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This study aimed at evaluating the effectiveness and the compatibility of two alternative treatments, in view of their possible use for conservation of prehistoric paintings in the Magura cave (Bulgaria). The paintings are made of bat... more
This study aimed at evaluating the effectiveness and the compatibility of two alternative treatments, in view of their possible use for conservation of prehistoric paintings in the Magura cave (Bulgaria). The paintings are made of bat guano applied over limestone; therefore, two sets of laboratory specimens were considered: stone specimens and stone specimens covered with a layer of sterilized bat guano. The two investigated treatments were a commercial product based on ethyl silicate (“ES”) and a solution of diammonium hydrogen phosphate (“DAP”), aimed at forming calcium phosphates. The results of the study indicated that both treatments were able to increase the mechanical properties of stone, the increase being higher for “DAP”. Both consolidants caused acceptable color changes, but the “ES” treatment significantly decreased stone wettability, water absorption, and water vapor permeability, while the “DAP” treatment slightly affected those properties. In the stone + guano specime...
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In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for structural strengthening, and several researches have validated the effectiveness of SRP for masonry strengthening. Research has been carried... more
In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for structural strengthening, and several researches have validated the effectiveness of SRP for masonry strengthening. Research has been carried out to study the bond behavior of SRP composites applied to a masonry substrate. However, how the moist and salt on masonry surface will affect bond, which is the weak link in real strengthening applications, is little known yet. This study aims at investigating the bond behavior of SRP composites applied to moist and salt-laden masonry blocks that were subjected to an artificial weathering protocol. Single-lap shear tests were conducted to determine the bond behavior, while ion chromatography provided the salts distribution of weathered specimens to interpret some results of the shear tests.
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Given the lack of satisfying treatments for consolidating marble affected by thermally induced grain detachment (the so-called "sugaring"), the use of aqueous solutions of diammonium hydrogen phosphate (DAP) has recently been... more
Given the lack of satisfying treatments for consolidating marble affected by thermally induced grain detachment (the so-called "sugaring"), the use of aqueous solutions of diammonium hydrogen phosphate (DAP) has recently been proposed. The idea is to form a new binding mineral (hydroxyapatite, HAP) as the reaction product between the DAP solution and the calcitic substrate. In this study, we investigated the effects of adding small quantities of ethanol (EtOH) to the DAP solution, with the aim of favoring HAP formation. The results of the study indicate that, when a 0.1 M DAP and 0.1 mM CaCl2 solution in 10 vol% EtOH is used, complete coverage of marble surface with a crack-free coating with reduced porosity is achieved (whereas no coating is formed without EtOH addition). This is thought to be a consequence of the weakening of hydration shells of phosphate ions in the DAP solution, thanks to the presence of ethanol molecules. When used to restore mechanical properties of ...
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ABSTRACT This paper reports on the diagnostic investigations on the bronze panel in the Church of San Moisè in Venice (Italy), aiming at the identification of materials and causes of corrosion. Both the bulk metal and surface layers were... more
ABSTRACT This paper reports on the diagnostic investigations on the bronze panel in the Church of San Moisè in Venice (Italy), aiming at the identification of materials and causes of corrosion. Both the bulk metal and surface layers were investigated by a wide range of techniques: alloy composition and microstructure were determined by VP-SEM/EDS, the corrosion products by Raman spectroscopy and XRD. The organic compounds were analysed by pyrolysis gas chromatography mass spectrometry (Py-GC-MS). The adjacent mortars were analysed in terms of mineralogical composition and soluble salts content, in order to highlight their role in the degradation processes at the contact areas between the masonry and the bronze panel.The alloy is a quaternary bronze (Cu-Sn-Zn-Pb): high-relief figures were cast separately then mechanically joined to the panel. Traces of the clay core were detected in the back of the panel. The bronze surface was artificially patinated by potassium sulphide. The organic protective layer consisted of stearin and paraffinic wax. However, siccative oil was detected at the interface with the metal, likely corresponding to the original protective treatment. Also pine resin traces were detected.The corrosion products mainly consisted of basic copper chlorides (paratacamite, atacamite) and mixed copper/sodium carbonates (chalconatronite), deriving from the interaction with mortar.
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ABSTRACT In this study, the use of hydroxyapatite (HAP), recently proposed for limestone consolidation, was investigated on unweathered and artificially weathered Carrara marble and the behaviour of HAP-treated samples towards thermal... more
ABSTRACT In this study, the use of hydroxyapatite (HAP), recently proposed for limestone consolidation, was investigated on unweathered and artificially weathered Carrara marble and the behaviour of HAP-treated samples towards thermal weathering was evaluated, by means of an accelerated thermal weathering test. The results of the study indicate that HAP is a very promising consolidant for marble, able to significantly improve mechanical properties without substantially altering pore size distribution and to provide some mitigation against thermal weathering.
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ABSTRACT 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... more
ABSTRACT 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.
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ABSTRACT The so-called "sugaring" of marble is a very common degradation phenomenon, affecting both historical monuments and modern buildings, which is originated by environmental temperature fluctuations. Thermal cycles... more
ABSTRACT The so-called "sugaring" of marble is a very common degradation phenomenon, affecting both historical monuments and modern buildings, which is originated by environmental temperature fluctuations. Thermal cycles are indeed responsible for micro-cracks formation at the boundaries between calcite grains, so that marble is subjected to granular disintegration and can be reduced to a sugar-like powder of isolated calcite grains by just the pressure of a finger. Since no effective, compatible and durable treatment for sugaring marble consolidation is currently available, in this paper a novel consolidating treatment recently proposed for limestone, based on the formation of hydroxyapatite (HAP) inside the stone, was investigated for weathered marble. To test the new treatment on suitably decayed marble samples, some naturally sugaring marbles from the Monumental Cemetery in Bologna (Italy, XIX century) were firstly characterized by scanning electron microscope (SEM), mercury intrusion porosimetry (MIP) and ultrasonic pulse velocity (UPV) measurement. Then, artificially weathered samples were produced by heating fresh Carrara marble samples at 400 °C for 1 hour. The effects of artificial weathering were characterized using the same techniques as above and a very good agreement was found between microstructure and mechanical features of naturally and artificially weathered samples. Then, the hydroxyapatite-based treatment was tested on the so-obtained artificially weathered samples and the treatment effects were characterized by UPV, MIP, SEM equipped with energy dispersive spectrometry (EDS) and Fourier transform infrared spectroscopy (FT-IR). The hydroxyapatite-based treatment exhibited a remarkable ability of restoring marble cohesion and a good compatibility in terms of modifications in pore size distribution, which leads to regard this treatment as a very promising consolidant for weathered marble.
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ABSTRACT This study presents an intermingled fractal model capable of simulating the porous microstructure of natural stones used in historical buildings. The developed model is aimed at predicting, by an analytical approach, the... more
ABSTRACT This study presents an intermingled fractal model capable of simulating the porous microstructure of natural stones used in historical buildings. The developed model is aimed at predicting, by an analytical approach, the sorptivity of these materials. To verify the actual ability of the proposed method to predict stone sorptivity, in this study the intermingled fractal units model was applied to eight types of natural stones. The results are in very good agreement with sorptivity values obtained by experimental tests on the investigated stones. Compared to other analytical formulas proposed in the literature for predicting the sorptivity of porous materials, the newly proposed method better matches with the experimental results, and this can be attributed to that fact it takes into consideration the whole pore size distribution of the analyzed material, rather than the average pore radius only. Thanks to the proposed method, the sorptivity of natural stones used in historical buildings can be calculated from their pore size distribution determined by MIP, which, contrary to standard tests for sorptivity determination, only requires small and irregular samples.
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The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural... more
The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural characteristics, were used. Four acidic aqueous solutions were prepared to simulate acid rain (two adding H(2)SO(4) and two adding HNO(3) to deionized water, in order to reach, for each acid, pH values of 5.0 and 4.0), and deionized water at pH=5.6 was used to simulate clean rain. Stone samples were then immersed in such aqueous solutions, the surface alteration being periodically inspected and the weight loss periodically measured. After 14 days of immersion, a good correlation was found between weight loss and the product of carbonate content and specific surface area in the starting materials. This was explained considering that this product accounts for the weight loss owing to the sample's fraction actually composed of calcite (the most soluble fraction) and the effective surface area exposed to dissolving solution (which depends on stone porosity and pore size distribution). Such correlation between stone microstructure and degradation may be useful for comparing the durability of different lithotypes, in given environmental conditions, and quantitatively predicting the weight loss of a lithotype, compared to another one. Hence, the correlation found in this study may be used to specifically tailor to various stone types, with different microstructural characteristics, some results that have been calculated in literature for specific stone types and then proposed as possibly representative for a broad category of stones with similar characteristics.
Research Interests: Microstructure, Construction Materials, Environmental Monitoring, Air pollution, Acid Rain, and 13 moreMultidisciplinary, Weight Loss, Durability, Dissolution, Specific surface area, Surface Area, X ray diffraction, Environmental Conditions, Microstructures, Calcium Carbonate, NITRIC ACID, Aqueous Solution, and Silicon Dioxide
ABSTRACT Ethyl silicate (tetraethylorthosilicate, TEOS) is one of the most used consolidants for natural stones in the restoration of architectural and cultural heritage and the literature concerning its performance in this application is... more
ABSTRACT Ethyl silicate (tetraethylorthosilicate, TEOS) is one of the most used consolidants for natural stones in the restoration of architectural and cultural heritage and the literature concerning its performance in this application is quite abundant. In this paper, the need, and sometimes urgency, of preserving ancient fired-clay elements (bricks and terracotta decorations) is highlighted as well, and the effects of ethyl silicate consolidation (75 wt% TEOS in white spirit) are investigated from a microstructural, physical–mechanical and aesthetic point of view. Fired-clay brick samples (open porosity ≈45 %; compressive strength ≈14 N/mm2) were treated and then characterized by mercury intrusion porosimetry, scanning electron microscopy, water absorption, compressive strength test and spectrophotometry, to assess the effects of the treatment. The TEOS treatment gave encouraging results: a good penetration depth (about 10 mm), a limited reduction in porosity, a large decrease in water absorption, a significant improvement in compressive strength and a positive aesthetic outcome. The results obtained pointed out TEOS treatment as a promising solution for fired-clay bricks consolidation.
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ABSTRACT A new consolidating treatment for limestone, based on the reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP), has recently been proposed. Thanks to the formation of HAP at... more
ABSTRACT A new consolidating treatment for limestone, based on the reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP), has recently been proposed. Thanks to the formation of HAP at grain boundaries, so that grains are more effectively bonded, HAP-treated limestone undergoes a significant improvement in mechanical properties. Considering that the HAP treatment has the advantage of not substantially altering the transport properties of treated stones, unlike many other consolidating products currently used, in this paper, the effectiveness of HAP as a consolidant for sandstones with varying carbonate content and porosity was investigated and compared with that of a TEOS-based consolidant. Two lithotypes were used: Giallo Siena (a highly porous calcareous sandstone) and Pietra Serena (a quartzitic sandstone with low porosity). After preliminary artificial weathering according to previously developed methodologies, each lithotype was treated: (i) with a 1 M aqueous solution of DAP; (ii) with a solution of TEOS oligomers in isopropyl alcohol, each applied by brushing until apparent refusal. The effects of the two consolidating treatments were assessed by comparing microstructural, physical and mechanical properties of treated and untreated stones. HAP-treated specimens experienced an increase in dynamic elastic modulus and tensile strength substantially similar to that achieved by TEOS-treated ones. However, differently from samples consolidated with TEOS, HAP-treated stones experienced very low variations in porosity and pore size distribution, leading to substantially no variation in the rate of water sorption and only a small decrease in water vapor permeability. Considering the good performance on both lithotypes, comparable to that achieved by a TEOS-based treatment, HAP is confirmed as a promising consolidating treatment, which has the advantage of being effective after just two days, not substantially altering the transport properties of treated stones and not being hazardous for human health, thanks to its aqueous solvent.
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ABSTRACT Since the effectiveness of stone consolidants significantly depends on the weathering level of the stone samples on which they are tested, in this study the suitability of heating stone to high temperature, as an artificial... more
ABSTRACT Since the effectiveness of stone consolidants significantly depends on the weathering level of the stone samples on which they are tested, in this study the suitability of heating stone to high temperature, as an artificial weathering method to induce controllable microstructural, physical and mechanical alterations, was investigated. Three lithotypes with different characteristics were used: Giallo Terra di Siena (GS, a highly porous calcareous sandstone), Globigerina limestone (GL, a highly porous limestone) and Pietra Serena (PS, a porous quartzitic sandstone with low porosity). The lithotypes were characterized in terms of mineralogical composition, pore size distribution and water absorption, as well as dynamic modulus, static modulus, compressive and tensile strength. They were then heated for 1 hour, in different conditions: (i) dry samples were heated to 100, 200, 300 and 400 °C; (ii) water-saturated samples were heated to 200 °C; (iii) water-saturated samples were heated to 200 °C and, after cooling to room temperature, re-heated to 400 °C. After heating, all the lithotypes experienced an increase in open porosity and water absorption, as a consequence of the anisotropic thermal deformation of calcite crystals. Correspondingly, GS and GL exhibited an increasing reduction in mechanical properties for increasing heating temperature. PS, on the contrary, exhibited an increase in compressive and tensile strength, which was attributed to chemical-physical transformations undergone by secondary mineralogical fractions (clay minerals, etc.) at high temperature. All things considered, heating proved to be a fairly effective and reproducible method to cause artificial weathering in stone samples for the testing of consolidants. However, depending on the microstructural characteristics of the lithotypes, the effectiveness of heating may vary significantly, which requires a case-by-case adjustment of the most suitable heating procedure and the development of complementary methods for artificial weathering.
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Rising damp is one of the main issues affecting masonry buildings. However, its consequences on the mechanical performance of masonry structures are not so largely explored. In this paper, the compressive and shear behaviour of masonry... more
Rising damp is one of the main issues affecting masonry buildings. However, its consequences on the mechanical performance of masonry structures are not so largely explored. In this paper, the compressive and shear behaviour of masonry triplets, manufactured with solid fired-clay bricks and cement-based mortar, is investigated in dry and moist conditions. The results are interpreted on the basis of the features of the single materials, from both a mechanical and microstructural point of view.
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The resistance of ethyl silicate-consolidated bricks to sodium sulfate crystallization cycles was evaluated. A commercial ethyl silicate (ES) based product was applied by brushing with 5 or 10 strokes to assess the effect on... more
The resistance of ethyl silicate-consolidated bricks to sodium sulfate crystallization cycles was evaluated. A commercial ethyl silicate (ES) based product was applied by brushing with 5 or 10 strokes to assess the effect on distribution/accumulation of the consolidant inside the pores. After long-term curing, aimed at making ES-treated samples lose their temporary hydrophobicity, samples were characterized by assessing the penetration depth of consolidants, tensile strength and modifications in open porosity and pore size distribution. Resistance to salt crystallization was evaluated by carrying out sodium sulfate crystallization cycles. The capillary suction of the salt solution was let occur through the untreated surface of cubic samples treated in the upper face, in order to investigate brick response to salts coming from behind the consolidated layer (the situation usually occurring when rising damp is present). Treatment with either 5 or 10 strokes provided protection against ...
The plasters of the XVI cent. Cavallerizza Courtyard in the Ducal Palace in Mantua (Italy) were designed to imitate natural stones (rustication work, carved marble, etc.). They were produced for both aesthetic and manufacturing purposes... more
The plasters of the XVI cent. Cavallerizza Courtyard in the Ducal Palace in Mantua (Italy) were designed to imitate natural stones (rustication work, carved marble, etc.). They were produced for both aesthetic and manufacturing purposes with highly variable formulations, resulting in highly variable microstructures of the final elements. Because the plasters have been exposed to high concentrations of atmospheric pollutants in the last decades, they currently exhibit severe decay, differing on the basis of microstructural characteristics. The aim of this paper is to analyze the complex interaction between environmental aggressiveness, plaster microstructure, and degradation phenomena in view of their restoration. Plaster samples were collected from the Loggia side of the courtyard at short distance from one another, so that exposure conditions could be considered constant. The samples were characterized in terms of mineralogical composition, overall open porosity, and pore size dist...
A new inorganic consolidant for limestone, based on the reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP), has recently been proposed. This consolidant was found to cause a... more
A new inorganic consolidant for limestone, based on the reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP), has recently been proposed. This consolidant was found to cause a significant increase in the mechanical properties of limestone, due to the bonding action between the stone grains, and, at the same time, a very slight alteration in the transport properties of treated stones, unlike many other consolidating products currently used. Moreover, HAP treatment is expected to exhibit a good acid resistance and low solubility, with corresponding benefits in terms of durability. The short reaction time (just two days) and the use of a solvent not hazardous for human health (water) are further advantages of this consolidant. Due to the good performance on limestone, its use for the consolidation of sandstone was investigated in the present paper, in comparison with a TEOS-based consolidant. Two lithotypes with varying carbonate co...