Assessment of residual bonding performance for bimetallic steel bar-seawater concrete after exposure to high temperature

The bimetallic steel bar (BSB) is a new type of corrosion-resistant reinforcement material composed of carbon steel and stainless steel, which can effectively improve the durability of structures. Reinforced concrete structural strength depends on the bond between steel bars and concrete. This mechanism can be compromised after exposure to a fire, but it has been less considered in research, and is not addressed in concrete design codes. To evaluate the residual bearing capacity of BSB reinforced concrete structures after a fire, it is necessary to clarify the bonding performance between BSBs and concrete after exposure to high temperatures. In this study, 45 BSB-seawater concrete (BSBSC) pull-out specimens were prepared, and the bonding performance of BSBSC after high temperature was studied by heating treatment and pull-out tests. The results showed that the BSBSCs changed from bluish-gray to grayish-yellow with the increase in heat treatment temperature. After exposure to 400 °C, cracks appeared on the surface of BSBSCs. As the heat treatment temperature increased, the slope of the rising and descending stages for the bond stress-strain curve decreased gradually. In addition, as the thickness of the concrete cover increased, the bonding strength of BSBSCs also improved. The higher the heat treatment temperature, the less significant the improvement effect. Based on test results, a predictive model for the bonding performance characteristics of BSBSCs after high temperature was proposed, and a constitutive model for bonding stress-slip relationship was established.