Geomaterials and decay forms of the coastal towers of Piscinni and Foghe, Weastern Sardinia

[EN] The distribution of Coastal Towers in Sardinia testify that foreign invasions, which occurred several times over the centuries, were particularly frequent and dangerous. The beginning of the eighth century signed an increase of the attacks from the sea. The most of Coastal Towers were built in the period of Spanish rule, from 1583 to 1720. Despite numerous restorations over the years, many of these defensive structures are in critical conditions, some also affected by structural collapse. The building materials are closely related to local geological outcrops, and consist of sedimentary, magmatic and metamorphic rocks. Study of different lithotypes allowed assessing the vulnerability of different materials in different environmental conditions. Salts, transported by aerosols and deposited inside the porous structures, are the principal cause of decay of the building materials. Chemical-physical and mineralogical-petrographic analyses, performed on some Towers allowed making some general assessments on their conservation status and restoration projects.Carcangiu, G.; Meloni, P.; Palomba, M.; Cocco, O.; Sitzia, F.; Murru, A.; Carboni, M.... (2015). Geomaterials and decay forms of the coastal towers of Piscinni and Foghe, Weastern Sardinia. En Defensive architecture of the mediterranean: XV to XVIII centuries. Vol. I. Editorial Universitat Politècnica de València. 345-352. https://doi.org/10.4995/FORTMED2015.2015.1753OCS34535

Durability of repair mortars used in restoration of a Sardinian coastal tower: assessment after ten years

[EN] This study reports the results of investigations on conservation conditions of an ancient tower, called Torre del Pozzo, located in the S-W coast of Sardinia, restored about ten years ago. The tower suffers from serious problems related to vulnerability of building materials, particularly limestone and sandstones and aerial lime mortar with poor physical-mechanical properties. Over the centuries the materials were subjected to aggressive actions (wind corrasion and salt crystallization) causing an intense erosion of the walls with consequent partial collapse of the structure. About ten years ago a restoration involved the mortars and only the replacement and integration of ashlars deteriorated. After about 10 years from this intervention, some inspections have been carried out in order to assess the effectiveness of the intervention and the state of preservation of the tower. This paper focuses on analyses and tests carried out to assess condition and durability of the repair mortars.Meloni, P.; Carcangiu, G.; Palomba, M.; Enzo, S.; Carboni, M.; Cocco, O.; Casti, M.... (2015). Durability of repair mortars used in restoration of a Sardinian coastal tower: assessment after ten years. En Defensive architecture of the mediterranean: XV to XVIII centuries. Vol. II. Editorial Universitat Politècnica de València. 397-44. https://doi.org/10.4995/FORTMED2015.2015.1761OCS3974

Methodological approach in the conservation of coastal fortifications

[EN] The historical and artistic value of Coastal Towers justifies the recovery of these emblematic artifacts. For the achievement of this objective we propose a methodological approach including: i) architectural relief also by 3D laser scanner and collection of historical data; ii) macroscopic semi-quantitative evaluation of the decay, iii) application of diagnostic quantitative chemical-physical-mechanical methodologies, to assess the decay intensity, and define the criticalities for planning the restoration. The i step allows the graphic rendering of the building showing the geometry and the relationships between the parties. The ii step allows a preliminary understanding of the building materials, macroscopic alteration forms, monument features, acquisition of information about potential causes and decay mechanisms. During the iii step, sampling of building materials is planned. Laboratory analyses, to determine the soluble salts, crystalline phases, porosity as well as micro-textural features of the materials, are carried out by the application of suitable techniques.Carcangiu, G.; Columbu, S.; Meloni, P.; Carboni, M.; Casti, M.; Cocco, O.; Murru, A.... (2015). Methodological approach in the conservation of coastal fortifications. En Defensive architecture of the mediterranean: XV to XVIII centuries. Vol. I. Editorial Universitat Politècnica de València. 341-344. https://doi.org/10.4995/FORTMED2015.2015.1752OCS34134

End-to-end numerical simulator of the Shadow Position Sensor (SPS) metrology subsystem of the PROBA-3 ESA mission

PROBA-3 - PRoject for OnBoard Autonomy is an ESA mission to be launched in 2022 where a spacecraſt is used as an external occulter (OSC-Occulter Spacecraſt), to create an artificial solar eclipse as observed by a second spacecraſt, the coronagraph (CSC-Coronagraph Spacecraſt). The two spacecraſts (SCs) will orbit around the Earth, with an highly elliptic orbit (HEO), with the perigee at 600 Km, the apogee at about 60530 Km and an eccentricity of 0.81. The orbital period is of 19.7 hours and the precise formation flight (within 1 mm) will be maintainedforabout6hours overthe apogee, in ordertoguarantee the observation ofthe solarcoronawith the required spatial resolution. The relative alignment ofthe two spacecraſts is obtained bycombining information from several subsystems. One ofthe most accurate subsystem (with accuracy >0.5 mm) is the Shadow Position Sensors (SPS), composed by eight photomultipliers installed around the entrance pupil of the CSC. The SPS will monitor the penumbra generated by the occulter spacecraſt, whose intensity will change according to the relative position ofthe two satellites. A dedicated algorithm has been developed to retrieve the displacementof the spacecraſts fromthe measurements ofthe SPS. Several tests are requiredin ordertoevaluate the robustness of the algorithm and its performances/results for different possible configurations. A soſtware simulator has been developed for this purpose. The simulator includes the possibility to generate synthetic 2-D penumbra profile maps or analyze measured profiles and run different versions ofthe retrieving algorithms, including the “on-board” version. In order to import the “as built” algorithms, the soſtware is coded using Matlab

Metrology on-board PROBA-3: The shadow position sensors subsystem

PROBA-3 is an ESA mission aimed at the demonstration of formation flying performance of two satellites that will form a giant coronagraph in space. The first spacecraft will host a telescope imaging the solar corona in visible light, while the second, the external occulter, will produce an artificial eclipse. This instrument is named ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). To accomplish the payload's scientific tasks, PROBA-3 will ensure sub-millimeter reciprocal positioning of its two satellites using closed-loop on-board metrology. Several metrology systems will be used and the Shadow Position Sensor (SPS) subsystem senses the penumbra around the instrument aperture and returns the 3-D displacement of the coronagraph satellite, with respect to its nominal position, by running a dedicated algorithm. In this paper, we describe how the SPS works and the choices made to accomplish the mission objectives

PROBA-3 mission and the Shadow Position Sensors: Metrology measurement concept and budget

PROBA-3 is a space mission of the European Space Agency that will test, and validate metrology and control systems for autonomous formation flying of two independent satellites. PROBA-3 will operate in a High Elliptic Orbit and when approaching the apogee at 6·104 Km, the two spacecraft will align to realize a giant externally occulted coronagraph named ASPIICS, with the telescope on one satellite and the external occulter on the other one, at inter-satellite distance of 144.3 m. The formation will be maintained over 6 hrs across the apogee transit and during this time different validation operations will be performed to confirm the effectiveness of the formation flying metrology concept, the metrology control systems and algorithms, and the spacecraft manoeuvring. The observation of the Sun's Corona in the field of view [1.08;3.0]RSun will represent the scientific tool to confirm the formation flying alignment. In this paper, we review the mission concept and we describe the Shadow Position Sensors (SPS), one of the metrological systems designed to provide high accuracy (sub-millimetre level) absolute and relative alignment measurement of the formation flying. The metrology algorithm developed to convert the SPS measurements in lateral and longitudinal movement estimation is also described and the measurement budget summarized

Shedding light on typical species : implications for habitat monitoring

Habitat monitoring in Europe is regulated by Article 17 of the Habitats Directive, which suggests the use of typical species to assess habitat conservation status. Yet, the Directive uses the term “typical” species but does not provide a definition, either for its use in reporting or for its use in impact assessments. To address the issue, an online workshop was organized by the Italian Society for Vegetation Science (SISV) to shed light on the diversity of perspectives regarding the different concepts of typical species, and to discuss the possible implications for habitat monitoring. To this aim, we inquired 73 people with a very different degree of expertise in the field of vegetation science by means of a tailored survey composed of six questions. We analysed the data using Pearson's Chi-squared test to verify that the answers diverged from a random distribution and checked the effect of the degree of experience of the surveyees on the results. We found that most of the surveyees agreed on the use of the phytosociological method for habitat monitoring and of the diagnostic and characteristic species to evaluate the structural and functional conservation status of habitats. With this contribution, we shed light on the meaning of “typical” species in the context of habitat monitoring

Cristallizzazione del solfato di sodio in calcari biomicritici: l'uso di inibitori per la mitigazione del degrado

Salt crystallisation is one of the most harmful decay problems in porous materials. Especially ancient building and archaeological sites can show very intense damage (e.g. detachment and pulverization of the materials) that produce a strong loss of matter and so cultural identity. Mainly hypogea show salt crystallisation due to capillary rising. However also anthropic sources like pollution or cement can be found in these sites producing decay. Sodium sulphate is very common where there is the combination between cement and pollution. This salt is very harmful for porous materials due to his high crystallization pressure and the possibility to change to anhydrous phase to hydrated one. When microclimatic variations occur due to semi-confined environment, phase transitions of sodium sulphate take place with consequence on porous material decay. This research studied sodium sulphate crystallisation on a Mediterranean biomicritic limestone and the action of crystallisation inhibitors to mitigate it. The early Christian burial of Munazio Ireneo was studied to understand sodium sulphate crystallisation in biomicritic limestone. Diagnostic investigation and microclimatic monitoring were carried out to understand decay phenomena. The hypogeum is a semi-confined environment and high damage can be found due to phase transition of sodium sulphate. Crystallisation of a Mediterranean biomicric limestone was also studied in laboratory by XRD, OM, SEM, MIP and NMR analysis. Crystallisation inhibitors were tested on the limestone in sodium sulphate solution capillary rising. Two different inhibitors were applied with two distinct system (immersion and poultice). XRD, MIP and SEM analysis were carried out to understand the modification of the inhibitor on the stone microstructure. The loss of material was evaluated to understand the effect of the inhibitors comparing the loss of material in the blank sample. A greater loss of material than the blank sample was found when the first inhibitor was applied through both of the system; the second inhibitor had a minor loss of material but chromatic variations could be found on the stone

Differential damage in the semi-confined Munazio Ireneo cubicle in Cagliari (Sardinia): a correlation between damage and microclimate

The Early Christian Munazio Ireneo cubicle in Cagliari (Sardinia) is carved into the rock and is one of the rare monuments of Sardinia belonging to Early Christian Age. It is 166 cm under the planking level and is a semi-confined chamber in which a gate allows exchange with the outside. In 1888, when it was discovered, it was completely painted, but over the years, it suffered a serious damage and all the paintings are nearly disappeared. Now the site shows a high moisture and a differential damage characterised by delamination, powdering, salt crystallisation and biological colonisation. The research offers a multidisciplinary approach to study the salt crystallisation damage, which is a phenomenon still not completely understood today. Studies and analyses highlight that different kinds of damage can be recognised. The cement mortar and the air pollution cause crystallisation of the sulphates. Constant capillary rising and the presence of water infiltration due to the rains, which travelled into the site from the vault, were detected during qualitative inspection. Although the microclimate did not change much in the site and the humidity was almost constant during the monitoring period, the variations in temperature allowed the phase transitions of sodium sulphate, especially in summer. The greatest damage of the porous stone is associated with the phase transitions and crystallisation inside the stone of sodium sulphate, one of the most harmful salts for porous materials because of its high crystallisation pressure