Predicting Durable Service Life Of Reinforced Concrete Exposed To Chloride Environment

This paper bases on a background of The Sixth Group Researching Subject of National Concrete Code Project' and focus on the durable problems in active concrete code and practice. Effect of chloride on durability of reinforced concrete component and service life prediction are discussed in this paper.In chloride environment, chloride penetrates into concrete that will dispassivate the rebar in concrete and induces rebar corrosion. With corrosion developing, the volume expanding of corrosion product lead cover cracking or spalling, a kind of durable failure. Predicting service life of reinforced concrete component is a problem that need be resolved urgently, since it can be used for reinforced concrete structure durability design, evaluation and maintenance strategies decision. In this paper, research on predicting service life of reinforced concrete component exposed to chloride environment was made:Firstly, a finite difference model is developed for predicting the process of chloride penetrating into concrete. Water cement ratio and mixing fly ash or slag into concrete effect on ability of resisting chloride penetrating that are considered in the model. The effect of environment that include temperature, relative humidity and cumulating of surface chloride concentration of concrete are also considered. Moreover, chloride diffusion changing with time is included in this model as well as.Secondly, by loading a pressure simulate the corrosion product induced expansive effect on concrete around rebar. ANSYS that is a famous FEA software is used for analysis a real model. According the result of ANSYS analysis, a new model based elasticity mechanics is developed for calculating the corrosion loss that need for concrete cover cracking. The influence of relative cover C/d on corrosion failure model and maximal principal tension stress, the position of rebar located, corrosion of adjacent rebar induced additional stress are considered in this model.Thirdly, according to the conclusion of some experimentations that the maximum crack width and rebar section loss keep a approximate linear relationship after cover initial crack, a relationship between the maximum crack width and rebar section loss is developed based on a hypothesis that the increase in the volume of crack is equal to the volume of the corrosion products produced after cover initial crack.Fourthly, assuming that corrosion current density is a constant, a model for calculating the time from corrosion initial to the cover maximum crack width developing to critical value is established.Fifthly, based the established model of chloride induced rebar initiation corrosion time and the model of concrete cover cracking time due to corrosion products volume expanding, a probability based model is established for service life predicting of reinforced concrete structure in chloride environment. The prediction model regard corrosion induced concrete cover cracking matching the cracking limitation as durable limit state, or as termination of the component service life.Sixthly, the Monte-Carlo method is used for calculating the failure probability of durable failure under different service time, and drawing a plot of relationship between failure probability and service time. According to the plot, the service life based a acceptable failure probability can be found easily.At last, according to the result, several influence issue on durable service life prediction are discussed.Based the result of calculation and analysis in this paper, it is feasible that predicting of the service life of reinforced concrete component exposed to chloride environment with a probability based method .The result of analysis is consistent with the changing rules of service life in practice. Probability based limit state method is used for service prediction. It is more reasonable than a deterministic model and satisfied with the required method of national structure designing uniform code. This model can be used for the designing and predicting of durable life of new...