Accelerating CO2 sequestration in cementitious materials using carbonic anhydrase: Experimental insights into performance and mechanisms

Abstract

Increasing atmospheric CO₂ levels require innovative mitigation strategies. Cementitious materials offer significant potential for CO₂ sequestration through carbonation. This study investigates the application of carbonic anhydrase (CA), an enzyme that catalyzes CO₂ hydration, to accelerate CO₂ sequestration in cementitious materials. We applied pH monitoring and p-NPA assay to evaluate CA activity under artificial cementitious environments. The results showed that CA activity significantly decreased at pH 13 but remained stable at pH below 12, suggesting potential applications of CA in lower-pH systems, such as demolished concrete, mineral waste, or cementitious materials with a low clinker content. Mixing CA directly into fresh cement pastes showed more carbonates formed and a higher reduction in pore volume than the control groups, demonstrating that CA accelerated early-stage CO₂ sequestration. When spraying the CA solution on crushed cement paste, we observed a dense layer of calcite on the surfaces of cement paste particles, meaning that early-stage carbonation resulted in a higher carbonate content than the control samples, particularly for smaller particles with larger surface areas. However, the carbonation efficiency decreased at the later stage, which is likely due to CA deactivation or surface densification limiting ions diffusion, reducing further carbonation enhancement at later stages. This study highlights the potential of CA to accelerate CO₂ sequestration in cementitious materials while emphasizing the challenges of high pH and complex ionic composition for CA performance. The findings suggest the need for stabilizing the enzyme’s activity or applying CA to low-clinker cementitious materials, and partially carbonated materials, such as recycled concrete aggregates, for CO₂ sequestration.