Synergistic carbonation pretreatment for performance enhancement and CO2 uptake in limestone–blended cement

초록

High proportions of carbonated supplementary cementitious materials (SCM) are needed to decarbonize the cement industry but the traditional technologies frequently negate the workability and long-term strength, constraining industry use. This research fills an important knowledge gap regarding the influence of carbonation on particle surface texture and the time when the CO<inf>2</inf> sequestration process starts to slow down the kinetics of hydration. A two-step carbonation pretreatment and curing method was designed to improve environmental as well as mechanical properties of cementitious pastes. Limestone powder (LP) was pretreated under 0.5 bar CO<inf>2</inf> pressure using a dry carbonation process after 0.5, 3 and 5 h and replaced with ordinary Portland cement (OPC) at 5–25 % proportions. The cementitious pastes were subjected to carbonation curing to determine CO<inf>2</inf> sequestration, hydration and strength development. The characterization by FTIR, XRD, TGA, SEM, and particle size analysis showed gradual conversion of portlandite to stable calcite with an increase in carbonation period. A major finding is a surface-polishing mechanism, carbonation pretreatment decreases the surface roughness of the LP particles, reducing the water adsorption and enhancing the flowability of the paste. The 5 % HCLP/3 h mixture proved to be the most effective with a 47.7 % increase in 28-day compressive strength. This has been explained by synergistic action in which nanocrystal calcite seeds from pretreatment catalyzes a heterogeneous nucleation in the later hydration and curing. On the contrary, kinetic threshold was observed to be at 5 h where excessive generation of surface carbonates results in a thick passive film that halts the hydration. Life Cycle Assessment showed a 21 % decrease in Global Warming Potential, offset by a decrease in clinker and possible use of renewable energy in precast environments. This study represents a scientifically based concept of sustainable, high-performance cementitious systems. © 2026 The Authors.

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