3D printed concrete with sewage sludge ash: Fresh and hardened properties

In this study, the possibility of application of sewage sludge ash (SSA) in 3D printed concrete (3DCP) technology was explored. The replacement of partial cement with SSA in the concrete mix design was investigated, followed by a comprehensive analysis of its impact on the workability, printability, and mechanical properties of the 3DCP. The findings indicated that the incorporation of SSA accelerated the loss of workability of 3DCP, such as fluidity and consistency. However, it significantly improved the green strength and buildability. Further investigation revealed that the addition of SSA hampered the hydration process of cement, resulting in a reduction in the mechanical properties of the hardened material. CT scanning indicated that the addition of SSA increased the interlayer porosity, leading to further degradation of the mechanical properties. The toxicity characteristic leaching procedure demonstrated that the maximum leaching concentration of 3DCP incorporating SSA was 0.14 mg/L. This result confirmed the effective immobilization of heavy metals, fulfilling the prerequisites for the application of 3DCP incorporating SSA.