A STUDY OF RHEOLOGICAL PROPERTIES OF LIME TREATED PAVING ASPHALTS AGED AT 60°C IN A PRESSURE AGING VESSEL

Abstract

The oxidation and age-hardening propensities of eight widely varying petroleum asphalts used for paving were studied with and without hydrated lime, and with inert particulate matter in place of lime. The results show that oxidation of sulfides to sulfoxides and benzyl carbon to ketone is affected very little by the presence of lime. However, the addition of lime does inhibit age-hardening in asphalt whereas the inert particulate matter in the same amount and particle size has little effect other than the filler effect exhibited by the lime and the inert particulate. The principal inhibition of age-hardening of asphalt by hydrated time occurs at high pavement temperatures (> 60°C). At low and moderate temperatures (<50°C), age-hardening is very slow and typically not a major problem in pavement. It is speculated elsewhere in detailed aging studies that the high temperature age-hardening of paving asphalts results from formation of multimolecular, three dimensional matrices in asphalt formed among polar molecules. Hydrated lime appears to interfere with this type of matrix formation, probably by chemical reaction with carboxylic and other acids, to reduce the sizes and/or strengths of the matrices. As a practical result, lime reduces the rate of hardening of asphalt hence prolonging the expected lifetime of a roadway.