Carbonation behavior of aged alkali-activated fly ash/slag binder modified by MgO with different reactivities

This study focused on characterizing the carbonation behavior of 90-day aged alkali-activated fly ash/slag blended by MgO. Effects of MgO reactivity on the carbonation behavior of the synthesized binders were explored. A 0.3% CO₂ concentration was adopted for an accelerated carbonation environment. The samples were characterized using compressive strength tests, X-ray diffraction, thermogravimetry, ²⁷Al solid-state magic angle spinning nuclear magnetic resonance spectroscopy, and scanning electron microscopy with energy-dispersive spectroscopy. Notably, the compressive strengths of all the samples significantly increased after 28 days of carbonation. Moreover, aragonite was identified as the major carbonation product formed in all samples; nevertheless, its precipitation was scarcely affected by the degree of MgO reactivity. In particular, carbonation results in the decalcification of calcium silicate hydrate gels and the formation of layered double hydroxides. The results illustrate that the sample with relatively higher MgO reactivity exhibits improved carbonation durability.