Читать книгу Monument Future - Siegfried Siegesmund - Страница 211

Eleven Portuguese limestones were evaluated regarding their bowing behavior. Only one variety showed meaningful bowing values under thermohydric conditions. The slabs of this variety, named Valverde, show a constant rate of deformation and reach bowing values of about 8 mm/m. While under dry heating cooling cycles no deformation was observable, the addition of water lead to increasing deformation values. On the contrary, alternating dry and wet cycles enable the limestone samples to recover during the dry cycles. Only continuously wet conditions imprint permanent bowing.

Petrographic observations and dilatometry tests allow to identify several stylolites filled with iron oxides as a possible reason for this behavior. These irregular fractures open under thermohydric conditions. Beyond a certain opening limit, the asperities inhibit the minerals to retake the initial position and deformation will be permanent. Therefore, this stone should not be used under wet conditions combined with higher temperatures. Those conditions would cause a bowing behavior as reported in several cases.

Keywords: limestone; bowing; petrographic properties