Circular binder design using CDW and conventional precursors: Engineering and environmental performance assessment

This study investigates the feasibility of developing geopolymer binder systems using construction and demolition waste (CDW)—specifically brick waste (BW) and concrete waste (CW)—as primary precursors, in combination with varying mix parameters and supplementary cementitious materials (SCMs) such as blast furnace slag (BFS), silica fume (SF), and metakaolin (MK). The engineering properties of the mixtures were evaluated through flow table, buildability, and compressive strength tests under ambient curing conditions. Moreover, A life cycle assessment (LCA) was conducted to benchmark the environmental performance of the developed systems against a hybrid Portland cement-based reference. Results showed that increasing NaOH molarity and the proportion of CW enhanced flowability but decrease buildability performance. A higher aggregate-to-binder ratio improved shape stability despite reducing flowability. The addition of BFS and SF resulted better workability, while replacing MK with CDW-based precursors led to decreased flow performance. Higher NaOH molarity and the incorporation of Ca(OH)₂ notably enhanced compressive strength. While 100 % CDW-based mixtures yielded compressive strengths ranging from 4 to 10 MPa after 28 days, blends incorporating SCMs achieved strengths between 8 and 26 MPa. Additionally, LCA results showed that CDW-based geopolymers demonstrated up to 69 % lower environmental impacts in key categories compared to a hybrid Portland cement reference, highlighting their potential as a sustainable binder alternative.