Corrosion Analysis Model And Probabilistic Evaluation Method Of Corrosion Level For Steel Reinforcement In Concrete

Corrosion of steel reinforcement in concrete often occurs due to the environmental action of chloride ion attack and concrete carbonation.Corrosion of steel reinforcement in concrete may not only produce corrosion-induced expansion pressure,which results in cracking and spalling of concrete cover and as a result degrades the service performance of RC structures,but also reduce the cross section of the embedded steel reinforcement bars,which weakens the load-carrying capacity and safety performance of RC structures.Corrosion of steel reinforcement in concrete is a complex electrochemical process,which is affected by material parameters(e.g.,water-to-cement ratio and chloride content)and environmental conditions(e.g.,ambient temperature and ambient relative humidity).Hence,it is difficult to accurately and efficiently analyze and evaluate the corrosion rate and corrosion level for steel reinforcement in concrete.This thesis focus on the corrosion analysis model and evaluation method of corrosion level for steel reinforcement in concrete.The main contents of this thesis include:(1)Based on the electrochemical principle of steel reinforcement corrosion in concrete and by taking into account the influence of electrode reverse reaction current density on the anode active polarization overpotential as well as the influences of ambient temperature and ambient relative humidity on parameters for corrosion analysis model(e.g.,equilibrium potential,exchange current density,limiting current density and electrical resistivity of concrete),an improved corrosion analysis model for steel reinforcement in concrete was developed.The proposed model provides an efficient approach to determine the distribution of corrosion potential and corrosion rate for steel reinforcement in concrete,since it takes into account the influences of various key factors,such as water-to-cement ratio,chloride content,ambient temperature and ambient relative humidity,on steel reinforcement corrosion.The applicability and efficiency of the proposed model were verified by comparing with available experimental data of natural exposure corrosion tests and existing corrosion analysis models.(2)Based on the collected 89 groups of tested data of concrete resistivity,the influences of various major influential factors including water-to-cement ratio,chloride content,ambient temperature and ambient relative humidity on concrete resistivity were investigated first.Then a probabilistic prediction model of concrete resistivity in terms of the above major influential factors was developed by using the Bayesian theory and the Markov Chain Monte Carlo(MCMC)method.The accuracy and applicability of the proposed model were verified by comparing with the tested data and existing deterministic prediction models.Meanwhile,the evaluation criterion for corrosion level of steel reinforcement based on concrete resistivity was proposed according to the relationship between concrete resistivity and corrosion rate of steel reinforcement.Finally,a probabilistic evaluation method for corrosion level of steel reinforcement in concrete was developed by means of the proposed probabilistic prediction model of concrete resistivity.Analysis results show that the proposed probabilistic evaluation method not only can identify the dominant level of steel reinforcement corrosion,but also can determine the probabilities of steel reinforcement under different corrosion levels(e.g.high,moderate,low,and negligible),which could avoid the misjudgment of corrosion level of steel reinforcement often encountered by the traditional deterministic evaluation methods.(3)Based on the collected 76 groups of tested data of corrosion rate of steel reinforcement,the influences of various major influential factors including water-to-cement ratio,chloride content,ambient temperature and ambient relative humidity on corrosion rate of steel reinforcement were investigated first.Then a probabilistic prediction model of corrosion rate of steel reinforcement in terms of the above major influential factors was developed by using the Bayesian theory and the Markov Chain Monte Carlo(MCMC)method.The accuracy and applicability of the proposed model were verified by comparing with the tested data and existing deterministic prediction models.Meanwhile,the relationship of corrosion rate under both natural exposure condition and artificially accelerated corrosion condition was established.Finally,a probabilistic evaluation method for corrosion level of steel reinforcement in concrete in terms of the corrosion rate was developed.The accuracy and applicability of the proposed probabilistic evaluation method were verified by comparing with the probabilistic evaluation method that based on concrete resistivity.Analysis results show that the accuracy and applicability of the above two probabilistic evaluation methods are satisfied.