Complex weathering effects on durability characteristics of building stone
Published:January 01, 2007
P. A. Warke, B. J. Smith, 2007. "Complex weathering effects on durability characteristics of building stone", Building Stone Decay: From Diagnosis to Conservation, R. Přikryl, B. J. Smith
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Durability characteristics of five stone types are assessed and compared using the standardized sodium sulphate salt crystallization test and a modified laboratory weathering simulation in which a combination of salt weathering (Na2SO4) and freeze–thaw cycles are used. Data indicate significant differences in durability rankings between the two test methods especially in lower-order durability stone types. Both the standard salt crystallization test and the modified durability test identify Leinster Granite and Stanton Moor B Sandstone as the most durable of the five stone types, with the granite performing well under both sets of conditions. Discrepancy between rankings arises in the lower orders, with Portland Limestone, Stanton Moor A Sandstone and especially Dumfries Sandstone responding differently to the two sets of experimental conditions. In the modified durability test the range of permeability values for each stone type produced the same ranking as that indicated by mean percentage weight change values but mean permeability values for each stone type do not appear to be reliable predictors of weathering response. Differences in durability rankings between the two test regimes are attributed in the first instance to the temperature conditions used, with more extreme and unrealistic heating to 103 °C in the standardized test ‘over-weathering’ stone while conditions in the modified test allowed the development of stone-specific decay characteristics. Inclusion of salt weathering and freeze–thaw cycles in the modified test introduced complexity into the decay process that more accurately reflects ‘real-world’ conditions. Data also indicate that relatively minor structural and mineralogical differences between samples of the same stone type can significantly influence weathering behaviour, resulting in distinct rates and patterns of breakdown.
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Building Stone Decay: From Diagnosis to Conservation
Stone buildings and monuments from the cultural centres of many of the world's urban areas. Frequently these areas are prone to high levels of atmospheric pollution that promote a variety of aggressive stone decay processes. Because of this, stone decay is now widely recognized as a severe threat to much of our cultural heritage. If this threat is to be successfully addressed it is essential that the symptoms of decay are clearly identified, that appropriate stone properties are accurately characterized and that decay processes are precisely identified. It is undoubtedly the case that successful conservation has to be underpinned by a comprehensive understanding of the causes of decay and the factors that control them. The accomplishment of these demanding goals requires an interdisciplinary approach based on co-operation between geologists, environmental scientists, chemists, material scientists, civil engineers, restorers and architects. In pursuit of this collaboration, this volume aims to strengthen the knowledge base dealing with the causes, consequences, prevention and solution of stone decay problems.