Research On Carbonation Life Prediction Of Fly Ash Concrete Structure In-service

Carbonization is a major disease of concrete structure deterioration and damage.As an industrial waste,fly ash is widely used in engineering.Although it has many positive benefits,it also brings more serious carbonization problems.Compared with ordinary concrete structures,fly ash concrete structures have a larger carbonation depth and shorter structural durability.According to the whole process of concrete structure deterioration and damage in general atmospheric environment,carbonation life is the first link of structural durability analysis.As the concentration of CO₂ in the atmosphere continues to rise and my country’s construction industry is shifting to a situation where both new construction and maintenance and renovation are emphasized,the study of the carbonation life of fly ash concrete structures can not only provide a scientific basis for the safety assessment of actual projects,but also provide a basis for the removal of It provides a reasonable reference for the determination of the timing of risk reinforcement.Aiming at the carbonation durability analysis of fly ash concrete structure of spillway gate pier in Yanshan Reservoir,according to the field detection of the engineering structure,the carbonation life of the pier structure is predicted by the combination of test and theoretical calculation.The main research work and results are as follows:（1）A series of field tests were carried out on the fly ash concrete structure of the gate pier of Yanshan Reservoir.The main test contents include:apparent damage,concrete compressive strength,thickness of reinforcement protective layer,carbonation depth,etc;The carbonation depth of different structural parts with the same concrete condition and similar environmental conditions as the gate pier structure is detected.The existing research methods are used to predict the carbonation life of the gate pier structure.The results show that the existing structural carbonation life prediction methods can not well obtain the carbonation life of the gate pier fly ash concrete structure.（2）Based on the fly ash concrete mix proportion of the gate pier structure and the fly ash content as the single factor variable,six groups of mix proportion were designed,and specimens with the same raw material grade as the gate pier concrete are poured for indoor rapid test;On the basis of Niu Ditao carbonization model,the influence coefficient of fly ash is fitted according to the test data,and the carbonization model is improved.By comparing the calculation difference between the carbonation model and the measured value before and after the test,it is determined that the improved carbonation model is more suitable for the carbonation life prediction of fly ash concrete structure of Yanshan Reservoir.（3）Bayesian posterior estimation theory is introduced to update the carbonation model of fly ash concrete,and the updated object of carbonation model is transferred from carbonation depth X to carbonation speed coefficient K;Combining the carbonation data of different structural parts under the same concrete condition and similar environmental conditions as the gate pier structure and the carbonation model as a priori information,a super parameter calculation method under the condition that the mean value and variance of carbonation population samples are unknown is proposed,and a Bayesian posterior model of carbonation depth is derived.The Niu Ditao model,the improved fly ash concrete carbonation model and the Bayesian posterior model of carbonation depth are compared,and they are substituted into the carbonation life criterion for reliability calculation.The results show that the structural carbonation life result based on Bayesian posterior estimation is the most realistic and reliable,and can better represent the actual situation of the gate pier structure of Yanshan Reservoir.