Effect of desulphurization gypsum on hardening mechanism of the geopolymer produced with steel slag and granulated blast furnace slag

Desulphurization gypsum (DG) is the by-product of wet desulphurization of flue gas in power plant, with a large yields and low resource utilization rate. However, it is rich in CaSO₄·2H₂O. This work reused the DG for the activation of steel slag (SS)-alkalied-granulated blast furnace slag (GBFS) and produced a DG–SS–GBFS-based geopolymer. The compressive strength, dehydrated polymeric products and their generation and micromorphology, and pozzolanic activity were studied. Results show that the DG–SS–GBFS-based geopolymer produced with 15 wt.% DG, 51 wt.% SS and 34 wt.% GBFS is 1.20 MPa and 14.66 MPa at 3 and 28 days, which is increased by 990.91% and 18.13% compared to that without DG; this increase is attributed to the fibrous AFt formed in the DG–SS–GBFS-based geopolymer. Also, the C-A-S-H gel and Ht phase were generated. The produced geopolymer’s pozzolanic activity is 84.19% (> 65.00% in accordance with GB/T 2847–2005 “Pozzolanic materials of Portland cement”) at 28 days, and no more than 30 wt.% of the DG–SS–GBFS-based geopolymer can be applied to the production of 42.5-grade composite cement specified in the GB 175–2020 “common Portland cement”. This work contributes to the reuse of DG on a large scale, which fits well with the concept of cleaner production.