Ultra-stable CO₂-aqueous foams for carbon sequestration and internal mineralization in cellular cements

Utilization of cellular materials is an effective strategy for enhancing energy efficiency and reducing emissions in the construction sector. Incorporating CO₂ into aqueous foam bubbles to fabricate porous cement materials offers a new pathway for carbon sequestration. However, for CO₂ gas-entraining foamed cement (CFC), stabilizing CO₂-aqueous foam precursors remains a major challenge due to the high water-solubility of CO₂ molecules. This study pioneered a polymer sol-based modification for producing ultra-stable CO₂ foam bubbles with lifespans exceeding 8 h—20 ∼ 50 times longer than conventional foaming agents. The self-assembled 3D colloidal networks within the foam films exhibited high viscosity, modulus, and low CO₂ gas permeability, significantly improving CO₂ foam stability. Two new indices, drainage and coalescence factors, were first proposed to guide CO₂ foam design. Accordingly, the engineered CO₂ foams successfully created CFC with ultra-low density (∼300 kg/m³), excellent strength (superior to normal foamed concrete), low thermal conductivity, and considerable CO₂ storage capacity. The CO₂ foams also facilitated internal CO₂ mineralization effect by in-situ growing micro calcite and nano aragonite on pore walls. The findings of this study resolve the critical issue of CO₂ foam stability and provide new insights for the design and fabrication of carbon-sink construction materials.