Research On Damage Evolution And Fracture Mechanism Of Concrete-rock Composite Under Complex Environmen

Concrete-rock composite is a complex structure formed by the cementation of rock and concrete in rock foundation concrete engineering,which is widely used in rock foundation concrete engineering.Complex environments such as high temperature,chemical erosion,and complex stress threaten structural safety due to the deterioration of the physical and mechanical properties of the concrete-rock composite.Therefore,the research on damage evolution and fracture mechanism of the concrete-rock composite under complex environments has great research value and engineering guiding significance in the engineering application of bedrock concrete structures.In this paper,the concrete-rock composite as the research object,the laboratory tests,theoretical analysis and other methods were comprehensive used.With the mechanical testing machine and acoustic emission equipment to carry out mechanical tests,the physical and mechanical properties of the samples under complex environment deterioration and fracture process were analyzed.In addition,the pore structure and mineral changes of the concrete-rock composite under complex environments were analyzed by using nuclear magnetic resonance,X-ray diffraction and other technologies.Meanwhile,the mechanism of macro-damage evolution and fracture process of the sample under complex environments was revealed from a microscopic perspective.The main research contents and achievements are as follows:（1）Systematically analyzed the mechanical properties,failure modes and failure mechanisms of the concrete-rock composite under uniaxial,triaxial and cyclic loading and unloading conditions.The results showed that the peak strength of the concrete-rock composite is smaller than that of sandstone and larger than that of concrete.Under cyclic loading,the tensile fracture degree of the concrete-rock composite specimens decreases with the increase of confining pressure,while the shear failure fracture becomes more obvious with the increase of the interface.With the increase of the number of cycles,the elastic modulus of pressure unloading in each cycle first increases and then decreases.The axial strain increases with the increase of roughness.The larger the height of the interface saw-tooth isosceles triangle,the smaller the transverse deformation ratio.With the increase of the interface zigzag isosceles triangle height,the failure mode of concrete-rock complex specimens gradually changes from splitting failure to shear failure.（2）The mechanical properties of the composite rock,concrete and the concrete-rock composite under high temperatures were studied,and the time-space effect of the failure process of the samples under high temperature was analyzed by acoustic emission.The constitutive model of thermal damage of the concrete-rock composite was established to study the evolution law of thermal damage of the samples after high-temperature treatment.The results showed that the peak strength of the preloaded sandstone increased with temperature,but the peak strain was opposite,and high softening occurs at high temperatures.High temperature changed the mechanical properties of concrete and the maximum AE quantity decreases with the increase of temperature.In addition,with the increase of temperature,the peak strength and elastic modulus of concrete rock composite gradually decreased.The cumulative count of AE number at different time-sample locations during the loading process reflected the time-space effect of the fracture process of concrete-rock composite after high temperature.A new damage constitutive model was established to reveal the damage evolution law of pre-peak strength and post-peak strength.The calculated values were in good agreement with the experimental data,which verified the validity of the damage model.（3）The evolution law of mass-time,mass-p H value and mechanical parameters of the concrete-rock composite under the chemical soaking,different soaking duration and different preloading conditions were systematically analyzed.Combined with the chemical reaction of the sample in the acid solution,the mechanism of strength deterioration and damage law of samples were analyzed.The results showed that the p H value of the solution increased with the increase of soaking time,and the mass decreased with the increase of p H value.The peak strength and elastic modulus of the samples decreased after the acid attack.The damage constitutive model of the sample after acid erosion was established to verify the damage evolution law.The mechanism of failure characteristic change of concrete-rock composite caused by acid erosion was revealed.（4）The physical parameters of the concrete-rock composite under high temperatures after the acid attack were measured,and the mass and wave velocity of the concrete-rock composite changed with the chemical attack and temperatures.Then,uniaxial compression test was carried out on the concrete-rock composite to study the relationship between physical and mechanical parameters with temperatures and p H values.And the deterioration effect and failure process of the samples after high-temperature and chemical erosion were studied in combination with energy evolution,acoustic emission characteristics and failure mode during loading.Finally,established the damage evolution constitutive equation of the samples considering the damage effects of chemical erosion and high temperature.Through the experiment comparison,verify the applicability and reliability of the constitutive model.（5）Nuclear magnetic resonance technology（NMR）and X-ray diffraction（XRD）were used to observe the pore changes and mineral evolution of the concrete-rock composite.And analyzed the influence of high temperature,initial preloading and p H value of the chemical solution on the T₂spectrum,nuclear magnetic imaging and XRD characteristics of the samples.The results showed that high temperature and chemical erosion increase the peak area of the T₂spectrum,and the bright spots of NMR imaging increase,indicating that the number of microscopic pores increases,pore size increases,and pore cracks develop and widen.Moreover,the mineral composition changed with temperature and chemical erosion.Based on the micropore and mineral evolution of the samples,the microscopic damage characteristics were studied.The macroscopic mechanical deterioration and damage mechanism of the concrete-rock composite was revealed from the microscopic point of view.This study provides guidance and suggestions for engineering design,construction and operational monitoring of bedrock concrete structures in complex environments.