Single-point Magnetic Resonance Imaging (MRI) of cement based materials

The use of Magnetic Resonance Imaging (MRI) as a tool for non-destructive testing of moisture distribution and moisture migration in concrete and mortar is described. MRI spatially resolves in one, two, or three dimensions, the evaporable water content in cement based materials as a function of time, treatment or processing conditions. The use of the technique is demonstrated through studies of drying and freezing behavior in partially saturated materials. Studies of one-dimensional drying of concrete cylinders show a clear dependence of the capillary and diffusive drying rates on moist curing time and water-cement ratio. Three-dimensional imaging is demonstrated to visualize the internal moisture distribution in concrete. MRI experiments may spatially resolve the freezing behavior of concrete, and thereby determine the occupied pore size distribution. In addition two-dimensional time resolved imaging of a propagating freezing front into a model concrete wall is demonstrated. Finally a modification of the basic methodology is described which permits imaging of nuclei other than hydrogen. Chloride and sodium distribution in mortar, associated with salt water invasion, may thereby be determined.