FILLING OF CAVITIES 117 



three-quarters cubic feet of gravel, and five gallons 

 of water will make a medium wet mixture which 

 will make four and a quarter cubic feet of concrete. 

 So by dividing the number of cubic feet in the 

 cavity by 4j4 you can obtain the number of bags 

 of cement to order, and by multiplying the num- 

 ber of bags of cement by 3^, you can obtain the 

 number of cubic feet of gravel required. If the 

 sand and stone or gravel are secured separately, 

 the amounts required can be calculated from the 

 proportions of the ingredients of a cubic foot of 

 concrete. A cubic foot of i :2 14 concrete con- 

 tains approximately .015 of a bag of cement, .016 

 cubic yard of sand, and .032 cubic yard of stone or 

 gravel. 



The cost of materials varies greatly in different 

 parts of the country, but a fair average would be 

 $1.50 a barrel for cement, $.80 a yard for sand, 

 and $1.20 for stone. A combination of these fig- 

 ures with those above indicates that a cubic foot of 

 1:2:4 concrete contains $.056 worth of cement, 

 $.013 of sand, and $.04 worth of stone, making 

 the cubic foot cost, for materials, approximately 

 eleven cents. It is more likely to exceed than not 

 to reach that figure. 



Asphalt. — It is now generally recognized that 

 concrete is not fitted to serve as a filling material 

 for every kind of cavity. With that recognition 

 has come a demand for a more elastic material. 



