The concrete for the base of walks is usually composed of 1 part Portland cement, 3 parts sand, and 5 parts stone or gravel. Sometimes, however, a richer mixture is used, consisting of 1 part cement, 2 parts sand, and 4 parts broken stone; but this mixture seems to be richer than what is generally required. The concrete should be thoroughly mixed and rammed, and cut into uniform blocks. See Fig. 78. The size of the broken stone or gravel should not be larger than one inch, varying in size down to 1/4 inch, and free from fine screenings or soft stone. All stone or gravel under 1/8 inch is considered sand.

Fig. 77. Double Arch. Culvert, 14 by 5 1/2 Foot.

Fig. 77. Double Arch. Culvert, 14 by 5 1/2-Foot.

The thickness of the concrete base will depend upon the location, the amount of travel, or the danger of being broken by frost. The usual thickness in residence districts is 3 inches, with a wearing thickness of 1 inch, making a total of 4 inches. In business sections, the walks vary from four to six inches in total thickness, in which the finishing coat should not be less then 1 1/4 inches thick. The concrete base is cut into uniform blocks.

Fig. 78. Square Tamper

Fig. 78. Square Tamper.

The lines and grades given for walks by the Engineer, should be carefully followed. The mould strips should be firmly blocked and kept perfectly straight to the height of the grade given. The walks usually are laid with a slope of \ inch to the foot toward the curb.

Fig. 79. Concrete Sidewalk and Curb.

Fig. 79. Concrete Sidewalk and Curb.

The blocks are usually from four to six feet square, but sometimes they are made much larger than these dimensions. The joints made by cutting the concrete should be filled with dry sand, and the exact location of these joints should be marked on the forms. The cleaver or spud that is used in making the joints should not be less than 1/8 of an inch or over 1/4 of an inch in thickness.