Avaliação do impacto de caruncho pequeno em estruturas antigas de madeira

A madeira foi um dos primeiros materiais de construção a ser utilizado pelo Homem, devido não só à sua relativa abundância na natureza, como também por possuir excelentes características mecânicas, físicas e de durabilidade. No entanto, por se tratar de um material orgânico de origem biológica, é suscetível a degradação, que é frequentemente causada por agentes biológicos, nomeadamente fungos e insetos. Enquanto a ação dos fungos de podridão tende a ser localizada, a ação dos insetos pode ser extensa e a infestação, geralmente, leva a uma deterioração mais generalizada na estrutura de madeira. Em Portugal, os insetos que mais problemas causam às estruturas de madeira são as térmitas subterrâneas e os insetos de madeira seca, de onde se destacam os carunchos. Os danos causados por estes agentes são justificação frequente para uma substituição total ou parcial das estruturas afetadas, uma vez que a avaliação da integridade estrutural existente se torna difícil. Esta remoção ou substituição de elementos degradados pode não ser necessária, uma vez que a segurança estrutural pode continuar garantida. Além disso, este tipo de operações é, geralmente, difícil de realizar e dispendioso. Torna-se necessária, então, uma avaliação estrutural rigorosa e devem ser tomadas medidas apropriadas para que se garanta um nível de segurança adequado, racionalizando a intervenção. No caso de ataque por carunchos pequenos, uma das grandes dificuldades que existe prende-se com a necessidade de quantificar a resistência das secções transversais da madeira com danos devido à ação destes agentes. Os efeitos desta ação podem ser considerados, de forma geral, assumindo uma redução da secção transversal ou propriedades mecânicas inferiores para essas secções transversais. No entanto, desconhece-se o impacto real da ação do inseto em estruturas de madeira, desconhecendo-se, portanto, o nível de intervenção necessário na estrutura. Assim, o objetivo principal deste trabalho é avaliar o impacto da ação de caruncho pequeno em estruturas antigas de madeira. Numa primeira fase, realizaram-se ensaios de compressão paralela às fibras e de arrancamento perpendicular às fibras em provetes de madeira antiga (Pinus pinaster Ait.) degradados por caruncho (PN), em provetes com tentativa de simulação da degradação (PA) e em provetes de controlo de madeira sã (PS). Os resultados são apresentados e discutidos. Numa segunda fase, recorreu-se à técnica de micro tomografia computadorizada (micro-CT) para a determinação da percentagem de material perdido (consumido pelos carunchos). Conhecendo-se este valor, é possível determinar-se a perda de massa volúmica decorrente da degradação. O conhecimento deste parâmetro é de extrema importância para a avaliação do estado da madeira, uma vez que é altamente correlacionável com a maioria dos parâmetros de avaliação mecânica. Foram submetidos a micro-CT 18 provetes. Estabeleceram-se correlações entre a percentagem de material perdido e as massas volúmicas (original e residual). Concluiu-se sobre os resultados obtidos e refletiu-se sobre a aplicação da técnica de micro-CT ao estudo. Apresentou-se um modelo de avaliação in situ para madeira degradada por caruncho pequeno, com base na realização de um ensaio semidestrutivo de arrancamento de um parafuso. Realizaram-se ensaios mecânicos de arrancamento perpendicular às fibras e de corte paralelo às fibras. A possibilidade de prever as propriedades da madeira através da aplicação da técnica foi discutida com base em modelos simples de regressão linear. Correlacionou-se a perda das propriedades mecânicas do elemento com a perda de massa volúmica existente e, consequentemente, a perda de massa volúmica com a resistência ao corte paralelo do elemento. Finalmente, propõe-se uma ferramenta de avaliação in situ do estado e qualidade da madeira existente

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

Vernacular Earthen Buildings from Leiria, Portugal–Material Characterization

In Portugal, a large number of vernacular earthen buildings present an advanced state of degradation. These buildings comprise historical, technological, architectonic, cultural and social recognized values and, therefore, efficient interventions are needed for their conservation. The knowledge of the properties that the materials used in their construction show nowadays is one of the bases to support future interventions. Unstabilized earthen samples were collected from the walls of six earthen buildings located in the region of Leiria, Portugal, built with rammed earth and/or adobe masonry. The samples were characterized by particle size distribution and through XRD, density, capillary absorption, drying, dry abrasion, compressive and tensile flexural strength. Mechanical results of rammed earth were lower than adobe’s, contrary to what was commonly found in other studies, and capillary coefficients of adobe were comparable to lime-stabilized adobe from other regions. A surface protection by compatible renders, respectively, earthen-based and air lime-based, is strongly encouraged to extend the walls durability. Although based on a short sampling, this data gives initial support to future compatible, effective and reversible interventions in Leiria vernacular earthen buildings, contributing to the preservation of this earth-built heritage.authorsversionpublishe

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

Effects of anobiid damage on shear strength parallel to the grain in single step joints

ABSTRACT: Traditional carpentry joints can be found worldwide in many timber truss structures connecting rafter and tie beam. One failure mode of this connection result from shear in the tie beam beyond the notch either due to bad design or deterioration. In this article, the reduction in shear strength of Single Step Joints (SSJ) resulting from biological attack by anobiids was analysed. For this purpose, tests were carried out in non-degraded scots pine (Pinus sylvestris L.) specimens (reference) and compared to artificially degraded specimens with three different levels of degradation. The reduction of shear resistance was analysed in relation to the density of holes drilled during the degradation simulation, the loss of mass, and the reduction of the shear-resistant area. At lower degradation levels, no significant reduction in shear strength was observed. On the other hand, the linear regression shows a trend of resistance reduction with increasing degradation. Despite the relatively low coefficient of determination (r2 = 0.25), the parameter that best correlated with the residual strength was the reduction in the shear-resistant area.info:eu-repo/semantics/publishedVersio

It’s what’s inside that counts: an assessment method to measure the residual strength of anobiids infested timber using micro-computed tomography

The safety assessment of old timber structures is an important issue due to the long-term behavior of wood and the structural complexity found in some older constructions. If the structure is de-graded due to the action of wood-boring insects, the complexity of the analysis increases. The objective of the work reported in this paper is to provide an assessment method to measure the residual strength of pine structural elements degraded by anobiids. Samples of degraded tim-ber were submitted to micro-computed tomography (μ-XCT) to quantify density loss being this parameter of fundamental importance for the assessment of timber structures as it is highly corre-lated with timber mechanical properties. During the μ-XCT study an empirical correlation be-tween lost material percentage (consumed by beetles) and timber apparent densities (original – before degradation and residual – after degradation) was established. The results showed an experimental high correlation (r2=0.66) between original apparent density and lost material percentage and an even higher correlation (r2=0.87) between residual apparent density and lost material percentage which confirms that μ-XCT can be validly used contributing to the 3D visualization and quantification of timber degraded elements. After the μ-XCT study, screw withdrawal and shear parallel to grain tests have been made in mar-itime pine degraded timber. Screw withdrawal force and shear strength values were related with density loss (r2=0.64 for screw withdrawal; r2=0.65 for shear strength parallel to grain). A novel assessment method for evaluating the impact of anobiid damage on timber degraded structural elements based in four major steps is proposed enabling a more quantitative assessment of the timber elements residual strength and, therefore, contributing to reduce unnecessary replacement and to provide foundations required to perform experimental modelling tests.authorsversionpublishe

Mineralogical and microstructural characterisation of rammed earth and earthen mortars from 12th century Paderne Castle

PTDC/EPH-PAT/4684/2014In many countries, earth was a very common construction material until the middle of the 20th century, being rammed earth one of the most widespread construction techniques. Nowadays, there are still a large number of constructions with this traditional technique, from vernacular dwellings to monuments. Therefore, rammed earth constructions integrate cultural, historical, technical and architectonic recognised value and the constant neglect of this type of constructions, without maintenance and conservations measures over time, or with inadequate interventions, presents a worrying reality. This paper aims to contribute towards increasing the knowledge on materials from 12th century Paderne castle, located in Algarve, south of Portugal. Data from interventions performed on the castle in the 20th and 21st centuries were gathered. Samples from the rammed earth castle tower and walls and mortar from a more recent chapel were collect during the 21st century interventions and characterised, mainly by microstructural and mineralogical techniques. Most of them present calcareous and siliceous aggregates in their composition, except for samples collected from the wall where no siliceous aggregates were detected. Rammed earth samples present a brownish colour being the binder a mixture of clayey earth and lime, and the coarse aggregate mostly limestone. Iron oxide/hydroxide and clay minerals, very common in earth composites, are detected and a lime + clay binder/aggregate ratio of 1:1.5 in volume is the most frequently found. The large amount of calcite in all rammed earth samples is an indication of the use of carbonate gravel mixed with a high content of air lime. The presence of white nodules in the earthen matrix induces that the lime was probably applied as quick lime and, afterwards, hydrated by mixing with the moistened earth. The lime was used as a stabiliser (technique called “military” rammed earth) to promote a hardening process by carbonation and increase durability to weathering. Therefore, characterisation results obtained in this study allow to draw conclusions about the materials and construction techniques used in the past, in order to support future compatible, effective and reversible interventions in this and in similar historic military rammed earth constructions.authorsversionpublishe

Vernacular earthen buildings from Leiria, Portugal – Architectural survey towards their conservation and retrofitting

Fundação para a Ciência e Tecnologia (FCT) , Portugal for funding José Lima's PhD scholarship ( SFRH/B/119703/2016 ); the research project PTDC/EPH-PAT/4684/2014: DB-Heritage - Database of building materials with historical and heritage interest; The strategic project of CERIS research center (UIDB/04625/2020).In Portugal, rammed earth monolithic walls and adobe masonry were, for several centuries, important construction techniques for dwellings. The frequent unnecessary demolition of these buildings, mainly due to lack of information related to them, lack or inadequate maintenance interventions, and advanced state of degradation, has been leading to great cultural and material loss. To preserve this vernacular built heritage and all the technological knowledge related to it, it is fundamental to understand the constructive technologies. Several earthen buildings from Leiria region were mapped and inspected, and two of them were taken as case studies. This architectural survey allowed studying their construction specificities, main building pathology, and thus contributing to Leiria's vernacular earthen buildings efficient preservation and use.authorsversionpublishe

Efficacy of iron-based bioproducts as surface biotreatment for earth-based plastering mortars

The authors acknowledge the support of the Fundação para a Ciência e Tecnologia (FCT) through research project PTDC/EPH-PAT/4684/2014 : DB-Heritage, Database of building materials with historical and heritage interest. Part of this work was supported by the Applied Molecular Biosciences Unit-UCIBIO which is financed by national funds from FCT / MCTES (UID/Multi/04378/2019). Nídia Almeida is supported by the Radiation Biology and Biophysics Doctoral Training Programme ( RaBBiT-PD/00193/2012 ; UCIBIO-UID/Multi/04378/2019 and CEFETIC-UID/FIS/00068/2013 ) and by a PhD fellowship from FCT/MCTES (PD/BD/106034/2015).The use of bacteria for the enhancement of construction materials has been a focus of study in the past few years. Microbial cells have been applied to consolidate the surface of different materials. Earthen plasters are eco-efficient building products that can be applied on new buildings but also used to protect cultural heritage structures, with several advantages. They are based on abundant, affordable and easy to obtain materials, but are vulnerable to water. New eco-efficient bioproducts were developed based on E. coli cultures supplemented with iron, that can be obtained as an industrial by-product. They were applied in laboratory on an earth plaster surface and the biotreatment efficacy was assessed. The main objective was to improve the durability of the plastering mortar when exposed to water. An optimized E. coli-iron based surface biotreatment strongly increased the plaster resistance to water with the application of only 0.0625 mL/cm2 of E. coli++Fe leading to a significant increase of water absorption time in comparison with similar plasters where the same amount of water was applied. Moreover, all biotreatments produced an increase of resistance to water absorption creating a slight waterproofing effect, ensuring compatibility. Their loss of efficacy with time guarantees reversibility of the intervention. The results show the interest to perform an in-depth study on the microstructure of biotreated earth mortars to understand the biotreatment effect.proofpublishe

Effect of innovative bioproducts on the performance of bioformulated earthen plasters

Fundação para a Ciência e Tecnologia (FCT) through research project PTDC/EPH-PAT/4684/2014: DB-HERITAGE, Database of building materials with historical and heritage interest. Part of this work was supported by the Applied Molecular Biosciences Unit-UCIBIO and the Civil Engineering Research and Innovation for Sustainability Unit-CERIS, which are financed by national funds from FCT (UIDB/04378/2020 and UIDB/04625/2020, respectively).Biotechnologies mainly based on precipitation of chemical compounds produced by microbial metabolism can be used as biotreatment or bioformulation of construction materials. Bioformulation of cement-based materials has been a common research practice, though its application to earthen-based building materials is still limited. Although earth mortars are vulnerable to water damage, they are nowadays often used as plasters on new constructions but also for the retrofitting of existent buildings. Their reversibility and compatibility with old substrates make them also interesting for conservation interventions, namely when applied to protect archaeological structures as sacrificial renders. In this study, an innovative bioproduct based on cellular extracts of Escherichia coli, cultured in Lysogeny broth (LB) medium and supplemented with iron, was developed and used as a component for earth mortars’ bioformulation. The Escherichia coli strain used is classified as not hazardous. An additional earth mortar bioformulated with LB medium as mixing liquid was also tested to assess the influence of the culture medium. The iron supplement was chosen to infer about iron oxide biomineral formation, a less toxic mineral than calcite, since no toxic by-products are produced, and iron oxide minerals have a longer lifetime when compared with calcite crystals. Bioformulated mortars presented a very distinct porous structure, with a significant decrease on mechanical properties. Nevertheless, they also showed a decrease on thermal conductivity, a slight consolidative effect, and a significant decrease on vulnerability towards water. Apart from the possible use as mortar air entraining agents, the obtained results show the interest on further studies on the use of nontoxic iron-based bioproducts for earthen mortars optimization.authorsversionpublishe