Meso-Numerical Simulation On Mechanical Properties Of Fully Recycled Coarse Aggregate Concrete

As a kind of green and environment-friendly building material,recycled aggregate concrete can effectively use construction waste,solve the problems of natural stone consumption and waste generation,improve resource utilization efficiency and improve environmental quality.In this paper,theoretical analysis and numerical simulation are used to study the damage and failure mechanism of fully recycled aggregate concrete with the aggregate replacement rate of 100%,and the factors affecting the mechanical properties of recycled concrete are analyzed.The main research contents and achievements are as follows:1.A five-phase model of reclaimed concrete random aggregate was established.Based on Monte Carlo theory,the random convex polygon and spherical aggregate models of RAC are established,which are closer to the real aggregate shape.The comparison with the experimental results verifies the effectiveness of the models,and verifies the validity and feasibility of using the random aggregate model for finite element numerical analysis of RAC.2.The failure process of reclaimed concrete is analyzed.The results show that large particle size aggregate is the key to failure mode of RAC,and it spreads from the weak point of interfacial transition zone to the overall failure of mortar,which can be summarized as the process of fracture initiation,development and penetration.Whether under compression or tensile load,the concentration of tensile stress and shear stress and the accumulation of mesolevel damage caused by the load are the causes of RAC compression failure.However,the distribution of stress is different in the direction,and the failure causes are the same.3.Face constraint effect in uniaxial compression tests.The end face constraint effect has a significant influence on the failure mode of RAC,and with the increase of the end friction coefficient,the peak stress and strain increase to varying degrees.The unrestrained test block presents a fracture development mode similar to the splitting mode,while the fully restrained test block presents an inverted conical failure mode.Therefore,it is suggested that the friction coefficient μ should be greater than 0.8 in the numerical simulation.4.The influence of meso-composition on mechanical properties of RAC.Under uniaxial compression numerical test,new mortar,as the main load-bearing material except aggregate,has the largest energy absorption,so the strength of new mortar has the greatest influence,followed by old mortar,new interface transition zone,old interface transition zone in turn.In the splitting tensile numerical test,the effect of the old mortar is significantly improved relative to the axial compression condition.The influence degree of the tensile strength of the old mortar is higher than that of the new mortar,followed by the tensile strength of the old interface transition zone and the new interface transition zone.At the same time,the thickness of the old mortar has a significant effect on the mechanical properties of the reclaimed concrete.The strength decreases with the increase of the thickness of the old mortar,but the influence on the tensile strength is more significant.The meso-numerical analysis method of the random aggregate model of RAC proposed in this paper can provide a new research approach for the analysis of the mechanical properties of RAC,and also provide a theoretical reference for the promotion and application of RAC,which has important theoretical significance and engineering application value.