22 



BULLETIN" 230, U. S. DEPARTMENT OP AGRICULTURE. 



specimen is spherical in shape, with a radius of 3 centimeters. Speci- 

 mens 6 inches in diameter and 6 inches high were tested after first 

 bedding them in plaster of Paris before mounting on the anvil of the 

 machine. The following results show that the toughness of concrete 

 is very little influenced by the addition of a small amount of oil to 

 the mixture: 



Table 9. — Number of blows required to produce failure. 





1:3:5 concrete. 



1:3:6 concrete. 



Per cent 

 of oil 

















No. 4923. 



Air- 



Water- 



Air- 



Water- 





cured. 



cured. 



cured. 



cured. 







18 



15 



15 



21 



2J 



15 



33 



14 



18 



5 



23 



20 



15 



20 



10 



13 



20 



12 



21 



15 



14 



20 



13 



16 



A view of the impact machine with a specimen under test is shown 

 in Plate V. 



STIFFNESS OR MODULUS OF ELASTICITY. 



For testing the effect of oil on the stiffness of concrete, specimens 

 8 inches in diameter and 16 inches high were made. The deforma- 

 tions under various loads were measured with a double micrometer- 

 screw compressometer of the type described by J. M. Porter in the 

 Proceedings of the American Society for Testing Materials, Volume 

 X, 1910. Loads were applied in 2,500 and 5,000 pound increments 

 and were released to 500 pounds after each increment of 5,000 pounds, 

 and deformation readings were taken for permanent set. Typical 

 stress deformation and permanent set curves are shown in figure 5. 

 In all cases the initial modulus of elasticity was obtained from the 

 slope of the stress-strain curve at its origin. A view of a specimen 

 mounted in the testing machine with compressometer attached is 

 shown in Plate VI. 



Table 10. — Initial modulus of elasticity (age 28 days). 



Per cent of 



oil 



No. 4923. 



1:3: 5 concrete. 



1:3:0 concrete. 



Air-cured. 



Water-cured. 



Air-cured. 



Water-cured. 





 2i 

 5 

 10 



15 



1,300,000 

 1,350,000 

 1,250,000 

 1,700,000 

 1,300,000 



2,550,000 

 2,700,000 

 2,350,000 

 3,950,000 

 2,500,000 



1,300,000 



1,000,000 



50,000 



1,150,000 



-,.;iuHin 



2,200,000 

 2,400,000 

 1,900,000 

 1. 900, (ton 

 2,050,000 



The above results show that oil has little effed on the stiffness of 

 concrete. The increased value of the modulus of elasticity of the 



