Experimental investigation of the interfacial bonding properties between polyurethane mortar and concrete under different influencing factors

Abstract

As a repair material, polyurethane mortar has excellent mechanical properties. The aim of this study is to explore the mechanical properties and microstructure of the interface between polyurethane mortar and concrete. The effects of curing temperature (−20 °C, −10 °C, 0 °C, 10 °C, 20 °C), water saturation of concrete (0 %, 30 %, 70 %, 100 %) and roughness (0, 1.5, 3.0, 4.5, 6.0 mm) on the bonding interface strength (shear strength and splitting tensile strength) were investigated through shear and splitting tests. The microstructure of the bonded interface was analysed by scanning electron microscopy at different curing temperatures and water saturation of the concrete, and an interfacial bonding mechanism was proposed. The results of the study show that the strength of the bonded interface increases gradually as the curing temperature rises. At the same curing temperature, the strength of the bonded interface decreases with increasing water saturation of the concrete and is essentially linear. The rate of strength loss of high-water-saturation specimens increases gradually as the temperature rises. When the temperature is positive, the interfacial bond strength increases and then decreases with increasing roughness, and a critical value (4.5 mm) of roughness exists that makes the bond strength reach a maximum. At negative temperatures, the interfacial bond strength increases with increasing roughness. The grey correlation analysis shows that roughness has the greatest influence on the interfacial bonding performance, followed by curing temperature and then water saturation. The interfacial shear strength and splitting tensile strength have a good linear relationship under the influence of all factors. Microscopic tests show that the polyurethane mortar body structure loosens gradually as the curing temperature decreases. As the water saturation of the concrete increases, the interface width between the polyurethane mortar and concrete shows an overall tendency to increase.