Durability of slag-fly ash blended geopolymer composites incorporating reject brine waste

This study investigates the incorporation of rejected brine waste (BW) into geopolymer (GP) composites made of different binder blends of blast furnace slag (BFS) and fly ash (FA), while varying the alkali-activated solution-to-binder (A/B) ratio. The mechanical and durability performance of the GP mortars was assessed through various tests, including compressive strength, bulk resistivity, water absorption, sorptivity, accelerated carbonation, and resistance to sulfuric and hydrochloric acid attacks. Microstructure characterization was carried out to evaluate the changes to the mineralogy due to acid exposure. Results indicated that the BW-based GP mixture composed of 100 % BFS with an A/B ratio of 0.55 exhibited superior mechanical and durability performance among all BW-based mixes. Furthermore, BW integration into the GP mortar had a limited impact on its performance, morphology, and durability and caused insignificant leaching of sodium, chloride, and sulfate ions. Yet, the electrical conductivity was marginally improved (up to 7 %) due to BW incorporation. Sulfuric acid exposure revealed the vulnerability of FA-rich mixes, with extensive gypsum formation and structural degradation. Compared to hydrochloric acid, GP composites exposed to sulfuric acid experienced up to 1.5 and 3 times less mass and strength retention, respectively. Microstructure analysis revealed the deterioration of crystalline and amorphous phases in GP composites having higher FA and alkaline solution contents upon acid exposure. These findings provide evidence for the ability to replace potable water with BW and cement with GP binders while also recycling industrial waste in cement-free composites. • Geopolymer composites were developed using desalination reject brine. • Geopolymers incorporating brine demonstrated similar durability performance to those produced with tap water. • Brine-based geopolymer composites achieved compressive strengths of up to 100 MPa. • The optimal mixtures for overall mechanical and durability performance contain 100 % BFS and an A/B of 0.5. • Geopolymers encapsulated anionic leachate from brine in its structure effectively without compromising its microstructure.