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.