A simple direct current model for residual bond strength assessment of embedded rebars in thermally damaged concrete

Fire events are highly fatal to human lives and properties, and should be considered at structural design phases. Concrete structures are essentially fire resistant up to certain level, beyond that structural components would degrade away from their design values. Residual capacities of fire exposed structures should be properly assessed before strengthening tasks can be carried out. Among those, the residual bond strengths between reinforcing bars and concrete are of particular importance because they determine the mechanical performance of all reinforced concrete components. This study focused on proposing novel nondestructive approaches to assess the residual bond strengths after thermal exposures. Specifically, a simple direct current (DC) model was implemented to yield electrical resistivity indices that can closely reflect the bond strength degradations up to 400 ℃. DC polarization measurements were split into three phases through which each index induced the degradations differently. Capability and efficiency of the DC indices to assess residual bond strengths of thermally damaged concrete were analyzed and discussed. Results presented have suggested that the proposed DC approach performed better than using residual compressive strengths to assess residual bond strengths, and was more advantageous for its nondestructive features.