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

Abstract

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 degrees C or carbonation curing under a 5 % CO2 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 CO2 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 SiO2 and the precipitation of CaCO3. 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.