Insights on solid CO2 mixing method for hybrid alkaline cement (HAC): performance, sustainability, and experimental system improvement

Abstract

New low-carbon concrete materials and technologies are urgently needed to reduce CO₂ emissions and achieve sustainable development in the cement industry. Hybrid alkaline cement (HAC) is a new cement-based material that combines the advantages of ordinary Portland cement and alkali-activated cement. This study introduces a solid CO₂ mixing method and investigated its impact on the performance and sustainability of HAC. Research results show that the initial internal temperature of HAC decreases after solid CO₂ is mixed. The temperature gradually increased and surpassed that of the control sample within 12 h. The sequestration of solid CO₂ triggers a carbonation reaction within the material, leading to a reduction in calcium hydroxide and an increase in calcium carbonate content. An increase in solid CO₂ leads to a decrease in workability. Tests lasting up to 90 days demonstrated that the method substantially enhanced the strength and resistivity of HAC. This study considers two boundary conditions due to CO₂ escape when quantifying the CO₂ emissions of HAC and clarifies the specific levels under actual dose and optimized dose scenarios. The findings demonstrate the potential of the solid CO₂ mixing method to optimize material performance while highlighting its dual impact on sustainability. In addition, this study proposes an experimental idea for recovering the escaped CO₂ and using it for carbonation curing. These findings provide valuable insights and practical foundations for advancing the concrete industry to achieve sustainable development.