Bestimmung der Wasser- und Salzgehaltsverteilung durch Kombination von NMR- und γ-Durchstrahlungsmessungen / Determination of water and salt content distributions by means of combined NMR- and γ-transmission measurement

Abstract

When a masonry loaded with salt is exposed to natural weather conditions there are occurring two interdependent mechanisms of transport: moisture- and salt transport. For the purpose of investigating these coupled processes, the Fraunhofer- Institute of Building Physics developed a measurement technique which allows a non-destructive determination of both water content distribution and salt content distribution in capillary porous building materials. This system includes two different nuclear physical measurement procedures: Nuclear Magnetic Resonance (NMR) and gamma-ray attenuation. The NMR unit produces a signal that depends just on the number of protons in the specimen. Because of this, the water content of the specimen is linked to the signal of the NMR-measurement. During a gamma-ray attenuation measurement salt and water content distribution are gauged simultaneously. The larger the density of the measured specimen is, the stronger is the attenuation of the gamma-rays when they pervade the matter. By combining the results of these two measurement methods it is possible to determine the salt and water content distribution simultaneously in a non-destructive way. From this profiles it is possible to draw conclusions in respect of the occurring transport processes and the correlative parameters such as for example capillary transport coefficients and water absorption coefficients of salt loaded building material. These results yield the preconditions for first concrete basic approaches to describe the coupled moisture and salt transport and furthermore the influence of the salt on the moisture transport. Lately numerous absorption tests on Sander Sandstone were carried out. The specimens sucked saline solutions of different salts and concentrations. After defined time steps the profiles of water and salt content were measured. Furthermore tests during the drying period were preformed on specimens loaded with defined saline solutions.