CO₂-enriched ammonium solutions for enhanced carbon capture and sequestration in cement systems

The cement industry is a significant contributor to global CO₂ emissions, creating an urgent need for innovative sequestration strategies. This study proposes a method to enhance CO₂ capture in cement by using CO₂-enriched ammonium solutions as mixing water. Unlike conventional carbonation curing, this method integrates CO₂ directly into the hydration process, enabling uniform in-situ carbonation. Ammonium addition increased CO₂ uptake to 18.6 g/L, about 25 times that of conventional carbonated water, while preserving mechanical integrity. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed selective consumption of portlandite and calcite formation without disrupting C–S–H, and Micro-computed tomography (µ-CT) revealed substantial pore refinement and densification. Thermogravimetric analysis supported the proposed chemical mechanism and indicated greater carbonate formation and apparent thermal stability in ammonium-assisted mixes compared with CO₂-only mixes. Ammonium-modified CO₂ solutions offer a scalable strategy for carbon capture in cement systems and could enable the utilization of ammonium-rich water streams.