Abstract
Fire is a major decay agent of rocks and can generate immediate catastrophic effects as well as directional and anisotropic damage that affect long-term weathering processes. Temperature increase is the most relevant factor, among other components in a fire, generating mineral transformations and bulk mechanical damage. Mineralogical changes at high temperatures are key to understanding the overall mechanical behaviour. However, most studies to date were carried out after rock specimens were heated to a target temperature and cooled down to room temperature. Therefore, these studies are missing the observation of the actual mineral processes during heating. This paper aims to compare mineralogical changes in crystalline rocks during heating by means of XPS and different XRD techniques. Samples of four different granitoids were heated to several temperatures up to 1000 °C to evaluate their chemical and structural changes. Results show how standardised thermal expansion coefficients are not a suitable indicator of the bulk effect of high temperatures on rocks. Results also show how thermal expansion estimations from XRD lattice measurements may be an alternative to bulk dilatometric tests, as they can be performed with limited sampling, which may be necessary in some studies. Nevertheless, XRD and XPS results need to be interpreted carefully in relation to the bulk effects of temperature increase in the rocks, as the structural behaviour may seemingly contradict the macroscopic effect.
Highlights
Fire is a major catastrophic event for rock outcrops and stone structures, as it can generate both immediate and long-term damage [1,2]
Eagle Red (ER) is a medium-coarse grained reddish alkali-feldspar-rich granite quarried from the Wiborg batholite in the south of Finland
XRD lattice measurements can give an estimate of rock thermal expansion for crystalline rocks when a dilatometric test is not available or its use is not possible due to sampling restrictions
Summary
Fire is a major catastrophic event for rock outcrops and stone structures, as it can generate both immediate and long-term damage [1,2]. Recent events such as the Notre Dame of Paris fire, Brazil’s National Museum [3], or the increasingly frequent summer fires in southern. Climate change scenarios predict an increase in the frequency of these events [4,5,6]. Fumes, and gases generate different effects on rocks during a fire [7], temperature increase is arguably the main factor causing short-term mineralogical changes during a fire. Observations [8] noted the forest fires as a major factor causing scaling of rocks
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