Publications

The durability of pultruded GFRP composites is critical to their performance in civil engineering applications, for which comprehensive and validated data is limited. To address this issue, this study presents an extensive experimental programme on the effects of hygrothermal ageing on the performance of pultruded GFRP profiles made of two alternative resin systems – unsaturated polyester (UP) and vinyl ester (VE) – both comprising identical fibre architecture. The ageing environments included immersion in demineralised and salt water at three different temperatures (20°C, 40°C, and 60°C), and continuous condensation at 40°C, for durations up to two years. Physical, viscoelastic and mechanical (tensile, flexural, in-plane and interlaminar shear) properties were assessed after a desorption period. As expected, the VE profile had overall better performance than the UP profile. After 24 months, the highest reductions in tensile strength occurred for water immersion at 60°C, namely 45% and 33% for the UP and VE profiles, respectively. This paper provides a wealth of test data that can be used for degradation models for the prediction of their long-term mechanical property retention.

Fibre reinforced polymer (FRP) composites are being increasingly used in the construction sector, especially in corrosion-prone applications. However, there is still a lack of knowledge about their long-term behaviour under real service conditions. This paper presents a study about the in-service performance of FRP constructions, which involved the field inspection of 410 FRP constructions included in 31 water and sewage treatment plants in various locations in Portugal. The analysis of the data gathered in these inspections allowed (i) validating a classification system previously proposed by the authors for anomalies, causes, inspection methods and rehabilitation techniques for FRP constructions; determining (ii) the most common anomalies that occur during their service stage and (iii) their most probable causes; and (iv) predicting the most suitable diagnosis and rehabilitation techniques for each anomaly. Moreover, this study provided a better understanding of the long-term in-service behaviour of FRP constructions when exposed to different environmental conditions. The analysis of the data obtained in the field study allowed identifying the main parameters governing the in-service performance and durability of this type of constructions. The results obtained show that non mechanical anomalies are the most common. As expected, the durability performance is very different in indoor and outdoor constructions, the latter presenting much more frequent and severe anomalies. UV radiation and chemicals are found to be the most aggressive exposure environments. The results obtained also show that visual inspection is the most effective diagnosis method for this type of constructions and that surface cleaning and protection is the most commonly recommended rehabilitation technique.

In the past few decades, the construction industry has been increasingly using fibre reinforced polymer (FRP) materials, due to their advantages in comparison with traditional materials, especially in aggressive environments. However, the information regarding the long-term behaviour of FRP constructions under real service conditions is limited and scattered. In this paper, a system for the inspection, diagnosis and rehabilitation of FRP constructions is presented and validated, providing a standardized and systematic tool for the maintenance of these constructions during their service life. A classification system for the anomalies and most probable causes is first presented. To assist the diagnosis of the anomalies, several in situ non-destructive methods are included in the system, as well as various rehabilitation techniques, able to maintain and/or restore the functionality of FRP elements. Several correlation matrices are proposed, interrelating different anomalies, and relating them with probable causes, and diagnosis and rehabilitation techniques. The system is validated and calibrated through an extensive field campaign of inspections of 410 substructures in 31 facilities. Although developed for FRP profiles and moulded gratings of all-FRP constructions, the system can also be used to inspect FRP components of sandwich or hybrid structures. The implementation of this system supports the inspection activities of a proactive maintenance strategy and, at the same time, the standardization of inspections, resulting in an increase of the effectiveness and objectivity of the actions to be taken upon the occurrence of anomalies in FRP constructions.

This study aims to evaluate the effect of mineral fillers on bitumen ageing. Two different bitumens and four mastics were investigated in the unaged and long-term aged states, based on different properties (consistency, rheology, fatigue resistance and ductility). Mastics stiffened less due to ageing treatment than bitumens, especially with granite filler. However, the results of the performance tests were not definitive regarding the effect of the filler. Aged bitumen showed greater fatigue resistance and higher specific energy of ductile fracture than unaged bitumen, whereas the mastics showed minor variations in the specific energy of ductile fracture with ageing treatment, which is indicative of less ageing, but the fatigue resistance decreased significantly in mastics with one of the bitumens.

This paper presents an experimental and numerical study about the durability of adhesively bonded joints between pultruded glass fibre reinforced polymer (GFRP) adherends for civil engineering applications. Single lap joint (SLJ) specimens were manufactured using either epoxy (EP) or polyurethane (PUR) adhesive and exposed to the following hygrothermal and outdoor ageing conditions for up to 730 days: water and salt water immersion at 20 °C and 40 °C, continuous condensation at 40 °C, salt fog spray at 35 ºC, and outdoor ageing in Lisbon, Portugal. At predetermined times, the mechanical behaviour of the SLJs was assessed through shear tests, in a dry condition. Results obtained show that hygrothermal ageing detrimentally affected the failure load and stiffness of the SLJs made with both adhesives, although this degradation was balanced to some extent by post-curing effects and the desorption period. The magnitude of such degradation was not significantly influenced by the immersion media, but was largely affected by temperature. Outdoor ageing did not cause significant changes in terms of stiffness; for both adhesives, ultimate load presented a moderate increasing trend, with cyclic pattern, reflecting the effects of seasonal changes in weather. For both adhesives, failure always initiated in one of the GFRP adherends, regardless of the ageing process. However, ageing seemed to affect the portion of bond area with either (light) fibre-tear or adhesive failure: in EP-GFRP specimens, the area with adhesive failure (initially null) increased due to ageing, while in PUR-GFRP specimens (significant in unaged joints) it decreased. The final part of the paper presents non-linear finite element (FE) models of the SLJs; these models were developed to numerically simulate the mechanical performance of the joints and to estimate the influence of ageing on the bond vs. slip laws that describe the interaction between the GFRP adherends.

Fibre Reinforced Polymer (FRP) composites have been the source of an increasing interest in the field of rehabilitation, namely for repair and strengthening of reinforced concrete (RC) structures. One of the most effective techniques comprises externally bonded FRP composites, in which the efficacy of rehabilitation depends considerably on the integrity and durability of the bond established between the FRP and the substrate, which is provided by a structural adhesive. This paper presents a concise review of critical durability issues associated with the structural bond between FRP and concrete for rehabilitation purposes. A number of factors determining the durability of FRP-concrete bonded joints have been identified and grouped into the following categories: materials – adhesive and adherends, joint characteristics and in-service conditions. For each of those factors, the main findings obtained in previous studies are summarized and the aspects that need fuarther investigation are outlined.

This paper presents an experimental study about the effects of thermal cycles on adhesively bonded joints between pultruded glass fibre reinforced polyester (GFRP) adherends used in civil engineering structural applications. Single lap bonded joints were produced with two commercial polymeric adhesives - epoxy (EP) and polyurethane (PUR) - and exposed to a mild (Mediterranean) range of thermal variations (-5 °C to 40 °C) for up to 350 cycles in a dry condition. The mechanical performance of the adhesively bonded joints was assessed by means of single lap shear tests. Regardless of the inherent differences between both adhesives, results obtained show that the global effect of thermal cycles on the load vs. displacement response of EP-GFRP and PUR-GFRP joints was similar. For both adhesives, thermal cycles caused considerable reduction of joint stiffness and strength, with maximum reductions of 18% and 22% for EP-GFRP joints, respectively, and 19% and 11% for PUR GFRP joints. The degradation of performance was influenced by post-curing effects, more relevant in the PUR adhesive. Before exposure to thermal cycles, both types of specimens exhibited similar failure mechanisms, which generally (80-90% of cases) involved light fibre tear and fibre tear modes, attesting the effectiveness of the adhesion process and material compatibility. Exposure to thermal cycles did not influence the failure modes of the PUR-GFRP joints; however, EP-GFRP joints became more prone to adhesive failure after being subjected to thermal cycles. Overall, the results obtained indicate that thermal cycles degrade bonded joints between pultruded GFRP adherends; however, for the conditions used in this study, this degradation seems to be compatible with the structural use of this type of joints in civil infrastructure.

This paper presents an experimental study about the effects of hygrothermal and outdoor ageing on a polyurethane (PUR) adhesive used in civil engineering applications. Small scale adhesive coupons were exposed to different types of ageing environments for up to two years: (i) immersion in demineralised water at 20 and 40 °C, (ii) immersion in salt water at 20 and 40 °C, (iii) continuous condensation environment at 40 °C, and (iv) outdoor ageing in Lisbon, Portugal. At predetermined times, after a desorption period until constant mass, the effects of such exposure on the physical and mechanical responses of the PUR adhesive was investigated using the following techniques: (i) water sorption, (ii) dynamic mechanical analyses (DMA); (iii) flexural; and (iv) in plane shear tests. The diffusion mechanisms observed were not purely Fickian; a long relaxation period was noticed, with water molecules being continuously incorporated in the adhesive until the end of the experiments; two alternative analytical modelling approaches were successfully used to simulate the diffusion processes. After immersion in water and salt water for two years, the viscoelastic behaviour of the adhesive showed signs of post-curing phenomena, and some of the physical degradation was found to be reversible due to drying, although it was not explicitly quantified; accordingly, the Tg showed increasing trends (11 14%). The mechanical properties of the adhesive showed signs of irreversible degradation mechanisms, more relevant on the in-plane shear properties, with reductions up to 26% in strength and 44% in modulus under the harsher conditions. Flexural properties also exhibited irreversible degradation, with maximum reductions up to 30% in strength and 36% in modulus. Increased temperature did not have a significant effect in the flexural and shear strength, but caused higher degradation in the corresponding moduli. The degradation caused by salt water immersion and continuous condensation was comparable to that in demineralized water immersion (at the same temperature).

This paper presents an experimental study about the durability of a cold curing structural epoxy (EP) adhesive exposed to different hygrothermal and outdoor ageing environments, typical of civil engineering applications, for up to two years: water and salt water immersion at 20 °C and 40 °C, continuous condensation at 40 °C, and outdoor ageing in a mild Mediterranean climate. After specific exposure periods, changes in the following physical properties and mechanical behaviour of the adhesive were assessed: (i) media diffusion, through water uptake (in hygrothermal environments); (ii) viscoelastic behaviour, through dynamic mechanical analyses (DMA); and (iii) flexural and (iv) in plane shear behaviour. Regarding media diffusion, water uptake did not follow a Fickian behaviour and a final saturation stage was not reached; two alternative non Fickian analytical models were successfully fitted to the test data and the corresponding diffusion parameters were determined. In what concerns the viscoelastic behaviour, while continuous condensation and outdoor ageing caused negligible changes, the Tg of the adhesive generally decreased due to immersion (around 20% in water and 10% in salt water after two years); in addition, at later stages of water immersion, the tan ? curve showed significant shape differences, with the usual curve peak being replaced by two different peaks; a generalised reduction of the storage modulus at the glassy plateau was also noted. In terms of mechanical performance, such plasticization effects were visible in the flexural and shear stress strain behaviours. The flexural properties exhibited irreversible degradation, with the highest reductions (two years of ageing in water at 40 °C) being about 24% and 30% in strength and modulus, respectively. Regarding the shear properties, in hygrothermal environments the shear modulus showed similar decreasing trends to the flexural modulus (43% reduction after one year), but the shear strength increased (~25%); the outdoor ageing affected the shear properties in the same way, but the magnitudes of the changes were lower.

N/A

Neste artigo apresenta-se resultados de um estudo experimental, ainda em curso, sobre a durabilidade em ambientes marítimos de perfis pultrudidos de GFRP, constituídos por resinas de poliéster insaturado e viniléster reforçadas com fibra de vidro. Diversos provetes foram submetidos a imersão durante 12 meses em (i) água desionizada e (ii) água salgada, a diferentes temperaturas (20 ºC, 40 ºC e 60 ºC), e a (iii) nevoeiro salino durante 2000 horas, após o que as suas propriedades físicas, químicas, mecânicas e estéticas foram avaliadas.

To assess the quality of polyethylene pipes compounded with recycled polyethylene for applications in drainage and sewerage, several analysis techniques were applied, some of them being not previewed in the performance characteristics standards. The measured physical, chemical and mechanical properties of raw-materials, intermediate compounds and final products, were used to evaluate the performance of the different formulations, allowing to an understanding of the thermo-mechanical effects of the several transformation processes. The analysis of the results will help us to optimising the manufacture parameters and to check the formulations, in view of its upgrading. The effect of a nanoclay was also studied. INTRODUCTION

Neste artigo é abordado o tema da utilização de materiais compósitos de matriz polimérica reforçados com fibras na reabilitação de estruturas. Procuraram-se sistematizar os motivos que têm conduzido ao sucesso da aplicação desta família de materiais, designadamente por darem aos projectistas a possibilidade de construir soluções “por medida” que se adeqúem aos requisitos específicos de uma dada aplicação.

Neste artigo apresentam-se resultados da apreciação da resistência a variações térmicas de dois tipos de perfis estruturais fabricados por pultrusão e reforçados com fibras de vidro, que diferem na natureza da sua matriz: poliéster insaturado e viniléster. Este trabalho encontra-se inserido num projecto de investigação em curso, cujo objectivo é analisar a durabilidade deste tipo de produtos, utilizados em aplicações estruturais na Engenharia Civil.

In most of polymer ageing studies conducted at laboratory, there is a trend to subestimate some of the parameters involved in natural exposure, leading to a poor simulation results and low reliability of the real world phenomena. Moreover the nature of polymer and its formulation should be taken into account due to possible synergies and antagonisms between environment and polymer additives. Among the subestimated parameters, we can stress the role of ambient humidity and inorganic fillers. These last additives are usually considered to be inert regarding the degradation induced by radiation. In this work we used X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIRS) to evaluate the influence of the different photo-oxidation conditions. Different PVC formulations, designed for outdoor applications, in the form of calendered films, were submitted to artificial accelerated ageing under different radiation sources, with and without water spray, and also to natural exposure in Lisbon. Usually, PVC degradation is evaluated by dosing evolved chlorine under the form of HCl or Cl2. XPS results show that, in technical PVC formulations, the fraction of chloride ions trapped in the inorganic filler is a better parameter to measure the PVC degradation (measured by the yellowing index variation) than the total lost (or remaining) chlorine in the surface. FTIRS measurements were used to follow the formation of oxidation products of the carbonyl type, which are due to radical attack on the double bonds in the molecular structure of PVC. Results show that relative rates of PVC degradation reactions are different under different photo-oxidative conditions. Combination of XPS and FTIRS analyses have shown that the best simulations of the natural weathering of such PVC materials under laboratory conditions needs to consider, besides the light, the intervention of water jets and/or humidity as well as the existence of light and dark periods.

In most of polymer ageing studies conducted at laboratory, there is a trend to underestimate some of the parameters involved in natural exposure, leading to poor simulation results and low reliability of the real world phenomena. Moreover, the nature of polymer and its formulation should be taken into account due to possible synergies and antagonisms between environment and polymer additives. Among the underestimated parameters, we can stress the role of ambient humidity and inorganic fillers. These additives are usually considered to be inert regarding the degradation induced by radiation. In this work, four different PVC formulations, designed for outdoor applications, in the form of calendered films were submitted to artificial accelerated ageing under different radiation sources, without and with spray of water, and to natural exposure. The influence of the different photo-oxidation conditions was evaluated by means of Xray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIRS). The photo-oxidation of PVC can be studied by FTIR measurements following the formation of oxidation products of carbonyl type, due to radical attack to the double bonds in the molecular structure of PVC, enhanced by radiation and temperature. Results have shown that relative rates of PVC degradation reactions are different under different photo-oxidative conditions. XPS results show that, in technical PVC formulations, the fraction of chloride ion trapped in the inorganic filler is a better parameter to measure the PVC degradation (measured by the yellowing index variation) than the amount of total remaining (or lost) chlorine in the surface. When the ageing method includes water jets, the top superficial layer made from the inorganic filler and the organic products from the PVC degradation is removed and leaves behind a much more homogeneous layer which is more resistant towards ageing than the “as processed” one that contains defects introduced by the calendering process. XPS also makes clear that zinc-calcium additive is a better thermal stabilizer than the dibutyltinmaleate and the presence of the tinuvin P retards the PVC degradation. The best simulation of the natural weathering of such PVC materials in laboratory conditions needs to consider, besides the light, the intervention of water jets and/or humidity as well as the existence of light and dark periods.

N/A

An experimental program was undertaken to evaluate the durability of three commercial epoxy adhesives used for bonding repairing and strengthening Carbon Fibre Reinforced Plastics (CFRP) to concrete structures. The changes in physical and mechanical properties after exposure for up to 18 months under different environmental conditions are reported and discussed.

No presente relatório apresentam-se os dados meteorológicos do ano de 2019 recolhidos na estaçãometeorológica existente no Núcleo de Materiais Orgânicos do Departamento de Materiais do LNEC, em Lisboa

No presente relatório apresentam-se os dados meteorológicos do ano de 2020 recolhidos na estaçãometeorológica existente no Núcleo de Materiais Orgânicos do Departamento de Materiais do LNEC, em Lisboa

No presente relatório descrevem-se os procedimentos adotados pelo LNEC, no âmbito do estudo a efetuar para a concessão de um Documento de Aplicação (DA), relativo a revestimentos por pintura elastoméricos para rebocos de cimento e para betão aplicados em paredes exteriores de edifícios. Consideram-se as condições de exposição atmosférica no exterior sem a influência de ações químicas severas. Indicam-se, também, as ações a desenvolver periodicamente para comprovar que continuam reunidas as condições que terão permitido a concessão do DA.

No presente relatório descrevem-se os procedimentos adotados pelo LNEC para a concessão de um Documento de Aplicação (DA) relativo a revestimentos por pintura de base aquosa para aplicação em paredes e tetos de interiores de habitações, sobre superfícies de estuque de gesso, de gesso cartonado, de reboco de cimento ou de betão. Indicam-se, também, as ações a desenvolver periodicamente para comprovar que continuam reunidas as condições que permitiram a concessão do DA.

No presente relatório apresentam-se os dados meteorológicos do ano de 2016 recolhidos na estação meteorológica existente no Núcleo de Materiais Orgânicos do Departamento de Materiais do LNEC, em Lisboa

No presente relatório descrevem-se os procedimentos adotados pelo LNEC no âmbito do estudo a efetuar para a concessão de um Documento de Aplicação (DA) relativo a revestimentos por pintura para rebocos de cimento e de betão aplicados em superfícies exteriores (tintas não elastoméricas). Consideram-se as condições de exposição atmosférica no exterior, sem influência de ações químicas severas. Indicam-se, também, as ações a desenvolver periodicamente para comprovar que continuam reunidas as condições que terão permitido a concessão do DA. Este relatório constitui uma revisão do relatório do LNEC nº 252/2013-DM/NMO.

No presente relatório apresentam-se os dados meteorológicos do ano de 2014 recolhidos na estação meteorológica existente no Núcleo de Materiais Orgânicos dom Departamento de Materiais do LNEC, em Lisboa

No presente relatório apresentam-se os dados meteorológicos do ano de 2013, recolhidos na estação meteorológica existente no Núcleo de Materiais Orgânicos do Departamento de Materiais do LNEC, em Lisboa.

No presente relatório descrevem-se os procedimentos adoptados pelo LNEC no âmbito dos estudos para concessão de um Documento de Aplicação (DA) a produtos de pintura para proteção de superfícies madeira, em condições de exposição atmosférica no exterior. Indicam-se também as ações a desenvolver periodicamente para comprovar que continuam reunidas as condições para a concessão do DA.

Nesta publicação apresenta-se o critério presentemente seguido pelo LNEC para concessão de homologação com certificação, bem como posterior controlo periódico da qualidade a sistemas de tubagem de poli(cloreto de vinilo) não plastificado (PVC-U) destinados à extração de água em profundidade. Após uma breve introdução e a definição do objetivo, indicam-se: - Os requisitos para o sistema da qualidade seguido pelo fabricante; - as caraterísticas e as especificações para a matéria-prima constituinte dos tubos e acessórios; - as caraterísticas e as especificações para os produtos finais, designadamente os tubos e as suas uniões; - a classificação das condições de serviço; - as recomendações para a utilização dos produtos, relativamente ao seu transporte e manuseamento, armazenagem e instalação; - os requisitos do LNEC para o autocontrolo do fabricante; - os requisitos de amostragem do LNEC durante as auditorias técnicas ou campanhas de recolha realizadas ao fabricante pelos técnicos do LNEC, no âmbito da concessão e manutenção da homologação.

Os resultados experimentais, obtidos através da medição de propriedades dos materiais e produtos, requerem tratamento específico e adequado, de forma a garantir a sua qualidade. É por isso muitas vezes necessário recorrer a métodos estatísticos para fazer a análise do tipo de distribuição dos resultados, proceder à deteção de valores suspeitos num conjunto de observações e à eventual rejeição de resultados anómalos. Este tipo de tratamento estatístico é principalmente adequado a ensaios de intercomparação, quer do foro metrológico (comparação de valores de padrões ou materiais de referência, mediante medição efetuada por operadores de diferentes laboratórios metrológicos, com incerteza variável), quer do âmbito dos laboratórios de ensaio. Os ensaios de Comparação Interlaboratorial realizados por laboratórios de ensaio, constituem uma ferramenta de garantia da Qualidade e são utilizados para a validação de métodos de ensaio (incerteza e robustez) e como um meio para a determinação das características de desempenho dos laboratórios, nomeadamente da reprodutibilidade e da repetibilidade. Nesta publicação faz-se uma descrição dos vários parâmetros que devem ser determinados em ensaios interlaboratoriais do tipo “Intercomparações com valor de consenso” e respetivos métodos de cálculo. A estatística aqui apresentada pode, numa boa parte dos casos, ser também aplicada à análise de resultados de medições experimentais correntes.

The main purpose of this Paper is to present a state of the art about weathering and polymer degradation. This review was presented during a training course promoted by the 5th European Weathering Symposium EWS (XXVIIth Colloquium of Danubian Countries on Natural and Artificial Ageing of Polymers), which was held in Lisbon on September 21 - 23, 2011, organised on behalf of CEEES (Confederation of European Environmental Engineering Societies) by the German Management Society for Environmental Engineering GUS (Gesellschaft für Umweltsimulation e.V.) and supported by SOPSAR (Sociedade Portuguesa de Simulação Ambiental e de Avaliação de Riscos), APIP (Associação Portuguesa da Indústria de Plásticos) and LNEC (Laboratório Nacional de Engenharia Civil). The main topics of this review are the weathering of polymers and composites, the determination, simulation and effects of relevant climatic quantities, innovative polymer additives, new test procedures and devices, instrumental methods of analysis to evaluate polymer degradation, recent developments in polymeric materials and composites designed for outdoor applications and methods for service-life prediction.

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A