SAND AND CEMENT 197 



SAND AND ITS MIXTURES 



SAND 



Sand is an aggregation of loose grains of crystalline struc- 

 ture, derived from the disintegration of rocks. It is called 

 silicious, argillaceous, or cakareous, according to the char- 

 acter of the rock from which it is derived. Sand is obtained 

 from the seashore, from the banks and beds of rivers, and 

 from land deposits. The first class, called sea sand, contains 

 alkaline salts that attract and retain moisture and cause 

 efflorescence in brick masonry. This efflorescence is not at 

 first apparent but becomes more marked as time goes on. 

 It can be removed temporarily at least by washing the stone- 

 work in very dilute hydrochloric acid. The second, termed 

 river sand, is generally composed of rounded particles, and 

 may or may not contain clay or other impurities. The third, 

 called pit sand, is usually composed of grains that are more 

 angular; it often contains clay and organic matter. When 

 washed and screened, it is a good sand for general purposes. 



Sand is used in making mortar because it prevents excess- 

 ive shrinkage and reduces the quantity of lime or cement 

 required. Lime adheres better to the particles of sand than 

 it does to its own particles; hence, it is considered that sand 

 adds strength to lime mortar. On cement mortar, on the 

 contrary, sand has a weakening effect. 



Properties of Sand. The weight of sand is determined by 

 merely filling a cubic -foot measure with dried sand and 

 obtaining its weight. Dry sand weighs from 80 to 120 Ib. 

 per cu. ft.; moist sand, however, occupies more space and 

 weighs less per cubic foot. The weight of sand is more or 

 less dependent on its specific gravity and on the size and shape 

 of the sand grains, but, other things being equal, the heaviest 

 sand makes the best mortar. 



The specific gravity of sand ranges from 2.55 to 2.80. 

 For all practical purposes the specific gravity may be 

 assumed to be 2.65 with little danger of error. 



By percentage of voids is meant the amount of air space 

 in the sand. Structurally, it is one of the most important 



