OIL-MIXED PORTLAND CEMENT CONCRETE. 23 
water-cured over the air-cured specimens is as marked in the oil- 
mixed as in the plain specimens. Tests at one year, although not 
here recorded, show that oil-mixed concrete gains as much in stiffness 
with age as the plain concrete does. 
ABSORPTION. 
The resistance of concrete to the penetration of moisture is meas- 
ured by its absorptive qualities. To test the absorption of oil-mixed 
concrete compared with plain concrete, cylindrical specimens 6 inches 
in diameter and 6 inches high were dried to constant weight in an 
oven, after being cured for 15 days in air. They were then immersed 
in water and weighed from time to time. The results of these tests 
are plotted on figure 6. It will be seen that the oil greatly decreases 
the percentage of absorption; the cylinder containing 10 per cent of 
oil absorbed 1.7 per cent of water, based on the dry weight, while the 
cylinder containing no oil absorbed 6.25 per cent. 
PERMEABILITY. 
To investigate permeability, specimens 3 inches in thickness and 6 
inches in diameter were molded with a surrounding ring of 1 : 1 mor- 
tar. Before testing, the top and bottom surfaces were chipped off 
in order to eliminate the waterproofing effect of the rich surface 
layers. Plain 1 : 3 mortar at the age of 28 days under 30 pounds' 
pressure became damp after half an hour. Under 40 pounds' pres- 
sure the leakage amounted to 146 cubic centimeters after 24 hours' 
application. Specimens containing 5 and 10 per cent of oil No. 4923 
remained perfectly tight under 40 pounds' pressure. 
All permeability specimens made of gravel concrete and contain- 
ing admixtures of oil have remained perfectly tight under 40 pounds' 
pressure per square inch. Some of the plain gravel specimens made 
to compare with the oil-mixed specimens leaked, while others re- 
mained tight. Broken-stone concrete made with a very inferior grade 
of crushed gneiss is not perfectly water-tight under pressure at early 
periods. 
Even this inferior grade of concrete, however, tends to become 
much less permeable at later periods. The results of all permeability 
tests seem, however, to indicate that the resistance to water pressure 
is dependent more on the care used in proportioning and mixing the 
specimens than upon the addition of any extraneous waterproofing 
materials. 
BOND TESTS. 
To determine the adhesion of oil-mixed concrete to steel reinforce- 
ment, bond tests were made on specimens mixed in the proportions 
of 1:2:4 and containing various percentages of oil Rods 12 inches 
long were embedded in the center of cylinders 8 inches in diameter 
