"Azul Valverde" slabs applied on exterior cladding - Degradation and alteration study

"Azul Valverde" limestone is a well known Portuguese natural stone that occurs as is extracted in Valverde - Alcanede, located in the Maciço Calcário Estremenho (centre of Portugal). It´s a fine grained calciclastic and bioclastic greyish limestone with some light-coloured spots. Azul Valverde is used in lots of exterior and interior industrial applications such as paving, cladding, masonry and decorations. Slabs made of "Azul Valverde" limestone 500x375x30 (mm) were used for exterior cladding with "kerf" fixing system in a building located in Valencia (Spain). After five years of its application signs of degradation were detected on the exterior facades where limestone slabs started to change color, and presented cracks and fissures that caused instability and breaks on the slabs. "Azul Valverde" limestone contains irregular patterns due to rock cutting across stylolites. These features represent ideal paths for fluid circulation through the rock slab and can be identify as weakness zones for exterior applications. Laboratory rock analysis were made in order to determine the clay and and the iron oxide contents in the limestone. Microscopic petrography, XRD and SEM observations were important to identify the interaction of the weathered clay material in stylolites and fossil contours. The results show the importance of using complementary characterization techniques for selecting stone on cladding applications, especially for sedimentary rocks with weakness planes. From the results it is possible to see that "Azul Valverde" stylolite planes influence on flexural and anchorage strength. Among other important remarks, results show the importance to acknowledge the rock structure and mineral composition before setting these natural products as construction materials. In the present work, the need for a proper stone selection was found important to avoid rock degradation, and hence contribute to avoid accidents and promote people safety as well as economic impacts.