Workability and hardened properties of 3D printed engineered cementitious composites incorporating recycled sand and PE fibers

3D concrete printing technology has seen rapid development due to its high digitalization and automation. Using recycled sand from solid waste construction resources to replace natural sand has great environmental and economic benefits. The objective of this study was to investigate the workability and anisotropic hardened properties of 3D printed engineered cementitious composites (3DP-ECC) incorporating recycled sand. Effects of recycled sand replacement ratio, fiber content, and printing direction on workability and hardened mechanical properties of 3DP-ECC were investigated. The test results show that the addition of recycled sand reduced fluidity, while strengthened buildability of 3DP-ECC. Compressive strength of the casted concrete dropped 2.1% and 7.2% when the replacement ratio of RS was set at 50% and 100%, respectively. The highest compressive strength in X axis of the 3D-printed specimens was observed. At 100% replacement ratio of recycled sand, the tensile strain capacity of both casted and 3D printed specimens increased by 57% and 55% respectively, compared with the reference group with natural sand. It is demonstrated that the ductility of the proposed 3DP-ECC could be significantly improved. The proposed 3DP-ECC incorporating recycled sand provides a potential solution for utilization of sustainable 3DP concrete in large-scale 3D concrete printing construction.