Verificação probabilística da segurança das estruturas

Neste artigo, abordam-se as técnicas probabilísticas desenvolvidas para a anáilse da segurança de estruturas: as metodologias baseadas nas técnicas clássicas de fiabilidade, nomeadamente os métodos do segundo momento, de primeira (FORM) e de segunda ordem (SORM), e as baseadas nas técnicas de simulação numérica. Destas últimas, que são as de uso mais divulgado, destaca-se o chamado método de Monte Carlo, em relação ao qual se apresentam ainda alguns métodos para redução da variância

Environmental life cycle assessment of concrete made with fine recycled concrete aggregates

The majority of worldwide structures use concrete as its main material. This happens because concrete is economically feasible, due to its undemanding production technology and case Of use. However, it is widely recognized that concrete production has a strong environmental impact in the planet. Natural aggregates use is one of the most important problems of concrete production nowadays, since they are obtained from limited, and in some countries scarce, resources. In Portugal, although there are enough stone quarries to cover coarse aggregates needs for several more years, Supplies of fine aggregates are becoming scarcer, especially in the northern part of the country. On the other hand, as concrete structures' life cycle comes to an end, an urgent need emerges to establish technically and economically viable solutions for demolition debris, other than for use as road base and quarry fill. This paper presents a partial life cycle assessment (LCA) of concrete made with fine recycled concrete aggregates performed with EcoConcrete tool. EcoConcrete is a tailor-made, interactive, learning and communications tool promoted by the Joint Project Group (JPG) on the LCA of concrete, to qualify and quantify the overall environment impact of concrete products. It consists of an interactive Excel-spreadsheet in which several environmental inputs (material quantities, distances from origin to production Site, production processes) and outputs (material, energy, emissions to air, water, soil or waste) are collected in a life cycle inventory, and are then processed to determine the environmental impact (assessment) of the analysed concrete, in terms of ozone layer depletion, smog or "greenhouse" effect

The influence of curing conditions on the mechanical performance of concrete made with recycled concrete waste

Research on the use of Construction and Demolition Waste (CDW) as recycled aggregate (in particular crushed concrete) for the production of new concrete has by now established the feasibility of this environmentally-friendly use of otherwise harmful waste. However, contrary to conventional concrete (CC), no large applications of concrete made with recycled concrete have been made and there is still a lack of knowledge in some areas of production and performance of recycled aggregate concrete (RAC). One issue concerns curing conditions: these greatly affect the performance of concrete made on site and some potential users of RAC wonder how RAC is affected by far-from-ideal curing conditions. This paper shows the main results of experiments to determine the influence of different curing conditions on the mechanical performance of concrete made with coarse recycled aggregate from crushed concrete. The properties analyzed include compressive strength, splitting tensile strength, modulus of elasticity, and abrasion resistance. The general conclusion in terms of mechanical performance is that RAC is affected by curing conditions roughly in the same way as CC. (C) 2011 Elsevier Ltd. All rights reserved

Physical-chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants

Construction and demolition waste (CDW) represents around 31% of all waste produced in the European Union. It is today acknowledged that the consumption of raw materials in the construction industry is a non-sustainable activity. It is thus necessary to reduce this consumption, and the volume of CDW dumped, by using this waste as a source of raw materials for the production of recycled aggregates. One potential use of these aggregates is their incorporation in reinforced concrete as a replacement of natural aggregates. A concrete that incorporates these aggregates and still performs well requires them to be fully characterized so that their behaviour within the concrete can be predicted. Coarse recycled aggregates have been studied quite thoroughly, because they are simpler to reintroduce in the market as a by-product, and so has the performance of concrete made with them. This paper describes the main results of research designed to characterize the physical and chemical properties of fine recycled aggregates for concrete production and their relationship with mineralogical composition and preprocessing. The constraints of the incorporation of fine aggregates in reinforced concrete are discussed. It is shown that, unless a developed processing diagram is used, this application is not feasible. (C) 2013 Elsevier Ltd. All rights reserved

Comparação da eficácia de diferentes colmeias, na extração de néctar pelas abelhas, na cultura de framboesa em estufa

A framboesa tornou-se recentemente numa importante cultura no Algarve. Cultivada em estufa, esta cultura tem uma relação estreita com o meio envolvente, sobretudo quanto aos polinizadores: a quantidade de frutos produzidos e a sua qualidade dependem da polinização das flores. Para atrair os insetos polinizadores, as flores de framboesa secretam néctar que, quando não extraído, serve de substrato para o desenvolvimento de fungos e bactérias. Além de essenciais na polinização das flores, as abelhas também extraem grandes quantidades de néctar, reduzindo o potencial de proliferação dos agentes patogénicos que deterioram os frutos. É, assim, importante que as colónias de abelhas sejam suficientes para as duas funções na cultura: polinização e extração de néctar. Neste trabalho comparou-se a eficácia de diferentes subespécies de abelhas (italiana, ibérica e híbrida ibérica/caucasiana) e dois tipos de colmeias (reversível e supercolmeia, com o dobro do tamanho e do número de quadros) na extração de néctar nas estufas, através da alteração diária do peso das colmeias. Comparou-se também o comportamento das abelhas de colmeias dentro e fora da estufa, através da observação do seu voo e da acumulação de abelhas mortas dentro das estufas. A pesagem diária das colmeias revelou oscilações sincronizadas, com perdas e ganhos simultâneos, sendo a magnitude destas diferenças variável. As abelhas selecionadas (híbridas ibérica/caucasiana) foram aquelas cujas colmeias perderam menos peso. A colmeia com abelhas italianas teve a maior perda de peso. Estes estudos são essenciais para determinar o número e tipo de colmeias a instalar, para extrair todo o néctar produzido pelas flores, reduzindo a quantidade de melada. Este trabalho permitiu concluir que colocar as super-colmeias dentro das estufas a 2 metros de altura é mais conveniente para as colónias. A utilização de super-colmeias é mais adequada, permitindo constituir colónias maiores e facilitando a tarefa do apicultor.info:eu-repo/semantics/publishedVersio

Viability of two new mixture design methodologies for self-consolidating concrete

This paper presents the results from an experimental study of the technical viability of two mixture designs for self-consolidating concrete (SCC) proposed by two Portuguese researchers in a previous work. The objective was to find the best method to provide the required characteristics of SCC in fresh and hardened states without having to experiment with a large number of mixtures. Five SCC mixtures, each with a volume of 25 L (6.61 gal.) were prepared using a forced mixer with a vertical axis for each of three compressive strength targets: 40, 55, and 70 MPa (5.80, 7.98, and 10.15 ksi). The mixtures' fresh state properties of fluidity, segregation resistance ability, and bleeding and blockage tendency, and their hardened state property of compressive strength were compared. For this study, the following tests were performed. slump-flow, V-funnel, L-box, box, and compressive strength. The results of this study made it possible to identify the most influential factors in the design of the SCC mixtures

An overview on concrete carbonation in the context of eco-efficient

Carbonation is a major cause of concrete structures deterioration leading to expensive maintenance and conservation operations. The eco-efficient construction agenda favours the increase of the use of supplementary cementing materials (SCMs) to reduce Portland cement’s consumption and also the use of recycled aggregates concrete (RAC) in order to reduce the consumption of primary aggregates and to avoid landfill disposal of concrete waste. There is a wide range of literature published on the field of concrete carbonation related to the use of SCMs and/or RCA. However, the different conditions used by different authors limit comparison and in some cases contradictory findings are noticed. Besides, since most investigations are based on the use of the phenolphthalein indicator, which provides a poor estimate of the real concrete carbonation depth, there is a high probability that past researches could have underestimate the corrosion potential associated to concrete carbonation. This paper reviews current knowledge on concrete carbonation addressing carbonation depth’s measurement, the use of SCMs and or RAC