Arianna Murru

Synthesis, characterization and DFT-modeling of novel agents for the protection and restoration of historical calcareous stone substrates

The ammonium salts of oxamate (AmOxam) and monomethyloxalate (AmMeox), structurally related to ammonium oxalate (AmOx), were synthesized and characterized as protecting agents/filler for calcareous stone substrates. Both compounds featured an improved solubility in water and alcoholic-water mixtures with respect to AmOx. While AmOxam is stable in aqueous solution and reacts with calcite to afford the corresponding insoluble calcium oxamate (CaOxam), AmMeox spontaneously undergoes hydrolysis to give ammonium monohydrogen oxalate hemihydrate (AmBiox) and calcium oxalate (CaOx). Both compounds have been tested for the restoration of naturally weathered marble and biomicritic limestone. The formation of a superficial layer of CaOxam and CaOx was observed on stone samples treated with AmOxam and AmMeox, respectively, depending on the solvent mixture. A quantum-mechanical study was carried out at DFT level in order to investigate the nature of the interactions occurring between the lithic substrate (calcite) and the passivating agents, showing how the structural modifications on oxalic acid derivatives can be exploited to fine-tune their interaction with the calcite surface.

Crime art on the stone: graffiti vandalism on cultural heritage and the anti-graffiti role in its surfaces protection

Apparently perceived like an easy thing commonly used, spray paint is a very complex product composed by substances strongly penetrating particularly into the porous materials. This characteristic is very hazardous for our cultural heritage. The problem concerning the surfaces protection from paints and signs is very hard to solve, both for the difficulty to remove these substances and for the variety of the materials that react in a different manner to the various paints and cleaning treatments because of their different physical-chemical characteristics. With the aim to evaluate the damages originated by the spray paints on the stones and the efficacy of anti-graffiti products, some laboratory tests have been carried out. Two different limestones have been selected like supports: a little porous, polishable wakestone and a very porous bio-calcarenite with very scarce mechanical properties. Both these limestones are used as coverings and structural elements of buildings and monuments around Mediterranean basin. Concerning the spray paint cans, the most popular Montana mtn94 has been used, and two commercial anti-graffiti have been applied as protective products. Using Scanning Electron Microscope, Infrared Spectrometry, Colorimetry, Mercury Intrusion Porosimetry and Contact Angle Analysis the interactions stone-paint, stone-anti-graffiti and paint-anti-graffiti have been investigated. In order to evaluate the real efficacy of the anti-graffiti, some cleaning and removal paint tests have been carried out. The research highlights that the anti-graffiti cause variations concerns the colour and/or the wettability in both limestones. Their effects are strictly related to the stonework and their microstructure but also the interaction with the paint is influent too.

Oxamate salts as novel agents for the restoration of marble and limestone substrates: case study of ammonium N-phenyloxamate

The ammonium salt of N-phenyloxamic acid (AmPhOxam) was synthesised, characterised by FT-IR, FT-Raman, UV-Vis, 1H-NMR spectroscopic methods and single crystal X-ray diffraction, and evaluated as a protective and consolidating agent for calcareous stone substrates under mild conditions. Hydro-alcoholic solutions of AmPhOxam were tested for the treatment of naturally weathered white marble and biomicritic limestone. Mercury intrusion porosimetry, FT-NIR spectroscopy measurements and SEM microscopy showed the formation of a superficial protective layer of crystals of the corresponding monohydrated calcium salt, CaPhOxam, on both treated stones.

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

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. DOI: http://dx.doi.org/10.4995/FORTMED2015.2015.1761

Methodological approach in the conservation of coastal fortifications

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. DOI: http://dx.doi.org/10.4995/FORTMED2015.2015.1752

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

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. DOI: http://dx.doi.org/10.4995/FORTMED2015.2015.1753