 13.7 17.2 17.6 13.2
───────────────────────────────────────────────────────────────────────
The practice has been heretofore, and is at the present time, to attempt
to make specifications for asphalt pavements broad enough to include all
the various varieties of asphalts, under general requirements which
shall admit these, and any new varieties that may appear on the market
suitable for the purpose, the object being to permit a wide range of
competition. This makes it exceedingly difficult if not impossible to
frame specifications that shall be sufficiently explicit and at the same
time sufficiently broad to admit these several differing materials. This
practice has been adhered to in these specifications, though in this
respect they are far from satisfactory to the author. So long as it
continues to be the policy of cities to admit these various varieties of
bitumen under the same general requirements for crude and refined
material, such objectionable specifications cannot be avoided. Even with
the great latitude now provided they exclude some materials with which
good pavements have been made.
Two remedies for this unsatisfactory condition seem practicable.
1. A city might purchase a sufficient supply of refined asphalt for its
use after asking for proposals under suitable specifications with
alternative requirements for the different varieties on the market, and
after bids are received and the samples accompanying them have been
properly examined in the laboratory, award contracts for a supply of one
or more kinds, as might seem best for the interests of the city. Stocks
of these would be delivered, tested and stored accordingly, in good time
for the season’s work. Specifications for construction with special
reference to the kind of asphalt it is proposed to use could then be
prepared, the contractors to be supplied with asphalt at the city
storage yard at a stipulated price per ton. This plan would possess a
number of advantages. A similar plan is quite commonly in use with
reference to hydraulic cement.
2. Specifications might be framed with special reference to the
properties and qualities to be possessed by the _asphaltic cement_,
permitting a liberal range as to the crude and refined bitumens to be
used in manufacturing this cement. This would be considered, at the
present time, a radical departure from well established custom, but the
author sees no reason why it should not be satisfactorily employed.
A sheet asphalt pavement is composed of two essential elements; a
mineral aggregate made up of sand of assorted sizes and mineral “dust”
and a bituminous cement. When properly compounded, manipulated and
compressed these elements make up a bituminous concrete suitable for use
as a wearing surface for streets and roads.
The character of the sand is important and we have now sufficient
knowledge from experience to specify a sand that will give,
approximately, the best results.
The bituminous cement is, however, the element of most importance, and
upon its suitability for the purpose depends very largely the utility
and durability of the pavements made with it.
It is important that this asphaltic cement shall possess certain
properties and qualities, most of which we are now able to define
satisfactorily, but others require further practical and experimental
study, and some tests not now in use would doubtless be desirable.
It is not a matter of importance what particular crude or refined
materials enter into the composition of this cement if the resulting
product is satisfactory in use. The prime requisite is a paving cement
that shall possess in a high degree the chemical and physical qualities
required for making an asphalt pavement of the best quality. If we can
devise standards and tests that will enable us to secure such a cement
we need not be concerned about its antecedents.
It would be well worth while for paving engineers and those who have
laboratory facilities to give attention to this matter. If it shall be
found practicable to define satisfactorily the qualities the cement
should possess without reference to the materials from which it is
compounded, a great advance will have been made, and our asphalt paving
specifications could not only be greatly simplified, but much greater
precision and definiteness secured.
While great advances have been made in the art of building sheet asphalt
pavements and in the framing of specifications for its construction, too
many of the specifications still in use are antiquated, indefinite and
unsatisfactory. Some of these contain requirements that, if literally
enforced, would prevent the attainment of the best results. They are
largely survivals of the time when little was known either practically
or technically of the science and art of constructing the pavements,
outside of the promoters and contractors in the business, who
consequently dictated, in a large measure, the specifications used. City
engineers were compelled to rely largely on the presumption that the
guarantee clauses of the contracts would insure good results, and
allowed the contractor wide latitude in the conduct of the work.
While there is undoubtedly much yet to learn, even by the experts, in
the matter of the materials to be used, a quite satisfactory working
basis has been arrived at, particularly as to the practical side of the
work, and a large mass of data accumulated by study and experience is
available to the municipal engineer, and the services of independent
experts is readily obtainable. There is no longer any good reason,
therefore, why the character of the materials to be used, the methods
followed, and the quality of the work secured should not be quite
definitely and fully specified in the same manner and to the same extent
as in the case of other kinds of pavement and with equally satisfactory
results.
SPECIFICATIONS
=42. General.=—Asphalt pavement surface shall be laid upon a foundation
of hydraulic cement concrete, or of stone blocks relaid, over a
sub-grade, to be constructed in accordance with Articles 26, 28, 29, 30,
31, 32, 33, 34, 35, 36 and 37.
Asphalt pavement surface shall be constructed in two courses, called the
base-course and the surface-course. The base-course may be from one (1)
inch to one and one-half (1½) inches thick, and the surface-course may
be from one (1) inch to two (2) inches thick, as shall be hereafter
specified.
=43. Crude Asphalt.=—The cementing element in asphalt pavements shall be
prepared from crude native, solid asphalts or from the proper
distillation of crude asphaltic oils.
Crude asphalts as obtained from the mines or natural deposits shall be
properly refined to drive off water and to separate foreign substances,
by melting at a temperature not exceeding four hundred and fifty degrees
F. (450° F.). Crude asphalts of the quality commonly called “glance
pitch” or “iron pitch” which do not distinctly soften at a temperature
of two hundred degrees F. (200° F.), and detached or deteriorated
material from deposits otherwise acceptable will be rejected.
=44. Refined Asphalt.=—Refined asphalt produced from native crude
asphalt shall be free from water and shall not contain an injurious
quantity of light oils or foreign matter. It shall not contain more than
four per cent. (4%) of organic matter nor more than thirty-six per cent.
(36%) of inorganic matter other than bitumen, and not more than eighteen
per cent. (18%) of fixed carbon, and not less than fifty-five per cent.
(55%) of bitumen soluble in cold carbon di-sulphide. Of the bitumen
soluble in carbon di-sulphide not less than sixty-three per cent. (63%)
shall be soluble in Pennsylvania petroleum naphtha of specific gravity
eighty-eight (88) degrees Baume at a temperature of sixty-five degrees
Fahrenheit (65° F.) and not less than ninety-eight per cent. (98%) shall
be soluble in chemically pure carbon tetra-chloride. When exposed for
seven hours to a temperature of three hundred and twenty-five degrees F.
(325° F.) in a shallow dish the bottom of which is covered with bitumen
to a depth of three-fourths (¾) inch, the refined asphalt shall not lose
more than five per cent. (5%) by evaporation.
Asphalts that are injuriously affected, in the pavement, by water (to be
determined by the test immediately hereinafter described), shall not be
used except under the conditions specified in Section 45. Cylinders made
from the surface mixture it is proposed to use, one (1) inch in diameter
and two (2) inches long, compressed to a density of two and one-tenth
(2.1), when immersed forty-five (45) days in ten (10) times their volume
of rain-water, shall retain a sound surface, unchanged and uncorroded by
the action of the water.
Refined asphalts resulting from the distillation of crude asphaltic oils
will not be accepted unless the distillation shall have been effected by
the use of suitable apparatus, at a temperature not exceeding seven
hundred (700) degrees F. The bitumen must not be over-distilled and “cut
back” by adding oil. The product, to be acceptable, shall possess the
following qualities: It shall melt and flow at a temperature not below
one hundred and forty (140) degrees F., but below a temperature of one
hundred and eighty (180) degrees F., and when tested in the standard New
York State closed oil-testing apparatus shall not flash at a temperature
below four hundred and fifty (450) degrees F. When exposed in a shallow
dish, the bottom of which is covered to a depth of three-fourths (¾)
inch with the bitumen, to a temperature of four hundred (400) degrees
F., for seven (7) hours, it shall not lose by evaporation more than
seven (7) per cent. by weight. Not less than ninety-eight (98) per cent.
shall be soluble in cold carbon di-sulphide, and not less than
sixty-five (65) per cent., nor more than seventy-five (75) per cent. of
the bitumen shall be soluble in cold Pennsylvania naphtha of gravity
eighty-eight (88) degrees Baume. Not less than ninety-nine (99) per
cent. of the bitumen shall be soluble in carbon tetra-chloride, and it
shall not contain more than sixteen (16) per cent. of fixed carbon.[15]
Bitumens resulting from destructive distillation or from artificial
oxidation, and bituminous compounds prepared from oil or oil residuums
heated with sulphur or other substances, or coal or gas tars, will not
be accepted, nor shall they be mixed with the asphalt used.[16]
=45.= Asphalts that are injuriously affected by water, and those whose
practical value for making pavements has not been established, in the
judgment of the City, by sufficient experience, will not be accepted
except under such special bond and guaranty provisions as the City may
prescribe.[17]
=46.= Full information as to the source and character of the crude
asphalt and the method of refining it shall be furnished to the Engineer
and verified by such evidence as he may require.
=47. Softening or Tempering Agent.=—For softening and tempering refined
asphalt, petroleum residuum oil or liquid asphalt shall be used. It
shall be free from water, coke, and other impurities. Its specific
gravity shall not be below 0.92, nor above 1.04. Its flash test
(determined in the standard New York State closed oil-testing apparatus)
shall not be under three hundred and fifty (350) degrees F., and when
exposed for seven (7) hours to a temperature of three hundred and
twenty-five (325) degrees F., in a shallow open dish, the bottom of
which is covered by the oil to a depth of three-fourths (¾) inch, it
shall not lose more than five (5) per cent. by evaporation. It shall not
contain more than ten (10) per cent. of paraffine scale.
=48. Sand.=—A superior quality of sand will be required and this must be
secured, if necessary, by the admixture of two or more sands. The sand
shall be silicious and so free from organic matter, mica, soft grains,
and other impurities, that these shall not aggregate more than two (2)
per cent. of the mass. The grains shall, preferably, be moderately
“sharp” or angular, and must be of assorted sizes so that the voids in
the compacted mass of dry sand shall not exceed thirty three (33) per
cent. A typical sand, to be approximated as closely as practicable, will
give the following sieve tests, the sieves being used in the order
named:
3 per cent. of the whole will pass No. 200 sieve.
15 per cent. of the whole will pass No. 100 sieve.
18 per cent. of the whole will pass No. 80 sieve.
30 per cent. of the whole will pass No. 50 sieve.
24 per cent. of the whole will pass No. 30 sieve.
10 per cent. of the whole will pass No. 10 sieve.
and none will fail to pass the No. 10 sieve.[18]
=49. Pulverized Stone.=—This may consist of limestone or other sound
stone or sand, pulverized to such fineness that the whole will pass the
No. 50 sieve, not more than ten (10) per cent. will be retained on the
No. 100 sieve, and at least seventy (70) per cent. of it will pass the
No. 200 sieve. Portland cement may be partly substituted for pulverized
stone, where the Engineer shall so direct.[19] Portland cement thus used
will be paid for at the price bid per barrel for the same, in addition
to the price paid per square yard for the pavement surface. The
pulverized material must be thoroughly dry when used.
=50. Asphaltic Paving Cement.=—Asphalt Paving Cement shall be prepared
from the refined asphalt described in Sect. 44 and the tempering agent
described in Sect. 47. The refined asphalt, together with the asphalt in
the tempering agent, shall constitute not less than sixty per cent.
(60%) of the asphaltic cement.
The refined asphalt and the tempering agent shall be mixed and melted
together at a temperature not below two hundred and seventy-five degrees
F. (275° F.), and not above three hundred and twenty-five degrees
Fahrenheit (325° F.), and thoroughly incorporated by agitation until a
homogeneous cement is produced. The agitation shall be continued until
the cement is used.
The asphaltic cement at a temperature of seventy-seven degrees F. (77°
F.) shall be of such consistency as to show a penetration of from forty
to eighty hundredths of a centimeter, as the engineer may direct for
each street, when tested with the standard Dow penetration apparatus,
using a number two cambric needle loaded with one hundred grams. When a
cement of a consistency satisfactory to the engineer has been produced
and approved for any street a sample of it shall be kept as a standard
and all subsequent batches or kettles must be made to conform thereto,
suitable apparatus and tests being employed to determine the
correspondence of each new batch with the standard.[20] The asphaltic
cement when at its melting temperature shall be so viscous that it will
draw out into moderately long fine threads which shall be free from
lumps or raggedness and shall possess satisfactory adhesive and
cementitious qualities.[21]
=51. Composition and Preparation of Asphalt Surface Mixture.=—The
surface-course shall be composed of the materials specified in Sections
43, 44, 45, 46, 47, 48, 49, and 50 mixed in such ratios by weight as the
Engineer may direct or approve. A typical mixture will contain:
Sand 100.0 lbs.
Pulverized mineral matter passing No. 200 screen, including
that found in the paving cement 17.5 lbs.
Pure bitumen (in paving cement) 13.5 lbs.
But the quantities of pulverized stone and of asphaltic cement shall be
varied as may be found necessary or desirable by the Engineer to suit
the purity of the asphaltic cement, the character of the sand, the
climatic conditions, and the varying quantity and character of travel on
the street to be paved; and Portland cement may be substituted partly or
wholly for the pulverized stone, when directed by the Engineer. The
surface-course mixture shall be submitted to the Engineer and approved
by him before any is laid upon the street.
The mixing shall be accomplished in a mechanical mixing apparatus
capable of rapidly and effectually incorporating the materials together,
and each batch must remain in the mixer a sufficient length of time to
effect a perfect mixture. The sand shall be separately heated and shall
reach the mixing apparatus at a temperature not above three hundred and
fifty (350) degrees F., nor below three hundred and twenty (320) degrees
F. The pulverized stone shall be at such a temperature that when mixed
with the sand the temperature of the mixed mass shall not be above three
hundred and fifty (350) degrees F., nor below three hundred and twenty
(320) degrees F. The sand shall be first placed in the mixer, followed
by the pulverized stone, and these two materials shall be thoroughly
mixed together before the asphaltic cement is added. The asphaltic
cement at a temperature not above three hundred and fifty (350) degrees,
nor below three hundred (300) degrees F. shall then be added in such a
way as to evenly distribute it over the sand and pulverized stone, and
the mixing continued until the materials are thoroughly incorporated
into a perfectly uniform and homogeneous mass, with the grains of sand
completely covered with cement. Suitable thermometers shall be
constantly used to determine the temperatures specified herein. Great
care must be taken to accurately weigh and proportion the materials
charged into the mixer.[22]
=52. Stone for Base-course.=—Stone screenings for base-course shall be
of crushed, hard, durable stone. The portion used shall all be retained
upon a No. 8 sieve, or screen, and shall all pass a screen having square
meshes, the linear dimensions of the openings in which are one-half (½)
inch less than the thickness of the base-course.
=53. Composition of Base-course.=—The base-course shall be composed of
the crushed stone specified in Section 52, mixed with the asphaltic
cement, sand and pulverized stone specified in Sections 50, 48 and 49,
but the asphaltic cement shall be of such hardness as the engineer may
direct.
A typical base-course mixture will be composed as follows:
Crushed stone 100 lbs.
Sand 42 lbs.
Pure bitumen (in asphaltic cement) 7 lbs.
Pulverized stone 7½ lbs.
But the mixture shall be such that when placed on the street and
compressed by the roller the mass shall be dense and the voids in the
stone completely filled; and to accomplish this the quantity of crushed
stone used in the mixture may be increased or decreased, as the volume
of its voids may require, in order that they may be completely
filled.[23]
=54. Mixing the Base-course.=—The materials for the base-course shall be
heated and mixed in the same general manner as prescribed for the
surface-course (Sect. 51), the crushed stone being delivered first in
the mixer. The temperature of the mixture as it comes from the mixer
being not above three hundred and twenty-five (325) degrees F., nor
below three hundred (300) degrees F.
=55. Laying Asphalt Pavement, General.=—Asphalt pavement must not be
laid except when the surface upon which it is to be placed is dry; nor
when the temperature of the air is below thirty-two (32) degrees F., or,
if a strong wind prevails, when the temperature of the air is below
forty (40) degrees F.
The pavement mixture, whether for base- or surface-course, shall be
taken to the street as soon after it leaves the mixer as practicable.
When the temperature of the air is below seventy (70) degrees F., the
loaded vehicles conveying the mixture to the street shall be covered by
canvas covers to prevent the escape of heat. When unloaded upon the
street, the temperature of the mass should not be below two hundred and
eighty (280) degrees F., and any load or portions of a load found under
two hundred and forty (240) degrees F. must be rejected. After being
unloaded on the street, the mixture must be shoveled into place in such
a manner that the whole of it will be moved from the pile into which it
was unloaded.
=56. Laying the Base-course.=—The base-course will have an average
thickness of one and one-quarter (1¼) inches after compression. It shall
be laid directly upon the pavement foundation, which must be free from
all loose fragments and rubbish and be swept clean in advance of the
application of the base-course. The base-course mixture shall be spread
upon the foundation and evenly and regularly graded to such a depth that
after compression by the roller its surface will be ... inches below,
and truly parallel to, the pavement datum.
Great care must be taken in handling, spreading and grading the mixture
to maintain the uniform admixture of the crushed stone throughout the
mass. The rakes used must have tines wide apart, and the back of the
rake must be principally used for grading. Immediately after being
graded, and while still hot, the base-course shall be rolled with an
asphalt roller weighing not less than five tons, the rolling being
continued until no further compression takes place.
The base-course must not be laid more than one day’s work in advance of
the surface-course.
When the base-course is completed it must present a uniform appearance
and texture over the whole surface, which must conform so truly to the
designed grade and contour that a twelve-foot template, when applied,
will show no departure from the true surface greater than one-quarter
(¼) inch.
=57. Laying the Surface-course.=—In delivering the surface-course
mixture upon the base-course, care must be taken not to break or disturb
the latter. Any breaks made in the base-course must be so repaired,
before the surface-course is spread, as to be equal in density and
surface to the adjoining base.
Before the surface-course is spread the base-course must be thoroughly
cleaned and all rubbish, loose material and street dirt removed.
The material for the surface-course shall be so evenly spread and graded
with asphalt rakes that after it is properly compacted by rolling, the
surface will coincide with the pavement datum within the limits named
below. In grading the material, all lumps must be broken up and the
whole reduced to a finely comminuted mass of equal density throughout.
Directly after being so graded it shall be rolled with a hand-roller, or
light steam-roller, to partly compress the material, and, when so
directed by the Engineer, the surface shall then be ironed with
smoothing irons heated to a temperature that will melt, but not burn,
the asphaltic cement. A thin layer of hydraulic cement, just sufficient
to prevent adhesion between the material and the roller, shall then be
swept over the surface, which shall at once be thoroughly rolled with a
ten-ton asphalt roller until the material shall be thoroughly compressed
and its surface be brought to the exact grade and contour designed for
the street surface. The work of the ten-ton steam-roller must begin
before the material has cooled below two hundred (200) degrees F., and
be continued until the roller makes no further impression upon the
surface. The first course of the heavy rolling shall be parallel to the
street beginning at the curb and working toward the center on each side,
after which it should be diagonally rolled, and also cross-rolled if the
width of the street permits.[24] Any portions of the surface not
accessible to the roller shall be tamped with hot tampers until
compacted equally with the rolled portion. When completed, the surface
shall have an average thickness of ... inches and must be so free from
waves or irregularities that a template not less than twelve feet long,
when applied to the street surface shall nowhere show a divergence from
the designed true surface of more than three-sixteenths (³⁄₁₆) inch, and
a template sixteen (16) feet long applied to the gutters shall show no
divergence from the true gutter grade greater than one-eighth (⅛) inch.
Before the surface-course is placed, all exposed surfaces of curbs,
crosswalks, manholes, etc., with which the surface-course will be in
contact, must be well painted with hot paving cement or approved pitch.
The street shall not be opened to travel until the pavement has become
cold and hard.
=58. Street Railroad Tracks.=—Where railroad tracks exist on the
streets, the sub-grade and the pavement foundation shall extend under
the tracks, uninterrupted except by the ties and other structures
connected with the track. Where concrete foundation is used, special
care must be taken with the concrete directly under or around the rails,
and concrete made of fine crushed stone and a higher ratio of cement and
sand may be required in contact with the rail. The concrete must be
thoroughly tamped under and against the rail.
The asphalt surface shall be laid directly against the rails, which, if
their temperature be under fifty (50) degrees F., shall be heated by
suitable appliances to a temperature of, or above, sixty (60) degrees F.
immediately before the asphalt material is placed around the rail. The
hot asphalt material must be thoroughly tamped against and along the
rail and under any projecting portions of it, and the surface of the
pavement must be even with, or slightly (not more than one-eighth (⅛)
inch) above the top of the rail. Slot-rails will be treated in the same
manner, subject to such modifications as their forms may
necessitate.[25]
=59. Plant.=—The plant for making asphalt paving mixtures must be of
approved modern design, adapted to do the work properly, and equipped
with efficient machinery. It shall be of sufficient capacity to turn out
at least twelve hundred square yards of pavement surface daily without
crowding. Weighing and measuring devices shall be accurate and adapted
to the purpose, and must be frequently tested and adjusted. Each plant
must be supplied with the apparatus necessary to make all determinations
and tests required at the plant to properly conduct the work in
accordance with these specifications. Steam-rollers must be properly
balanced and the rolling surface must be true and smooth. All the street
tools used must be of approved kind and quality and must be kept in good
working order.
ASPHALT BLOCK PAVEMENT
=60. Sub-grade.=—The sub-grade for asphalt block pavement shall be
prepared as specified in Sect. 26 of these specifications.
=61. Foundation.=—The foundation for asphalt block pavement shall be
hydraulic concrete or broken stone.[26]
Concrete foundation shall be constructed in accordance with Sections 28
to 37 inclusive of these specifications and shall have a thickness
of ... inches.
Broken stone foundation shall be constructed in accordance with Section
40 of these specifications and shall have a thickness, when completed
of ... inches.
=62. Asphalt Blocks.=—Asphalt blocks shall be not less than ten (10)
inches nor more than twelve (12) inches long, not less than four (4) nor
more than six (6) inches wide and not less than two (2) inches nor more
than four (4) inches thick. Blocks for the same street must be of the
same standard size throughout and individual blocks shall not vary in
any dimension more than three-sixteenths (³⁄₁₆) inch from the standard
size. Blocks that are chipped, cracked or are otherwise defective shall
be rejected.
=63. Material and Composition.=—Asphalt paving blocks shall be composed
of crushed trap rock[27] or equally hard and durable rock, sand,
pulverized stone and asphaltic cement.
The crushed rock shall be of such sizes that all will pass a screen
having circular openings one-third (⅓) inch in diameter and that all
will fail to pass a number ten (No. 10) sieve. The stone shall be
freshly crushed, free from foreign substances and clean and bright.
The sand shall be clean and sharp and of such sizes that all will pass
the number ten sieve and not more than five per cent. will pass the
number two hundred sieve. The grain-size of the sand shall preferably be
such that at least fifty per cent. (50%) of it will pass the number
eighty sieve. The screenings from the crushed stone passing the number
ten sieve may be used in place of sand, or thoroughly mixed with the
sand to produce a mass of the above composition. The pulverized stone
shall comply with Section 49 of these specifications. Portland cement
shall be used in place of not more than ten per cent. of the whole if
directed by the engineer, in which case the Portland cement will be paid
for as extra work at the prevailing market price.
The asphaltic cement shall comply with the requirements of Sections 43,
44, 45, 46, 47 and 50 of these specifications.
=64. Typical Composition.=—A typical composition of the blocks, which
must be complied with as nearly as practicable, is as follows; (by
weight)
Bitumen 7%
Mineral material passing No. 200 sieve 13%
Mineral material passing No. 80 sieve 9%
Mineral material passing No. 40 sieve 7%
Mineral material passing No. 10 sieve 28%
Mineral material passing No. 3 sieve 36%
————
100%
=65. Manufacture.=—The crushed rock, sand and pulverized stone shall be
thoroughly mixed together at a temperature not above three hundred and
seventy-five degrees Fahrenheit (375° F.) and not below three hundred
and twenty-five degrees Fahrenheit (325° F.) and the asphaltic cement,
at a like temperature, added and the mixing continued until a perfectly
uniform mass is produced, with every fragment of stone completely coated
with cement.
The hot mixture will then be compressed in molds under a pressure not
less than four thousand (4000) pounds[28] per square inch, after which
the blocks will be removed from the molds and allowed to cool, either in
the air or in water.
The completed blocks after cooling in air shall have a specific gravity
of not less than 2.5. They shall not absorb, when immersed in water for
twenty-four hours, more than one-half of one per cent. of water. When
tested in the standard rattler for testing paving brick the average loss
by abrasion shall not exceed twelve per cent. (12%) of their original
weight, after 1800 revolutions of the rattler.
=66. Laying the Blocks.=[29]—The foundation shall be first cleaned of
dirt, rubbish or loose material.
When the blocks are four (4) inches or less in depth as laid, they shall
be set upon a bed of mortar made and applied to the foundation in the
following manner:
The mortar shall be composed of Portland cement and sand, in the ratio
of one (1) part cement to three (3) parts of sand, thoroughly mixed with
sufficient water to make a rather soft mortar. This mortar shall be
spread over the foundation, which shall be previously wetted, in a layer
approximately one-half (½) inch thick and its top graded by the use of
templates to a surface at such depth below, and truly parallel to the
pavement datum, that when the blocks are firmly set in it and rammed
their tops will be in the true grade and contour of the pavement. The
mortar shall be made and spread only as required in the progress of
block laying, and any mortar that has begun to set before the blocks are
in place and rammed, shall be removed and fresh mortar substituted. The
blocks shall be set upon this mortar bed with their longest dimension
across the street, in continuous courses which shall be straight and at
right angles to the axis of the street. The block layers must stand upon
the blocks already laid and not upon the mortar. The blocks and the
courses of blocks shall be set as closely together as practicable.
Blocks in adjoining courses must break joint not less than four inches.
Whole blocks only will be used, except as fillers at the ends of the
courses or in fitting the pavement around manholes or other structures,
and where thus used the broken ends of the blocks must be dressed to
make close joints. Unless otherwise permitted, each course must be laid
continuously across the street without interruption in time. As each
course is completed the end joints shall be forced close together by the
use of wedges, levers or mauls. Upon the completion of every third
course, the courses shall be forced together by placing a timber
scantling against the face of the last course and striking it with a
sledge or maul. When the blocks are thus laid, and before the mortar
under them begins to set, they shall be well rammed to a solid bearing
in the mortar with a wooden street rammer weighing not less than thirty
(30) pounds, a two inch plank ten (10) inches wide and three (3) feet
long being interposed between the block and the rammer and moved about
so that the whole surface shall be covered and rammed. When the ramming
is completed, the top of the blocks must conform so closely to the
pavement datum that when a template or straight-edge is placed upon the
pavement, its surface shall nowhere depart from the true surface more
than three-sixteenths (³⁄₁₆) inch. Blocks, or portions of the pavement
found too high or too low, must be taken up and reset in fresh mortar to
the true grade. When thus completed to the satisfaction of the Engineer,
a layer of one-half (½) inch of fine dry sand shall be placed over the
surface and swept about with brooms until all joints are completely
filled. The remaining sand shall be removed from the pavement at such
time as the Engineer may direct.
When the depth of the blocks exceeds four (4) inches, they may be set
upon a cushion course of sand, as prescribed for brick pavement, Section
86, the joints to be filled with sand, as specified above in this
Section.
=67. Railroad Tracks.=—Where railroad tracks exist on the street to be
paved, the construction shall be the same as prescribed for granite
block pavement, Section 78.
=68.= The street shall not be opened to travel until the mortar under
the blocks shall have become fully set, and in no case under five days
after the blocks are laid.
GRANITE BLOCK PAVEMENT
=69.= Granite block pavement shall be laid upon a foundation of
hydraulic cement concrete.[30]
=70. Sub-grade and Foundation.=—The sub-grade shall be prepared as
specified in Section 26. The foundation shall be constructed in
accordance with the requirements of Sections 28 to 38 inclusive.
=71. Granite Blocks.=—The blocks shall be made from sound, durable
granite, of uniform texture, composition and hardness throughout. No
outcrop, deteriorated, soft, brittle, or seamy stone shall be used. If
the blocks are obtained from different quarries, or from different parts
of the same quarry where the quality or appearance of the rock differs,
the product of each must be kept separate and laid together on the
street.[31]
The blocks shall be not less than eight (8) nor more than twelve (12)
inches long, not less than three and one-half (3½) nor more than four
and one-half (4½) inches wide, and not less than four and three-quarters
(4¾) nor more than five and one-quarter (5¼) inches deep.[32] They shall
be well-shaped, rectangular, with full edges and corners. Their tops
shall not depart more than one-fourth (¼) inch from a true plane, and
their sides shall be dressed so that joints between the courses will
nowhere exceed three-fourths (¾) inch wide, and their ends so that end
joints shall not exceed one-half (½) inch wide.[33] The size of the
blocks may be varied where necessary to fit the pavement against or
around bridge stones or other street structures.
=72. Sand Cushion.=—The foundation shall be cleaned of all dirt and
rubbish. There shall then be spread evenly over it a layer of clean,
coarse sand to a uniform depth of one and one-half (1½) inches.
=73. Setting the Blocks.=—The blocks shall be set in this bed of sand
perpendicular to the street surface, with their length at right angles
to the street, in courses extending entirely across the street, and at
right angles to its axis, except at street intersections where the
courses shall be arranged as the Engineer may direct.[34] Only stones of
the same width shall be set in the same course. The stones in each
course, and in adjoining courses, shall be set firmly against each
other. The blocks shall be set in the sand bed in such a manner that
their bottom surface shall rest evenly upon the sand and that their tops
shall be even with each other and to such an elevation that after the
pavement is rammed, as hereinafter directed, its general surface shall
conform closely to the pavement datum. Stones in adjoining courses shall
break joint not less than three (3) inches.
=74. Ramming.=[35]—After the blocks are set each individual block shall
be thoroughly rammed to give it a firm bearing in the sand and to bring
its top to the prescribed pavement datum. The rammers used shall have
wooden faces not more than four inches in diameter, and shall weigh not
less than thirty (30) pounds. Blocks or sections of blocks whose tops
under the ramming remain above or sink below the pavement datum shall be
taken up and reset so that after the ramming is completed their tops
shall coincide with the pavement datum.
=75. Filling the Joints.=[36]—After the ramming specified in Sect. 74
shall have been completed, the joints between the paving blocks shall be
filled in the following manner:
All the joints for a distance of three feet out from the curbstones, and
three contiguous joints continuous across the street, with the included
end joints, at intervals of about fifty (50) feet in the length of the
street, shall be filled with gravel and bituminous paving cement. The
gravel used shall be of such size that all will pass through a screen
having five-eighths (⅝) inch meshes, and all will be held on a screen
having one-fourth (¼) inch meshes. When used, the gravel must be free
from refuse and street dirt. The bituminous paving cement shall be
composed by weight of straight-run coal-tar pitch of the hardness
commonly known as number six, to which has been added and thoroughly
mixed, while both are in a melted condition, twenty per cent. (20%) by
weight of refined Trinidad asphalt, or other asphalt, equal for the
purpose, and twenty per cent. (20%) by weight of Portland cement. These
ingredients must be thoroughly mixed, and kept agitated until used.[37]
The joints will first be filled with the gravel, which shall be
perfectly dry, and heated so that when put in the joints it will be at a
temperature of about three hundred (300) degrees F. The paving cement,
heated to a temperature of about three hundred (300) degrees F., shall
be at once, while the gravel is still hot, poured from a spouted vessel
into the joints until the interstices of the gravel are entirely filled
to the surface of the pavement, repouring being resorted to to
accomplish this result whenever necessary.
All the joints in the pavement other than those named above shall then
be completely filled with Portland cement grout, in the following
manner:
The grout shall be composed of equal parts by volume of sand (Sect. 30)
and Portland cement (Sect. 29), a quick-setting cement being preferred.
The sand and cement shall be first thoroughly mixed dry and then enough
water added to make a grout of such consistency that it will flow like
thick cream, and the mixing continued until a homogeneous mass is
produced and until the grout is applied to the pavement. The grout shall
be prepared in water-tight boxes of a convenient size. Before applying
the grout the pavement shall be thoroughly dampened by sprinkling. The
grout shall be removed from the mixing box and spread over the pavement
with scoop shovels, in two courses, the first being sufficient to about
half fill the joints, and the second, which shall be applied before the
first has begun to set, shall be sufficient to entirely fill the
remaining space in the joints. As the grout is applied to the pavement
it shall be swept about with brooms until it all enters the joints.
=76. Order of Work.=—The sand bed shall not be put in place more than
fifty (50) feet ahead of the block setters. The ramming and filling of
the joints shall follow closely the block setting, but no ramming shall
be done within less than six (6) feet of the face of the block setting;
and the final joint filling shall be kept completed to within
twenty-five (25) feet of the ramming; except that all the work rammed
during any day shall have the joint filling completed before the
cessation of work on that day. The street shall not be opened to travel
until the grout has thoroughly set.
=77. Fitting Paving Around Other Structures.=—The size of blocks and the
width of courses shall, as the block laying approaches bridge stones,
curbs and other structures, or in making closures with other sections of
pavement, be so selected and adjusted that joints not over
three-quarters (¾) inch in width shall result, without breaking blocks
or splitting courses.
=78. Street Railroad Tracks.=—Where railroad tracks exist in the street
the paving blocks shall be laid against the rail in the following
manner:
The sub-grade and the pavement foundation shall extend under the rails
uninterrupted except by the ties or other structures connected with the
railroad track. For a distance of sixteen (16) inches, on each side of
the rail, measuring from the center thereof, there shall be spread on
the pavement foundation a layer of mortar not less than one and one-half
(1½) inches thick, composed of one (1) part of cement and three (3)
parts sand, complying with the requirements of Sections 29 and 30. Upon
this layer of mortar shall be set, against the rail, and on each side of
it, selected paving blocks, securely bedded in the mortar before it
shall have begun to set.[38] Alternate blocks shall be long and short so
as to break joint with the blocks of the adjoining pavement. Selected
blocks with well dressed top surfaces shall be used and their tops shall
be set as nearly as practicable at the level of the top of the rail, but
not so high that the car wheels will ride upon them. In setting the
blocks they shall be firmly bedded into the mortar by the use of paving
hammers, but they shall not be thereafter rammed. As the blocks are set,
any space between the paving blocks and the web of the rail shall be
filled with mortar of the quality described above. The placing of these
blocks shall not precede by more than ten (10) feet the block laying on
the street. Care must be taken not to disturb the bedding of these
blocks in the laying of the adjoining pavement, or otherwise. The joints
shall be filled with grout as specified in Sect. 75.
The construction along slot-rails shall be the same as described above,
except that blocks of special size or shape may be required, as the
Engineer may direct.
=79. Bridge Stone Crossings.=—Where directed by the Engineer, the old
bridge stone shall be redressed and relaid, as hereinafter specified for
new bridge stone, and shall be moved from the point where taken up to
the point where they are to be relaid, by the Contractor at his expense.
New bridge stone shall be of the same quality of granite as the paving
blocks and free from imperfections. They shall not be less than three
and one-half (3½) nor more than six (6) feet long, eighteen (18) inches
wide and of a uniform thickness not less than six (6) nor more than
eight (8) inches, but these dimensions may be varied by the Engineer
where necessary to fit the stone into special locations.
Their top shall be well dressed to a true plane surface not varying in
evenness more than one-quarter (¼) inch. The sides shall be dressed
perpendicular to the face so as to joint closely against the paving
blocks. The ends shall be cut to lines making an angle of from 60° to
45° with the longitudinal axis of the stones[39] and so dressed and to
such a bevel that when set in the curved surface of the street, the
joint between adjoining stones shall not be wider than three-eighths (⅜)
inch from top to bottom.
Bridge stones shall be set in advance of the block laying, over the
concrete street foundation, in a bed of sand or gravel in which they
shall be firmly bedded. Their upper surface shall conform truly to the
pavement datum. They shall be set accurately to the lines given by the
Engineer. Where the crosswalk requires more than one width of bridge
stone, the courses shall be laid parallel to, and at such distance from
each other as the Engineer may direct, and the space between courses
shall be filled with paving blocks laid as specified for other parts of
the street.
BRICK PAVEMENT[40]
=80. Sub-grade.=—The sub-grade for brick pavement shall be prepared in
accordance with Sect. 26, and shall be finished to a surface ... inches
below and parallel to the pavement datum.
=81. Foundation.=—The foundation for brick pavement shall be of
hydraulic concrete[41] prepared in accordance with Sections 28 to 37
inclusive. Its thickness shall be ... inches and its upper surface
shall, when completed, be parallel to and at a depth below the pavement
datum equal to the depth of the brick plus one and one-fourth (1¼)
inches. The surface of the foundation shall not vary more than one-half
(½) inch above or below that depth.
=82. Paving Brick.=—The linear dimensions of paving brick may vary
between the following limits: In length, from eight and one-half (8½) to
nine and one-half (9½) inches; in width, from two and one-fourth (2¼) to
three and one-half (3½) inches; in depth, from four (4) to four and
one-eighth (4⅛) inches; but the length shall not be less than two and
one-half (2½) nor more than three and three-fourths (3¾) times the
width.[42] The corners shall all be rounded off to a radius of not less
than one-eighth (⅛) nor more than three-sixteenths (³⁄₁₆) inch. The
brick for any one contract shall be all of the same kind and of the same
standard size, and the individual bricks shall not vary in length more
than three-sixteenths (³⁄₁₆) inch, nor in width more than one-eighth (⅛)
inch from the size adopted as standard. Raised lugs or letters are
permissible on one side of each brick but must not project more than
three-sixteenths (³⁄₁₆) inch from the general surface.[43]
The brick must be specially manufactured for paving purposes. They may
be made from shale or from suitable clay. In either case the material
must be thoroughly pulverized, mixed and tempered, and must be free from
lime nodules or other substances that may disintegrate the brick when
immersed in water. The brick shall be molded in efficient brick machines
to a truly rectangular form, free from cracks, flaws and injurious
laminations. After being dried the brick shall be properly and uniformly
burned in down-draft kilns. Shale brick shall be burned to the point of
incipient fusion or vitrification. After the burning is completed, the
brick shall be allowed to cool with sufficient slowness to insure
thorough annealing.
The completed brick shall be free from flaws, cracks, ragged corners,
and from such distortion or warping as will interfere with their utility
or good appearance in the pavement. Paving brick shall not be
salt-glazed.
=83.= The brick shall be subjected to the following tests to determine
their quality:
When broken by the blows of a hammer the brick shall be strong and
tough. The broken surface shall show a homogeneous composition
throughout the broken section, free from flaws, injurious laminations,
nodules and voids, and shall appear to be uniformly burned from surface
to center.
When subjected to the standard “Rattler” test, in accordance with the
rules adopted by the National Paving Brick Manufacturers’ Association,
the average loss in weight shall not exceed eighteen (18) per cent.[44]
and the loss in weight of any individual brick in the test shall not be
more than twenty-five (25) per cent. greater than the average loss of
the whole charge.
When subjected to the absorption test, in accordance with the rules
adopted by the National Paving Brick Manufacturers’ Association, shale
bricks shall not absorb more than two (2) per cent. nor less than
one-half (½) of one per cent. of their weight of water,[45] and clay
bricks shall not absorb more than six (6) per cent. of their weight of
water; the absorption of any individual brick shall not be more than
fifty (50) per cent. greater than the mean absorption of the whole lot
tested.[46] Brick that do not successfully pass all these tests will not
be accepted.
=84. Samples.=—Where samples of paving brick have been required and
submitted by successful bidders, and tested as described above, it will
be assumed that these samples fairly represent the quality of the brick
to be subsequently supplied for the work, and brick that do not come up
to the standard thus established will not be accepted.
=85. Delivering Brick on Street.=—Unless the sidewalks are too narrow to
permit of it, the brick shall all be delivered upon the street before
the foundation is constructed, and neatly piled upon the outer edge of
the sidewalks; occasional openings being left in the piles for the
accommodation of foot passengers. One-half the brick required shall be
thus delivered and piled upon each sidewalk. In delivering the bricks
from these piles to the bricklayers, they must be carried on pallets, or
other suitable devices must be used to prevent mutilation by rough
handling; they must not be dumped from wheelbarrows upon freshly-laid
brick pavement.
If for any reason the bricks are not delivered before the foundation is
laid, or if the sidewalks are too narrow to permit of the brick being
stored upon them, they may be delivered over the foundation, but not
until the concrete has set so hard that it will not be injured by
transportation over it.
=86. Sand Cushion.=—Directly before the brick are laid into the pavement
there shall be spread over the foundation a layer of sand one and
one-half (1½) inches in depth. The sand shall be free from vegetable or
other refuse matter, and shall not contain more than five (5) per cent.
of clay and loam. Pebbles and fragments of stone exceeding one-fourth
inch in diameter must be screened out. When spread on the street the
sand shall be sufficiently dry to permit of proper gaging by templates,
as hereinafter described. The sand shall be spread and correctly gaged
to the proper thickness and surface by the use of templates formed to
the true designed cross-sectional contour of the pavement. If the width
of the street between curbs does not exceed twenty-five (25) feet, the
template shall be made in one length sufficient to cover the full width
of the street, and its ends shall be so constructed and fitted with iron
rollers, that it will rest upon and roll along the top of the curb at
each end; if the width of the street between curbs be not more than
fifty (50) feet, the template shall be of sufficient length to reach
from the curb to the middle of the street, and constructed to move on
rollers on top of the curb at one end and upon a plank six (6) inches
wide and one and one-half (1½) inches thick laid upon the foundation
along the center line of the pavement. The template shall be worked
forward and backward along the line of the street until the surface of
the sand conforms exactly to the designed contour of the pavement, at a
depth below the pavement datum equal to the depth of the paving brick
minus one-fourth (¼) inch. The whole surface shall then be rolled with a
garden roller not less than thirty-six inches long and not less than
thirty inches in diameter, weighing not less than three hundred pounds.
When completed the surface of the sand cushion shall be smooth and
unbroken, and care must be taken not to disturb it before the bricks are
set upon it.
=87. Setting the Brick.=—Several courses of brick, aggregating a strip
having a width of not less than twelve (12) inches nor more than fifteen
(15) inches on each side of the street, beginning against the curb,
shall be first laid; the brick being set with their long dimension
parallel to the curb.[47] The pavement intervening between these gutter
courses will then be set in courses at right angles to the axis of the
street, except in street intersections, where the courses shall make an
angle of forty-five (45) degrees with the axis of the street. The brick
shall be set upon edge on the sand cushion with their top faces parallel
to the pavement datum, in straight courses, continuous across the
street, the long dimension of the brick being parallel to the courses;
they shall be set as closely together as possible, so that the joints
both between the courses and between individual bricks shall not exceed
one-eighth (⅛) inch, where the bricks are without lugs, and not more
than one-fourth inch where the brick have lugs. Broken bricks and bats
shall not be used except as closers at the ends of the course and in
fitting the pavement around manholes, etc., and nothing smaller than
half-bricks shall be used in either case, and the broken ends must be
shaped to make reasonably close joints. Filling up with bats must follow
the brick-laying closely. Brick with lugs shall be laid with the lugs
all in one direction.
=88. Inspection.=—After the bricks are laid the pavement will be
inspected by the Engineer, or his agent. He may require that the surface
shall be previously wetted by sprinklers, or by a sprinkling nozzle, in
order to detect soft or porous bricks.[48] Defective bricks indicated by
him shall be removed and replaced by acceptable brick.
=89. Rolling and Ramming.=—The surface of the pavement shall then be
rolled and rammed in the following manner:
The roller used shall be of the asphalt roller style, driven by steam
and weighing not less than three and one-half (3½) nor more than five
(5) tons. The rolling shall begin as near the curb as practicable, the
roller being operated slowly, parallel to the axis of the street, and
working outwardly until the center of the street is reached, when the
roller will proceed to the opposite side of the street and the operation
proceed as before. After this longitudinal rolling is completed the
pavement will be continuously rolled a second time, the roller operating
back and forth at an angle of forty-five degrees to the axis of the
street, and a third time, the roller operating at right angles to the
course of the second rolling. After the rolling is thus completed the
brick in the gutters not reached by the roller shall be rammed with a
street rammer weighing not less than thirty (30) pounds, a plank not
less than four (4) feet long, ten (10) to twelve (12) inches wide and
two (2) inches thick being interposed between the pavement and the
rammer and moved about so that the whole surface of the gutter shall be
thoroughly and equally rammed and its surface brought to an even
junction with the rolled portion of the work.
When the rolling and ramming is thus completed the surface of the
pavement shall conform so truly to the designed pavement datum that it
will nowhere depart more than three-sixteenths (³⁄₁₆) inch from properly
formed templates and straight-edges applied to its surface.
=90. Filling the Joints.=[49]—Directly after the completion of the
rolling and ramming, the joints between the bricks shall be filled as
follows:
The joints in the longitudinal gutter courses, and the joints between
six contiguous courses running across the street, from gutter to gutter,
in each length of fifty (50) feet of the pavement, shall be filled with
bituminous cement composed of coal-tar pitch, commercially known as
Number Four, to which has been added twenty (20) per cent. of refined
Trinidad asphalt and twenty (20) per cent. of hydraulic cement, all by
weight. In preparing this bituminous cement, the pitch shall first be
melted and the asphalt, also melted, added and thoroughly incorporated
by agitation. The hydraulic cement shall then be added and the whole
agitated until a complete and uniform mixture results. The bituminous
cement thus prepared shall while sufficiently hot and liquid to flow
freely, be poured from a spouted vessel into the joints until they
appear to be nearly or quite full. After allowing time for the filling
to subside, the joints will be gone over a second time and completely
filled.
All the remaining joints in the pavement shall be filled with Portland
cement grout, as follows:
The grout will be composed of equal parts by volume of sand (Sect. 30)
and Portland cement (Sect. 29), a quick-setting cement being preferred.
The sand and cement shall be first thoroughly mixed dry and then enough
water added to make a grout of such consistency that it will flow like
thick cream, and the mixing continued until a homogeneous mass is
produced and until the grout is applied to the pavement. The grout shall
be prepared in water-tight boxes of a convenient size. Before applying
the grout the pavement shall be thoroughly dampened by sprinkling. The
grout shall be spread over the pavement with scoop shovels, in two
courses, the first being sufficient to nearly fill the joints, and the
second, which shall be applied before the first has begun to set, shall
be sufficient to entirely fill the remaining space in the joints. As
rapidly as the grout is applied it shall be swept with brooms until it
all enters the joints.[50]
=91.= Travel must be excluded from the pavement until the grout has set
firmly; in no case less than five days, and the grout must be kept moist
during this period.
WOOD-BLOCK PAVEMENT
=92. Sub-grade.=—The sub-grade for wood-block pavement shall be prepared
as specified in Section 26, and shall be finished to a surface ...
inches below the pavement datum.
=93. Foundation.=—The foundation for wood-block pavement shall be
Portland cement concrete ... inches thick, prepared as specified in
Sections 28, 29, 30, 31, 32, 33, 34, 35, 36 and 37. The upper surface of
the concrete foundation, when completed, shall be at a distance below
the pavement datum equal to the depth of the blocks to be laid, plus
one-half (½) inch, and must not vary more than one-fourth (¼) inch above
or below that depth.
MATERIALS
=94. Wood-blocks.=—The wood-blocks may be made of Long-leaved yellow
pine (Pinus palustrus), Lob-lolly pine (Pinus tæda), Short-leaved pine
(Pinus echinata), Cuba pine (Pinus heterophylla), Black gum (Nyssa
sylvatica), Red gum (Liquidambar styraciflua), Norway pine (Pinus
resinosa), or Tamarack (Larix laricina), or of other species of wood of
equal strength and toughness and of a texture permitting as satisfactory
preservative treatment as those herein named. But, as far as
practicable, only one species of wood shall be used on any one
contract.[51]
Only wood from live, sound trees shall be used. The lumber from which
the blocks are cut shall be properly manufactured, free from bark, and
with full square corners. It shall be free from decay, dottiness,
brashness, shakes, large season cracks, loose or unsound knots over
three-fourths (¾) inch in diameter, and all other imperfections which
may, in the opinion of the Engineer, be detrimental. “Fat” pine
containing so much resin that it will not take up the specified quantity
of creosote oil in treatment may be rejected. Second-growth timber, and
Southern pine showing, outside of a radius of three (3) inches from the
heart, nine (9) or less annual growth rings to the inch, will not be
accepted.
The paving blocks made from the lumber hereinbefore specified shall be
well manufactured and truly rectangular and square edged. Their depth
(parallel to the fiber) shall be ... inches,[52] their length shall not
be less than six inches nor more than three times their depth, and their
width shall be from two and one-half (2½) to three and one-half (3½)
inches, but at least one-fourth inch less than their depth.
All the blocks for any one contract shall be of the same standard depth
and width, and the individual blocks shall not vary more than one-eighth
inch from the designated depth and width.
=95. Creosote Oil.=[53]—The oil used for the preservative treatment of
the paving blocks shall be coal-tar creosote oil, commonly known as dead
oil of coal-tar, without admixture or adulteration with other oils or
tars. Oils produced or resulting from the distillation of water-gas tar,
blast-furnace tar, producer-tar, lignite-tar, petroleum-oil tar, or
wood-tar, or, containing an admixture of any of these will not be
accepted. The creosote oil shall not contain more than five per cent.
(5%) of tarry matter nor more than two per cent. (2%) of water. Its
specific gravity at a temperature of 100° F. shall be not below 1.03 nor
above 1.08. Not less than ninety-nine per cent. (99%) shall be soluble
in hot benzol. It shall not contain more than eight per cent. (8%) of
tar acids. When two hundred (200) grams are subjected to distillation at
gradually increasing temperatures, not more than five per cent. (5%) of
distillate shall distil over up to a temperature of four hundred degrees
F. (400° F.), nor more than thirty-five per cent. (35%) shall distil
over up to a temperature of four hundred and fifty-five degrees F. (455°
F.), and not more than eighty per cent. (80%) shall distil over up to a
temperature of six hundred degrees F. (600° F.). After complete
distillation there shall not remain more than two per cent. of coke. The
residue remaining, upon sulphonating a portion of the total distillate,
shall not exceed one per cent. (1%). The above tests shall be made in
accordance with the methods prescribed in the “Report of the Committee
on Preservative Treatment of Poles and Cross-arms” of the National
Electric Light Association, 1911.
=96. Preservative Treatment.=—The paving blocks shall, after they are
cut to the proper dimensions, be subjected to preservative treatment
with the creosote oil specified in Section 95.
The contractor may employ any of the standard methods in common use for
impregnating the blocks, provided that uniform results are attained,
complying with the following requirements:
The wood shall not be heated during any part of the process to a
temperature exceeding two hundred and sixty degrees Fahrenheit (260°
F.).
All parts of every block shall be reached and penetrated by the oil. The
quantity of oil found in the blocks after treatment shall average not
less than ... pounds per cubic foot of wood.
The oil in the treating tanks during the process of impregnation shall
not become diluted with water to the extent of more than five per cent.
(5%) and if the percentage of water in the oil during the process of
treatment shall exceed two per cent. (2%) the quantity of the oil to be
injected in the wood as stipulated hereinbefore shall be increased in a
like ratio; for example, if the oil in the treating tanks shall be found
to contain four per cent. (4%) of water the quantity required to be
found in the blocks after treatment shall be four per cent. (4%) greater
than herein specified.
The quantity of oil injected shall be determined primarily by tank
measurements, but shall be verified by actual determination of the
quantity of oil in the treated blocks by the following method:
representative treated sample blocks shall be selected and an auger hole
one inch in diameter bored entirely through the block parallel to the
fiber, the borings all collected, thoroughly mixed, and the quantity and
ratio of oil to wood in the borings determined by extracting the oil
completely with carbon di-sulphide. The center of the auger hole shall
be located midway between the sides of the block and at a distance from
the end of the block equal to one-third (⅓) of the length of the block.
At the time of treatment the blocks shall not be green or saturated with
water, but they shall, preferably, not be thoroughly seasoned. After
treatment, and until used, the blocks shall, during dry weather, be
frequently well drenched with water to prevent excessive drying out and
cracking.
=97. Laying the Wood-Blocks.=—The concrete foundation shall be cleaned
and swept to remove all dirt and débris and shall be thoroughly dampened
immediately in advance of the setting of the blocks. Upon the concrete
foundation shall be spread a layer of mortar about one-half inch thick,
made of one part Portland cement and two parts sand with sufficient
water to make a moderately stiff paste.[54] The mortar shall be
thoroughly mixed and shall be spread in place over the concrete
foundation immediately in advance of setting the blocks to such a
thickness that when the blocks are set and properly tamped their tops
shall conform accurately to the pavement datum.
Upon this mortar bed the blocks shall be set with their fiber vertical,
in straight, parallel courses at right angles to the axis of the street,
except at street intersections where they shall be set at an angle of
forty-five degrees with the axis of the street. The blocks shall be set
as close together as practicable. Blocks in adjoining courses shall
break joint at least three inches. Blocks of such lengths shall be
selected as to make as little splitting as practicable in filling out
ends of courses. Where splitting is necessary, no fractional block shall
be used whose length is not at least equal to its width.
After the blocks are thus set the whole surface of the pavement shall be
rammed with a rammer weighing not less than twenty pounds, a plank ten
(10) inches wide, two (2) inches thick and four feet long being
interposed between the rammer and the pavement and moved about as the
ramming progresses until the blocks are forced into a firm seat in the
mortar bed and their tops brought accurately to the pavement datum. The
ramming shall be completed before the mortar under them has begun to
set, but no ramming shall be done, during the progress of the work,
nearer than three feet to the edge of the block setting, except where
the block setting may be suspended, as at the end of the day’s work,
when all the blocks then set shall be rammed.
The top surface of the pavement when completed shall conform so truly to
the pavement datum that correctly formed templates twelve (12) feet long
applied to the surface shall show at no place a departure of more than
three-sixteenths (³⁄₁₆) inch therefrom.
=98. Filling the Joints.=—After the block setting is completed,
perfectly dry, fine sand shall be spread over the pavement surface and
swept about until every joint into which the sand will penetrate shall
be completely filled. The remaining sand shall be left upon the pavement
for such time as the Engineer may direct, when it shall be removed by
the Contractor.[55]
=99. Inspection.=—The lumber for paving blocks will be inspected before
it is cut into blocks. The blocks will also be inspected upon delivery
to the street and as they are laid. Blocks that have, in treatment or
subsequent handling, developed open season cracks or wind shakes or
other imperfections that may prevent their durability or usefulness in
the pavement shall be rejected and removed from the street.
=100. Chamfered Blocks.=—Where wood-block pavement is laid on streets or
parts of streets having a gradient of more than 3%, the blocks shall not
be less than four (4) inches long, and the upper side-corners of the
blocks shall be chamfered to a depth of three-eighths (⅜) inch, the
chamfered surface to make an angle of 40 degrees with the vertical sides
of the blocks; or such other construction shall be used as will, in the
opinion of the Engineer, provide an equally good foot-hold for horses.
=101. Expansion Joints.=—Before the blocks are set there shall be placed
along and against each curb a board of trapezoidal section having a
width one inch greater than the depth of the blocks, the upper edge of
which shall have a thickness of three-eighths (⅜) inch for each ten feet
or fraction thereof of the width of the street between curbs, and a
bottom width one-fourth (¼) inch less than the top. The paving blocks at
the beginning and end of each course shall be set against this board.
After the ramming of the blocks has been completed, these boards shall
be carefully withdrawn and the space between the curbs and the paving
blocks shall be completely filled with the bituminous paving cement
described in Section 90.
=102.= The street shall not be opened to travel until such time as the
mortar under the blocks shall have become well set, nor until the
Engineer shall so direct.
BITUMINOUS CONCRETE PAVEMENT
_Note._—The phrase, Bituminous Concrete Pavement, has been applied to a
large variety of roadway surfaces differing materially from each other
in composition, construction and utility. Some of these are covered by
United States patents, the scope and limitations of which are not yet
fully determined or understood. The necessity of avoiding infringement
of these patents has to be kept in mind in framing specifications for
public use, and this consideration does not permit the presentation here
of specifications which, in the opinion of the author, would secure an
ideal pavement of this general character.
Bituminous concrete pavements constructed in substantial conformity with
these specifications have been laid on a number of city and town streets
and country roads and have proved satisfactory and fairly durable in
use. It is believed that they do not infringe any existing patents.
Our rather limited experience with pavements of this character seems to
indicate that if good materials are used and the work properly done,
they are suitable for use on city streets of light travel, and on
suburban streets and country roads carrying an amount of travel
considered heavy for these classes of roadways. Where the results have
been unsatisfactory, the cause can generally be traced to unsuitable
materials or unskillful construction, the result of ignorance or
carelessness on the one hand, or of the attempt to reduce first cost
below normal figures on the other. Many people are searching for a
pavement or roadway that will have all the good qualities of the
standard pavements but can be built about as cheaply as a common macadam
road. It is possible that something of the kind may be discovered; but
in the present state of the art it is chimerical. High quality and low
first cost do not go together in street paving. The question to be
considered is, rather, how can we invest a dollar in street or road
building so that it will, in the long run, yield the best return upon
the investment. The pavement provided for in these specifications is not
a cheap pavement, but where it is suitable for the conditions to be met,
it will be well worth its cost.
SPECIFICATIONS
=103. Sub-grade.=—The sub-grade except where old pavement is utilized
for foundation shall be prepared in accordance with Section 26 of these
general specifications.
=104. Foundation.=[56]—The foundation for bituminous concrete pavement
shall be a properly prepared old pavement, or hydraulic concrete, or
compressed broken stone, as determined by the engineer.
=105.= Old macadam pavement or road to be utilized for foundation, shall
be prepared in the following manner:
All high places or humps shall be dressed down to a plane two (2) inches
below the pavement datum, the work being done with care so as to disturb
as little as possible the macadam that is to remain. Depressions in the
old macadam shall be carefully cleaned out so as to remove all earth and
other débris and loose material, and filled with hydraulic concrete.
Newly dug or filled trenches and holes extending through the macadam
shall be excavated and cleaned out so as to admit the use of at least
four (4) inches of hydraulic concrete. The hydraulic concrete for thus
leveling up the roadway shall be composed of one (1) part of approved
Portland cement, four (4) parts of clean sand and nine (9) parts of
sound, hard crushed stone, well mixed into a wet concrete. After
placing, the concrete shall be well tamped so as to form a compact body,
conforming to a plane two (2) inches below the pavement datum. The
concrete shall be protected from travel and allowed to become well set
before the surface of bituminous concrete is applied.
=106.= Old stone block or brick pavement may be utilized for foundation,
provided that the blocks or bricks do not require to be taken up and
reset, or, if so taken up and reset, that the joints shall be completely
filled with grout composed of one (1) part Portland cement and two (2)
parts of good sand. Depressions, trenches and holes shall be treated as
specified in Section 105.
=107.= Hydraulic concrete foundation shall be constructed in compliance
with the requirements of Sections 28, 29, 30, 31, 32, 33, 34, 35, 36 and
37 of these specifications. Its depth or thickness shall be ... inches.
=108.= Broken stone foundation shall be ... inches in thickness after
completion. It shall be constructed in accordance with Section 40 of
these specifications.[57]
=109.= When completed the upper surface of the foundation shall nowhere
be more than two and one-half (2½) inches nor less than one and
three-fourths (1¾) inches below the pavement datum. No travel shall be
permitted upon the foundation until the bituminous concrete shall have
been laid.
=110. Bituminous Concrete.=—The bituminous concrete shall be composed of
crushed stone, sand, pulverized stone, and asphaltic cement.
A typical composition for the bituminous concrete, to be as closely
approximated as practicable, is as follows, the percentages being by
weight:
Pure bitumen in asphaltic cement. 8.5%
Pulverized stone passing No. 200 sieve. 8.5%
Sand passing No. 80 sieve. 10.0%
Sand passing No. 40 sieve. 23.0%
Sand and fine stone passing No. 10 sieve. 15.0%
Crushed stone passing a screen having four meshes to the linear
inch. 25.0%
Crushed stone passing a screen having two meshes to the linear
inch. 10.0%
——————
100.0%
The crushed stone shall be trap rock, granite, or hard, sound, durable
limestone. It shall be crushed to such sizes that all will pass through
a screen with two meshes to the linear inch and shall be of such
assorted sizes of fragments as will, when incorporated with the sand,
pulverized stone, and bitumen, produce a mixture substantially
conforming to the percentages of each named in the preceding paragraph.
The stone shall be freshly crushed, clean and free from clay, loam,
organic matter and refuse of every kind.
The sand shall be silicious, and free from clay, loam and refuse of all
kinds. The grains shall be of such sizes that approximately twenty-five
per cent. (25%) of the whole will pass the number eighty (80) sieve,
fifty-eight per cent. (58%) shall pass the No. 40 sieve and not more
than seventeen per cent. (17%) will pass the number 10 sieve, when used
in the order named. The pulverized stone shall conform to the
requirements of Sect. 49. Portland Cement may be substituted for not
more than twenty per cent. (20%) of the pulverized stone if the Engineer
so directs, in which case the Portland Cement actually so used shall be
paid for extra at the prevailing market price, to be agreed upon in
advance. The asphaltic cement shall comply with the requirements of
Sects. 43, 44, 45, 46, 47, and 50, except that it may have a somewhat
higher penetration, as may be determined by the Engineer.[58]
=111. Mixing.=—The materials composing the concrete shall all (except
the pulverized stone and Portland cement) be uniformly heated to a
temperature not exceeding three hundred and fifty degrees Fahrenheit
(350° F.) and not below three hundred degrees Fahrenheit (300° F.), and
while at such temperature shall be incorporated and mixed in a
mechanical mixer. The stone, sand, and pulverized stone shall be placed
in the mixer in the order named and well mixed together, after which the
asphaltic cement shall be added and the mixing continued until each
fragment is thoroughly coated with cement.
=112. Laying on the Street.=—The mixed concrete shall be taken to the
street as soon as practicable after leaving the mixer. It shall be
unloaded on the street, properly spread and truly graded with asphalt
rakes to such a depth that after compression by rolling it will have a
thickness of not less than two inches. The concrete when unloaded on the
street shall be at a temperature not below two hundred and eighty
degrees Fahrenheit (280° F.). In spreading and grading, all material
must be moved from the pile into which it was unloaded. As soon as
practicable after the concrete shall be graded, the surface shall be
thoroughly rolled with a ten-ton asphalt roller and the rolling
continued until the roller makes no further impression on the concrete
surface. When completed the surface must conform closely to the pavement
datum so that there will be no depressions or elevations exceeding
one-fourth inch above or below the pavement datum.
HYDRAULIC CONCRETE ROADWAY PAVEMENT[59]
=113.= The sub-foundation for hydraulic concrete pavement shall be
prepared as specified in Section 26.
=114.= The pavement shall be constructed in two courses called the
bottom course and the top course, as hereinafter specified.[60]
=115. Bottom Course.=—The bottom course shall be four (4) inches in
thickness[61] and shall be composed of the materials specified in Sects.
29, 30, and 31. The concrete shall be composed of one part Portland
cement, three parts sand and six parts of broken stone, and shall be
mixed and placed as specified in Sects. 35 and 36, but its top surface
when properly compacted shall be parallel to and not less than two (2)
nor more than two and one-half (2½) inches below the pavement datum.
=116. Top or Surface Course.=—The top course shall be composed of the
Portland cement specified in Sect. 29, the sand specified in Sect. 30
except that it shall be especially clean, and the grains shall be of
such size that at least seventy-five per cent. (75%) of the mass will
fail to pass a screen having thirty (30) meshes to the linear inch, and
shall be of superior quality for making concrete; and of crushed Trap
Rock,[62] or of stone equally hard, strong and durable.
The trap rock shall be crushed to such sizes that all will pass through
a screen having meshes one and one-fourth (1¼) inch square and that none
will pass through a screen having meshes one-half (½) inch square,[63]
and it shall be free from clay, refuse or other foreign substances.
=117.= The surface-course concrete shall be composed of one part
Portland cement complying with Sect. 29, one and three-quarters (1¾)
parts of sand, and, generally, three and one-half (3½) parts of crushed
stone, but the ratio of crushed stone shall be such that in the
completed concrete the volume of mortar in the compressed mass shall
exceed by about fifteen per cent. (15%) the voids in the stone.[64] The
cement and sand shall be thoroughly mixed together dry, enough clean
water then added to make a rather wet mortar and the mixing continued
until the materials are thoroughly incorporated into a homogeneous mass.
The crushed stone shall then be added, and the mixing continued until
every fragment of stone is completely covered with mortar. Sufficient
water shall be added during the mixing, if necessary, to make a “wet”
concrete, but not so wet that free water will flow from the mixed mass.
In handling and adding the stone to the mortar care must be taken to
prevent the stone segregating into masses of different sizes. The
concrete for the top course shall be made with special care and thorough
work, the intention being to secure a superior quality of concrete.[65]
=118.= The concrete thus prepared shall be placed upon the bottom course
before the latter has begun to set[66] and carefully graded so that when
properly compacted its top surface will coincide with the pavement
datum. The concrete will then be well rammed by rammers having a face of
6 by 6 inches and weighing not less than twenty (20) pounds after which
the surface will be completed by rolling with a power roller of the
asphalt type weighing not less than five (5) tons.[67] All these
operations must be completed before any of the concrete in either course
shall have begun to set. The surface shall not be plastered with neat
mortar nor shall it be trowelled.
=119.= The completed surface must coincide with the pavement datum to
the extent that a properly formed template when applied to the surface
shall show no departure from the pavement datum exceeding
three-sixteenths (³⁄₁₆) inch.
=120.= After the laying of the pavement has been completed it shall be
allowed to stand until the concrete of both courses shall be fully set,
which period shall be not less than ten (10) days, or longer, if
conditions make a longer time necessary, as the engineer may direct, of
which he shall be the sole judge. During this period the concrete shall
be kept in a moist condition throughout, by sprinkling with hose or
otherwise. No travel shall be allowed upon the street until the engineer
shall open it for public use. The concrete shall not be laid during rain
storms or when the thermometer is below forty-five (45) degrees F., and
in case there may be danger from frost the whole surface of the concrete
shall be covered by straw or hay. Manure must not be used for this
purpose.
=121. Expansion Joints.=[68]—An expansion joint along the curbing on
each side of the street shall be provided in accordance with Sect. 101.
Expansion joints shall also be provided and constructed as follows:
Wherever the width of the pavement exceeds twenty (20) feet between
curbs there shall be a expansion joint along the longitudinal center of
the street; expansion joints shall also be made, at right angles to the
street and extending continuously from curb to curb, at distances apart
not exceeding twenty (20) feet. These expansion joints in the body of
the pavement shall be made by cutting entirely through both courses of
concrete along a straight line, using a special straight-edged cutter
not more than three-sixteenths (³⁄₁₆) inch thick, when the concrete is
laid in hot weather and not more than three-eighths (⅜) inch thick if
the concrete is laid when the thermometer is below sixty (60) degrees F.
The cutting of the expansion joints shall be carefully and skillfully
done, and after each joint is cut a special T-shaped smoother, the stem
of which is one inch deep and of the same thickness as the cutter shall
be worked back and forth in the joint until the edge of the concrete
adjoining the joint shall be well and smoothly compacted. The smoother
shall be so formed as to round off the corners of the concrete to a
circular form having a radius of one-fourth (¼) inch. All these
operations shall be completed before the concrete has begun to set.
After the concrete has set and before the street is opened to travel all
expansion joints shall be poured full of bituminous cement, as specified
in Section 90.[69]
=122. Bituminous Coating.=[70]—After the concrete shall have become
fully set as determined by the engineer and before the street is opened
to travel the whole surface of the pavement shall be covered by a
finishing coat of bituminous road oil as hereinafter specified.
The road oil shall be prepared from native asphalt or from a crude oil
having an asphaltic base. Not less than 95 per cent. of the oil shall be
soluble in cold carbon di-sulphide, and it shall contain not less than
thirty (30) per cent. of solid asphalt, nor more than ten per cent. of
fixed carbon. It shall be of such consistency as to flow freely at a
temperature of seventy-five degrees (75°) F. The oil shall not be
applied except when the road surface is perfectly dry and when the
temperature of the air is not below 60° F.
The oil shall be evenly distributed over the whole surface of the street
at the rate of one-half (½) gallon of oil per square yard of surface,
and well worked over the surface with squeegees or other suitable
devices.
Not less than twenty-four hours after the application of the oil the
surface of the pavement shall be evenly covered to a depth of one-fourth
inch with clean, dry stone screenings or coarse sand, after which the
street may be opened to travel.
GENERAL SPECIFICATIONS FOR EXPERIMENTAL OR UNTRIED PAVEMENTS[71]
=123.= Contractors or promoters submitting proposals for the
construction of new, experimental, or special street pavements, the
merits of which have not been established by experience in the city
of ..., must submit with their proposal a full and complete set of
specifications for the construction of the pavement. If contract shall
be awarded under said proposal, said specifications will be made a part
of the contract entered into. The Engineer will enforce compliance with
these specifications, as the construction work proceeds, without
assuming or incurring any responsibility for the character, quality,
serviceability or durability of the resulting pavement. But the
Contractor shall be subject to and shall comply with the requirements
and stipulations of Sects. 1 to 25, inclusive, of these specifications.
=124. Special Guaranty.=[72]—Inasmuch as the pavement to be constructed
under the special specifications submitted by the Contractor is more or
less of an experimental character, having not been heretofore used in
the city of ... to an extent sufficient to establish its value, the
Contractor shall be held wholly responsible for the utility,
serviceability and durability of the pavement so constructed; and he
shall enter into a guaranty to the effect as follows:
That the pavement will fulfill all the usual and legitimate requirements
of a satisfactory roadway pavement upon the street upon which it is to
be laid.
That the pavement will successfully serve and endure the travel to which
the street may be subjected for a period of ... years next following the
date of the certificate of its completion and acceptance, and shall be
in good condition at the end of that period, ordinary and reasonable
wear and tear, and accidental or other injuries not due to defects in
the pavement itself, excepted.
That the Contractor will, at his own cost, keep the said pavement in
satisfactory repair during said period of ... years, and will leave it
in a condition of satisfactory repair at the end of that period.
That the Engineer, or his successor or successors in office, shall be
the sole and final judge as to whether the conditions of this guaranty
shall be, or shall have been complied with.
That in case the pavement shall not, in the judgment of the Engineer,
fulfill the terms and conditions of this guaranty at any time during
said period of ... years, or upon its expiration; or in case the
Contractor shall fail to make all or any of the repairs that may in the
judgment of the Engineer be or become necessary during said period
of ... years, within a reasonable period to be determined by the
Engineer, but not to be less than twenty (20) days after notice to make
such repairs has been given him by the Engineer, he (the Engineer) may
proceed to make or to have made such repairs, or to repave the street,
in any manner that he may deem necessary or advisable, and to charge the
cost of such repairs or repavement to the Contractor, provided, that the
sum or sums so charged against the Contractor shall not, in the
aggregate, be more than the amount paid to the Contractor for the
construction of the pavement.
=125. Bond.=—The Contractor shall give bond with sureties satisfactory
to the Engineer in a sum not less than the estimated cost of the
pavement at the contract prices, the term of the bond to extend over the
entire period of ... years, for which the pavement is guaranteed.
=126.= During the said period of ... years the Contractor shall, upon
being notified by the Engineer so to do, make any repairs to the
pavement that may become necessary by reason of cutting into it for the
purpose of constructing or repairing pipes, conduits or other
underground structures, or street railroad tracks, or by reason of
accidental or unusual causes, or of any causes other than those due, in
the opinion of the Engineer, to the failure of the pavement to meet and
fulfill the terms of the guaranty stipulated in Section 124. And for
making such repairs the Contractor shall be paid the price of ... per
square yard for the repairs actually so made. Repairs so made shall be
subject to the terms of the guaranty, stipulated in Section 124, until
the expiration of the said term of ... years after the date of the
original certificate of completion and acceptance. In case the
Contractor shall neglect or fail to make such repairs within a period of
twenty (20) days after he shall have received notice to do so, the
Engineer may proceed to make or to have made such repairs, and he shall
charge to and collect from the Contractor the cost of the repairs so
made.
HYDRAULIC CONCRETE COMBINED CURB AND GUTTER[73]
=127.= Hydraulic concrete combined curb and gutter shall be constructed
in accordance with general plan No. ... attached to and made a part of
these specifications, but the rise from the gutter to the top of the
curb may be varied so as to facilitate drainage.[74]
=128. Excavation.=—All excavation required for the curb and gutter shall
be completed and trimmed to the proper lines as shown by the drawing.
The drainage trench under the curb and gutter shown on the drawing shall
have the top width and general form shown in the drawing but its depth
may be varied to secure proper drainage, as the engineer may direct,
provided that its depth below the base of the concrete shall not be less
than nine inches nor more than two feet.
=129. Broken Stone Drainage.=[75]—After the excavation shall have been
completed the trench shall be filled up to the level of the base of the
concrete with sound, durable broken stone, or coarse gravel, from which
the small fragments shall have been removed by screening over a wire
screen having openings not less than one inch square. The stone or
gravel shall be thoroughly tamped in the trench in layers not more than
six (6) inches thick by the use of rammers weighing not less than thirty
(30) pounds and having a face area not exceeding thirty-six (36) square
inches, and its completed top surface shall conform truly to the
designed base of the concrete. These drains shall be connected at
suitable intervals with sewers, drains or other outlets to keep them
free from standing water. The trench filling shall be completed at least
twenty-five feet in advance of placing the forms for the concrete.
=130. Concrete.=[76]—The concrete shall be made of one (1) part Portland
cement, one and three-fourths (1¾) parts of sand and three (3) parts of
crushed stone or clean gravel. The Portland cement shall comply in all
respects with the requirements of Section 29 of these specifications.
The sand shall be clean, sharp silicious sand made up of grains of such
size that not more than fifteen per cent. (15%) will pass a number
thirty (30) sieve. It shall not contain more than five per cent. (5%) of
clay or loam nor more than two per cent. (2%) of organic matter or other
refuse. The stone shall be sound, hard, durable, and freshly broken,
free from clay, loam, organic matter, or other impurities. Trap rock or
granite will be preferred, but limestone, if hard and sound, may be used
with the approval of the engineer. Only those fragments of the crushed
stone that pass a screen with openings three-fourths inch square and
those that are held on a screen with openings one-fourth inch square
shall be used in the concrete.
=131. Mixing and Placing Concrete.=—The concrete shall be mixed in
accordance with Section 35 of these specifications. Very thorough mixing
will be required.
The mixed concrete shall be handled so as to prevent as far as
practicable any separation or segregation of the stone and mortar. When
in place it shall be compacted by tamping and where placed against
forms, forking or other effective means must be used to bring mortar to
the surface and to secure complete contact between mortar and forms, so
as to leave a solid, homogeneous and unbroken surface when the forms are
removed. Where the concrete may not be laid against forms, all exposed
surfaces must be troweled to a true surface conforming accurately to the
lines shown by the plans, templates and straight-edges being used where
necessary.
=132. Weather.=—Concrete in combined curb and gutter shall not be laid
in freezing weather nor shall frozen materials be used in the work.
Completed work must be securely protected from frost for at least seven
days after it is laid. Any concrete curb and gutter that may become
frozen within that period shall be wholly removed and replaced with new
work.
=133. Expansion Joints.=—The combined curb and gutter shall be divided
into blocks or panels not more than twelve feet long, by clear, open
expansion joints perpendicular to the face of the curb, extending
entirely and continuously through the whole mass of the concrete. These
expansion joints shall be three-eighths inches wide and may be formed
either by cutting through the completed curb and gutter with a suitable
tool, or by the use of iron forms or partitions, but in either case the
corners at the ends of the blocks must be made solid and dense and
troweled with a suitable tool.
=134. Circular Corners.=—At the intersections of streets, circular
corners, having a radius equal, generally, to one-fifth of the width of
the roadway of the narrower street, shall be constructed of the same
dimensions and quality as on the body of the street, and the curb and
gutter will be extended along the line of the cross street back to the
front lot-lines. Properly curved circular curb and gutter shall also be
constructed at all angles exceeding five degrees in the line of the
curbing.
=135. Corner Protection.=—Galvanized steel corner protectors or
nose-pieces shall be used to protect the upper and outer corner of the
curb at all circular corners and angles in the street. This steel
protection may be of any pattern or section procurable in the market and
approved by the engineer. It shall be firmly anchored and secured into
the concrete.
=136. Finishing.=—After the forms have been removed and before the
concrete has set up too hard to be affected by the brush, the face and
top of the curb shall be lightly scrubbed by a suitable wire brush so as
to completely remove any glazed surface and to produce a surface of
uniform texture and appearance. Dry cement or neat cement mortar shall
not be used for dressing up exposed surfaces.[77]
=137. Forms.=—The forms used may be of dressed lumber or of metal as the
contractor may prefer. But they shall have sufficient strength and
rigidity to hold the concrete firmly in place, and to preserve the
correct dimensions, alignment and levels of the curb and gutter.
=138. Protection.=—The completed curb and gutter shall be protected from
fracture, deformation or spalling until the concrete has fully set. The
concrete must be kept moist for at least five days after it has been
laid. Any part of the curb and gutter that shall have become injured
before it is accepted or the street is opened for travel shall be taken
up and replaced by the contractor.
=139. Payment.=—Concrete combined curb and gutter will be paid for by
the linear foot in place, the measurement to be made along the upper and
outer corner of the curb. The price per linear foot named in the
contract will cover all the excavation or grading required and all the
materials and labor, including all necessary forms, for constructing the
curb and gutter complete. But the crushed stone used for drainage will
be paid for by the cubic yard measured in place, and steel corner
protection will be paid for by the linear foot in place, at the prices
named in the contract.
HYDRAULIC CONCRETE SIDEWALKS
_Note._—These specifications conform to the common practice of laying
the sidewalk in two courses.
In the author’s judgment this is neither necessary nor desirable. He
believes that it would be better and somewhat cheaper to use a single
course of concrete four inches in thickness. He suggests for this
concrete the ratios of one cement, two sand, and three and one-half
stone, the latter to be crushed to pass a screen with five-eighths inch
square openings.
Tamping will bring a sufficient quantity of mortar to the surface to
permit of satisfactory finishing. While the materials for such a single
course of four inch concrete would cost somewhat more, the saving in
cost of labor would, at usual prices of material and labor, make the
single-course construction somewhat cheaper, while the solid four inches
of richer concrete would make the walk much stronger. In fact, a single
course of such concrete three inches thick would be sufficient in a
great majority of cases. While the surface might not have the glazed
appearance common in the two-course work it would be really better for
use—a polished and slippery surface on sidewalks is not desirable.
SPECIFICATIONS[78]
=140.= The hydraulic concrete sidewalk shall be ... feet in width and
its outer edge shall be ... feet from the outer face of the street
curbing. It shall be constructed with two courses of Portland cement
concrete as hereinafter specified.
=141. Excavation and Grading.=—The ground to be occupied by the sidewalk
shall be excavated or filled to a sub-grade which after being compacted
shall be ... inches[79] below the finished surface of the sidewalk. The
sub-grade shall be neatly dressed to a plane surface sloping downward
toward the street one-fourth inch in one foot horizontal, and to such
longitudinal gradients as the engineer may prescribe. The completed
sub-grade shall project four (4) inches in excavation and eighteen (18)
inches in embankment on each side beyond the edges of the completed
sidewalk. After the grading is completed the surface shall be compacted
by rolling or ramming.
=142. Drainage Course.=—Upon the sub-grade prepared as specified in
Section 141 a drainage course composed of broken stone, gravel or
boiler-plant cinders, ... inches[80] in thickness shall be laid. Broken
stone for this purpose may be of any durable stone crushed to such size
that all will pass through a screen with two inch openings. Crusher-run
material may be used unless it contains an excessive quantity of fine
material. Gravel for the purpose may be any sound durable gravel all of
which will pass through a two inch screen and be retained upon a
one-fourth (¼) inch screen. If cinders are used they must be good
boiler-plant cinders from which the ashes have been screened out. The
cinders must be thoroughly drenched with water at least one week before
they are placed in the sidewalk.[81]
=143.= This drainage material shall be placed on the sub-grade and
properly graded. After grading it shall be thoroughly compacted by
ramming or rolling, and its surface shall be brought to a plane parallel
to and ... inches below the designed surface of the sidewalk, after
which the surface inequalities may be leveled up with screenings or
small gravel.
The bottom of the drainage course shall be connected with the street
drains or sewer inlets by three-inch hard drain pipe at such points, not
more than three hundred feet apart, as will drain all standing water out
of the drainage course.
=144. Concrete, Bottom Course.=—The bottom course of concrete ...[82]
inches in depth, shall be constructed and placed in accordance with
Sections 28, 29, 30, 31, 32, 33, 34, 35 and 36 of these general
specifications, except that the maximum size of the crushed stone shall
not exceed one-half the thickness of the bottom course of concrete and
the concrete shall be uniformly composed of one part Portland cement,
three parts sand and six parts of crushed stone. Its upper surface shall
be brought to a plane parallel to and one inch below the designed
sidewalk surface.
=145. Surface or Finishing Course.=—The surface or finishing course
shall be of concrete, one inch thick, composed of one part Portland
cement, one and one-half parts sand and two and one-half parts of hard,
durable stone, crushed to such sizes that all will pass through a screen
having openings one-half (½) inch square and none will pass through a
screen having openings one-eighth (⅛) inch square.[83] This concrete
shall be made as specified in Sections 28, 29, 30, 31, 32, 33, 34, 35
and 36 except in the particulars named in the preceding paragraph. Care
must be taken to make the mixing very thorough. The quantity of water
used in this concrete shall be just sufficient to make a moderately wet
mixture, and care shall be taken to make the different batches as nearly
as practicable of the same consistency.
The surface concrete shall be spread over the bottom-course concrete
before the latter has begun to set,[84] properly graded, well compacted
by ramming, and its upper surface brought to the true designed plane and
surface of the sidewalk by the use of straight-edges and troweling,[85]
after which the surface shall be lightly gone over with a wire broom or
brush to slightly roughen the surface. The finished plane of the
sidewalk shall have a transverse downward slope toward the street of
one-fourth (¼) inch to one foot of horizontal width. At no place shall
the thickness of the surface-course be less than three-fourths of one
inch. The outer top corners of the sidewalk shall be rounded off with a
suitable tool to a radius of three-fourths (¾) inch.
=146. Forms.=—Substantial and suitable forms of wood or iron shall be
furnished and used by the contractor to support the concrete until it is
hard set, when they shall be removed at his expense.
=147. Expansion Joints.=—After the laying of both courses of concrete is
completed expansion joints at right angles to the sidewalk, and not more
than four (4) feet apart shall be constructed in the sidewalk in the
following manner: the joint will be located by a line on the surface of
the sidewalk and a straight-edged cutting tool one-fourth (¼) inch thick
will be used to cut entirely through both courses of concrete,
accurately along the line marked out, entirely across the sidewalk,
after which a T-shaped trowel or tool shall be used to smooth and
compact the cut surfaces for a depth of one inch, and to round off the
corners of the sidewalk blocks to a radius of one-fourth (¼) inch.[86]
Where the ends of the sidewalk abut against the curbing a clear
expansion joint one and one-fourth (1¼) inches wide shall be left
between the sidewalk and the curb.
=148.= After the concrete laying is completed it shall be protected from
use or injury until the concrete is set hard enough to withstand travel,
and it shall be kept continuously damp for at least five days after the
concrete is laid.
=149. Weather.=—Concrete in sidewalks shall not be laid in freezing
weather nor shall frozen materials be used in the work. Completed work
must be securely protected from frost for at least seven days after the
concrete is laid. Any concrete sidewalk that shall become frozen within
that period of time shall be wholly taken up and replaced with new work,
at the expense of the contractor.
=150. Regrading.=—Directly after the concrete is completed, the forms
removed, and the work inspected by the engineer, the space between the
outer edge of the sidewalk and the street curb shall be excavated or
filled up and dressed to a plane one inch below the top of the sidewalk
and the top of the street curb; and the space on the inner side of the
sidewalk shall be graded to a plane one inch below and parallel to the
surface of the sidewalk for a distance of two feet back from the edge of
the sidewalk and completed with a slope of one and one-half to one to
the natural surface of the ground. Where this regrading requires filling
up the filling material, for a depth of four inches from the surface,
shall be good, rich surface soil.
=151.= Should any defects due to faulty material or workmanship develop
in the sidewalk within one year after the completion of the same the
contractor shall repair or reconstruct all such defective places at his
expense, doing the work in accordance with these specifications.
=152. Measurement and Payment.=—Concrete sidewalk will be measured and
paid for by the square foot of completed sidewalk surface, and the unit
price per square foot shall cover the entire cost of the work, including
grading, drainage work, all material and labor, forms, and the regrading
or dressing up after the completion of the concrete work; except that
the drain pipe used will be paid for per linear foot at the price named
in the contract which price shall cover the cost of furnishing and
putting the pipe in place complete.
PART II
INSTRUCTIONS TO INSPECTORS ON STREET PAVING WORK
INTRODUCTORY NOTE
Any general code of instructions for inspectors on street paving work
must necessarily be little more than tentative or suggestive, as applied
to any one city.
That here presented is intended for use in connection with the
specifications in Part I of this book. Different specifications might
make necessary many changes in the instructions that follow. The local
or special conditions in any city might also make them inapplicable
without material modifications and additions.
The author believes that in every city where considerable street
pavement work is prosecuted and a number of inspectors employed on such
work, some such code of instructions to inspectors should be formulated
and used. Even where the inspectors are of high character and fully
competent, the adoption of a system of rules and regulations relating to
their work will tend to unify procedure, prevent misunderstandings and
promote good discipline.
The preparation of such a code of instructions requires no little time
and thought, especially where there are no precedents to suggest what is
needed, or to be used as rough patterns. It is with the hope that the
code here presented may be found useful in this way, even though it may
be not appropriate for adoption in any given city, that it is offered to
municipal engineers.
GENERAL REMARKS ABOUT INSPECTION AND INSPECTORS
The necessity of having competent and honest inspectors upon any public
work during its construction need not be here argued. It is generally
understood and recognized in the case of work carried out by contract.
Where the contractor is incompetent, careless or unreliable, inspection
is absolutely necessary if good work is to be secured. Even where the
contractor thoroughly understands his business and intends to faithfully
comply with the specifications and to do all his work in a proper
manner, the inspector cannot safely be dispensed with. The contractor
cannot at all times be on the work; whatever may be his intention and
instructions, foremen and laborers cannot be depended upon to exercise
the proper care and judgment, even where they have no inclination,
motive or interest to do otherwise, which is not always the case. It
seems to be deeply and almost irradicably fixed in the mind of the
average foreman on municipal work that he is expected to show his
ability and skill by evading or circumventing the strict requirements of
the specifications and the watchfulness of the municipal agents,
whatever his employer may _say_ to the contrary. Even when fairly
careful, honest and conscientious he may need friendly oversight. He is
naturally and properly anxious to save all the money he can for his
employer, whether from a desire to loyally serve that employer’s
interest, or to enhance his reputation for doing work cheaply. He may
not appreciate the importance of minor requirements of the
specifications and may believe they can be ignored without real
detriment to the utility of the completed work. Like other men he may
sometimes be careless or forgetful, however good his intentions.
These human qualities are not confined to foremen on _contract_ work.
They are liable if not likely to be found in the foremen on work done
for the municipality by the direct, or day’s work system. They may be
encouraged by the impression or belief that they will not be held by the
municipal authorities to as strict an observance or accountability as
they would be if the work were being done by a contractor—which is too
often true. The absence of some of the motives of foremen employed by
contractors is, therefore, not a sufficient reason for dispensing with
inspectors on work done by the city direct.
It should be trite to say that inspectors should be chosen with some
regard to their qualifications for the work they are expected to do. One
cannot, of course, expect to secure experts for such positions at the
rate of compensation usually paid; but it is reasonable to require that
an appointee to such positions shall possess the following
qualifications:
That he shall be honest, trustworthy and loyal.
That he shall be a man of at least average intelligence and common
sense.
That he shall have some practical knowledge of or experience in the work
he is employed to inspect.
That he shall be a man of good personal habits.
That he shall be habitually punctual, industrious, and alert, and shall
possess a fair share of that quality commonly called “backbone.”
It will not, I am sure, be denied that a very large number of the
inspectors found upon municipal public work fall short in one or more of
these qualifications.
Inspectors who habitually expect or accept compensation or gratuities
from the contractor violate the first requirement, and their number is
astonishingly large. These are useless, or worse than useless, to the
municipality. There are not a few contractors who will take advantage of
the presence on the work of such inspectors to do things that they would
not do if thrown wholly on their own honor and responsibility.
Contractors can hardly be blamed for expecting some compensation for the
money thus exacted or accepted by the inspector from them.
The requirement that the appointee shall have some practical knowledge
of and experience in the work he is expected to do, while often
disregarded, is of real importance. Good workmanship embraces many small
details that are essential, and inferable from the specifications, but
cannot be stated at length therein, and the inspector should have a good
working knowledge of these.
Unfortunately, large numbers of inspectors are employed for personal or
political reasons, or because more competent men are not available. They
know little or nothing from practical knowledge and experience about the
work they are assigned to inspect. Efficient service cannot be expected
from such, even if they possess the other necessary qualifications. The
obvious remedy, where a sufficient number of qualified inspectors cannot
be obtained at call, would be to train up a permanent force by having
the promising tyros serve a sufficient apprenticeship under older and
more experienced inspectors; but this is seldom done.
Inspectors, whether appointed by the engineer in charge or not, should
be absolutely under his control, including the power of dismissal
without unnecessary formalities. Where they are under civil service
regulations and can be dismissed only upon charges and after a hearing
before some third person, the obstacles in the way of promptly getting
rid of an incompetent or unfaithful inspector are often so great as to
be discouraging if not deterrent. He may be clearly below a reasonable
standard of honesty or efficiency but it may be very difficult to
formulate distinct charges and support them with positive evidence.
Thus, one may be morally certain that an inspector is accepting
gratuities from a contractor, but unable to prove it by legal evidence.
If in such cases the judgment and integrity of the responsible engineer
cannot be trusted, he is not fit, himself, for the position he occupies.
The question of how much authority and power shall be given to the
inspector is always a troublesome one. If he be too much limited or
restricted, he cannot properly discharge his duties or command the
necessary respect from the contractor and his employees; if he be given
too much authority and is disposed to be arbitrary or unreasonable, the
contractor may be unjustly treated. So far as the definite requirements
of the specifications are concerned there can usually be no room for
going astray, but in the numberless little details not specifically
covered in the specifications, or where their language and intent is not
clear, differences and disputes may result which require a degree of
knowledge and judgment that the inspector may not possess, and where his
decisions might be against the interests of the municipality or unjust
to the contractor. In such cases the matter should always be referred to
the engineer or his assistant.
Where inspectors are employed upon work done directly by the
municipality the relation between them and the superintendent or foreman
should be clearly defined and understood. Briefly stated, this relation
should be the same as that between the inspector and the contractor on
contract work.
INSTRUCTIONS FOR THE GUIDANCE OF INSPECTORS ON STREET PAVING AND
INCIDENTAL WORK
GENERAL
=1.= The chief duty of the inspector is to see that the work to which he
is assigned shall be carried out in full and strict accordance with the
plans and specifications therefor, and with such additional instructions
as may from time to time be given by the engineer.
=2.= These instructions are intended to supplement but in no case to
take the place of the specifications for the work, which must be fully
and strictly complied with, unless they are changed or modified by the
engineer.
=3.= Wherever the words “_the engineer_” are used in these instructions
they refer to the chief engineer in charge of the work for the
municipality, or his authorized deputies or agents.
Wherever the words “_the contractor_” are used they refer to the person,
or firm, or corporation under contract to perform the work to which you
are assigned, or his agents or employees engaged upon the work.
=4.= You will report to and be under the exclusive direction and control
of the engineer.
=5.= Upon being assigned to any work you will obtain copies of the plans
and specifications under which it is to be done, and will carefully read
and acquaint yourself with all their provisions and requirements. If any
part of these plans and specifications are not clearly understood by
you, you will ask the engineer for explanations and instructions, and
will be governed thereby. Failure to understand or to be familiar with
the plans and specifications will in no case be accepted as an excuse
for not complying with and enforcing them.
You will also obtain, study and familiarize yourself with all the blank
forms, reports, etc., that are to be used by you on the work, so that
they may be correctly utilized; you will also obtain a proper supply of
such apparatus, tools, stationery, etc., as you will need upon the work.
=6.= In inspecting any work done under contract you are to assume that
the contractor is bound to carry out in good faith the plans and
specifications attached to his contract, and that he may be, and must
be, held to a strict compliance with them unless you receive
instructions to the contrary from the engineer. You will be held
responsible for the enforcement of these plans and specifications so far
as they relate to the doing of the work.
=7.= In case the contractor or his agents shall neglect or refuse to
comply with the plans and specifications or to perform the work in a
proper manner, or in accordance with the instructions of the engineer,
you will direct him to suspend the particular work in fault and will
report all the facts promptly to the engineer and await his
instructions, which, when received, you will proceed to enforce.
=8.= You will be expected to be upon the work at all times when work is
in progress, whether during ordinary working or office hours, or not.
But in case the contractor shall work continuous day and night forces,
or otherwise so conduct the work as to require the presence of an
inspector for unusual or unreasonable hours of service, you will notify
the engineer and ask instructions or assistance. If for any reason you
are to be unable to be present whenever work is in progress you will
promptly notify the engineer in time to enable him to supply a
substitute.
=9.= All reports and records required of you by the engineer must be
promptly made up and forwarded to him at the time and in the manner he
may direct. You will promptly acknowledge in person or writing any
instructions received from the engineer and in case such instructions
are not clearly understood by you, you will ask for explanation or
advice.
You will keep a notebook or diary in which all occurrences or matters of
interest relating to the work will be recorded each day, which book will
be delivered to the engineer on the completion of the work, or whenever
your connection therewith may end. All diaries, notebooks and records
kept on the work are the property of the city.
=10.= While your first duty is to see that the work is done in
accordance with the plans and specifications, you will, so far as
consistent with this duty, be considerate of the interests of the
contractor and facilitate his work as much as practicable. Materials
should be inspected promptly upon delivery and in such a manner as not
to delay or discommode the contractor more than is necessary. Errors,
defects or delinquencies in the work should be detected and called
attention to promptly, so as to avoid tearing up and re-construction as
far as practicable.
=11.= Orders and instructions should be given to the contractor or his
foremen or representatives on the work and not to the laborers, unless
in urgent cases.
=12.= You shall not at any time, before, during, or after the completion
of the work, ask or accept from the contractor or any of his agents or
employees, or from any other person whom you may have reason to believe
is acting for the contractor, any money, gifts, gratuities or other
considerations of value, whether as compensation for services rendered
him or otherwise. The penalty for violation of this rule will be
dismissal from the service followed by such legal prosecution as the
engineer may direct. This rule does not apply to the ordinary small
courtesies common between gentlemen associated in business.
=13.= It is a condition of your employment that your services shall be
loyal to the interests of the municipality, efficient, and satisfactory
to the engineer, and that whenever in his opinion your service falls
short of this standard he may dismiss you at any time, without previous
notice.
STREET PAVING WORK
=14. Sub-foundation.=—The usual procedure in preparing the
sub-foundation for a pavement is:
The removal of the old pavement if one exists on the street.
The setting of new or the resetting of the old curbing. (If concrete
combined curb and gutter is used it is not constructed until after the
rough grading is done.)
The rough grading of the street.
The fine grading of the street.
In this work the main things for the inspector to look after are the
following:
If an old pavement is to be taken up and any part of it is to be
reserved for use by the city, see that the material is not injured in
handling and is disposed of as the specifications or the instructions of
the engineer require.
=15. Curbing.=—New curb stone should be inspected as soon as practicable
after it is delivered on the street so that the contractor may have time
to replace any that may be rejected. Rejected stones should be plainly
marked on their tops with red paint, and the contractor required to
remove them from the street. Stones that are defective in dressing
should be given some distinctive mark and the attention of the
contractor called to them so that the necessary redressing may be done
well in advance of the setting, and reinspected.
If the old curb stone is to be redressed and reset, it should be
inspected as soon as possible after it is taken out and all stones that
are not suitable for re-use rejected and removed from the work. The
redressing of the stones should be looked after carefully. The tendency
in this work is toward the use of old stones that do not, or cannot be
made to comply with the specifications, and toward laxity in the
dressing.
=Setting Curbing.=—In the setting of curbing the points to be looked
after are:
To see that the trenches are excavated to the full dimensions so as to
provide space for the use of the full quantity required of concrete,
gravel or broken stone in which the curb is to be embedded.
To see that the stones are set to true grade and alignment.
That the concrete, gravel or crushed stone used is of the proper
quality, the proper quantity used, and that it is placed and compacted
so as to fill the spaces designated under and around the stone. The
tendency of the workmen is to treat these details as unimportant and to
slight the work.
After the curbing is set any spaces between it and the edge of the
sidewalk are to be cleaned out, filled and trimmed with Portland cement
mortar.
=16. Rough Grading.=—If plows and scrapers are used in the rough
grading, see that they are not allowed to penetrate or to disturb the
natural soil below the true grade, and to prevent this it is better to
require that the plowing and scraping shall not approach nearer than one
or two inches to the true grade.
If embankment or filling is necessary, the filling material must be
deposited in regular layers not more than six inches deep and each layer
must be well compacted by rolling or ramming before the next layer is
applied.
=17. Fine Grading.=—The fine grading (with pick or mattock and shovel),
to bring the sub-grade to the true grade and contour required, should be
done with reasonable accuracy and care. Allowance must be made for
compression under the roller, so that when completed the surface shall
not vary more than half an inch below nor more than a quarter of an inch
above the true grade, in order that room for the full thickness of
concrete foundation may be provided, and no more. Humps, depressions and
irregularities of the surface are to be avoided. The fine grading will
be completed by thoroughly rolling or tamping the surface to make the
soil firm and dense. On some soft or wet, clayey soils, excessive
rolling may produce a plastic or “liver-like” condition and the rolling
should be discontinued where such a tendency appears.
=18. Work Incidental to Grading.=—Where it is a part of the contractor’s
work to reconstruct or readjust catch basins, manholes, covers, and
other structures, he should be required to keep this work done well in
advance of the laying of the concrete foundation. If this work is
delayed until after the main body of the concrete is in place, leaving
openings to be filled later, hurriedly and perhaps carelessly, it may
result in weak patches in the concrete around these structures, where,
in fact, the concrete should be strongest.
CONCRETE FOUNDATIONS
=19.= The concrete foundation of a pavement is a most important part of
the work, and must not be slighted in any way.
=20. Quality of Materials.=—The quality of the materials used for making
the concrete are fully described in the specifications, and they must be
substantially and uniformly adhered to.
The Portland cement delivered on the street will presumably have been
previously inspected and accepted by the engineer, but any change in the
kind, or brand, or apparent quality of the cement delivered after the
beginning of the work should not be permitted without the approval of
the engineer. Barrels or bags of cement not plainly marked with the
brand, or name of the manufacturer must be rejected. You will frequently
make balls of stiff mortar from the cement and sand used (1 part cement,
2 parts sand) and set them aside for observation. If in eight hours
these balls do not set up hard the fact should be promptly reported to
the engineer.
The sand and stone will naturally vary slightly from time to time, but
should not differ materially from the requirements of the specifications
or the standards adopted by the engineer. Stone or gravel that contains
any considerable quantity, say more than 5%, of foreign matter, such as
soil or refuse, should be rejected. Stone containing an excessive
quantity of fine fragments or screenings bunched together in the pile,
should be mixed with the mass of larger stone before it is used, so as
to produce a mass of fairly even composition. Stone that is coated with
mud, or that is not sound and hard should be thrown out.
Sand that is moderately coarse and does not contain more than 7½% of
clay or soil, and is free from vegetable refuse, may be used.
=21. Storing Materials.=—Cement stored on the street must be stacked up
on dry lumber floors at least four inches from the ground and
effectually covered to protect it from rain or snow. Packages of cement
which, when turned out for use contain hard lumps should be rejected.
Sand and stone must be stored on tight lumber floors to prevent their
admixture, when being shoveled up, with street soil or other impurities.
This requirement must be enforced.
=22. Proportioning Concrete.=—The proportions of cement, sand and stone
or gravel named in the specifications must be strictly adhered to.
A barrel of Portland cement will be considered as four cubic feet and a
standard bag of cement as one cubic foot.
It is usual for the contractor to measure the sand and stone by
wheelbarrow loads. In that case you will measure and determine the
capacity, in cubic feet, of the convenient or average wheelbarrow load,
and determine the size and number of loads each of sand and stone
required for one batch of concrete (if made by hand) and thereafter see
that the quantities thus determined are used, and the wheelbarrow
loading uniform. To measure the contents of a wheelbarrow load, use a
square box holding one cubic foot. It cannot be accurately measured on
the barrow.
As a check upon the proportioning of materials, you should occasionally
keep a record of the quantities of cement, sand and stone used for, say,
one or two hours, and mark and measure up the quantity of concrete made
with them, and from this data compute the ratios of the materials used.
(In ordinary street concrete, proportioned 1:3:6, the volume of rammed
concrete made will just about equal the volume of the stone used.)
Where the concrete is mixed by a machine with automatic feeding devices,
reliance must not be placed upon the machine for proper proportioning.
Frequent tests of the materials used and the volume of concrete turned
out should be made as described above, and any necessary corrections
made in the feeding devices of the machine. This test should be made
daily if practicable. The eye will usually detect any material change in
the composition of the concrete, and whenever such changes are observed
the composition ought to be at once checked up by measurement.
=23. Mixing Concrete.=—See that the specifications are followed. Use
sufficient water to make what is commonly called a wet concrete but not
so wet that free water will drain from the mixed batch before ramming.
The test for proper mixing will be that all the fragments of stone are
completely covered with mortar.
=24. Placing Concrete on Street.=—All concrete must be placed and rammed
before it begins to stiffen or set. Concrete should be so handled that
the mortar will segregate or separate from the stone as little as
possible. When in place on the street it should make a mass of uniform
consistency and appearance. The concrete should, as soon as placed on
the street, be graded to a proper thickness and surface, and then well
compacted by ramming. Insist on good ramming; this part of the work is
not often properly done. The surface of the concrete should be brought
to the true grade by proper grading and tamping. Where necessary to
raise the surface, additional concrete, made of small stone, may be
applied during the tamping. Neat mortar should not be used for this
purpose. Sweeping mortar over the surface with street brooms should not
be permitted—it is useful only to cover up defects and to produce an
extra smooth surface (which is not usually desirable). To measure the
thickness of the bed of concrete, lay a straight-edge upon the surface
with the end of the straight-edge projecting a foot or two beyond the
edge of the concrete, and measure the space from the lower edge of the
straight-edge down to the sub-foundation.
Care must be taken to finish the surface of the completed concrete at
the proper distance below and truly parallel to the grade and contour of
the finished pavement. This is more important in the case of sheet
asphalt pavements, since irregularities in the concrete will cause
variation in the thickness of the finished asphalt surface, which will
affect the durability of the pavement. The grade stakes for the concrete
should therefore be carefully set and worked to, and humps or
depressions between the stakes should be avoided.
=25.= In hot, dry, weather the concrete must be kept damp by watering it
until it is at least five days old, and horse-travel over it must be
prohibited until it has set up hard enough not to be injured thereby.
=26. Old Paving Stone Foundations.=—If a foundation is to be made of old
paving stone blocks reset, the important points to be looked after are,
The preparation of the sub-foundation.
The sand bed.
The setting of the blocks.
The grouting of the blocks.
The sub-foundation should be prepared, where necessary, as stipulated in
Sects. 16 and 17 of these instructions. This part of the work is likely
to be carelessly done unless proper work is insisted upon.
The sand used as a cushion course must be of good quality and reasonably
clean. The use of mixed sand and soil taken from the street excavation
should not be permitted.
The blocks, after being cleaned from adhering dirt, should be set with
reasonable care, well bedded in the sand cushion, and laid at such an
elevation below the completed pavement surface, that after being well
rammed, the surface will be at the proper elevation below the pavement
datum.
The grouting of the joints is the most important part of the work. See
that the mortar is made and used in accordance with the specifications,
and that the joints are completely filled.
=27. Broken Stone Foundations.=—The specifications for broken stone
foundations are sufficiently explicit, and compliance should be insisted
upon. Thorough rolling is especially important.
SHEET ASPHALT PAVEMENTS
=28.= The manufacture of the mixture for sheet asphalt pavement, and the
laying of it on the street, involve a number of separate elements or
operations. The quality and durability of the pavement will depend
largely upon the skill, intelligence and accuracy with which each and
all parts of the work are carried out. The inspector, both at the mixing
plant and on the street, must give constant and intelligent attention to
the work.
=29. Inspecting at Paving Plant.=—Inspectors at the plant where the
asphalt paving mixture is made will be provided with the following
apparatus:
1 nest of standard sieves, Nos. 10, 30, 50, 80, 100 and 200
2 thermometers for sand
1 tank thermometer
2 standard flow-plates and one dozen cartridges for same
1 balance for weighing sand
6 dishes, glass or porcelain, 4 inches in diameter.
=30.= The more important things for the Plant Inspector to watch during
the manufacture of asphalt paving mixture are:
_a._ Quality and grading of the sand.
_b._ Temperature of heated sand.
_c._ Uniform quality of the refined asphalt and flux.
_d._ Temperature of melted bitumens.
_e._ Uniform consistency of asphaltic cement.
_f._ Correct ratios of sand and asphaltic cement.
_g._ Thorough mixing of materials.
=31. Sand.=—The general quality and grain-size of the sand, required by
the specifications, must be closely watched and adhered to.
It is hardly ever possible to secure a natural sand that will conform
strictly to the theoretical composition, but _substantial_ compliance
should be required unless the Chief Engineer directs otherwise. After
any sand has been approved for a given contract or street, all the sand
thereafter used for that street should conform closely to the standard
so approved; for any material change in the quality of the sand will
change the quality of the pavement produced, unless the proportions of
the other materials are changed accordingly. Any material change in the
sand should therefore be promptly reported to the Chief Engineer.
=32.= Sand for the sieve tests should be taken from the hot-sand box and
allowed to become cold. From the sample thus taken, weigh out 50 grams.
Arrange the nest of sieves with the No. 200 at the bottom followed by
Nos. 100, No. 80, No. 50, No. 30 and No. 10 at the top.
Place the weighed sample upon the No. 10 sieve and thoroughly shake the
nest until all the sand that will, has passed through the various
sieves; then weigh the various portions, beginning with that which has
passed the No. 200 (deducting in each case the weight of the dish). The
portion _remaining_ on the No. 200, is the quantity _passing_ the No.
100, etc. The sum of all these portions should be 50 grams, though it
will usually be slightly less because of unavoidable waste. In use, keep
the sieves clean and as free as possible from adhering grains by using a
bristle brush.
=33. Temperature of the Sand.=—The temperature of the heated sand should
be frequently noted by plunging the thermometer into the mass. It should
not fall below 315° F. nor exceed 375° F. It is very important to avoid
over-hot sand, because, in the mixer, the very thin films of bitumen
covering the hot-sand grains are readily and quickly scorched by the
excessive heat in the sand.
=34. Refined Asphalt and Fluxing Oil.=—Unless otherwise notified by the
Chief Engineer you will assume that the stock of refined asphalt on hand
at the beginning of the work has been inspected and is satisfactory. You
will, however, note the appearance of the material and the character and
marking of the barrels or packages, and will not permit the use of any
new shipments of materials of different appearance or brand without
authority from the Chief Engineer. The above instructions apply also to
the oil used for fluxing.
=35. Ratio of Asphalt and Flux.=—You will frequently note and record the
weight of asphalt and of flux used in charging the melting tanks.
=36. Temperature in Melting Tanks.=—The melting kettles are usually
equipped with fixed thermometers, but their reading should be frequently
checked with your detached tank thermometer. You will see that the
temperatures in the kettles are kept within the limits named in the
specifications. See that the melted asphaltic cement is kept constantly
agitated as required by the specifications.
=37. Uniformity of Asphaltic Cement.=—It is very important that the
asphaltic cement shall be of uniform composition and consistency, or
hardness.
When the composition and consistency of the asphaltic cement to be used
for the surface-course of any street has been determined upon and
approved by the engineer, you will take out and preserve a sufficiently
large quantity to be used thereafter as a standard, and each subsequent
tank of cement, before it is used, should be tested by comparing it with
this standard in the following manner, using the flow-plate apparatus:
Melt and fill two cartridges with the standard cement, and two with the
cement to be tested, marking them for identification. When cold,
carefully remove with a wetted dull knife any surplus cement from the
ends of the cartridges so as to leave them exactly full and the metal
ends clean. Immerse them in cold water until they are all of the same
temperature. Then place and fasten these filled cartridges on the
grooved plate with their lower ends exactly to the zero line on the
plate, the standard samples alternating with the new. Then place the
plate, at an inclination of about 45°, in front of a source of uniformly
distributed heat, as, for instance, near a steam boiler or large steam
pipe, or (when the weather is favorable) in the sunshine, facing the
sun. Leave the plate in this position until the bitumen in the
cartridges shall have melted and flowed down the grooves an average of
from four to five inches. Then measure the lengths of flow of each from
the zero line on the plate. If the average flow of the new samples
differs more than 5 per cent. from that of the standards, the new cement
should be regarded as unsatisfactory and should be corrected by adding
more asphalt or flux, as may be required.
(If a _penetration apparatus_ is supplied or is available, the
penetration method may be used instead of this flow-method for
determining the consistency of the cements. Proper instructions for its
use will accompany the apparatus.)
=38. Ratio of Sand and Cement.=—When the proper ratio of sand and
asphaltic cement has been determined for any street you will see that
this ratio is carefully adhered to. The correctness of the weighing
scales used should be frequently tested.
=39. Mixing.=—When the sand and asphaltic cement are properly mixed the
appearance of the mass will be perfectly uniform throughout, with every
grain of sand entirely and evenly coated with cement. The mixing should,
however, be continued somewhat beyond the attainment of this condition,
so as to insure thoroughness. After the proper result has been arrived
at, either the _time_ in the mixer, or the _number of revolutions_ of
the mixer shaft should be noted and the standard thus determined
substantially adhered to thereafter. With the standard mixers commonly
used, the hot sand and the filler (dust) should first be put into the
mixer and mixed for about fifteen seconds; then the asphaltic cement
added and the mixing continued as long as necessary (in the usual mixer
not less than sixty seconds).
=40. Records.=—You will keep complete records of the results of your
observations and tests in a book which will be provided for the purpose,
and will make such reports to the Engineer as he may direct.
=41. Inspection on the Street.=—The leading things to be kept in mind by
the street inspector, in the laying of asphalt pavement on the street,
are the following:
_a._ Temperature of mixtures when applied to the street.
_b._ Proper preparation of the street surface before material is laid.
_c._ Laying and rolling of the binder-course.
_d._ Laying of the surface-course.
_e._ Rolling the surface-course.
=42. Inspector’s Equipment.=—The inspector will be supplied with the
following apparatus:
1 armored thermometer reading from 200° F. to 500° F.
1 graduated spatula.
1 twelve-foot straight-edge.
1 fifty-foot tape line.
=43. Temperature of Mixture.=—If proper care has been taken at the
mixing plant the mixture will not arrive on the street at too high a
temperature, and your principal care will be to see that it is not laid
at too low a temperature. The minimum temperature named in the
specifications should be adhered to. While the main or interior mass of
a wagon load may be well above that temperature, the top and outer part
of the load may be, particularly in cold weather, too cold to be safely
used. Some of this colder portion may usually be sufficiently reheated
by mixing it with the hotter material, if properly handled in unloading;
but any material that is so cold as to be lumpy when unloaded, or, more
particularly, when being raked out, should be discarded. This applies to
both surface and binder mixtures.
It must not, however, be overlooked that the different kinds of asphalts
have different appropriate working temperatures, and for some asphalts
the minimum temperature named in the specifications may be too low. The
best practical guide is the manner in which the mixture behaves in
raking. It must always be so hot that it will, under the rake, break up
into a uniform, crumbling or powdery mass. If it does not do this it is
(unless the mixture is excessively rich in bitumen or improperly
compounded) too cold.
=44. Preparation of Street Surface.=—Before the binder-course is laid,
all loose material, rubbish, street dirt and other matter foreign to the
concrete surface must be removed and the concrete surface swept, if
necessary, to properly clean it, with street brooms. Neither binder nor
surface mixture shall be laid upon wet surfaces. Before the spreading of
the surface mixture on the binder the latter must be cleaned of all
foreign matter and, if necessary, swept. If the binder is covered with
mud from wagons or other travel, the surface must be scrubbed clean. Any
part of the binder-course that may have become broken or loosened before
the surface-course is applied must be taken up and new material laid in
its place with the same care as the original.
=45. Laying Binder-course.=—The binder mixture must be carefully spread
and raked to such thickness that after being rolled it will present an
even, true surface not varying more than one-fourth inch from the
intended finished surface of the binder. The tendency is to lay the
binder-course carelessly and to roll it insufficiently. Nearly the same
care in raking and rolling as for the surface-course, should be insisted
upon. If the binder is not thoroughly compressed before it becomes cold
it is likely, in future hot weather, to soften and yield under heavy
travel and thus to start depressions in the pavement which will increase
with time.
=46. Laying the Surface-course.=—The requirements of the specifications
should be rigidly enforced in the laying of the surface-course. Joints
against a cold edge of previously laid surface must be cut back until
solid, fully compressed material of full thickness is reached, and the
raw edge completely but thinly painted with liquid paving cement or
pitch. No masses or fragments of cold mixture, whether of binder or
surface, must be allowed to remain on the surface of the binder in
advance of the placing of the surface-course, to be covered up by the
latter. Such cold masses will not be compressed by the roller, but will
later, under a hot sun and heavy travel, yield and start depressions in
the pavement. The raking out requires to be properly and skilfully done.
The tines of the rakes must penetrate to the binder, so that the raked
material will be a uniform mass from top to bottom.
=47. Rolling.=—You will insist upon the rollers being placed upon the
freshly raked surface just as soon as the material will bear them
without being squeezed out or displaced laterally. The tendency is to
keep the rollers off too long, thus permitting the chilling of the
surface and preventing its proper compression. Do not take the
contractor’s word as to how soon the rolling may be begun, but have
trials made until you are able yourself to judge. The rolling by the
heavy roller should be very thorough: keep the roller at work constantly
until the surface is too cold to be impressed. In operating the roller
lengthwise of the street begin at the gutters and work toward the center
of the street. Cross rolling and diagonal rolling must be insisted upon
wherever the width of the street will permit it.
=48. Proper Thickness and Surface.=—While the completed surface is still
warm enough to permit it, measure the thickness of the surface-course by
forcing the graduated spatula through it to the binder and noting the
depth of penetration. Also test the trueness of the finished surface
with the straight-edge, and if found defective in either thickness of
pavement or trueness of surface, insist on more careful grading and
raking on the further work. Try the completed gutters with water to see
that they are so truly laid that puddles of water will not stand in
them.
=49.= Asphalt surface must not be laid when rain or snow is falling, or
so long as the street surfaces are wet. Surface mixture raked out and
caught in a shower before it is well enough rolled to exclude water must
be taken up and discarded.
Unless unavoidable, neither binder nor surface should be laid when the
street surface or the air is below 40° F. As a rule, the lower the
temperature the of air the greater is the care necessary to properly lay
asphalt pavement.
=50.= Measure each day the area of pavement laid and record that, and
the quantity (number of batches) of surface mixture used, and note any
lack of uniformity in the area laid per batch.
ASPHALT BLOCK PAVEMENT
=51.= You may assume, unless otherwise instructed, that the Engineer has
inspected and approved the general character of the blocks already
delivered for the work, unless their inferiority be obvious, but you
will be expected to observe them carefully as laid and to reject blocks
that vary in dimensions from those permitted by the specifications, and
those that are broken, disfigured or injured. But during the progress of
the work you will note the character of subsequent deliveries and report
to the Engineer any apparent change in the quality of the blocks.
The more important points to look after in the laying of the asphalt
blocks are: the quality and grading of the mortar bed in which the
blocks are set, and the care and accuracy of the block setting. The
mortar must be of cement and sand in the ratios specified, and
sufficient water used to make a medium stiff mortar; the use of merely
moistened powder must not be permitted; and any mortar that has begun to
set up before the blocks are laid and rammed must be discarded.
=52.= In setting the blocks the principal requisites are: that they be
well bedded in the mortar; that they be set so that after ramming their
tops will be accurately in the pavement datum; that they be set and
pressed as closely together as possible, levers or mauls being used to
force them into close contact, both at ends and sides.
GRANITE BLOCK PAVING
=53.= Assuming that the foundation has been properly constructed, the
more important things for the inspector to look after are:
_a._ The quality and shape of the blocks.
_b._ The sand cushion.
_c._ The setting of the blocks.
_d._ The ramming of the blocks.
_e._ The filling of the joints.
=54. The Blocks.=—Assuming that the general _quality_ of the granite has
been approved, you will need only to observe and reject blocks made from
soft or weathered or otherwise defective stone. Any material divergence
of the blocks from the correct form or from the sizes specified as
permissible will be readily caught by the eye as they are brought to the
street, and they can then be thrown out. The proper dressing of the
blocks is important and should be watched carefully. While you are not
expected to examine each individual block, close observation of the
blocks as they are handled and laid will enable you to detect and reject
those that are materially defective in shape or dressing; or excessively
wide joints will call attention to these defects as the blocks are set.
=55. Sand Cushion.=—The sand used for the cushion bed should be
moderately coarse and must be fairly clean and pure. The tendency with
contractors is to use any dirty sand or sandy loam available on the
street. Such material, especially if it becomes filled with water, will
yield under the blocks and will not support them properly. The sand bed
should not vary materially in thickness. It should be laid and graded
not more than fifty nor less than twenty feet in advance of the setting
of the blocks.
=56. Setting of the Blocks.=—The blocks should be delivered in front of
the block setters on the blocks already set. The blocks must be set in
straight courses from curb to curb, the courses running at right angles
to the street (except at street intersections). All the blocks in any
one course must be of the same width. Each block should be so set that
the whole of its bed will be seated upon sand. The usual practice of
block setters is to make a bed by drawing the sand into a small ridge
upon which the outer edge of the block is rested, its weight canting it
against the course already laid. This usually leaves a cavity under the
back edge of the block which neither the subsequent joint filling or
ramming closes up, so that the block may rest permanently on only a part
of its bed. The practice is so fixed with block setters that it will
require firmness and persistency to prevent it, but you should insist
that it be so modified as to give a solid bearing for each block over
its whole base.
The blocks must be set solidly against each other so as to make the
joints of the least possible width. Unless close attention is given to
this the joints are likely to greatly exceed the width permitted by the
specifications. Care should be taken that the blocks are set truly
vertical so that their upper face shall be parallel to the plane of the
street. In setting the blocks their straightest and truest face should
be placed upward so as to make the surface of the pavement as smooth and
even as possible. Block setters are often careless about this.
Ordinarily no grade stakes are set for the surface of the pavement and
templates are seldom used, the block setters using only their eyes to
make the surface conform to the intended contour of the street. This
usually results in the completed street being more or less wavy and
irregular, and in a lack of regular and uniform cross-section in
different parts of the street, often very perceptible to the eye. Care
should be taken to avoid this as much as possible. Straight-edges and
templates, cut to the proper curve for the surface, should be provided
and used.
=57. Ramming the Blocks.=—This part of the work is likely to be slighted
unless carefully watched. The important thing is to have each block
equally and sufficiently rammed to bring it to a firm bearing on the
sand, as well as to bring its top to the proper grade. The rammers will
be disposed to touch lightly blocks or areas which if thoroughly rammed
would be driven below the true surface of the pavement, and subsequent
travel may force these down, making depressions in the surface. It is a
very common practice for the men working the rammers to shirk on this
work by allowing the rammers to fall with little more force than that
due to their own weight. This should be detected and remedied.
=58. Filling the Joints.=—The specifications are quite full and clear
regarding this part of the work and little further need be said.
Care is necessary, whether the joints be filled with gravel and
bituminous cement or with grout, to secure the complete filling of all
the joints. If the weather is cold at the time the work is done, the
gravel filling may become so chilled before the bituminous cement is
poured that it will not flow to the bottom of the joints. For this
reason it is important that the cement be worked at the highest
temperature that it will bear without injury.
If grout filling is used care is necessary to make the mortar of the
right consistency. If too thick it will not flow freely to the bottom of
the joint; if too thin its strength will be materially reduced.
Experiments should be made to determine the proper consistency, and when
this is found, the quantity of water used in making the mortar should be
determined and thereafter measured out for each batch.
The mortar must be kept constantly stirred until used, otherwise the
sand is likely to settle to the bottom. Whatever filling is used, a
second and sometimes a third pouring will be necessary to completely
fill the joints.
BRICK PAVEMENT
=59.= The matters requiring most attention in the construction of brick
pavement (assuming that the foundation is in place) are the character
and quality of the brick, the sand cushion, the setting of the brick,
and the filling of the joints between the brick.
=60. Inspecting the Brick.=—The examination, testing and acceptance, in
a general way, of the brick to be used for the work will be made in the
engineer’s office, and your duty will be confined in this matter to
seeing that the brick delivered and used are in accordance with the
standard established and the general requirements of the specifications.
You can best inspect the brick as they are being laid or after they have
been laid, and before the surface has been rammed or rolled. Presumably
the brick-setters will discard most of the unsuitable brick during the
progress of their work, particularly if they are given to understand
distinctly the defects that will cause rejection.
As the setting is completed, go carefully over the surface of the
pavement and mark plainly all the bricks that are to be removed for
defects and see that all such are taken out and replaced with good
brick. The principal defects that should be observed are: soft or
underburned bricks; those that are warped or deformed so that they will
not fit closely to their neighbors, or have warped or ill-shaped tops;
those that are broken or chipped or show injurious cracks, and those
that are perceptibly wider or narrower than their neighbors in the same
course.
Soft or underburned brick may be detected with most certainty by having
the contractor wet the surface of the pavement by sprinkling. The soft
brick will absorb more water and remain damp longer than the hard brick
and can thus be readily detected. This test can be applied, however,
only to pavements the joints of which are to be filled with grout, as
bituminous filling should not be applied to brick with wet surfaces, and
to wait until they become dry after the wetting would delay the work
unwarrantably.
=61. Sand Cushion.=—See that the sand used is free from foreign matter
and pebbles, as required by the specifications, and that the sand bed is
of uniform thickness, correctly gaged, and rolled to the true plane of
the pavement, additional sand being added or surplus removed where
necessary to secure this result. See that the cushion is not thereafter
disturbed or, if disturbed, that it be restored to its original
condition.
=62. Setting the Brick.=—The bricks are to be set as closely together as
possible both at sides and ends, so that the joints will not be wider
than permitted by the specifications. Where the bricks have lugs or
letters on one side, the lug-sides shall in no case be laid together.
The courses must be reasonably straight entirely across the street. See
that the bricks in adjoining courses break joint not less than three
inches. Brick-setters are likely to be careless about this. Do not
permit bats to be used except where necessary at the ends of courses or
to fit the pavement against street railroad rails or around manholes or
other structures in the street, and insist that this filling in shall
follow immediately after the brick-setting, and that close fits shall be
made.
=63. Rolling the Pavement Surface.=—This should be carefully and
uniformly done so as to insure the even surface and contour of the
pavement. Do not allow the roller to make sharp turns on the freshly
laid brick surface as it will disturb and cant the loose brick. The
roller should run back onto the fully completed pavement to make any
necessary turns or considerable changes of direction. Quick starts or
stops of the roller on the fresh-laid brick should be avoided for the
same reason.
=64. Filling the Joints.=—Whether grout or bituminous filling be used
the important thing is to get all the joints completely filled. Where
bituminous cement is used, if the work is done in very cool weather the
brick is likely to chill the cement before it reaches the bottom of the
joints unless the cement be applied as hot as possible without injuring
it, and the pouring be rapidly and carefully done.
If grout filling be used, see that the mortar is made of the proper
ratio of sand and cement and that it is of the proper consistency to
just flow into the joints, and that after mixing it is kept stirred
until used. Repour all joints where necessary to completely fill them.
=65. Gutters and Expansion Joints.=—See that the gutters are laid with
longitudinal courses of brick and their joints filled with bituminous
cement as provided in the specifications.
WOOD-BLOCK PAVEMENT
=66. Foundation.=—The instructions relating to the preparation of the
sub-foundation and the concrete foundation already given apply to
wood-block pavement.
=67. Inspection of Blocks.=—However carefully the lumber may have been
inspected before its manufacture into blocks, the subsequent seasoning,
treatment, handling and exposure to the weather will develop many
defects and you will need to observe the delivered blocks closely,
either before or after they are set, and reject those that do not comply
with the specifications. The principal defects that you will be able to
detect after the blocks are treated are the following: Southern pine
blocks made of second-growth or inferior wood, partly shown by the
number of annual growth rings per inch. Blocks having a less number of
these annual growth rings per inch than is permitted by the
specifications should be rejected. The treated blocks, especially when
they are exposed to the weather for some time, are likely to develop
seasoning cracks, “shakes” and loose knots, not observable in the
lumber, and blocks showing these to an injurious extent should be
rejected, though in many cases the defective part may be split off and
the remainder of the block used for closers. If the blocks have become
very dry and thoroughly seasoned out, they should be well sprinkled with
water about twenty-four hours before they are to be set, to forestall
excessive swelling and “humping” when a rain storm comes upon the new
pavement.
=68. Mortar Bed.=—It is the common practice in preparing the mortar for
the mortar bed under the blocks to simply dampen the mixed sand and
cement so that it may still be spread and handled like damp sand. See
that sufficient water is used to make a moderately stiff mortar,
suitable for being worked with a trowel. This mortar should be prepared
in sufficiently small quantities at a time to insure that it will not
begin to set before the blocks be placed in it and rammed.
=69. Setting the Blocks.=—The setting of the wooden blocks is a
comparatively simple operation and the specifications are sufficiently
full and clear for your guidance. See that the blocks are so set that
their tops, after the ramming is completed, shall be truly in the
pavement datum, without humps or depressions.
=70. Filling the Joints.=—See that the sand used is perfectly dry, fine
and clean, and that it is swept about on the pavement until the joints
are completely filled.
BITUMINOUS CONCRETE PAVEMENT
=71. Preparation of Foundation.=—Where a bituminous concrete wearing
surface is to be placed upon an old pavement or Macadam road the
specifications must be closely followed. A good foundation is as
necessary, if good results are to be attained, as in the case of other
pavements. The dressing down of high points and the filling up of
depressions in the old pavement should be carefully done, so that the
bituminous wearing surface shall be of uniform thickness, and shall be
rigidly supported at all points.
=72. Bituminous Concrete Surface.=—The instructions given for the
manufacture and laying of sheet asphalt pavement should be followed here
insofar as they are applicable.
HYDRAULIC CONCRETE ROADWAY PAVEMENT
=73.= Like other structures made of hydraulic concrete, the utility and
durability of concrete roadway pavement depends largely upon the good
quality of the materials used and the skill and fidelity with which the
work is done. It is especially important that the second, or surface,
course of the concrete shall be made and placed in strict accordance
with the specifications and that a high degree of _uniformity_ shall be
secured in the composition, consistency and workmanship of that part of
the work.
=74. Sub-foundation and Foundation.=—The preparation of the
sub-foundation will be the same as for other pavements, and the first,
or foundation course, of concrete, will be constructed as in the case of
the concrete foundation for other pavements.
=75. Material for Surface-course.=—It may be assumed that, in general,
the materials intended to be used on the work have been inspected and
approved by the Engineer, but this should not prevent you from calling
his attention to any defective or inferior materials that may be
delivered on the street when the work is begun, or thereafter, and
preventing the use of any materials that are not fully up to the
requirements of the specifications.
=76. Mixing the Surface Course.=—See that the cement sand and stone are
proportioned accurately and that the quantity of water used with each
batch is measured, so as to make the concrete of uniform consistency. Do
not permit any defective batches of concrete to be used in the
surface-course—if suitable for the bottom course they may be used in it.
Care in this respect is particularly necessary with machine-mixed
concrete where the machine is not working normally or the men operating
it are careless or unskillful.
=77. Placing Surface Course Concrete.=—See that the surface course is
placed, graded and rammed _before the bottom course concrete begins to
set_. This is imperative. Also that the concrete is distributed and
graded in such a way as will not separate or segregate the mortar from
the stone; that the grading of the surface is so accurate that it will
not be necessary later to add additional concrete to that already graded
and rammed; that the ramming is thorough and uniform over the whole
surface, and that the rolling is well done.
=78. Expansion Joints.=—Care should be taken to have the expansion
joints made as the specifications require. See that they extend entirely
through both courses of concrete; that the corners are properly
compacted and troweled; that the joints are kept clean until they are
filled with the bituminous cement, and are completely filled with the
cement.
=79. Care of Finished Work.=—Do not permit the completed work to be
disturbed by travel over it, and see that the concrete is kept moist,
until it shall be set up hard, and that the street is not opened for
travel until the engineer so directs.
CONCRETE COMBINED CURB AND GUTTER
=80. General.=—The specifications for the construction of Hydraulic
Concrete Combined Curb and Gutter are quite full and clear and the duty
of the inspector will consist mainly in seeing that they are faithfully
carried out.
=81. Concrete.=—As in other concrete construction, the utility of the
work depends largely on the care and skill with which the concrete is
made and placed. See that the prescribed quality and ratio of materials
are used and that the concrete is thoroughly mixed and properly placed
in the forms and well tamped. Especial care is necessary to secure a
continuous and satisfactory exposed surface by forking and working the
mortar into contact with the forms, which must be placed and maintained
in true line and surface.
[Illustration: Concrete Combined Curb and Gutter]
=82. Removing Forms.=—Good judgment is required as to the proper time to
remove the forms. They must remain until the concrete has set hard
enough to be fully self-sustaining, but before it has set so hard that
the wire brush will have no effect on the surface.
=83. Corner Protection.=—See that the metallic corner or nose piece is
correctly placed and that it is solidly anchored by and fully embedded
in the body of the concrete.
=84. Patching.=—The practice of patching up cavities or irregularities
in the exposed face of the curb and gutter with neat mortar, or dressing
the surface with dry cement, must not be permitted. If a section of the
curb is found, when the forms are removed, to be imperfect, the whole
section must be removed and replaced.
HYDRAULIC CEMENT SIDEWALKS
=85. General.=—While the work of constructing concrete sidewalk is
comparatively simple it is often carelessly and unskillfully done. The
things that need most attention by the inspector are the following:
=86. Materials.=—The materials used in the work must be fully up to the
quality called for by the specifications. This applies more particularly
to the cement and sand. These are not always properly tested by the
engineer and you should frequently make samples of stiff mortar (1
cement, 2 sand) and set them aside for observation. If they do not, in
summer weather, become very hard at the end of nine hours, the fact
should be reported to the engineer.
=87. Drainage.=—See that the necessary grading is properly done and that
the drainage course is made of suitable material properly compacted. See
that drain tiles are properly laid and connected as designed by the
engineer. If cinders are used for the drainage course, see that they are
screened to remove ashes and fine material, and that they are thoroughly
drenched with water at least five days before they are placed in the
walk.
=88. Two-course Work.=—If the sidewalk is laid in two courses, see that
the surface-course is put on and tamped before the bottom-course
concrete has begun to set. This requirement must be strictly enforced.
=89. Finishing the Surface.=—Dry or pure cement must not be used for
trimming up or smoothing off the surface of the walk. After the surface
has been properly completed by straight-edge and trowel, see that the
wire broom is used as directed to remove the glaze and to slightly
roughen the surface.
See that the expansion joints are made as specified, and that they
extend entirely through both courses of concrete.
=90.= See that the walk, after completion is properly protected from
injury and from frost, and that the concrete is kept moist until it
becomes well set.
-----
Footnote 1:
In specifications to be used in any particular city the official name
of the city government, as the City Council, the Commissioners of
Public Works, etc., should be used instead of this general
designation.
Footnote 2:
Such a proviso as this seems proper in justice to both the city
engineer and the contractor; the former should not be held responsible
for the acts of his assistants when they transcend the authority
conferred upon them, and the latter should be put upon his guard with
reference to requirements which he is not satisfied are sanctioned or
approved by the city engineer.
Footnote 3:
It may be objected that this requirement is unusual and unnecessary,
since such practices are recognized as wrong, and as presumptive of
fraud and malpractice on the part both of the contractor and the
inspector. It cannot, however, be denied that in many cities such
means are employed by contractors to unduly influence the action of
inspectors and that not infrequently the latter not only accept, but
persistently demand, valuable considerations from the contractor.
Silence of the specifications on this point cannot, of course, be
construed into consent, but there is no good reason for the silence.
There should be left no excuse for misconception of the position of
the city or of the engineer upon this point.
Footnote 4:
This section is intended as much for the control and limitation of
city officials as of contractors. The practice of carelessly or
purposely allowing municipal contracts to be expanded greatly beyond
the stated limits or the original intended volume and cost without
formal authorization by the proper municipal body in which the power
to make contracts is lodged, is dangerous and wrong and should be
prohibited. In one instance coming to the notice of the author a
contract originally intended to cover $50,000 worth of work was
expanded by the department head without any authority from the city
council until the final estimate reached the enormous sum of over
$400,000.
Footnote 5:
As outlined in the introduction, these specifications are designed to
secure the construction of the pavement in a proper manner, the city
assuming responsibility for the character and utility of the work. The
guarantee here proposed is therefore intended to cover only a proper
compliance with the specifications, for which the contractor may
properly be held responsible, and not the sufficiency or utility of
the work, if constructed according to the specifications. The period
of guaranty should therefore be short, not exceeding two years.
Footnote 6:
In the great majority of cases the most satisfactory and, in the end,
the most economical foundation for a pavement is hydraulic cement
concrete. Old paving-block foundation, if constructed as specified in
Sect. 36, will give results equally as satisfactory, but if a fair
market exists for the blocks taken up from the street, it will usually
be found more economical to sell them and construct a concrete
foundation for the new pavement. Broken stone or gravel foundations
may serve the purpose fairly well upon a street of light travel, but
it should never be used on streets of considerable or heavy travel.
Its lower first cost is the only thing in its favor, but this will, in
nearly every case, be more than offset by the better service and
greater durability of the pavement, even on streets of light travel,
if laid upon an adequate hydraulic concrete foundation. Proper repairs
to pavement surfaces cut into for pipe work, etc., are difficult to
make and hardly ever satisfactory over broken stone foundation for the
reason that the lack of cohesion in the material allows it to loosen
or crumble away from under the edge of the pavement surface, and it is
difficult to restore it to its original solidity and strength. The
first cost saved by its use is usually not great; for whenever its use
would be permissible at all, a comparatively thin and lean concrete
would give better results, at a very slight increase in cost. To
illustrate: On a suburban street with light travel a concrete
foundation four inches in thickness, the concrete made with Portland
cement in the ratio of 1 cement, 4 sand, and 8 stone, would be
stronger and in every way better than a foundation eight inches in
depth of broken stone. At the usual prices of materials and labor, the
former may cost about $0.46 per sq. yd., and the latter about $0.40
per sq. yd.; but for the latter there would be required ⅑ cu. yd. more
sub-foundation excavation, worth about four cents, so that the
equivalent cost would be $0.44 per sq. yd. The difference, two cents
per sq. yd., is insignificant when compared with the greater value,
better service, and greater durability of a pavement on the concrete
foundation. It is sometimes held that the broken stone foundation
provides necessary sub-drainage. But all the standard pavements are,
or soon become, impermeable to water from the surface, and seepage
from the sub-foundation can be better taken care of by the
sub-drainage specified in Sect. 26, which should usually cost not more
than five cents per square yard of the pavement; and if drainage be
required, these sub-drains should be used even with the broken stone
foundation.
The practice of laying pavement surfaces, particularly those of
asphalt, upon a foundation of old stone blocks, carelessly reset, with
the joints unfilled with mortar, is all wrong and should never be
resorted to. The integrity and durability of an asphalt pavement
depends largely upon the strength and rigidity of its foundation; to
lay an asphalt surface, however good, over such an old block
foundation, is an inexcusable waste of money.
Old stone block and cobble-stone pavements, that have become
solidified in place by long travel over them, make a good foundation
for asphalt or other pavements, provided they can be utilized without
taking up or disturbing the old pavement; but such cases occur so
rarely that they have not been considered in these specifications.
A thoroughly consolidated old McAdam pavement, if not worn too thin,
also makes a very satisfactory pavement foundation if it can be used
undisturbed, or by simply trimming off the high points.
Low places in old pavements, that are otherwise satisfactory for a
foundation, may be brought to the proper elevation with hydraulic
concrete. “Binder” material is usually specified for this purpose in
foundations for asphalt pavements, but hydraulic concrete is both
better and cheaper.
Footnote 7:
The specifications for Portland cement here given are practically
those adopted by the “American Society for Testing Materials.”
=Natural Cement.= While these specifications uniformly refer to the
use of Portland cement, it is not intended to convey the idea that
natural cement concrete is not suitable for pavement foundations; on
the contrary, it may be used with entire confidence, as the experience
in a large number of cities has proven beyond question. Whether
Portland or natural cement shall be used is usually a question of
relative cost. At the present very low prices of Portland cement in
most cities, more strength in pavement foundations can usually be
obtained per dollar expended for cement, from Portland than from
natural cement. The specifications for natural cement, as adopted by
the American Society for Testing Materials differ from those for
Portland cement in the following particulars:
The =specific gravity= shall not be less than 2.8.
=Fineness.= The residue left on a No. 100 sieve shall not exceed 10
per cent., and on a No. 200 sieve shall not exceed 30 per cent.
=Setting.= It shall not begin to set in less than ten minutes, nor set
hard in less than thirty minutes; but shall set hard within three
hours.
=Tensile Strength= (per sq. in.).
=Neat.= 24 hours in moist air 50 to 100 lbs.
7 days (1 day in air, 6 days in water) 100 to 200 lbs.
28 days (1 day in air, 27 days in water) 200 to 300 lbs.
=1 part cement, 3 parts sand.=
7 days. (1 day in air, 6 days in water) 25 to 75 lbs.
28 days. (1 day in air, 27 days in water) 75 to 150 lbs.
=Soundness.= Standard pats kept in air and in water should remain firm
and hard and show no signs of cracking or disintegration.
Footnote 8:
The frequent requirement that the fine material shall be screened out,
is not necessary or advisable. Experiments and experience have shown
conclusively that unless an unusual amount of fine material and “dust”
be present, or unless this fine material be allowed to separate and
aggregate in masses by itself, the resulting concrete is improved
rather than deteriorated by its presence.
Where there is an unusual excess of “dust” in the crushed stone, the
quantity of sand used in the concrete should be decreased accordingly.
Footnote 9:
Many specifications do not require this and in a number of cities
where the specifications do require it, contractors habitually neglect
to comply. When stone and sand are deposited directly upon the earth,
it is very difficult to avoid taking up earth and mud with the
materials, particularly when the street is wet and muddy. Lumps of
soil and débris unquestionably injure the concrete. The cost of
providing a lumber floor is comparatively small, as the plank may be
used over and over again. Specifications should, therefore, contain
this requirement and it should be enforced.
Footnote 10:
The ratios of the materials may appropriately be varied with the
strength and soundness of the sub-foundation, the amount of travel on
the street, and with the thickness of foundation it is proposed to
use. Where good materials are used and the work is properly done, a
1:3:5 concrete six inches thick is sufficient for streets of the
heaviest travel. For streets of light travel a 1:5:9 concrete will
usually give entirely satisfactory results. The most economical
thickness for a concrete foundation is an important consideration. The
strength of concrete may be said to increase, within usual limits of
practice, with the ratio of cement in it. The strength of concrete
beams or slabs increases in the ratio of the square of their depth. To
secure a required amount of strength in a pavement foundation, we may
therefore vary the richness of the concrete and the depth of the
foundation so as to secure the requisite strength at the least total
cost of materials and labor. This will be influenced by the cost of
materials and labor in each particular locality.
Within certain workable limits there is no reason why the same
principles of proportioning the strength of a pavement foundation to
the work required of it should not be applied as are employed in
designing other engineering structures.
The practice, usual in many cities, of adopting general specifications
requiring a standard thickness of foundation and composition of
concrete, and applying these to all streets, regardless of the
quantity and character of travel which the pavement is expected to
carry, is illogical and often very wasteful. If such a standard
foundation is sufficient for the streets of heaviest travel, it is
obviously a sheer waste of money to use it on the suburban streets
carrying the lightest travel. It is therefore better in preparing
standard specifications for pavement in any city to leave blanks for
the ratios of the concrete and for the thickness of the foundation, to
be filled in, in each individual case, as the judgment of the engineer
may dictate.
While it is important that the foundation of any pavement shall be
adequate, it is inexcusable to waste money in providing superfluous
strength. For the great majority of suburban streets, carrying but
little except the local travel, a foundation four inches thick made of
good Portland cement concrete in the ratios of 1:4:8 will prove
entirely satisfactory. Hundreds of such streets paved over a
foundation of that thickness, made of natural cement concrete in the
ratios of 1:2:4 can be cited where the foundation has proved entirely
satisfactory.
The character and firmness of the sub-foundation must, of course, be
taken into consideration in designing the foundation.
Footnote 11:
The routine here described produces better concrete with less
expenditure of labor, than the one often followed of putting all the
dry materials on the concrete board before any mixing is begun. The
writer has proved this from actual records covering a large quantity
of work.
Footnote 12:
The objections to using mortar for plastering over the concrete are:
that it is more costly than concrete; that the two materials may,
under certain conditions, separate and the thin mortar surface break
up under travel; that, if permitted, the mortar may be used to cover
up defective concrete, and that in the case of asphalt pavements the
pavement surface is more likely to “shift” on the smooth surface of
the mortar than on the rough surface of the concrete. The practice of
going over the fresh concrete with street brooms should not be
permitted. The only argument in favor of it is that it may be used to
conceal defective patches in the concrete.
Footnote 13:
See foot-note[6], p. 23. The cost of filling the joints of old block
pavement with mortar or grout is considerable. It will hardly ever be
less than 20 cents and may exceed 35 cents per square yard, depending
on the volume of joints and the local cost of material and labor. The
cost of resetting and ramming the blocks with proper care will usually
be from 10 cents to 12 cents per square yard, so that the cost of the
foundation, exclusive of the value of the blocks, may vary from 30
cents to 47 cents per square yard.
As a good concrete foundation 6 inches in depth can be laid for from
70 to 90 cents per square yard, it is obvious that if the old blocks
can be sold for as much as the difference between the cost of the old
block and the concrete foundation, nothing will be saved by using the
old block foundation. In at least one city, asphalt pavement has been
extensively laid over old stone block foundation relaid in a very
careless manner, the joints being filled usually with the old sand or
loam found in the street. This practice cannot be too strongly
condemned. Asphalt pavement surfaces resting on such a foundation are
necessarily short-lived and unsatisfactory. The practice of opening
the street to travel for a period after the blocks are relaid and
before the asphalt surface is applied, helps, under favorable
conditions, to consolidate the foundation, but does not remove the
objections to it. If heavy rains intervene, the sub-foundation becomes
saturated with water, and its resistance so reduced that the stone
blocks settle out of shape, particularly in soft spots, and they are
usually hastily raised and reset just before the asphalt surface is
applied. The result is an insecure foundation fatal to the durability
and usefulness of the pavement.
Footnote 14:
Where there is a possibility that gravel may be used, the contractor
should be asked to name prices for the gravel foundation as well as
the stone foundation, since, unless this be done, the change from the
one material to the other might be held to be illegal.
Footnote 15:
There has been much discussion as to the suitableness of these oil
asphalts, called “residual pitches,” for use in making asphalt
pavements. When properly prepared from suitable asphaltic oils, so as
to comply with the specifications here given, there can be no doubt
that good pavements can be made with them. But as they appear on the
market, being usually produced at different localities and refineries
from crude oils of differing qualities, distilled by somewhat
differing methods, and usually at temperatures of from 900 degrees to
1200 degrees, they are likely to vary so greatly in quality as to make
their use inadvisable without careful technical inspection. Unless,
therefore, the engineer is prepared to make, or to have such
inspection made, it is hardly wise or safe to permit their use. They
stand, in this respect, upon a footing different from the better-known
natural asphalts obtained from large deposits of practically uniform
character and quality, where the simpler process of refining is less
likely to effect injuriously the chemical quality of the material.
It may be confidently predicted that any of these “residual pitches”
which comply with these specifications will, if properly handled, make
a good pavement.
Footnote 16:
The possibility that some of these compounds or artificial asphalts,
may be suitable for use in pavements is not denied. But in the absence
of a fuller knowledge of them than we now have, and in the light of
present experience, the only safe course is to reject them.
Footnote 17:
It is not intended here to enter into an extended discussion of the
fact that some asphalts are injuriously affected by water, and the
bearing which this fact should have upon the selection of an asphalt
for pavement purposes. There can be no doubt that modern treatment and
methods of construction have tended to diminish but not wholly to
prevent the disintegrating effect of water upon pavements made with
such asphalt, and if the engineer could be certain that his pavements
would be constructed by contractors guided by long experience and the
best expert advice, he might perhaps safely disregard this provision.
Since in practice he can have no such assurance, the provision is a
wise one and it does not involve any serious or material hardship to
the contractor.
Footnote 18:
It is now well recognized that the character and quality of the sand
used is one of the most important elements in determining the utility
and durability of an asphalt pavement. A satisfactory sand should be
insisted on, even if it involves a very considerable increase in the
first cost of the work.
While our knowledge of the subject is not complete, experience seems
to indicate pretty clearly that a sand of the quality and size-grading
here specified as typical, may be depended upon to produce a good
pavement.
Footnote 19:
The use of Portland cement in surface mixtures to be laid on streets
of heavy travel, or those exposed to damp foundations, is very
strongly recommended. On streets of the heaviest travel, or where the
pavement will be exposed to unfavorable conditions of dampness,
particularly if the pulverized stone is not very finely ground, the
Portland cement may constitute twenty per cent. of the pulverized
material, or “dust,” as it is commonly called. Ordinarily from five to
ten per cent. may be used to advantage on all streets of moderately
heavy travel.
Footnote 20:
For determining the consistency of individual batches of asphalt
paving cement with a standard sample, the flow-plate method is most
convenient and sufficiently accurate. For a description of the latest
improved form of this apparatus see Engineering News of Aug. 22, 1912,
p. 347. It can only be used, however, where the cements to be compared
are of the same general composition—the same refined asphalt and
tempering agent—as the standard.
Footnote 21:
The practical value of the exact determination of the ductility of
asphalt paving cements is regarded by the author as not well
established. It is customary, however, in most recent specifications
to require it. Some asphaltic cements that have been quite
successfully used for pavements have not complied with such
requirements, while good coal-tar pitches will greatly exceed them.
Where this test is used the usual specification requires that a
briquette of asphaltic cement having a cross-section of one square
centimeter, at penetration 50, shall elongate to the extent of not
less than 20 nor more than 85 centimeters at 77° F. If the asphaltic
cement varies from 50 penetration an increase or decrease of at least
2 centimeters will be required for each five points above or below 50
penetration (Dow apparatus to be used).
Footnote 22:
It should be noted, in a general way, that there is quite a difference
in the temperature to which different asphalts may be safely
subjected.
Trinidad asphalt, and the California residual pitches, will not be
injured by the higher range of temperatures named in these
specifications, while Bermudez and some other asphalts should be
worked at as nearly as possible to the lower range of temperatures
named. The relative amount of loss of the different asphalts when
exposed for seven hours to the temperature of 325 degrees (Sect. 44)
will supply a rough practical guide as to the temperature
permissible—the greater the loss, the closer should the lower range of
temperatures be adhered to.
Footnote 23:
The open base-course, or “binder,” composed only of crushed stone,
coated with pitch or asphaltic cement, extensively and almost
exclusively used up to a recent date, is no longer advocated by the
best authorities on asphalt pavements. The aim is now to make the
base-course as dense and strong as the surface-course.
Footnote 24:
The importance of proper and thorough rolling is not usually fully
appreciated, and this part of the work is often shirked by the
contractor. Not only should the heavy roller be at work as soon as the
material will bear it, but the roller should, when work is progressing
regularly, be kept at work all the time. It is a safe motto that the
final rolling cannot be overdone.
Footnote 25:
There is still a wide difference of opinion as to the advisability of
laying the asphalt surface directly against the rail, many engineers
preferring to set one or more courses of paving brick, or stone paving
blocks between the rail and the edge of the asphalt. The writer’s
experience is to the effect that, if the work is properly done, the
first-named form of construction is preferable. If the asphalt be laid
against a rail so cold that the asphalt material in contact with or
near the rail is chilled before it can be compressed, the work will
necessarily be unsatisfactory. As to durability, wheels following the
line of the rail or of the paving blocks will sooner or later form a
rut in the asphalt which will require repair—and there is not much
difference in the results. The attempts to prevent the formation of
ruts by setting blocks alternately as headers and stretchers is not
always successful, even when the work is well done, and the difficulty
of properly compressing the tongues of asphalt between the headers is
so great that it is usually not well done. The asphalt settles under
travel or is gouged out, leaving a streak of rough pavement, and the
difficulty and cost of repairs is considerably increased. When paving
blocks or bricks are used, they should be firmly and carefully set in
the concrete foundation. Probably the most satisfactory construction
of this kind consists of two or three lines of the best paving brick
set with their length parallel to the rail. It is somewhat easier to
get at and repair rail joints with this construction.
Footnote 26:
The practice of laying asphalt block pavement upon crushed stone, or a
sand foundation, on streets carrying a considerable travel, is
inadvisable. See foot-note[6], page 23.
Footnote 27:
Hard limestone may be used where trap is not procurable except at a
prohibitive cost; but unless the difference in cost is very great the
trap will be the most economical in the end.
Footnote 28:
The pressure commonly specified is 5000 lbs per. square inch, but
recent investigations make it doubtful if that pressure is ever
attained, or is, indeed, practicable with any presses so far
constructed.
Footnote 29:
Asphalt blocks are now very commonly laid upon their sides, even where
they are made as thin as two inches, on streets carrying very
considerable travel. The practice is not to be recommended unless the
blocks are at least four inches thick. Blocks two inches thick will
give good service on private driveways and streets of quite light
travel.
Footnote 30:
Granite block pavement is, as a rule, used upon, and appropriate for
streets of the heaviest class of travel, and should, therefore, be
provided with the best and strongest foundation. It is nearly always
poor economy to lay granite blocks upon a broken stone, gravel, or
sand foundation.
Footnote 31:
Like other stones, granite from various localities differs widely in
strength, hardness and brittleness. Great hardness, accompanied with
comparative brittleness, is not desirable in granite for paving
blocks. Such material usually polishes by travel and becomes quite
slippery, and it is likely to become “turtle-backed,” that is, the
corners are likely to be chipped off or worn off, making the pavement
very rough and uneven. The quality of the granite to be used in any
one city is generally determined by the available supply, and
specifications must be drawn with reference thereto.
Footnote 32:
Except on streets of excessively heavy travel there seems to be no
good reason for making the blocks more than five inches deep. Blocks
of this depth are quite sure to become deformed by irregular wear
before the pavement will need to be renewed.
Footnote 33:
The widths of joints here specified as allowable are based upon the
assumption that they will be filled with Portland cement grout as
specified in Sect. 75. If this grout filling is used narrower joints
are not necessary, as the grout has sufficient strength to support the
corners of the blocks, and sufficient hardness to resist the wear of
travel (largely protected as it is by the blocks themselves) and to
cause the blocks to wear down quite evenly.
In many European cities the specifications require much closer joints.
The granite there available appears to break out naturally to truer
lines and better surfaces than that used in the Eastern states, at
least, so that the cost of dressing the blocks abroad is not as great
as here.
The City of New York has recently adopted specifications for “Special
Improved” Granite Block pavement intended to approximate the Liverpool
standard. These require that the blocks shall be not less than 6 nor
more than ten inches long, not less than 3½ nor more than 4½ inches
wide and five inches in depth. “The blocks are to be rectangular with
tops and sides uniform in thickness, to lay closely, and with fair and
true surface, free from bunches and so cut or dressed that when laid
stone to stone the joints shall not exceed ⅜ of one inch. The head of
the block shall be so cut that it shall not have more than one-quarter
of an inch depression from a straight-edge laid in any direction
across the head and held parallel to the general surface of the
block.” The joints are filled with bituminous cement.
The above specification is very difficult to meet from the granite
available to New York without excessive and expensive cutting, and
examination of the pavements laid under these specifications shows
that the joints greatly exceed the width specified.
It is believed that equally good results may be secured by permitting
somewhat wider joints filled with grout, and the cost would be
materially reduced.
Footnote 34:
The most satisfactory arrangement of courses at street intersections
is that shown by Fig. 14, page 208, Tillson’s Street Pavements and
Paving Materials, 2d edition.
Footnote 35:
The practice of filling the joints with gravel to a depth of one inch
or more before the blocks are rammed is of doubtful utility. If the
blocks are set closely against each other they will be well held in
place while the ramming proceeds. In practice it is hardly possible to
closely gage the depth of such preliminary gravel filling, and the top
or final filling whether of grout or of gravel and bituminous cement,
is likely to vary greatly in depth, and the lateral support of the
blocks is thus likely to vary in strength and rigidity.
Footnote 36:
It has been the almost universal custom, in this country at least, to
fill the joints in granite paving either with gravel alone or with
gravel and bituminous cement. But the reasons that have led engineers
to prefer grout filling for brick pavements apply with equal force to
granite pavement. It makes a stronger and harder filling than the
gravel and bituminous cement, and gives a better support to the edges
of the paving blocks, thus tending to prevent chipping and
“turtle-backing” in the pavement. It is also a materially cheaper
filling than the gravel and bituminous cement. But to provide for the
expansion and contraction of the pavement by changes of temperature,
it is desirable that a strip in the gutters, and an occasional strip
across the whole street, shall be filled with the more yielding
material, as specified.
Footnote 37:
The object of adding asphalt and Portland cement is to make the cement
stronger and less susceptible to changes of temperature. Pure coal-tar
pitch is very brittle at low temperatures, and is liable to flow from
the crown of the street to the gutters in hot summer weather. A cement
made as here specified is not only much stronger and less brittle in
cold weather, but requires a materially higher temperature to cause it
to flow than does pure pitch.
Footnote 38:
As the wheels of vehicles frequently follow along the lines of the
rails, thus concentrating their effect on a narrow strip near the
rails, and as the continuous joint against the rail makes the pavement
weaker there, the mortar bed, and the greater care in setting the
blocks along and near the rail are advisable.
Footnote 39:
If the joints are parallel to the direction of travel on the street
the wheels of vehicles are more likely to abrade or break off the
corners of the stone and form incipient ruts.
Footnote 40:
These specifications conform in most particulars to those adopted by
the “Association for Standardizing Paving Specifications,” and are
substantially the same as those recommended by the “National Paving
Brick Manufacturers’ Association” though they differ in some details
from each. The latest specifications adopted by the Association for
Standardizing Paving Specifications are very full and satisfactory and
are to be highly commended.
Footnote 41:
Here again a good concrete foundation is recommended, as being in the
end the most satisfactory and economical. See foot-note[6], page 23.
Footnote 42:
The Association for Standardizing Paving Specifications (New Orleans
meeting) adopted a standard size for paving bricks and blocks as
follows: Paving brick, 8½ inches long, 2½ inches wide and 4 inches in
depth. Paving blocks 8½ inches long, 3½ inches wide and 4 inches deep.
There seems to be no sufficient reason for confining the brick to
these dimensions.
Footnote 43:
The specifications of the Association for Standardizing Paving
Specifications require that all paving brick shall have lugs on one
side, and allow a projection of ¼ inch from the face of the brick. The
object is to provide a wider joint between the bricks in order to
facilitate the filling of the joints. The author does not believe
these lugs necessary, nor that brick without lugs, but otherwise
acceptable, should be excluded. It is certain that many of the best
brick pavements ever constructed have been built of bricks without
lugs. If lugs are required they should preferably not project more
than one-eighth inch. The same reasons that make narrow joints
desirable in other block pavements apply equally to brick pavements.
Footnote 44:
The A. S. P. S. Specifications permit a loss of 22% with the block
size, but do not name a permissible loss for “brick” size.
Footnote 45:
Absorption of less than one-half of one per cent., usually indicates
that a shale brick has been over-burned, resulting in increased
brittleness.
Footnote 46:
The absorption test is falling into disfavor, particularly with the
manufacturers. The author believes that it possesses a distinct value
and should be retained.
Footnote 47:
The object of this is to make a gutter offering less obstruction to
the flow of water.
Footnote 48:
This is the simplest and most effective way to detect soft and
underburned brick.
Footnote 49:
_If the joints are to be filled with bituminous cement_, substitute
for sections 90 and 91 the following:
Directly after the completion of the rolling and ramming, all the
joints in the brick pavement and between it and the curbing, manholes
or other structures, shall be filled with a bituminous cement in the
following manner:
The bituminous cement shall be composed, by weight, of one hundred
(100) parts of straight-run coal-tar pitch commercially known as
number four and twenty (20) parts of refined Trinidad asphalt melted
and thoroughly mixed together at a temperature of about 350° F., to
which shall be added twenty (20) parts of dry Portland cement, which
shall be thoroughly incorporated with the hot bitumen until a
homogeneous mass is produced, and kept agitated so as to prevent
settlement or separation until the cement is used. If another asphalt
is used instead of Trinidad the quantity added to the pitch must be
sufficient so that the cement will not flow at a temperature lower
than one hundred and twenty-five degrees Fahrenheit (125° F.). This
cement while at a temperature of about 325 degrees F. shall then be
poured from a spouted vessel into all joints and vacancies in the
pavement until they are completely filled, repouring being resorted to
if necessary to accomplish the complete filling of the joints. After
the joints are thus filled a layer of sand one-half inch thick will be
spread over the whole surface of the pavement and allowed to remain
until the engineer shall direct its removal.
Footnote 50:
The bituminous-cement joints are principally for the purpose of
providing for the expansion of the pavement in very hot weather.
Experience seems to have proved that cement grout is, everything
considered, the best and cheapest filling for the joints in brick
pavement. If the filling is properly done, the edges of the brick are
supported and the corners do not chip off. With the expansion joints
provided at intervals by the bituminous-filled joints, the curbs will
not be forced out of line, nor will the pavement be raised from its
sand bed by expansion, causing the rumbling sound sometimes noticed.
Where grout filling is used there seems to be no necessity for
covering the surface of the pavement with sand, as is usually done,
provided the grout is kept damp.
Footnote 51:
Since immunity from early natural decay is secured by preservative
treatment, the important requisite for wood paving blocks is capacity
to withstand the wear and tear of the travel on the street. We have as
yet no very satisfactory data as to the ability of the various species
of wood to endure the somewhat peculiar and special duty to which
paving blocks are subjected.
The test which seems to most nearly approach to what is wanted is that
of crushing strength, when the force is applied to the end of the
sample, parallel to its fibers; but this does not embrace the effect
of impact to which paving blocks are subjected under street travel.
Whether this may be considered a function of the end-crushing strength
or not is an open question, though there seems good reason to believe
that it will prove to be so; and if so, there is no good reason why
woods of substantially equal strength under the end-crushing test
should not show about the same endurance under street travel,
independent of the element of natural durability, which is practically
eliminated by preservative treatment.
The end-crushing strength per square inch of some of the kinds of
timber named as acceptable is about as follows:
Southern long-leaved yellow pine 6900 lbs.
Lob-lolly pine 6500 lbs.
Short-leaved pine 5900 lbs.
Cuban pine 7900 lbs.
Norway pine 6700 lbs.
Red gum 7100 lbs.
It was formerly very customary to specify that only Southern
long-leaved yellow pine might be used for paving blocks, though this
requirement was seldom strictly enforced. The fact is, that with the
exception of the test based upon the number of growth rings per inch,
it requires an expert knowledge, acquired only by long experience, to
distinguish with certainty the species of Southern pine from the
appearance of the lumber alone. It is now almost impossible to obtain
in the market shipments of strictly long-leaved yellow pine, and while
that wood is undoubtedly superior to the other pine timbers for paving
blocks it seems useless to specify its exclusive use, or to propose
specifications designed to exclude lumber made from other species of
pine. It was doubtless the recognition of this situation that
influenced the Association for Standardizing Paving Specifications, at
its last (New Orleans) convention to adopt a specification which
practically admits everything known in the market as “Southern yellow
pine” having annual growth rings averaging less than eight to the inch
and excluding all timber having less than six rings to the inch.
Within these limits these specifications practically admit all pine
lumber shipped from Southern mills.
The specifications here proposed, by limiting the number of growth
rings to nine per inch, would not confine the lumber to true
long-leaved yellow pine, but would secure a more mature and solid
quality of lumber. It is true, however, that both these specifications
and those adopted by the A. S. P. C. exclude most “Cuban pine” lumber
which is very rapid growing, the growth rings often numbering but
three or four to the inch, though the strength of the wood from this
species indicates that it may safely be used for pavement.
Footnote 52:
The question of the most economical depth for wood paving blocks is as
yet unsettled. In New York City, blocks 3½ inches in depth are adopted
as the standard and are being used on streets of the heaviest travel,
the practice of Berlin, Paris and other foreign cities being thus
followed. The arguments in favor of these short blocks are lower first
cost, and that, with much deeper blocks, the usual uneven wear of a
wood pavement will make it so rough as to require removal before the
blocks are worn down so as to be split up and dislodged from their
places. While reliable data on these points are wanting, it seems to
the writer very unwise to use such short blocks on streets of heavy
travel, and he would recommend that the minimum length for use on such
streets be 4½ inches, and he would prefer 5 inches.
On streets of light travel a length of 3½ inches should be
satisfactory.
Recent observations on heavy travelled streets in New York indicate
that when long-leaved yellow pine blocks become worn down to a
remaining depth of about 2⅛ inches they split up into fine slivers and
the pavement goes to pieces.
Footnote 53:
Most of the more recent specifications require the use of a heavy oil,
said to be composed of creosote oil with an admixture of refined tar,
on the ground that the tar is necessary as a water-proofing agent to
prevent the creosote oil from being dissolved out by water or
evaporated into the air. It is claimed that if moisture can thus be
excluded from entering the wood, decay will be prevented, even in the
absence of the antiseptic elements of creosote oil. It is not intended
to discuss this matter at length here. We know from long experience
that genuine creosote oil is the best preservative of wood so far
found; also that creosoted piles have stood in tidal waters,
alternately exposed to water and air, for twenty-five years and still
retain sufficient creosote oil to resist the Teredo—a very severe
test. Why experiment with a comparatively untried material,
particularly when it costs as much as the genuine creosote oil, is
rather more difficult to force into the wood, and has some admitted
objectionable qualities?
Footnote 54:
It is a common practice of contractors in some cities, in the laying
of both wood-block and asphalt block pavement, where a mortar bed is
called for, to substitute a bed of mixed sand and cement, dampened
only to such a degree as will make the mass pulverulent like damp
sand, the claim being made that ordinary mortar cannot be spread and
gaged properly. This claim is unfounded. The objection to the practice
is that the dampened mixture does not contain sufficient water to
cause the cement to set, and with the practically water-tight paving
surface, does not receive, even in rainy weather, the necessary amount
of water. If the weather be dry, the small quantity of moisture in the
mixture quickly evaporates, leaving the so-called mortar bed not much
better than a layer of sand alone. The writer has found such alleged
mortar dry and unset two weeks after the pavement had been completed.
If real mortar is not to be used, a layer of sand might almost as well
be substituted at first.
Footnote 55:
In a number of cities the specifications require the joints in
wood-block pavement to be filled with Portland cement grout. If the
blocks are set as closely together as they should be, the joints will
be so narrow that no grout, thick enough in consistency to be of
value, will enter them, except for a short distance down from the top,
the remaining depth of the joints remaining unfilled. An examination
of any well-laid wood-block pavement soon after it has been attempted
to fill the joints with grout will verify this statement. Furthermore,
the oil which exudes from the blocks, acting on the thin films of
grout, seems to deteriorate the mortar and to render it practically
inert. On the contrary, fine dry sand will readily run into and
completely fill the joints, and under travel the joints will soon
become impervious to water. The sand filling is therefore regarded as
better, and it costs less than the grout filling.
Footnote 56:
Wherever an old pavement or macadam road can be utilized it makes an
excellent foundation for a pavement of this kind, provided it is not
in too dilapidated a condition, extends from curb to curb, and its
surface conforms near enough to the desired street surface so that the
necessary changes and repairs will not be too expensive. Where the new
pavement is expected to carry quite a heavy travel it is not advisable
to use plain crushed stone for filling depressions and leveling up the
surface. It is difficult, even where proper care is used, to make such
patches of broken stone as firm and strong as the adjoining old
pavement, which is a necessary condition to secure satisfactory
results; for if the masses of broken stone yield under travel, slight
depressions will form over them in the bituminous surface, which will
in time become holes requiring repairs. The 1:4:9 concrete specified
for this work is not very much more expensive than plain broken stone,
it will not shift or break up under travel, and will in the end prove
a better investment.
Footnote 57:
Where a new foundation is required broken stone or macadam is most
frequently used for bituminous concrete pavements. Unless such
foundations are constructed in the same way and with about the same
care as is necessary for a macadam road it is liable to prove
unsatisfactory. Under the very heavy wheel loads that may occasionally
pass over the streets, imperfectly compacted broken stone is likely to
shift sufficiently to start incipient ruts which will enlarge and in
time necessitate expensive repairs. Such conditions are frequently
seen on bituminous concrete pavements subjected to heavy travel. These
pavements, like sheet asphalt pavements, require a foundation that
will be absolutely unyielding under travel. For this reason a concrete
foundation will generally be found more economical in the long run
than a broken stone foundation. The increased first cost per square
yard is not very great and this additional money will in most cases
prove a good investment. At the usual prices of material and labor a
square yard of 4 inch concrete should cost about 50 cents, while a
properly constructed broken stone foundation 6 inches thick (which
would not nearly equal in strength and rigidity 4 inches of concrete)
would cost about 45 cents per square yard. Considering the much
greater durability and lower cost of repairs of the pavement on the
concrete foundation, this small additional cost is not worth
consideration. While the specifications are made to cover the three
kinds of foundation, it is assumed that the kind of foundation to be
used will be decided in advance, and that the part of these
specifications relating to the others kinds of foundation will, in
actual use be omitted.
Footnote 58:
A bituminous cement composed largely of coal-tar pitch has heretofore
been most used in pavements of this character. It is not denied that
very good pavements have been, and can be built with this material,
but the superiority of the asphaltic cement here specified is so great
that it is true economy to use it. The difference in cost at
prevailing prices of material will be ten to twelve cents per square
yard. The greater durability and serviceability of the pavement made
with the asphaltic cement will, particularly on streets of
comparatively heavy travel, far more than justify this additional
cost.
Footnote 59:
Hydraulic concrete pavement is to be recommended only for country
roadways and for city streets of very moderate travel. While our
experience with this kind of pavement is yet limited there is reason
to believe from the nature of the material that it will not prove to
be a satisfactory or economical pavement for streets of heavy travel.
But in all cities and towns there are many residence streets where the
travel is very light, and yet where a permanent pavement is wanted and
warranted. For these, it is believed that a properly constructed
concrete pavement will prove very satisfactory and durable, and the
low cost at which it can be constructed should make it very attractive
to city officials and property owners. The author has advocated its
use under such conditions for many years (see Engineering News, July
21st, 1904). Like other composite pavements its utility and durability
will depend largely upon the good quality of the materials used and
the skill and thoroughness with which the work is done.
The specifications here offered are the result of the observation and
experience of the author, and it is believed that pavements laid in
accordance with them will give very satisfactory results.
Footnote 60:
A number of engineers advocate the construction of concrete pavement
in one homogeneous course, and quite a number of pavements have been
constructed in this way.
Like any other composite pavement, it is called upon to perform two
functions; to safely sustain the weight of loads passing over it, and
to resist wear and abrasion of its surface. A material and form of
construction that meets the first requirement may not meet the second.
Experience has proved that ordinary 1:3:6 concrete makes an entirely
satisfactory foundation for any pavement, but it lacks the hardness
and strength to successfully resist the surface abrasion of travel. To
secure this quality a richer and harder concrete is called for, but it
is unnecessary that the foundation should be equally hard. To
construct the pavement in two courses as here specified would seem to
be the logical way, especially as it decreases the total cost, and
should make a more durable pavement.
Footnote 61:
Some engineers advocate a greater total thickness of the pavement than
is here specified (6 inches). Considering that this pavement should
never be used on heavy traveled streets, a total thickness of concrete
of six inches will have ample strength to carry the loads to which it
will be subjected. If so, it is a useless waste of money to increase
the thickness of the concrete.
Footnote 62:
The use of limestone for the top course (unless it is of very superior
quality) is not advisable or economical unless the cost of trap rock
is so high as to be prohibitive, which, considering its superior
durability under the wear of travel, will not often be the case.
Footnote 63:
It is advisable to remove the screenings from this surface mixture for
two reasons: first, to secure greater uniformity of composition. If
the screenings are allowed to remain in the aggregate, there is danger
of segregation into patches of different sized aggregate and different
ratios of materials, which it is very important to avoid, and second,
the small fragments of stone are more likely to be crushed under the
concentrated weight of wheels than the larger masses, and to thus
start disintegration. Lack of uniformity in the composition and
homogeneity in this surface-course concrete is especially to be
guarded against, otherwise the surface of the pavement will wear
unevenly and depressions and ruts are likely to result.
Footnote 64:
The ideal composition of this surface-course concrete is one where the
stone forms the largest possible part of the mass consistent with
sufficient mortar to fill the voids and thoroughly bind the fragments
of stone together.
Footnote 65:
The importance of securing high quality and great uniformity in the
surface course cannot be urged too strongly.
Footnote 66:
This requirement must be strictly enforced. Otherwise there will be
danger that the two courses may not properly adhere to each other. It
is the writer’s experience that if this rule is observed there will be
no danger of the two courses separating.
Footnote 67:
The purpose of this rolling is mainly to evenly compress the mass and
thus secure its uniform density. It also produces a truer surface than
can usually be secured by ramming alone.
Footnote 68:
Among engineers there is quite a wide difference of opinion as to the
proper spacing of expansion joints, and, in fact, as to the necessity
or advisability of providing them at all. It has been suggested that
it might be better to omit them entirely, allowing the pavement to
form its own expansion joints by cracking along lines where natural
forces dictate. Such cracks by their irregularity give a bad
appearance to the surface, but observation seems to indicate that the
edges of these natural joints wear as well as those made by expansion
joints. Further observation and experience is needed in the matter. In
most concrete it is known that some contraction takes place during the
setting of the cement, regardless of temperature changes, and cracking
is probably due as much to this permanent contraction as to that
caused by low temperature. The coefficient of expansion of concrete by
heat is variable but so small that expansion joints ⅛ inch wide every
fifty feet along the street should provide for temperature changes.
Footnote 69:
If the expansion joints are not thus filled with bituminous cement
they will become filled and packed with incompressible stone, sand,
etc., that will not permit expansion.
Footnote 70:
The practical value of oiling concrete pavements has not yet been
determined by sufficient experience. There is reason, however, to
believe that the slight coating of bitumen will materially preserve
the surface from abrasion and that its benefit will thus be greater
than its cost. It will also tend to prevent the very slight dust that
might otherwise exist on the pavement.
Footnote 71:
In this class of pavements the contractor or promoter may properly be
required to assume responsibility for the character and utility of the
work produced, and the municipal authorities should assume no part of
such responsibility.
Footnote 72:
Upon the general subject of time guarantees of municipal work, see
Chapter XI, “Municipal Public Works,” by the author.
Footnote 73:
Concrete combined curb and gutter is suitable for use on the great
majority of residence streets, and others where the travel is not
excessive, or where it will not be subjected to specially severe use,
as on business streets where heavy vehicles are likely to be often
backed against the curb. If properly constructed it will have
sufficient hardness and strength to withstand all ordinary usage; it
makes a better appearance, particularly on residence streets, than any
other kind of curbing, is durable, and is usually less expensive than
any other suitable, equally durable and equally well-finished curbing
of natural stone, since the gutter displaces an equal area of
pavement.
Footnote 74:
The sketch here presented conforms pretty closely to usual practice
except in the width of the gutter. It is not uncommon to make the
gutter from two to three feet wide. This is not necessary or
desirable. A width of 15 to 18 inches forms a sufficient gutter to
carry away all drainage except during very heavy rainfalls. Where the
gutter projects out into the street sufficiently far to be exposed to
large numbers of heavily loaded wheels the outer corner is likely to
become broken off or unduly abraded.
Footnote 75:
Curbing of all kinds is more likely to be injured by freezing and the
heaving of frost under and around it than from any other cause. Good
drainage is the best protection against such injury. It is important
that these drains shall be connected with sewers, drains or other
outlets, so that water will not stand in them.
Footnote 76:
The most notable departure of these specifications from usual practice
is the use of a solid body of rich, homogeneous concrete for the whole
section of the structure, thus avoiding the use of two courses and
qualities of concrete—the core concrete and the facing. The most
common cause of failure of concrete curbs and gutters is the
separation, more or less, of the facing from the core concrete.
Without doubt this can be prevented by the use of proper materials,
careful work, and the strict observance of the rule that the facing
course must be applied before the core concrete has begun to set. But
it is difficult to always secure these favorable conditions.
Computation will show that the difference in cost of materials,
between the usual two-course construction and a single body of rich
concrete throughout, is not very great, while the saving in cost of
labor is so considerable as to make the actual difference in cost of
the two types very small. There can be no doubt that the simpler
construction and the consequent greater certainty of securing a
durable and satisfactory job is greatly in favor of the construction
here recommended.
Footnote 77:
The appearance of “hair cracks” on the surface of rich concrete,
finished by troweling, and the blotched appearance of the surface of
concrete curbing, are usually caused by improper finishing. The glazed
surface produced by troweling, particularly where pure, dry cement or
neat mortar is applied is almost sure to develop hair cracks, and the
varying texture of the surface is likely to absorb water unevenly and
thus produce, in time, the unevenly colored or blotched surface so
often seen.
Footnote 78:
The utility and durability of hydraulic concrete sidewalks depends
largely on the quality of materials and workmanship employed in the
work. Too frequently, specifications for this work are not
sufficiently full, or not prepared with the requisite care, or the
work is not properly supervised or inspected while in progress. The
aggregate importance and cost of this sidewalk work in our cities
warrants more care and attention than it generally receives.
Footnote 79:
Determined by the thickness of the drainage course adopted.
Footnote 80:
It is customary in many cities to require that the drainage course
under the concrete shall have a depth of twelve or more inches. This
deep-drainage is designed to prevent the heaving of the sidewalk by
freezing. Experience seems to prove that this is not necessary,
particularly if tile drains are provided to carry off the water from
the drainage course, as specified. Comparatively dry material, even
earth, does not heave with freezing; on the other hand, if the
material and the trench in which it is placed is wholly or partly
filled with water, heaving is liable to occur in severe freezing
weather, whatever the depth of the drainage course. Experience has
proven, however, that four inches of drainage material is sufficient
if the water is drained out of it, while if allowed to stand saturated
with water, deeper drainage will give little if any better results.
Where the soil is sandy or the natural drainage is otherwise good, no
drainage course is necessary.
Footnote 81:
Except in the matter of low first cost cinders are not desirable for
the drainage course. In time, this material is likely to slack, or
decompose, and shrink in volume more or less and to allow the sidewalk
to settle. The hollow sound one often notices when walking over a
sidewalk and the cracks that frequently appear, are usually caused by
the irregular settlement of the drainage course. The object of wetting
down the cinders several days before they are used is to cause as much
as possible of this slacking to take place before the cinders are used
in the drainage course.
Footnote 82:
There is a good deal of diversity of practice in the thickness of the
concrete to be used. For all ordinary sidewalks three inches of bottom
course and one inch of surface-course are ample, and in many cases the
thickness of the surface course has been reduced to one-half inch with
satisfactory results. Three-fourths inch of surface-course, if fairly
uniform in thickness and of good quality, will generally be ample for
ordinary sidewalks.
Footnote 83:
It is customary to make the surface-course concrete much richer than
this, but it is not necessary if the materials are good and the work
well done.
Footnote 84:
This requirement is very important and should be strictly enforced,
otherwise there is danger that by the action of water, frost, and
time, the two courses may separate and the surface-course break up—a
condition not infrequently observed.
Footnote 85:
The troweling not only helps to secure a true surface, but tends to
produce a dense surface on the concrete; but it is not desirable that
this surface shall be smooth and glassy, hence the slight roughening
of the surface with a wire brush.
Footnote 86:
Care must be taken to make and leave these expansion joints open to
their full width entirely through the concrete. The practice of
forming these expansion joints by partitions of iron plate, against
which the blocks of sidewalk are built is not advised, for the reason
that they are likely to prevent the thorough compression of the
concrete surface against or near the plates.
------------------------------------------------------------------------
TRANSCRIBER’S NOTES
1. Silently corrected obvious typographical errors and variations in
spelling.
2. Retained archaic, non-standard, and uncertain spellings as printed.
3. Re-indexed footnotes using numbers and collected together at the end
of the last chapter.
4. Enclosed italics font in _underscores_.
5. Enclosed bold font in =equals=.
6. Denoted subscripts by an underscore before a series of subscripted
characters enclosed in curly braces, e.g. H_{2}O.
*** End of this LibraryBlog Digital Book "Specifications for street roadway pavements: with instructions to inspectors on street paving work" ***
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