Sustainable 3D concrete printing : utilising industrial by-products and alkali-activated materials for low-carbon construction

In the past decade Additive Manufacturing of concrete has developed rapidly in the construction industry. This technology has addressed several challenges associated with old traditional casting methods, including eliminating the need for formwork, significantly reducing costs and labour intensity for projects. Additionally, it provides flexibility in creating complex architectural designs. However, the primary concern in 3D concrete printing is the substantial carbon emissions resulting from the heavy use of cement in the mixture (2-3 times higher than conventional concrete). A primary solution to address the impact of 3D printing material, and reduce the cement content in the concrete mix is achieved by utilising industrial by-products and/or recycled waste material as supplementary cementitious materials. The 3DConcrete Project (Research Excellence Programme, Xjenza Malta) addresses the development of low-carbon concrete for 3D concrete printing by incorporating Maltese globigerina limestone waste as a partial replacement of ordinary Portland cement to reduce the carbon footprint, without compromising on the required performance of the 3D printed elements. Furthermore, alkali-activated materials (AAMs) can be considered as promising alternative to cement. AAMs can be formed through a chemical reaction between a solid material rich in aluminosilicates with an alkaline solution. Specific sources of Construction and Demolition Waste with the right composition are exploited as ingredients for AAMs as an alternative to cement-based materials. The SMACORT project (TUBITAK, Xjenza Malta) investigates alkali-activated materials based on waste concrete developed for 3D concrete printing of facade cladding elements with enhanced performance. Ultimately, this study develops a novel type of 3D-printed concrete that offers both economic and environmental benefits, providing a promising solution for sustainable and low-carbon construction using 3D concrete printing.