Meso-mechanical Properties Of Recycled Concrete Based On Elliptical (Spherical) Random Aggregate Model

Recycled concrete is a green ecological environmental protection building material,and its application prospect is extensive.At present,many researchers have carried out related research on recycled concrete and obtained certain research results.Related model tests mainly study the overall macro damage and failure of recycled concrete under stress,but it is often difficult to achieve the damage development process of recycled concrete in meso-structure and the interaction degree of each phase meso-component under loading.The finite element numerical simulation method can realize the in-depth study on the mechanical mechanism of recycled concrete and the properties of each phase material from the meso-level.In this paper,the shapes of recycled concrete aggregate are simplified into ellipses and ellipses,and the finite element software program of ABAQUS based on Monte Carlo method,Fuller gradation and Python language is developed.Based on natural aggregate,the interface area,old hardened mortar,external surface area and new hardened mortar phase material of the recycled concrete mesoscopic structure of 2 d and 3 d model,carried out with recycled aggregate replacement rate,each phase micromechanical components of material strength and phase boundary layer thickness for the numerical simulation analysis of variable parameters,This paper systematically studies the key performance indexes of recycled concrete under uniaxial stress,and puts forward some conclusions which have practical value for engineering practice.The main research results are as follows:(1)It is assumed that the recycled aggregate is composed of five-phase meso-materials,such as natural aggregate,inner interface area,old hardened mortar,outer surface area and new hardened mortar.Based on Monte Carlo method,Fuller gradation formula and Python language,the random aggregate model construction algorithm of 2-D elliptical and 3-D ellipsoid recycled aggregate concrete is developed.This algorithm realizes the automatic processing of the post-processing technology of ABAQUS software,such as grid division,boundary conditions setting,constraints loading and submission calculation,and can efficiently and quickly simulate the recycled concrete.(2)Two dimensional elliptical mesoscopic models of recycled concrete with aggregate replacement rates of 30%,45%,60%,75%and 90%and three dimensional ellipsoid models with aggregate replacement rates of 0%,30%,50%,70%and 100%were constructed respectively by using self-compiled algorithms.The established calculation model is controlled by the random aggregate particle size function and the random aggregate release function in the self-programmed algorithm,which can realize the random distribution of aggregate particle size and aggregate position,which shows that the algorithm is reasonable and effective.(3)Uniaxial force simulation analysis was carried out on the calculation model of recycled concrete under different replacement rates of recycled aggregate.The results show that the greater the proportion of recycled aggregate,the weaker the mechanical properties of recycled concrete.The mechanical properties of recycled concrete are different in each phase,and the stress and stress distribution in the recycled concrete are different.The main reason for the damage of recycled concrete is that the tensile stress and shear stress which exceed the stress limit of the specimen inside the model lead to the stress concentration phenomenon in the internal weak area.(4)The mechanical strength of the four phase composite materials,such as inner interfacial transition zone,new hardened mortar,old hardened mortar and new interfacial transition zone,was taken as the variable,and the uniaxial force numerical simulation analysis was carried out for the calculation model of recycled concrete with different strength material components.The analysis shows that the strength of components in different surface areas has different effects on the strength and strain performance of recycled concrete,and the different strength of new and old mortar has a great influence on the strength performance of recycled concrete.(5)The thickness values of the four phase composite materials,such as the inner interfacial transition zone,the old hardened mortar,the outer surface transition zone and the new interfacial transition zone,were taken as variables,and the uniaxial force numerical simulation analysis was carried out on the calculation model of recycled concrete established by the material groups with different thicknesses.The analysis shows that the thicker the hardened mortar is,the weaker the mechanical properties of recycled concrete are,which indicates that the content of hardened mortar in recycled concrete has a great influence on the mechanical properties of recycled concrete.The effects of interfacial transition zone,new interfacial transition zone and external transition zone on the mechanical properties of recycled concrete are relatively low.