Hydration Properties of STS‐Refining Slag‐Blended Blast Furnace Slag Cement

The refining process using an aluminum deoxidizer for fabricating stainless steel generated steel slag (STS‐refining slag (SRS)) that contains a large amount of Al 2 O 3 and is a compound of mainly 12CaO·7A l2 O 3 and 3CaO·A l2 O 3 . When SRS was mixed with slag cement, rapid exothermic reaction occurred in the initial phase of hydration. During the hydration of slag cement and SRS, a large quantity of x CaO‐ y Al 2 O 3 ‐ z H 2 O hydrate was observed. Until 10% weight replacement ratio of SRS to slag cement, the compressive strength was in the same level as in the existing slag cement. However, 20% replacement was accompanied by much strength degradation and high drying shrinkage. When a mixture of SRS and gypsum was added to slag cement, ettringite (3CaO·Al 2 O 3 ·3CaSO 4 ·32H 2 O) was actively created in the initial hydration phase. The compressive strength of the OPC‐BFS‐SRS‐gypsum binder at 91 days was 91% of that of slag cement (B50) and was similar to that of OPC (O100). Besides, drying shrinkage was almost half that of slag cement, which indicates excellent performance for shrinkage. In case SRS is adequately used, which is an industrial by‐product of the steel‐making process, high shrinkage, a basic problem of slag cement, will be mitigated.