Study On Durability Of Concrete With Fly Ash As Fine Aggregate Under The Coupling Action Of Stress Damage And High Temperature

At present,concrete durability has become a topic of interest for research scholars across the world,it is closely related to the service environment.With the continuous acceleration of industrialization,the environment of today's building structures is also deteriorating.Concrete structures are faced with accidental factors such as heavy impacts,heavy loads,explosions,and fires,resulting in concrete failure to reach the predetermined durability service life.Based on this,this paper carried out the durability(freeze-thaw,carbonation)of concrete with fly ash as fine aggregate under the coupling action of stress damage and high temperature.Taking the concrete with fly ash as fine aggregate as the research object and the ordinary concrete as the control group,by analyzing the macroscopic property change law and microstructure evolution,the freeze-thaw resistance and carbonation resistance of the concrete with fly ash as fine aggregate are explored.The research results have important scientific value and practical significance for the promotion and application of concrete with fly ash as fine aggregate in complex environments.A multifactor coupling test protocol was designed to determine the freeze-thaw resistance of concrete with fly ash as fine aggregate.Rapid freeze-thaw tests were conducted to measure the mass loss and relative dynamic modulus of elasticity of concrete specimens to evaluate their freeze-thaw resistance.The test results show that the freeze-thaw resistance of the concrete decreases with the increase in the initial stress damage.High temperature has a significant effect on the compressive strength and freeze-thaw resistance of concrete.The higher the temperature,the lower the freeze-thaw resistance of concrete.The coupling effect of stress damage and high temperature accelerates the attenuation of mass and relative dynamic modulus of elasticity of concrete.Concrete with fly ash as fine aggregate has a higher freeze-thaw resistance than concrete.A multifactor coupling test protocol was designed to determine the carbonation resistance of concrete with fly ash as fine aggregate.Rapid carbonation tests were conducted to determine the carbonation depths in different carbonation time and evaluate the carbonation resistance of concrete.The results show that the carbonation depth of concrete increases with the rise of initial stress damage and carbonation time.High temperature has a significant impact on the carbonation resistance of concrete.The higher the temperature,the deeper the carbonation depth.The deterioration of durability of concrete under the coupling action of stress damage and high temperature is much greater than that under single action,which greatly reduces the carbonation resistance of concrete.In addition,compared with ordinary concrete,replacing fine aggregate with fly ash can improve the carbonation resistance of concrete.Based on the macro damage mechanics theory and the test facts,the damage law of concrete with fly ash as fine aggregate in freeze-thaw environment was studied.By defining the freeze-thaw damage variables,the third-order mathematical model was introduced to predict the damage degradation process of concrete under multifactor coupling in the freeze-thaw environment.The damage evolution equation and general formula of ordinary concrete and concrete with fly ash as fine aggregate under the coupling action of stress damage and freeze-thaw,high temperature and freeze-thaw,stress damage?high temperature and freeze-thaw were established.Based on Fick's first law,Matlab was used to fit the carbonation depth of concrete in different modes,and an important parameter was given through the regression of test data,that is,the calculation formula of the coupling damage factor K in different test modes.Finally,the prediction models for the carbonation depth of concrete under single stress damage,single high temperature and alternation of stress damage and high temperature were established.According to the results of laboratory tests,based on the freeze-thaw damage and neutralized life criteria,the life prediction model of concrete with fly ash as fine aggregate under multiple factors was established.