Effect of Corrosion on the Behavior of Reinforced Concrete Beams Subject to Blast Loading

Abstract

Corrosion of reinforcing steel embedded in concrete due to the presence of moisture, aggressive chemicals, inadequate cover, and other factors can lead to deterioration that substantially reduces the strength and serviceability of the affected structure. Accounting for corrosion degradation is critical for evaluation and assessment of the load carrying capacity of existing reinforced concrete (RC) structures. However, little is known about the relationship between high strain rate blast loading and the degradation effects that govern corrosion damaged structures such as concrete cover cracking, reduction in reinforcement areas, and deterioration of bond between concrete and steel. Ten identical RC beams were constructed and tested, half under blast loading conditions produced using the Virginia Tech Shock Tube Research Facility and the other half under quasi-static loading. The blast tests were conducted to investigate how increasing blast pressure and impulse affect the global displacement response and damage modes of beams subjected to blast loads. The quasi-static tests were performed to establish fundamental data on the load-deflection characteristics of corroded RC beams. One beam from each testing group served as a control specimen and was not corroded while the remaining beams were subjected to varying levels of corrosion (5%, 10%, 15%, and 20%) of the longitudinal reinforcement along the midspan region. The specimens were corroded using an accelerated corrosion technique in a tank of 3% sodium chloride solution and a constant electrical current, creating a controlled environment for varying levels of corrosion. An analytical model was also created using a single degree of freedom (SDOF) approach which predicted the performance of corroded RC beams under blast loading. The results of the quasi-static tests revealed that as corrosion levels increased, the load to cause yielding decreased, the yield displacements decreased, and failure occurred earlier for all specimens. This was accompanied by increased damage to the concrete cover and the addition of longitudinal corrosion induced cracking. For the blast loaded specimens, the results demonstrated that the maximum displacements and residual displacements increased beyond the expected response limits for corrosion levels greater than 5%, but at corrosion levels less than 5% there was no significant change in displacements. Damage levels increased by one or more categories with the introduction of even small levels of corrosion of less than 5%. At corrosion levels greater than 5%, before loading was applied, the specimens exhibited moderate damage due to the introduction of corrosion induced cracking. After loading, the specimens sustained hazardous damage at progressively lower blast volumes. The failure mode changed from ductile to sudden and brittle failure at corrosion levels greater than 5% but remained ductile with flexural failures at low corrosion levels below 5%. The experimental results could be predicted with a high level of accuracy using the SDOF approach, provided that the degraded strength of corroded concrete cover, degraded mechanical properties of corroded steel, length of the corroded region, and determination of either uniform or pitting corrosion are accounted for. Overall, the introduction of corrosion to an RC beam subjected to blast loading resulted in decreased strength and ductility across all specimens but with most disastrous effects occurring at corrosion levels of 5% or greater. A recommendation is made to adjust the response limits in ASCE/SEI 59 to account for corrosion in RC beams.