Nonlinear relationships between parameters of simplified diffusion-based model for service life design of concrete structures exposed to chlorides

This paper presents an approach toward performance-based durability design of concrete structures based on a simplified diffusion-based model, which overcomes some of the limitations of the current prescriptive rules of existing design standards. Numerical nonlinear relationships and relative sensitivities between the four parameters that govern the time to corrosion initiation of reinforced concrete structures are determined, including chloride diffusion coefficient, chloride threshold value of reinforcement, concrete cover and surface chloride exposure condition. To achieve a specified design life, it is found that in aggressive chloride-laden environments: (i) increasing the minimum concrete cover is more effective than selecting a corrosion-resistant steel; (ii) it is necessary to use both high-performance concrete and corrosion-resistant steel; (iii) a relative decrease in the concrete cover has to be compensated by a much greater increase in the corrosion resistance of steel; and (iv) the variations in chloride diffusion coefficient have a large impact on required concrete cover and chloride threshold value, especially in increasingly aggressive environments. These relationships can be used to identify the most relevant parameters and serve as a guide for service life-based design for durable concrete structures.