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Salt crystallization is widely recognized as a cause of deterioration of porous building materials. In particular, the crystallization pressure of salt crystals growing in confined pores is found to be the main cause for damage. The aim of this study is to better understand the degradation of porous rocks induced by salt crystallisation and correlate such processes with the intrinsic characteristics of materials. With this intend, an experimental salt weathering simulation has been carried out on two limestones widely used in the Baroque architecture of eastern Sicily. A systematic approach including petrographic, porosimetric and colorimetric analyses, was used to evaluate the correlation among salt crystallisation, microstructural and chromatic variations of limestone. Results showed a quite different resistance of the two limestones to salt damage, and this was found to be strongly dependent on their pore structure and textural characteristics.

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.

In the last decades, many researchers investigated the relation between environmental pollution and the degradation phenomena on the built heritage, because of their rapid increase and growing harmfulness. Consequently, the identification of the main pollution sources has become essential to define mitigation actions against degradation and alteration phenomena of the stone materials. In this way, the present paper is focused on the study of the effect of air pollution on archaeological buildings in Historic Cairo. A multi-methodological approach was used to obtain information about the chemical composition of examined black crusts and to clarify their correlation with the air pollution, specifically the heavy metals and the carbonaceous fraction, their main sources, and their impact on the state of conservation of the studied sites. All specimens were characterized by polarized optical microscopy (POM), X-Ray Diffraction (XRD), Electron Probe Micro Analyser coupled with energy dispersive X-ray spectrometry (EPMA-EDS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and Thermo-gravimetric analysis (TGA). The study conducted on heavy metals and carbonaceous fraction showed that the greatest contribution of the accumulation of pollutants is attributable to vehicular traffic and industrial activities, the main polluting sources in Cairo city. Furthermore, the comparison with other studies conducted on the carbonaceous fraction in the black crusts coming from both European and non-European cities, has allowed to discriminate the contribution of the primary and secondary polluting sources. Finally, the correlation of the data obtained on the heavy metals and the carbonaceous fraction allowed to formulate important hypothesis about the processes of sulphation.