Carbonation curing of belite-rich cement: The role of fly ash and strengthening mechanism

Belite-rich cement (BRC) has gained increased attention in recent years due to its low energy consumption and high long-term performance. However, the carbonation behavior of the binder formed by its combination with fly ash (FA) has been scarcely revealed. This study investigated the influence of carbonation curing and FA replacement level on the carbon capture and mechanical properties of BRC. The carbon uptake, phase composition, microstructure, and micromorphology of BRC-FA composites after carbonation curing were characterized through quantitative XRD, TG, FT-IR, MIP, and SEM-EDS. The results indicated that carbonation curing significantly increased the compressive strength by up to 81.6% of BRC compared to standard curing due to the high reactivity of belite phase with CO2, whilst the hydration products of BRC gradually disappeared, and calcite and amorphous silica became the main phase accompanied with pore refinement behavior. Moderate addition of FA increased the degree of carbonation and compressive strength of BRC-FA composites, however excessive addition (45%) of FA results in adverse effect. Additionally, FA accelerated the phase recombination but coarsened the pore structure. The rapidly formed calcium carbonate crystals stacked and squeezed together, its blend with amorphous silica gel, and the pore structure rapidly densified explain the carbonation strength growth of BRC-FA composites.