| Resumo : |
Natural weathering is known as one of the key mechanisms responsible to cause degradation in building materials used in the external environment. Great effort has been done to develop new materials and new processes for protecting those already existent in order to face this challenge. Natural stones are an example of natural materials extensively used, since ancient times, that fit the durability need. Moreover, due to their unique aesthetic feature and the low CO2 emission in their exploitation chain, particularly important nowadays, these materials still have great importance in the construction business. While chemical interactions in natural stones, such as oxidation or hydrolyses, have been widely studied for a long time, the physical weathering due to daily variation of temperature in some kinds of metamorphic rocks has been considered as a key mechanism of degradation and incorporated in international standards just a few decades ago. A phenomenon, known as bowing, causes intergranular decohesion of calcite that might induce large warping of marble slabs and significant loss of strength in periods that vary from years to decades after exposition in the external environment. In this dissertation, thermoelastic analyses of slabs used in ventilated façades were explored. Firstly, a numerical approach to evaluate the influence of the anchoring systems and the restraint conditions of the slabs is presented. Afterward, the development of internal stresses due to thermal expansion in the transient and stationary heat flux is discussed for fixed boundary conditions. Finally, a model based on an exact solution to evaluate the thermal stresses considering the daily variation of temperature at the Pescara Justice Court's façade is presented. The outcomes indicate a greater influence of the changing in the thermal gradient through slab thickness rather than the absolute value of the thermal gradient between the surfaces on the induced stresses due to thermal actions. Furthermore, the rapid decrease of temperature on the exposed surface of an external covering system can be responsible to induce a higher level of tensile stress. |