Effect of hydroxide, carbonate, and sulphate anions on the β-dicalcium silicate hydration rate

Abstract

The effect of fixed (0.8 M) Na+ balanced by either OH−, SO42−, and CO32− anions on β-dicalcium silicate (C2S) reactivity is investigated. The exothermic reaction of varying water-to-solid ratios and chemical activation is monitored. Subsequently, the hydration products are characterized via FTIR, TG/DTG, QXRD, and SEM analysis. The findings showed that the carbonate ions expedited the reactivity up to 55% at 1–7 days due to the simultaneous precipitation of calcium silicate hydrate (C-S-H) and calcite. At 7–28 days, the lack of transportable cations between the solid surface and solution impeded further hydration, as confirmed by in-situ pH and conductivity measurements. The sulphate ions accelerated the reactivity only upon calcium sulphate dissolution at high pH. The hydroxide ions decelerated the hydration due to the earlier precipitation of portlandite than C-S-H. Overall, the β-C2S reaction with water exhibited the highest hydration degree (~67%) after 28 days of hydration.