22 
BULLETIX 230, V. S. DEPABTMEXT OF AGRICULTURE. 
speciraen 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 
Xo. 4923. 
Air- 
Water- 
Air- 
Water- 
cured. 
cured. 
cured. 
cured. 

IS 
15 
15 
21 
2| 
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 Y. 
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 
Xo. 4923. 
1:3: 5 concrete. 
1:3: 6 concrete. 
Air-cured. 
Water-cured. 
Air-cured. 
Water-cured. 

2| 
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 
850,000 
1,150,000 
730,000 
2,200,000 
2,400,000 
1,900,000 
1,900,000 
2,050,000 
The above results show that oil has little effect on the stiffness of 
concrete. The increased value of the modulus of elasticity of the 
