| With the rapid development of China’s transportation industry,high-performance concrete(HPC)is more and more widely used in major projects.However,due to the erosion of various factors such as environment and load in the long-term use process,there are potential safety hazards such as cracks,pavement subsidence,and pier fracture.Therefore,it is necessary to crush and dismantle these structures with potential safety hazards.Considering the shortcomings of traditional crushing technology,such as limited crushing capacity and low precision,the new concrete crushing technology,high-pressure water jet technology,is applied to the crushing field of HPC to improve the accuracy and efficiency of such structures in the emergency demolition process.In view of this,this thesis carried out abrasive water jet(AWJ)impact HPC experiments to observe the external macro-fracture morphology and crack propagation characteristics.Based on the computer tomography(CT)equipment,the internal damage scanning experiment of HPC after AWJ impacting was carried out,and the distribution characteristics of internal damage were revealed by image processing technology and MATLAB program language.Scanning electron microscopy(SEM)was carried out to analyze the fracture morphology of typical fracture sites.Based on the coupling method of smoothed particle hydrodynamics(SPH)and finite element method(FEM),a numerical model of AWJ impact HPC was constructed to reveal the damage mechanism.Finally,the concept of comprehensive damage factor is introduced to quantify the internal damage of concrete and explore the damage evolution characteristics and parameter influence law.The main conclusions are as follows:(1)The external macroscopic failure characteristics of HPC show that the crushing pit is small,which presents the ‘V’ funnel-shaped,ranging from 2.3 to 5.7 cm,and the depth of erosion pit is in the range of 0-5.2 cm.The cracks extend horizontally and vertically with the crushing pit as the center.There is only one continuous transverse penetrating crack on the impact surface,and the impact side is accompanied by radial vertical splitting crack.(2)The internal damage distribution of HPC is characterized by more mortar cracks and penetrating cracks with fewer cracks along the bone,and the cracks mainly expand in the form of vertical splitting or oblique penetration.The internal damage evolution shows a nonlinear attenuation trend,including two stages of rapid attenuation zone and slow attenuation zone.The rapid attenuation zone is about 24 times the jet diameter near the erosion pit,while the slow attenuation zone is about 48 times.The average attenuation rate of the former is about 4 times that of the latter.(3)The micro fracture morphology of HPC is brittle fracture,the crack grow is coherent,the evolution path is single and the development path is long,there is no obvious fine derivative crack,the fracture surface of mortar is flat,and the fracture surface of aggregate is smooth ‘cliff’ morphology.(4)The formation process of HPC crushing pit is that the surface particles of the crushing pit produced compression-shear failure under the continuous action of high intensity stress field,and the particles deform and fail,which leads to the continuous evolution of damage to the axial and radial directions,and eventually forms an approximate ‘V’ funnel-shaped crushing pit.The crack is developed by three stages:initial vertical crack derivation,polymorphic crack derivation and final crack evolution.There are three main mechanical damage mechanisms: tensile failure,compressive-shear failure and tensile-shear failure.(5)The internal damage distribution of HPC is more concentrated,the local effect is obvious,and the damage development path is more single.The transverse and longitudinal damage attenuation rates are 3.28 times and 1.51 times that of ordinary concrete,respectively.In addition,the optimum initial parameters of AWJ crushing HPC are abrasive concentration 15%,jet diameter 2 mm and pump pressure 300 MPa. |
PDF Full Text Request