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 thepulverized 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:
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 materialwill 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 shallbe 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, providedthe 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 thicknessbeing 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.
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 becompletely 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 thatthe 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.
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.”
The practice has been heretofore, and is at the present time, to attempt to make specifications for asphalt pavements broad enough to include allthe 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 theasphaltic 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, butothers 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.
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 gastars, 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 notexceed 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:
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 andmelted 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:
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:
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 placedis 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-coursemust 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 mustbe 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.
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 becomposed 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)
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, addedand 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.