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The surface free energy is an important parameter that can be used to estimate the adhesion work of asphalt binder and aggregates system. Based on the theory of surface physical chemistry, the surface free energy of the base asphalt and asphalt modified by natural asphalt is determined by measuring contact angles with the sessile drop method. The adhesion grade of asphalt and aggregate is obtained by the boiled water method. The method of calculating adhesion work is studied first. Then, the adhesion work of asphalt aggregate systems and asphalt aggregate water systems are determined, respectively. Test results show that by increasing the additive of natural asphalt, the adhesion work of natural asphalt modifier asphalt and aggregate elevates distinctly, and the adhesion work of the modified asphalt, aggregate and water system decreases. There is a good relation between the adhesion grade and the adhesion work of dry and the adhesion work in the presence of water. The additive of natural asphalt improves the moisture damage resistance. [ABSTRACT FROM AUTHOR]