230 



TABLE 212.— EFFECT OF QUANTITY OF MIXING WATER ON STRENGTH 



OF CONCRETE 60 



W/C ratio, U. S. gal. per sack 



of cement (94#) 5.0 



Compressive strength at 28 



days— lb/in. 2 5000.0 



00 Portland Cement Association, Design and control of concrete mixtures, 9th ed., p. 7. 



TABLE 213.— COMPARISON OF STRENGTH AND ELASTIC PROPERTIES 



OF CONCRETE 81 



Modulus of elasticity psi X 10" 



Values given are approximations only since the ratios between the different properties 

 depend on age, aggregates, cement, and other factors. 



61 Stanton, T. E., Amer. Soc. Test. Mat. Bull. No. 131, p. 17, 1944; Witte and Price, ibid., p. 20; 

 Schuman and Tucker, Nat. Bur. Standards Journ. Res., vol. 31, p. 107, 1943; Gonnerman and 

 Shuman, Proc. Amer. Soc. Test. Mat., vol. 28, p. 527, 1928. 



* As determined on specimens with length to diameter ratio of 2. 



TABLE 214.— EFFECT OF ENTRAINED AIR ON COMPRESSIVE STRENGTH 



OF CONCRETE 62 



Percent change in strength due to 5 percent 

 added air * 



Cement , A , 



Sacks per yd 3 7-day 28-day 



4.5 +9 +4 



5.5 —12 —16 



6.5 —17 -20 



62 Walker and Bloem, Journ. Amer. Concrete Inst., vol. 42, p. 629, 1946. 



* Strengths given are for mixes in which full advantage was taken of the sand and water-content 

 reductions made possible by the increased workability resulting from entrained air. 



TABLE 215.— WEIGHTED AVERAGE STRENGTH AND WATER ABSORPTION 

 FOR HARD AND SALMON BRICKS MADE IN U. S. A. 63 



63 McBurney and Lovewell, Proc. Amer. Soc. Test. Mat., vol. 33, p. 1, 1933. 



SMITHSONIAN PHYSICAL TABLES 



