3D printing of recycled materials for sustainable construction: A comprehensive economic and life cycle assessment

The demand for sustainable materials and technologies has risen due to the construction sector's substantial impact on the ecosystem, natural resources and human health. Therefore, this study aims to investigate the sustainability potential of recycled materials for the construction 3D printing (3DP) process. Mortar mixtures are designed using recycled binder materials (fly ash and blast furnace slag) and aggregate materials (waste concrete-based recycled fine aggregate (RFA)) for the 3D printing process. The adequacy of different geopolymer mixtures for the printing process is assessed through the open time, slump and spread diameter. The results showed that geopolymer mixtures containing RFA offered adequate fresh properties and more dimensional stability for the 3D printing process. The compression testing of the RFA-based geopolymers (along with different testing orientations) also yields better strength than the natural fine aggregate (NFA) in 3D printing. Apart from lab-scale experimentation, a case study of 3D printed and casted walls (using NFA and RFA based geopolymer mixtures) has been considered for comprehensive economic and life cycle analysis (LCA). The results showed that the 3D printed wall using RFA offered a lower burden on the ecosystem, natural resources, and human health; moreover, the lowest cost was observed in the case of the 3D printed wall containing RFA. The higher overall environmental and economic impact of casted wall was primarily due to the usage of plywood formwork. Sensitivity analysis showed that reusing formwork up to 10 times can potentially reduce economic and ecological burdens, depending on construction complexity, but still, traditional construction's overall burden remains higher than 3D printing. As 3D printing technology matures and economies of scale are realized, 3D printing is expected to reduce costs and environmental impacts further.