47 



stone put into the barrel. Assume that 5 gallons of 

 water were displaced and 42 cu. in. measured in the 

 graduate as the final fraction of a gallon. 



5x231 = 1155 

 Graduate= 42 



1197 cu. in. (call it 1200). 



Therefore there are 1200 cu. in. of solid stone in 

 2000 cu. in. of crushed stone. The voids are 800 parts 

 in 2,000 or 40 parts in 100, 40 per cent. 



The same method can be applied to sand or any 

 aggregate, and the method of working this out is the 

 same as noted previously, the only difference being that 

 the amount of solid material in a certain volume is 

 determined by water displacement instead of by weight. 

 One uncertain factor in this last is the ability of cer- 

 tain stones to absorb water, which would affect the 

 results, consequently the stone should be wet before 

 the test. 



These are two commonly accepted methods of de- 

 termining the amount of voids, and the proportion re- 

 quired between the sand and the bulk aggregate. 



In carrying on these tests, be very careful to use 

 samples that are the average run of the stock. Wheel 

 a barrow around the pile and take a small shovelful 

 from different localities, middle and edges. Then mix 

 this thoroughly in the barrow, and use it for the 

 sample. 



The simplest and most effective way of applying 

 either of the above methods to obtain a propor- 

 tion between the sand and aggregate is by experi- 

 ment. Voids in broken stone run generally be- 

 :i 40 and 50 per cent. As specifications come 

 now into the field, the mix is usually specified as 

 1-2-4 or xing arbitrarily the proportion be- 



tween the sand and the larger aggregate. To check 

 on this it is a good plan to experiment with the water 



