Enhancing effect and mechanism of blast-furnace slag in one-part geopolymers from alkali-fused marine waste

Incorporating ground granulated blast-furnace slag (GGBS) into low-calcium geopolymers is a strategy that has proven effective for boosting the performance of geopolymer binders synthesized from inherently inert aluminosilicate precursors. This work investigates the enhancement effect and mechanism of GGBS incorporation in one-part geopolymer binders produced from alkali-fused marine wastes (AMW) comprising of marine clay and oyster shell. Experimental results demonstrate that the GGBS incorporation drives significant microstructural refinement of AMW-based geopolymers, evidenced by 50% reduction in critical pore size and 50.9% increase of compressive strength, with merely 20 wt% GGBS incorporation. This performance enhancement of AMW-based geopolymers owes to the compositional and microstructural modification, resulted from activation of GGBS by the high alkalinity provided by the AMW. The supplementary calcium and aluminosilicate released from GGBS reaction act as structural units that refine the pores, concurrently strengthen the gelation product of AMW-based geopolymers. Such chemical modification transforms the original Na‑dominant, loose gel in (slag‑free) geopolymers into a calcium-rich, compact one. However, when GGBS addition exceeds the activation capacity of the available alkalinity from AMW, further improvement in performance stagnates. Furthermore, GGBS incorporation substantially mitigates environmental impact of the synthesized AMW-based one-part geopolymers, with up to 56% reduction in embodied carbon emissions.