Use of Surface Free Energy Method to Evaluate Effect of Hydrate Lime on Moisture Damage in Hot-Mix Asphalt

Abstract

One of the convenient approaches to decreasing moisture sensitivity in hot-mix asphalt (HMA) is coating the aggregate surface with a suitable agent. Hydrate lime (HL) is the most common antistrip additive used to treat aggregate properties in hot-mix asphalt. In this study, the effect of HL-treated aggregate on moisture sensitivity of HMA was evaluated by applying thermodynamic concepts and surface free energy (SFE) method. The SFE components of aggregates and asphalt binders were evaluated by using a universal sorption device (USD) and dynamic Wilhelmy plate method (DWPM), respectively. The results showed that the use of HL reduced the acid SFE and increased the base SFE of the two types of aggregates used in this study. These changes promote adhesion between asphalt binder and aggregate with and without water, particularly in the mixtures containing acidic aggregates prone to moisture damage. Covering the aggregate with HL decreased the total SFE of aggregate, leading to the increase in wetability of asphalt binder over the aggregate. Moreover, HL decreased the difference between surface free energies of asphalt-aggregate and water-aggregate, decreasing the detachment tendency of asphalt binder over the aggregates. Finally, the treatment of aggregate surface with HL reduced the difference between the free energy of adhesion of aggregate-asphalt binder in dry and wet conditions, decreasing the rate of moisture damage.