Service life of concrete structures rehabilitated with polymers

Keynote paperThe estimation of the service life of concrete rehabilitation works is more and more important. The rehabilitation techniques appeared as a need to solve problems posed by the degradation of concrete structures. Some years ago the rehabilitation techniques were not developed and it was important to find solutions for the problems. Now, there is more preoccupation with the service life of concrete rehabilitation techniques, like external strengthening with FRP, increase of concrete sections or reinforcement of cracked sections. The increase of the service life started with the quality of the concrete rehabilitation works. This includes the quality of the design, the products and the execution. Some standards are now available and establish specifications for concrete rehabilitation works. This paper presents the main questions related with this subject. The use of polymers in concrete rehabilitation imposes a different analysis related with durability

Estudo e caracterização de espécies portuguesas de madeira termicamente modificada

A modificação térmica tem-se revelado um método eficaz na melhoria da durabilidade de elementos de madeira. Até ao momento, as aplicações da madeira termicamente modificada (MTM) têm sido limitadas a revestimentos já que o tratamento térmico de tratamento conduz a uma redução significativa das resistências mecânicas da madeira. Contudo, este tratamento térmico poderá valorizar e potenciar a utilização de espécies de madeira menos utilizadas na construção, como são o Eucalipto e o Pinho bravo nacional. Com o objetivo de avaliar o efeito do tratamento térmico nas espécies referidas e, complementarmente, na madeira de Faia e Freixo, realizou-se uma campanha experimental composta por ensaios de caracterização mecânica (compressão paralela às fibras e flexão) e de estabilidade dimensional (retração, inchamento e teor de água de equilíbrio (TAE)). Para efeitos de comparação, todos os ensaios envolveram séries de provetes de cada espécie de madeira natural e MTM. Os resultados obtidos são coerentes com a bibliografia disponível, o aumento da estabilidade dimensional, assim como a diminuição do TAE e das propriedades mecânicas de flexão foram verificadas, permitindo, assim, avaliar a influência da modificação térmica nas propriedades de espécies de madeira presentes em Portugal.The thermal modification has proved to be an effective method to improve the durability of wood elements. Until the moment, applications of thermally modified wood (MTM) have been limited to non-structural applications, because the heat treatment leads to a significant reduction in the mechanical performance of wood. However, this heat treatment can promote the use of less used wood species in construction, as the national Eucalyptus and Pine. In order to evaluate the effect of heat treatment on the species of Pine, Eucalyptus, Beech and Ash, was held an experimental program that consisted in mechanical characterization tests (compression parallel to grain and flexion) and tests of dimensional stability (shrinkage, swelling and equilibrium moisture content (EMC)). For comparison, all tests were made with samples of non-modified and thermally modified wood. The results are consistent with the available literature, the dimensional stability increased, as well as the reduction of TAE and mechanical properties, allowing the evaluation of the thermal modification on the properties of wood species present in Portugal

Influência da temperatura no comportamento de elementos de betão armado reforçados à flexão com laminados de CFRP

A necessidade de reabilitação estrutural de elementos de betão armado tem-se revelado cada vez mais frequente. O reforço por adição de armaduras exteriores através da aplicação de compósitos de fibra de carbono é, actualmente, a técnica de utilização mais generalizada e com maior potencial. Em muitos casos, a aplicação de compósitos pode significar um meio de aumentar a vida útil de uma estrutura que possivelmente não poderia ser reforçada utilizando materiais convencionais. A possibilidade de se proceder à operação de reforço em períodos de tempo muito curtos, sem que seja necessário interromper, completamente, a utilização da estrutura, apresenta-se como uma das maiores vantagens associadas ao reforço de elementos de betão armado com materiais compósitos. A união entre o reforço e o suporte, geralmente, é realizada com colas de base epoxídica. Contudo, é nesta parte do sistema que a integridade do reforço pode ser afectada. Entre vários factores, destaca-se a exposição a temperaturas elevadas que pode influenciar a eficácia da colagem. Nesta comunicação, apresenta-se um estudo experimental, cujos resultados evidenciam que a resistência térmica deste tipo de sistema de reforço não é muito elevada

Influência de temperaturas elevadas no comportamento de reforços exteriores de betão armado

Hoje em dia, há a necessidade de resolver problemas em estruturas de betão armado. O reforço por adição de armaduras exteriores à base de materiais compósitos é uma das técnicas que tem vindo a adquirir cada vez mais potencial. A união entre o reforço e o suporte, geralmente é realizada com colas de base epoxídica. Contudo, é nesta fracção do sistema que a integridade do reforço pode ser afectada. Entre várias razões, destaca-se a exposição a temperaturas elevadas. Para estudar a variação do comportamento do sistema de reforço perante o aumento da temperatura ambiente, foram produzidas várias vigas de betão armado onde foram colados laminados CFRP. Após exposições térmicas cíclicas de 25 dias com uma temperatura máxima de a 20ºC, 40ºC, 60ºC e 80ºC, as vigas foram ensaiadas à flexão. Os resultados demonstram que a melhoria conseguida com o reforço à temperatura ambiente, se torna menos expressiva com o aumento da temperatura ambiente. A resistência térmica deste sistema de reforço não é muito elevada, pelo que a sua aplicação em locais quentes, requer cuidados especiais.Nowadays, there is a need to solve problems of reinforced concrete structures. The external reinforcement of concrete with composite materials is a technique that has acquired more and more potential. The bond between the reinforcement and the support is usually accomplished with epoxy adhesives. However, it is in this part that the integrity of the system can be affected, namely by exposure to high temperatures, amongst various other reasons. In order to study the behaviour of the external reinforcement with the increase of air temperature, several beams were prepared and strengthened with bonded CFRP laminates. After cyclical thermal exposure of 25 days with maximum temperatures of 20ºC, 40ºC, 60ºC and 80ºC, the beams were subjected to bending tests. The results demonstrate that the improvement achieved with the reinforcement, at air temperature, have no significance with the increase of the environment’s temperature. The thermal resistance of this strengthened system is not very high, thus special needs are to be taken in to account when applied in warm locations.Sika Portugal, S.A. Socitrel (Soc. Ind. Trefilaria, S.A.). Secil (Companhia Geral de Cal e Cimento, S.A.)

Predicting mechanical properties of enhanced performance concrete using compressive strength

Mechanical properties of concrete are usually evaluated from compressive strength test results. Extensive literature, codes and regulations recommend the prediction of mechanical properties such as splitting and flexural tensile strength using the compressive strength of cylindrical specimens. These expressions are not related with the type of concrete and, generally, are only a function of the cylindrical compressive strength. It is the objective of this research work to investigate the validity of the existing relationships for enhanced performance concrete, obtained by replacing cement with fly ash for up to 60% in weight. The experimental program investigated the effect of replacing cement with fly ash on the mechanical properties, i.e. compressive strength, splitting-tensile strength and flexural-tensile behaviour. Results obtained show that, in most cases, a good linear correlation exists between the evaluated mechanical properties, i.e. splitting-tensile strength, flexural-tensile strength and elasticity modulus in flexure, and the square root of compressive strength. This further indicates that an increase in the compressive strength produces a less pronounced increase of the tensile strength

Performance of concrete in aggressive environment

Surface treatments act as a barrier between the environment and the concrete, preventing or retarding the entry of harmful substances and cutting off the transportation path into concrete. The effectiveness of a surface protection preventing the permeation depends on how close and strongly connected are the resin molecules. This work intends to contribute to a better understanding of the performance of protected concrete in chemically aggressive environments, by presenting results of ion diffusion and resistance to aggressive solutions of several hydrophobic agents and coatings used to protect concrete. Three different types of surface protections were tested: silicone hydrophobic agent, acrylic and epoxy coatings. The obtained results indicate that the overall performance of epoxy resin was better than the other selected types of protections

Biomass and coal fly ash as cement replacement on mortar properties

Nowadays, construction sector tries to implement several options to solve the issues related to concrete. The main goal of this work was to study the effect of biomass fly ash, blended with coal fly ashes or alone, as cement replacement in the mortars properties. Mortars with biomass fly ashes have lower slump value than the reference. Mortars with 20% of cement substitution presents better results for all curing time. However, in the three percentages of substitution, and for all curing periods, the best results were found for mortars composed with biomass fly ashes. This work showed that is possible to use biomass fly ashes as partial cement substituent with good results in terms of durability and quality of concrete. Its utilization at an industrial level of concrete production can decrease the energy and raw materials consumption related to cement production and allows a more sustainable option on the ash management.FCT (Fundação para a Ciência e Tecnologia – Portugal) and to the Doctoral Program Eco-Construction and Rehabilitation for supporting the PhD scholarship (with the reference PD/BD/52661/2014

Systems for superficial protection of concretes

Nowadays, it is consensual that the biggest degradation of concrete happens from outside to inside actions, due to the penetration of moisture, active gases and aggressive ions, by mechanical, physical and chemical causes that frequently act together. A low porosity, permeability and concrete penetration to moisture and gases are the first lines of defence against several deterioration mechanisms. The durability of concrete depends largely on how hard or easy fluids (water, carbon dioxide, oxygen) in liquid or gas form can migrate through the concrete hardened mass. When selecting the paint coating for concrete protection, importance is given to the properties of diffusion and permeability resistance, besides the properties of durability and chemical resistance. The paint coatings must stop the penetration of water and delay the influence of aggressive agents (CO2, SO2, Cl- ions), allowing the structure to breathe by a water vapour diffusion mechanism. Through tests of capillarity absorption, immersion absorption, porosity, water and oxygen permeability, a comparison was made between painted and non painted concrete specimens. Three different coating types were tested: silicon varnish; acrylic and epoxy paints. The results showed that, in general, all coatings reduce the porosity and the permeability. The epoxy paints proved to be the best ones

Comportamento à tracção em flexão de betões de desempenho melhorado

A substituição parcial de cimento por cinzas volantes tem sido utilizada por razões económicas e de trabalhabilidade da mistura. O conhecimento acerca da influência da idade e da percentagem de cinzas no comportamento em flexão do betão, principalmente na sua capacidade de absorção de energia, é reduzido. O presente trabalho pretende dar um contributo nesta área