Industrially relevant early-age carbonation curing of high-calcium fly ash blended mortars: CO2 uptake, strength development, and dimensional stability

Early-age carbonation curing has emerged as a promising approach for enhancing the performance of cement-based materials while utilizing CO 2 , particularly when incorporating supplementary cementitious materials for carbon reduction. However, in high-calcium fly ash (HFA) systems, increasing replacement levels may induce volumetric instability and strength reduction; therefore, performance under curing conditions relevant to precast production requires further investigation. To address this gap, this study experimentally evaluated early-age carbonation curing under curing conditions relevant to precast production schedules. Mortar mixtures incorporating 10-30% HFA were subjected to 12 h of pre-curing, followed by carbonation curing in a 20% CO 2 atmosphere for 8 h and 24 h. Specimens were analyzed in terms of carbonation depth, CO 2 uptake (TG-DTG), compressive strength (up to 56 days), length change (up to 180 days), and pore structure characteristics. The results indicated that prolonged carbonation curing (24 h) increased both CO 2 uptake and carbonation depth and was associated with microstructural refinement. Under the investigated conditions, mixtures containing up to 20% HFA exhibited compressive strength comparable to ordinary Portland cement (Plain), while reduced long-term length change was observed relative to standard curing. In contrast, at a 30% replacement level, the improvements in strength recovery and length change mitigation were more limited. Overall, the results suggest that HFA replacement levels of the mixture containing 20% HFA with 24 h carbonation curing provided the most favorable balance among the investigated performance indicators within the scope of this study. The findings provide experimental data relevant to the evaluation of HFA-blended cementitious systems under early carbonation curing while contributing to the understanding of CO 2 utilization strategies in HFA-blended cementitious systems.