Research On Accelerated Carbonation Test Method And Damage Mechanism Of Concrete Under Coupled Loading

Concrete carbonation is due to the carbon dioxide in the atmosphere entering into the concrete structure through the pores,which reacts with the alkaline concrete to cause the structure itself to reduce the alkalinity and lose the protection of the reinforcement,and finally lead to the damage of the concrete structure,which seriously affects its service life.Therefore,it is of great significance to carry out the research on the durability and damage mechanism of RC beams in the carbonation environment it is of great significance in engineering application.Based on the National Natural Science Foundation of China’s major research instrument development project "Development of structural fatigue testing system under complex environment"(No.11627802),this paper carried out the damage test research of concrete materials and reinforced concrete beam specimens under the coupling effect of carbonation environment and load,and established the accelerated test method of carbonation environment and load coupling by combining theoretical analysis and finite element numerical simulation the carbonation damage mechanism and evolution law of concrete are analyzed.The main research work and conclusions are as follows:Firstly,through the data analysis of the factors affecting the concrete carbonation in the service environment of the bridge,the carbonation environment spectrum of the service environment is obtained.The parameters of the carbonation environment spectrum are converted by using the equivalent relationship,and the action time of each environmental factor in the accelerated test environment spectrum is determined.The coupling of load and environment is completed,and the accelerated test method of the coupling of carbonation environment and load is established.Secondly,through the accelerated carbonation environment test of concrete blocks,it is concluded that the compressive strength,elastic modulus and carbonation depth increase with the increase of carbonation time.The compressive strength after carbonation for 28 days increases by 21.7% and the elastic modulus increases by 6.6%.Through the study of carbonation depth,the prediction model of carbonation depth is proposed,and the relationship between carbonation depth and carbonation depth is verified At the same time,the relationship between the carbonation depth test results of accelerated carbonation test and the actual bridge carbonation depth test results is established,and the equivalent relationship between 1d test in artificial accelerated carbonation environment and 48.5d service in natural carbonation environment is obtained.Thirdly,the accelerated carbonation bending capacity test of RC beams under load coupling is carried out,and the bearing capacity of RC beams under different carbonation time and different loads is analyzed,it is found that the bearing capacity of RC beams under load is lower than that under no load,which indicates that the load will accelerate the decline of the bearing capacity of RC beams.The longer the carbonization time is,the more the bearing capacity will decline,and the largest decline will be achieved after carbonization for 7 days.Then,through the analysis of carbonation depth in compression and tension zone of RC beam under load coupling,it is found that compression stress can inhibit the carbonation reaction,while tensile stress can promote the carbonation reaction.After carbonation for 28 days,the carbonation depth in tension zone is 34.7% higher than that in compression zone.The influence coefficient of compressive stress and tensile stress are proposed to characterize the influence of stress state on carbonation depth,and the concrete carbonation model is established the predicted values of carbonation depth are in good agreement with the experimental data.Finally,ABAQUS finite element software is used to analyze the flexural capacity of RC beams with different carbonation time,and the accuracy of the finite element model is verified by comparing with the experimental results.Furthermore,the carbonation damage in compression zone and tension zone of RC beams with different carbonation time is analyzed by finite element method.The change rule of carbonation damage in compression zone and tension zone increases with the increase of carbonation time is obtained,and the change rule of damage is analyzed systematically.