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Prolonged weathering tests on asphalts disclose marked differences in surface behavior, cracking pattern and crack-healing tendencies, as between self-healing and non-self-healing asphalts; also as between asphalts of those two classes from different specific geographical sources. These performance differences between asphalts from different specific sources are in general borne out by corresponding differences revealed by Weather-Ometer tests and by a number of other tests that have been suggested by various investigators during the last few decades. It is now revealed that they are also being borne out by the relative homogeneity of the internal structure of the asphalts as disclosed by the 30-year-old spot test. However, it is shown that while quality-probing tests of the type here discussed may, each in its particular way, throw valuable light on one or more of the many different functional properties that happen to be vital to the proper performance of an asphalt for its particular purposes, they may each be insensitive to other equally vital properties. Until, therefore, some test or combination of tests of this type has proved itself capable of adequately measuring all those vital functional properties, only longtime actual service tests, or longtime weathering tests accurately simulating the latter, remain the most reliable criteria of true durability.
Oliensis, G L
Director of Research, Lloyd A. Fry Roofing Co., Summit, Ill.