The nucleation of C-S-H via prenucleation clusters.

Area of Science:

• Materials Science
• Chemistry
• Civil Engineering

Background:

• Calcium-silicate-hydrate (C-S-H) is essential for concrete's strength and durability.
• The nucleation and growth mechanisms of C-S-H are not fully understood.
• Understanding C-S-H nucleation is key to improving concrete performance.

Purpose of the Study:

• To investigate the nucleation process of C-S-H during tricalcium silicate hydration.
• To analyze the aqueous phase composition and species involved in C-S-H formation.
• To elucidate the non-classical nucleation pathways of C-S-H.

Main Methods:

• Inductively coupled plasma-optical emission spectroscopy (ICP-OES) to analyze aqueous species.
• Analytical ultracentrifugation (AUC) to determine size, density, and molar mass of species.
• Characterization of prenucleation clusters (PNCs) and liquid precursor droplets.

Main Results:

• C-S-H formation follows non-classical nucleation pathways involving prenucleation clusters (PNCs).
• Two types of PNCs were detected with high accuracy, alongside other ionic species.
• Nucleation initiates with low-density, high-water-content liquid C-S-H droplets that shrink upon growth.

Conclusions:

• C-S-H nucleation is initiated by liquid precursor droplets, not direct ion-to-solid precipitation.
• The study provides experimental data on the size, density, and shape of nucleating species.
• Findings offer insights into aggregation processes and advance the understanding of C-S-H formation in cementitious systems.