Abstract
The study explored the chemical, micromechanical, and morphological evolution of the principal binding phases of Portland cement under carbonation. Accelerated carbonation under 20% CO2 at 80% relative humidity was applied on C-(A-)S-H powders until equilibrium. The crystallinity of C-(A-)S-H disappeared due to decalcification and subsequent formation of highly polymerized silica gels. A high carbonation content (33.4–35.2%) was achieved. CaCO3 polymorphs dominated by aragonite and vaterite were observed as the main carbonation products. A significant reduction in the indentation elastic modulus was revealed in compacts produced with carbonated powders. In contrast, compacts followed by carbonation attained an improved micromechanical property, attributed to a reinforcing action of integral CaCO3 nanocrystallites and pore-filling effects. The carbonated C-(A-)S-H powders achieved an overall lower pore volume and exhibited a more fibrous morphology characterized by thin foils of silica gels bound with CaCO3 crystals to form agglomerates.
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