Surface area and size distribution of cement particles in hydrating paste as indicators for the conceptualization of a cement paste representative volume element

The conceptualization of a representative volume element (RVE) of hardened cement paste for numerical homogenization of mechanical problems rests on identifying the largest discernible microstructural feature, i.e. unreacted cement grains. While the particle size distribution (PSD) of anhydrous cement is a well -controlled production parameter, the size evolution of a representative cement grain throughout hydration remained unresolved. This study analyzes digitized 3D cement paste microstructures obtained from X-ray micro-computed tomography, coupled with CEMHYD3D hydration model, and segmented by image-processing tools, to obtain the full PSD and specific surface area evolutions of unreacted grains throughout hydration. Results provided indicate a representative grain size in the range of 30-40 mu m regardless of hydration elapsed, implying a cement paste RVE should amount to 150-200 mu m to realistically represent cement grains. The PSD shape remained self-similar and two distinctive hydration regimes were identified, differing in dissolution rate and specific surface area decrease, correlating with calcium sulfate reactivity peak. Both measures provide easily accessible microstructural features that may be used for constructing artificial RVEs of hardened cement paste in micromechanical models and related simulations, resting on experimental data.

Automated summary

An analysis of digitized 3D cement paste microstructures found a consistent size of cement grains ranging from 30-40 µm throughout hydration. The shape of the particle size distribution (PSD) remained self-similar, and the hydration process was identified to have two distinct stages, correlating with the reactivity peak of calcium sulfate.