Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The lack of relevant chemical bond between carbonate minerals and TEOS-based consolidants was addressed by using a fine-grain porous carbonate stone to investigate alternative single treatments and functionalization pre-treatments for a commercial TEOS-based product (BS) (combined treatments). Solutions of tartaric (T) and citric (C) acids with different aggressiveness (by varying the concentration, pH and number of applications) and one solution of an amino-functional alkoxysilane solution (SiD) were developed and tested. The 0.035 M (pH ≈ 4.5) solutions of T and C applied 3 times revealed the best potential to act as single treatments while more aggressive treatments showed to have negative outcomes: formation of a superficial dense layer (T case) and excessive dissolution of calcite gains (C case). Although the formation of new crystal phases was confirmed, advantages on their use as pre-treatments for BS were hardly unveiled. The SiD was capable to form a thin layer of an ORMOSIL material covering calcite and showed potential to act as single treatment, while also having some potential to improve the superficial consolidation action of BS.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Distinctive characteristics are commonly used to define Ançã stone; it is notably white, homogeneous and fine-grained [31,33,34,38]. Ançã stone from d'El Rei quarry is described in literature as a micritic limestone of very low hardness and highly porous [38][39][40][41]. It have an extremely low content of clay and dolomite and a few quartz grains [31]. ...
... Important research work focused or used Ançã stone from many perspectives: pure characterization studies (e.g. mineralogical, petrophysical [31,47] and mechanical properties [31]), assessment of its bioreceptivity [35], test of diagnostic tools [45], development and test of consolidation products [39,46], among others. Many studies are consensual in considering Ançã stone as a pure, homogeneous, porous and white limestone, however, some authors report different pore systems and physical characteristics for Ançã stone [33,38,48]. ...
Article
Soft limestones are widely present in noteworthy constructions, but they are prone to decay due to their specific characteristics. In this paper, soft Ançã stone possessing a wide range of properties are analyzed to explain the degradation patterns and degradation rates that can be found in monuments and to estimate decay susceptibility. Experimental results indicated good correlations between physical, hydric and mechanical properties, allowing to propose drilling resistance and shore hardness as the key to estimate several other properties of soft limestones in-situ. Integrity loss rate of soft limestones submitted to freeze-thaw cycles, was found to be closely related to the saturation coefficient. Analytic relation to estimate decay of soft limestones and number of freeze-thaw cycles required to reach a pre-collapse state are drawn.
... 25 In order to reduce the effects of weathering processes, restoring and consolidating chemicals can be applied as either solutions or colloidal suspensions, able to penetrate the stone void network where a solid phase can precipitate or polymerize, 26 thus partially restoring the cohesion between stone grains and reducing the rate of rock decay and the loss of material. 27 Consolidation treatments need to comply with compatibility and durability requirements, 3 as well as with other general conservation ethics, and as a consequence, choosing a suitable consolidant is a challenging task. 28 Since the 19 th century, craftsmen and restorers have been applying a variety of natural and synthetic products to stone elements with the aim of regaining strength and cohesion. ...
Article
The ammonium salt of monoethyloxalate (AmEtOx) was investigated as a novel precursor for the conservation of carbonate stone substrates, such as biomicritic limestone and marble. A full characterization of treated and untreated authentic stone samples was carried out by means of SEM microscopy, X-ray powder diffraction, synchrotron tts-µXRD measurements, mercury intrusion porosimetry, determination of water transport properties, and pull-off tests. The improved solubility (1.49 M, 20.1% w/w) of AmEtOx as compared to ammonium oxalate (AmOx; 0.4 M, 5% w/w) results in the formation of microcrystalline phases 30–50 and 200–500 µm thick of calcium oxalate mono- (whewellite) or dihydrate (weddellite) on marble and biomicrite samples, respectively, after the treatment with AmEtOx 5% and 12% w/w water solutions. As a result, a reduction in the porosity of the stone samples and an enhancement of their cohesion is observed. DFT calculations, carried out to investigate the hydrolysis reaction leading from AmEtOx to AmOx, showed that the localization of the Lowest Unoccupied Molecular Orbital (LUMO) and the natural charge distribution account nicely for the tendency to hydrolysis observed experimentally, eventually leading to the formation of whewellite and weddellite on the stone surface.
Chapter
In this chapter an overview of the main invasive/non-invasive techniques used in situ for the evaluation of conservation treatments is provided. The conservation treatments considered are cleaning, consolidation, and protection of stone, mainly for architectural heritage. After a brief introduction, a paragraph is dedicated to the current process of drafting the standards, starting from previous experiences. In each paragraph dealing with conservation treatments, a reminder of commonly used laboratory tests carried out on stone samples, following either standardized protocols or not, are briefly reported. Details about testing protocols and threshold values for the selection of the best conservation treatment and for the monitoring will be described.
Chapter
This chapter deals with basic considerations about stone consolidation and aims to advance thoughts and clues to help professionals bridge the gap between science and practice. Scientific literature and personal experience serve to support and interpret the complex and intricate difficulties raised by practical consolidation needs. The reasons for these difficulties stem from the often-complex patterns of deterioration, the high potential risks of obtaining a very high or very low consolidation action, the uncertainty of medium- and long-term behaviour, and the lack of adequate guidelines for selecting a product and configuring a treatment consolidation solution for the intended objective. The purpose of this chapter is to help professionals to adapt existing knowledge on stone consolidation issues to each specific case and help them to make decisions, keeping in mind that there is no universally applicable product or treatment and that universal recipes should be clearly discarded. It is assumed here that the user works with products available on the market and, therefore, this chapter is not sufficiently detailed and is not intended to serve as a guide for testing or certifying new products or treatment techniques to be introduced to the market.
Article
The consolidation of weathered sandstone has been an important subject in cultural heritage conservation. Due to the loss of cementing materials, the structure of sandstone becomes loose, thus mechanical strength decreases dramatically. To restore cohesion between sand grains, a novel nano-MgO-based consolidant (MMH dispersion) is studied. In this paper, the MMH dispersions with different concentrations and number of applications are applied on artificial weathered sandstone specimen with trickling infiltration treatment to select the optimal consolidation method. The consolidation products that formed in the pores between sand grains are characterized through XRD analysis and SEM observation. The effectiveness of consolidation treatment is evaluated in terms of mechanical properties (i.e., compressive strength and surface hardness) and compatibility (i.e., color variation and capillary water absorption). Due to the formation of 5Mg(OH)2·MgCl2·8H2O, sand grains are more effectively bonded. Therefore, the treated specimens experience a significant improvement in mechanical strength. Finally, the specimens are subjected to a salt crystallization test, the results of which show that the MMH consolidant increased the durability of the specimens. After treatment, the intermediate concentration of MMH consolidant with five applications reveals the best potential to act as a promising consolidation method for the conservation of the weathered sandstone.
Article
The effects induced by diammonium hydrogen phosphate (DAP) on coarse marble varieties susceptible to granular disintegration as consolidation material is still poorly addressed. The work aims at investigating the behavior and efficacy of diammonium hydrogen phosphate(DAP)-based consolidant prepared in laboratory onto weathered coarse-grained marbles and, in the process, to unveil if the treatment investigated is a possible option to consolidate Trigaches marble elements from Roman Villa of Pisões. Sound, artificially and naturally weathered coarse marble samples were used for the purpose. The condition of naturally weathered marble slabs was assessed to reproduce artificially aged samples and used for testing the efficacy of DAP consolidant. Naturally weathered slab fragments showed a uniform damage in depth, an increased porosity and water absorption, and very similar conditions were successfully achieved in laboratory by heating sound marbles up to 300 °C for 1 h. DAP consolidant has low viscosity and can easily penetrate within the porous structure of coarse marble in granular disintegration. It promotes the formation of new calcium phosphate phases with binding capabilities that partially restore cohesion in-depth. Alteration of the color was negligible which is also a positive characteristic. Pilot tests in naturally weathered marbles revealed some interference of superficial bioorganisms residues in the absorption of DAP, however this was able to treat the entire thickness of the slab fragments, improving its cohesion state to an acceptable or good condition. Good correlations between the results of artificial aged samples with those of naturally weathered marble were achieved and the DAP-based treatment revealed to be an effective option to consolidate Trigaches marble elements from Roman Villa of Pisões.
Article
Full-text available
This study deals with the effect of a water colloidal suspension of nanosilica applied as a consolidant on a porous limestone. The stone performances were investigated by several analyses and tests. They fulfilled basic requirements such as consolidating effectiveness and compatibility with the original colour and water transport properties. A point of weakness was found in the behaviour under the salt crystallisation test, showing a decreased durability for the treated stone. The modification of the porous structure accounts for this result, suggesting that the distribution of the nanoparticle fillers into the stone substrate should be improved.
Article
Full-text available
For several years functional organosilanes containing NH group have been tested to improve the performance of TEOS-based consolidants for carbonate stones, however divergent efficacies are being reported and the role of side-effects on sol-gel routes is still unclear. The present study aims at improving the efficacy of a formulation for carbonate stone consolidation by adding N1-(3-trimethoxysilylpropyl)diethylenetriamine (SiDETA) to previously developed TEOS-based consolidants. While xerogels derived from reference sols were transparent, dense, and with smooth morphology, SiDETA-modified xerogels were translucent, coarser and composed by interconnected nanosized particles. It was concluded that SiDETA changed the mechanism of silica network formation by modifying the sol’s pH, acting as a nucleation center and by ionic interactions. Despite the changes on the silica network structure, SiDETA incorporation showed to cause additional strength increments on the treated stone.
Article
Full-text available
The overall performance of alkoxysilanes as stone consolidants is constrained by stone mineralogy (particularly in the carbonate varieties) and by their tendency to crack during drying. In an attempt to overcome these problems, polyethylene glycol “chains” with two carboxylic acid end-groups (PEG-CA) were introduced in siloxane sols obtained by sol-gel chemistry using tetraethoxysilane (TEOS) as precursor. Different pre-condensation degrees (by varying the stirring times of sol-gel reaction: 10 min, 2, and 24 h) and PEG-CA chains with different molecular weights were studied as variables affecting the initial efficacy of the consolidants when applied into a limestone. The sol containing siloxanes with the lowest pre-condensation degree (10 min stirring) was quite susceptible to the carbonate media and thus a poor consolidation was achieved. The sol with the highest pre-condensation degree (24 h stirring) together with the PEG-CA chains with intermediate molecular weight produced significant and uniform strength gains along the stone depth. The consolidation also showed to be highly dependent on the molecular weight of the PEG-CA chains, the PEG-CA with highest molecular weight produced a non-uniform strength increase with potential harmful side effects. The results confirmed the role of carboxylic acid end-groups as efficient sol-gel catalysts and their ability to be incorporated into the silica matrix in the presence of carbonate stone.
Article
Full-text available
Hydroxyapatite (HAP) has a much lower dissolution rate and solubility than calcite, especially in an acidic environment, so it has been proposed for the protection of marble against acidic rain corrosion. Promising results were obtained, but further optimization is necessary as the treated layer is often incomplete, cracked and/or porous. In this paper, several parameters were investigated to obtain a coherent, uncracked layer, and to avoid the formation of metastable, soluble phases instead of HAP: the role of the pH of the starting solution; the effect of organic and inorganic additions, and in particular that of ethanol, as it is reported to adsorb on calcite, hence possibly favoring the growth of the HAP layer. Finally, a double application of the treatment was tested. Results were compared to those obtained with ammonium oxalate treatment, widely investigated for marble protection. Results indicate that adding small amounts of ethanol to the formulation remarkably increases the acid resistance of treated samples, and yields better coverage of the surface without crack formation. The effectiveness of the treatment is further enhanced when a second treatment is applied. The efficacy of ethanol-doped DAP mixtures was found to be remarkably higher than that of ammonium oxalate based treatments.
Article
Full-text available
In this study a conservation treatment of stone monuments meant for consolidation, protection, and inhibition of biofilm formation is proposed. The method is developed as a part of a systematic investigation aimed at producing nanocomposite coatings able to exert a marked biological activity over a long period of time thanks to their peculiar structure. Zinc oxide nanoparticles, synthesised by means of simple and reproducible electrochemical procedures, are embedded in commercially available and commonly used consolidant/water repellent matrices to obtain nanostructured materials. Products based on tetraethoxysilane and/or polysiloxanes were tested. In a first step the nanomaterials were applied on stone samples and studied with scanning electron microscopy and spectrophotocolorimetry. Then, in situ experimentation was undertaken by applying nanocomposite coatings on the exterior of a 12th-century church in the south of Italy. The performances of the ZnO-nanoparticles based composite coating were compared with a previously investigated copper nanoparticles based material, successfully tested and monitored in situ for more than two years. Finally, preliminary tests on the inhibitory effect on the growth of the fungus Aspergillus niger were also carried out. The results showed that in case of zinc oxide a tenfold higher concentration of nanoparticles as compared with Cu-NPs can be utilized in the matrices without affecting the colour of the stone substrate, which means that the new material should be able to exert a long-lasting biocide activity. Laboratory and in situ tests of the developed innovative nanomaterials yielded very promising, though preliminary, results in terms of chromatic changes, morphological characteristics and bioactivity. Constant monitoring of the coatings will be continued in order to obtain all necessary information on their long term behaviour and inhibition of biological colonisation.
Article
Full-text available
This work studies the suitability of the “Torrent” air-permeability test method for testing dimension stones. To test its feasibility, measurements were performed on stone slabs with porosities in the range of 0.2–17.2 %. Statistically, accurate and reliable measurements were achieved on stones with open porosities above 2 %. Close relations were found between air-permeability coefficient and other transport-related properties. Therefore, the air-permeability coefficient can be a parameter, on its own, providing useful information about the stone susceptibility to decay. Moreover, a graded classification is suggested with the purpose of providing information for a proper application of stones in constructions.
Article
Full-text available
Understanding the influence of additives on crystal growth is required to engineer the crystal properties according to their functional applications. In this work, the sorption behavior of tartrate on calcite surfaces is investigated employing molecular dynamics simulations to understand additive-mediated crystal growth. The free energy landscapes for the sorption of tartrate are calculated using metadynamics. The adsorption binding energies of favorable conformations, orientations and positions of tartrate near the (104) and (1-10) calcite surfaces are determined. The obtained results provide a molecular-level explanation of the experimentally observed tartrate-stabilized exposure of prismatic {1-10} faces during calcite growth. The simulations show that tartrate preferentially adsorb directly to the (1-10) calcite surface, whereas tartrate is more loosely adsorbed on the (104) surface, mainly by solvent-mediated binding. The (1-10) geometry of calcite surface sites closely matches the structure of tartrate, with a specific role of carboxylate and hydroxyl groups in recognizing the calcium and carbonate ions, respectively. Two stable adsorption configurations are identified for the (1-10) face: (1) adsorbed tartrate with the effect of surface-induced conformational change and (2) incorporated tartrate into the surface by fitting one of the carboxylate groups into lattice position normally occupied by carbonate ions and additionally stabilized by binding of both hydroxyl groups to neighboring carbonate ions. The results indicate that surface energetics, structural matching and adsorbed water layer play a major role in the strength of the interactions and hence in the expression of calcite morphology. Preferential adsorption of tartrate on {1-10} surfaces could stabilize these otherwise fast-growing faces and thus inhibit crystal growth in {1-10} directions.
Article
Full-text available
The efficacy of stone consolidating treatments is significantly affected by the application procedure, including the technique used and the amount of product applied. Indeed, in the common on-site practice, consolidants are not applied until ‘apparent refusal’ (i.e. a drastic slowing down of the liquid absorption by the substrate), as usually recommended in commercial products’ technical data sheets and performed in laboratory tests, but a lower number of applications is performed for practical and economic reasons. Nevertheless, the influence of the application procedure on the absorption mechanism and distribution of the consolidant has not been fully elucidated yet, especially for solvent-based products, for which a competition between capillary uptake and solvent evaporation might arise. In this study, the influence of the treatment conditions on the consolidant efficacy was investigated with the aim of determining whether increasing the number of applications results in a deeper penetration depth and remarkably higher mechanical properties or in a higher saturation of the surface layer. For the experimental tests, an organic solvent-based ethyl silicate (or tetra-ethyl-ortho-silicate, TEOS) was selected, as it is the most commonly-used product in stone consolidation. Brushing was selected as the application method, because it is widely used in current practice and because it involves a discontinuous fluid supply to the stone, possibly causing an over-accumulation of product near the surface. Two different treatments were compared: brushing application by 5 strokes (T1) and 10 strokes (T2). The effect of the two treatments, applied on a porous limestone, was evaluated in terms of increase in mechanical properties (tensile strength, resistance to abrasion), alteration in microstructural features (determined by mercury intrusion porosimetry) and penetration depth (assessed by visual inspection of fractured samples, water sorptivity test and dynamic X-ray radiography). The results of the study indicate that increasing the number of TEOS applications from 5 to 10 brush strokes leads to a higher (but less than proportional) increase in mechanical properties (+33 % for T1, +47 % for T2) and a higher penetration depth (7–8 mmfor T1, 12–13 mmfor T2), while no accumulation of the additional product near the surface and no hard crust formation were found.
Conference Paper
Full-text available
Stone consolidation is almost always a very risky intervention. It is a non-reversible intervention and has serious harmful side effects. Due to these shortcomings, a decision to go for a consolidation action is always difficult to take and it is simple only when it is taken as a "last option" when replacement or full destruction are the unique alternatives at sight. Stone consolidation is needed because stones decay and loose cohesion in the exposed surfaces down to a certain depth. This conservation operation should take into account that type, extent and rate of decay largely depend on the intrinsic properties of the stone and on the extrinsic or environment factors. The combination of the intrinsic and extrinsic decay factors can give raise to multiple degradation forms that largely influence the decision on to consolidate and the options on the type of consolidant and on its application forms. The identification and characterisation of decay profiles is also a relevant step in stone conservation, namely when consolidation is concerned. The paper gives a brief introduction to a few topics on stone consolidation exemplifying with some current stone consolidation products. It quotes some cases of stone consolidation in recent Portuguese experience and presents some illustrations on the use of the microdrilling instrument in the detection of past consolidation actions.
Article
Full-text available
The aim of this research work was to test the influence of stone properties, consolidation product, and application procedure on the potential harmfulness of consolidation on carbonate stones as assessed 1 through the impacts on colour and water absorption kinetics. This article contributes to understanding the immediate and delayed impacts of consolidation treatments through the assessment of colour variation and modification of water absorption kinetics. The investigation was carried out on two limestones having a porosity of 10 and 27%, which were treated with three consolidating products (ethyl silicate, acrylic, and epoxy resins) using three treatment procedures: capillary absorption, brush, and full immersion. All products showed negative impacts at different degrees. We could show that their impact on a given stone depends not only on the consolidant type, but also on the treatment procedures. We demonstrated this way that the assessment of the potential harmfulness of a consolidation treatment for a specific intervention should be carried out in conditions as similar as possible to those expected to occur in practice and should never be based on extrapolations made from any other different conditions. The results also contribute to the definition of standard testing protocols in stone consolidation, privileging the application of a consolidant by direct contact capillary absorption when reproducibility is pursued, or by brushing when the potential highest impacts on colour are the target to evaluate.
Article
Full-text available
This article demonstrates the importance of treatment application procedures on the consolidation effectiveness obtained by comparison of the results obtained using three different consolidants on four carbonate stone types, and proposes a general methodology for assessing the potential effectiveness of consolidants in laboratory conditions. It stresses the relevance of taking into account the treatment methodology, given the influence application protocols can have on the overall behaviour of the consolidated material. Several mechanical properties were assessed to demonstrate this influence on the performance of the consolidant. The results demonstrate that the strengthening action achieved with a specific product can only be defined in a strict relation to the treatment protocol used to produce it. The results also contribute towards the definition of standard testing protocols on stone consolidation. The application of a consolidant by direct contact capillary absorption is a reliable procedure and the results are easier to interpret than others obtained by brushing or by full immersion, thus making this procedure a good candidate for an eventual standard laboratory assessment method of the consolidation action of any specific stone/consolidant combination. This study also showed that the best test method to assess the strengthening action of stone consolidants in soft stones is DRMS (Drilling Resistance Measuring System). Moreover, the collection of longitudinal ultrasound velocity profiles determined in stones specimens treated by contact capillary absorption was shown to be a useful non-destructive method to assess the depth of the strengthening action achieved.
Article
Full-text available
The authors propose a way of tackling the difficulty to deal with compatibility, namely on what concerns the aspects linked with the multiplicity of components involved and the diversity of criteria that can be called to integrate an assessment procedure. The paper aims at providing a management instrument having the compatibility model as its central operative tool. The guiding concepts of this instrument are supported in criteria of technical, operational, environmental, social and cultural types.
Article
Full-text available
Four types of carbonate stones and three consolidation products were used in a systematic study to assess the influence of the application procedures on the amount of product applied, as a primary step to evaluate consolidation treatments. Microdrilling, ultrasonic velocity and flexural resistance were used as performance indicators. The amount of product of a specific treatment and its action depend on the application procedures, both when the treatments are carried out in the laboratory and on site. The results are expected to contribute to the standardisation of testing protocols on stone consolidation.
Book
Full-text available
Petra, Angkor, Copan, Venice, Lascaux, Easter Island—all are examples of irreplaceable cultural heritage built in stone and now slowly disappearing. In 1996 the Getty Conservation Institute published Stone Conservation: An Overview of Current Research as a tool for conservators and conservation scientists to guide policy, practice, and research in the preservation of stone in monuments, sculpture, and archaeological sites. This second edition reflects the explosion of new research, enlarging the discussion of preventive conservation and adding new sections on rock art and other subjects. It provides a strategic overview of the intervening fifteen years in stone conservation research and an updated critique of the field's strengths and weaknesses. The accompanying bibliography summarizes material published between 1995 and 2009 and provides a framework for building a coherent base of useful knowledge for practicing conservators and scientists. Eric Doehne is a scientist at the Getty Conservation Institute. Clifford A. Price is emeritus professor of archaeological conservation at University College London.
Article
Full-text available
The hydrolysis kinetics of 14 alkoxy silane coupling agents were carried out in an ethanol:water 80:20 (w/w) solution under acidic conditions and were monitored by H, C, and Si NMR spectroscopy. Acidic conditions were selected in order to enhance the silanol formation and to slow down the self-condensation between the resulting hydrolysed silanol groups. In situ Si NMR spectroscopy allowed the determination of the intermediate species as a function of the reaction time. Thus, the following silane coupling agents were studied: 3-methacryloxypropyl trimethoxy silane (MPMS), 3-mercaptopropyl trimethoxy silane (MRPMS), 3-cyanopropyl triethoxy silane (CPES), triethoxy vinyl silane (VES), trimethoxy (2-phenylethyl) silane (PEMS), octyl triethoxy silane (OES), trimethoxy (7-octen-1-yl) silane (OEMS), 3-aminopropyl triethoxy silane (APES), 3-aminopropyl trimethoxy silane (APMS), 3-(2-aminoethylamino)propyl trimethoxy silane, (DAMS), 3-[2-(2-aminoethylamino)-ethylamino]propyl trimethoxy silane (TAMS), 4-amino-3,3-dibutyl trimethoxy silane (ADBMS), trimethoxy [3-(phenylamino)propyl] silane (PAPMS), and triethoxy-3-(2-imidazolin-1-yl) propyl silane (IZPES). A parameter quantifying the grafting potentiality of each silane coupling agent towards OH-rich solid substrates (such as cellulose) was established as a function of the nature of the alkoxy groups (methoxy or ethoxy), as well as that of the fourth substituent (vinyl, aminopropyl, etc.) of the silane studied.GRAPHICAL ABSTRACT
Article
Full-text available
Incorporating the results of a meeting held in London in December 2000, sponsored by English Heritage and The Getty Conservation Institute, this article reviews both consolidants and protective treatments for the conservation o f deteriorated limestone and lime plaster. Carbonate deposition (including both inorganic solutions and bio-mineralization), barium hydroxide treatment, ammonium oxalate and tartaric acid treatments are covered. The article reviews selected literature, identifies open questions and promotes discussion o f a range o f issues, encompassing application techniques, performance, compatibility and retreatability. While many questions concerning these important systems have been addressed in published sources, there are significant opportunities for new research.
Article
Full-text available
In this paper a comparison between the standard uniaxial compressive strength test (UCS) and a new portable instrument called Drilling Resistance Measurement System (DRMS) is presented. This instrument is part of a new methodology developed and validated within a European research project (Hardrock) with the aim to evaluate the performances of consolidation treatments applied on stone monuments. The tests have been done on different stone categories in order to evaluate the influence of the mineralogical, structural and physical characteristics in the results obtained with the two methods.
Article
Surface consolidation is a common practice in the conservation of the built heritage. However, the effec- tiveness of consolidation of calcareous materials is often doubtful, due to the lack of effective and com- patible consolidation products. Dispersions of calcium hydroxide nanoparticles in alcohol, the so-called nanolimes, can recover the superficial consolidation of calcareous substrates. Nevertheless, they are often not able to guarantee an in-depth consolidation. Previous research by the authors has demonstrated that the effectiveness of nanolime can be improved by fine-tuning the properties and the application protocol of the dispersions, based on the moisture transport properties of the material to be treated. In this paper, we verify the consolidation effectiveness and physical compatibility of the developed nanolimes, when applied on coarse porous calcareous materials like Maastricht limestone and lime- based mortars. The results show that a suitable mass consolidation can be achieved with nanolimes, while maintaining a good compatibility with the substrate material
Article
The response to thermal variations is the primary cause of marble deterioration in ancient and modern buildings. In this study, the thermal behavior of Carrara marble after consolidation by an innovative hydroxyapatite-based treatment was investigated in comparison with ammonium oxalate and ethyl silicate. Samples were subjected to heating-cooling cycles up to 80 °C. All the consolidating treatments were found to be fairly compatible, as in no case the residual strain after the thermal cycles was found to increase compared to the unweathered untreated marble. Anyway, the hydroxyapatite-treatment has the advantage of causing the highest increase in marble cohesion and the lowest residual strain, besides being more chromatically compatible and durable than the alternative commercial consolidants.
Article
No fully satisfactory consolidant for sugaring marble currently exists, hence the use of ammonium phosphate to form hydroxyapatite (HAP) inside marble micro-cracks has recently been proposed. This study was aimed at: (i) investigating different treatment formulations (application of a 3M aqueous solution of diammonium hydrogen phosphate (DAP), with/without addition of 1mM or 3mM CaCl2, with/without subsequent limewater poultice application) and characterizing the new Ca-P phases; (ii) systematically testing mechanical effectiveness and compatibility with the substrate of the most promising formulations, in comparison with ethyl silicate and ammonium oxalate; (iii) performing a pilot application of the most promising formulation to a real marble artwork affected by sugaring. The results of the study indicate that application of a 3M DAP solution, followed by limewater poultice application, produces remarkable consolidation of weathered marble, with only slight alterations in pore size distribution and color change, thus providing much better results than both ethyl silicate and ammonium oxalate. Notably, while the above-described treatment conditions caused formation of tricalcium phosphate and octacalcium phosphate in artificially weathered samples, the same conditions caused formation of HAP in the historic artwork, presumably because some gypsum residues were present and calcite grains had high surface roughness.
Article
This paper is a review of the literature that addresses the testing of products and tools for stone conservation. Cleaning products and tools are considered, as are products for consolidation and for the surface protection of natural and artificial stones (e. g., mortars or bricks). After an outline of the historical development of testing methods from the mid-nineteenth century to the present day, the development of the field is discussed with particular regard to the parameters that are measured, the measuring methods and evaluation criteria. This paper also discusses the weaknesses still existing in current methodologies, the aspects that should be investigated in greater depth and the increasing use of non-destructive testing methods to improve the evaluation of the long-term performance of treatments.
Article
William Strickland's Philadelphia Merchants' Exchange is notable for its early, innovative, neoclassical design, especially the colossal order colonnades surmounted by their Carrara marble capitals. These capitals are among the most exceptional examples of public architectural sculpture produced in the United States in the early 19th century. The mineralogic composition of the stone and the intricately carved geometry of the capitals render them highly susceptible to atmospheric weathering. Current conditions, including dimensional loss of volutes and other carved elements, prompted a year-long study to determine appropriate sequential methods for conservation, especially with regard to the compatibility of individual treatment phases. Laboratory analyses and field observations indicate a well-formed gypsum crust that retains the highly carved details of the stone while partially concealing highly friable subsurface conditions. Retention and stabilization of the external crust became the foremost objective of treatment. Passivation of the gypsum-encrusted surface was attempted with the application of barium hydroxide, followed by a series of cleaning techniques, including laser, chemical, and low-pressure microabrasive cleaning. Pretreatment with a commercial hydroxylating conversion treatment followed by ethyl silicate were applied to consolidate the friable stone. Spalling elements were micropinned with alumina ceramic pins, and visually significant losses were filled with hydraulic lime mortars. The following article discusses and evaluates the authors' conservation treatments applied in sequence in both laboratory and field tests.
Article
Protective agents based on tetraethoxysilane (TEOS) have been widely used for the protection of stone heritages. However, TEOS-based protective agents suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developed capillary force, which is typical for TEOS-based protective agents. In this paper, we have prepared new TEOS-based protective agent containing flexible hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and colloidal silica particles (167 nm) using n-octylamine as a catalyst in order to reduce capillary force development and increase hydrophobicity, and have characterized them for the application of stone protective agent. The extent of surface hydrophobization depends on concentration of colloidal silica particles and reaches a maximum value of 123° at 0.2% (w/v) of colloidal silica particles for the case of treated with the modified composition. The presence of n-octylamine is a key factor which promotes the increase of the gel pore size. The protective performances were also evaluated by its ability to resist acid corrosion. The results reveal that the protective effects are satisfying.
Article
Deterioration of monuments constructed of limestone could be potentially arrested by applying a combination of coupling agents with consolidants, which can prevent acid attack and mechanical weakening. Two different coupling agents including N-(2-aminoethyl)-3-aminopropyl methyl dimethoxysilane (AE-APMDMS) and diethyl phosphatoethyl triethoxysilane(DEPETES) were used to link calcite. Calcite was impregnated with these coupling agents and studied by FTIR, TG-DSC and contact angle measurement. According to these techniques, new bands, a two stage decomposition pattern appeared and a slight increase in surface hydrophobicity for AE-APMDMS and DEPETES that indicated interactions between the coupling agents and calcite. The Scotch Tape test and compressive strength test showed that the cohesion between consolidant and limestone powder improved, while the ability of consolidation decreased, which were resulted by coupling agents. Resist acid test on limestone powder coated with the coupling agents resulted in a decreased deterioration rate. Limestone treated with combined consolidant plus AE-APMDMS or DEPETES showed a significant decrease in capillarity water absorption.
Article
This paper discusses the effectiveness of hydroxyapatite (HAP) as an inorganic consolidant for physically weathered Indiana Limestone, and as a coupling agent between limestone and a silicate consolidant. A double application is investigated, in which samples are coated with HAP followed by a commercially available silicate-based consolidant (Conservare® OH-100). To artificially weather limestone, a thermal degradation technique was utilized. Diammonium hydrogen phosphate (DAP) salt was reacted with limestone, alone and with cationic precursors, to produce HAP films. The dynamic elastic modulus, water sorptivity and tensile strength of the treated stones were evaluated. HAP was found to be an effective consolidant for weathered Indiana Limestone, and its performance was enhanced by addition of millimolar quantities of calcium chloride. However, HAP was not useful as a coupling agent; a double treatment with DAP is more effective than sequential treatment with DAP and Conservare®.
Article
The feasibility and the effectiveness of using hydroxyapatite (HAP) formed by reacting limestone with a solution of diammonium hydrogen phosphate (DAP) in mild conditions, as a consolidant for carbonate stones were investigated. Firstly, a novel method for predamaging limestone was developed. Then, the effects of DAP solution concentration and reaction duration were evaluated to define the best treatment conditions, and the strengthening effect was evaluated on artificially damaged Indiana Limestone samples. Treated samples exhibit a significant increase in the dynamic elastic modulus and tensile strength, which is attributed to microcrack reduction and pore filling consequent to formation of calcium phosphate phases at grain boundaries, as assessed by SEM/EDS and ESEM/EBSD. Consequent to a slight reduction of coarser pores, as revealed by MIP, the sorptivity of treated samples is only slightly reduced, so that water and water vapor exchanges with the environment are not significantly blocked.
Article
Consolidants are sols or solutions that are used to restore the strength of weathered stone. The liquids are drawn into the pores of stone by capillary suction, then they harden by gelation and/or drying. In this chapter, we discuss the requirements that such a material must fulfill, and demonstrate the effectiveness of consolidants based on alkoxysilanes and alkylalkoxysilanes.
Article
The molecular structure of γ-aminopropyltriethoxysilane (γ-APS) coupling agent was studied on silicon powder by diffuse reflectance Fourier Transform Infrared (FT-IR) spectroscopy. The coupling agents are chemically bound to the surface in two ways; (1) the Si-OH groups forming Si-O-Si bonds and (2) hydrogen bonding through the organofunctional groups of the coupling agent with surface S-OH groups. There are structural differences between the chemisorbed silane molecules (interacting directly with the substrate) and the physisorbed silane molecules. These differences can be summarized as follows: (1) the chemisorbed silanes are bound to the surface through Si-O-SiO2 bonds, while the physisorbed layers are bound to each other through Si-O-Si bonds; (2) the chemisorbed layers are less condensed than the physisorbed layers; and (3) the amine groups of the chemisorbed layer are hydrogen-bonded to the surface in the NH3+ form while in the physisorbed layers it is free NH2 or in an aminebicarbonate salt form NH3+(HCO3)−. The formation of the Si-O-SiO2 bond is responsible for the hydrothermal stability of the γ-APS coupling agent.
Article
We report the synthesis and Fourier Transform Infrared spectroscopy characterization results dealing with the surface modification of silica aerogels obtained via a two-step sol–gel process where various sil-icon precursors and co-precursors were used. The hydrolysis and poly-condensation steps were followed by carbon dioxide supercritical drying (T c = 31.1 °C; P c = 73.7 bar). The silicon precursors contain four identical hydrolysable alkoxy groups (methoxy or ethoxy), while in the co-precursors, one of the alkoxy groups is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n-propyl, iso-butyl, n-octyl, vinyl or phenyl). Identically, surface-functionalized silica aerogels were obtained from various silicon precur-sor/co-precursor combinations and their chemical structures were compared. The infrared spectroscopy revealed the existence of chemically comparable solid networks with some differences due to the nature of the silicon precursors.
Chapter
Since antiquity, replacement and repair of damaged stone has been practised to delay the deterioration of buildings and monuments. Today, the aim of stone conservation is the preservation of these historic and/or artistic objects for future generations in the state in which we have received them. The approach that has been taken to address this challenge has direct links to the emergence of chemistry in the 19th century. Chemicals such as water glass, fluorosilicates and ethyl silicate were tested as consolidants for stone shortly after their synthesis in the laboratory. After World War II, organic compounds, such as acrylic and epoxi resins found their way into conservation practice. This chapter deals with all the steps required in a conservation intervention, such as the problems presented by cleaning as well as those of desalination. It includes a review of conservation materials, such as consolidants, water repellents and biocides. Silicon organic compounds are given special attention since they are the main chemicals used in the formulation of both consolidants and water repellents. The requirements for the various mortars that may be needed, including renders, as well as that of other finishes such as paints and antigraffiti coatings are also discussed.
Article
The reaction of citric acid with calcite was investigated using the rotating disk apparatus. The effects of disk rotational speed, system pressure, and presence of magnesium and ferric ions on this reaction were examined. Scanning electron microscope (SEM) was also used to characterize the surface of the calcite disks at the end of each experiment.The reaction of citric acid and calcite is mass-transfer limited up to 500 rpm. The reaction rate of citric acid–calcite is limited by the precipitation of calcium citrate on the surface, especially at atmospheric pressure. Increasing the system pressure from 1000 to 1500 psi has no significant effect on the dissolution rate of calcite. The diffusion coefficient of 7.5 wt% citric acid in the presence of calcium citrate and calcium ions is at and 1000 psi. The presence of magnesium ions in citric acid solutions results in higher concentration of calcium ions in solution.Calcium citrate forms only on the disk surface, but not in the bulk solution. The morphology of the calcium citrate layer is dependent on the rotational speed of the calcite disk. More calcium citrate precipitation occurs at high disk rotational speeds, above 500 rpm, and at system pressures less than 100 psi. Calcium citrate appears to precipitate as feathery aggregates of radiating platy crystals on the surface of calcite.
Article
Calcite and magnesite dissolution rates were measured at 60 °C, 30 atm pCO2, 0.1 M NaCl, and pH from 4.95 ± 0.05 to 5.60 ± 0.05 as a function of organic (acetate, oxalate, malonate, succinate, phthalate, citrate, EDTA) and inorganic (sulphate, phosphate, borate, silicate) ligand concentration in the range of 10− 5 to 10− 2 M. These conditions can be considered as boundary model environments for sedimentary oil-field basins of underground CO2 storage. Experiments on dissolution of magnesite powders (100–200 µm) and calcite crystal planes were performed in a batch reactor with in-situ pH measurements and under controlled hydrodynamic conditions using the rotating disk technique. At 60 °C in circumneutral solutions in the presence of 0.02 M NaHCO3 and 30 atm pCO2 (pH = 4.95), calcite dissolution is weakly affected by the presence of ligands: the rates increase at the maximum by a factor of 2 and, at 0.01 M ligand concentration in solution, the order is: silicate < citrate < NaCl ∼ borate < malonate < EDTA < sulphate < acetate. The order of ligand effects on calcite dissolution at pH = 5.55 (0.1 M NaHCO3, 30 atm pCO2) is: phosphate < NaCl < citrate < acetate < succinate < malonate < phthalate < EDTA. Magnesite dissolution rates at 60 °C, 30 atm pCO2 and 0.02 M NaHCO3 (pH = 4.95) were weakly affected by the presence of acetate, silicate, borate and NaCl but increase in the presence of sulphate, EDTA, citrate and oxalate. These ligand-affected rates were rationalized using a phenomenological equation which postulates the Langmuirian adsorption of a negatively-charged or neutral ligand on rate-controlling surface sites, presumably > MeOH2+ (Me = Ca, Mg). Proposed equations of rate–ligand concentration dependencies can be directly incorporated into reaction transport codes. Results obtained in this study demonstrate that both magnesite and calcite reactivity is not appreciably affected by acetate, oxalate, citrate, succinate, sulphate, and phosphate that are most likely present in deep carbonate aquifers at the physical and chemical conditions pertinent to CO2 geological sequestering sites. The concentration of ligands necessary to increase the rates by a factor of 3 to 10 is on the order of 0.01 M. Such a high concentration is unlikely to be encountered in deep sedimentary basins. Therefore, as a first approximation, reactive transport modelling of dissolution induced by CO2 injection in carbonate rocks does not require to explicitly account for the effect of dissolved organics.
Article
The effects of seven carboxylic acids, i.e., acrylic acid, maleic acid, tartaric acid, malic acid, succinic acid, and citric acid, on CaCO(3) crystallization were studied using the unseeded pH-drift method along with a light-scattering technique. Experiments were started by mixing solutions of CaCl(2) and NaHCO(3) in the presence or absence of additives. The crystallization was studied by recording the decrease in pH resulting from the reaction Ca(2+)+HCO(3)(-)-->CaCO(3)+H(+). A given amount of carboxylic acid was added to the solution of CaCl(2) or NaHCO(3) before mixing the reactants. The pH profiles obtained in the case of the CaCl(2) solution containing an additive were similar to those for the NaHCO(3) solution containing one, and when an additive was added after the onset of crystallization, the growth of CaCO(3) immediately stopped. The light-scattering observations, in all cases, indicated that CaCO(3) nucleation occurred at 10-20 s after mixing of the reactants. The results indicated that the nucleation of CaCO(3) was not influenced by the presence of carboxylic acids, but CaCO(3) crystal growth was reduced by their adsorption to the surface of the CaCO(3) crystals. These phenomena were explained by assuming a stronger affinity of the carboxylic acids for CaCO(3) particles than for the free Ca(2+) ions in solution. The crystallization of CaCO(3) in the presence of additives was divided into three stages: nucleation, growth incubation, and growth periods. Copyright 2001 Academic Press.
Article
The influence of four calcium complexing substances, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), on the crystal growth rate of the calcium carbonate polymorphs aragonite and calcite has been studied. Using a seeded constant supersaturation method supersaturation was maintained at 4 by keeping a constant pH of 8.5 through addition of sodium carbonate and calcium chloride solutions. The unique composition of each solution was calculated using chemical speciation. The growth rate was interpreted in terms of an overall growth rate. For both calcite and aragonite, the crystal growth rate is significantly reduced in the presence of the calcium complexing substances. The growth retarding effect depends on both the concentration and the polymorph. The relative crystal growth rate was correlated to the total complexing agent concentration using a Langmuir adsorption approach. Aragonite appeared fully covered for lower total concentrations than calcite. Furthermore, CIT very efficiently blocked aragonite growth contrary to what was observed for calcite. This is thought to be related to certain distinct features of the dominant aragonite crystal faces compared to the dominant calcite faces.
Conservação de Pedras Carbonatadas
  • A P Ferreirapinto
A.P. FerreiraPinto, Conservação de Pedras Carbonatadas. Estudo e Selecção de Tratamentos, U.T.L., Lisboa, 2002.
ASTM E2167-01 Standard Guide for Selection and Use of Stone Consolidants
  • W Ginell
  • D Wessel
  • C Searles
W. Ginell, D. Wessel, C. Searles, ASTM E2167-01 Standard Guide for Selection and Use of Stone Consolidants, ASTM International, West Conshohocken, PA, 2001.
Performance criteria and evaluation parameters for the consolidation of stone
  • P Theoulakis
  • I Karatasios
  • N.-A Stefanis
P. Theoulakis, I. Karatasios, N.-A. Stefanis, Performance criteria and evaluation parameters for the consolidation of stone, in: International Symposium Eu-ARTECH-Stone Consolidation in Cultural Heritage-Research and Practice, Lisbon, 2008.
Alkoxysilanes and the Consolidation of Stone
  • G Wheeler
G. Wheeler, Alkoxysilanes and the Consolidation of Stone (Research in conservation), The Getty Conservation Institute, Los Angeles, 2005.
Evaluation of alkoxysilane coupling agents in the consolidation of limestone
  • G Wheeler
G. Wheeler, et al., Evaluation of alkoxysilane coupling agents in the consolidation of limestone, in: V. Fassina (Ed.), Proc. the Ninth International Congress on Deterioration and Conservation of Stone, Venice, 2000, pp. 541-545.
Hydroxylating conversion treatment and alkoxysilane coupling agent as pre-treatment for the consolidation of limestones with ethyl silicate
  • A P Ferreira Pinto
  • J Delgado Rodrigues
A.P. Ferreira Pinto, J. Delgado Rodrigues, Hydroxylating conversion treatment and alkoxysilane coupling agent as pre-treatment for the consolidation of limestones with ethyl silicate, in: Proceedings of the International Symposium on Stone Consolidation in Cultural Heritage -Research and Practice, Lisbon, 2008.
Morphology of surfaces of stones pre-treated and further treated with BS; CH (citric acid at 0.175 M at pH % 4 -3 ap
  • Fig
Fig. 12. Morphology of surfaces of stones pre-treated and further treated with BS; CH (citric acid at 0.175 M at pH % 4 -3 ap.) + BS (a and b), TH (tartaric acid 0.175 M at pH % 4 -3 ap.) + BS (c) and SiD (1% SiDETA 3 apl.) + BS (d).
Development and assessment of a conversion treatment for calcareous stone
  • N R Weiss
  • I Slavid
  • G Wheeler
N.R. Weiss, I. Slavid, G. Wheeler, Development and assessment of a conversion treatment for calcareous stone, in: V. Fassina (Ed.), 9th International Congress on Deterioration and Conservation of Stone, 2000. pp. 533-540.
Alkoxysilane film formation on quartz and calcite crystal surfaces
  • E S Goins
  • G Wheeler
  • M T Wypyski
E.S. Goins, G. Wheeler, M.T. Wypyski, Alkoxysilane film formation on quartz and calcite crystal surfaces, in: Proceedings of the Eighth International Congress on Deterioration and Conservation of Stone, Berlin, 1996.
Silicones: Hidrofugantes de silicona Silres: Protección duradera para los edificios
  • Wacker
Wacker, Silicones: Hidrofugantes de silicona Silres: Protección duradera para los edificios, p. 42.
Method for protecting and consolidating calcareous materials, Google Patents
  • I Slavid
  • N Weiss
I. Slavid, N. Weiss, Method for protecting and consolidating calcareous materials, Google Patents, 2002.
Handbook of Polymers in Stone Conservation, Smithers Information Limited
  • E Princi
E. Princi, Handbook of Polymers in Stone Conservation, Smithers Information Limited, 2014.
Influence of etidronic acid and tartaric acid on the growth of different calcite morphologies
  • M Ukrainczyk
M. Ukrainczyk et al., Influence of etidronic acid and tartaric acid on the growth of different calcite morphologies, J. Cryst. Growth 369 (2013) 21-31.