Hydration Properties and Interlayer Organization in Synthetic C-S-H

Area of Science:

• Materials Science
• Chemistry
• Geology

Background:

• Water in calcium silicate hydrate (C-S-H) is crucial for cement's macroscopic properties.
• Water vapor partial pressure influences C-S-H's Young's modulus and volumetric characteristics.

Purpose of the Study:

• To investigate the dehydration/hydration behavior of C-S-H with varying Ca/Si ratios.
• To understand the influence of water pressure on C-S-H structure and properties.

Main Methods:

• Characterization using ²⁹Si NMR, water adsorption volumetry, X-ray diffraction, and FT-NIR.
• Experiments conducted under controlled water pressures and temperatures.

Main Results:

• Increased Ca/Si ratio correlates with Si bridging tetrahedra omission and interlayer Ca compensation.
• Water conditioning affects C-S-H layer-to-layer distance and NMR spectral resolution.
• Dehydration leads to decreased layer-to-layer distance and partially reversible shrinkage/swelling.

Conclusions:

• Interlayer Ca and water interactions are key when Si tetrahedra are omitted.
• A mid-plane water monolayer in the interlayer space constitutes ~30% of C-S-H particle volume.
• Understanding C-S-H hydration is vital for cement material performance.