Analytical Chloride Diffusion Model for Durability Assessment of Concrete-Lined Tunnels

The presence of chloride ion de-passivates reinforcing steel, thereby accelerating the corrosion of reinforcement and deterioration of reinforced concrete elements. Chloride ion diffusion constitutes the major deleterious factor undermining the durability of concrete-lined tunnels, especially tunnels through aquifers with high salinity. Hence, the service life prediction of concrete-lined tunnels should reliably take into account the chloride diffusivity in the concrete lining. Conventional serviceability design of reinforced concrete considers the exposure conditions in a categorical manner, with corresponding prescribed measures such as cover thickness and strength grade applied to the design. However, as a basis for quantitative assessment of durability, the chloride diffusion is generally dependent on the diffusivity of concrete, chloride ion concentration, environmental condition and the age. This paper devises an analytical chloride diffusion model with explicit formulation, which provides practical reference for adoption by design engineers. The application of the model is illustrated by examples of durability assessment of reinforced concrete tunnel lining.