Pore water distribution in mortar during drying as determined by NMR

The drying of a saturated mortar sample was measured using Nuclear Magnetic Resonance. NMR is a technique which gives the total moisture content of a specific volume at a certain time. By looking also at the relaxation behaviour of the NMR signal, more information can be obtained. For every time and every position, the pore size distribution of the mortar was measured. Other techniques show that NMR is a reliable method to measure pore size distributions. Two distinctive pore sizes can be seen in the pore size distribution. This corresponds to the microstructure of mortar, which has small (< 10 nm) gel pores and bigger (approximate to 10 to 1000 nm) capillary pores. A one-dimensional drying experiment was carried out by blowing dry air (relative humidity = 0 + 5%; temperature = 20 +/- 1 degreesC) over the top of a cylindrical mortar sample, while all the other surfaces were scaled to prevent drying in other directions. The changing moisture content in the pores was followed with time during drying for about 3 days. This leads to the conclusion that the water cannot be extracted from the gel pores, while the capillary pores dry within about 20 hours under the drying conditions and time adopted.