Hydration phase and pore structure evolution of hardened cement paste at elevated temperature

Abstract

To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste, several measuring methods including X-ray diffraction (XRD), atomic absorption spectroscopy (ASS), ion chromatography, conductivity meter, alternating-current impedance spectroscopy and nuclear magnetic resonance (NMR) are employed to investigate the hydration characteristics, pore solution composition and conductivity, resistivity and pore structure during the steam curing process. Experimental results show that steam curing promotes the hydration process, greatly raises the resistivity, and decreases the porosity of specimen at early age. Compared with being treated at 45 °C, higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period, which improves the relative content and ionic activity of the conductive ions in pore solution. Furthermore, the number of pores larger than 200 nm increases significantly, which reduces the resistivity of the hardened cement paste. Cement paste treated at 45 °C has a more stable and denser microstructure with less damages.

Keywords

cement paste / high-temperature curing / pore structure / AC impedance / nuclear magnetic resonance

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