Study On The Pseudo Fatigue Effect Of Concrete When Suffering Periodic Temperature And Humidity

The temperature-humidity variation in the service environment will produce a corresponding temperature-humidity response within the concrete,which is closely related to various durability problems of concrete.In addition,cyclical temperature-humidity variations due to seasonal changes,day-and-night cycles,etc,will produce corresponding cyclical temperature-humidity stresses within the concrete,which may cause the temperature-humidity fatigue which is similar to loads fatigue.Therefore,studying the possible pseudo fatigue effect and the associated damage accumulation of concrete has a profound guiding significance for deep understanding and active prevention of the deteriorative effects of concrete when suffering periodic temperature and humidity.In terms of the pseudo fatigue effect of concrete when suffering periodic temperature and humidity,the research work conducted in this paper and the findings obtained include:(1)Taking C20,C30,and C40 strength concrete as the research objects,a dynamic elastic modulus test of concrete under periodic temperature-humidity conditions was conducted.The test results show that the loss rate of dynamic elastic modulus of concrete increases continuously in the early period of cyclical temperature-humidity cycle,and with the cyclical temperature-humidity cycle continuing,the loss rate of dynamic elastic modulus tends to stabilize.(2)Compared with the basic model(based on the assumption that the ratio of dynamic elastic modulus loss is proportional to the temperature-humidity cycle number)and the fatigue damage theory model(based on the fatigue damage theory),the trigonometric Gaussian function model(based on the assumption that the variation of relative dynamic elastic modulus satisfy trigonometric Gaussian function)has good fitting effect and the best prediction accuracy,and can be used to verify or predict the mechanical properties of the concrete when suffering periodic temperature and humidity.(3)Taking C30 concrete as the research object,the volumetric deformation test of concrete under periodic temperature-humidity was carried out.The test result shows that all the shrinkage deformation of C30 concrete under cyclic temperature-humidity appears in the low-temperature and low-humidity phases at the beginning and end of the cycles,and the total shrinkage of the C30 concrete decreases in the fluctuations and finally tends to zero.(4)While monitoring the volumetric deformation of concrete under cyclical temperature-humidity,the temperature-humidity response monitor of concrete was conducted,and the monitoring results show that under the cyclical temperature-humidity,the temperature-humidity differences between the internal and external of concrete also show a periodic trend,and the deeper the depth of the measuring point or the farther away from the longitudinal boundary of the specimen is,the more obvious the temperature-humidity difference is.(5)With COMSOL-MATLAB co-programming,a concrete meso-scale model was constructed.Based on the COMSOL platform,a concrete meso-scale numerical simulation study was conducted on the concrete shrinkage deformation under cyclical temperature-humidity.The simulation results show that with the increase of the concrete shrinkage deformation,the internal stress of the concrete gradually increases,and eventually exceeds the concrete tensile strength value.