Dry ice-driven CO ₂ sequestration in cementitious materials: effects on hydration, microstructure, and mechanical performance

This study investigates the influence of incorporating dry ice into cement-based materials at dosages of 0, 2, 10, and 20% (by cement weight) on hydration behaviour, microstructural development, mechanical performance, and CO2 sequestration potential. Dry ice (DI) was explored as a novel in situ CO2 source, and its effects were evaluated through compressive strength, split tensile strength, modulus of elasticity, and durability-related indicators. A comprehensive experimental program involving isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), and electrical resistivity measurements was conducted. Results show that moderate DI dosages of 2% and 10% enhanced mechanical properties and promoted significant microstructural densification. An additional stage of DI dissolution occurred during early hydration, leading to a slight delay in reaction kinetics, however, it did not hinder the formation of calcium-silicate-hydrate or ettringite phases. XRD, SEM/EDS, and TGA analyses confirmed partial conversion of calcium hydroxide into calcium carbonate, contributing to a denser cement matrix. The net CO2 sequestration efficiency reached up to 96% at 2% dosage, 87% at 10% dosage, and 23% at 20% dosage of DI without compromising the compressive strength. The splitting tensile strength increased by 6.8%, 3.4%, and 1.5% for 2%, 10%, and 20% DI addition, respectively. The static modulus of elasticity of DI-2% was 15% higher than the control, while DI-10% and DI-20% showed 4.8% and 11.2% increases respectively. The 28-day electrical resistivity increased by approximately 25% for DI-2% relative to the control. Overall, the findings highlight the importance of optimising DI dosage to balance enhanced CO2 sequestration with improved material performance.