Experimental Investigation of Rate-Dependent Hardening-Softening Behavior of Hot Mix Asphalt in Compression

The characteristic behaviors of hot mix asphalt (HMA) in compression are studied using various repetitive creep and recovery tests. Important characteristic behaviors of HMA, i.e., rate-dependent hardening and softening, are observed from the experimental study. Rate-dependent softening is found to have a significant effect on viscoplastic strain development. The implication of this effect is that the flow number test, which has been developed as a simple performance test to supplement the Superpave volumetric mix design, is not sufficiently comprehensive to evaluate the viscoplastic characteristics of HMA pavement subjected to loadings with various rest periods. The experimental results and mathematical derivations suggest that for a more realistic prediction of the viscoplastic behavior of HMA, a hardening rule, which is capable of describing both rate-dependent hardening and softening, needs to be incorporated into viscoplastic models.