Mechanism of the Influence of Multi-Scale Pore-Structure on the Triaxial Mechanical Properties of 3D Printed Concrete with Recycled Sand (2024-07)¶

The mechanical properties of concrete when subjected to triaxial compression are crucial for designing structures. In this study, environmentally friendly 3D printed recycled mortar (3DPRM) was prepared with recycled sand at 0%, 50%, and 100% replacement rates. The pore structure and mechanical properties of the 3DPRM under triaxial compression, taking into account the influence of replacement rate and anisotropy, were investigated. The results showed that the plane porosity of the 3DPRM specimens was uniformly distributed along the X-direction, while the plane porosity along the Y and Z directions increased at the filament-fusion interface and the layer-fusion interface. Although the incorporation of recycled sand marginally increased the porosity of the specimens, it did not alter the pore structure. During triaxial compression, the strength and confining pressure efficiency of the 3DPRM specimens exhibited significant anisotropy, with the order of strength being X > Y > Z direction. By establishing a multiscale stress equivalence model for typical pores influenced by stress concentration, the mechanism of recycled sand replacement rate affecting the strength of specimens with different directions was revealed. Additionally, a two-stage stress-strain prediction model applicable to different replacement rates and directions was proposed.