高温后混凝土单轴拉伸和压缩破坏规律及力学性能研究

Uniaxial Tensile and Compressive Failure Law and Mechanical Properties of Concrete after High Temperature

本文对常温及高温作用后的混凝土进行单轴拉伸和压缩试验,同时使用数字图像相关方法(DIC)观测混凝土试件表面的变形演化过程,探究高温后混凝土拉伸和压缩过程中裂缝的变形演化及力学性能衰减规律。结果表明,随着温度升高,混凝土表面裂缝的萌生和扩展时间逐渐提前,破坏时表面应变集中区的宽度及相应的应变数值逐渐增大,裂缝扩展程度更加显著,当温度达到800℃时,甚至呈多裂缝扩展形态。裂缝的显著扩展增加了混凝土的耗能,使高温损伤后混凝土的延性增加。比较高温后混凝土拉伸和压缩应变云图可知,裂缝开裂引起的应变集中区宽度相近,但压缩试件的应变数值略高于拉伸试件。裂缝的萌生和扩展影响混凝土的力学性能,随着温度升高,混凝土抗拉强度、抗压强度及弹性模量不断下降,峰值应力处的应变逐渐增加;拉伸应力应变曲线由双阶段逐渐转变为三阶段,破坏特征由脆性转变为延性;而压缩应力应变曲线始终为三阶段,与单轴拉伸相比,压缩破坏的延性特征更加明显。

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.