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 (LC3) 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 LC3-MC compared to LC3-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 LC3-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 LC3 systems to enhance the sustainability and performance of cementitious materials by optimising clinker replacement strategies.