Study On Carbonation Performance And Mechanism Of Radiation Protection Concrete After High Temperature

Radiation protection concrete may face the challenge of high temperature environment during normal service.Its carbonization reaction after high temperature will lead to reinforcement corrosion,concrete cracking and spalling of nuclear radiation source facilities.This paper studies the carbonation performance and evaluation method of radiation protection concrete after high temperature,and analyzes the influence of relevant factors on it,so as to provide reference for further understanding the Carbonation Mechanism of radiation protection concrete after high temperature and carbonation prediction and control.The main contents and conclusions are as follows:（1）The carbonation depth of concrete at different carbonation ages after different high temperature is evaluated by phenolphthalein solution method and apparent p H value method,and the two evaluation results are compared.The results show that the p H value method is more suitable than the phenolphthalein solution method for the analysis of the carbonation performance of concrete after high temperature.After high temperature,the acid gas enters the deep concrete along the high temperature damage crack to produce partial carbonation reaction,and the phenolphthalein solution method will underestimate the carbonation depth;The phenolphthalein test value of concrete carbonation depth is between complete and incomplete carbonation depth,and its value is about 1.5-2 times of the depth of complete carbonation area.（2）XRD、SEM and thermal imaging techniques were used to analyze the effect of aggregate on the carbonation performance of radiation protection concrete after high temperature.The results show that the thermal stability of magnetite aggregate is more important than that of concrete.When the temperature exceeds 300℃,Barite Concrete begins to burst and peel off at edges and corners,while the apparent characteristics of magnetite concrete are still complete when heated to800℃.Therefore,magnetite concrete is more suitable for high temperature environment.（3）The effect of concrete uniformity on the carbonization of radiation proof concrete after high temperature is analyzed by compressive strength test and ultrasonic detection.The results show that high temperature will lead to crack propagation and structural looseness of concrete,and there is a good correlation between relative sound velocity and carbonation rate.Ultrasonic testing can be used to detect the carbonation resistance of radiation resistant concrete after high temperature.（4）The changes of phase composition and carbonatable substances of concrete before and after high temperature were studied by thermogravimetric analysis.Ca（OH）₂is dehydrated and decomposed at400～500℃and Ca CO₃is decomposed at 600～700℃.When it is kept at 600℃for 2 hours,the mass fraction of Ca（OH）₂in concrete decreases from 3.86%to 0.75%.The overall alkalinity of concrete decreases and the carbonation reaction is accelerated.