Meso-numerical Simulation And Study On Size Effect Of Compressive Strength Of Recycled Concrete

As a green building material,recycled concrete not only solves the problem of construction waste accumulation,but also alleviates the problem of building material shortage.The mechanical properties of recycled concrete are more discrete and poor compared with ordinary concrete because the recycled coarse aggregate is wrapped with the residual mortar with poor mechanical properties.Size effect exists in the mechanical properties of ordinary concrete,that is,the mechanical properties decrease with the increase of size,while the size effect of recycled concrete is more significant due to the influence of recycled coarse aggregate.Due to the limitation of test conditions,it is often impossible to obtain more effective data at a smaller test cost in the experimental research on the size effect of recycled concrete.However,the meso-numerical simulation of recycled concrete can break through the restriction of test conditions and obtain more effective data.The use of meso-numerical simulation to study the size effect of recycled concrete not only verifies the validity of the classical theory of size effect of recycled concrete in a large size range,but also makes it convenient to study the size effect phenomenon of recycled concrete from a meso-perspective.The work of this paper mainly includes the following three aspects:(1)From the meso-level,the recycled concrete was regarded as a five-phase composite material composed of natural coarse aggregate,old interfacial transition zone,old mortar,new interfacial transition zone and new mortar,and a random aggregate model of recycled concrete was established and verified.The prediction formula of cement mortar strength is applied to improve the application range of recycled concrete meso-model.By comparing and analyzing the simulation results with the experimental results,the feasibility of the random aggregate model to simulate the size effect phenomenon of recycled concrete under different substitution rates was verified,and the simulation error was less than 3.7%.Therefore,the random aggregate model of recycled concrete with defects proposed in this paper can be applied to predict the compressive strength of recycled concrete with different sizes.(2)Based on the effective model,the effects of strength grade of recycled concrete,replacement rate of recycled coarse aggregate,strength grade of matrix concrete and content of residual mortar on the size effect of recycled concrete were simulated and analyzed.Based on the random aggregate model with defects and the energy size effect,the size effect formula of recycled concrete was deduced.(3)In view of the well-developed experimental research direction of size effect of recycled concrete,the design of material property experiment scheme,cylinder size effect experiment scheme and round steel pipe size effect experiment scheme was carried out.The design of measuring scheme of full stress-strain curve of large size specimen was carried out.The feasibility of measuring radial stress of concrete filled steel tube with BW micro earth pressure chamber is studied.