Life cycle assessment of construction and demolition waste-based geopolymers suited for use in 3-dimensional additive manufacturing

This study performs a life cycle assessment (LCA) on a novel process to produce geopolymer binders for 3-dimensional additive manufacturing (3D-AM). The method utilises construction and demolition waste (CDW) [hollow brick (HB), red clay brick (RCB), roof tile (RT), and glass (G)] as a sustainable resource for geopolymers production to replace Portland cement. The life cycle assessment is performed to identify hotspots (relevant processes or raw material) to improve the environmental performance of the whole process at an early stage of development and to evaluate the environmental impacts of energy, water, and waste emissions at various points in the life cycle. The CDW requires crushing, milling/grinding, and mixing with electrical input to produce the geopolymer binders. The alkali activators' composition [6.25M NaOH, 10% Ca(OH)₂] is selected as the base case for the assessment. The life cycle impact assessment (LCIA) results show the environmental impacts to be 635 (kg CO₂ eq.), 5.06 (kg SO₂ eq.), 0.104 (kg N eq.), 3.14E-10 (kg N eq.), and 12.2 (CTUe.) for the global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), ozone layer depletion potential (ODP), and Ecotox air respectively for 1 m³ of geopolymer binder produced. Electricity contributes over 60% to the GWP, AP, EP, and Ecotox Air; therefore, a sensitivity analysis is performed with varying sources of renewable electricity. Also, compared to ordinary Portland cement (OPC), the GWP for the geopolymer binder produced is 21% less.