Artificial weathering assessment of Persepolis stone due to heating to elucidate the effects of the burning of Persepolis

Abstract Historic buildings can suffer from the effects of fire due to either accident or warfare. Temperature increases due to fire play an important role in the degradation of monument stones. This article presents the results of research dealing with the effect of fire and high temperature on limestone as the principal construction stone of the Persepolis complex. This study tries to convince the relevant authorities to protect the already fire-weathered stones against further damage. The physical and mechanical properties of Persepolis stone (in the saturated and dried state) were studied under various temperatures ranging from 20 °C to 600 °C. Observations revealed changes in colour and cracking development, which are thought to be the effects of heat on this stone. Decomposition of organic matter is probably the main factor responsible for the colour changes in the specimens as it is most prominent above 400 °C. Cracks grew preferentially along the crude lamination rich in clay minerals. Furthermore, the density of the specimens decreases with increasing temperature, while their porosity increases slightly when they are heated to 200 °C and above. Up to 0.57 and 0.92 % mass losses were also observed in the dried and saturated specimens, respectively, when the specimens were heated to 600 °C. This negligible mass loss could be attributed to the low porosity of the specimens. Both point load strength index (Is50) and Brazilian tensile strength values of the specimens increased at temperature of 20–600 °C. This is probably due to closure of the original cracks/voids as a consequence of clay mineral recrystallisation after heating. Although the Burning of Persepolis created some cracks in the Persepolis stones, it increased their inherent strength.

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