58 BULLETIN 1077, IT. S. DEPAETMEXT OF AGRTCULTUEE, 



Crete pavement only and do not include the cost of grading, cul- 

 verts, or bridges. This tabulation is given in the appendix, pages 

 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. When cup 

 holes first appear they are usually from 1 to 2 inches in diameter 

 and from 4 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 j)avement 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 reoairs 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 j)atch 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 



