Bond behaviour of reinforced concrete exposed to lagoon water under aggressive saline conditions

Abstract

The strength, durability, and serviceability of reinforced concrete structures are largely governed by the bond between concrete and reinforcing steel. This study employed pull-out testing, mass variation analysis, scanning electron microscopy, and general linear modelling (GLM) to investigate the influence of aggressive saline exposure on bond performance. C30 and C40 concrete specimens were exposed to freshwater and lagoon water for 28, 90, 220, and 365 days to simulate long-term deterioration. A GLM with log-transformed age was used to evaluate the effects of age, exposure condition, and concrete grade while accounting for nonlinear behaviour. The results indicated that bond strength increased with age and was significantly influenced by concrete grades. Nevertheless, experimental data revealed a 36.70% reduction in peak bond strength for C40 specimens after 365 days of saline exposure, although the GLM indicated no statistically significant overall effect of exposure condition (p > 0.05). These findings suggest that chloride ingress and associated interfacial deterioration occurring during prolonged exposure may be masked by early-age hydration effects. The slip distance of the reinforcing bar relative to the surrounding concrete was consistently greater in saline environments and increased with exposure duration, indicating progressive degradation of the steel–concrete interface. When evaluating early-stage durability degradation in saline conditions, slip distance proved more sensitive than peak bond strength. The findings demonstrate that deformation-based indicators provide earlier evidence of bond deterioration than ultimate bond strength and may improve durability assessment of reinforced concrete structures exposed to aggressive saline environments.