In-situ characterisation of early hydration of low-carbon cements containing thermally and mechanically activated kaolin

This study investigates the early hydration mechanism of limestone calcined clay cement (LC 3 ) system containing mechanically activated clay (MC) replacing thermally activated clay (calcined clay, CC). The phase assemblage including portlandite, ettringite, and carboaluminates was monitored using in-situ confocal Raman microscopy (CRM) and X-ray diffraction (XRD), and the hydration kinetics were studied through isothermal calorimetry (IC). Results revealed accelerated hydration in LC 3 -MC compared to LC 3 -CC, attributed to enhanced filler effect, increased reactivity, and the earlier formation of reaction products such as C-S-H gel. The different characterisation techniques demonstrated the earlier formation of portlandite and ettringite in LC 3 -MC, with significant differences in water distribution and composition patterns. Mechanical activation also led to more rapid and extensive formation of carboaluminates, improving early-age compressive strength. These findings highlight the potential of mechanically activated clay in LC 3 systems to enhance the sustainability and performance of cementitious materials by optimising clinker replacement strategies. • The incorporation of mechanically activated clay (MC) enhanced early hydration. • MC exhibited accelerated pozzolanic activity compared to calcined clay (CC). • Carboaluminate precipitation occurred earlier in the blended cement containing MC. • Strength of limestone calcined clay cement with MC was higher than that with CC.