This study aimed at evaluating the effectiveness and the compatibility of two alternative treatme... 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...
To prevent soiling of marble exposed outdoors, the use of TiO 2 nano-particles has been proposed ... more To prevent soiling of marble exposed outdoors, the use of TiO 2 nano-particles has been proposed in the literature by two main routes, both raising durability issues: (i) direct application to marble surface, with the risk of particle leaching by rainfall; (ii) particle incorporation into inorganic or organic coatings, with the risk of organic coating degradation catalyzed by TiO 2 photoactivity. Here, we investigated the combination of nano-TiO 2 and hydroxyapatite (HAP), previously developed for marble protection against dissolution in rain and mechanical consolidation. HAP-TiO 2 combination was investigated by two routes: (i) sequential application of HAP followed by nano-TiO 2 ("H+T"); (ii) simultaneous application by introducing nano-TiO 2 into the phosphate solution used to form HAP ("HT"). The self-cleaning ability was evaluated before and after prolonged exposure to simulated rain. "H+T" and "HT" coatings exhibited much better resistance to nano-TiO 2 leaching by rain, compared to TiO 2 alone. In "H+T" samples, TiO 2 nano-particles adhere better to HAP (having flower-like morphology and high specific surface area) than to marble. In "HT" samples, thanks to chemical bonds between nano-TiO 2 and HAP, the particles are firmly incorporated in the HAP coating, which protects them from leaching by rain, without diminishing their photoactivity and without being degraded by them.
In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for s... 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.
Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultur... more Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultural heritage conservation. Such damage is related to the fact that repulsive forces arise between the salt crystals and the pore wall, generating a disjoining pressure that frequently exceeds the tensile strength of stone. In this paper, new treatments are proposed, aimed at preventing salt damage by depositing a thin layer of polymeric coatings over the stone's pore surfaces. These coating are expected to change the surface chemistry, eliminating the repulsion between the growing crystals and the pore wall and hence the development of the disjoining pressure. Several biopolymers were tested on these substrates: silica glass, calcite, and calcite subjected to a pre-treatment with diammonium hydrogen phosphate (DAP), aimed at preventing calcite dissolution and acting as an anchoring substrate for the polymer coating. Selected polymer treatments were applied to porous Globigerina limestone samples, which were subjected to crystallization tests with sodium sulfate, obtaining promising results (i.e., significant reduction in stone damage), especially when the polymers were applied after the DAP treatment.
IOP Conference Series: Materials Science and Engineering
Soiling of external surfaces is an increasing issue for conservation of architectural heritage. P... more Soiling of external surfaces is an increasing issue for conservation of architectural heritage. Providing architectural surfaces with self-cleaning ability is one of the most promising routes of preventive conservation. To this aim, several methods have been proposed in the literature, based on the use of photocatalytic TiO2 nanoparticles, either directly applied onto the surfaces or incorporated in protective coatings. However, when nano-TiO2 is directly applied onto architectural surfaces, the particles are easily removed by rain. When TiO2 is incorporated in polymeric coatings, durability issues arise as well, because the photoactivity of TiO2 nanoparticles can promote degradation of the polymer. Here, we present an innovative alternative method, based on combination of TiO2 nanoparticles and hydroxyapatite (HAP). The incorporation of nano-TiO2 into an HAP coating protects the nanoparticles from leaching by rain, thanks to the chemical bonding between TiO2 and HAP, without diminishing their photoactivity. As a result, marble treated with HAP-TiO2 composites exhibits high self-cleaning ability and high durability, with results superior to those achieve by direct application of nano-TiO2 onto the surface, as frequently performed on site.
Reversibility is a mandatory requirement for materials used in heritage conservation, including h... more Reversibility is a mandatory requirement for materials used in heritage conservation, including hydrophobic protectives. Nevertheless, current protectives for stone are not actually reversible as they remain on the surfaces for a long time after their hydrophobicity is lost and can hardly be removed. Ineffective and aged coatings may jeopardise the stone re-treatability and further conservation interventions. This paper aims at investigating the performance of PHAs-based coatings for stone protection, their main potential being the 'reversibility by biodegradation' once water repellency ended. The biopolymer coatings were applied to three different kinds of stone, representative of lithotypes used in historic architecture: sandstone, limestone and marble. Spray, poultice and dip-coating were tested as coating techniques. The effectiveness and compatibility of the protectives were evaluated in terms of capillary water absorption, static and dynamic contact angles, water vapour diffusion, colour alteration and surface morphology. The stones' wettability after application of two commercial protectives was investigated too, for comparison. Finally, samples were subjected to artificial ageing to investigate their solar light stability. Promising results in terms of efficacy and compatibility were obtained, although the PHAs-based formulations developed here still need improvement for increased durability and on-site applicability.
Given the lack of satisfying treatments for consolidating marble affected by thermally induced gr... 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 ...
In this paper three methodologies for artificially deteriorating natural stones and producing sam... more In this paper three methodologies for artificially deteriorating natural stones and producing samples suitable for consolidants testing were investigated and compared. Three very different lithotypes were used: Giallo Siena (a calcareous sandstone with high porosity), Globigerina limestone (a limestone with very high porosity) and Pietra Serena (a quartzitic sandstone with low porosity). In addition, to investigate the role of porosity in determining the effectiveness of artificial deterioration by heating, additional lithotypes with basically the same mineralogical composition but significantly different porosity were also used: three limestones (Pietra di Trani, Crema Luna and Pietra di Vicenza) and one marble (Carrara marble). The stones were subjected to three artificial deterioration methods, meant to reproduce and accelerate weathering processes occurring in the field: heating at 400 °C for 1 hour, immersion in HNO 3 0.025 M for 24 hours, mechanical pre-stress by applying a compression load of about 70% of the failure load (parallel to bedding planes). The effects of the artificial deterioration were evaluated in terms of alterations in mechanical properties, pore size distribution and water absorption. The results show that the most effective method for artificial deterioration depends on the microstructural properties of the lithotypes. Indeed, the effectiveness of heating varies with carbonate content and porosity of the heated stone; the acidic attack is most effective on stones with high sorptivity; pre-stress seems potentially effective but has the limitation of being hardly controllable and reproducible.
In this study, the performance of a new inorganic consolidant, based on the formation of hydroxya... more In this study, the performance of a new inorganic consolidant, based on the formation of hydroxyapatite (HAP) by reaction between calcite and a solution of diammonium hydrogen phosphate (DAP), was investigated for the conservation of a highly porous limestone, Globigerina limestone (GL), extensively used in historical and modern architecture in Malta. The influence of the substrate deterioration level was preliminarily evaluated by comparing the effects of a 1.0 M DAP solution on unweathered GL samples and on artificially weathered ones (obtained according to previously developed methodologies). The effects of the treatment in terms of modifications in stone microstructural, physical and mechanical properties were then evaluated and compared to those brought by a commercial TEOS-based treatment. Novel methods for improving the performance of the HAP-based treatment and promoting the formation of HAP were also investigated. From the results of this study, HAP is confirmed as a very promising consolidating treatment, that can allow an increase up to +52% in tensile strength, without significantly occluding the pores and altering stone transport properties (which represents one of the limitations of the TEOSbased consolidants).
ABSTRACT This paper reports on the diagnostic investigations on the bronze panel in the Church of... 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.
ABSTRACT In this study, the use of hydroxyapatite (HAP), recently proposed for limestone consolid... 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.
The use of aqueous phosphate solutions to produce hydroxyapatite (HAP) inside weathered carbonate... more The use of aqueous phosphate solutions to produce hydroxyapatite (HAP) inside weathered carbonate stones has recently been proposed as a new consolidating technique. In this paper, the resistance of HAP-treated stone to soluble salt crystallization was investigated. Globigerina limestone, a porous stone typically used in historic architecture in Malta and often severely affected by salt crystallization, was used. After preliminary artificial weathering by heating at 400 °C for 1 hour, aimed at producing micro-cracks opening in the stone, cylindrical samples (5 cm height, 2 cm diameter) were treated by brushing application of a 3 M aqueous solution of diammonium hydrogen phosphate, followed by application of a limewater-impregnated poultice. For comparison's sake, a similar set of samples was treated with a commercial TEOS-based product, while a third set was left untreated. After proper curing, HAP-and TEOS-treated samples, together with untreated ones, were subjected to sodium sulfate crystallization cycles, by partial immersion in a 14 wt% sodium sulfate decahydrate solution for 7 hours and then drying at 50 °C for 15 hours. After each cycle, damage evolution was monitored by visual assessment and weight measurement. Five cycles were carried out in total. From the results of the study, the performance of the novel phosphate treatment can be regarded as promising, as HAP-treated samples exhibited less microcracking and lower mechanical damage than untreated and also TEOStreated samples.
In this paper three methodologies for artificially deteriorating natural stones and producing sam... more In this paper three methodologies for artificially deteriorating natural stones and producing samples suitable for consolidants testing were investigated and compared. Three very different lithotypes were used: Giallo Siena (a calcareous sandstone with high porosity), Globigerina limestone (a limestone with very high porosity) and Pietra Serena (a quartzitic sandstone with low porosity). In addition, to investigate the role of porosity in determining the effectiveness of artificial deterioration by heating, additional lithotypes with basically the same mineralogical composition but significantly different porosity were also used: three limestones (Pietra di Trani, Crema Luna and Pietra di Vicenza) and one marble (Carrara marble). The stones were subjected to three artificial deterioration methods, meant to reproduce and accelerate weathering processes occurring in the field: heating at 400 °C for 1 hour, immersion in HNO 3 0.025 M for 24 hours, mechanical pre-stress by applying a compression load of about 70% of the failure load (parallel to bedding planes). The effects of the artificial deterioration were evaluated in terms of alterations in mechanical properties, pore size distribution and water absorption. The results show that the most effective method for artificial deterioration depends on the microstructural properties of the lithotypes. Indeed, the effectiveness of heating varies with carbonate content and porosity of the heated stone; the acidic attack is most effective on stones with high sorptivity; pre-stress seems potentially effective but has the limitation of being hardly controllable and reproducible.
This study aimed at evaluating the effectiveness and the compatibility of two alternative treatme... 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...
To prevent soiling of marble exposed outdoors, the use of TiO 2 nano-particles has been proposed ... more To prevent soiling of marble exposed outdoors, the use of TiO 2 nano-particles has been proposed in the literature by two main routes, both raising durability issues: (i) direct application to marble surface, with the risk of particle leaching by rainfall; (ii) particle incorporation into inorganic or organic coatings, with the risk of organic coating degradation catalyzed by TiO 2 photoactivity. Here, we investigated the combination of nano-TiO 2 and hydroxyapatite (HAP), previously developed for marble protection against dissolution in rain and mechanical consolidation. HAP-TiO 2 combination was investigated by two routes: (i) sequential application of HAP followed by nano-TiO 2 ("H+T"); (ii) simultaneous application by introducing nano-TiO 2 into the phosphate solution used to form HAP ("HT"). The self-cleaning ability was evaluated before and after prolonged exposure to simulated rain. "H+T" and "HT" coatings exhibited much better resistance to nano-TiO 2 leaching by rain, compared to TiO 2 alone. In "H+T" samples, TiO 2 nano-particles adhere better to HAP (having flower-like morphology and high specific surface area) than to marble. In "HT" samples, thanks to chemical bonds between nano-TiO 2 and HAP, the particles are firmly incorporated in the HAP coating, which protects them from leaching by rain, without diminishing their photoactivity and without being degraded by them.
In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for s... 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.
Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultur... more Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultural heritage conservation. Such damage is related to the fact that repulsive forces arise between the salt crystals and the pore wall, generating a disjoining pressure that frequently exceeds the tensile strength of stone. In this paper, new treatments are proposed, aimed at preventing salt damage by depositing a thin layer of polymeric coatings over the stone's pore surfaces. These coating are expected to change the surface chemistry, eliminating the repulsion between the growing crystals and the pore wall and hence the development of the disjoining pressure. Several biopolymers were tested on these substrates: silica glass, calcite, and calcite subjected to a pre-treatment with diammonium hydrogen phosphate (DAP), aimed at preventing calcite dissolution and acting as an anchoring substrate for the polymer coating. Selected polymer treatments were applied to porous Globigerina limestone samples, which were subjected to crystallization tests with sodium sulfate, obtaining promising results (i.e., significant reduction in stone damage), especially when the polymers were applied after the DAP treatment.
IOP Conference Series: Materials Science and Engineering
Soiling of external surfaces is an increasing issue for conservation of architectural heritage. P... more Soiling of external surfaces is an increasing issue for conservation of architectural heritage. Providing architectural surfaces with self-cleaning ability is one of the most promising routes of preventive conservation. To this aim, several methods have been proposed in the literature, based on the use of photocatalytic TiO2 nanoparticles, either directly applied onto the surfaces or incorporated in protective coatings. However, when nano-TiO2 is directly applied onto architectural surfaces, the particles are easily removed by rain. When TiO2 is incorporated in polymeric coatings, durability issues arise as well, because the photoactivity of TiO2 nanoparticles can promote degradation of the polymer. Here, we present an innovative alternative method, based on combination of TiO2 nanoparticles and hydroxyapatite (HAP). The incorporation of nano-TiO2 into an HAP coating protects the nanoparticles from leaching by rain, thanks to the chemical bonding between TiO2 and HAP, without diminishing their photoactivity. As a result, marble treated with HAP-TiO2 composites exhibits high self-cleaning ability and high durability, with results superior to those achieve by direct application of nano-TiO2 onto the surface, as frequently performed on site.
Reversibility is a mandatory requirement for materials used in heritage conservation, including h... more Reversibility is a mandatory requirement for materials used in heritage conservation, including hydrophobic protectives. Nevertheless, current protectives for stone are not actually reversible as they remain on the surfaces for a long time after their hydrophobicity is lost and can hardly be removed. Ineffective and aged coatings may jeopardise the stone re-treatability and further conservation interventions. This paper aims at investigating the performance of PHAs-based coatings for stone protection, their main potential being the 'reversibility by biodegradation' once water repellency ended. The biopolymer coatings were applied to three different kinds of stone, representative of lithotypes used in historic architecture: sandstone, limestone and marble. Spray, poultice and dip-coating were tested as coating techniques. The effectiveness and compatibility of the protectives were evaluated in terms of capillary water absorption, static and dynamic contact angles, water vapour diffusion, colour alteration and surface morphology. The stones' wettability after application of two commercial protectives was investigated too, for comparison. Finally, samples were subjected to artificial ageing to investigate their solar light stability. Promising results in terms of efficacy and compatibility were obtained, although the PHAs-based formulations developed here still need improvement for increased durability and on-site applicability.
Given the lack of satisfying treatments for consolidating marble affected by thermally induced gr... 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 ...
In this paper three methodologies for artificially deteriorating natural stones and producing sam... more In this paper three methodologies for artificially deteriorating natural stones and producing samples suitable for consolidants testing were investigated and compared. Three very different lithotypes were used: Giallo Siena (a calcareous sandstone with high porosity), Globigerina limestone (a limestone with very high porosity) and Pietra Serena (a quartzitic sandstone with low porosity). In addition, to investigate the role of porosity in determining the effectiveness of artificial deterioration by heating, additional lithotypes with basically the same mineralogical composition but significantly different porosity were also used: three limestones (Pietra di Trani, Crema Luna and Pietra di Vicenza) and one marble (Carrara marble). The stones were subjected to three artificial deterioration methods, meant to reproduce and accelerate weathering processes occurring in the field: heating at 400 °C for 1 hour, immersion in HNO 3 0.025 M for 24 hours, mechanical pre-stress by applying a compression load of about 70% of the failure load (parallel to bedding planes). The effects of the artificial deterioration were evaluated in terms of alterations in mechanical properties, pore size distribution and water absorption. The results show that the most effective method for artificial deterioration depends on the microstructural properties of the lithotypes. Indeed, the effectiveness of heating varies with carbonate content and porosity of the heated stone; the acidic attack is most effective on stones with high sorptivity; pre-stress seems potentially effective but has the limitation of being hardly controllable and reproducible.
In this study, the performance of a new inorganic consolidant, based on the formation of hydroxya... more In this study, the performance of a new inorganic consolidant, based on the formation of hydroxyapatite (HAP) by reaction between calcite and a solution of diammonium hydrogen phosphate (DAP), was investigated for the conservation of a highly porous limestone, Globigerina limestone (GL), extensively used in historical and modern architecture in Malta. The influence of the substrate deterioration level was preliminarily evaluated by comparing the effects of a 1.0 M DAP solution on unweathered GL samples and on artificially weathered ones (obtained according to previously developed methodologies). The effects of the treatment in terms of modifications in stone microstructural, physical and mechanical properties were then evaluated and compared to those brought by a commercial TEOS-based treatment. Novel methods for improving the performance of the HAP-based treatment and promoting the formation of HAP were also investigated. From the results of this study, HAP is confirmed as a very promising consolidating treatment, that can allow an increase up to +52% in tensile strength, without significantly occluding the pores and altering stone transport properties (which represents one of the limitations of the TEOSbased consolidants).
ABSTRACT This paper reports on the diagnostic investigations on the bronze panel in the Church of... 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.
ABSTRACT In this study, the use of hydroxyapatite (HAP), recently proposed for limestone consolid... 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.
The use of aqueous phosphate solutions to produce hydroxyapatite (HAP) inside weathered carbonate... more The use of aqueous phosphate solutions to produce hydroxyapatite (HAP) inside weathered carbonate stones has recently been proposed as a new consolidating technique. In this paper, the resistance of HAP-treated stone to soluble salt crystallization was investigated. Globigerina limestone, a porous stone typically used in historic architecture in Malta and often severely affected by salt crystallization, was used. After preliminary artificial weathering by heating at 400 °C for 1 hour, aimed at producing micro-cracks opening in the stone, cylindrical samples (5 cm height, 2 cm diameter) were treated by brushing application of a 3 M aqueous solution of diammonium hydrogen phosphate, followed by application of a limewater-impregnated poultice. For comparison's sake, a similar set of samples was treated with a commercial TEOS-based product, while a third set was left untreated. After proper curing, HAP-and TEOS-treated samples, together with untreated ones, were subjected to sodium sulfate crystallization cycles, by partial immersion in a 14 wt% sodium sulfate decahydrate solution for 7 hours and then drying at 50 °C for 15 hours. After each cycle, damage evolution was monitored by visual assessment and weight measurement. Five cycles were carried out in total. From the results of the study, the performance of the novel phosphate treatment can be regarded as promising, as HAP-treated samples exhibited less microcracking and lower mechanical damage than untreated and also TEOStreated samples.
In this paper three methodologies for artificially deteriorating natural stones and producing sam... more In this paper three methodologies for artificially deteriorating natural stones and producing samples suitable for consolidants testing were investigated and compared. Three very different lithotypes were used: Giallo Siena (a calcareous sandstone with high porosity), Globigerina limestone (a limestone with very high porosity) and Pietra Serena (a quartzitic sandstone with low porosity). In addition, to investigate the role of porosity in determining the effectiveness of artificial deterioration by heating, additional lithotypes with basically the same mineralogical composition but significantly different porosity were also used: three limestones (Pietra di Trani, Crema Luna and Pietra di Vicenza) and one marble (Carrara marble). The stones were subjected to three artificial deterioration methods, meant to reproduce and accelerate weathering processes occurring in the field: heating at 400 °C for 1 hour, immersion in HNO 3 0.025 M for 24 hours, mechanical pre-stress by applying a compression load of about 70% of the failure load (parallel to bedding planes). The effects of the artificial deterioration were evaluated in terms of alterations in mechanical properties, pore size distribution and water absorption. The results show that the most effective method for artificial deterioration depends on the microstructural properties of the lithotypes. Indeed, the effectiveness of heating varies with carbonate content and porosity of the heated stone; the acidic attack is most effective on stones with high sorptivity; pre-stress seems potentially effective but has the limitation of being hardly controllable and reproducible.
Uploads
Papers by Elisa Franzoni