Effect Of Humidity On Mechanical Properties Of Concrete With Different Strength Grades

The hydraulic concrete is used for a long time in the water environment,and its internal humidity state has a significant influence on its mechanical properties.In this paper,physics experiments are carried out,and four strength grades of C20,C30,C40 and C50 are set.Firstly,the reasonable humidity control method of concrete with different strength grades is studied,and concrete specimens with different humidity conditions are obtained,and the size of the specimens is considered.The effects of humidity on concrete compressive strength,splitting tensile strength and fracture toughness of different strength grades are systematically investigated,which provides a reference for the safety evaluation of hydraulic structures.The main work and conclusions of the thesis are as follows:(1)Using the drying method of oven heating and ventilation,five temperature gradients of 60 ℃,80 ℃,105 ℃,120 ℃,and 150 ℃ were set to study the variation of strength before and after drying.Under different drying temperatures,the compressive strength and splitting tensile strength are improved to some extent.Based on the drying process with minimal impact on concrete strength and highest efficiency,the best drying process for concrete of different strength grades is obtained.(2)Based on the optimal drying process,the dried concrete specimens were immersed in water to study the variation of water content and saturation during the free water absorption process of concrete specimens of different strength grades and sizes,and the humidity prediction model was established to obtain reasonable humidity control method for concrete.Through the three-dimensional free water absorption test data fitting,the variation law of concrete water absorption coefficient of different strength grades is obtained.Based on Fick’s second law to simulate the humidity diffusion process of concrete when it is free to absorb water,the three-dimensional concrete water absorption model was established.(3)Based on the law of humidity variation,the saturation of concrete specimens with different strength grades was controlled to be 0%,20%,40%,60%,80%,100%,respectively.The variation of concrete compressive strength and splitting tensile strength under different humidity conditions were studied.The regularity,that is,the compressive strength and the splitting tensile strength decrease linearly with the increase of humidity,the splitting tensile strength decreases more,and the low-strength concrete specimens are more sensitive to humidity.Taking C30 concrete as an example,cube specimens with side lengths of 70.7mm,100 mm and 150 mm were set to study the effect of humidity on the strength size effect of concrete.With the increase of humidity,the size effect of concrete compressive and splitting tensile strength is more obvious.The splitting and tensile size effect is more sensitive to humidity.Based on the Ba(?)ant size effect law,a formula for the size effect law of C30 concrete considering the influence of humidity is established.(4)Based on the acoustic emission technology,the cracking point and the instability point of the three-point bending beam of concrete are obtained.The concretes of different strength grades are compared with 0%,20%,40%,60%,80% and 100%.The change of cracking toughness and instability toughness in the state,the system explores the effect of humidity on the fracture toughness of concrete.With the increase of humidity,the concrete cracking toughness and instability toughness decrease linearly.