Effects of an Amine Anti-Stripping Agent on Moisture Susceptibility of Sasobit and Aspha-Min Mixes by Surface Free Energy Analysis

Warm mix asphalt (WMA) is a fairly recent technology developed primarily to address issues such as high vapor emissions and high energy costs associated with the traditional hot mix asphalt (HMA) paving. Although the WMA is becoming a popular paving technology through field and laboratory evaluations, many researchers and transportation personnel are concerned about its moisture resistance. The present study analyzes the free energy of adhesion or wetting ability between eight different aggregates and an asphalt binder modified with varying dosages of two warm mix additives, namely Sasobit and Aspha-Min. Sasobit showed a maximum of 20.9 % and an average of 12.8 % increase in the free energy of adhesion in dry condition. The adhesion in the presence of moisture, referred to as free energy of reduction, was also evaluated to understand the moisture susceptibility of the WMA. The lower the free energy of reduction, the lower the asphalt binder’s tendency to de-bond from aggregates in the presence of moisture. A maximum of 20.5 % and an average of 13.2 % decrease in the free energy of reduction were observed for asphalt binder with 3 % Sasobit. However, Aspha-Min did not exhibit any significant effect on any of the surface properties. One amine-based anti-stripping agent, AD-here HP Plus, is studied to evaluate its effect on adhesion and moisture susceptibility of the WMA. While its performance as an anti-stripping agent was good on the plain asphalt binder, AD-here HP Plus did not improve the adhesion of the selected binder modified with WMA additives either in dry or wet condition. The free energy of adhesion in wet and dry conditions showed either detrimental or no effect with selected aggregates, suggesting a negative or no influence of AD-here HP Plus on the WMA additive-modified binder.