Mechanistic study of the effect of aggregate surface wettability on mortar performance and interfacial strength

Aggregates account for approximately 65-75 % of the concrete volume, significantly influencing its performance. However, the effect of aggregate surface wettability on concrete performance is frequently neglected. In this study, 12 types of aggregates were prepared with surface contact angles ranging from 34.0 degrees to 77.9 degrees, using a silane coupling agent (SCA) to modify quartz sand. The effects of contact angle on the fluidity and mechanical performance of mortar, as well as the performance of the interface transition zone (ITZ), were investigated. Further analysis explored the mechanism by which the contact angle affects mortar performance. The results showed that the optimal performance of mortar was achieved at a contact angle of 60.8 degrees, resulting in flexural and compressive strengths of 8.8 MPa and 59.1 MPa, respectively-representing increases of 9 % and 19.5 % compared to unmodified aggregates. Additionally, microscopic tests confirmed that the mechanical performance of the ITZ improved by 53.2 %, while its porosity decreased by 19.2 %, leading to enhanced interfacial bonding performance. However, when the contact angle exceeds 60.8 degrees, the mortar performance gradually decreases. Based on these findings, this study proposed a mechanism for the influence of aggregate surface contact angle on mortar performance, providing a new way to improve the quality of cement concrete and offering important theoretical significance and practical value.