Effect of fly ash on hydration and carbonation of carbonation-cured Portland cements

This study investigates the impact of fly ash on hydration and carbonation processes in carbonation-cured fly ash cements. Cement paste samples with fly ash replacement levels of 0 %, 5 %, 10 % and 30 % underwent carbonation curing for 28 days. Results reveal that the CaO content does not affect the final CO 2 absorption capacity. Instead, optimal fly ash replacement of 10 % enhances CO 2 uptake, yielding 52.9 g of CaCO 3 on the surface after 28 days of curing, compared to 43.4, 43.1 and 48.4 g for 0 %, 5 % and 30 % replaced samples, respectively. Additionally, fly ash incorporation significantly enhances belite reaction and improved CO 2 binding capacity. However, the reaction extent of alite was lower when exposed to CO 2 -curing conditions. These findings advance understanding of blended cements in carbonation-curing, facilitating the development of environmentally friendly and durable concrete structures. • The role of fly ash in hydration of carbonation-cured fly ash cements was studied. • The CaO content of the binder does not significantly affect CO 2 absorption capacity. • The ideal fly ash amount improves CO 2 absorption, with higher amounts leading to faster uptake. • Fly ash incorporation speeds up belite reaction during carbonation curing, enhancing the CO 2 binding capacity of blended PC. • CO 2 -curing reduces alite reaction extent, with higher fly ash replacement ratios correlated with lower alite content.