Petrophysical properties of selected Quaternary building stones in western Austria
Michael Unterwurzacher, Ulrich Obojes, Roland Hofer, Peter W. Mirwald, 2010. "Petrophysical properties of selected Quaternary building stones in western Austria", Natural Stone Resources for Historical Monuments, R Přikryl, Á Török
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In west Austria Quaternary building stones, such as lithic breccias of alluvial fans and talus slopes or calcareous spring tufa, have been frequently used as building stones since Roman times. Spring tufas are a widely used building material of historical objects in west Austria. This porous calcareous rock, formed by carbonate precipitation from calcium carbonate supersaturated spring waters, is an appreciated building stone: easy to quarry, lightweight, easily workable and relatively resistant to weathering. The Hötting Breccia, a lithified talus and alluvial breccia, has only been extracted in a few quarries near Innsbruck/Tyrol, however. Many of the mediaeval buildings of the towns of Innsbruck and Hall are built of this decorative type of stone. Petrography, mineralogical composition, porosity parameters and hygric properties have been investigated in this study from two tufas and one breccia occurrence. The results obtained reveal that these Quaternary stones, being formed at the Earth's surface, exhibit pore properties and hygric behaviour which differ considerably from other stone materials which have been subjected to the physical-chemical formation conditions of the upper Earth crust. This has implications for their workability, internal stability and weathering behaviour.
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Natural stone is considered to be a versatile, durable and aesthetically pleasing building material. From the beginning of civilization, important structures and monuments have been built from, or based on, natural stone. Until the end of the nineteenth century, the use of local stone resources was mostly in balance with the local environment. Strict environmental legislation has resulted in the closing of many long-standing quarries in industrialized countries, which has led to a shortage of traditional stone varieties. This has caused problems for restoration practice. Cheap, imported stone from less industrialized countries has become more widely available in recent years.
Some of the issues related to built stone conservation and restoration covered by this volume are: the establishment of inventories of possible replacement stones; understanding the decay mechanism and use of preventive conservation methods for slowing down decay processes; evaluation of the properties of natural stone; and assessing the risks of using replacement stones of different qualities.