Multiscale understanding of tricalcium silicate hydration reactions

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• Tricalcium silicate (Ca3SiO5) hydration is crucial for Portland cement performance.
• The nanoscale mechanisms of hydration, particularly C-S-H gel formation, remain poorly understood.
• Understanding atomic arrangements in nanocrystalline phases is complex, especially with multiple crystalline phases.

Purpose of the Study:

• To quantitatively investigate the nanoscale hydration process of tricalcium silicate.
• To identify the specific nanocrystalline structure of calcium-silicate-hydrates (C-S-H) gel.
• To elucidate the multiscale properties of the C-S-H nanocomposite gel.

Main Methods:

• Calorimetry was employed to monitor the hydration reaction kinetics.
• Synchrotron X-ray powder diffraction, specifically pair distribution function (PDF) analysis, was used for nanoscale structural determination.
• Additional laboratory characterization techniques were utilized for comprehensive analysis.

Main Results:

• The nanocrystalline component of C-S-H gel was identified as a defective clinotobermorite (Ca11Si9O28(OH)2·8.5H2O).
• PDF analysis revealed the presence of monolayer calcium hydroxide within the C-S-H gel, consistent with theoretical predictions.
• A multiscale model for the C-S-H nanocomposite gel was developed, explaining observed densities and Ca/Si ratios.

Conclusions:

• The study provides a detailed nanoscale understanding of tricalcium silicate hydration and C-S-H gel formation.
• The identified C-S-H structure advances fundamental knowledge in cement chemistry and materials science.
• The findings offer insights into the relationship between atomic structure and macroscopic properties of cementitious materials.