The Study On Adhesion Ability Of Asphalt To Aggregate And Methods To Improving The Water Stability Of Asphalt Mixture

Water damage is one of the main reasons that cause the early damage of highway asphalt pavement. To a large extent, the adhesion of the asphalt and aggregate influences on the water stability of asphalt concrete pavement. It is complicate for most existed theories to calculate each evaluation indicator, it can only qualitatively describe the formation mechanism of adhesion of asphalt and aggregate, so as to say it lacks quantitative indicators. For this problem, the article presents the surface energy theory to evaluate the adhesion ability of different asphalt and different aggregate and then verifies the correctness of it by indoor sheer strength experiment. Finally, use surface energy theory to discuss the function of adopting lime slurry treatment to improve the water ability of acidic aggregate-asphalt interface.Measuring the contact angle, Seton method and hanging method are used to determine the surface energy parameters of three kinds of asphalt and three kinds of stone, so that we can calculate the work of adhesion, the work of cohesion, contact angle and the variation of Gibbs free energy index. Under anhydrous condition, the contact angle of hot molten asphalt and stone and the Gibbs free energy which is needed to damage the asphalt-aggregate interface are chosen to be evaluation indicators of adhesion ability. Under hydrous condition, we choose the variation of Gibbs free energy of water damage stage and asphalt’s work of cohesion as evaluation index. It turned out that at the anhydrous first stage, the asphalt and stone system that has maximum work of adhesion possesses best adhesion ability. At the third stage, the lager the absolute value of the variation of Gibbs free energy is, the better adhesion ability the system will have, and the outside world has to do more work to bring out the non-spontaneous process. So it means that it is more difficult to damage the asphalt-aggregate interface. At the hydrous third stage, if the value of variation of Gibbs free energy is positive, the water damage is spontaneous, otherwise, it will be a non-spontaneous process. Then water damage happens more easily if the absolute value of variation of Gibbs free energy is larger when the value of it is negative. What’s more, the work of cohesion of the asphalt is larger the water stability of the system will be better, and the water is more difficult to penetrate the asphalt film to damage the interface. Among three kinds of stone, the limestone which exhibits strongest basicity has best adhesion ability with asphalt. Among three kinds of asphalt, the adhesion ability of SBS modified asphalt and rubber asphalt with aggregate is superior to the matrix asphalt.In this article, the indoor sheer strength experiment is adopted to verify the adhesion ability of asphalt and aggregate interface under anhydrous condition, and the testing result is consistent with the result of theoretical analysis. In the end, use lime slurry to change the performance of acidic aggregate and asphalt system, and analyze its adhesion ability by surface energy theory. The result shows that lime slurry treatment can obviously improve the adhesion ability of acidic aggregate and asphalt, and promote the system’s water stability.