Carbonation reactivity of calcium silicate glasses at various calcium to silicate ratios and comparison with wollastonite

Amorphous calcium (alumino) silicates are the main component of industrial byproducts (e.g., blast furnace slag and fly ash) and can be generated by grinding silicate minerals that are abundant in steel slag and carbonated calcium silicate binders. To promote the production of CO₂-activated building material from diverse materials, this study investigated the carbonation of synthetic calcium silicate glasses, model compounds of these amorphous silicates. A dissolution-controlled carbonation mechanism was revealed, in contrast with a nucleation-controlled counterpart for the carbonation of wollastonite, a model compound of silicate minerals. The former mechanism is governed by the number of Q³ species in the silica layers on carbonated particle surfaces serving as sites for ionic exchange. The latter is evidenced by well-aligned CaCO₃ nuclei precipitating on wollastonite particles under high CaCO₃ supersaturation. Overall, high Ca/Si ratios favor carbonation. At Ca/Si = 1, the calcium silicate glass shows faster carbonation kinetics than wollastonite at early ages.