NON DESTRUCTIVE MONITORING IN LABORATORY. UNDERSTANDING OF DAMAGING PROCESSES BY THE USE OF NMR ON MASONRY

摘要

Moisture content in laboratory specimens is generally determined by weighing the complete specimen, whereas moisture and salt distribution have to be assessed in a destructive way, either by slicing the specimen or by drilling powder at different depths. Disadvantage is that the result is rather imprecise or that the specimen is partially or completely destroyed as a part of the analysis procedure. MNR offers the opportunity to monitor moisture transport and to assess moisture distribution as a function of time, without the necessity to destroy the specimen. The use of NMR will be shown here in the context of damage analysis and as part of the research aiming at developing better compatible mortars for the observed damage case. Frost damage to bedding mortar appears to be a recurrent type of damage found in many restored Dutch monuments. The use of incompatible re-pointing mortar in the restoration was found to be an important cause of the damage. An example from practice of such a damage is shown and the research aiming at developing better compatible re-pointing mortars is shortly described, referring to the help NMR can offer in the understanding of the moisture transport process taking place in the brick-mortar system.