Influence of aluminates on the hydration kinetics of tricalcium silicate

Abstract We used a combination of experimental and modelling techniques to study the effect of NaAlO 2 on C 3 S hydration. pH sensitive inhibition of C 3 S hydration occurred at an early age of reaction, but was followed by an increased amount of hydrates formed later. Most results suggest that aluminates hinder C 3 S dissolution. It is hypothesised that this takes place in active dissolution areas, present with a higher density on finer particles. Annealing reduces their number and increases retardation for a given dosage of aluminates. The view that aluminates act by hindering dissolution is supported by molecular dynamics (MD) simulations. They establish that aluminates can adsorb on the hydroxylated C 3 S mainly through strong ionic interactions between aluminate and calcium ions on the surface of silicate. Upon progress of hydration and at higher pH values, the binding strength of aluminates to the hydroxylated C 3 S decreases so that its passivating effect, and retardation, are reduced.