In situ synchrotron powder diffraction study of LC3 cement activation at very early ages by C-S-H nucleation seeding

Limestone Calcined Clay Cements, LC3, are being widely researched as low-carbon binders. However, the hydration reactions during the first day are key for their performances and they were not well known. Here, we employ in situ synchrotron X-ray powder diffraction to understand the hydration reactions that take place during the first day. The influence of two superplasticisers and three strength-enhancing admixtures have been investigated. The diffraction data were analysed by the Rietveld method and the results compared to mass balance calculations. For LC3 binders and in the absence of strength-enhancing admixtures, the hydration rates of the clinker phases, i.e. C3S, C3A and C4AF, are accelerated because of the filler effect. The C-S-H based-admixtures further accelerate the hydration of tricalcium aluminate and ferrite. Chiefly, it is firmly proved that the pozzolanic reaction takes place from 7 h onwards in the studied experimental conditions. The estimated degree of hydration of metakaolin at 22 h, in the studied binders, was ∼10 %.