The distinct impacts of in-situ formed calcite and vaterite on the mechanical strength and microstructure of carbonated γ-C2S

Given that calcite and vaterite are isomerism with distinct morphologies, it is of great importance to investigate which morphology is more beneficial for enhancing the properties of carbonated materials. In this study, glycine (Gly) was used to regulate γ-2CaO·SiO 2 (γ-C 2 S) carbonation to promote the in-situ formation of vaterite instead of the usual calcite. The distinct effects of the two crystal types CaCO 3 on the mechanical strength and microstructure were compared. The results indicated that under Gly optimal concentration of 0.5 mol/L, the flexural strength and compressive strength of γ-C 2 S mortar specimens reached 9.8 MPa and 59.8 MPa after 7 d of carbonation, respectively, which were 60.7 % and 51.8 % higher than the reference mortar specimens dominated by calcite. Additionally, the total porosity decreased by 7.4 %, and the most probable pore size was reduced from 2.2 μm to 1.8 μm. Analysis showed that, compared to cubic calcite, spherical vaterite more effectively filled pores, thereby significantly enhancing the mechanical strength of the material. This finding provided a novel design strategy for optimizing the structure and performance of carbonated materials. • In-situ vaterite formation enhanced flexural strength and compressive strength of γ-C 2 S mortar. • In-situ vaterite formation altered pore structure of γ-C 2 S mortar. • In-situ vaterite formation improved the microstructure of γ-C 2 S mortar.