Regulating mechanism of ammonium salt on mechanical and microstructural properties of γ-C2S binder via CO2 curing

The effects of different ammonium salts (ammonium carbonate, diammonium hydrogen phosphate, ammonium sulfate, and ammonium chloride) on the carbonation mineralization performance of γ-C 2 S were investigated. Various analytical techniques were employed to characterize the mechanical properties, carbonation product compositions, morphology and pore structure of the hardened matrix. The results indicate that the performance of the hardened matrix after carbonation curing is closely related to the mineralization degree, the types of formed products, and the calcium carbonate structure. The introduction of ammonium salts altered the carbonation products and microstructure of the materials, reducing the Q 4 /Q 3 content of the silica gel and modifying the formation of vaterite, particularly in the systems containing ammonium sulfate, diammonium hydrogen phosphate, and ammonium carbonate. These changes consequently affected the pore structure. Among the different salts, the use of a 2 mol/L ammonium chloride solution showed the most significant improvement in the performance of the hardened material. Compared to the control group, the compressive strength and carbonation degree increased by 42.04 % and 7.33 %, respectively. This enhancement was primarily attributed to the increased calcium carbonate content, which reduced harmful pores and led to a more regular and stable structure of calcite particles. This study identifies key factors influencing the performance changes of γ-C 2 S-based carbonated materials under different ammonium salt dosages, providing new possibilities for the development of high-performance carbon-cured cementitious materials.