Chloride Penetration And Durability Assessment Of Harbor Concrete Structures

Marine environment is one of the most aggressive exposure conditions for concrete structures.The corrosion of the steel reinforcement may lead to concrete fracture cracking,the concrete cover delaminating and spalling,concrete and reinforcement cross sections reducing,and can also cuause the loss of bond between the reinforcement and concrete,and the reduction in strength and ductility,which give rise to the reduction of durability of the concrete structures.In this work,a field investigation was carried out at the Beibu Gulf.Based on the observed data,the most aggressive exposure conditions under marine environments were analyzed.Depending on the Kolmogorov-Smirnov test,the probabilistic distribution of concrete cover depth,chloride diffusion coefficient,surface chloride concentration,critical chloride concentration and age factor m was analyzed.In addition,the influence of those parameters on the durability of the structure was also analyzed.The corrosion initiation time was predicted by the probabilistic approaches,while the concrete cover corrosion-cracking time was assessed by both the probabilistic approaches and deterministic approaches.The main contributions of this paper are as follows:1.Based on the in-situ tested data,the most aggressive exposed condition of concrete structures and the probabilistic distribution of random variables were analyzed.According to the chloride profiles in the different zones,we can conclude that the most unfavorable exposure conditions of the reinforced concrete structure under marine environment were the splash zone.An improved K-S test method was proposed to improve the efficiency of K-S test and reduce the probability of type II errors by selecting a reasonable sample size.The distribution test results of measured data show that concrete cover depth is normally distributed;the age factor is also a random variable following the normal distribution.Depending on the data collected from the published literatures,critical chloride concentration can be described by a lognormal distribution.Furthermore,based on the characteristics of limit error,the limit error criterion was proposed on the basis of 3?criterion.When the sample size is less than 10,it is appropriate to use this criterion to judge the gross error of the tested data.2.The Fick chloride diffusion model was modified according to the data collected from the Beibu Gulf concrete dock.Then,based on this modified model,the optimization algorithm was introduced to predict the corrosion initiation time and analyze the sensitivity of random variables on corrosion initiation time prediction.Compared with the Life 365 model and LNEC E465 model,the modified model was verified to be more reasonable to describe the chloride corrosion process in the given concrete dock.Under the target reliability index of 1.3,prediction results made by optimization algorithm and Monte Carlo simulation with 1,000,000 simulations shows that the steel corrosion initiates about 40 years after construction.Considering the coefficient variation and the distribution pattern of random parameters,sensitivity analysis indicates:the most influential parameter to corrosion initiation time was concrete cover depth,followed by apparent chloride diffusion coefficient,the impact of surface chloride concentration,critical chloride concentration and the age factor in corrosion initiation time prediction was comparatively less.3.The duration of corrosion propagation phase t_p was studied by comparative analysis between the determined and the probabilistic approaches.In the determined method,a new prediction model was proposed in the work by using the elastic-plastic theory,and the corresponding result of t_p was 11.5 years.The value of t_p obtained from the probabilistic model was 12.7 years when the randomness of limit crack width and time-varying characteristics of corrosion rate were taken into account.Considering the side effects of steel corrosion on the reliability of reinforced concrete structures,illustrative example verified that the pollution dispersion model,which proposed by this paper,can effectively describe the impact of chloride corrosion on the resistance degradation of reinforced concrete structures.4.The Fuzzy AHP was introduced to assess the durability of the given concrete dock.Durability evaluation objects include the quay wall,breast wall and ancillary components of the concrete dock.The influence of chloride corrosion,carbonation,steel corrosion,concrete crack,quality and damage of concrete was taken into consideration in the durability evaluation.The results indicate that the given concrete dock is still in good condition,and an extensive maintenance is not necessary.