Spatially resolved pore-size distribution of drying concrete with magneticresonance imaging

A study of the spatially resolved water-occupied pore size distribution in a drying concrete cylinder is reported. Pore sizes are obtained from freezi ng point depression of pore water for a temperature range of 0 to -40 degre es C, assuming that the freezing point is inversely proportional to pore di ameter. Single-point magnetic resonance imaging techniques were used to mon itor unfrozen water content as functions of position and temperature. It wa s observed that freezing began at -10 degrees C in the cylinder center, whi ch had the highest moisture content, and with a further temperature decreas e, the freezing region gradually spread to the exposed end surfaces. The ce ntral region had a broad water-occupied pore size distribution, with pore d iameters as large as 10 nm. The occupied pore sizes became progressively sm aller as the moisture content decreased in proximity to the exposed surface s. (C) 2000 American Institute of Physics. [S0021- 8979(00)02619-0].