24. Placing Concrete on Street.—All concrete must be placed and rammed before it begins to stiffen or set. Concrete should be so handled that the mortar will segregate or separate from the stone as little as possible. When in place on the street it should make a mass of uniform consistency and appearance. The concrete should, as soon as placed on the street, be graded to a proper thickness and surface, and then well compacted by ramming. Insist on good ramming; this part of the work is not often properly done. The surface of the concrete should be brought to the true grade by proper grading and tamping. Where necessary to raise the surface, additional concrete, made of small stone, may be applied during the tamping. Neat mortar should not be used for this purpose. Sweeping mortar over the surface with street brooms should not be permitted—it is useful only to cover up defects and to produce an extra smooth surface (which is not usually desirable). To measure the thickness of the bed of concrete, lay a straight-edge upon the surface with the end of the straight-edge projecting a foot or two beyond the edge of the concrete, and measure the space from the lower edge of the straight-edge down to the sub-foundation.
Care must be taken to finish the surface of the completed concrete at the proper distance below and truly parallel to the grade and contour of the finished pavement. This is more important in the case of sheet asphalt pavements, since irregularities in the concrete will cause variation in the thickness of the finished asphalt surface, which will affect the durability of the pavement. The grade stakes for the concrete should therefore be carefully set and worked to, and humps or depressions between the stakes should be avoided.
25. In hot, dry, weather the concrete must be kept damp by watering it until it is at least five days old, and horse-travel over it must be prohibited until it has set up hard enough not to be injured thereby.
26. Old Paving Stone Foundations.—If a foundation is to be made of old paving stone blocks reset, the important points to be looked after are,
The preparation of the sub-foundation.
The sand bed.
The setting of the blocks.
The grouting of the blocks.
The sub-foundation should be prepared, where necessary, as stipulated in Sects. 16 and 17 of these instructions. This part of the work is likely to be carelessly done unless proper work is insisted upon.
The sand used as a cushion course must be of good quality and reasonably clean. The use of mixed sand and soil taken from the street excavation should not be permitted.