Bending Beam Rheological Evaluation of Wax Modified Asphalt Binders

Abstract

A simple Bending Beam Rheometer (BBR) test to determine binder low temperature properties from asphalt mixtures was recently developed by the University of Minnesota. The mixture BBR test was performed concurrent with binder BBR testing to evaluate the effect wax addition has on stiffness/physical hardening and potential for low temperature cracking in asphalt mixtures. Asphalt mixture and binder BBR tests were performed at low temperatures typical of binder grading, after equivalent low temperature conditioning in air for incremental extended periods up to 32 days. Results from temperature saturation are compared to conditioning corresponding to normal 20 hours of PAV aging and testing in accordance with parameters specified in AASHTO M320. Data produced by the BBR suggests that at temperatures close to or below the glass transition temperature mixture beams became less stiff with time when held at a constant temperature. This effect appears to be reversible if a heating/annealing cycle is applied to the beams. This paper reports further investigation of the observed phenomenon and the potential that observations may be indicative of low temperature micro-cracking and subsequent healing in asphalt mixture.