Experimental Study On Fatigue Residual Strength Of Concrete Under Simulated Acid Rain Environment

Concrete structure with its superior performance is widely used in bridge structure,water conservancy structure,building structure and other building structures,these structures in the service process in addition to static load,but also subject to repeated load,which makes the structure easy to produce fatigue damage and even damage.In addition,because most concrete structures are in open service,they are easily affected by various environmental corrosion factors,such as acid rain,salt lake,seawater chloride ions,etc.,which causes different degrees of damage to concrete structures and shortens their service life.Based on the project of National Natural Science Foundation of China(51968021),this paper mainly studies the fatigue properties of concrete under acid rain corrosion environment.The specific work is as follows:(1)Referring to the characteristics of acid rain in Jiangxi Province,a sulfuric acid type acid rain simulation solution with a p H value of about 3 was prepared to corrode 50 prism specimens.Conduct static load damage test on the test piece,and compare the damage characteristics of the test piece before and after corrosion;The fatigue test and residual strength test were conducted on the specimens,with the stress levels of 0.7,0.75,and 0.8,respectively.The fatigue life changes of corroded and uncorroded specimens under three different fatigue loads were observed.The results show that the static load failure of the specimens before and after corrosion is obviously brittle failure;After corrosion,the fatigue life of concrete has decreased to varying degrees,with the maximum decrease being 49.83% when the stress level is 0.8.(2)According to the characteristics of acid rain in Jiangxi Province,a simulated solution of sulfuric acid rain with p H value of about 3 was prepared to carry out corrosion and fatigue tests on 50 prismatic specimens.The results show that the fatigue lives of specimens with S=0.7,S=0.75 and S=0.8 all decrease after corrosion,and the decrease is the largest when S=0.8,reaching 49.83%.(3)The residual strength tests of corroded and uncorroded concrete specimens were carried out respectively,and the P-R-N curves of compressive fatigue under corresponding conditions were drawn based on the theory of reliability.The residual strength of concrete could be predicted by using the P-R-N curve equations drawn.The results show that the fitting degree of P-R-N curves obtained under each condition is high.After concrete is subjected to fatigue load,the change trend of residual strength of specimens before and after corrosion is basically the same,and the decay degree is small in the initial loading stage,and the decay speed is relatively slow.When the specimens are close to failure,the strength will drop sharply,which is consistent with the previous research conclusions.(4)Based on fatigue damage theory and stiffness attenuation model,the internal damage evolution and stiffness attenuation of concrete under different fatigue loads before and after corrosion were analyzed.The results show that the decay curves of the residual stiffness of concrete under the two environments have the same trend,showing slow decay in the early stage,accelerated in the late stage and then steep decline in the late stage.The variation trend of fatigue damage curves of concrete under the two environments is basically the same.The damage increases very slowly in the first 30%～40% of fatigue life,and the damage value of concrete joints will increase rapidly beyond this point,showing obvious brittleness characteristics,and this feature is more obvious for uncorroded specimens.