The mechanical properties of the interface between concrete–epoxy mortar: Splitting tensile vs. direct shear testing

Abstract

This study investigated the effects of low-temperature curing environment, moisture content of concrete, and surface roughness of concrete on the interfacial bond performance of concrete–epoxy mortar composite specimens. The mechanical and microstructural properties of concrete–epoxy mortar composite specimens were studied systematically via splitting tensile strength test, direct shear strength test, and scanning electron microscopy test, and the failure modes were observed. Further, the factors that remarkably affect the mechanical properties of the concrete–epoxy mortar composite specimen were investigated by analysing the images obtained using grey correlation analysis. The results indicated that the compressive strength of epoxy mortar, interfacial splitting tensile strength, and shear strength of composite specimens decreased gradually with the decrease in curing temperature. The splitting tensile strength and shear strength at the interface of the composite specimens first increased and then decreased with increasing surface roughness of the concrete. However, these parameters gradually decreased with the increase in moisture content. Moreover, based on the results of grey correlation analysis the three factors, the curing temperature had the most influence on these two strengths, followed by surface roughness and then moisture content. In this case, the surface roughness and moisture content have a comparable degree of influence. The relationship between shear strength and splitting tensile strength was investigated and a good linear relationship was found between these two parameters. The microstructure performance analysis show that as the curing temperature decreased, pores appeared around the foundation concrete. Consequently, the aggregate structure became loose, and the overall denseness was remarkably reduced. As the moisture content of the concrete increased, the pores and cracks at the interface increased, and the width of the interface transition zone became larger.