Stability And Time-Depth Dependency Of Chloride Diffusion Coefficients

Chloride-induced corrosion is one of the most common deterioration mechanisms to cause a premature failure of reinforced concrete(RC)structures,since once corrosion initiates,the sectional area loss of reinforcement will be accelerated,leading to a reduced loading capacity of RC members.Therefore,the corrosion initiation phase is a crucial phase to explore the service life prediction of RC structures in chloride environment.The time to corrosion initiation is mainly determined by the cumulation rate of chloride concentration(Cl~-)at the surface of reinforcement bar.Studying the stable process and time-depth dependent of chloride diffusion coefficient will increase accuracy for predicting chloride concentration and time to corrosion initiation of steel bars as well as the durability life assessment of RC structures.To investigate the time-depth distribution of chloride diffusivity,which is one of the important factors affecting the time to corrosion initiation of steel bars,it is necessary to investigate the stability,depth dependent,and time-depth coupling of chloride diffusion coefficient based on chloride diffusion theory and verify the exposure test results in different tidal environments.The main research contents in this paper are as follows:1.Based on Fick's second law and the improved Boltzmann-Matano method,the calculated models of instantaneous chloride diffusion coefficient,stable time of apparent and instantaneous chloride diffusion coefficient,depth dependent chloride diffusion coefficient in drying-wetting environment and the probability of the time to corrosion initiation of concrete reinforcement are established.2.Based on field tests in two different tidal environments that were exposed to 840d and 600 d,respectively,the effects of water-binder ratio,admixture,and environment factor on the stable time of chloride diffusivity were analyzed,and the validity and practicability of the stable time model were verified.3.Based on the experimental results of natural marine tidal environment exposed for 840 d,the depth dependent chloride diffusion performance in concrete with different w/b ratios is studied.According to the value of chloride diffusion coefficient at different exposure times in different depths,the model for time-depth coupling dependent chloride diffusion coefficient is established.4.Time to corrosion initiation of an existing sluice gate in service for many years is predicted based on the probabilistic prediction model,and the randomness and sensitivity of influencing parameters are analyzed.In addition,the influence of time-depth coupling dependence of chloride diffusion coefficient on time to corrosion initiation is studied.