Ceramics-Silikáty 69, (1) 75 - 92 (2025)

As an environmentally friendly building material, recycled aggregate has broad application prospects in the digital construction of buildings. In this paper, 3D-printed recycled concrete with the simultaneous incorporation of recycled coarse aggregate and recycled fine aggregate was prepared, and research on its working and mechanical properties was carried out with the type of recycled aggregate and substitution rate as the parameters. The time-varying fluidity loss and yield stress of different recycled aggregate substitution rates were analysed, and the variation trend with the recycled aggregate substitution rate was explored. Its compressive strength and anisotropy were studied, and the mechanism of the influence of different types of recycled aggregates on the compressive strength was analysed in combination with low-field NMR experiments. The results show that the recycled fine aggregate significantly influences the flow properties of 3D-printed recycled concrete. Moreover, its effect is weakened with the recycled coarse aggregate replacement rate increase. The impact of the recycled fine aggregate on the dynamic yield stress was more significant than that of recycled coarse aggregate. In contrast, the opposite was true for the static yield stress; the recycled fine aggregate dominated the influencing factors of extrudability, and the recycled coarse aggregate dominated the influencing factors of constructability. The compressive strength was significantly reduced by either the single or double substitution of recycled aggregates in different printing orientations, with the effect of recycled coarse aggregate being more significant. The pore defect distribution characteristics of the 3D-printed recycled concrete varied with the layer height, and both recycled aggregates increased the porosity to a greater extent. It provides a theoretical reference for research into 3D-printed recycled concrete containing multiple recycled aggregates and its engineering application.