Good conservation and restoration practices of cultural heritage assets rely on the knowledge of original materials. In the framework of the HERACLES Project (HERACLES-HEritage Resilience Against CLimate Events on Site, H2020 Grant Agreement 700395), dealing with the effects of climatic actions and natural hazards on built heritage, a set of important heritage sites are currently under study to improve their resilience against climate events. Among these are the medieval Gubbio Town Walls in Italy. The present work focuses on the mortars and binders of this monument and collected samples related to different parts of the Walls, corresponding to various historical periods of construction and interventions. They were characterized to determine their minerochemical composition, thermal behavior, and morphology. For that purpose, ex-situ laboratory techniques, such as X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WDXRF), optical microscopy (OM), polarized light microscopy (PLM), scanning electron microscopy (SEM), and simultaneous differential thermal analysis and thermogravimetry (TG-DTA) were used to discern trends in different sampling areas due to construction/reconstruction periods and building techniques.
The study of building materials constituting cultural heritage is fundamental to understand their characteristics and predict their behavior. When considering materials from archaeological sites, their characterization can provide not only relevant information for a broader understanding of the site and its importance and significance but can also increase knowledge about ancient materials and their performance. The Palace of Knossos is a very important archaeological site in the European history context, and its preservation benefits from the characterization of the constituent materials. Samples of mortars from this monument were collected under the scope of the H2020 HERACLES project, where a multi-analytical approach was chosen using established protocols for the different sample typologies. Instrumental techniques such as optical microscopy (OM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and simultaneous thermogravimetry and differential thermal analysis (TG–DTA) were used for the chemical, mineralogical, and morphological characterization of these mortar samples. The results indicate that the majority are lime mortars, both aerial and hydraulic, but gypsum-based mortars were also identified. Differences in the chemical composition of the samples in distinct areas of the monument allowed us to reflect on the variety of materials used in the construction of the Palace of Knossos.
The sheltered environment of the Algares +30 level adit (underground mine gallery) contributes to the preservation of secondary water-soluble minerals formed on the tunnel walls. The massive sulphide and related stockwork zone are hosted by the Mine Tuff volcanic unit and are exposed in the walls of the gallery, showing intense oxidation and hydrothermal alteration. Minerals from the halotrichite group were identified on the efflorescent salts, typically white fine-acicular crystals but also on aggregates with dark orange/brownish colour. Mineral characterization was performed using several methods and analytical techniques (XRD, XRF-WDS, SEM-EDS, DTA-TG), and the chemical formulas were calculated maintaining the ratio A:B ≅ 1:2 in accordance with the general formula of the halotrichite group, AB2(SO4)4·22H2O. This methodology allowed the assignment of the orange colour to the presence of trivalent iron on iron-rich pickeringite in partial substitution of aluminium.
<p>The preservation of archaeological sites, often considered as open-air museum, is a priority and a challenge due to their exposure to environmental actions and natural hazards. Every day, the artifacts populating these sites, which can have either structural or decorative functions, are subjected to continuous degradation processes, related to frost-thaw cycles, humidity and temperature variations, causing a deterioration of the materials mechanical properties. Anthropogenic pressure (visitors, human actions) can acts towards his direction, as well. In order to evaluate the ongoing process of degradation affecting a specific site, the study of the actual conditions of the materials is typically one of the first steps of the analysis. With this perspective, in this work, the results of the investigations carried out on the constituent materials of the Knossos Palace in Crete are presented. The Knossos Palace is one of the most important archaeological sites in Crete. The main excavation work took place at the beginning of the 20<sup>th</sup> century, directed by Sir Arthur Evans. The importance of this site led him and his collaborators to design and perform preservation actions, which included the reconstruction of relevant parts of the Knossos Palace. In addition for preserving the site, reconstructions were a way of highlighting the palace magnificence and the importance of the Minoan civilization. At that time concrete was already one of the most widely used building material. Considered a durable material, the concrete was used in the construction of reinforcement structures and new architectural elements, often placed in direct contact with the original ones. Nevertheless, the restoration/reconstruction made by Evans, using concrete, is nowadays considered an integral part of the monument and its history, to be studied and protected.</p><p>In the context of the HERACLES Project [1], samples of stones and concrete used in the Palace of Knossos were analysed to determine their morphological and chemical characteristics and their mechanical properties. For this purpose, an integrated approach, i.e. the use of several analytical techniques, was considered essential to support the material preservation actions.</p><p>[1]European Project HERACLES has received funding from the European Union Framework Programme for Research and Innovation HORIZON 2020 under GA n&#176; 700395</p><p>&#160;</p>
<div> <p>The Minoan Palace of Knossos and the Venetian coastal fortress &#8220;Rocca a mare&#8221; (Koules), located in Heraklion, Crete, Greece, are two important monuments for the history of mankind particularly vulnerable to environmental conditions, since they are located in an island subjected to strong variations in humidity and, as in the case of the Venetian fortress, in direct contact with sea water. In this type of surrounding environment, the formation of salt efflorescence as well as various other soluble salts crusts is a common situation. They occur according to the existing solubilization and crystallization conditions and can happen either in exterior or interior areas of the monuments. Their presence may stimulate further degradation, either due to the chemical dissolution of the substrate materials or due to the mechanical actions created by the formation of crystals, which may result in the decay of the substrate.</p> <p>A set of samples from both monuments were analysed using various laboratory (ex-situ) analytical methods such as optical microscopy (OM), X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Raman spectroscopy and Laser-Induced Breakdown Spectroscopy (LIBS). In-situ measurements using portable Raman and LIBS instruments were also performed. The comparative results from ex-situ analysis and in-situ measurements will be presented with emphasis to the chemical composition of the crusts and their origin. Results indicate that observed stalactites and salt efflorescence are directly related to the type of supporting material and the conditions of the surrounding environment. In general, the formation of crusts and salts are due to processes of alteration of the supporting material while the high impact of sea salt on the formation of the efflorescence at the Venetian coastal fortress was also confirmed.</p> <p>&#160;</p> <p>[1] This work was supported by the European Union&#8217;s Framework Programme for Research and Innovation HORIZON 2020 under Grant Agreement 700395 project HERACLES.</p> <p>Acknowledgment to the Portuguese Foundation for Science and Technology (FCT) UID/EAT/00729/2013 and EAT/00729-3 by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT&#8212;Portuguese Foundation for Science and Technology under the project number POCI-01-0145-FEDER-007688, Reference UID/CTM/50025/2013 NOVA.ID.FCT, and the PhD Scholarship SFRH/BD/145308/2019.</p> </div>
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