Surface free energy method for evaluating the effects of anti-stripping agents on the moisture damage to asphalt mixtures

Abstract

The moisture stability of an asphalt mixture was enhanced with cement, hydrated lime, and an anti-stripping agent (called AMR II) to improve the adhesive bond of asphalt with the aggregate. A total of eight asphalt binders and three aggregates (crushed gravel, limestone, and granite) were used for the preparation of different asphalt mixtures. Indirect tensile strength and residual stability tests were carried out to determine the moisture stability. The surface free energy (SFE) of the asphalt binder and aggregates were measured using the sessile drop method and universal sorption device method, respectively. Based on the SFE method, the cohesive, adhesive, and stripping energies of the asphalt and asphalt mixtures were studied. Moreover, the SFE parameters were introduced while analyzing the correlation of the cohesive, adhesive, and stripping energies of the asphalt with the moisture stability. The results show that the incorporation of a single or compound anti-stripping agent can improve the moisture stability of the asphalt mixture, and the improvement effect of compound agents is greater. Furthermore, the SFE components improved after the addition of the anti-stripping agent. The addition of the anti-stripping agent influenced the cohesive and adhesive energy remarkably, whereas the aggregate type, especially its silica content and specific surface area, has a significant effect on the adhesive and stripping energy of the asphalt mixture. A linear regression analysis suggested that the SFE parameters have a good correlation with the moisture damage properties. The SFE parameters can be used to determine the moisture damage performance, and the SFE method can be used to verify the moisture stability of asphalt mixtures.