Study On The Adhesion Of Asphalt Aggregate Interface Based On Surface Energy Theory

Asphalt concrete pavement is a typical form of highway pavement structure, water damage often occurs in the early completion of the road based on years of observation of the road has been built, and has become one of the main forms of early failure of asphalt pavement.The main underlying causes of the water damage of asphalt concrete pavement is the poor adhesion between asphalt and aggregate or smaller adhesiveness of asphalt itself. At present, many evaluation theories of adhesion between asphalt and aggregate are only suitable for qualitative description and lack of quantitative evaluation index. The quantitative evaluation indexes to evaluate different asphalt and aggregate adhesion under different conditions are put forward based on surface free energy theory in this paper, and the improved indoor water boiling test and asphalt mixture semicircular specimen bending test are utilized to verify its correctness.Firstly, through scanning electron microscope experiment observed the micro structure of SBS modified asphalt, crumb rubber modified asphalt, composite of crumb rubber modified asphalt which suffered intact, short-term aging, long-term aging,freeze-thaw cycles of water solution and salt solution, and by laser microscope test to observe the surface microstructure of limestone, basalt and granite before and after freeze-thaw cycles of salt solution.The test results show that the interface between asphalt and modifier becomes more and more clear after the short-term and long-term aging, the degree of integration between the asphalt and the modifier is gradually reduced, and the combination ability becomes worse; Compared with the SBSM, the influence of freeze-thaw cycles of water solution on CRM and CCRM is relatively small, and after freeze-thaw cycles of salt solution salt crystals appear in three kinds of polymer modified asphalt, and with the increase of freeze-thaw cycles and salt concentration the number of asphalt containing salt crystals gradually increases; After freeze-thaw cycles stone surface shows no obvious change, the structure has not been destroyed, the distribution of salt crystal particles is small or basically can not be seen in the pore, that under freezing and thawing in a relatively short time of salt freezing cycle of stone of the impact is not great, it shows that the influence of freeze-thaw cycles of salt solution on stone is not very large in the case of short freeze-thaw cycle time.Secondly, the contact angles of asphalt before and after aging and freeze-thaw cycleand aggregate were measured by contact angle measuring instrument under different temperature, respectively, the surface free energy parameters of asphalt and aggregate under different conditions were obtained, finally, the evaluation index of the adhesion of asphalt aggregate system is calculated so as to determine the aging, temperature and freeze-thaw cycle on the adhesion properties of the asphalt and aggregate system.Experimental results show that the aging and freeze-thaw cycle can not only reduce the cohesiveness of asphalt itself, and decrease the adhesion between asphalt and aggregate;with decreasing temperature, the cohesiveness of asphalt itself and the adhesion between asphalt and aggregate increase but the anti water damage ability weaken.Finally, the improved indoor water boiling test and the semi-circular specimen bending test were done, the experimental results and the surface free energy theoretical analysis results are completely consistent, and the relationship between the peeling rate and water stability index ER and fracture toughness and adhesion work were established, the correlation coefficients are all above 0.9 that turns out the feasibility of surface free energy theory to evaluate the adhesion between asphalt and aggregate interface.