Life Prediction Of Concrete Bridge Based On Predicting Initial Corrosion Time Of Steel-Bar

Due to the durability insufficiency of concrete structure, calamities caused by structural failure happened frequently in the recent few decades, the durability of concrete structure is considered increasingly important. The influence factors of durability of concrete structure are numerous and the mechanism of action is complex, especially the concrete bridges exposed to atmosphere environment. Considering the significance of highway traffic in national economy, it is extremely important to study the durability and life prediction method of concrete bridges. The corrosion of reinforcing steel bar is the intuitionistic phenomenon of concrete durability deterioration. Combine with the previous scholars's research findings, based on initial time prediction of steel bar corrosion, this thesis makes a series of study on concrete bridge life prediction. The main contents are as follows:1,Main factors influencing the concrete durability are analysed, form four hierarchies including environment, material, structural design and construction maintenance.2,The study of durability and life prediction of concrete has obtained some achievement, but the life prediction models and the calculation results are different. To find appropriate prediction models, some works of comparing and commenting existing models have done in this thesis.3,A curve that describes the concrete pH value changing with concrete depth is fitted, and a pH diachronism model in concrete is proposed in this thesis, by which the concrete pH value at any time and any concrete depth can be predicted. The [OH-] of concrete at any time could be calculated by the pH model proposed in this paper, the [Cl-] of concrete at any time could be calculated by diffusion model. Regarding the critical value of [Cl-]/[OH-] as a criterion to judge whether the steel bar is corroded, the initial corrosion time of steel bar could be predicted. Consequently the service life of concrete bridge could be predicted.The present models of forecasting initial corrosion time of steel-bar are only applicable to single-factor action environment, either concrete carbonization or chloride ions corrasion. However, the prediction model that proposed in this thesis has synthetically considered the multi-influence factors, not only applicable to carbonization environment and chloride ions environment, but also applicable to the coexistent environment of both. Therefore, the study of this thesis is of practical significance on predicting service life of concrete structure appropriately.