CO2 mineralization of wollastonite-Portland cement (WPC) is proposed for concrete curing.
WPC containing 5–25% of natural wollastonite show considerable CO2 uptake capacity.
Dominating effects controlling the evolution of pore structure are revealed.
CO2 mineralization of wollastonite remarkably enhances the compressive performance.
Carbonation curing to produce building products could provide a promising route to energy-efficient cementation process and economic CO2 sequestration. The potential benefit from material selection and optimization should be explored to optimize the environmental performance of CO2-cured materials. In this study, the accelerated mineral carbonation of wollastonite-Portland cement (WPC), a low carbon binder, is investigated by combining a detailed study on its CO2 mineralization capacity and on the physicochemical evolution in microstructure. Up to 25 wt.% of natural wollastonite is employed to replace the CO2-intensive ordinary Portland cement. During the carbonation curing process, WPC pastes exhibited CO2 uptakes up to 20 wt.% under moderate pressures (≤2.5 MPa). Also, a dense structure with substantially high polymerization degree and fine pores was clearly discerned in cured WPC paste. The pore-creating effect from evaporated pore water and the porosity-filling effect from carbonated calcium silicates were found to dominate the microstructure in the early-stage and mid-late stage reactions, respectively. Results also revealed the positive impacts of adding the wollastonite mineral: (i) The diluted effect of wollastonite enhanced the pore-creating effect in the early-stage; (ii) The consumption of wollastonite and formation of Ca-modified silica gel primarily happened in the mid-late stage, which helped increasing the degree of polymerization. Associated with the structural evolution, the cured WPC pastes exhibited superior compressive strength (over 80 MPa) after the carbonation curing: the maximum increment could exceed 350%. These results demonstrate the feasibility of CO2 mineralization of WPC to produce green building material without compromising mechanical performance.