It is believed that equally good results may be secured by permitting somewhat wider joints filled with grout, and the cost would be materially reduced.
[34]. The most satisfactory arrangement of courses at street intersections is that shown by Fig. 14, page 208, Tillson’s Street Pavements and Paving Materials, 2d edition.
[35]. The practice of filling the joints with gravel to a depth of one inch or more before the blocks are rammed is of doubtful utility. If the blocks are set closely against each other they will be well held in place while the ramming proceeds. In practice it is hardly possible to closely gage the depth of such preliminary gravel filling, and the top or final filling whether of grout or of gravel and bituminous cement, is likely to vary greatly in depth, and the lateral support of the blocks is thus likely to vary in strength and rigidity.
[36]. It has been the almost universal custom, in this country at least, to fill the joints in granite paving either with gravel alone or with gravel and bituminous cement. But the reasons that have led engineers to prefer grout filling for brick pavements apply with equal force to granite pavement. It makes a stronger and harder filling than the gravel and bituminous cement, and gives a better support to the edges of the paving blocks, thus tending to prevent chipping and “turtle-backing” in the pavement. It is also a materially cheaper filling than the gravel and bituminous cement. But to provide for the expansion and contraction of the pavement by changes of temperature, it is desirable that a strip in the gutters, and an occasional strip across the whole street, shall be filled with the more yielding material, as specified.
[37]. The object of adding asphalt and Portland cement is to make the cement stronger and less susceptible to changes of temperature. Pure coal-tar pitch is very brittle at low temperatures, and is liable to flow from the crown of the street to the gutters in hot summer weather. A cement made as here specified is not only much stronger and less brittle in cold weather, but requires a materially higher temperature to cause it to flow than does pure pitch.
[38]. As the wheels of vehicles frequently follow along the lines of the rails, thus concentrating their effect on a narrow strip near the rails, and as the continuous joint against the rail makes the pavement weaker there, the mortar bed, and the greater care in setting the blocks along and near the rail are advisable.
[39]. If the joints are parallel to the direction of travel on the street the wheels of vehicles are more likely to abrade or break off the corners of the stone and form incipient ruts.
[40]. These specifications conform in most particulars to those adopted by the “Association for Standardizing Paving Specifications,” and are substantially the same as those recommended by the “National Paving Brick Manufacturers’ Association” though they differ in some details from each. The latest specifications adopted by the Association for Standardizing Paving Specifications are very full and satisfactory and are to be highly commended.
[41]. Here again a good concrete foundation is recommended, as being in the end the most satisfactory and economical. See foot-note[[6]], page [23].
[42]. The Association for Standardizing Paving Specifications (New Orleans meeting) adopted a standard size for paving bricks and blocks as follows: Paving brick, 8½ inches long, 2½ inches wide and 4 inches in depth. Paving blocks 8½ inches long, 3½ inches wide and 4 inches deep. There seems to be no sufficient reason for confining the brick to these dimensions.