关键词: 混凝土, 裂缝, 高温, 单轴拉伸, 单轴压缩, 数字图像相关方法

Abstract: In this paper, uniaxial tensile and compressive tests were carried out on concrete at room temperature and after high temperature. At the same time, digital image correlation method (DIC) was used to observe the deformation evolution process of concrete specimen surface, and to explore the deformation evolution and mechanical properties attenuation of cracks in concrete during tensile and compressive processes after high temperature. The results show that with the increase of temperature, the initiation and propagation time of cracks on the surface of concrete gradually advance, the width of surface strain concentration zone and the corresponding strain value gradually increase, and the degree of crack propagation is more significant. When the temperature reaches 800 ℃, it even shows a multi-crack propagation form. The significant expansion of cracks increases the energy consumption of concrete and increases the ductility of concrete after high temperature damage. Comparing the tensile and compressive strain contours of concrete after high temperature, it can be seen that the width of strain concentration zone caused by crack cracking is similar, but the strain value of compressive specimen is slightly higher than that of tensile specimen. The initiation and propagation of cracks affect the mechanical properties of concrete. With the increase of temperature, the tensile strength, compressive strength and elastic modulus of concrete decrease continuously, and the strain at peak stress increases gradually. The tensile stress-strain curve gradually changes from two stages to three stages, and the failure characteristics change from brittleness to ductility. The compressive stress-strain curve is always three stages. Compared with uniaxial tension, the ductility characteristics of compression failure are more obvious.

Key words: concrete, crack, high temperature, uniaxial tension, uniaxial compression, digital image correlation method