Comparative effects of calcite, aragonite, and vaterite on Portland cement hydration, mechanical performance, and microstructure

Abstract

Calcite, aragonite, and vaterite were comparatively evaluated as partial Portland cement replacements (10 wt.% and 20 wt.%) to assess their effects on hydration, mechanical performance, and microstructure. Neat cement pastes with or without inert quartz sand served as reference systems. A comprehensive multi-scale experimental framework was employed, encompassing isothermal calorimetry for hydration kinetics, X-ray powder diffraction for crystalline phase assemblage, mercury intrusion porosimetry and small-angle neutron scattering (SANS) for pore structure and nano-structural features, respectively, and compressive strength and Ca2+ adsorption tests. Calcite exhibited the highest nucleation efficiency, accelerating hydration and enhancing amorphous hydrate formation, owing to its higher SSA, while largely preserving strength, particularly at 10 wt.%. Aragonite and vaterite predominantly promoted the formation of crystalline hydrates (ettringite, calcium monocarboaluminate hydrate, and portlandite), with vaterite exerting the strongest influence and aragonite enabling a more extensive overall hydration. Microstructural analyses revealed that aragonite’s acicular habit introduced local discontinuities and finer capillary porosity, while vaterite formed loosely incorporated agglomerates that altered pore refinement and strength development. Specific surface area-independent assessments showed that vaterite possessed the highest affinity for Ca2+ and the greatest capacity to promote C–S–H nucleation, consistent with nanoscale insights obtained from SANS. The findings demonstrate that, in addition to calcite, tailored incorporation of vaterite, and to a lesser extent aragonite, can serve as effective functional alternatives in low-carbon cement formulations.

Keywords: Calcite, aragonite, vaterite, cement hydration, small-angle neutron scattering