Investigation of early hydration dynamics and microstructural development in ordinary Portland cement using 1H NMR relaxometry and isothermal calorimetry

Benchtop 1H NMR relaxometry was used to measure the fine temporal resolution of microstructural development during the early hydration of ordinary Portland cement under different levels of retardation. Isothermal calorimetry was used to correlate the various distinct events in water transformation with the progress of hydration reactions. The low field (2 MHz) NMR technique used in this study detected signals from only the mobile water contained in the capillary and gel pores with water incorporation into hydration products highly correlated with heat production, including the reproduction of subtle features. Following the induction period, an initial T2 decline period, which encompassed the acceleration period of hydration, was characterized by incorporation of water into hydration products without any associated gel pore formation. Gel pore formation commenced at the peak in hydration rate, indicating a change in the morphology of C-S-H growth. All the observed features of microstructural development were preserved under retardation.