Bond behaviour between steel fibre and cement mortar exposed to elevated temperature

In order to accurately evaluate the deterioration of the mechanical properties of steel fibre reinforced concrete (SFRC) after exposure to elevated temperature, it is particularly important to study the bonding properties between steel fibre and concrete matrix. In this paper, four types of steel fibre and five types of cement mortars with different strengths were selected to investigate the bond behaviour of the steel fibre-mortar interface after exposure to elevated temperature. The results showed that the compressive strength and flexural strength of each mortar decreased significantly after elevated temperature treatment, and the attenuation degree of flexural strength was greater than that of the compressive strength. In addition, the ultimate pull-out load of specimen with the straight steel fibre gradually decreased with the increase of temperature. However, the ultimate pull-out load of specimen with the end-hooked steel fibre had no significant change between 20degree celsius and 400degree celsius. When the temperature exceeded 400degree celsius, the ultimate pull-out load gradually decreased with the increase of elevated temperature. Subsequently, the damage mechanism of the interface between steel fibre and mortar matrix under condition of elevated temperature was analyzed by testing the interfacial microstructure and phase change of cement paste. Finally, the calculation formula of the ultimate bond strength and temperature was established.