A methodological approach to define the state of conservation of the stone materials used in the Cairo historical heritage (Egypt)

The use of stone materials in cultural heritage and architecture represents a practice that has its roots in ancient times. Stone buildings, depending on the construction materials and their location in the urban context, are particularly vulnerable to weathering phenomena. These can be often accelerated by changes in environmental conditions linked mostly to the anthropic activities. In this way, the present work is addressed on the minero-petrographic and geochemical characterisation of samples taken from the built historical heritage in Cairo (Egypt), related to seven monumental areas. These sites have been chosen based on their historical importance, type of material, state of preservation and position in the Cairo context. The construction materials used and their degradation products were studied comparing the results obtained by means of different analytical techniques such as polarised light optical microscopy (POM), ion chromatography (IC), Fourier transform infrared spectroscopy (FT-IR) and the carbonaceous fraction, detected by using the thermogravimetry (TG). The results achieved demonstrated that black crusts and salt crystallisation represent the most common and damaging degradation products affecting all the monumental sites. Moreover, the environmental pollution produced by industrial activities and vehicular traffic has been identified as the main cause of these processes, followed by a marginal contribution of natural sources such as the sea spray. The data collected provide useful information to plan efficient conservation strategies in the future.