Effect of Active Filler on the Interfacial Adhesion between Granite Aggregate and Asphalt Mastic: Investigation of the Mechanism

To investigate the characteristics and mechanism of fillers’ influence on the interfacial adhesion properties between asphalt mastic and granite aggregate, four kinds of active fillers were selected to replace limestone mineral powder (LMP) in four proportions. Firstly, composite asphalt mastic (CAM) was prepared, and the adhesion property of the interface between different asphalt mastic and granite aggregate was evaluated based on the surface free energy (SFE). The optimum replacement rates were recommended by immersion Marshall tests and freeze–thaw splitting tests, and the water-temperature durability performance of granite asphalt mixtures under different treatment measures was verified by Hamburg rutting tests. Microproperty tests were carried out to analyze the effect of fillers on interfacial adhesion properties and mechanisms. The results showed that the alkaline minerals in the active fillers increased the Lewis base fraction of the asphalt mastic, which enhanced the SFE of the mastic. The maximum increase of the energy ratio (ER) with calcium carbide slag powder (CCSP) was 17%, and its enhancement of interfacial adhesion performance exceeded that of the other three active fillers. In addition, at the 60% replacement rate, CCSP improved MS0 and freeze-thaw split test strength ratio (TSR) by 9% and 15%, respectively, which exceeded the improvements from using OPC (7% and 14%, respectively). Comprehensive analysis indicated the optimal replacement rates of the four active fillers [steel slag powder (SSP), CCSP, slag powder (SP), and OPC] were 30%, 60%, 15%, and 60%, respectively. The results of microscopic tests revealed that the surface morphology and oxide mineral content of active fillers were more complex than those of LMP, which supported their ability to effectively absorb light oils from the asphalt on the granite aggregate surface and displace low-valent cations on the granite surface, thereby improving the state of the asphalt mastic–granite interface.