592 



CEMENTS, LIMES, AND PLASTERS. 

 TABLE 226. 



Sand cement. Sand cement, or silica cement, is the name given to 

 the product made by grinding up together Portland cement with an 

 equal or greater quantity of sand, limestone, or other chemically inert 

 substance. Description of the making and properties of sand cement 

 is not properly part of a discussion of the manufacture of Portland cement, 

 but rather a matter for the engineer to consider in connection with the 

 uses of cement. For this reason the question will be touched on very 

 briefly. 



It is found that if Portland cement be mixed with an equal quantity 

 of sand or limestone and the mixture ground very finely in a tube 

 mill, the resulting product (sand cement) will show a strength almost 

 or quite as great as the Portland cement from which it was made, not- 

 withstanding the fact that the sand cement consists only half of Port- 

 land cement. When Portland cement is very expensive, economies 

 are, therefore, possible in this line. 



The gain in strength is due entirely to the extra fineness given by 

 the extra grinding. The sand does not enter into chemical combina- 



