Mechanisms and kinetics of C-S-H nucleation approaching the spinodal line: Insights into the role of organics additives

TL;DR

This study investigates the nucleation mechanisms and kinetics of calcium-silicate-hydrate (C-S-H) formation near the spinodal line, highlighting how organic additives influence the process through multi-step pathways and distinct regimes.

Contribution

It provides new insights into how organics affect C-S-H nucleation kinetics and identifies two precipitation regimes, advancing understanding of mineralization processes in cement chemistry.

Findings

Organic additives increase the kinetic prefactor of nucleation.

Two distinct C-S-H precipitation regimes were identified.

Spinodal nucleation occurs at high supersaturation with low energy barriers.

Abstract

Wet chemistry C-S-H precipitation experiments were performed under controlled conditions of solution supersaturation in the presence and absence of gluconate and three hexitol molecules. Characterization of the precipitates with SAXS and cryo-TEM experiments confirmed the presence of a multi-step nucleation pathway. Induction times for the formation of the amorphous C-S-H spheroids were determined from light transmittance. Analysis of those data with the classical nucleation theory revealed a significant increase of the kinetic prefactor in the same order as the complexation constants of calcium and silicate with each of the organics. Finally, two distinct precipitation regimes of the C-S-H amorphous precursor were identified: i) a nucleation regime at low saturation indexes (SI) and ii) a spinodal nucleation regime at high SI where the free energy barrier to the phase transition is found to be of the order of the kinetic energy or less.