Ceramics-Silikáty

The C₄A₃$-C₄AF-C₂S-C₅S₂$ cement system, as a low-carbon cement, relies critically on mineral composition for hydration and performance, yet specific impact has not been thoroughly investigated. In this study, C₄A₃$-C₄AF-C₂S-C₅S₂$ clinkers with different mineral compositions were calcined to evaluate the influence of the mineral compositions on the cement performance. After identifying the optimal mineral proportion, the effects of the gypsum type and dosage on the cement performance were further investigated. The workability, strength, and drying shrinkage were tested, and the hydration behaviour of C₄A₃$-C₄AF-C₂S-C₅S₂$ cement was also analysed using XRD, hydration heat, and TG-DSC. The results indicate that a balanced C₄A₃ $/C₅S₂$ ratio of 1:1 yields the optimal performance, with the composition of 35 wt.% C₄A₃$ and 35 wt.% C₅S₂$ achieving a 28-d compressive strength of 48.6 MPa and low drying shrinkage. A microstructural analysis revealed that the continuous formation of AFt, sustained by SO₄^2- released from the gradual hydration of C₅S₂$, is the key mechanism ensuring the long-term strength development and volume stability. Furthermore, 15 wt.% natural gypsum is identified as the optimal dosage to regulate the early hydration and shrinkage, while desulfurisation gypsum leads to increased later shrinkage due to its lower dihydrate content and insufficient AFt formation.