Enhanced carbonation reactivity of wollastonite by rapid cooling process: Towards an ultra-low calcium CO₂ sequestration binder

To enhance the carbonation reactivity of wollastonite (CS), three different calcination processes were adopted to synthesis CS with different crystal structures. The effects of the cooling process on the polymorphs, carbonation reactivity, and CO₂ sequestration capacity of CS were measured and evaluated, and its carbonation hardening properties and microstructure evolution were also explored. The results indicated that the carbonation reactivity of CS was enhanced by the rapid cooling process due to the inhibition of the polymorphic transition of α-CS to β-CS. The enhanced carbonation reactivity was attributed to the distorted CaO_x polyhedra and extended Ca-O distance in α-CS, which made the dissolution of α-CS to leach Ca²⁺ easier. The CO₂ sequestration capacity and compressive strength of highly reactive CS reached 27.2% and 92.3 MPa, respectively, after carbonation for 24 h. Therefore, it was demonstrated that highly reactive CS can be adopted as ultra-low calcium and CO₂ sequestration binder.