Evaluation Method of Resistance to Water Damage for Foamed Warm-Mixed Asphalt Mixture Based on Surface Free Energy Theory

Weak adhesion between asphalt and aggregates is the main cause of moisture-induced damage for asphalt pavement, especially for foamed warm-mixed asphalt pavement, because of low mix temperatures and residual moisture left behind by the microscopic foaming process. In order to improve the road performance of foamed warm-mixed asphalt mixture, the law of moisture evaporation of foamed asphalt was discussed through laboratory foaming test in this article. The surface free energy of foamed asphalt in different foaming stages and two kinds of aggregates were obtained by measuring contact angle via the sessile drop method. The work of cohesion and adhesion between asphalt and aggregates and the work of stripping were calculated through using their surface free energy parameters. On this basis, the energy ratio (ER) is proposed as an indicator to evaluate the anti-water damage property of foamed warm-mixed asphalt mixture, and the ER is obtained by calculating the ratio of work of adhesion and the work of stripping. This method can be used as the reference for the evaluation of asphalt adhesion. The results may show that the resistance to moisture-induced damage of asphalt is improved after foaming process.