The essential difference between recycled concrete and ordinary concrete lies in the existence of old mortar,which is the main factor affecting the mechanical properties of recycled concrete.A discrete element numerical model of recycled concrete under uniaxial compression is established based on DEM software,and the mechanical response and crack propagation mechanism of recycled concrete under uniaxial compression are simulated.The reliability of the numerical model is verified by comparing with the existing experimental data.The results show that when the strength of old mortar is low,the uniaxial compressive strength and elastic modulus decrease and the peak strain increases with the increase of thickness.When the strength of old mortar is high,the thickness of old mortar has little influence on the compressive properties of recycled concrete.From the microscopic perspective,the crack first appears in the interfacial transition zone under uniaxial compression load,and gradually expands to the new and old mortar until the penetration failure,which is dominated by tensile crack.In addition,the proportion of shear crack increases with the increase of loading rate.
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