Fire effects on itacolomi quartzites from stonework historical buildings: implications for conservation of the cultural heritage

Fires can be a real threat to stone-built cultural heritages, and understanding the behavior of stones under thermal stress is strategic knowledge for efficient restoration and conservation management. In Ouro Preto, settled as a world heritage site by UNESCO, and Mariana, a living register of Brazilian colonial history, fire events are a critical factor threatening the historical stonework buildings. Ouro Preto and Mariana architecture is home to Baroque art based on Itacolomi quartzite record centuries-old Brazilian Portuguese stone mansory techniques. Therefore, this research aims to characterize the effects of fire in Itacolomi quartzites and its respective implications for Ouro Preto and Mariana stone-built heritages. Itacolomi quartzite blocks were sampled from three different mining areas, and characteristics such as aesthetics, mineralogy, and strength were observed before and after the fire experiment. A GRION furnace following the NBR 5628:2001 was applied for the fire experiment. Micromorphology and mineralogy variations were observed through scanning electron microscopy coupled with an energy-dispersive spectrometer and an X-ray diffraction. Compressive strength was used to assess the mechanical behavior after the fire. Significant aesthetics variations were observed after the fire experiment. Fe-oxidation and dehydroxylation of phyllosilicates seem to inflict aesthetic and mineralogical changes in quartzite samples. Compressive strength in quartzite blocks varies from 11.69 to 38.95 MPa before and 11.89 to 22.80 MPa after the fire experiment. This research shows that Itacolomi quartzites are susceptible to fire effects, and variations in mineralogy and strength should be considered in terms of restoration and conservation of the historical stone-built heritages.