Abstract
We discuss the influence of calcium sulfates on the fluidity of high-flow concrete made with ground granulated blast-furnace slag (BFS) and polycarboxylate-based superplasticizer (PC). Gypsum, hemihydrate and anhydrate were added to BFS and the effect of each was examined. Gypsum and anhydrate had no effect on the fluidity of high-flow concrete with BFS. By addition of hemihydrate, the fluidity of high-flow concrete is reduced at very early stages, but it is improved rapidly after 5 minutes. The amount of adsorbed PC, amount of ettringite and sulfate ion concentration in the aqueous phase of cement paste with BFS and PC were measured to clarify the mechanisms for the changing of fluidity. Fluidity was decreased linearly with the increase of sulfate ion concentration. The results of present study suggest that the change in fluidity of high-flow concrete with BFS and PC due to calcium sulfates in BFS caused by a change in the dispersion of particles by sulfate ions in the aqueous phase.
