Estimating Moisture Resistance of asphalt mixture containing epoxy resin using Surface Free Energy Method and Modified Lottman test

Abstract

ABSTRACT Using modified bitumen has been one of the few reliable methods adopted for improving asphalt performance against moisture sensitivity. This research offers an approach in which both mechanical methods and micro-mechanism investigations have been employed to study the effect of bitumen modified with epoxy resin on the moisture sensitivity of asphalt mixtures. Six bitumen samples: base bitumen and bitumen modified with 1% to 5% epoxy resins, and two types of aggregates (limestone and siliceous) were selected for this study. Surface Free Energy method and Modified Lottman test were used to investigate the moisture sensitivity of asphalt mixtures containing each bitumen-aggregates combination. In the first method, surface free energy values of bitumen and aggregates were estimated and then used in predicting energy parameters related to the moisture sensitivity parameters, using which the changes in adhesion and wetting properties of each bitumen-aggregates mixture were analyzed. In the second method, the indirect tensile strength test was performed on dry and wet asphalt samples, and the tensile strength ratios were obtained for each asphalt mixture, through which the moisture resistance of samples were investigated. Based on the values obtained for the three parameters, it was concluded that epoxy resin addition decreased the moisture sensitivity of asphalt mixtures containing siliceous aggregates by increasing the bitumen and aggregates adhesion as well as increasing the wetting of the aggregates surface with bitumen. Also, in asphalt mixtures containing limestone aggregates, epoxy resin improved moisture sensitivity, but this improvement was only due to increased adhesion between bitumen and aggregates, while the impact of bitumen coating on aggregates surface did not change significantly with the addition of epoxy resin. Among the asphalt mixtures studied, the highest moisture resistance was observed in asphalt mixture containing 4% epoxy resin, at which the Tensile Strength Ratio parameter showed an increase of 11.3% and 21.5% for limestone and siliceous mixtures, respectively, compared to the base asphalt mixture.