Experimental Research On Dynamic Mechanics And Damage Constitutive Relationship Of Concrete In Temperature And Compound Salt Environment

The performance and service life of concrete in mines are not only affected by complex geological conditions such as ground pressure and disturbances,but also by the long-term effects of environmental factors such as temperature,groundwater and salt solution erosion.Consequently,concrete suffers from both mechanical and chemical erosion.In the paper,the mechanical property tests and microstructure tests of concrete under static compression,single impact,cyclic impact and lateral confinement cyclic impact were carried out to analyze the accumulative damage evolution law of concrete in temperature-complex salt environment by using test systems such as separated hopkinson compression bars,SEM scanning electron microscopy and X-ray diffraction.The main conclusions are as follows.(1)Static compression tests,splitting tensile tests and cyclic loading and unloading tests were carried out to derive the static damage constitutive models and damage evolution equations of concrete at different temperatures,and to analyze the mechanical properties,failure modes and energy evolution of concrete in different temperaturecomplex salt environments under uniaxial compression.The results show that the compressive strength,peak strain,modulus of elasticity and splitting tensile strength show decreasing exponential functions with decreasing temperature.The peak strength and deformation modulus were larger at the temperature of 20 °C when cyclic loading was applied.As the temperature decreases,the various energy densities required by the concrete during cyclic load action decrease.Statistical damage constitutive models and damage evolution equations for the joint action of temperature and load were constructed to obtain static uniaxial compressive stress-strain relationships and damage evolution behaviors of concrete after the action of different temperature-complex salt environments.(2)Dynamic impact compression and dynamic splitting tests were conducted to investigate the effects of strain rate and stress rate on the stress-strain relationship,dynamic peak strength,deformation modulus,peak strain,damage characteristics and energy dissipation of concrete in different temperature-complex salt environments.Based on the theory of viscoelasticity and damage mechanics,a dynamic damage constitutive model of concrete after salt freezing action was constructed based on the Zhu-Wang-Tang(ZWT)model constitutive equation.The results show that the deformation modulus,peak stress and peak strain of concrete increase with the increase of strain rate at the same temperature.The dynamic splitting tensile strength and dissipation energy of concrete increase with the increase of stress rate.The dynamic compression strength of concrete satisfies the exponential function with temperature.The fractal dimension of concrete after impact increases with the increase of strain rate,and the fractal dimension increases with the increase of dissipation energy required for specimen fragmentation.The damage constitutive model constructed reveals the dynamic impact compression stress-strain relationship and damage evolution behavior of concrete after the action of temperaturecomplex salt environment.(3)By conducting cyclic impact tests on concrete in a temperature-complex salt environment,the characteristics of the variation of each mechanical parameter with impact number and temperature were obtained.It was found that the accumulated damage inside the concrete under the same impact air pressure increased with the increase of impact number and decrease of temperature.The impact resistance of concrete decreases with the increase of impact air pressure and decrease of temperature.The relationship between the accumulated damage and impact number was constructed,and the variation law of the internal accumulated damage of concrete without lateral restraint under the cyclic impact load with impact number was found.(4)The triaxial cyclic impact compression test of concrete found that under the same impact air pressure,the stress-strain curve of concrete specimens under lateral restraint in cyclic impact compression showed rebound phenomenon compared with the uniaxial cyclic impact test.The higher the impact air pressure,the lower impact number the concrete with lateral restraint can withstand.The lower the temperature,the lower the impact number of the concrete with lateral restraint can withstand.The accumulated damage of concrete increases with the increase of the number of impacts.The lower the temperature,the faster the accumulated damage increases with the increase in the number of impacts.With the increase of impact number,the rupture surface has a certain angle with the impact loading direction and shows a shear damage mode.The accumulated damage was regressed as a function of the number of impacts,and the variation law of its internal accumulated damage with the number of impacts was obtained for concrete under the action of lateral restraint under cyclic impact loading.(5)The microstructural characteristics of C60 concrete were analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD)to clarify the damage mechanisms of concrete in different temperature compound salt environments.The internal structure of concrete was denser after immersion in salt solution at 20 °C.The concrete was melted again after the low temperature effect,and the number of its internal microcracks and microporosity increased.The degree of defects in C60 concrete after immersion in salt solutions of different temperatures and then placed at room temperature to melt is,-20 °C >-15 °C >-10 °C >-5 °C > 20 °C,corresponding to the deterioration of its macroscopic mechanical properties.Figures [122] Tables [33] References [206]...