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The weathering characteristics of coating-grade asphalts cannot be associated with the crude-oil source of the asphalt alone because fluxing stocks, catalysts, fillers, and added materials can affect the weatherability markedly. The results are not general, however, but vary with different asphalts.
A fluxing oil added to the base residuum doubled the weatherability of one asphalt but reduced the life of another asphalt to less than half of the unfluxed asphalt. Similarly, a catalyst doubled the durability of one asphalt system but reduced that of another by one third.
Asphalts responded differently to the addition of polymers. Of the three asphalts tested, the weatherability of one was unaffected, another was improved, and the third was made poorer. The response to the addition of limestone dust stabilizer varied among the several asphalts. The improvement in weatherability ranged from only 20 per cent to as high as 140 per cent. The weatherability of products produced from crude oils obtained from different areas of the same field can also vary. Such differences were observed for asphalts derived from different areas in three different fields. The difference was as large as 100 per cent in one field.
Research Chemist, California Research Corp., Richmond, Calif.
Research Chemist, Asphalt Roofing Industry Bureau, National Bureau of Standards, Washington, D. C.