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

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 degrees 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 degrees 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. (C) 2000 American Institute of Physics. [S0021- 8979(00)02619-0].