Cr6+‐doped C2S towards an ultra-high CO2 sequestration material: Clinker characterization, carbonation hardening and solid solution tendency

Ion doping was regarded as an effective method for the adjustment of dicalcium silicate (C 2 S) mineral phase composition and then improve the corresponding carbonation activity according to recent studies. However, the main drawbacks of the previously reported about the carbonated compacts made by various ions-doped C 2 S were their low degree of carbonation (DOC). In this work, a typical heavy metal ion (i.e., Cr 6+ ) was used for the sintering of C 2 S, the effect of Cr 6+ doping on crystal transformation, mineral phase composition, carbonation hardening and solid solution tendency of clinkers was investigated. The results show that the moderate Cr 6+ doping (i.e., 1.5 %) led to an ultra-high DOC (i.e., around 59.2 %) and compressive strength (i.e., 137 MPa) of the corresponding carbonated compacts after 24 h. Comparing with blank group (i.e., without Cr 6+ ), the improvement degree of DOC and compressive strength was 27.4 % and 80.2 %, respectively. The reasons could be disclosed as following: comparing the single γ-C 2 S in blank group and excessive β-C 2 S with small amount of γ-C 2 S in Cr-2.0 % clinker, the moderate proportion of β-C 2 S and γ-C 2 S in Cr-1.5 % clinker, leading to their superior “transfer effect” (i.e., from the each other activation of β-C 2 S and γ-C 2 S). The superior “transfer effect” leading to their higher total carbonation activity and the combined CO 2 sequestration ability, which benefits the compressive strength and DOC in turn, respectively. This study provides new choice for preparing ultra-high CO 2 sequestration ability carbonate solidified materials based on ion-doped C 2 S clinker, and new insight on the reaction mechanism of binary C 2 S clinker. • An ultra-high CO 2 sequestration material (i.e., DOC was around 60 %) was prepared by Cr 6+ -doped C 2 S. • The addition of Cr 6+ significantly changed the mineralogical composition of C 2 S (i.e., β-C 2 S and γ-C 2 S). • The distribution of Cr element shows an obvious enrichment tendency, i.e., more likely enriched in β-C 2 S. • The superior “transfer effect” of Cr-1.5 % explains their ultra-high 24 h compressive strength and DOC.