Use of Cyclic Direct Tension Tests and Digital Imaging Analysis to Evaluate Moisture Susceptibility of Warm-Mix Asphalt Concrete

This paper presents a simplified viscoelastic continuum damage material model for the evaluation of moisture susceptibility of asphalt concrete. The model is based on cyclic direct tension testing and layered viscoelastic analysis. The visual stripping inspection afforded by digital imaging analysis is also proposed as an intuitive and straightforward method for moisture susceptibility evaluation. These methods were applied to a Superpave^® 19-mm hot-mix asphalt mixture and corresponding warm-mix asphalt mixtures modified by a polyethylene wax-type additive with and without an antistripping agent. The fatigue life predicted by the simplified viscoelastic continuum damage and layered viscoelastic analysis models had a strong correlation with the percentage of stripping determined from specimen surfaces that were fractured during cyclic direct tension testing of the hot-mix and warm-mix asphalt mixtures with various asphalt contents. In addition, a polyethylene wax-type additive combined with an antistripping agent was found to provide a longer fatigue life and less stripping than a pure polyethylene wax-type additive. The findings from this paper should provide guidance to agencies and material engineers in developing asphalt binder modifiers that lengthen the fatigue life of pavements and reduce moisture susceptibility.