Limits and Advantages of Different Techniques for Testing Moisture Content in Masonry

The research presents the innovative techniques used to measure different parameters related to water content in masonry. The MOdihMA (MOisture detection in historical MAsonry) research project involves experts from many research laboratories. The first objective of this project was to compare the effectiveness of the different methods to understand how the quantitative data obtained are directly related to water content. The second objective of the MOdhiMa project to compare the ability of the different techniques to map water as a function of its location and depth within the masonry structure, both on macro and micro-scale. The experimental phase on a case study was recently published in the scientific literature (1). The innovative techniques have application at different depth into the structure. The techniques based on IR Thermography (IRT) (2, 3) have application on the most superficial layers, and they allow to detect the “attitude “ of the surface to exchange water with the environment. The unilateral Nuclear Magnetic Resonance (NMR) (4), the Holographic Radar (HR) (5) and the Evanescent Field Dielectrometry (EFD) (6) probe the sub-surface at different depths (0.5 cm the NMR, 2 cm the EFD, up to 4 cm the HR). The fixed points of measurement (7) has application at different depths, from a few cm from the surface up to 20-30 cm deep inside the structure. This method, together with TRIME system and Fiber Optic Relative Humidity Sensor probe have their application at variable depths, with the only limit to have a sealed hole where the probe has to be kept. They are among the few techniques that allow to measure directly the variation of humidity in the deepest layers of the structure. The final part of the paper presents an overall discussion of the results, and an evaluation of the techniques according to measured parameters and values, the accuracy and reliability of the results, feasibility, the required environmental conditions for optimal performance, the time needed for measurements, and costs. The comparison between the nondestructive techniques showed the reliability of the applications and helped to determine the best use of each technique. It showed, for example, the suitability of each technique for noncontact investigation, as well as application on extended and non –planar surfaces. The new trend of this applied research in the field of diagnostics for Cultural Heritage is to make the use of instruments on-site reliable, feasible and affordable. Diagnostics on-site application depict a broader view of the building elements under investigation, as well as allows researchers to study those parts affected by moisture in comparison to the environment. This information is crucial to evaluate the risk of damage due to the environment and to plan the necessary actions for preventing further damages and loss of materials.