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 



