Study on rheological properties and mechanical properties of double-mixed recycled coarse and fine aggregate concrete

While recycled aggregates are widely studied, the dual effects of recycled coarse and fine aggregates on concrete rheology-mechanical synergy remain unclear. In order to promote the comprehensive treatment of various solid wastes in the construction industry, the working properties, rheological properties, mechanical properties, and microstructure of recycled concrete were measured by using recycled aggregate as the alternative material of concrete aggregate and C40 as the trial strength, and the substitution rates of recycled aggregate were 25%, 50%, 75% and 100%. The results show that with the increase in the content of recycled coarse and fine aggregates, the workability of concrete becomes worse, the overall trend decreases, and the yield stress and plastic viscosity increase. The mechanical properties decreased with the increase in recycled aggregate content and had the greatest influence on the tensile strength of splitting, followed by the compressive strength and the elastic modulus. Scanning electron microscopy and pore structure analysis showed that the air content, specific surface area, and spacing coefficient of the microcracks inside the recycled concrete structure were greater than those of natural concrete, resulting in a non-dense structure of the recycled concrete and high water absorption, which affected the mechanical properties and fluidity properties of the concrete.