. Economic Papers. not be any more than is sufficient for thispurpose. In Fig. 10 is an illustration (magnified) of a mass of sandand clay where the grains are touching each other and the voids areexactly filled with clay. If too large a proportion of clay is used, thegrains of sand are prevented from touching each other and are able tomove about each other in the mass of clay so that the resistance of themass to the wearing effect of traffic is practically no more than if theroad was composed simply of clay. Water is also able to act upon themass of clay and the road becomes sticky and muddy.
. Economic Papers. not be any more than is sufficient for thispurpose. In Fig. 10 is an illustration (magnified) of a mass of sandand clay where the grains are touching each other and the voids areexactly filled with clay. If too large a proportion of clay is used, thegrains of sand are prevented from touching each other and are able tomove about each other in the mass of clay so that the resistance of themass to the wearing effect of traffic is practically no more than if theroad was composed simply of clay. Water is also able to act upon themass of clay and the road becomes sticky and muddy. In Tig. 11 isillustrated a section of road where there is too large a proportion ofclay. If there is too small a proportion of clay used, the grains ofsand are not cemented tightly together and the road disintegrates veryquickly under traffic and rain. Fig. 10.—Section of sand-clay roadshowing a complete and thorough mix-ture of the clay and sand. Just sufficientclay to fill the voids between the grains Fig. 11.—Section of road where there isa large excess of clay, which prevents thegrains of sand from touching each other. HIGHWAY WORK IN NORTH CAROLINA. 4 1 The exact proportions of sand and clay for making the best sand-clay road cannot be stated, as the proportions vary with the characterof the sand, according to its sharpness, percentage of foreign material,and size of grains. Approximately there is in a sand-clay road about80 per cent sand and 20 per cent clay. One simple means of determin-ing the theoretical amount of pure clay that should be added to anysand that is to be used in the construction of a sand-clay road is to filla glass tumbler brimful with the sand that is to be used and then fill asimilar tumbler with water; pour the water carefully onto the sanduntil the water comes flush with the surface, which will mean that allthe voids between the grains of sand are now filled with water. Theamount of water that has been poured into the tumbler containin
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