Insight into the role of β-cyclodextrin on the hydration of white Portland cement

Impacts of β-cyclodextrin (β-CD) on hydration of white-Portland-cement (WPC) are studied by calorimetry, ICP-OES, TOC, TG, XRD and time domain NMR. Strong retardation effect of β-CD has been confirmed in both WPC and pure C3S pastes. Much stronger retardation in C3S pastes suggests the aluminate phases (C3A and ettringite) in WPC pastes mitigates the retardation effect of β-CD on C3S hydration, probably by adsorbing β-CD molecules and thus reducing β-CD concentration in the aqueous solution. Together with precipitation experiments of pure CH and C-S-H, it is concluded that β-CD remaining in the aqueous solution of the WPC pastes blocks CH and C-S-H formation and the induction period is remarkably extended as additional time is needed to clean up the aqueous solution by slowly formed hydrates e.g., AFt. NMR results suggest high dosage of β-CD promotes C-S-H precipitation directly in aqueous solution in acceleration period, besides the surface of cement grains.