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The specific surface areas of sealed-cured hardened cement pastes (HCP) were evaluated during the hydration process using three types of Portland cement and with two different water-to-cement ratios. The BET surface area was measured by water vapor/nitrogen sorption and directly compared with that obtained by the fast exchange model measured by 1H NMR relaxometry. The results confirmed that the total surface area evaluated by 1H NMR was consistently 2–2.5 times larger than the water vapor BET surface area for different HCPs. This difference is attributed to the local stacking of C-S-H layers: the surface between adjacent stacked layers is not measurable by water vapor due to the nature of the pre-treatment, while 1H NMR is able to measure the entire interlayer surface. The nitrogen surface area is better able to include the majority of the HCP gel pore surface by 1H NMR for white and high-early-strength Portland cement.
Kurihara et al. (Tue,) studied this question.