TESTS OF SAND AND CEMENT CUBES. 



339 



where y is the strength at the end of x weeks, c is 

 the crushing strength at the end of one week, and d is 

 a constant, which for the above cases has values of 339 

 for the neat cement, 312 for the .three to one, and 274 for 

 the five to one mixture. 



Thus, take the case of neat cement, tested 10 weeks after 

 gauging. Here c is 1,800, d is 339, and a; is 10. So that 



y = 1,800 + 339 V 10 - 1 



that is to say, a cement which has a compressive strength 

 of l,8001bs. per square inch at the end of seven days, will 

 require 2,8171bs. to produce fracture at the end of 10 weeks. 



For cement compression pieces it is noted that, as in 

 tension, samples kept in water yield higher results than 

 those kept in air ; and also that in a good cement the 

 strength should steadily increase with age. 



The strength of neat cement cubes kept in water for 

 four weeks varies from 5,0001bs. to 2,0001bs. per square 

 inch. When mixed with sand the strength continually 

 diminishes with the ratio of sand to cement. 



Kirkaldy gives the following results of crushing tests 

 of cubes of cement and sand : 



*KIRKALDY'S TESTS OF SAND AND CEMENT 



CUBES. 



* Kirkaldy'a " Testing. 



