Читать книгу Monument Future - Siegfried Siegesmund - Страница 104

Thermal decay induced by fire produces chemical and mineralogical alterations, which are often accompanied by discoloration changing the aesthetic characteristics of the stone surfaces. It may compromise also the load-bearing capacity of the masonry elements and lead to stability problems.

Here we report on the investigation of the fire effects on a soft calcarenite used within a masonry building.

Mineralogical transformations of iron hydroxides were detected through XRD and accounted for red discolouring. They were confirmed by DSCTGA analyses and indicated a temperature around 300 °C affecting the stone. Microstructural modifications were investigated by means of optical microscopy and UPV propagation test. A quantitative determination of physical parameters such as color, bulk density, porosity and water uptake was also performed. Implications of thermal stress with the mechanical properties were assessed through uniaxial compressive tests. Thermal effects on the stone microstructure were not microscopically evident. On the contrary, UPV decreases indicated a microfissuring, but this slightly affected porosity, water uptake and compressive strenght.