Cement for the Farm. 



411 



The average price of cement in 1880 was $3.00 per barrel (75 

 cents per bag) ; in 1907, $1.10 per barrel (27i/^ cents per bag) ; in 

 1908, $0.85 per barrel (21^4 cents per bag) at the mills. 



CEMENT CONCRETE. 



Composition — Cement concrete is composed of a mixture of cement, 

 sand and a third material, usually rock or gravel. It is composed of 

 two parts, namely: Mortar, a mixture of sand and cement, and the 

 aggregate, a course material (rock or gravel). These two parts, 

 mortar and the aggregate, compose the mixture, commonly called 

 concrete. 



To many people this appears to be simply a mixture of cement, 

 sand and stone, mixed together in any way or proportion to suit the 

 individual fancy of the user. This is not a fact, for there is a definite, 

 well defined theory involved in proportioning concrete. 



A correctly proportioned mortar is one which contains enough 

 cement to perfectly coat every particle of sand and completely fill 



/ c e -m e -n jf 



^ ^ O c ^ 



Figure 2. Illustrating the proportions of a 1-3-6 concrete. 



all voids. The mortar in turn should coat every particle and fill 

 every void of the aggregate. As a matter of fact, this condition 

 is never exactly obtained in practice, but it follows without argument 

 that the materials must be thoroughly mixed, and that a thoroughly 

 mixed lean concrete is stronger than a richer proportion poorly 

 mixed. 



Concrete is usually a 1-2-4, l-2yo-5, 1-3-6 or 1-4-8 mixture, mean- 

 ing that a 1-3-6, for example, contains 1 part cement, 3 parts sand 

 and 6 parts broken stone or gravel, all parts by volume. Fig. No. 2. 

 As for example, if 1 cubic foot of cement (one bag) is used, there is 

 required 3 cubic feet of sand, 6 cubic feet of stone. About 40 cubic 

 feet of these ingredients, each measured to itself, will make one cubic 

 yard (27 cubic feet) of tamped concrete. 



These proportions roughly approximate the voids in the sand 

 and aggregate (stone). The accurate way is to measure the voids in 



