The influences of different alkaline conditions on the kinds and morphologies of steel slag's hydration products, Ca(OH)2 content of hydration products, pore structure of hardened paste, non-evaporable water content of hydration products, and strength of steel slag mortar were investigated by changing the initial alkalinity of the hydration condition of steel slag. The results showed that increasing the initial alkalinity of hydration condition can promote the early hydration of steel slag's active components (e.g., C2S, C3S, and C12A7 ), but it has little influence on their late-age hydration degree. The hydration degree of non-active components (e.g., RO phase and Fe3O4 ) of steel slag is very low even under strong alkaline condition with pH value of 13.8. The excitation effect of alkaline condition on the early hydration of steel slag is more obvious with the increase of pH value, but the kinds of steel slag's hydration products are not influenced by changing the alkaline condition. The amount of steel slag's hydration products is limited, so the strength of alkali-activated steel slag mortar is very low though the strong alkaline condition significantly promotes the early hydration of steel slag. Steel slag is not an ideal raw material for alkali-activated cementitious material.
The initial hydration of steel slag with high Al2O3 content and its influence on the initial hydration of cement were investigated in this study.Steel slag with high Al2O3 content may contain much calcium aluminate mineral but very little gypsum.The steel slag hydrates much more quickly than cement in the initial hydration period,producing many flake products which have a great influence on the fluidity,initial setting time,and adsorption level of superplasticizer of paste.Replacing part of cement by steel slag with high Al2O3 content can change the hydration condition of calcium aluminate mineral of the cement by decreasing the gypsum to calcium aluminate mineral ratio,resulting in accelerating the hydration rate of calcium aluminate mineral in the initial hydration period.Paste containing steel slag with high Al2O3 content has a shorter initial setting time,higher adsorption level of superplasticizer,and greater loss in fluidity than the pure cement paste.
The hydration properties of cement-GGBS-fly ash blended binder and cement-GGBS-steel slag blended binder were compared. The experimental results show that the hydration rate of cement-GGBSsteel slag blended binder is higher than that of cement-GGBS-fly ash blended binder within 28 days, but lower than the latter after 28 days. The hydration of cement-GGBS-steel slag blended binder tends to produce more Ca(OH)2 than the hydration of cement-GGBS-fly ash blended binder, especially at late ages. Cement-GGBSsteel slag mortar exhibits higher strength than cement-GGBS-fly ash mortar within 28 days, but at late ages, it exhibits similar compressive strength with cement-GGBS-fly ash mortar and even slightly lower bending strength than cement-GGBS-fly ash mortar. Cement-GGBS-steel slag paste has finer early pore structure but coarser late pore structure than cement-GGBS-fly ash paste. Cement-GGBS-steel slag paste can get satisfied late pore structure and cement-GGBS-steel slag mortar can get satisfied late strength as compared with pure cement paste and pure cement mortar, respectively.
