Investigating carbon sequestration in cementitious mortars with low-carbon binders and carbonated water

The use of carbonated water in cementitious systems as a carbon sequestration strategy is promising, offering operational simplicity and high CO₂ binding efficiency compared to approaches such as gaseous CO₂ injection and carbonation curing. However, its application in low-carbon cement systems, particularly emerging binders such as limestone calcined clay cement (LC³), remains underexplored. As the shift to low-carbon binders is critical for reducing embodied carbon in cement, it is essential to understand their interactions with carbonated water, given their distinct reactivity, pH evolution, and fresh-state behaviour. This study systematically investigates the effects of carbonated water on conventional low-carbon binders (Slag-50% and Slag-80%), emerging LC³, and OPC mortars. Evaluations covered fresh-state properties, mechanical performance, durability (sorptivity and porosity), and microstructural evolution at early and later ages. Results show the strongest interaction of carbonate ions with C₃A and its hydration products, with CO₂ binding governed by the nature of early hydrates and pH conditions. Contrary to the hypothesis that high-calcium systems such as OPC are most favourable for CO₂ binding, they exhibited reduced strength and durability. In contrast, LC³ and Slag-50% demonstrated the greatest benefits, with improved CO2 binding, shortened setting times, enhanced strength and reduced sorptivity and porosity. Microstructural analysis confirmed CO₂ binding predominantly influenced calcium-silicate-hydrate gels with minimal calcite formation. Overall, carbonated water emerges as a practical pathway to improve performance while enabling additional CO₂ binding in LC³ and slag-50% cement systems, reinforcing their superior potential for carbon sequestration to OPC.