Distribution of Water in Synthetic Calcium Silicate Hydrates

Area of Science:

• Materials Science
• Chemistry
• Civil Engineering

Background:

• Calcium silicate hydrates (CSHs) are crucial components of cementitious materials, governing their macroscopic properties.
• Understanding the atomic-scale water content and structure of CSHs is essential for predicting material behavior, similar to clay minerals.

Purpose of the Study:

• To quantify water distribution within CSH samples.
• To differentiate between water sorbed on external and internal (interlayer) surfaces.
• To elucidate the influence of water on CSH properties and explain variability in published data.

Main Methods:

• Utilized a multi-analytical approach, including water vapor isotherms, X-ray diffraction (XRD), and thermal gravimetric analysis (TGA).
• Water vapor isotherms were employed to analyze water distribution within the CSH microstructure.
• Quantified interlayer water and observed its role in reversible swelling/shrinkage behavior.

Main Results:

• CSHs exhibit multilayer adsorption of water molecules on external surfaces due to their hydrophilic nature.
• Interlayer water quantification revealed non-reversible swelling/shrinkage in response to moisture cycling.
• The study successfully explained previously dispersed data on CSH properties under various relative humidity conditions.

Conclusions:

• Accurate quantification of water distribution, including interlayer water, is key to understanding CSH behavior.
• Proposed stoichiometric formulas for CSH samples (0.6 < Ca/Si < 1.6) incorporating interlayer water contributions.
• This research provides a framework for interpreting CSH property variations based on water content and distribution.