Hydration, mechanical properties, and life cycle assessment of high-volume fly ash CSA-OPC cementitious systems

To meet the requirements for rapid setting and early strength development while addressing the need for life cycle low-carbon design, this study investigates a composite cementitious system comprising ordinary Portland cement (OPC), calcium sulfoaluminate (CSA), and high-volume fly ash (HVFA). The hydration process and strength development patterns of composite systems with varying proportions of CSA, OPC, and FA were investigated. In particular, the setting behavior of the composite system under HVFA conditions was examined. Furthermore, a life cycle assessment was conducted to evaluate the carbon footprint and cost of the composite system. The results indicate that the binary 66% OPC–33% FA blend without CSA exhibited an initial setting time of 62 minutes but insufficient early-age strength. In contrast, the ternary 33% CSA–33% OPC–33% FA system shortened the initial setting to 50 minutes and achieved a 6 h compressive strength of 5.6 MPa, indicating markedly improved early strength development. The hydration heat and hydration product analysis revealed significant interactions between CSA and OPC during the early hydration stage. Life-cycle assessment (LCA) further shows that, compared with the pure OPC system (1028 kg CO₂ e/m³ and 1422.8 CNY/m³ for carbon emission and cost, respectively), the ternary 25% CSA and 50% FA blend achieves a 59.9% reduction in carbon footprint and an 11.2% reduction in cost. This system represents a low-carbon, cost-effective, and high-performance green composite material.