EXERCISE No. 70 

 MAKING CONCRETE 



Object : To learn how to make concrete. 



Material : Sand, gravel, cement, sieve, shovel, and bucket. 



Method : Make some concrete from one of the formulas in 

 the book. The proportion of each material will depend upon 

 where the concrete is to be used. The formula used should 

 be the one that is used in the community where the pupils 

 can also see the men making it. 



Concrete is a mixture of cement and sand, or of cement, 

 sand, and gravel or crushed stone. It is used for building 

 sidewalks, silos, reservoirs, dams, and a variety of other things. 



Sand and stone are bought by the cubic yard or load, and 

 cement by the sack or barrel. 



A sack of cement is \ of a barrel and a barrel is estimated 

 to contain 4 cu. ft. and to weigh 376 Ib. 



The materials which make up concrete are mixed in 

 varying proportions, depending upon the purpose for which 

 the concrete is to be used. A very common mixture is 1, 2, 4. 

 This means that for making a cubic yard of concrete a 

 certain amount of cement is used, 2 times as much sand (by 

 volume), and 4 times as much stone. 



The table (ninth line) shows the number of barrels of cement required 

 for one cubic yard of concrete mixed in the proportion 1, 2, 4. The amounts 

 of sand and stone required, expressed as parts of a cubic yard, may be figured 

 as follows: 



1.51 bbl. cement = 1.51 x4 cu. ft. =6.04 (cu. ft.). 



6.04 cu. ft. = - or .2237 cu. yd. 



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2 x.2237 cu. yd. = .4474, or approximately .45 cu. yd. of sand. 

 4 x.2237 cu. yd. = .8948, or approximately .89 cu. yd. of stone. 



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