Validation of conventional concrete water transport test methods by spatially resolved 1H magnetic resonance.

Concrete is the most used man made material worldwide with about 1.4 m3 being produced per person every year. As the service life of civil engineering structures is usually 50-100 years, the long-term durability of concrete is a significant issue. The content and mobility of water especially in the surface layers plays an important role in most durability aspects of concrete. Conventional tests of water transport in concrete are empirically derived and usually based on mass increase or visual observation. These tests give no information on the state of water or the saturation within the pore structure of concrete and are not linked to transport theories. Few, if any in-situ, non- destructive test method exists that provides spatial resolution of water content as a function of distance from the surface. A recently developed one-sided ‘H nuclear magnetic resonance (NMR) setup allows the investigation of samples larger than the equipment itself and gives spatial resolution of water profiles down to a depth of circa 25 mm. Moreover, in principle, NMR allows the classification of water in porous materials by pore type. The aim of this work was to use a one-sided NMR with a standard procedure for water content that can be readily applied and easily interpreted and understood. Both the test protocol and the instrument, which were developed under laboratory conditions, required refinement for application in an industrial setting. This required the calibration of the measurement and the optimisation of data acquisition and analysis for concrete and mortar. The practical limitations of the NMR method are discussed. To provide a scientific background for these tests the water profiles obtained by NMR were compared to conventional capillary absorption and permeability test results. Further investigations of water transport revealed that swelling of the calcium-silicate-hydrate gel is a probable cause for the sorptivity anomaly. The NMR results showed that visual observation is a poor indicator of water penetration depth as there is a significant amount of water present beyond the visual waterfront