Bond Strength and Interfacial Transition Zone between Aggregate and Cement Paste: Effect of Aggregate Type

Abstract A comprehensive understanding of the bond strength and bonding mechanism within the aggregate–cement interfacial transition zone (ITZ) is fundamental to achieving durable and high-performance concrete repairs. This study simplifies the intricate bonding interface between concrete substrates and repair materials and systematically investigates the effect of aggregate types including granite and limestone on bond strength and ITZ microstructure of aggregate–cement samples. A distinctive multiscale method was employed to characterize the ITZ, allowing precise analysis of microstructural features and mechanical properties. Experimental results show that granite–cement interfaces exhibit higher bond strength than limestone–cement interfaces. Compared with limestone, the granite–cement ITZ was denser, contains fewer unreacted cement particles, and no new chemical products are found in the ITZ of either sample. Additionally, the ITZ width of the granite–cement sample is 33.3% narrower, and the modulus is 43.0% higher than that of limestone–cement sample. These findings highlight the role of aggregate type in ITZ performance and demonstrate the effectiveness of a controlled, multiscale method in elucidating the bonding mechanism of concrete interfaces.