The influence of sodium and potassium hydroxide on alite hydration: Experiments and simulations

The basic nature of alkali hydroxides (NaOH, KOH) when added to mixing water, increases the pH in proportion to the level of salt addition. For alite (impure tricalcium silicate; MIII-Ca3SiO5) hydration, this pH increase accelerates the rate of hydration and reduces the duration of the induction, acceleration and deceleration regimes. This study evaluates alite hydration in solutions of varying compositions and alkalinities (0.1 M, 0.2 M and 0.5 M NaOH and KOH) in context of their heat release behavior and analysis of the solid/liquid phases. The modeling platform, μic, is used to simulate, describe and discriminate the impact of the pore solution chemistry and reaction product formation parameters on alite hydration (Bishnoi and Scrivener, 2009 [1]). Numerical predictions of the solid and liquid phase compositions and the heat release response show good agreement with experimental determinations. The simulations indicate that the effects up to the end of the induction period follow directly from a change in the pore solution composition under a solution controlled dissolution mechanism, which leads to the faster precipitation of portlandite. The changes in the main heat evolution peak appear to be related to an increase in the nucleation density of C–S–H in alkali hydroxide solutions. Examination under the SEM did not indicate significant difference in C–S–H morphology and composition in the presence of NaOH/KOH.