Carbonation curing of ultra-high-performance concrete produced with Portland cement of varying belite content

This study explores the potential application of carbonation curing to ultra-high-performance concrete (UHPC) produced with Portland cement of varying belite content. After an initial curing phase, the UHPC samples underwent either steam curing at 90 °C or carbonation curing under a 5 % CO 2 concentration. Test results indicated that the mechanical strength of the carbonation-cured UHPC samples was generally lower than that of the steam-cured counterparts. Among all cement types, the UHPC samples made with type III cement exhibited the highest strength regardless of the curing regime and/or age. Carbonation curing significantly altered both clinkers and hydrates, with the most pronounced changes observed in the UHPC samples made with type IV cement, suggesting high levels of CO 2 ingress and uptake. In addition, as silica fume contributed minimally to the reactions in the carbonation-cured UHPC samples, microstructural development was primarily driven by the carbonation of clinkers, which led to the formation of C-S-H and Ca-modified SiO 2 and the precipitation of CaCO 3 . While steam curing was found to accelerate the reaction of clinkers in a limited timeframe, type IV cement demonstrated potential advantages as part of a carbonation curing strategy when considering environmental benefits. These results suggest that the carbonation curing of UHPC, particularly with belite-rich cement, could provide a low-energy and low-carbon alternative to conventional steam curing practices, thereby offering practical value for sustainable construction applications.