Synergistic effect of DTPA-5Na and FGD gypsum on basic oxygen furnace slag-based cementitious materials

Basic oxygen furnace (BOF) slag remains underutilized due to its low reactivity. This study introduces a novel activation method combining pentasodium diethylenetriamine pentaacetate (DTPA-5Na) with flue gas desulphurization (FGD) gypsum to enhance slag dissolution and hydration. The advantages of the synergistic activation of BOF slag were assessed through mineralogical, thermal, and microstructural analyses. Results reveal that 1.0 wt% DTPA-5Na effectively boosts brownmillerite and belite reactivity through the chelation process, accelerating monocarboaluminate and C-S-H gel formation and raising compressive strength by 140% at 28 d. Synergistic use of FGD gypsum regulates calcium and sulphate release, promoting ettringite and hydrocalumite formation while reducing porosity by 31%. The binder achieves 35.8 MPa compressive strength (28 d) while meeting Dutch Soil Quality Decree leaching limits. The addition calcium can retard the hydration process, while the strength performance is related to the sulphate content. The developed hydration model indicates low water demand (0.22–0.26, water-to-binder slag ) and superior volume stability (chemical shrinkage 2.0–3.5 ml/100 g slag ) of BOF slag-based cementitious materials. These findings support the sustainable valorisation of BOF slag through low-dosage chelator activation combined with the concurrent recycling of sulphate-bearing industrial waste.