Using an Ultrasonic Echo Technique to Inspect the Structure of a Pumice Brick Vault in a Church

摘要

Currently, the assessment of ultrasonic methods on pumice bricks is not a state-of-the-art technology. The vault of a neo-Gothic church made of pumice brick showed large cracks resulting from World War II and the structure of other areas was damaged. Normally, tasks like these are solved by visual inspection combined with drilling cores at a few measuring points. By this means, only the surface and just a few areas of the structure can be inspected. With ultrasonic echo it is possible to study the internal structure of the vault laminar. The investigations are non-destructive and have no effect on the monument. The entire vault of the nave and aisles was examined, using the ultrasonic echo technique. The structural constitution differs even in one nave. The results show the need for quality control of the various restoration measures (some of which are only "cosmetic") by means of the ultrasonic echo technique. With the results, a detailed restoration concept and a priority list were developed in which the areas that need chemical strengthening (e. g. with silicic acid esters) are defined. By metering the application of the chemical strengthening agent to improve the structure, significant savings in material costs are possible. In addition, the wooden roof structure was examined visually, tapped with a hammer, examined by an ultrasonic echo and drilling resistance technique and core samples taken. Areas with strong degradation caused by brown rot as well as other areas with active insect infestation were identified.