Feasibility analysis of 3D printed concrete with sludge incineration slag: Mechanical properties and environmental impacts

Abstract

This study substituted sludge incineration slag for natural sand in the application of 3D printed concrete technology (3DCP). It analyzed the influence of the sludge incineration slag incorporation on the workability, printability, mechanical properties, and the solidifying effect of heavy metals in 3DCP. Furthermore, the environmental and economic benefits were also examined. The results indicated that the incorporation of sludge incineration slag accelerated the loss of workability factors such as flowability and consistency in 3DCP. However, it significantly enhanced the early strength of 3DCP and improved its constructability. Additionally, the addition of sludge incineration slag diminished the mechanical properties of 3DCP. When the substitution rate reached 50% of natural sand with sludge incineration slag, the strength of the 3D printed specimens decreased by 22.1%. Experimental investigations at a micro-scale indicated that the porosity of interlayer interfaces was a crucial factor causing strength reduction and could be ameliorated by appropriately increasing the extrusion amount to address excessive pore sizes. Toxicity leaching tests for heavy metals demonstrated that the maximum heavy metal leaching concentration in 3DCP specimens with sludge incineration slag incorporation was 0.14mg/L, meeting the specified requirements. The 3DCP with sludge incineration slag incorporation not only addressed the difficulty in handling incineration bottom slag but also conserved natural sand resources, presenting outstanding environmental and economic benefits. For instance, by substituting 100% natural sand with sludge incineration slag, there were 5% reduction in carbon emissions and 30% increase in economic benefits.