Meeting of the Materials Science and Restoration Society edition:6 location:Karlsruhe, Germany date:September 2003
Geo-electrical survey of masonry is a suitable non-destructive tool for the diagnosis of a deteriorated structure, for judging the need of restoration, for controlling the efficacy of injections. In the past the analysis of the measurements was carried out with the aid of apparent resistivity maps. More recently, the interpretation of the measurements was improved by using relative difference maps and by the incorporation of influences such as changing moisture content, the presence of soluble salts and geometric boundaries.
This paper describes how the most recent developments in geophysics, within the field of geo-electrical survey of soils, can be implemented for the conditions of masonry structures. The measurements are carried out to construct a pseudo-section, which is the graphical representation of the apparent resistivity values for a 2D-section of the masonry wall.
Inverse modelling enables to reproduce the resistivity distribution in the masonry structure that matches with the obtained data of apparent resistivity (pseudo-section). Inverse modelling apparently allows visualising the inner condition of the structure more accurately. Possibilities and limits of the measuring technique are given in order to create realistic expectations.
The analysis of the data, obtained during two on site measuring campaigns, clearly shows that the interpretation of the inverse model is many times easier than the interpretation of the apparent resistivity maps (the measured pseudo-section). The results of these experiments were verified by endoscopic survey of the measured structure. The method also proved to be capable of finding the buttresses at the rear side of a historical rampart.