Service Life Prediction based on Stochastic Approach for Cracked Concrete Structures exposed to Chloride attack

Cracks in early-age due to hydration heat and drying shrinkage may occur unavoidably. These can be the main routes for deteriorating agents and also can be one of the major reasons of steel corrosion in concrete structures exposed to chloride attack. Generally, deterministic method using Fick's 2nd Law is utilized for durability design, however, stochastic method is recently attempted for consideration of variable characteristics in material and construction. In this study, apparent diffusion coefficients in sound and cracked concrete structures, exposed to chloride attack with 8 and 11 years used, are derived through field investigation and service life is predicted by utilizing Monte Carlo Simulation (MCS) and Fick's 2nd law, respectively. For the purpose, random variables such as critical chloride amount, cover depth, and time-dependent diffusion coefficient are established and probability of durability failure is calculated using the derived diffusion in cracked concrete. Utilizing MCS in cracked concrete, the probability of durability failure is evaluated to be rapidly increased with growing crack width and accordingly, service life is also decreased. In Domestic Specification, allowable crack width is considered in crack effect on diffusion. However, if a concrete member is designed with increased allowable crack width, relatively more reduced diffusion coefficient may be obtained than that from the field investigation. The chloride behavior also may be underestimated due to the reduced diffusion coefficient so that derivation of relationship between crack width and chloride diffusion through extensive field investigation is necessary for durability design of concrete structures permitting allowable crack width under chloride attack.