Quantitative Analysis Investigation of the Water Stability of Asphalt Mixtures with Crushed Gravel Based on the Theory of Surface Free Energy

To quantitatively analyze and study the water stability of crushed gravel asphalt mixture by using surface energy theory, the surface energy parameters of crushed gravel samples at 20℃ are tested by using the gas sorption method, and the surface energy parameters of four anti-stripping agent asphalts with different dosages (0%, 0.2%, 0.4%, 0.6%) at 20℃ are tested by using the Wilhelmy plate method. Then, the binding energy of crushed gravel and anti-stripping agent asphalts with different dosages and the surface energy evaluation index of water stability are calculated. On this basis, quantitative analysis and sequencing of water stability of crushed gravel asphalt mixture were carried out. The microscopic mechanism of the anti-stripping agent's improvement on adhesion between crushed gravel and asphalt was analyzed from the angle of surface energy. Marshall test (immersion Marshall test, vacuum saturation Marshall test, freeze-thaw splitting test) with anti-stripping agent contents of 0%, 0.2%, 0.4%, and 0.6% was conducted through strict control of crushed gravel material, gradation, and oil-stone ratio. Results show that (1) the surface energy parameters of crushed gravel are dominated by polar alkali component; (2) the addition of anti-stripping agent will reduce the surface energy of asphalt, thus increasing the wettability of asphalt to aggregate; (3) the improvement of the adhesion between crushed gravel and asphalt by adding anti-stripping agent is mainly reflected in two aspects: reducing the cohesive energy of asphalt itself to increase its wettability to aggregate and increasing the surface energy acid component of asphalt to increase its adhesion binding energy to aggregate; and (4) the order of microscopic surface energy evaluation index of water stability of crushed gravel asphalt mixture is the same as that of macroscopic performance test index, thus demonstrating the accuracy of the surface energy system for quantitative analysis of the water stability of the crushed gravel asphalt mixture.