Clinker-Free Cement Manufactured with Metallurgical Slags

Steel slag is a significant environmental liability generated by pyrometallurgical processes. Residue generation, such as granulated blast furnace slag and basic oxygen slag (BOF), is intrinsic in steel production. Blast furnace slag, generated in the carbothermal reduction of iron ore, is almost entirely used as a supplementary cement material in Portland cement. BOF slag, produced in the conversion of pig iron into steel in a basic oxygen converter, is still not consolidated or valued for reuse. This research proposes the reuse and valorization of BOF slag combined with blast furnace slag in clinker-free cement production. Cement formulations were produced with different slag and gypsum contents, ranging from 80 to 90% blast furnace slag, 10 to 20% gypsum, and 10 to 15% BOF slag. All formulations were evaluated for compressive strength at ages of 3, 7, 14, 28, 91, and 180 days of curing. At the initial ages, the cement formulations exhibited high resistance. On the 3rd day, the cement formulations reached up to 10 MPa, and on the 7th day, 40 MPa. At late ages, the best-performing formulation, ECO2, showed, after 28 days of hydration, a compressive strength greater than 50 MPa, and at 180 days, a compressive strength greater than 80 MPa. It was possible to understand that BOF slag acts in cement alkaline activation with pH increase, more or less actively due to the presence of lime, portlandite, and calcite.

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