Early-age hydration of an EAF slag based alite–ferrite cement clinker in the presence of Na2CO3

Reducing the CO2 burden of cement manufacturing can be achieved by increasing the ferrite content in cement as ferrite requires less calcium than other major clinker phases and thus reducing CO2 emission from limestone (mainly CaCO3) calcination. The steel industry produces vast and increasing amounts of EAF (electric arc furnace) slag that consists of calcium, silicon, and iron oxides from scrap steel recycling. Clinkers manufactured using EAF slag as the major component will have a higher ferrite content than traditional clinkers, as EAF slags are rich in iron. The ferrite phase is generally less reactive in polyphase than other major clinker phases; thus, accelerating ferrite hydration by adding carbonates is assessed in this study. Alite-ferrite clinker was produced from EAF slag and pure natural materials at 1450 ºC and the hydration was studied in the presence of dissolved Na2CO3, a low-cost bulk/industrial chemical that provides labile carbonate during the hydration process. The hydration kinetics at different Na2CO3 dosages and water-to-binder ratios were measured using isothermal calorimetry, and the hydrated phases were determined with TGA and XRD. The Na2CO3 dosage increased the ferrite hydration as the monocarboaluminate peak in the XRD data increased with Na2CO3 dosage. We found that there is an optimum soda ash dosage (2.5% by mass of clinker for w/b = 0.35, and 5% by mass of clinker for w/b = 0.45) to accelerate the major alite hydration peak, as confirmed from the calorimetry data and the portlandite content indirectly observed from the XRD and TGA data.