Development of in-situ highly active calcium carbonate through anhydrous carbonation of OPC: Effect on hydration and properties of cement composites

Abstract

Cement production generates a significant amount of CO₂. This paper presents a novel technique requesting CO₂ capture during cement production, namely anhydrous carbonation (AC). By introducing CO₂ during the grinding stage of cement production, which involves mechanochemical effects, this method enhances the carbonation of cement to produce carbon-enriched cement. The results indicated that calcium carbonate was formed in situ on the surface of cement after AC. Compared with the Ref samples, at curing of 1d, the compressive strength of AC-30 min, AC-1 h, and AC-3 h samples increased by 18.1 %, 40.0 %, and 22.9 %, respectively, the 28-day compressive strength increased by 7.5 %,17.1 %, and 12.3 %, respectively. AC facilitated the dissolution of OPC clinkers and the subsequent precipitation of hydration products. The enhancement of OPC performance after AC is primarily attributed to several factors. First, highly active calcium carbonate was generated on the surface of the cement clinker, providing nucleation sites for the hydration products of OPC. Additionally, this calcium carbonate participated in chemical reactions, reacted with C₃A during hydration and formed Mc and Hc. Furthermore, the filling effect of unreacted calcium carbonate, combined with the formation of hydration products such as AFm, C-S-H, AFt, Mc, and Hc, contributed to the refinement of the pore structure. This research indicated that 14.4 kg of CO₂ could be captured for every ton of cement produced, which suggests that anhydrous carbonation holds substantial potential for CO₂ sequestration during the cement production process, which could significantly contribute to reducing CO₂ emissions in the industrial production of cement.