Effect of rice husk ash on carbon sequestration, mechanical property and microstructure evolution of cement-based materials with early-age carbonation treatment

Recycling of agricultural wastes to develop low-carbon supplementary cementitious materials requires the understanding of their effects on carbon sequestration, mechanical property and microstructure characteristics of cement-based materials. This work aims to disclose the mechanism of above-mentioned behavior in porous-structured rice husk ash (RHA) blended pastes using multi-technique investigations including mercury intrusion porosimetry (MIP), ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR), Scanning electron microscope/Energy Dispersive Spectrometer (SEM/EDS) techniques coupled with carbonation-hydration model. It was discovered that pastes with increased dosages of RHA (5%–15%) presented an increase of CO₂ uptake compared to that of control paste. It also showed an enhanced compressive strength after 12 h carbonation while simultaneously maintained a comparable strength development at 28 d. A declined permeability from water absorption experiment was also obtained especially in carbonated paste with 10% RHA. The enhanced polymerization degree of C–S–H and the decreased porosity due to the formation of calcite were the main contributors to the improved performances in RHA blended pastes.