Comparative studies of the effect of ultrahigh-performance concrete and normal concrete as repair materials on interfacial bond properties and microstructure

Abstract

This study aims to investigate the effects of repair materials such as ultra high-performance concrete (UHPC) and normal concrete (NC) on the bond performance and microstructure between a concrete substrate and the repair materials. Specifically, C25, C35, and C45 concretes were used as the substrate materials, and their surfaces were treated with high-pressure water. C45 and UHPC were used as the repair materials. Bond properties were evaluated through slant shear tests with various slant angles and splitting tensile strength tests. Cohesion strength and internal friction were obtained via the slant shear test at three angles using the Mohr–Coulomb approach to reflect the differences between different repair materials. In addition, combining the splitting tensile strength and slant shear tests at three angles, bond failure envelopes were obtained using second-order polynomial and bi-linear models, which can reflect the bond behaviour of repair materials more effectively. The results of the study indicate that UHPC combined with concrete substrates exhibit good interfacial bond performances compared with NC repair materials. Compared with NC, the interface transition zone between UHPC and a substrate is denser, stronger, and more uniform, which results in good bond performance. Using second-order polynomial and bi-linear models, the UHPC repair material are more beneficial to the full utilisation of the mechanical properties of the substrate compared with the NC repair materials. Therefore, it is envisaged that the use of UHPC combined with the high-pressure water treatment of a substrate surface will provide an effective repair.