115 



One Part Cement, Three Parts Sand. 



7 days (1 day In moist air, 6 days in water).. 150 to 200 Ib. 

 28 days (1 day in moist air, 27 days in water) 200 to 300 Ib. 



Constancy of Volume: Pats of neat cement, about 3 in. 

 in diameter, % in. thick at center and tapering to a thin 

 edge, shall be kept in moist air for a period of 24 hours. 

 Keep one pat in air at normal temperatures and observe at 

 intervals of at least 28 days. Keep another pat in water 

 at 70 F. and observe at intervals of 28 days. Expose 

 another pat to an atmosphere of steam, above boiling 

 water, for 5 hours. The pats during this test should re- 

 main firm and hard and show no signs of cracking) check- 

 ing or disintegrating. 



Sulphuric Acid and Magnesia: No more than 1.75% of 

 anhydrous sulphuric acid nor more than 4% of magnesia 

 should be present. 



If cements do not fill the 24 hour or 7 day tests and are 

 held for the 28 day tests and then fail to come up to the 

 above requirements they should be condemned and im- 

 mediately removed from the premises. 



For a more complete test of cement, see the U. S. 

 Government Specifications. 



Sand: All sand shall be clean, sharp sand, not having 

 an excessive amount of foreign material in the form of 

 loam or clay; 10% can be allowed. 



Broken Stone: Stone should pass a % in. ring for small 

 work, 1% for large work; screenings, if clean, are per- 

 mitted. All stone should be free from dirt which might 

 keep the cement from adhering to the stone. Sandstone, 

 limestone, granite, trap rock or other stone can be used. 



Gravel: Gravel should be not larger than that passing 

 a % in. ring and shall contain no sand, unless the pro- 

 portion of sand in the mixture used is reduced. It shall 

 also be free from clay, loam and other extraneous ma- 

 terial. 



Mixing and Placing: The mixing can either be done by 

 hand, the cement, sand and stone being placed on a 

 watertight mixing board, or mixed in a batch mixer. The 

 oroportion of water determined according to the nature 

 of the materials being mixed to give same a good, pasty, 

 well mixed consistency. 



The concrete shall be handled quickly and brought to 

 the points of placing by hoists, derricks, concrete buggies 

 or wheelbarrows, proper runs being supplied so that the 



