Hardened properties of layered 3D printed concrete with recycled sand

3D concrete printing has received worldwide attention while the development on new cementitious material compositions for 3D printing is inadequate. This study employed the recycled sand instead of natural sand to achieve 3D concrete printing and investigated the hardened properties of this extrusion-based material. The effect of replacement ratio of recycled sand, curing age, nozzle height and anisotropic behavior were evaluated based on the compressive tests, tensile splitting tests and flexural tests. Moreover, the digital image correlation (DIC) technique was adopted to capture the strain behavior and failure pattern of this layered and printed concrete. Owing to the high un-hydrated cement paste attached to the recycled sand and the internal curing mechanism, the compressive and flexural strengths of the 3D printed concrete with recycled sand were a little lower than those specimens without recycled sand. The compressive, tensile splitting and flexural strength of 3D printed concrete with recycled sand had obvious anisotropy. The replacement of recycled sand had limited effect on the anisotropy of compressive and flexural strength, but had certain effect on the tensile splitting strength. Since recycled sand is one of those major products derived from the construction and demolition waste, it is believed that the employment of recycled sand to the mix of 3D printed concrete will significantly improve the sustainability of 3D printed concrete structures.