Study On Probabilistic Prediction Model Of Chloride Diffusion Coefficient In Concrete

Durability degradation of concrete structures under chloride environment is often caused by steel reinforcement corrosion induced by chloride attack.Chloride diffusion coefficient is one of the key parameters which control the transformation speed of chloride ions within concrete and as a result affects the service life of concrete structures.Chloride diffusion coefficient is not only influenced by environmental conditions and material properties which exhibit obvious randomness,but also decreases with aging time of concrete which exhibit time-dependent behavior.Therefore,it is necessary to develop a probabilistic prediction model of chloride diffusion coefficient for durability analysis and service life prediction of concrete structures,which takes into account the influences of environmental conditions,material parameters and time-dependent behavior.In this thesis,probabilistic prediction models of chloride diffusion coefficient for concrete under artificially accelerated condition and natural exposure condition were developed respectively based on the database of artificially accelerated test(RCM)and natural exposure test.Then probabilistic method for service life prediction of concrete structures under marine chloride environment was proposed.The main contents of this thesis are as follows:(1)Based on collected 295 sets experimental data of chloride diffusion coefficient measured by the rapid chloride migration coefficient method(RCM),the influences of material parameters such as water-to-cement ratio,content of fly ash,content of slag on the chloride diffusion coefficient were investigated.Then deterministic prediction model of chloride diffusion coefficient for concrete under artificially accelerated condition was proposed by selecting the significant variables with the stepwise regression method.Finally,probabilistic prediction model of chloride diffusion coefficient for concrete under artificially accelerated condition which takes into account the aleatory and epistemic uncertainties was developed by combining the Bayesian theory and the Markov Chain Monte Carlo(MCMC)method.(2)Based on collected 913 sets experimental data of fitted chloride diffusion coefficient for concrete at initial age,deterministic prediction models of chloride diffusion coefficient in terms of expouse time and mix proportion parameter(water-to-cement ratio and content of mineral admixtures)for concrete under submerged zone,tidal zone,splash zone and atmospheric zone were develop respectively,which takes into account the influences of environmental condition,material parameters and time-dependent behavior.Then probabilistic prediction models of chloride diffusion coefficient which takes into account the aleatory and epistemic uncertainties were developed by combining Bayesian theory and the MCMC method.Furthermore,the relationship of chloride diffusion coefficients of concrete under artificially accelerated condition and natural exposure condition was investigated.(3)Probabilistic method for service life prediction of concrete structures under marine chloride environment was proposed by combing the probabilistic prediction model of chloride diffusion coefficient with the service life prediction model for steel reinforcement corrosion(initial time)for concrete.The influences of environmental condition(e.g.,submerged zone,tidal zone,splash zone and atmospheric zone),material parameters(e.g.,water-to-cement ratio and content of mineral admixtures)and concrete cover depth on service life of concrete structures under marine chloride environment were investigated.