Effects of circulating fluidized bed fly ash and desulfurization gypsum on the rheology and solidification of all-solid waste cementitious materials

To address the dual challenges of industrial solid waste accumulation and carbon emissions in the cement industry, this study innovatively develops high-performance all-solid waste cementitious materials (AWCM) using red mud (RM), circulating fluidized bed fly ash (CFBFA), desulfurization gypsum (DG), fly ash (FA), ground granulated blast slag (GGBS), and carbide slag (CS). The rheological, mechanical, and microstructural properties of three systems (CFBFA-RM-CS-FA, DG-RM-CS-FA, and DG-RM-CS-GGBS) were systematically investigated under the action of polycarboxylate (SPC) and naphthalene-based (SPN) superplasticizers. The results show that DG-RM-CS-GGBS achieved a 28-day compressive strength of 30.47 MPa at a water-to-binder ratio (w/b) of 0.4, significantly outperforming CFBFA-based formulations. Notably, SPC-enhanced pastes exhibited superior strength (compressive strength of SPC pastes was 4.2%–51.2% higher than that of SPN pastes) and faster setting times (at a 0.4 w/b ratio, the final setting time of the SPN paste was over 60% longer than that of the SPC paste). The effects of SPN and SPC on strength are mainly related to their influences on the morphology of ettringite generated during hydration. Rheological analysis demonstrated that all pastes conformed to the Herschel-Bulkley model. Increasing CFBFA by 25.2% increased the consistency coefficient by 1.058 Pa·sn (suitable for high w/b systems), while increasing DG by 14.8% reduced the yield stress by 4.687 Pa (suitable for low w/b applications). Microscopic tests revealed the critical role of calcium sulfate type in ettringite morphology: DG hydrated to produce more and more elongated ettringite than CFBFA.