Meso Numerical Simulation Of Mechanical Properties Of Hydraulic Large Aggregate And Wet Screened Concrete

Large volume concrete structures in hydraulic engineering often use three or even four graded concrete,with a maximum aggregate size of 150 mm.Therefore,wet screened concrete standard specimens are commonly used to replace them in mechanical tests.However,due to the significant difference in mechanical properties between the two types of concrete,the mechanical indicators of wet screened concrete cannot truly reflect the mechanical properties of hydraulic large aggregate concrete.Based on this,this article takes the wet screening effect of hydraulic large aggregate concrete as the research object,and from a microscopic perspective,uses three loading methods:uniaxial compression,uniaxial tension,and dynamic uniaxial compression to explore the changes in static and dynamic mechanical properties of hydraulic concrete materials.It analyzes the stressstrain relationship,failure mode,crack number,and internal contact force,as well as the relationship between wet screening effect and dynamic effect.The main content includes:(1)In order to investigate the differences in the mechanical properties of hydraulic and wetscreened concrete under uniaxial compression,numerical specimens of three-stage concrete were established using the PFC 2D particle flow discrete element software,and the stress-strain relationships obtained from the numerical simulations of uniaxial compression were compared with the experimental data available in the literature to calibrate the fine-scale parameters between mortar particles,between coarse aggregate particles and between mortar and coarse aggregate interfaces in hydraulic concrete.These parameters were then assigned to the wet-sieved concrete for uniaxial compression numerical simulations.The results show that the peak uniaxial compressive stresses in wet sieved concrete are 1.20-1.25 times higher than those in large aggregate concrete,and the strains at the peak are 1.35-1.73 times higher than those in large aggregate concrete,using the same fine-scale parameters;(2)In order to investigate the effect of wet sieving on the uniaxial tensile mechanical properties of hydraulic concrete,numerical specimens of tertiary concrete were established using the PFC 2D particle flow discrete element software,and the fine parameters of mortar particles,coarse aggregate particles and mortar-coarse aggregate interface in the hydraulic concrete simulations were calibrated according to the available literature data.The results show that the macroscopic mechanical indices of hydraulic and wet-sieved concrete under uniaxial tension are less inaccurate than the macroscopic basic parameters of physical tests and that the wet-sieving effect of the macroscopic mechanical properties of hydraulic concrete is directly related to the relative number of microcracks and the distribution of contact forces within the concrete.(3)In order to investigate the effect of loading rate on the mechanical properties and damage morphology of wet-sieved concrete,fine-scale numerical specimens of tertiary and wet-sieved secondary concrete were established using particle flow discrete element software,and the finescale parameters between mortar particles,between coarse aggregate particles and between the contact surfaces of mortar particles and coarse aggregate particles in the numerical specimens were calibrated based on the proposed static uniaxial compression(strain rate 10-5s-1)test data Dynamic loading with strain rates of 10-4s-1,10-3s-1 and 10-2s-1 was carried out to analyze the dynamic mechanical properties and their mechanisms.The results show that the compressive strength of tertiary concrete increases by approximately 21% to 38% compared to the compressive strength at rest,and the growth rate of wet-sieved secondary concrete is 7.3% to 37.9%,with a small increase in strain at the peak stress;the growth rate of the number of cracks is 6 to 8 times that of the peak stress.