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This paper shows how oven design and procedural variations alter the severity of oven heat tests for paving asphalts and thus cause disagreement between laboratories. The tests studied are the ASTM Method D 62 and the thin film oven test.
The paper shows that the reproducibility of the tests can be improved by standardizing such oven design factors as the levelness of the rotating shelves and the rate of air circulation and air transfer in the ovens. Better standardization of procedures also improves reproducibility. The placement of the oven thermometer, the sample size, and the manner of oven operation are shown to affect the severity of the tests. A well-defined procedure for insuring sample uniformity and avoiding penetration changes, except in the actual oven test, may be expected to improve the repeatability of the tests and also the agreement between laboratories. The procedure for obtaining the penetration of test residues can also be profitably standardized.
The thin film oven test is shown to be a more sensitive measure of the changes in weight and penetration occurring in the ovens than is the ASTM Method D 6 for paving asphalts.
Research Chemist, California Research Corp., Richmond, Calif.