Spatially resolved pore-size distribution of drying concrete with magnetic resonance imaging

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Abstract
A study of the spatially resolved water-occupied pore size distribution in a drying concrete cylinder is reported. Pore sizes are obtained from freezing point depression of pore water for a temperature range of 0 to −40 °C, assuming that the freezing point is inversely proportional to pore diameter. Single-point magnetic resonance imaging techniques were used to monitor unfrozen water content as functions of position and temperature. It was observed that freezing began at −10 °C in the cylinder center, which had the highest moisture content, and with a further temperature decrease, the freezing region gradually spread to the exposed end surfaces. The central region had a broad water-occupied pore size distribution, with pore diameters as large as 10 nm. The occupied pore sizes became progressively smaller as the moisture content decreased in proximity to the exposed surfaces.