In-situ dynamic WetSEM imaging and electrical impedance measurements on Portland cement during early hydration

Wet scanning electron microscopy (WetSEM) and electrical impedance measurements have been employed to study the physico-chemical processes during the early hydration of Portland cement. The WetSEM study employed the Quantomix WetSEM capsule, allowing examination of the morphology of hydrating cement directly in situ via 36 semi-electron-transparent windows under SEM vacuum conditions over the initial 24-h after gauging whilst maintaining the test sample under atmospheric conditions. This qualitative assessment was used to aid interpretation of the stages of early hydration identified from impedance measurements, which were taken on a replicate specimen over the frequency range 1 kHz-1 MHz. It is shown that detailed frequency- and time- domain impedance measurements allowed identification of key processes during setting and early hardening which were correlated with data from the WetSEM study. Attention is directed to the sequence of hydration obtained from the two techniques and how they provide both supporting and complementary information.