196 SAND AND CEMENT 



AVERAGE WEIGHTS OF HYDRAULIC CEMENTS 



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Portland cement may be distinguished by its dark color, 

 heavy weight, slow rate of setting, and greater strength. 

 Natural cement is characterized by lighter color, lighter 

 weight, quicker set, and lower strength. Slag cement is 

 somewhat similar to Portland, but may be distinguished 

 from it by its lilac-bluish color, by its lighter weight, and by 

 the greater fineness to which it is ground. 



Portland cement is adaptable to any class of mortar or 

 concrete construction, and is unquestionably the best mate- 

 rial for all such purposes. Natural and slag cements, how- 

 ever are cheaper, and, under certain conditions, may be sub- 

 stituted for the more expensive Portland cement. All 

 heavy construction, especially if exposed, ail reinforced- 

 concrete work, sidewalks, concrete blocks, foundations of 

 buildings, piers, walls abutments, etc. should be made 

 with Portland cement. In second-class work, as in rubble 

 masonry, brick sewers, unimportant work in damp or wet 

 situations, or in heavy work in which the working loads 

 will not be applied until long after completion, natural 

 cement may be employed to advantage. Slag cement is 

 best adapted to heavy foundation work that is immersed 

 in water or at least continually damp. This kind of cement 

 should never be exposed directly to dry air, nor should it be 

 subjected either to attrition or impact. 



