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:

3per cent. of the whole will pass No.200 sieve.
15per cent. of the whole will pass No.100 sieve.
18per cent. of the whole will pass No.80 sieve.
30per cent. of the whole will pass No.50 sieve.
24per cent. of the whole will pass No.30 sieve.
10per 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:

Sand100.0 lbs.
Pulverized mineral matter passing No. 200 screen, including that found in the paving cement17.5 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 stone100lbs.
Sand42lbs.
Pure bitumen (in asphaltic cement)7lbs.
Pulverized stone7½lbs.

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.