Numerical Study On The Meso-failure Of Recycled Concrete Based On Real Aggregate Model

On the premise of hypothesis of homogeneous medium,the macro test can not further study the RC, at meso-level the research is in need on the impact of RC internal components on RC macro mechanical properties.In the paper, a numerical analysis method is used to study the failure process of recycled concrete, mechanical properties of recycled concrete and the influence factors.Using MATLAB the image processing software, and combining the image predisposing, image segmentation transformation, median filtering noise, morphological image processing, the edge detection and geometry vectorization algorithms, the real aggregate numerical model of recycled concrete can be established. At meso-level, the RC be regarded as a heterogeneous six-phase composite material: natural aggregate,the old mortar,the new mortar, the interface transition zone of new mortar and natural aggregate(ITZ1), the interface transition zone of new mortar and old mortar(ITZ2), the interface transition zone of old mortar and natural aggregate(ITZ3). According to the mechanical properties of each phase material in RC and by using the automatic dynamic incremental nonlinear analysis software, the meso damage process and the macro mechanical properties of RC specimens can be simulated and analyzed under uniaxial tension/compression.By contrasting the simulation results and the test results, the established RC real meso model is verified reasonable. The parameters of RC is changed to find the influence on RC macro mechanical properties from the different mechanical parameters of natural aggregate, interface transition zone and the new/old hardened mortar.The study in this paper shows that the real aggregate model can more truly simulate the damage process of RAC under external loads compared with other meso-mechanical models, such as a random aggregate model, and can more accurately describe the macro-properties of heterogeneous concrete.the results of the real aggregate model are in a better agreement withthe experimental data. The natural aggregate has great influence on the damage process and damage path, but less influence on elastic modulus and strength of concrete. If the natural aggregate elasticity coefficient is oversized, the stress concentration phenomenon is even more obvious. The strength and rigidity of RAC linearly change with the changed mechanical properties of new hardened mortar. The old hardened mortar has little effect on the macroscopic mechanical properties of RAC. The concentration of tensile stress and shear stress appear in new and old ITZs, and the strength of ITZs has little effect on the macro mechanical properties of RAC. This paper can provide technical supports for the engineering practice of RAC and provide references for further study on meso properties of recycled concrete.