MIN Q S, ZHANG Z P, LIU Z C. Preparation of α-CS and its carbonation-hardening performance[J]. Journal of Henan Polytechnic University( Natural Science)， doi:10.16186/j.cnki.1673-9787.2026060029.

doi: 10.16186/j.cnki.1673-9787.2026060029

Received：2026-06-23

Revised：2026-08-18

Online：2026-09-09

Preparation of α-CS and its carbonation-hardening performance (Online)

MIN Qianshen1, ZHANG Zhipeng3, LIU Zhichao1, 2

1. School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, Hubei, China; 2. State Key Laboratory of Silicate Materials for Architectonics, Wuhan University of Technology, Wuhan 430070, Hubei, China; 3. School of Materials and Chemical Engineering, Hubei University of Technology, Wuhan 430068, Hubei, China

Abstract: Objectives To clarify the effects of firing regimes on the phase composition during the laboratory solid-state synthesis of α-CS clinker, as well as the carbonation-hardening process and strength-development mechanism of α-CS, α-CS clinker was prepared from Ca(OH)₂ and SiO₂. The effects of repeated calcination on the phase composition of the clinker were investigated, and the carbonation-hardening behavior and microstructural mechanism of clinker with a high α-CS content under CO₂ curing were elucidated. Methods α-CS clinkers subjected to different numbers of repeated calcination cycles were prepared by a solid-state calcination method. Their phase compositions were quantitatively characterized by X-ray diffraction with an internal standard, and clinker with a high α-CS content was selected. The clinker powder was mixed with water at a water-to-solid ratio of 0.15, compacted into specimens, and cured at room temperature under 99.9% CO₂ at 0.3 MPa. Compressive strength, thermogravimetric-differential thermal analysis, pH, electrical conductivity, temperature evolution, X-ray diffraction, and backscattered electron imaging were used to characterize the mechanical properties, degree of carbonation, dissolution-precipitation behavior, heat-release characteristics, and morphology of the hardening products. Results Repeated calcination significantly altered the phase composition of the clinker. The α-CS content of the B0 sample without repeated calcination was 34.4%, with considerable amounts of C₃S₂ and γ-C₂S remaining. After one and two repeated calcination cycles, the α-CS content increased to 64.9% and 89.7%, respectively. With a further increase in calcination cycles, the α-CS content of the B3 sample decreased to 85.9%, whereas the amorphous-phase content increased to 14.1%. The B2 clinker exhibited rapid hardening under CO₂ curing, reaching a compressive strength of 118.6 MPa and a carbonation degree of 41.5% after 24 h. At the early carbonation stage, both compressive strength and degree of carbonation increased rapidly; after CO₂ introduction, the pH decreased rapidly, electrical conductivity first decreased and then increased, and specimen temperature reached its maximum at 7 min. The carbonation products were mainly CaCO₃, predominantly aragonite, and silica gel, while a small amount of unreacted α-CS remained. Conclusions Under the present experimental conditions, two repeated calcination cycles promoted α-CS formation and produced clinker with a high target-phase content. The carbonation-hardening process of α-CS comprised an initial rapid dissolution-nucleation-precipitation stage and a subsequent slow densification stage controlled by the product layer. The synergistic deposition of CaCO₃ and silica gel in interparticle spaces and pores enhanced particle bridging and reduced porosity, thereby promoting strength development. These results provide a reference for optimizing the firing regime of α-CS clinker and its application in carbonatable binder.

Key words: α-CS; calcination regime; carbonation hardening; mechanical properties; microstructure