Study On The Macro-microscopic Failure Characteristics And Damage Law Of Hydraulic Concrete Breaking

High pressure water jet crushing technology has broad application prospects in the demolition of concrete structure.Nevertheless,the high pressure water jet crushing technology still has many issues,such as high threshold pump pressure and large specific energy consumption,which is difficult to achieve local precision crushing.In the emergency demolition of concrete structures,the influence range of the crushing zone need be accurately controlled to avoid new security risks caused by the disorderly expansion of cracks.Therefore,through the experiment of the water jet crushing concrete,based on the computer tomography(CT)and scanning electron microscopy(SEM)technology,this research revealed the macro-micro fracture characteristics of concrete under water jet impact by analyzing the macro-micro fragmentation morphologies of concrete subjected to the water jet impact.In addition,this paper also established the numerical model of water jet impacting concrete based on the coupling algorithm of smoothed particle hydrodynamics(SPH)and finite element method(FEM),and by the comprehensive damage factor of concrete X,this paper further explored the damage law of concrete subjected to water jet impact.The main conclusions are concluded as follows:(1)The macroscopic failure characteristics of concrete subjected to water jet impact show that an irregular crater formed on the impacted surface of concrete,with the rough morphology and obvious aggregate exposure on the wall of the crater.Cracks near the crater penetrated the impacted surface of concrete,and there is a network structure composed of radial cracks and circumferential cracks on the lateral surface of concrete.The exploration of the crack propagation law and damage evolution law in concrete by means of CT scanning,image binarization method and grey-scale processing technology indicate that the cracks mainly propagated along the interfacial transition zone of concrete,which generates a small effect on the strength of the undamaged zone of concrete.The strong action area of water jet was limited to the range of about 20 times of the water jet diameter,and the weak action area of water jet was outside the range of 40 times of the water jet diameter.(2)By the comparative analysis of the microstructure of concrete section under the impacts of abrasive water jet and pure water jet,results indicate that there were obvious different microscopic failure characteristics in aggregate,matrix and interface transition zone of concrete.For the aggregate part,under the impact of abrasive water jet,there was a typical twisted “lip-shaped” fracture in the aggregate part,and a cliff-like flat failure occurred on the fracture surface,with shallow grooves with different sizes distributed on the fracture surface;under the impact of pure water jet,the overall crushing degree in the aggregate part was higher,and there were concave sections on the fracture surface,with spalling particles at the bottom of the groove.For the mortar matrix part,under the impact of abrasive water jet,the mortar matrix part was relatively flat,but severe wear traces and obvious wear particles appeared on the fracture surface;under the impact of pure water jet,a large number of micro cracks and micro holes formed in the mortar matrix part with the uneven fracture surface.For the interface transition zone,the mortar matrix and aggregate on the fracture surface were well connected in the interface transition zone under abrasive water jet impact,while there were obvious cracks in the interface transition zone under pure water jet impact.(3)Through the exploration of the damage law of concrete subjected to water jet impact,results show that the pump pressure of water jet has the greatest influence on the fragmentation degree of concrete.The influence of abrasive concentration C,target distance H,nozzle diameter d and nozzle convergence angle α on the fragmentation degree of concrete was followed,and the influence of nozzle cavity length L on the fragmentation degree of concrete was the smallest.The fragmentation degree of water jet impacting concrete decreased first and then slightly increased with the increase of the d value.The fragmentation degree of concrete impacted by water jet increased significantly at first and then slowly increased to a stable state with the increase of the α value.As the L value increased,the fragmentation degree of concrete under water jet impact decreased.With the increase of the C value,the fragmentation degree of concrete was greatly improved,and when the abrasive concentration was higher than the optimal abrasive concentration,the fragmentation degree of abrasive water jet impact on concrete was no longer significantly improved with the increase of the C value.The overall fragmentation degree of concrete under water jet impact increased with the increase of the P value.The overall fragmentation of concrete under water jet impact first increased and then decreased with the increase of the H value.Under the conditions of water jet parameters in this research,the optimal combination of water jet parameters was as follows: the d value,the α value,the L value,the C value,the P value,and the H value were 2.5 mm,45°,6 mm,20 %,100 MPa,and 3 mm,respectively.