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.

3D混凝土印刷受到了全世界的关注，而用于3D打印的新型胶凝材料组合物的开发还不够。这项研究使用再生砂代替天然砂来实现3D混凝土打印，并研究了这种挤出型材料的硬化性能。根据压缩试验，拉伸劈裂试验和弯曲试验评估了再生砂替代率，固化时间，喷嘴高度和各向异性行为的影响。此外，采用数字图像相关技术（DIC）来捕获这种层状和印刷混凝土的应变行为和破坏模式。由于附着在再生砂上的高未水合水泥浆和内部固化机理，含再生砂的3D打印混凝土的抗压强度和抗弯强度比不含再生砂的3D打印混凝土的抗压强度略低。带再生砂的3D打印混凝土的抗压，抗拉劈裂和抗弯强度具有明显的各向异性。再生砂的替代对抗压强度和抗弯强度的各向异性影响有限，但对拉伸劈裂强度有一定影响。由于再生砂是源自建筑和拆除废物的主要产品之一，因此，相信将再生砂用于3D打印混凝土的混合物将显着提高3D打印混凝土结构的可持续性。再生砂对3D打印混凝土的拉伸劈裂和抗弯强度具有明显的各向异性。再生砂的替代对抗压强度和抗弯强度的各向异性影响有限，但对拉伸劈裂强度有一定影响。由于再生砂是源自建筑和拆除废物的主要产品之一，因此，相信将再生砂用于3D打印混凝土的混合物将显着提高3D打印混凝土结构的可持续性。再生砂对3D打印混凝土的拉伸断裂和抗弯强度具有明显的各向异性。再生砂的替代对抗压强度和抗弯强度的各向异性影响有限，但对拉伸劈裂强度有一定影响。由于再生砂是源自建筑和拆除废物的主要产品之一，因此，相信将再生砂用于3D打印混凝土的混合物将显着提高3D打印混凝土结构的可持续性。