| Moisture damage is one of the main types of failures for pavements. Currently, the surface free energy theory has been applied to study the moisture damage of asphalt-aggregate system, and some achievements have been made. However, this theory is only employed to evaluate the moisture damage of asphalt-aggregate in current researches, while there is no systemic work on correlation between the surface free energy of asphalts and their chemical compositions. Meanwhile, the behavior of moisture diffusion in asphalts and the diffusion mechanism have not been studied systematically, either. In this work, surface free energy of asphalt was determined firstly. Then 23 SHRP (Strategic Highway Research Program) asphalts were chosen to study the relationship between their surface free energies and their chemical compositions. The influence of short-term and long-term aging, and addition of polyphosphoric acid (PPA), Sasobit? wax, as well as anti-strip agents on surface free energies of these asphalts were investigated. Surface free energy of aggregate was also determined via the same way for determining the surface free energy of asphalt, through which the work of adhesion between asphalt and aggregate was studied. The process of moisture diffusion in asphalt was investigated by electrochemical impedance spectroscopy (EIS) and the diffusion mechanism was discussed preliminarily based on infrared analysis results.On the basis of Owens-Wendt theory, the dispersion and polar parts in surface free energy of asphalt were determined respectively by measuring contact angles between different probe liquids of various polarities and asphalt via sessile drop method. Then the total surface free energy of asphalt can be obtained. The sessile drop method is simple and easy to operate compared to other methods. The dispersion part is dominant in the total surface free energy, which is in accordance with asphalt composition primarily of nonpolar organic hydrocarbons.The relation between chemical compositions and surface free energies of asphalts were analyzed by a single regression analysis. It is found that saturates, naphthene aromatics and wax content have lower linear correlation coefficients with surface free energy. The general trend is that surface free energy decreases with quantity increase of the three components. Polar aromatics have positive linear correlation with surface free energy, with correlation coefficient of 0.826. The natural logarithms of asphaltenes content have negative correlation with surface free energy, with correlation coefficient of 0.892. The natural logarithms of ratios of polar aromatics over asphaltenes have positive correlation with surface free energy, with correlation coefficient of 0.905. Colloid indexes have positive correlation with surface free energy, with correlation coefficient of 0.800. There are good quadratic equation relations between carbon, nitrogen and sulfur contents with surface free energy of asphalt binder, with correlation coefficient of 0.745, 0.807 and 0.803, respectively. However, there are no significant correlation between hydrogen, oxygen, as well as nickel and vanadium content with surface free energy. Also, the relations between chemical components, elemental content and surface free energy were analyzed by a multiple regression analysis. Results showed that there is an obvious relation between four fractions contents and surface free energy of asphalts. The relation between four fractions, wax content and surface free energy is also significant. However, the relation between elemental contents with surface free energy is insignificant. But there is a very markable relation between four fractions, wax content, elemental content, and surface free energy.The influence of aging on the surface free energy of asphalt is rather complex. The variation of surface free energy after adding PPA is in correlation with the asphaltene content in the original asphalt. After the interaction of low asphaltene asphalt with PPA, its surface free energy increases and then decreases. But for high asphaltene content asphalt, its surface free energy generally keeps decreasing with addition of PPA. The surface free energy of asphalt increases after addition of anti-strip agent. The introduction of Sasobit? wax increases the hydrophobicity, and reduces the surface free energy of asphalt.The electrochemical impedance spectroscopy can be applied to study the process of moisture diffusion in the asphalt. The diffusion process can be described with 2 equivalent electrical circuits. And 2 diffusion stages are distinctive during the process, which are the forming of diffusion channels via the interaction between the water and asphalt, and fast diffusion of water in the asphalt. The former stage develops slowly, which is the control step of the whole diffusion process. The diffusion of water in asphalt depends on various interactions, such as hydrogen bond, orientation force, and induction force, between water molecules and polar functional groups / atoms with high electronegtivity in asphalt. And therefore the micro active centers are formed and further capillary channels for water enrichment and infiltration are constructed. Larger quantity of polar groups and existence of heteroatom including oxygen and nitrogen deteriorate the ability of water resistance of asphalt.
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