Historic Building Stones and Flooding: Changes of Physical Properties due to Water Saturation

Natural stone is a common material in historic constructions. Flood events may directly affect surfaces of historic stone buildings. Since ashlars and stone sculptures often carry valuable cultural information, a more detailed knowledge about changes in physical properties due to water saturation is crucial for the assessment of their surface stability in case of flooding. Water saturation of stones leads to loss of mechanical strength and to expansion of volume (hydric dilatation). On the basis of data from literature, a rough scheme of vulnerability is suggested for different kinds of building stones. The majority of igneous and metamorphic rock types with dense crystalline structure are not vulnerable to flooding, whereas some types of pyroclastic rocks (tuffs) as well as clay-bearing sandstones are highly vulnerable. Detailed laboratory investigations on Elbe sandstone demonstrate the influence of petrographic features on material behavior due to water saturation. Results of laboratory tests are in good accordance to on-site observations made after the great summer flood in Dresden, Germany in 2002.