Early hydration of belite-ye’elimite-ferrite cements: Role of admixtures

Abstract

The effect of TIPA and CaCl2 on early hydration, i.e. 24 h, of a B-BYF cement has been studied by in situ synchrotron X-ray powder diffraction, calorimetry, thermal analysis, NMR, and rheological measurements of the pastes and mechanical strength of the corresponding mortars. The addition of 0.05 %bwc (by weight of cement) of TIPA reduced the viscosity of the paste during the first minutes of hydration but, after the end of the induction period, ~7 h, it favored the formation of AFt compared to the reference paste. The latter is likely due to the acceleration of the dissolution of the amorphous aluminates and sulfates by the presence of TIPA. These results correlate with the increase of ~169% of the 1-day mechanical strengths. The addition of 2.0 %bwc of CaCl2 accelerated the dissolution rate of ye’elimite, causing an increase of the amount of precipitated ettringite even before the end of the induction period, which has been shorted to ~6 h. The 1-day mechanical strengths of the mortars with this admixture outperforms that of the reference mortar by 181%. Finally, ferrite and α’ H-belite reactivities were not affected by the addition of any of these admixtures during the first 24 h of hydration of this cement.