Properties and hydration mechanism of eco-friendly binder from circulating fluidized bed bottom ash, carbide slag, and desulfurization gypsum

Circulating fluidized bed bottom ash (CFB BA), the by-product of thermal power plants, poses environmental threats if treated improperly. This study investigated a novel treatment method of CFB BA to prepare an ecofriendly binder with carbide slag (CS), and flue gas desulfurization gypsum (DG). Results revealed that CS and DG showed the synergistic excitation of CFB BA and the alkaline environment provided by CS played an instrumental role in the mechanical properties, particularly in the later stage. The optimal mixture with 70 % CFB BA, 15 % CS and 15 % DG achieved 50.43 MPa at 28d and 60.97 MPa at 90d. Comprehensive characterization by XRD, FTIR, TG-DSC, and SEM-EDS revealed that the primary hydration products, C-(A)-S-H gels and ettringite, formed a robust and compact microstructure, significantly enhancing strength. SEM-EDS demonstrated the more uniformly distributed C-(A)-S-H gels and thicker ettringite with an average width of 0.26 mu m in C70, while that of C60 and C80 were 0.12 mu m and 0.16 mu m, respectively and MIP exhibited the lowest porosity of 27.99 % in C70. Additionally, leaching tests confirmed that heavy metal concentrations in the binder were below the limits of drinking water standards in China, demonstrating significant environmental safety. This work bridges gaps in understanding the hydration mechanisms of CFB BA-based binders and offers a sustainable solution for industrial waste management.