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.