Behavior and modeling of cover failure caused by corroded rebars

Abstract

Reinforced concrete (RC) is the most prevalently used construction material worldwide. Corrosion-caused cover failure, including cracking, spalling and delamination, not only cause water leakage and aesthetic problems, but also reduce the strength of concrete covers, accelerate the deterioration process and degrade the bonding strength between steel and concrete. Extensive studies with concrete cover specimens have been conducting to study the corrosion-caused cover cracking. However, those research results cannot be directly used to explain three typical failure behavior of cover spalling, cover delamination and corner cracking as the mechanism and process of concrete cover specimens are different from those of three typical failure modes. Therefore, in the thesis, the three typical failure behaviors of corrosion-caused cover deterioration are investigated. To study the corrosion-caused cover spalling, the mechanism and process of failure in cover and core specimens are experimentally investigated by using accelerated corrosion tests together with the digital image correlation (DIC). The phenomenon of the rotation of the cover is first observed. The direction of the crack propagation, crack opening displacement (COD) profiles and concrete expansion at the steel/concrete interface are measured. Furthermore, a novel elastic-body-rotation model is proposed to analyze the behavior of cover spalling caused by the non-uniform corrosion of rebars. The volume of rust can be predicted by using the proposed model with the crack mouth opening displacement (CMOD) and/or the bulging of the concrete surface. The proposed model is validated by comparing the analytical results with the experimental results. Moreover, the numerical results obtained from a nonlinear finite element (FE) analysis are used to verified the analytical results. To study the failure of cover delamination, the behavior of cracking in cover delamination specimens is experimentally investigated by using accelerated corrosion tests together with DIC. The phenomenon of uplifting movement of the cover is first observed. Furthermore, a novel analytical model for cover delamination, which considers the interaction between the neighboring corroded rebars, non-uniform distribution of rust and boundary conditions of the concrete surface, is proposed. This proposed model enables manual prediction of the bulging deformation of the cover surface and the maximum thickness of rust. This model is validated by comparing the analytical results with the experimental results, and verified with numerically derived results from a nonlinear FE analysis. To study the corner cracking, the behavior of cracking in corner cracking specimens is experimentally investigated by using accelerated corrosion tests together with DIC. The deformation caused by the rotation of corner cover is first proposed. The corrosion-caused cover failure mode, bulging of the cover surface,displacement at the steel/concrete interface and COD profiles are recorded. A novel analytical model, which considers both the non-uniform distribution of rust and the boundary conditions of cover surface, was proposed. This nondestructive evaluation method is capable of obtaining the volume of corroded steel by measuring the bulging of the cover surface and/or CMOD. This model is validated by comparing the analytical results with the experimental results, and verified by comparing the analytical and the numerical results.