Mechanical properties and pore structure of 3D printed mortar with recycled powder

This study investigated the hardened mechanical properties of 3D printed mortar (3DPM) with different contents (0-30% by mass of cement) of recycled powder (RP) by anisotropic compressive, splitting tensile and flexural strengths. The pore characteristics tested by X-ray computed tomography and mercury intrusion porosimeter as well as hydration products of 3DPM were analyzed to reveal the influence mechanism of RP on 3DPM. The results showed that the highest compressive strength of the 3D printed specimens was obtained on the loading direction paralleled with the length of printing filament (X direction). When the RP replacement ratio was 20%, the X-direction compressive strength of 3DPM was 24.11% lower than that of cast samples, while the splitting tensile strengths of 3DPM were closed to and the flexural strengths of 3DPM were higher than that of cast samples regardless of the loading directions. This can be attributed to the high fluidity loss rate of 3DPM with RP, leading to the reduction of the surface moisture of interlayer. Besides, more pores at the interlayer and interstrips led to the decrease of mechanical properties. In contrast, the addition of RP had a limited effect on the micro pore structure of the single printed filament without considering the interlayer and interstrip, owing to the secondary hydration and filling effect of RP.