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"Stone Malta"
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Geohistorical Structural Design Tables for the Building Stones of the Maltese Archipelago
The engineering properties of building materials are essential knowledge when it comes to structural design. In 1885, the Crown Agents for the Colonies published a study on the resistance of Malta stone to cracking and crushing, in an attempt to develop stress design tables for local masonry. This article addresses the evolution of geological maps in the nineteenth century and, then, introduces the content of this publication. The geological formations described in the latest map are still used to this day. Finally, the usefulness of these tables in determining the mechanical properties of Maltese stone is discussed. To identify the quality of the stone discussed in this publication, a geological map available at the time, namely that published by Andrew Leith Adams in 1870, which proved to be moderately accurate, was used. The testing procedures applied followed the accepted laboratory practice at the time. A retrospective analysis of the contents of this publication reveals that the results contained some mathematical errors.
Journal Article
Hunter-gatherer sea voyages extended to remotest Mediterranean islands
The Maltese archipelago is a small island chain that is among the most remote in the Mediterranean. Humans were not thought to have reached and inhabited such small and isolated islands until the regional shift to Neolithic lifeways, around 7.5 thousand years ago (ka)
1
. In the standard view, the limited resources and ecological vulnerabilities of small islands, coupled with the technological challenges of long-distance seafaring, meant that hunter-gatherers were either unable or unwilling to make these journeys
2
,
3
–
4
. Here we describe chronological, archaeological, faunal and botanical data that support the presence of Holocene hunter-gatherers on the Maltese islands. At this time, Malta’s geographical configuration and sea levels approximated those of the present day, necessitating seafaring distances of around 100 km from Sicily, the closest landmass. Occupations began at around 8.5 ka and are likely to have lasted until around 7.5 ka. These hunter-gatherers exploited land animals, but were also able to take advantage of marine resources and avifauna, helping to sustain these groups on a small island. Our discoveries document the longest yet-known hunter-gatherer sea crossings in the Mediterranean, raising the possibility of unknown, precocious connections across the wider region.
Archaeological discoveries from Malta suggest that humans were present on the Maltese islands from around 8,500 years ago, providing evidence that Mesolithic hunter-gatherers made sea crossings as long as 100 km.
Journal Article
TEOS-based treatments for stone consolidation: acceleration of hydrolysis–condensation reactions by poulticing
Ethyl silicate (TEOS) is nowadays the most widely used consolidant for stone, due to its efficacy on silicate stones and also on limestones containing small amounts of quartz. However, because of the very long time required for TEOS curing reactions to be completed, the final mechanical improvement caused by the treatment is reached only after several months and, during this period, the treated stone is temporarily hydrophobic. This latter aspect is one of the most relevant drawbacks of TEOS, as it makes it impossible to perform water-based interventions after consolidation. Therefore, in this study the possible acceleration of TEOS curing reactions by prolonged contact with water, some time after consolidant application, was investigated. A commercial TEOS-based product was applied on Globigerina limestone, a porous stone from Malta containing also small amounts of quartz. After that preliminary tests indicated that prolonged contact with water is actually effective in both removing hydrophobicity and improving mechanical strength, a new consolidation cycle, based on TEOS application followed by application of a water-impregnated poultice was tested. The results of the study indicate that water application by poultice, after curing for 7 days, allows to remove the hydrophobicity and achieve higher mechanical properties than those obtained after curing for 4 weeks in laboratory conditions. Moreover, such mechanical properties are around 90 % of those achieved after curing for as much as 7 months, which points out that the proposed method is a very promising technique for accelerating TEOS curing reactions.
Journal Article
Geomechanical, durability–hygrothermal and thermal shock properties of Kocaeli Kandira stone used as building stone in historical structures
This study investigated the mineralogical, chemical, physical, mechanical, durability–hygrothermal, thermal shock properties, and economic aspects of the Kandira stone, one of the well-known natural building stones, commonly used in many historical structures in the Marmara and Thrace regions. Especially, it has been preferred to Malta stone in historical structures in Istanbul due to economic reasons at the beginning of the 1900s. A similar appearance and lithology with Malta stone and closeness of the Kandıra stone to İstanbul made it attractive to be used as natural building stone in historical monuments and new structures. The mean physico-mechanical properties of Kandira stone yielded 2.24 g/cm3 apparent density, 2.72 specific gravity, 19.21% total porosity, 5.8% water absorption by weight, 48 MPa compressive strength, 11.4 MPa bending strength. In terms of durability properties, Kandira stone has high resistance to aging by CaCl salt mist and no or low resistance to SO2 aging in a humid environment. Also, the freeze–thaw test of Kandira stone yielded an exceptionally low mass loss (0.11%) indicating that the stone is resistant to freeze–thaw effect. Thermal shock tests indicated that Kandira stone is mainly resistant to thermal shock cycles. Economically, the calculated probable reserve of Kandira stone resulted in 40.8 × 106 tons of material and the potential economic value based on the probable reserve is calculated around 54.672 × 109 TL (approximately €7.2B). In conclusion, this study defined the petrographic, geomechanical, durability–hygrothermal and thermal shock properties essential for the use of Kandira stone as building stone and restoration material.
Journal Article
The Intermittent History of Exploitation of Terrestrial Biotic Resources on the Small Islands of the Western Mediterranean Basin
We provide a synthesis of the history and the extent of human impact on the terrestrial ecosystems of the small islands and islets of the western Mediterranean. We focus on the exploitation of islands smaller than a few thousand hectares. The use of microinsular biotic resources (e.g., timber, soda ash, wild mammals) began as early as the Upper Palaeolithic, intensified during the Neolithic, and expanded during the Iron Age, peaking around the end of the nineteenth to the mid-twentieth century. As a consequence of long-lasting land exploitation, in many cases local terrestrial ecosystems were severely damaged and some of their living components disappeared. In other cases, even with uninterrupted human occupation over millennia, several insular resources have been sustainably managed. Although these small islands are currently under less pressure compared with neighbouring mainland coastlines, their protection or even the restoration is unquestionably necessary.
Journal Article
Engineering Geological and Geophysical Investigations to Characterise the Unstable Rock Slope of the Sopu Promontory (Gozo, Malta)
Different engineering geological and geophysical investigations were performed at the Sopu promontory in the island of Gozo (Malta), involved in an impressive lateral spreading process due to the superimposition of a stiff limestone (ULC) on a ductile clay (BC). The applied techniques include: traditional geological and engineering geological surveys, unmanned aerial vehicles (UAV) survey, electrical resistivity tomography (ERT) survey, ground-penetrating radar (GPR) investigations, single-station seismic ambient noise measurements, and array seismic ambient noise measurements. The integration of the obtained results allowed us to reconstruct a subsoil model of the promontory that includes features related to the local geology of the slope and to the landslide process, as well as to define a conceptual model that describes the main evolution phases of the expansion process. The presence of back-tilted rock blocks with no features of polarization of Rayleigh waves evidenced the different failure mechanism of the rigid UCL plateau at the Sopu promontory with respect to the Selmun promontory, located in the close island of Malta, where the lateral spreading due to the same geological setting tends to produce unstable rock blocks with a toppling mechanism. This result encourages further future observations and analyses of this topic.
Journal Article
Geochemistry, Mineralogy and Textural Properties of the Lower Globigerina Limestone Used in the Built Heritage
The Lower Globigerina Limestone Member, the oldest member of the Globigerina Limestone Formation, outcrops over most of the Maltese archipelago, notably Malta. It has provided the islands’ main building material since the Neolithic period. This paper makes available a corpus of findings relating to the geochemistry, mineralogy and textural properties of this limestone—mostly unpublished and undertaken nearly three decades ago—which provide a useful source to understand its behavior. Bulk chemistry and mineralogy showed that non-carbonate and clay content is higher in limestone of inferior quality. Textural analyses gave insight into the fabric of the matrix, including inter- and intra-particle porosity. These analyses were supplemented by an array of petrophysical tests, including color (a parameter which has a correlation with density and Fe2O3 content), ultrasonic pulse velocity and compressive strength. The findings not only give insight into the composition of the limestone, using insoluble residue content of ≥5% as the threshold of inferior quality lithotype, but provided an insight into the physico-mechanical bonding present, a characteristic which has a bearing on the deterioration of this limestone.
Journal Article
Maritimity in Stone: An Archaeology of Early Modern and Modern Ship Graffiti in the Maltese Islands (ca. 1530–1945)
Ship graffiti in Malta can be understood as an archaeological manifestation of a Mediterranean island’s maritime identity. The profusion and distribution of graffiti must be contextualized within local histories, naval powers, and maritime industry, and the ways these shaped the demographic and religious landscapes in the early modern period. Ship graffiti has the capacity to fill gaps in scholarship as well as raise important historical and archaeological questions. Technological advancements continue to revolutionize the documentation, study, and communication of graffiti sites. Systematic methodologies demonstrate the value of interpreting ship graffiti through an archaeological lens.
Journal Article
The Essential Oil of Thymbra capitata and its Application as A Biocide on Stone and Derived Surfaces
Many chemicals used nowadays for the preservation of cultural heritage pose a risk to both human health and the environment. Thus, it is desirable to find new and eco-friendly biocides that can replace the synthetic ones. In this regard, plant essential oils represent effective alternatives to synthetic substances for the preservation of historical monuments. Thymbra capitata (syn. Thymus capitatus) is a medicinal and aromatic plant growing in the Mediterranean area and endowed with important pharmacological properties related to its essential oil. Among them, the antimicrobial ones make the T. capitata essential oil an ideal candidate for industrial applications; for instance, as biocide for the inhibition and elimination of biological patinas of cyanobacteria and green algae on historical monuments. In the present work, we studied the chemical composition of the essential oil from T. capitata growing in Malta by gas chromatography-mass spectrometry (GC/MS). The major volatile component is the phenolic monoterpene carvacrol (73.2%), which is capable of damaging the cytoplasmic membrane and to interfere both in the growth curve and in the invasive capacity, though the contribution of minor components γ-terpinene and p-cymene cannot be disregarded. For the oil application on the stone surface, Pickering emulsions systems were prepared with an essential oil/water 1:3 mass ratio stabilized with kaolinite at 4 mass% in the presence of Laponite®; this allowed to limit the fast volatility of the oil and guaranteed a better application and an easier removal from the artefacts attacked by biodeteriogens both indoor and outdoor. This formulation caused the elimination of biodeteriogens from treated surfaces without residuals or films on artworks surface, and the effect was retained up to four months.
Journal Article