Nanostructured lime-based materials for the conservation of calcareous substrates

Nanolimes, i.e. dispersions of lime (Ca(OH)2)nanoparticles in alcohol, have been extensively investigated over the last two decades as consolidation products for calcareous substrates.  The use of nanolimes for consolidation of mural paintings arises from the lack of effective and compatible consolidants for this type of substrates; the use of nanolimes was later extended also to limestone and lime-based mortars, as an alternative for silica-precursor consolidants (e.g. tetraethoxysilan - TEOS), which had shown to have a limited effectiveness and compatibility with calcareous substrates. Nanolime dispersions are characterized by a very small size of the lime particles, which should provide a proper penetration within the porous network of most building materials. In fact, a homogeneous and in-depth penetration of the consolidant is a crucial requirement when dealing with decayed stones and plasters/renders. The effectiveness of nanolime dispersions reported in literature appears controversial. Some authors observed a proper penetration and moderate consolidating action, whereas others report poor penetration, poor consolidation action and sometimes the formation of a white haze on the treated surface.  There is no agreement concerning the factors affecting the transport and deposition of the lime nanoparticles within a porous network, and the causes of the observed drawbacks are not well understood. Therefore, the main research question is:  Is nanolime a suitable alternative to silica-precursor consolidants (e.g. TEOS) for the consolidation of calcareous substrates? More specifically, the following research questions can be formulated: How and up to which extent can the effectiveness and compatibility of nanolime be improved? How can deposition of nanolime in depth be improved and the appearance of a white haze on the surface avoided? How can nanolime properties be fine-tuned to improve the effectiveness and compatibility of the treatment? What is the effect of different application methods on the effectiveness of nanolime consolidation? This research investigates and elucidates the behaviour of nanolime products for consolidation of calcareous substrates. Based on the developed knowledge, it proposes and validates a methodology (including solvent modification and application protocol) for improving the consolidation effectiveness of nanolime dispersions, making these a suitable alternative for TEOS products. Firstly, an experimental campaign was carried out in order to understand the penetration and deposition of commercial nanolimes on coarse porous calcareous substrates (Maastricht limestone). The main cause of the poor nanolime deposition in-depth was identified in the back-transport of the nanoparticles towards the drying surface, as a consequence of the high volatility and low kinetic stability of the dispersions.The modification of the nanolime properties, through the optimization of the solvent, appears thus a feasible strategy to improve the in-depth deposition of the lime nanoparticles. New nanolimes were synthetized and dispersed in a selection of solvents conferring different stability and drying rate to the obtained nanolime dispersions. A conceptual model, correlating the properties (i.e. drying rate and kinetic stability) of nanolimes dispersed in different solvents, to the moisture transport behaviour of the substrates to be treated, was conceived. The model was experimentally validated on coarse porous (Maastricht) and fine-porous (Migné) limestones.  Experimental results confirmed the predictions of the model that nanolimes dispersed in solvent with lower volatility and stability (e.g. water or butanol) have a good in-depth deposition within coarse porous networks. On the other hand, solvents with higher volatility and guaranteeing higher kinetic stability (e.g. ethanol or isopropanol) to the relative dispersions, should be preferred for substrates with fine porous networks. Fine-tuning the properties of the nanolime dispersion (by modification of the solvent) to the moisture transport behaviour of the substrate, is shown to be a successful strategy for improving in-depth deposition of lime nanoparticles.  On the basis of the obtained results, the solvent mixture was further fine-tuned using ethanol-water mixtures. Results proved that ethanol-based nanolime, mixed with a minor amount of water (5%), can provide better nanoparticles in-depth deposition within coarse porous substrates (e.g. Maastricht limestone), when compared to dispersions in pure ethanol.The application procedure of nanolime dispersions was also studied and optimized, this step being a crucial aspect for a successful consolidation; nanolimes were applied both by capillary absorption (method commonly used for laboratory tests) or by nebulization (method widely used in situ) on a coarse porous limestone and a mortar.  The research showed that results obtained by application through capillary absorption do not always correspond to those obtained by nebulization. The effectiveness and compatibility of nanolimes with improved properties and a fine-tuned application protocol were finally verified. Fresh and weathered Maastricht limestone, as well as lime-based mortars, were treated. Results showed that nanolime dispersions can guarantee an in-depth consolidation both in laboratory mortar specimens and weathered limestone, with only a moderate alteration of the total porosity and of the moisture transport properties of the investigated substrates.  Therefore, nanolime dispersions, provided that they are properly formulated and applied, can be a suitable and compatible alternative to TEOS for the consolidation of coarse porous substrates. This dissertation contributes to define guidelines to support restorers and professionals in the choice and application of nanolime dispersions for consolidation of calcareous substrates. &nbsp

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanolimes, i.e. dispersions of lime (Ca(OH)2)nanoparticles in alcohol, have been extensively investigated over the last two decades as consolidation products for calcareous substrates. The use of nanolimes for consolidation of mural paintings arises from the lack of effective and compatible consolidants for this type of substrates; the use of nanolimes was later extended also to limestone and lime-based mortars, as an alternative for silica-precursor consolidants (e.g. tetraethoxysilan - TEOS), which had shown to have a limited effectiveness and compatibility with calcareous substrates.Nanolime dispersions are characterized by a very small size of the lime particles, which should provide a proper penetration within the porous network of most building materials. In fact, a homogeneous and in-depth penetration of the consolidant is a crucial requirement when dealing with decayed stones and plasters/renders.The effectiveness of nanolime dispersions reported in literature appears controversial. Some authors observed a proper penetration and moderate consolidating action, whereas others report poor penetration, poor consolidation action and sometimes the formation of a white haze on the treated surface.  There is no agreement concerning the factors affecting the transport and deposition of the lime nanoparticles within a porous network, and the causes of the observed drawbacks are not well understood.Therefore, the main research question is: Is nanolime a suitable alternative to silica-precursor consolidants (e.g. TEOS) for the consolidation of calcareous substrates?More specifically, the following research questions can be formulated:– How and up to which extent can the effectiveness and compatibility of nanolime be improved? How can deposition of nanolime in depth be improved and the appearance of a white haze on the surface avoided?– How can nanolime properties be fine-tuned to improve the effectiveness and compatibility of the treatment?– What is the effect of different application methods on the effectiveness of nanolime consolidation?This research investigates and elucidates the behaviour of nanolime products for consolidation of calcareous substrates. Based on the developed knowledge, it proposes and validates a methodology (including solvent modification and application protocol) for improving the consolidation effectiveness of nanolime dispersions, making these a suitable alternative for TEOS products.Firstly, an experimental campaign was carried out in order to understand the penetration and deposition of commercial nanolimes on coarse porous calcareous substrates (Maastricht limestone). The main cause of the poor nanolime deposition in-depth was identified in the back-transport of the nanoparticles towards the drying surface, as a consequence of the high volatility and low kinetic stability of the dispersions.The modification of the nanolime properties, through the optimization of the solvent, appears thus a feasible strategy to improve the in-depth deposition of the lime nanoparticles. New nanolimes were synthetized and dispersed in a selection of solvents conferring different stability and drying rate to the obtained nanolime dispersions. A conceptual model, correlating the properties (i.e. drying rate and kinetic stability) of nanolimes dispersed in different solvents, to the moisture transport behaviour of the substrates to be treated, was conceived. The model was experimentally validated on coarse porous (Maastricht) and fine-porous (Migné) limestones. Experimental results confirmed the predictions of the model that nanolimes dispersed in solvent with lower volatility and stability (e.g. water or butanol) have a good in-depth deposition within coarse porous networks. On the other hand, solvents with higher volatility and guaranteeing higher kinetic stability (e.g. ethanol or isopropanol) to the relative dispersions, should be preferred for substrates with fine porous networks. Fine-tuning the properties of the nanolime dispersion (by modification of the solvent) to the moisture transport behaviour of the substrate, is shown to be a successful strategy for improving in-depth deposition of lime nanoparticles. On the basis of the obtained results, the solvent mixture was further fine-tuned using ethanol-water mixtures. Results proved that ethanol-based nanolime, mixed with a minor amount of water (5%), can provide better nanoparticles in-depth deposition within coarse porous substrates (e.g. Maastricht limestone), when compared to dispersions in pure ethanol.The application procedure of nanolime dispersions was also studied and optimized, this step being a crucial aspect for a successful consolidation; nanolimes were applied both by capillary absorption (method commonly used for laboratory tests) or by nebulization (method widely used in situ) on a coarse porous limestone and a mortar. The research showed that results obtained by application through capillary absorption do not always correspond to those obtained by nebulization.The effectiveness and compatibility of nanolimes with improved properties and a fine-tuned application protocol were finally verified. Fresh and weathered Maastricht limestone, as well as lime-based mortars, were treated. Results showed that nanolime dispersions can guarantee an in-depth consolidation both in laboratory mortar specimens and weathered limestone, with only a moderate alteration of the total porosity and of the moisture transport properties of the investigated substrates. Therefore, nanolime dispersions, provided that they are properly formulated and applied, can be a suitable and compatible alternative to TEOS for the consolidation of coarse porous substrates. This dissertation contributes to define guidelines to support restorers and professionals in the choice and application of nanolime dispersions for consolidation of calcareous substrates

Historical Heritage: A Study to Conservation

Considering ancient monuments and historical buildings, it seems that these mortars have proved to be durable and reliable materials. The restoration and maintenance of old renders is one of the key aspects of correct rehabilitation practice. The ideal course of action is to replace the damaged material by a material with compatible characteristics.The study in development presents the chemical, physical and morphologic analysis performed for ancient air lime mortars belonging to historical monuments: Santa Marta Fortress in the coast line Lisbon-Cascais dated from XVII century and Defense Wall of Lisbon dated from XI century, which layout could be associated to roman period. It is important to underline that the studied samples of ancient portuguese air lime mortars, have been submitted during centuries to very severe maritime environment that includes daily cycles of wet/dry, wind, friction and the constant presence of salts, generally aggressive. However, they show very good performance and conservation state, unlike most of the new air lime mortars, which are generally considered weak, not very durable, materials. This work is included in a study intending to determine key factors to the durability of these ancient materials in presence of water. Visible reaction rims around some aggregates suggests the occurrence of pozzolanic reactions between aggregates and the lime binder that creates neoformation products, such as calcium-silico-aluminates, which seems be, besides the pores filling, the responsible for the resistance and cohesion of these ancient mortars submitted to aggressive humid environments

Evaluation of ETICS characteristics that affect surface mould development

15th Edition of the International Conference on Durability of Building Materials and Components, Barcelona, Catalonia, October, 20-23, 2020 (DBMC 2020).External Thermal Insulation Composite Systems (ETICS) are nowadays often used in new constructions but are also one of the most frequently used thermal retrofitting solutions for buildings. These systems have several advantages such as low installation cost, ease of application and increased thermal efficiency. Nevertheless, a number of questions have been raised on their long-time durability particularly related to biodeterioration. Biological growth is strongly influenced by several parameters, such as water content, temperature, pH but also by the type and hygroscopic properties of the building materials. It is therefore essential to understand and correlate those properties with biological growth. This paper aims at evaluating some ETICS characteristics that might influence surface mould development which is recognized as one of the major groups of deteriorating organisms. The susceptibility of the surface finishing layer and thermal insulation to biological growth was assessed through natural inocula and selected fungi and, whenever possible, correlated with water absorption and drying capacity. This study is part of a wider research project: WGB_Shield (Shielding building‘ facades on cities revitalization. Triple-resistance for water, graffiti and biocolonization of external thermal insulation systems) that aims at the development of ETICS with improved durability in the urban environment. Further development on this issue are ongoing.(FCT) project PTDC/ECI-EGC/30681/2017 (WGB_Shield – Shielding building’ facades on cities revitalization. Triple resistance for water, graffiti and biocolonization of external thermal insulation systems).info:eu-repo/semantics/publishedVersio

Consolidation and chromatic reintegration of historical renders with lime-based pozzolanic products

Historical renders are exposed to several degradation processes that can lead to a wide range of anomalies,such as scaling, detachments, and pulverization. Among the common anomalies, the loss of cohesion and of adhesion are usually identified as the most difficult to repair; these anomalies still need to be deeply studied to design compatible, durable, and sustainable conservation treatments. The restitution of render cohesion can be achieved using consolidating products. Nevertheless, repair treatments could induce aesthetic alterations, and, therefore, are usually followed by chromatic reintegration. This work aims to study the effectiveness of mineral products as consolidants for lime-based mortars and simultaneously as chromatic treatments for pigmented renders. The studied consolidating products are prepared by mixing air lime,metakaolin, water, and mineral pigments. The idea of these consolidating and coloring products rises from a traditional lime-based technique, the limewash, widely diffused in southern Europe and in the Mediterranean area. Consolidating products were applied and tested on lime-based mortar specimens with a low binder–aggregate ratio and therefore with reduced cohesion. A physico-mechanical, microstructural, and mineralogical characterization was performed on untreated and treated specimens, in order to evaluate the efficacy and durability of the treatments. Accelerated aging tests were also performed to assess consolidant durability, when subjected to aggressive conditions. Results showed that the consolidants tested are compatible, effective, and possess good durability

Consolidação e reintegração cromática de revestimentos históricos – Estudo da influência da adição de pigmentos

4º Congresso Nacional CONSTRUÇÃO 2012, Coimbra, Portugal, 18-20 Dezembro 2012A consolidação de revestimentos antigos com perda de coesão acontece, geralmente, quando os mesmos apresentam um valor artístico elevado. Esta importante fase de intervenção conservativa deve ser levada a cabo através da utilização de produtos compatíveis com o revestimento; os produtos consolidantes comummemente aplicados são de natureza orgânica ou inorgânica. Os produtos orgânicos, à base de resinas acrílicas, vinílicas ou silicónicas, são incompatíveis com os suportes antigos; os consolidantes mais compatíveis encontram-se no grupo dos inorgânicos, onde se inserem a água de cal e o silicato de etilo, que também se caracterizam pela maior durabilidade e reversibilidade. Neste estudo, foram utilizados produtos consolidantes à base de hidróxido de cálcio, metacaulino (uma pozolana artificial), água e pigmentos inorgânicos. De facto, a água de cal, composta essencialmente por hidróxido de cálcio, é um dos consolidantes mais antigos de que se tem conhecimento; a adição do metacaulino prende-se com o facto de conferir ao produto propriedades hidráulicas, aumentando a sua resistência mecânica e durabilidade; a adição dos pigmentos inorgânicos pretende avaliar a viabilidade da reintegração cromática e também verificar a sua influência na consolidação das argamassas. A água de cal é um meio fortemente alcalino, sendo os pigmentos inorgânicos os que apresentam melhor resistência e durabilidade quando incorporados nesta solução. Os produtos estudados foram aplicados em provetes de revestimento de argamassa de cal aérea; estes provetes foram feitos com uma quantidade reduzida de ligante, para simular um revestimento antigo com perda de coesão superficial. Realizaram-se ensaios de carácter mecânico, físico e cromático, que possibilitaram aferir a eficácia dos produtos consolidantes aplicados. Executou-se também um ensaio de envelhecimento artificial acelerado, para avaliar a variação das características das superfícies tratadas quando expostas a ciclos climáticos. Concluiu-se que os produtos consolidantes testados são compatíveis, eficazes e apresentam boa durabilidade, e ainda que a adição dos pigmentos pode prejudicar ligeiramente o incremento das resistências mecânicas conferido pela consolidação das argamassas. Este trabalho insere-se no projecto LIMECONTECH desenvolvido no LNEC, Universidade de Aveiro e Universidade Nova de Lisboa e financiado pela Fundação para a Ciência e a Tecnologia

Impact of Water-Repellent Products on the Moisture Transport Properties and Mould Susceptibility of External Thermal Insulation Composite Systems

External Thermal Insulation Composite Systems (ETICS) are constructive solutions widely used to increase the thermal insulation in new and retrofitted buildings. However, these systems can present several anomalies due to their constant exposure to weathering agents and anthropic factors. Water is generally the major cause of degradation. Thus, the application of water-repellent products can minimize the appearance of anomalies and increase the durability of the systems. In this paper, acrylic-based and siloxane-based hydrophobic products were applied to ETICS, with the aim of assessing the compatibility, effectiveness, and durability of these products. The moisture transport properties and mould susceptibility were assessed through laboratory tests on untreated and treated specimens. The durability of the hydrophobic treatments was also evaluated through artificial aging tests (heat-cold and freeze-thaw cycles). Results show that the protection products generally decreased water absorption, slightly decreased the drying rate, and presented adequate water vapor permeability. After aging, the products still had reasonable effectiveness and, with one exception, improved the water vapor diffusion of the systems. Additionally, ETICS underwent an alteration in the finishing coat (possible modification of the porosity) due to the aging cycles. No clear linear correlation was found between the contact angle values and water absorption results, evidencing the influence of other factors related to the composition of the water-repellent products.This research was funded by Portuguese Foundation for Science and Technology (FCT) within research project PTDC/ECI-EGC/30681/2017 (WGB_Shield-Shielding building' facades on cities revitalization. Triple resistance for water, graffiti and biocolonization of external thermal insulation systems) and for the scholarship 2020.05180.BD (J. L. Parracha).info:eu-repo/semantics/publishedVersio

Effectiveness and Compatibility of a Novel Sustainable Method for Stone Consolidation Based on Di-Ammonium Phosphate and Calcium-Based Nanomaterials

External surfaces of stones used in historic buildings often carry high artistic value and need to be preserved from the damages of time, especially from the detrimental effects of the weathering. This study aimed to test the effectiveness and compatibility of some new environmentally-friendly materials for stone consolidation, as the use thereof has been so far poorly investigated. The treatments were based on combinations of an aqueous solution of di-ammonium phosphate (DAP) and two calcium-based nanomaterials, namely a commercial nanosuspension of Ca(OH)2 and a novel nanosuspension of calcite. The treatments were applied to samples of two porous stones: a limestone and a sandstone. The effectiveness of the treatments was assessed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, ultrasound pulse velocity test, colour measurements, and capillary water absorption test. The results suggest that the combined use of DAP and Ca-based nanosuspensions can be advantageous over other commonly used consolidants in terms of retreatability and physical-chemical compatibility with the stone. Some limitations are also highlighted, such as the uneven distribution and low penetration of the consolidants

Advances in Nanolime and Other Nanomaterials for Built Heritage Conservation

This Special Issue examines the synthesis, characterization, and manufacturing of nanoparticles and their potential advantages and applications for the conservation of built cultural heritage materials [...

The Boom in Nanomaterials for Built Heritage Conservation: Why Does Size Matter?

There is no doubt that nanotechnology and nanoscience open new doors to new applications and products that can potentially revolutionize the practice field and how we conserve built heritage materials. However, we are living at the beginning of this era and the potential benefits of nanotechnology to specific conservation practice needs are not always fully understood. This opinion/review paper aims to present reflections and answer a question that we are often asked when working directly with stone field conservators: why should we use a nanomaterial instead of a conventional product? Why does size matter? To answer this question, we revise the basic concepts of nanoscience with implications for the built heritage conservation field