Kinetics of mixing-water repartition in UHPFRC paste and its effect on hydration and microstructural development

The hydration of an ultra-high performance fibre reinforced concrete (UHPFRC) paste with a water to cement ratio of 0.18 was followed by proton nuclear magnetic resonance (1H NMR) alongside more classical techniques for hydration kinetics, and microstructural analysis. The states of water were quantified at different times by following the repartition of the “mixing water” after casting into “capillary water, gel water, CSH interlayer water and solid water” as hydration takes place. It was found that the capillary water is quickly depleted, and subsequently hydration continues with the consumption of the gel water. Overall the material becomes extremely self-desiccated with all water, bound in crystalline hydrates and the interlayer of C-S-H.