The Use of Dicalcium Silicate (C₂S) Based Composites for Environmentally Friendly Applications

Abstract

Dicalcium silicate (C₂S, Ca₂SiO₄), commonly known as belite, has attracted significant research attention as a versatile material for environmentally sustainable applications. As the second most abundant mineral phase in ordinary Portland cement clinker, C₂S offers distinct environmental advantages over tricalcium silicate (C₃S), including lower limestone requirements, reduced clinkering temperatures (approximately 200 °C lower), and consequently diminished CO₂ emissions during production. This comprehensive review examines the crystal chemistry and polymorphism of C₂S, covering its five well-established polymorphs (α, α′H, α′L, β, and γ), their interconversion pathways, and the implications of each polymorph for specific applications. The review critically evaluates three principal domains of environmentally friendly application: (i) low-carbon cementitious binders and carbonation-cured construction materials, where C₂S serves both as a low-energy binder and as a CO₂ sink capable of sequestering atmospheric carbon dioxide; (ii) biomedical materials, where the bioactivity, biocompatibility, and osteoconductivity of C₂S-based composites enable applications in bone tissue engineering, dental restorations, and drug delivery; and (iii) industrial waste valorization and environmental remediation, where C₂S phases present in steel slags and other metallurgical by-products are exploited for CO₂ mineralization and heavy metal immobilization. Synthesis strategies—including solid-state reaction, sol–gel processing, hydrothermal synthesis, and combustion methods—are discussed with emphasis on their influence on polymorph selection and reactivity. Finally, current challenges and future research directions are outlined, highlighting the need for enhanced early-age hydration kinetics, scalable activation strategies, and integrated life-cycle assessment of C₂S-based systems.