1,721,038 research outputs found
Effect of solvents and pH on in situ formation of hydroxyapatite for stone conservation
No full textIn situ formation of hydroxyapatite (HAP) inside the cracks and on the surface of calcareous substrates (e.g. marble and limestone) has been proposed for consolidation and protection of cultural heritage. HAP can be formed in situ by reacting the substrate with an aqueous solution of diammonium hydrogen phosphate (DAP). Taking inspiration from literature on bioceramics and from recent computational results, in the present study different strategies were explored to improve the consolidating efficacy of the DAP solution, namely by increasing pH or by adding organic solvents. A 1 M DAP +1 mM CaCl2 solution was taken as a reference and compared to 10-fold more diluted solutions (0.1 M DAP + 0.1 mM CaCl2) at pH 8, 10 or 12 and with addition of 20 wt% ethanol, isopropanol, or acetone. The solutions were applied onto weathered marble specimens and the formation of the new phases was characterized by FEG-SEM and XRD, while the strengthening ability was assessed in terms of bulk mechanical properties and surface properties. The results of this study indicate that apatite phases (mostly likely carbonate HAP with possible stoichiometric HAP) were formed as the result of all treatments, except at pH 12 when undesired ammonium calcium phosphate hydrate was formed. In terms of strengthening efficacy, when in-depth consolidation is needed, the more concentrated DAP solutions are able to provide higher strengthening ability. When consolidation of the most superficial layer is desired, less concentrated solutions are able to provide satisfactory results, allowing for a substantial reduction in the use of DAP with economic and environmental advantages
Lime and cement mortar consolidation by ammonium phosphate
Full text linkThe present study investigates the strengthening ability and the compatibility of two different ammonium phosphate solutions used for consolidation of mortars based on slaked lime, natural hydraulic lime or cement, to resemble historic and modern mortars. After impregnation for 24 h, new calcium phosphate phases were detected in all types of mortar. New calcium phosphates induced significant mechanical consolidation, with only slight alterations in the pore system and in water transport properties. In lime-based mortars (initially white) no color alteration was visible after treatment, while colored mortars experienced some color change when the more concentrated phosphate solution was used
Diammonium hydrogen phosphate (DAP) for consolidation of wall paintings: A pilot study on original fragments from eight churches (IX to XV century)
Full text linkConsolidation of wall paintings is a challenging task, as the available products often exhibit limitations. The use of aqueous solutions of diammonium hydrogen phosphate (DAP) has provided very encouraging results on natural stones and lime-based mortars, but its effects on pigmented plasters have not been reported yet in the literature. Therefore, the present study reports for the first time the performance of DAP on fragments of real mural paintings coming from 8 churches in northern Italy, differing in terms of creation time (IX to XV century), pigments and painting technique. Overall, more than 50 samples were treated with an aqueous solution containing 1 M DAP+ 1 mM CaCl2 and then characterized to assess the DAP-treatment effectiveness (by indentation, scotch tape test and ultrasonic test), compatibility (in terms of color change, alterations in water transport properties and composition of the new consolidating phases) and durability (by freeze-thaw cycles). The results of the study show that carbonate hydroxyapatite was formed when no dolomite was present in the substrate, while also struvite was formed in the presence of dolomite. In all cases, significant increases in mechanical parameters indicate strengthening of both the pigmented layer and the underlying plaster. Only in 7 cases out of 30 a color change exceeding the common acceptability limit was found after consolidation, which seems to have no obvious correlation with struvite formation, the nature of the pigment or the painting technique. In all cases, modest alterations in water transport properties were registered. Moreover, after 10 freeze-thaw cycles all the consolidated samples showed lower material loss than unconsolidated ones, thanks to the increase in mechanical properties experienced after consolidation. Overall, the DAP-based treatment appears as a promising method for consolidating wall paintings. To reduce chromatic alterations, the use of more diluted DAP solutions or the adoption of different applications methods could be explored in the future
Comparison between ammonium phosphate and nanolimes for render consolidation
Full text linkIn this study, a systematic comparison is presented between ammonium phosphate and commercial nanolimes for the conservation of lime-based renders. Such comparison is very significant, considering that nanolimes are the most widely used inorganic consolidant commonly applied onto plasters, renders and frescoes. Specimens made of slaked lime and siliceous sand were prepared, by applying the fresh mortar onto a solid brick substrate. After curing for 4 months, samples were consolidated by (i) an aqueous solution of diammonium hydrogen phosphate and (ii) commercial nanolimes. The effects of the treatments were evaluated in terms of composition and morphology of the new phases, effectiveness (ultrasounds and scotch tape test) and compatibility (color change and water absorption). The results of the study confirm the high potential of the phosphate treatment, able to provide higher mechanical consolidation in a shorter time (24 hours, instead of at least 4 weeks for nanolimes), while being equally compatible from the aesthetical and physical point of view
Air lime mortar consolidation by nanolimes and ammonium phosphate: Compatibility, effectiveness and durability
Full text linkIn this study, a systematic comparison is presented between a commercial dispersion of Ca(OH)2 nanoparticles (so-called nanolimes) and aqueous solutions of diammonium hydrogen phosphate (DAP) for consolidation of air lime mortars. The effects were evaluated in terms of compatibility (composition and morphology of the new phases, changes in color, porosity and water absorption), effectiveness (product uptake, dynamic elastic modulus, scotch tape test) and durability (permanence of the consolidating action after accelerated ageing). While both consolidants proved to be compatible, DAP solutions outperformed nanolimes in terms of effectiveness and durability, especially when highly concentrated DAP solutions were used
Ammonium Phosphate for “Green” Conservation of Cultural Heritage: 10 Years of Research in the Laboratory and in the Field
No full textThis paper presents a summary of results obtained in the last 10 years on
the use of ammonium phosphate solutions for conservation of heritage stones and
mortars.After a brief introduction about the genesis of this treatment, the most used
formulations are presented. Various functionalities of the treatment are reviewed,
then its compatibility and durability are discussed. Recent results on the treatment
environmental sustainability are also reported. The treatment’s performance in
comparison with alternative consolidants (ethyl silicate, nanolimes, acrylic resin)
is then evaluated and, finally, some pilot applications of ammonium phosphate onto
real buildings and monuments are reviewed. All the laboratory and field studies
published so far point out ammonium phosphate as one of the most promising
inorganic treatments currently available for conservation of heritage materials
Limestone Consolidation: How Much Product is Enough?
No full textThis study was aimed at evaluating the performance of four different consolidants (ammonium phosphate, nanolimes, ethyl silicate, acrylic resin) when applied onto a porous limestone (Lecce stone) by different number of brush strokes, with the aim of identifying the optimal product consumption for each consolidant. The results of the study indicate that, in the case of nanolimes and acrylic resin, insufficient mechanical consolidation and resistance to accelerated ageing is achieved even increasing the number of applications, likely because of a scarce penetration depth. In the case of ethyl silicate, increasing the product consumption leads to increasing mechanical effectiveness, which however is linked to significant color change and alteration in water absorption, as well as scarce resistance to freezing-thawing cycles. Ammonium phosphate was able to induce significant consolidation even for the lowest product consumption. By increasing the number of brush strokes, an increase in mechanical effectiveness was registered. For the highest number of applications, the mechanical improvement caused by ammonium phosphate was slightly lower than that caused by ethyl silicate, but ammonium phosphate had the important advantage of not causing any compatibility issue and resisting to freezing-thawing cycles better than all the other alternative consolidants
Nanolime, nanosilica or ammonium phosphate? Laboratory and field study on consolidation of a byzantine marble sarcophagus
Full text linkThe present paper aims at comparing commercial nanolime and nanosilica dispersions with an aqueous solution of diammonium hydrogen phosphate (DAP) for consolidation of marble. The consolidants were first tested in the laboratory on artificially and naturally weathered marble specimens. The DAP-treatment applied by poulticing outperformed nanolime and nanosilica in terms of consolidating effectiveness, while showing good compatibility with the substrate. After preliminary testing of all the three consolidants on small areas of a byzantine marble sarcophagus, the DAP-treatment applied by poulticing was finally selected for application onto the whole sarcophagus. Field results confirmed the promising performance of the DAP-treatment
Brushing, poultice or immersion? The role of the application technique on the performance of a novel hydroxyapatite-based consolidating treatment for limestone
No full textA novel inorganic consolidant has recently been proposed for the treatment of carbonate stones used in architectural and cultural heritage. The consolidant is an aqueous solution of diammonium hydrogen phosphate (DAP), which penetrates inside the stone and reacts with calcite to form hydroxyapatite (HAP). This HAP-based treatment seems very promising in several respects. It is effective in enhancing mechanical properties, only slightly alters stone transport properties, causes limited color change, and involves the use of non-toxic water solvent. However, several different treatment conditions and application methods have been investigated so far in the literature and the most suitable procedure for application in situ has not been identified yet. Therefore, in this paper a systematic investigation of the effects of different application methods of the DAP solution (brushing, poultice and immersion) was carried out. After DAP application, a further step consisting in a limewater-saturated poultice, aimed at overcoming possible issues connected to the presence of unreacted DAP in the treated stone, was performed and an "application cycle" was finally proposed. The treatments were tested on artificially weathered samples of Globigerina limestone ("Franka" type), a highly porous stone typically used in historical architecture in Malta and severely affected by decay processes. Even if Globigerina limestone is usually subject to salt-induced damage in the field, in this study artificial weathering was performed by heating to induce a controlled and uniformly distributed decay in the samples, as the presence of soluble salts would have interfered with the mechanisms of penetration and distribution of the DAP solution in the substrate, which was the main research objective. The outcome of the different treatments was evaluated in terms of consolidant penetration depth, mechanical properties, microstructure, contact angle, water sorptivity and color change, with respect to the untreated samples. The newly formed phases were characterized by SEM/EDS, FT-IR and ion chromatography. Based on the results of the study, brushing seems to be the most suitable method for DAP application, as it induces significant mechanical improvement but still limited microstructural, physical and chromatic alterations. Moreover, the benefits deriving from a higher consolidant absorption, as achieved by poultice and immersion applications (which are however much more laborious on site) are not so great in terms of HAP distribution in the substrate and consolidating performances
TEOS-based treatments for stone consolidation: acceleration of hydrolysis–condensation reactions by poulticing
No full textEthyl 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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