High Temperatures Impact on the Durability of Natural Stones: An Assessment by Means of Ultrasound Pulse Velocity Measurements

It is common knowledge that wildfires are one of the most severe threats to cultural heritage sites, especially in conditions of climate change. This work discusses the results from tests which were performed in order to study the effects of fire on the strength and cohesion of natural building stones. Particularly, the Italian natural building stones of Istria, Carrara and Lecce were studied, because of their extensive use in the construction and decoration of important cultural heritage sites of the Italian peninsula. One of the most common methods to simulate the fire event is by exposing the specimens on increased temperatures within ovens. In this study, specimens of the three above mentioned lithotypes are exposed to the different high temperatures of 300 °C, 400 °C, 600 °C and 900 °C in an oven for 6 h. The changes induced by thermal shock were assessed, by measuring ultrasound pulse velocity (US) before and after treatment. It was observed that the increase of the exposure temperature led to a reduction of ultrasound pulse velocity for all the specimens’ lithotypes. However, ultrasound pulse velocity decreased to different levels of the initial value for each lithotype per temperature interval. Thus, Istria stone demonstrated the greater reduction of ultrasound pulse velocity in the temperature interval of 300 °C–400 °C, Carrara marble in the temperature range of 400 °C–600 °C and Lecce stone in the temperature interval of 600 °C–900 °C, where it collapsed and lost completely its cohesion. It is concluded that Lecce stone after exposing to high temperatures presented the highest deterioration among the investigated lithotypes.