Reducing clinker factor in limestone calcined clay-slag cement using C-S-H seeding – A way towards sustainable binder

C-S-H seeding was used in limestone calcined clay cement (LC3) to reduce the ordinary Portland cement (OPC, equivalent to clinker factor) while maintaining strength similar to that of neat OPC. The combination of calcined clay with other supplementary cementitious materials (LC3+), including microsilica, slag (GGBFS), and fly ash, was investigated. The impact of anhydrite content and Na2SO4 was studied. The results showed that C-S-H seeding dramatically enhanced strength from hours to 1 year. The OPC content can be <50 wt% in LC3 and LC3+ cement with C-S-H seeding to achieve comparable strength. The combination of calcined clay, GGBFS and portlandite with C-S-H seeding significantly reduced the OPC content to 20 wt%. Replacing part of the calcined clay by fly ash, GGBFS or limestone improved the mortar flow. Correlations of heat release and pore size with strength showed that C-S-H seeding increased strength by not only acceleration but also through microstructural changes.