Читать книгу Monument Future - Siegfried Siegesmund - Страница 188

The tuffs are broadly used in the monuments of Europe, Asia and North-America. The physical properties of the studied mostly acid tuffs are very different. Despite the high porosity (from 17 to nearly 37 vol%), tuffs can have relatively high tensile strength in dry conditions. This is significantly reduced with water saturation. The loss in strength can be one-fourth of the original one, but for most of the studied tuffs, it is half or two-thirds of the initial dry value. Not only water saturation but also freeze-thaw cycles and salt crystallization lead to a loss in strength or even an ultimate disintegration. There are tuff lithologies that can survive more than 100 salt crystallization cycles or 90 freeze-thaw cycles, while others disintegrate after few cycles. These differences in durability are attributed not only to porosity but also to pore-size distribution and micro-fabric, and are influenced by formation processes such as welding. Despite these findings and variations of durability, the usage of tuffs is still common, but at several sites the tuff elements show signs of deterioration.