A wollastonite-based clinker and concrete slurry waste were carbonated in the laboratory using 100% CO₂. While the former contains wollastonite and rankinite as carbonatable phases, the latter contains hydrated cement. In the carbonation process, the wollastonite-based clinker took up 183 kg/t related to the carbonated dried product, while the concrete slurry waste took up 124 kg/t. As carbonation products, a silica-rich gel and calcium carbonate form. In blends with Portland cement, the former exhibits a pozzolanic reaction, while the latter can accelerate cement hydration due to the filler effect.
The acceleration of early hydration and the pozzolanic reaction contribute positively to compressive strength at all tested sample ages between 2 and 91 days when compared to reference samples with quartz powder. The carbonated slurry waste reacts very quickly and mainly improves early strength up to 7 days of hydration, while the impact on 28 and 91 days is low. The carbonated wollastonite-based clinker starts to react significantly between 2 and 7 days. After 28 and 91 days almost the same compressive strength is reached as in the plain Portland cement.