Clinker-free cement based on calcined clay, slag, portlandite, anhydrite, and C-S-H seeding: An SCM-based low-carbon cementitious binder approach

A clinker-free cement (CFC) based on portlandite, calcined clay, slag, limestone powder, anhydrite, and C-S-H seeding is reported. The aim was to develop a low-carbon clinker-free cementitious binder using supplementary cementitious materials (SCMs), portlandite, a sulfate source, and accelerators. The impacts of ordinary Portland cement (OPC), portlandite, calcined clay and anhydrite on the strength of the C-S-H-seeded CFC were investigated. Strength, flow, setting and expansion of the mortar were investigated. Hydration kinetics were studied using calorimetry and XRD Rietveld analysis. Results showed that the seeded CFC exhibited similar strength and flow to OPC but produced significantly less heat. The factors contributing to the enhanced strength and improved flow behavior of the CFC were examined. Expansion behavior of CFC and its relationship with anhydrite content and ettringite formation was analyzed. Additionally, the microstructure of the hardened paste was characterized using SEM and mercury intrusion porosimetry (MIP) to evaluate the impact of C-S-H seeding. The combination of a low-carbon binder mix design and C-S-H seeding effectively reduced the CO2 footprint of cementitious binders, with the seeded-CFC achieving >50 % reduction in CO2 emissions per MPa compared to OPC. The proposed CFC binder approach was further validated using other types of SCMs.