Service Life Prediction For Concrete Structure Materials In Western Region Of China Based On Probabilistic Method

There is a large amount of saline soil in the Western Region of China.Saline soil and harsh environment have a serious threat to the durability and service life of concrete structures.Service life is an important index of concrete structure engineering,and improving the service life of concrete structures is the most effective energy-saving emission reduction.The study of service life prediction for concrete structure materials in the Western Region of China under the specific environment has important theoretical significance and practical application.This paper is supported by National Science Foundation of “Study on durability prediction of concrete based on sulfate corrosion in western saline soil region of China”,and the project of “Study on durability design of subway structure concrete under strong corrosion environment with chloride and sulfate ”.The concrete structure materials used in the foundation construction was regarded as study object,such as concrete with optimized mix proportion and reinforced concret e used in Lanzhou Metro project.The damage process of concrete structure materials in service was revealed.Start with nondestructive testing.Considering the multiple degradation factors and their uncertainties in real environment,the multiple degradation factors are treated as random variables based on the collected data.The service life prediction of concrete structures is studied by using the probabilistic method.These studies can both guid the durability design of planed concrete structures and p rovide experimental basis and scientific criterion for service life prediction of existing structures in the Western Region of China.Specific studies and achievements are as follows:1.The testing program for accelerated life testing of concrete was designed to simulate the climate in Xining area.The program integrates many factors,especially considering the climatic factors of strong solar radiation in Xining area.Using the stochastic method,Weibull distribution and lognormal distribution,accelerated life reliability function and the density function of the concrete specimen were given by Weibull distribution function and the lognormal distribution function,and the accuracy of the two prediction models was compared.At last,the durability reliability evaluation of concrete structure materials was carried out.2.The testing program for field exposure test of concrete specimens in typical saline soil area of Xining was designed.The mass loss and ultrasonic velocity were choosed as the key factors in the whole service process of concrete in the field environment.Considering the degeneration correlation between various factors,a probabilistic life prediction method based on Copula function was proposed.The results show that the method can be used to describ e the relationship between the multiple degradation factors effectively and improve the accuracy of service life prediction.3.The testing program for accelerated life testing of reinforced concrete for Lanzhou Metro was designed.According to the situation of Lanzhou Metro Project,the constant current was used to accelerate the corrosion of steel bar,and the wet sand with complex salt solution was used as electrolyte.The accelerated life test ing was carried out,and a certain amount of accelerated life data was collected by electrochemical technique.The critical corrosion current density of Lanzhou Metro reinforced concrete was obtained.The linear model and exponential model were used to fit the average value of data corresponding to each time point respectively.Based on the Wiener stochastic process,a reliability model for the degradation of reinforced concrete(corrosion current density)was established.The accelerated life of reinforced concrete specimens was predicted,and the results show the effectiveness of the method.4.The testing program for the durability test of the Lanzhou metro reinforced concrete simulating the engineering site environment was designed.The ultrasonic velocity and the corrosion current density were chosed as the key degradation factors in the whole service process of reinforced concrete specimens.Marginal distributions of service life of reinforced concrete under different single degradation factors were determined by using different probability methods.After that,Copula function was adopted to establish the relationship between the degradation factors.The marginal distributions were mixed together,and the service life joint distribution function of concrete was obtained.The service life of reinforced concrete specimens was predicted,which shows the effectiveness of the method.