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.