Author(s):
R.N. Traxler
Publication Date
1961
Abstract
The objectives of this research were to (1) Investigate paving asphalts used by THD to determine how they can be evaluated for quality; (2) Establish specifications to assure use of superior asphalts by the Department, and (3) Determine how the durability of asphalts can be improved.|Experimental: Increase in absolute viscosity, determined by the microfilm apparatus, was used to evaluate the effect of heating asphalts at various temperatures and different times. Fifteen micron films were used because 15 microns seems to be within the range of average thickness of the asphalt in paving mixtures. Most of the work wee done in an atmosphere of air, but measurements were also made in nitrogen at 225°F to determine the effect of volatility without oxidation. Component analyses and asphaltene content were obtained on 25 asphalts.|Conclusions: A modified Shell Film Test was found to be more satisfactory than the Bureau of Public Roads Film Test. Data obtained by heating 15 micron films of asphalts in air at 275 to 350°F for times ranging from 15 to 60 minutes are useful for calculating the hardening of a particular asphalt for many of the temperature-time combinations that may be encountered in the preparation and laying of hot paving asphalts. Most asphalts show less hardening by volatilization than by oxidation. Causes for hardening of asphalts in decreasing order of importance are oxidation, volatilization, polymerization induced by actinic light (sunlight) and condensation polymerization (caused by relatively high temperatures). Less stable asphalts may show a decrease in viscosity when subjected to elevated temperatures for several hours. This is caused by depolymerization or thermal cracking.|Component analyses together with the asphaltene content of an asphalt can be used to calculate a Dispersion Coefficient which, in moat cases, predicts the resistance of the asphalt to hardening.
Report Number:
9-1
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