Study On The Influence Of Drying-wetting Cycle On The Physical And Mechanical Properties Of Concrete

Hydraulic concrete structure may be in the changing water environment during service,and the durability of concrete is closely related to its internal moisture.In the process of concrete drying-wetting cycle,it is often accompanied by the invasion and accumulation of harmful chemicals,the inhalation and escape of water and other physical and mechanical effects,which accelerate the deterioration of the physical properties of concrete and reduce the service life of concrete.Based on physical experiments,the strength variation of concrete with different strength grades,different temperature differences and different research scales under the action of drying-wetting cycle was studied.The ultrasonic testing technology and mercury intrusion method were used to explore the variation of internal pore structure and explain the mechanism of strength variation;Based on the test data,the relative strength prediction models of concrete with different strength grades are obtained by using Gauss 2D function fitting,which can provide reference for the safety evaluation of concrete in the dry wet cycle environment.The main work and conclusions are as follows:(1)The drying-wetting cycles of concrete and mortar with different strength grades were tested at 60 ℃and 40 ℃ respectively.The compressive strength and splitting tensile strength of concrete and mortar after different cycles were measured,and the evolution law of mechanical properties of concrete and mortar under drying and wetting cycles was obtained.With the increase of drying-wetting cycles,the relative strength of different strength grades of concrete and mortar increases first and then decreases,and the deterioration of splitting tensile strength is more significant than that of compressive strength.Under the same number of drying-wetting cycles,the higher the strength grade,the greater the relative strength;The larger the temperature difference during drying,the smaller the relative strength and the earlier the deterioration;The relative strength of concrete and mortar with the same water binder ratio is higher and the deterioration is later.(2)Ultrasonic nondestructive testing technology was used to measure the ultrasonic velocity and amplitude of concrete and mortar in the process of drying-wetting cycle.The results show that the ultrasonic velocity of concrete and mortar changes significantly after drying-wetting cycles.With the increase of drying-wetting cycles,the ultrasonic velocity increases first and then decreases;The smaller the water binder ratio,or the smaller the temperature difference,or the higher the mortar content,the greater the increase of ultrasonic wave velocity and the smaller the decrease.However,the amplitude of ultrasonic wave increases continuously,and the influence of intensity grade,temperature difference and research scale on the amplitude of ultrasonic wave is not significant.(3)The pore structure and pore size distribution of concrete and mortar were obtained by mercury intrusion method in the process of drying-wetting cycle.It was found that the pore structure and pore size distribution of concrete and mortar changed significantly in the alternate dry wet environment.With the increase of drying-wetting cycles,the porosity,total pore volume,average pore diameter and median pore diameter first decrease and then increase;The pore size distribution curve of concrete changes significantly under the influence of dry wet alternate environment.The most probable pore size first moves to small pore size,then drifts to large pore size,and finally shows the characteristics of pore size coarsening.(4)The results show that the damage of concrete and mortar is mainly caused by drying-wetting cycle.The smaller the water binder ratio and temperature difference,the smaller the damage.In the drying-wetting cycle process,the addition of coarse aggregate makes the damage of concrete greater,and in a certain range of coarse aggregate content,the smaller the content of coarse aggregate,the greater the damage of concrete.(5)Based on the experimental results,the numerical model reveals the moisture heat change law of concrete in the process of drying and wetting to a certain extent.The stress of concrete under the dryingwetting cycle is mainly concentrated in the aggregate of concrete and the interface layer around the aggregate.