The church of St. Saturnino in Cagliari, Sardinia, reading the levels of history through the use of digital survey and the petrophysical study of materials

The most ancient church in Cagliari is dedicated to Saint Saturno (commonly named Saint Saturnino), the first indications about this church came from the sixth century, but the building arrived to our time is only a part of the original one and it rises over the ruins of previous structures, inside a a walled area with the presence of a Palaeo-Christian necropolis. The original Greek cross plan with a transept and a semi-spherical dome; has seen meaningful transformations in time, with the partial destruction of large parts of the building. All the four arms had a nave and two aisles, but the current church consists only of the dome-covered area and of the eastern arm, with a nave and two aisles. The whole church shows very interesting parts coming from previous architectures of the Roman age, a rich catalog of rich materials and details. In summer 2013, a collaboration between the Departments of Chemical and Geological Sciences from Cagliari and the one of Architecture from Florence brought to the realization of a detailed study about this ancient church. The whole building and its surrounding area were surveyed with the following methods: photography, 3D Laser Scanner for the whole interior and exterior parts, 3D photogrammetry of a selected set of stone surface samples, direct sampling of representative rocks for geochemical and petrophysical analysis. All data were then treated and analyzed to deepen the knowledge about the most meaningful aspects of different construction techniques and use of materials, provenance of raw materials, stone and structure alterations. As the result, a base was created to read common behaviors, design choices, recursive constructive solutions, and the “models” guiding the ancient intentions. This contribution will present the progress state of this research and its results

Relations between static-structural aspects, construction phases and building materials of San Saturnino Basilica (Cagliari, Italy)

The construction site was used several times: in a first phase, in the republican era of Roman domination it hosted, probably, a temple whose height could reach 25 meters; in a second phase, during the Roman Empire, it was used as a burial area. Then around IV-V century AD a first Christian Basilica made of a naved building with an apse was built there, at the center of a large monastery. Subsequently in a third phase in VI century AD a Byzantine Martyrium, with a Greek cross-shaped plan, was built: the central part of it, supporting a dome is still standing. Finally after 1089 the church was given to Marsilian monks who deeply renovated it and changed its shape converting the plan to a Latin cross. A macroscopic material analysis shows the presence of various rocks, whose use appears to be inhomogeneous during all construction phases. Sedimentary rocks (limestones, sandstones, calcarenites etc belonging to local geological formations) are generally used for masonry structures. Marbles, mostly coming from abroad and previously used in Roman buildings have been adopted for architectural elements (columns, capitals, and so on). At a lower extent there are masonry blocks in Oligo-Miocenic volcanic rocks and seldom stone materials which are not originally from Sardinia. Both mineralogical and petrographic tests (e.g. XRF, XRD) and the most important physical properties (porosity, density, water absorption coefficients, compressive, flexural and tensile strength, etc) show that many of the more representative samples of rock materials (like limestonss, calcarenits) are often highly decayed, with a corresponding reduction of their mechanical strength. A structural analysis is particularly useful for helping in clarifying the historical evolution of the building, checking reconstruction hypotheses and assessing the true residual strength of the more important parts. An example, a FEM analysis of the Byzantine domed part is presented here

The coastal fortification of Cape de Forma (Menorca, Spain): petrophysical characterization and alteration of stones and ancient mortars

[EN] The site of Cap de Forma is frequently mentioned in the cartography of the 18th and 19th centuries, particularly the tower of Es Canutells. The archaeological site of Cap de Forma is on a coastal cape, and consists of a main cyclopean monument, which closes off an isthmus, a necropolis of rock-cut tombs (cuevas) dug out the cliff overlooking the sea and a second, very degraded, more central area. The promontory rises above the sea, with cliffs of more than 30 m in height. On the isthmus, the large elongated rectangular cyclopean construction protects the entrance from the interior. It is not a Talayot, at least not in the common sense of the term, as the building is different from the known types of this class of monument. The external wall is roughly built. It consists of local limestone slabs, mainly placed horizontally but with some vertical ones juxtaposed among them. Once one passes this wall, through an opening near the edge of the cliff, one can access the south of the structure. Here the slow collapse of the monument and its use as a modern military lookout post have combined to give the walls an untidy appearance. It consists of massive parallel walls arranged roughly in large steps, alternating with piles of small stones. Some walls were probably destroyed by the troops stationed in the adjacent fortified manor house in the 18th century AD, were also detected in this space. In a open space, between two living areas (central and eastern spaces), a large cylindrical hollow carved into the limestone was found in a depression filled with small stones. This may well have been a cistern for collecting rainwater for the resident community.Depalmas, A.; Columbu, S. (2015). The coastal fortification of Cape de Forma (Menorca, Spain): petrophysical characterization and alteration of stones and ancient mortars. En Defensive architecture of the mediterranean: XV to XVIII centuries. Vol. II. Editorial Universitat Politècnica de València. 381-388. https://doi.org/10.4995/FORTMED2015.2015.1758OCS38138

Alteration processes of geomaterials used on the pentagonal tower of Serravalle Castle (central-west Sardinia, Italy)

[EN] The pentagonal tower belong to medieval Serravalle castle area (81 m. above sea level), near the mouth of the Temo River. The castle is important medieval fortifications of Sardinia and was built in various stages. The oldest part was constructed by Marchesi Malaspina of Villafranca which arrived in Sardinia at the 12th century (1112-1121). The earliest fortification was the four corner towers about 10 m tall, linked by a thick wall. The pentagonal tower, located in the western corner of the boundary dates about 1330, probably was consisted of two storeys with wooden beams, now missing, and one stone one with a longitudinal arch. In the structure was used local volcanic rocks (i.e., pyroclastites) belonging to the Oligo-Miocenic volcanic cycle of Sardinia (32-11 Ma). According to De La Roche classification (1980), the pyroclastic rocks have a composition varying from dacite to rhyolite and show a porphyritic structure (I.P. from 10 to 20%) for phenocrystals of opaque (ilmenite, magnetite and/or titanomagnetite), plagioclase, ± biotite, and rare hornblend and quartz. Two main type of volcanics are present with different physical properties (porosity, density, etc.) and petro-volcanological characteristics (e.g., welding degree): cineritic pyroclastites, little welded, with average values of open porosity and bulk density of 36.3±2.6% and 1.50±0.07 g/cm3, respectively; lava-like ignimbrites, from medium to high welded, and average values of open porosity and bulk density of 22.5±5.9% and 1.99±0.15 g/cm3, respectively. As function of these different features and extremely heterogeneous, due to variable incidence of pumice, lithic- and crystal-clasts, the alteration is present mainly on volcanics with low welding and exposed to the sea-winds. Due to marine aerosol, salt efflorescences are present. These latter, together thermal and hydric cyclic dilatation, lead to various macroscopic physical alterations (decohesion, chromatic alteration, pitting, exfoliation, flaking, alveolation, differential degradation between the lithic-clasts and the vitreous matrix).Columbu, S.; Meloni, P. (2015). Alteration processes of geomaterials used on the pentagonal tower of Serravalle Castle (central-west Sardinia, Italy). En Defensive architecture of the mediterranean: XV to XVIII centuries. Vol. II. Editorial Universitat Politècnica de València. 373-380. https://doi.org/10.4995/FORTMED2015.2015.1757OCS37338

The ancient pozzolanic mortars and concretes of Heliocaminus baths in Hadrian s Villa (Tivoli, Italy)

The aim of this work is the physical and mineralogical-petrographic characterization of the mortars from the Baths with Heliocaminus, a special and unique ar- chitectural building in the complex of the Hadrian’s Villa in Tivoli. Thirty samples were investigated for composition and physical properties (density, porosity, water absorption, me- chanical strength, particle size distribution of aggregate, etc.), representative of eight mortar groups: cubilia bedding mortar, brick bedding mortars, floor-coating and wall-coating bedding mortars, floor (rudus) and wall conglomerates (trullisatio), vault concretes, and lime plasters (arriccio). Physical param- eters, together with the microscopic analysis and binder/ aggregate ratio determined in three ways using image analysis (on thin sections and on specimens) and weight-data from dissolution of binder, have shown an interesting relationship between the physical-compositional characteristics and the function of mortars within the structure of the Heliocaminus baths. To identify the minerals and the reactant phases be- tween binder and aggregate, as well as the hydraulic degree, selected samples were analyzed with x-ray powder diffraction, thermogravimetry, and differential scanning calorimetry tech- niques. The obtained results provide a close relation between pozzolanic characteristics and physical-mechanical properties of the mortars (i.e., punching strength index)

The construction materials and static-structural aspects of the Budello tower (Teulada, southwest Sardinia, Italy)

[EN] The Budello tower is located on a slight promontory from which it dominates the entire bay of Teulada and the towers of Sant’Isidoro, Pixinni, Malfatano and Porto Scudo. The tower, built in 1601 with irregular ashlars of local stones (mainly of magmatic-intrusive origin), has a truncated cone shape, an external diameter of 10,2 m and a height of 11,80 m. Inside it consists of a single room, with a domed vault and a central pillar, equipped with a embrasure, a fireplace, a trap door in the cistern, and a staircase, from which the square of arms was accessed. It was a torre de armas garrisoned by: 1 commander (in 1603), 1 artilleryman and 4 soldiers (1767), 1 artilleryman and 3 soldiers (1801), 1 artilleryman and 4 soldiers (1812). Although it underwent several restorations, documented as early as the years 1617-1619, the tower remained generally in good condition until the period 1763-1784, in which new restoration works were carried out including the closure of the parade ground with a classic parapet with gunboats and battlements. Other restoration works are carried out in 1808, 1819 and 1840. The tower remained in operation until 1843. Like all the other coastal fortifications, it was then definitively demilitarized with the Regio Decreto of 25 April 1867. Specific objectives of the research are the petrographic and physical-mechanical analysis of the stones and ancient mortars used in the construction of the tower, the structural analysis of the building and related geometric-constructive characteristics. The final intention is to understand the decay processes taking place on the tower both in terms of materials and static-structural aspects, and to envisage possible restoration interventions to be implemented aimed at its conservation.Columbu, S.; Picchizzolu, G.; Cazzani, A. (2020). The construction materials and static-structural aspects of the Budello tower (Teulada, southwest Sardinia, Italy). Editorial Universitat Politècnica de València. 1485-1492. https://doi.org/10.4995/FORTMED2020.2020.11549OCS1485149

Origin of Roman worked stones from St. Saturno christian Basilica (south Sardinia, Italy)

The work aims to define the origin of the architectural stone elements worked by Romans and reused in the St. Saturno Basilica, between the late Antiquity and Romanesque periods. Thus, different rocks (marbles, various facies of limestones, volcanic rocks) used to construct the ancient building were sampled and analysed. All the different kinds of stones were sampled from the Basilica, taking precise reference to the various construction phases and structural changes of the monument occurred in the centuries. The sedimentary and volcanic lithologies belong to the local outcrops of Cagliari Miocenic geological formation (e.g. limestone) and to other volcanic outcrops of south Sardinia, respectively. By means of a multi-method archaeometric study (mineralogical-petrographic observations on thin sections and O-18 vs C-13 stable isotope ratio analysis), the provenance of classical marbles used for manufacturing Roman architectural elements (column shafts, bases, capitals, slabs, etc.) were defined, which are thought to come from extra-regional sources. The results show that the marbles come mainly from Apuan Alps (Italy) and subordinately from Greek quarrying areas

K/Na-silicate, ethyl-silicate and silane nano-molecular treatments in the restoration of high porous limestone

Carbonate sedimentary rocks (i.e., limestones) have been frequently used in historical times due to easy availability and workability. These latter depend primarily by petrophysical characteristics (porosity, bulk density) that influence the mechanical strength. However, the limestones with high porosity (>30%) and a poorly cemented carbonate-matrix show chemical alteration (i.e., dissolution) and physical decay (e.g., decohesion). In this work it was taken as case study a biomicritic limestone belonging to the carbonatic miocenic series (lower Tortonian) of Cagliari (southern-Sardinia, Italy). This limestone has a low-medium cementing matrix containing hygroscopic clay and sea-salt phases, which make the rock degradable. To limit the decay it can intervene with consolidating products (K-Na-silicate, ethyl-silicate) and protective-chemicals (silane nano-molecular gel-coat) to reduce the porosity and permeability to the liquid aqueous phase. Results highlight an increase of strength after consolidation and a decrease of gas-permeability after protection-treatment, maintaining in both cases a good permeability to the vapor-phase

Archaeometric study of mortars from the Pisa's Cathedral Square (Italy)

The present work is focused on the study of forty-two mortars used in the construction of both Roman buildings, old Pisa’s Cathedral and Modern structures in the Miracles Square (Italy). This area, included since 1987 in the World Heritage List of the UNESCO, is famous for the presence of an important historical complex built in the Middle Ages (the Cathedral, the Baptistery, the Leaning Tower and the Monumental Cemetery). The archaeologists discovered some structures related to more ancient periods: the Roman domus (1st–5th centuries) and the older cathedral with its foundations and crypt (10th century). Based on OM, XRF, XRPD, TG-DSC and SEM-EDS analyses, the main characteristics of binder and aggregate of the mortars have been determined, and some raw materials used for the production of the analysed binding materials have been identified