Sensitivity analysis of parameters to corrosion-free life for steel embedment in concrete structures under chloride-bearing environments

Abstract

Research in the corrosion of reinforced concrete has been thoroughly investigated from the last decades and now. Especially, it is more important to evaluate the durability of the structure and to estimate the service-life of the RC structures, because it is difficult to repair/rehabilitation due to the various exposure influences: temperature, humidity, cement type, w/c, environmental conditions. Therefore, in this study, the parameters affecting the life expectancy of reinforced concrete structures (Diffusion coefficient, Surface chloride concentration, Chloride threshold level, Cover depth), and provide a basis for selective options for user in the actual life prediction design. In this study, binder types (OPC, 60% GGBS, 30% PFA, 10% SF) were used to determine the four parameters (D, Cs, Cth, Depth). The corrosion inhibiting ability was evaluated through experiments. Using the derived results, applying to the Fick’s 2nd law to predict the life and evaluate the influence factors. Chloride binding capacity indicated little difference between the four binders in the initial 28 days, but after 150 days, OPC> 30% PFA> 60% GGBS >> 10% SF. It is considered that the pore structure of each material affects the chlorine ion binding ability. Pozzolan material (GGBS, PFA, SF) concretes have more gel pores than OPC, 10% SF> 60% GGBS> 30% PFA> OPC. In addition, a half-cell potential measurement method and a polarization resistance measurement method for determining corrosion initiation were carried out. As a result, the corrosion initiation time and corrosion rate of each experimental method were OPC> 60% GGBS> 30% PFA> 10% SF and the critical chloride ion concentration was OPC, 60% GGBS, 30% PFA, 1.02-1.58%, 0.51-1.20%, 0.53-1.02%, 0.49-1.01%. The calculated service-life of OPC, 60% GGBS, 30% PFA, and 10% SF concrete were 30, 79, 65, and 86 years, respectively. However, the sensitivity of chloride diffusion coefficient and cover depth was the same regardless of the type of binder. And the effect of lifetime was changed by surface chloride concentration and chloride threshold level. Among them, OPC was disadvantageous at the initial lifetime due to the chloride threshold level, but OPC was the most influential in the long term, and the lifetime was relatively longer than that of the pozzolanic materials. Therefore, it is important to select concrete materials according to the exposure environment and concrete structures. The durability of the structures can be evaluated according to the material properties. It is expected that the durability of the structure can be accurately assessed according to its material properties, and the basis was established through sensitivity analysis.