The bond properties between ultra-high-performance concrete and normal strength concrete substrate: Bond macro-performance and overlay transition zone microstructure

This study investigates the bond performance between ultra-high-performance concrete (UHPC) and normal strength concrete (NSC) substrate. A hoop constraint method is designed to assess the shrinkage effect of repair materials on bond macro-performance. The bond strength and permeability of the same specimen are determined using the hoop constraint method. Additionally, the properties of repair materials, such as drying shrinkage, thermal gravity analysis, and mercury intrusion porosimetry, were investigated. The overlay transition zone (OTZ) microstructure is analysed to reveal the bonding mechanism. The results indicate that the hoop constraint method effectively reflects the ability of UHPC to overcome the significant autogenous shrinkage effect and achieve good bond macro-performance. Moreover, the UHPC-combined substrate exhibits better bond strength than that of the NSC because the repair interface of the UHPC is more compact than that of the NSC. Furthermore, the OTZ width of the UHPC-combined substrate is narrower than that of the NSC, and in the OTZ, the modulus of the UHPC is higher than that of the NSC.

Automated summary

This study investigates the bond performance between ultra-high-performance concrete (UHPC) and normal strength concrete (NSC) substrate. A hoop constraint method is designed to assess the shrinkage effect of repair materials on bond macro-performance. The results indicate that the hoop constraint method effectively reflects the ability of UHPC to overcome significant shrinkage and achieve good bond performance. Moreover, the UHPC-combined substrate exhibits better bond strength and a more compact repair interface than NSC.