Experimental Study On Mechanical Properties Deterioration Of Early Frozen Concrete

Our country has a vast territory,and the northern region is in a rather long low temperature season every year.Especially in many areas of arid northwest China,the low temperature weather lasts for up to 5 to 6 months.The construction of buildings in winter can not only accelerate the development of national economy,but also help to achieve perennial balanced operation,which is of great economic value.However,the sudden drop of temperature often occurs at this time,especially in the late autumn,early winter and early spring.The concrete just poured in the actual project may suffer one or more frost damage before taking anti-freezing measures in time,which will cause irreparable damage to the durability and bearing capacity of concrete buildings during their service life.In order to explore the influence of early freezing on the durability of concrete and analyze the law of early freezing damage of concrete,this paper chooses the hydraulic concrete building located in Jingdian Irrigation Area in Northwest China as the research object.According to field investigation,X-ray spectrum diffraction,chemical analysis and other means,the main corrosive media of buildings are clarified.The concrete specimens with the same mix ratio are designed according to relevant codes,and the concrete specimens with the same mix ratio are designed according to relevant codes.Through indoor simulation of different curing age(freezing time)and different freezing temperature environment,the early freezing test of concrete is carried out,and the later salt-freezing cycle test of early frozen concrete is carried out to explore the service performance of concrete in the study area.The effects of curing age(1h,3.5h,8h,24h)and freezing temperature(-5℃、-10℃)on the compressive strength and relative dynamic modulus of elasticity of concrete are compared,and the variation rules of compressive strength,relative dynamic modulus of elasticity and mass loss rate of early frozen concrete under salt-freezing are studied.The non-destructive testing technology is used to detect the early frozen concrete,and then the influence of curing age and freezing temperature on the thickness of damaged concrete layer is studied.The stress-strain curves of early frozen concrete are obtained by damage detection;the effects of curing age and frozen temperature on the shape,peak stress and peak strain of the stress-strain curves are discussed by studying and analyzing the stress-strain curves.The piecewise constitutive equation is used to fit the stress-strain curve of concrete,also the ductility and plastic deformation ability of concrete are analyzed by the parameters obtained,and the similarity between the measured curve and the fitting curve is compared.The change rule of constitutive curve and the deterioration rule of ductile plastic deformation ability of early frozen concrete under salt freezing are studied by the same research and fitting method change regulation.Relevant research can provide an effective basis for the later durability evaluation and maintenance of concrete buildings constructed in low temperature season.The conclusions are as follows:(1)The influence of curing age on concrete can be expressed as follows: 3.5h>1h≈8h>24h>normal state without freezing,and the compressive strength and relative dynamic modulus of frozen concrete with curing age of 3.5h are the smallest;the more serious the initial damage is,the greater the damage degree of concrete specimens under salt-frozen action.(2)The thickness of damaged concrete layer is measured by ultrasonic horizontal measurement method,and the stress of damaged concrete layer is calculated.The damage variable is introduced and the results show that: The more serious the initial damage of concrete is,the thicker the damage layer is,the smaller the stress of the damage layer is,and the larger the damage variable is,and vice versa.The non-destructive test results are consistent with the conclusion(1).The revised damage variable is basically the same as the relative dynamic modulus of elasticity and compressive strength damage variable.(3)TThe damage test results of concrete under uniaxial compression are consistent with the above conclusions.The more serious the initial damage is,the smaller the peak stress of the constitutive curve is,the larger the peak strain is,and the smaller the plastic and ductile deformation ability of concrete is.Origin software is used to fit the stress-strain curve and the fitting value is consistent with the mechanical properties of concrete expressed by the measured curve.The fitting degree between the measured curve and the fitting curve is higher.