58 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTURE. 
crete pavement only and do not include the cost of grading, cul 
verts, or bridges. This tabulation is given in the appendix, page^ 
64 to 66. In considering the costs given in these tables it should 
be borne in mind that the 1920 prices probably represent the peak 
of war prices. 
MAINTENANCE. 
The shoulders, slopes, and drainage structures of concrete roads 
require the same kind of maintenance as those of other types of 
improved roads. The maintenance of the pavement consists, for the 
most part, in repairing cup holes, cracks, joints, and perhaps the 
renewal of an occasional defective area. Cup holes are spots in the 
surface of the pavement which break down under traffic and which 
may result from a number of causes. The most frequent cause of 
such defects is the presence of sticks, lumps of clay, particles of 
unsound stone, or other soft material in the aggregates. \Vfren cup 
holes first appear they are usually from 1 to 2 inches in diameter 
and from J to 1 inch in depth, but they are gradually enlarged by 
the action of traffic, which loosens the concrete around their edges, 
and unless promptly repaired they may soon have an area of several 
square feet and a considerable depth. The action of traffic also 
gradually breaks away the concrete at the edges of cracks and joints, 
and if proper maintenance is not provided a considerable area of the 
surface of the pavement will be destroyed. The maintenance of 
cup holes, cracks, and joints usually consists of filling them with tar 
or asphalt and covering the bituminous material with coarse sand, 
pea gravel, or stone chips. Satisfactory results can be secured by 
this method only when a crew with proper equipment and materials 
goes over the road, making the necessary repairs at least once and 
preferably twice a year. 
Where defects of any considerable size are to be repaired the edges 
should be chiseled down until they are approximately vertical and 
not less than 1 inch deep. The hole should be thoroughly cleaned 
and painted with tar or asphalt, after which it should be filled with 
clean, coarse stone chips, thoroughly grouted with tar or asphalt. 
The surface of the patch should then be covered with coarse sand, 
pea gravel, or fine stone chips. A cold mix of small stone and bitu- 
minous material has sometimes been successfully used for this type 
of repair work. 
Either tar or asphalt may be used for making such repairs. Satis- 
factory results have been obtained with each. There is some differ- 
ence of opinion among engineers as to just what consistency the tar 
should possess in order to give the best results, but the most general 
requirement in this particular seems to be that the tar when sub- 
jected to the float test in water at 50° C. will permit the float to sink 
