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Protecting stone buildings from weathering and decay is a major challenge in the conservation of built heritage. Most of the stone consolidants currently available are well suited to silicate stones but are less compatible with limestone. In this paper, we present for the first time the results over a 4-year period of various consolidation treatmen...
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... application was repeated at 24-h intervals over a period of 6 days. Details of the treatments are reported in Table 1. The application took place under laboratory conditions at a temperature of 20 • C and relative humidity between 50-70%. ...Context 2
... highlighted in Table 1, Bath stone was treated following 3 different protocols: specimen #1 was pre-treated with distilled water prior to nanolime application; specimen #2 was not pre-treated, whereas specimen #3 was pre-treated with ethanol. As illustrated in Figure 4b-d, in the sample pre-wet with water (sample #1, Figure 4b) the drilling resistance increased up to a depth of 7 mm from the sample surface, whereas the sample that wasn't pre-wetted ( Figure 4c) showed an increase in drilling resistance up to a maximum of 4 mm. ...Similar publications
This research aimed to study a possible synergistic effect with inoculation with A. brasilense and N doses, associated with the application of silicon in acidity corrective form, evaluating the grain yield of irrigated wheat in Cerrado region. The experiment was conducted in Selvíria, MS, Brazil, under a no-till system, on a Latossolo Vermelho dist...
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... However, it is vital for the methodology to be adapted to the condition of the surface, the specific damage, and properties of the treated artefact. As examples, the conservator has the possibility to apply successive coatings (up to 10, for instance) by brushing a same low concentration (i.e. 5 g/L) of nanolime [6] , injecting a higher concentration (i.e. 25 g/L) with a reduced number of applications (up to 6, for instance) [51] , or again, using one application at a high concentration (i.e. > 25 g/L) by capillary adsorption until the full saturation of the surface [63] . ...
... Overview of the methodology Two areas measuring approximately 10 cm x 10 cm, were selected on each object. Area #1 was treated with the En-NCT , whereas Area #2 was treated by the control treatment, that is consolidation with the nanolime following the treatment guidelines as described in the literature [ 18,[49][50][51][52][53][54]. A summary of the strategy followed for the treatment of Areas #1 & #2 is given below. ...
Stone consolidation is one of the most important and complex treatment actions performed in museums. However, products routinely applied on limestone objects are often chemically incompatible with the treated substrate. Despites the established efficiency of nanolime for outdoor conservation and its chemical compatibility with the carbonate mineral matrix, its performance in a museum context needs to be verified. As a result, this work addresses a shortcoming in the field of Stone Conservation as nanolime has never been officially introduced in museums before. Three British Museum limestone objects affected by superficial damages were treated using an Enhanced Nanolime Consolidation Technique (En −NCT) which was developed in the Materials Engineering Research Institute (Sheffield Hallam University) and tested for the first time in a museum context. The results show that the use of alcoholic nanolime by means of a tailored consolidation technique is a realistic and promising museum conservation approach. The En −NCT does not impair the aesthetical appearance of the objects and restores the mineral cohesion of the treated surface by increasing the hardness of the near-to-surface layers.
... Chemical and biological approaches are used to obtain such coatings. Chemical approaches are the following: the use of a suspension of calcium-hydroxide nanoparticles which promotes the formation of calcium-carbonate particles binding the surface layer of limestone under the influence of atmospheric factors [10,11]; the use of a diammonium-phosphate solution which forms a hydroxyapatite film on the surface of limestone [12] or silicondioxide nanoparticles [13]. ...
Minimal interference with historical material and maximum preservation is one of the basic principles of the scientific restoration and conservation of monuments of historical and cultural heritage. The creation of nanoscale and microscale inorganic coatings is a promising way to protect limestone and marble cultural heritage objects. We conducted a laboratory testing of a method for stimulating biogenic mineral formation on the surface of limestone-masonry samples from the medieval cave town on the Eski-Kermen plateau (Crimea, Russia). The results showed the formation of a layer of crystallites of 0.4 to 1.3 µm on the surface of the limestone, an increase in the average strength values of the samples by 28% from 12.3 ± 2.8 to 15.8 ± 2.6 MPa, a 42% increase in the specific surface area of limestone, an 86% increase in salt attack resistance, and preservation of the capillary water-absorption level. The obtained results show the potential of using biogenic mineral formation for the conservation and restoration of limestone.
... Since then, nanolimes have been widely studied [4,7] and the literature can broadly be divided into two main groups: the first group concerns the study of the nanolimes themselves, determining the mechanism of the carbonation process [8][9][10][11] as well as improving the efficacy and synthesis of nanolime [12][13][14][15][16]. The second group mostly focuses on the application of these nanolimes to different substrates [1,[17][18][19][20][21][22][23][24][25], in various environmental conditions [5,26,27] and with different application procedures [28][29][30][31][32]. Within this second group, the compatibility and effectiveness of the nanolime treatment have been assessed in terms of penetration depth, strength, hardness, surface cohesion, capillary absorption and aesthetics. However, few studies have investigated the impact of nanolime treatment on the water drying kinetics despite reports of a decrease in measured porosity and accumulation of nanolimes near the surface [3,21,[33][34][35]. ...
... The influence of treatment on the drying kinetics was investigated at two different concentrations. Commercially available nanolime CaLoSiL E25 (IBZ-Salzchemie GmbH & Co, Germany) was selected due to its prevalence in nanolime research [10,12,16,17,20,21,30]. CaLoSiL E25 (E25 hereinafter) is a colloidal dispersion of Ca(OH) 2 nanoparticles in ethanol at a concentration of 25 g/L, with a particle size distribution reported between 50 and 300 nm, as shown in Fig. 1b, which is in agreement with literature values [48,49]. ...
Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment . These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport.
... Consequently, the literature reporting consolidation treatments of naturally aged stones addressed a vast variety of lithotypes. Naturally aged samples, limestones [49,59,63,70,82,97], marbles [19,43,75,84,85], biocalcarenites [32,33,58,90], sandstone [22,59,82], chert [40], chalk [28], and tuff [21] are examples, while from testing areas on monuments, marbles [75,85], biocalcarenite [47,80], marlstone [45], granite [25] and limestone [20] are examples. ...
This work aims to reveal the recent research trends in the consolidation of stone-built heritage and discuss the advantages and drawbacks of the options and strategies followed by researchers over the last 10 years. Peer-reviewed articles were used to build a database and analyze the details of the stone samples (chemical nature, type of voids, and condition), treatment protocols (application methods and consolidation products), and testing methods to assess the strengthening results of the treatments. In addition, the reported increments in the mechanical properties were also examined to reveal the strengthening capabilities of recent consolidation treatments. The statistical treatment of the results allowed pinpointing the stone varieties that need more frequent consolidation actions (limestone, biocalcarenite, and sandstone) and the aspects that make them more difficult and riskier. Other tendencies were discussed, for example, the predominant use of sound samples over decayed samples (61% vs. 39%) or the predominant use of alkoxysilanes (~46%) over other families of consolidants (e.g., nanolime, ~21%). The current consolidation treatments were found to improve stone strength; however, the most problematic issue in state-of-the-art is the difficulty of identifying high-risk situations of over-consolidation or poor distribution in depth because of either the lack of testing or limitations of the various assessment techniques.
... In the '90s nanolime was first synthesised and applied in heritage conservation, in order to overcome some of the drawbacks of limewater, which has been used to consolidate limestones and plasters for centuries ( Figure 2). Nanolime consists of a water/alcoholic dispersion of calcium hydroxide (Ca(OH) 2 ) nanoparticles in concentrations of 5-50 g/L, with sizes between 50 and 600 nm [28]. When exposed to atmospheric CO 2 at room temperature and in the presence of water, they carbonate, forming CaCO 3 cement that binds decayed stone or wall paintings [29]. ...
... Due to its nanostructured size and higher specific surface area, nanolime displays several advantages compared to traditional limewater: higher colloidal stability and good penetration into the stone pores, reducing the formation of white surface stains [31]; the avaialbility of several synthesis routes to finetune the particle size and control the reactivity and surface properties [32,33]; and higher reactivity resulting in a beneficial reduction of the carbonation time. Since the introduction of different commercial products, nanolimes have been widely applied for the consolidation of limestones [28,32,[34][35][36][37][38][39][40][41], lime mortars [35,[42][43][44][45], and wall paintings [32,46]. The selection of the concentration and type of solvent of the suspension and of the application methodology are important factors to consider prior to the conservation intervention. ...
... Nanolimes require a slow and accurate application to the substrates, as they can easily impregnate the most superficial layers, resulting in the formation of an instable and hard crust and whitening due to surface deposition [27]. Despite being on the market for several years, only limited results on the durability of nanolime treatments applied onsite on naturally aged stone surfaces are available [28,39,40,47]. ...
The unpredictable effects of climate change impose the safeguarding of Cultural Heritage (CH) with effective and durable materials as a vital solution in the invaluable socioeconomic resource of CH. Conservation products and methodologies are addressed under recent advancements in colloidal science providing multi-functional solutions for cleaning, consolidation, protection, and monitoring of the architectural surfaces. Nanoscience significantly contributes to enrich the palette of materials and tools that can guarantee an effective response to aggressive environmental agents. Nanostructured multi-functional nanoparticles, nanostructured fluids, and gels for stone conservation are reviewed and future perspectives are also commented. The stability and high flexibility in designing tailored made nanoparticles according to the specific characteristics of the substrate enable their use in a variety of applications. Stemming from the well-performed in lab applications with nanomaterials, the testing onsite and the monitoring of their effectiveness are of crucial importance, considering also the constructive feedback from conservators and heritage stakeholders that can unquestionably contribute to the improvement and optimisation of the nanomaterials for CH protection.
... However, MIP analysis carried out in the outermost 5 mm showed a higher apparent density (Table 1), the apparent density and the open porosity in accordance with [47] did not experience variations since all the values were around 2100 Kg/m 3 and 19-20%, respectively. These results are clearly in line with previous investigations on stone consolidations that suggest that nanolime treatments induce a minimal total open porosity variation after treatments on cubic samples measuring 30 mm × 30 mm × 30 mm [43,56] while noticeable reductions in the open porosity can be only detected by MIP on the superficial 1 cm layer [43]. In the current research, this decrease in the open porosity is certainly noticed by MIP in all impregnated samples in the outer 5 mm of the consolidated samples (Table 1) suggesting that all treatments affected the pore structure of the stone by reducing the modal pore diameter and the porosity. ...
Consolidation treatment with nanolime is a common conservation intervention which needs more research to enhance penetration and mechanical properties while also minimizing the undesired white veil on the surface which significantly alters the surface appearance. In this light, the application of a cellulose poultice soaked in
distilled water over the treated surface with nanolime tries to prevent the formation of white hazes and to favour nanolime carbonation and penetration in the pore structure. However, the real influence of this practice on the consolidation effectiveness has never been studied yet and is not yet well understood. In order to provide more insights about its most suitable application method, in this study, we investigated the effectiveness of a wet cellulose poultice for two different nanolime consolidation treatments on a weathered limestone. Nanolime has been synthetized by anion exchange processes and dispersed in two mediums: i) water and ii) 50% v/v of water and alcohol. The influence of the poultice on the penetration and aesthetic properties has been studied by drilling
resistance measurement, ultrasounds test, stereomicroscopy, measurements of roughness and static contact angle, spectrophotometry and scanning electron microscopy (superficial and cross sectioned samples). Additionally, consolidation effectiveness has been evaluated through the changes in apparent density, open porosity,
porosity network in the outer 5 mm of the surface by mercury intrusion porosimetry and surface cohesion by the peeling test. Results show that, contrary to what is usually assumed, samples where a wet cellulose poultice was applied after the consolidant reached the lowest penetration levels and retained lower dry matter in comparison
to their counterparts without poultice. A consolidation treatment with nanolime is more complex that it is generally considered, and the application of poultices is not always enhancing consolidation level; the most suitable application procedure must be chosen with regards to the nanolime and substrate specific characteristics.
... Generally, the most used consolidation materials in conservation treatments of calcareous-based stones (which are the ones most widely present in Cultural Heritage monuments) are silane-based consolidants, such as ethyl-silicates, alkoxysilanes and acrylic polymers. If, at first, these solutions seem to provide a protection against water and an increase of the surface resistance, over the years they present a scarce durability or cause detachment of the original material, adding a further reason of decay, even worse than the natural weathering [5][6][7][8]. Even the traditional limewater (a saturated solution of calcium hydroxide in water) or milk of lime (a suspension of calcium hydroxide in water), despite their potential chemical compatibility with the carbonate substrates, have shown limited performances. ...
... In the first case, due to the low solubility of lime in water, great amounts of limewater are necessary to guarantee enough consolidating product, leading to an extraordinary excess of water brought to the stone. In the latter, the dimensions of the particles (generally ranging from 1 to 10 μm or even more) are responsible for the incomplete carbonation process and the very limited penetration depth, leading to an insufficient consolidation efficacy and the formations of white superficial deposits [6,9,10]. ...
... However, the uses of the available alcoholic nanolime dispersions on natural stones revealed controversial results about their real efficacy. There are related to: a) the influence from the environment humidity conditions, strongly affecting the rate of carbonation as well as the type of CaCO 3 polymorphs which it forms; b) the reduced penetration ability of the alcoholic nanolimes treatments, proven by the back-migration of the nanoparticles during the evaporation of the solvent, [6,[14][15][16][17]. We recently tested the possibility to operate with aqueous nanolime dispersions which allow us to obtain a good consolidating efficacy together with a definite penetration depth up to 10 mm from the surface, confirmed in laboratory tests as well as in situ applications [18][19][20][21]. ...
In this paper we introduce new aqueous nanolime formulations, pure or properly chemically tailored, for innovative, compatible, and eco-friendly consolidation treatments on biocalcarenite stones, a renowned kind of stones used in ancient buildings throughout the Mediterranean region, which are however subject to severe decay. The phase composition, stability, and carbonation process of the nanolime formulations were investigated, while the treatments efficacy was evaluated in terms of aesthetical features, superficial cohesion, drilling resistance and durability. The aqueous nanolimes, applied by nebulization, increased the mechanical resistance on the surface and up to 2 cm in depth without appreciable surface variations, especially in the case of the tailored formulation, ensuring a good durability to UV/salt crystallization ageing.
... The selection of the four tested materials is justified since these are the most commonly used consolidants in Hungary and commonly applied worldwide [26] for stones other than limestone, such as sandstone [27,28] or volcanic tuffs [29]. For limestone, silica acid esters are also used but in recent years, studies dealing with nano-lime treatment are also known [30][31][32]. Another type of porous carbonate is travertine. This lithotype is more durable and less sensitive to freeze-thaw For strengthening pore structure, commercially available ethyl silicate agents are commonly used for deteriorated stones in the protection of historic buildings. ...
... The selection of the four tested materials is justified since these are the most commonly used consolidants in Hungary and commonly applied worldwide [26] for stones other than limestone, such as sandstone [27,28] or volcanic tuffs [29]. For limestone, silica acid esters are also used but in recent years, studies dealing with nano-lime treatment are also known [30][31][32]. Another type of porous carbonate is travertine. This lithotype is more durable and less sensitive to freeze-thaw damage [33][34][35][36] than the tested Miocene porous limestone [16], and it has been widely used as a replacement stone in Hungary [33,37]. ...
The durability of consolidated highly porous limestones was tested after salt and freeze–thaw cycles. Three porous limestone lithotypes that were commonly used in construction in the Central-European region during previous centuries were selected for the tests. Specimens of Miocene limestone were consolidated with four different types of ethyl silica-based consolidants (KSE 100, KSE 300, KSE 300 E, KSE 300 HV). After consolidation, the samples were exposed to freeze thaw cycles and salt crystallization tests. Water saturation under atmospherically pressure, capillary water absorption and splitting tensile strength were measured on treated and untreated samples to assess change attributed to consolidation in the open porosity and mechanical parameters. The increase in the tensile strength of the medium-grained samples was higher than that of the consolidated fine-grained lithotypes. The effect of consolidation treatment was very different in terms of pore-size distribution as obtained by Mercury intrusion porosimetry (MIP). Untreated and consolidated samples were subjected to 10 cycles of sodium sulphate crystallization (EN 12370) and 10 freeze–thaw cycles (EN 12371) tests. Experiments concluded that in addition to the initial strength increase after the conservation, the modified pore structure is the crucial factor to evaluate the long-term efficiency of stone conservation.
... Since its development in 2001, nanolime has been effectively tested for the consolidation of several substrates such as wall-paintings (Ambrosi et al. 2001), lime-mortars (Otero, Starinieri, and Charola 2018), limestones (Otero, Starinieri, and Charola 2019), biocalcarenites (Daniele et al. 2018;, and other historic materials such as paper (Sequeira, Casanova, and Cabrita 2006), canvas (Giorgi et al. 2002), bones (Natali et al. 2014) or wood (Poggi et al. 2016). Recently this type of nanolime has been also applied successfully on in-situ and long-term applications (Borsoi et al. 2016;Gherardi et al. 2020;Pondelak et al. 2017;Taglieri et al. 2019;Tzavellos et al. 2019). ...
The conservation of historic structures must be carried out through treatments that use materials which are compatible with the originals. In recent years, nanolime has been considered one of the most promising products for the consolidation of calcareous substrates due to its characteristics of high compatibility with the treated substrate and durability. The effectiveness of nanolime products has been proven for superficial consolidation treatments (e.g. plasters and wall-paintings), and research nowadays is focused on the study of the in-depth consolidation effectiveness of porous substrates. The aim of this paper is to undertake preliminary investigations of compatible nanolime treatments for Indiana limestone (US) and a weathered marble. Nanolime was synthesized by anion exchange resins and dispersed in isopropanol and ethanol. The consolidation effectiveness is assessed by studying changes in porosity, drilling resistance, surface cohesion and aesthetic appearance (colour). Results showed that nanolime yielded the highest consolidation effectiveness when treated samples were kept in high relative humidity environments (~75%RH) or regularly sprayed with carbonated water in a laboratory environment (~50%RH). These results suggest that for an on-site consolidation treatment with nanolime in dry environments, treated surfaces could be regularly sprayed with carbonated water to increase consolidation effectiveness.
... To improve the consolidation effectiveness of lime-based products, in the 1990s nanolime was first synthesized and applied in heritage conservation (Salvadori and Dei 2001). It consists of an alcoholic dispersion of calcium hydroxide (Ca(OH) 2 ) nanocrystals, in concentrations of 5-50 g/L, with sizes between 50 and 600 nm (Tzavellos et al. 2019). Thanks to their nanosize and their higher specific surface area, nanolimes are more reactive, resulting in a beneficial reduction of the carbonation time. ...
... By selecting the most appropriate synthesis route, it is possible to control the particle size, and modulate their chemical reactivity and their properties (Chelazzi et al. 2013). Especially since the introduction of the first commercial products, nanolimes have been widely used for the consolidation of limestones (Chelazzi et al. 2013;Borsoi et al. 2017;Daniele et al. 2018;Taglieri et al. 2018;Shekofteh et al. 2019;Tzavellos et al. 2019), lime mortars (Borsoi et al. 2017;Delgado Rodrigues et al. 2018;Otero, Starinieri, and Charola 2018;Taglieri et al. 2019) and wall paintings (Chelazzi et al. 2013;Natali et al. 2014). Different factors affect the effectiveness of nanolimes: the concentration of applied suspension and application procedure; the type of solvent and environmental conditions during curing of the treated surfaces, especially in terms of relative humidity (RH) and temperature (Chelazzi et al. 2013;Otero, Starinieri, and Charola 2018). ...
... Current research in stone consolidation is focusing on optimization of the application methodologies of nanolimes on fresh or artificially aged stone specimens, and the effectiveness of nanolimes has been evaluated in laboratory conditions. Only a few studies include testing of the consolidants on naturally weathered stones to evaluate the interaction of the treatment with lithotypes, characterized by features developed upon ageing that cannot be simulated with an artificial procedure (Otero, Starinieri, and Charola 2019;Tzavellos et al. 2019). In addition, laboratory tests cannot fully reproduce the complexity of outdoor environmental conditions, and only limited data on the durability of nanolime treatments applied on-site on naturally aged surfaces is available (Gherardi et al. 2017;Otero, Starinieri, and Charola 2019;Tzavellos et al. 2019). ...
Nanolimes are the first nanomaterials used in heritage conservation for natural stone consolidation. Thanks to their size, they show good penetration depth into substrates, high reactivity resulting in a faster carbonation process, and the ability to bridge cracks through the formation of a network of calcium carbonate cement. Two commercial nanolimes, CaLoSiL (IBZ Salztchemie) and Nanorestore (CSGI) and a dispersion of Ca(OH) 2 nanoparticles, synthesized by an anionic exchange process, were applied to fresh and naturally weathered limestone specimens, previously removed from the medieval Bishop's Palace in Lincoln, UK. A protocol of non-destructive tests was defined to study the treatment effectiveness, both in the laboratory and on-site. The two commercial nanolimes exhibit a low penetration depth, accumulating on the surface and creating a white coating, and lead to only a small increase in surface hardness. On the contrary, the laboratory-synthesized consolidant was able to effect a good superficial consolidation, without affecting the water absorption and aesthetic properties of the specimens. These results, together with those obtained from the application and monitoring of the consolidants on-site, will be crucial for the planning of interventive conservation at the Bishop's Palace.
