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- Experimental testing on the residual mechanical properties of ordinary concretes after firePublication . Santos, C.C.; Rodrigues, João PauloConcrete is known to have an enhanced behaviour in fire when comparing with bare steel, however there are some chemical and physical transformations in function of temperature that may compromise this performance. The mechanical and thermal properties of concrete at high temperatures and after fire have changes that have been evaluated in a lot of works around the World, however this is still an open field where a lot of research is needed. This paper summarizes the results of an experimental research to assess the residual mechanical properties of ordinary concretes after fire. It was studied the influence of the fire extinguishing methods, the maximum temperature that the concrete was subjected to and the loading level on the residual mechanical properties of calcareous and granite aggregate concretes. The properties studied were the residual compressive, tensile, splitting and flexural strengths and modulus of elasticity. Four levels of temperature; 20ºC, 300ºC, 500ºC and 700ºC; two loading levels (0.3fcd and 0.7fcd) and two cooling processes (cooling in the air and by water jet) were tested. The results showed that the mechanical properties of concretes are affected by the cooling process (fire extinguishing methods) used beyond the high temperatures and loading levels that were subjected to.
- Compressive behaviour of a tire recycled steel and textil fiber concrete subjected to firePublication . Santos, C.C.; Rodrigues, João PauloThe use of rubber aggregates, steel and textile fibres recycled from tires in concrete is a solution that it is being studied by several authors around the world. A few works have been carried out at room temperature but very scarce at high temperatures. This paper presents the results of a research with the aim to evaluate the behaviour at high temperatures of a concrete made with different amounts of recycled textile and steel fibres from tires. The study considered five concrete compositions, with the same water/cement ratio (W/C=0.43), differing only in the type and quantity of fibers incorporated in the mixture. Thus, a reference composition (0% fiber), two compositions with 30 and 70kg/m3 of steel fibers and a composition with 2 and 4kg/m3 of textile fibers from tires were tested. The concrete was tested for a load level of 0.5fcd and different maximum temperature levels (20, 300, 500 and 700ºC).
- Calcareous and granite aggregate concretes after firePublication . Santos, C.C.; Rodrigues, João PauloThis paper presents the results of an experimental research on the assessment of the residual mechanical properties of calcareous and granite aggregate concretes after fire. The influence of the following parameters was tested: the loading level (0.3 and 0.7fcd); the cooling process (cooling in the air and by water jet) and the maximum temperature that the concrete was subjected to (20, 300, 500 and 700 °C). The mechanical properties studied were the residual compression, direct and splitting tensile and flexural strengths, modulus of elasticity and Poisson's ratio. The results showed in general that the higher the temperature and faster the cooling process is, as the one by water jet, the higher the negative impact on the residual mechanical properties of the concrete is, being the strength nearly null for above 600 °C.
- Experimental research on the residual mechanical properties of an ordinary concretes after firePublication . Santos, C.C.; Rodrigues, João PauloThis paper summarizes the results of an experimental research to assess the residual mechanical properties of an ordinary concrete after fire. It was studied the influence of the cooling process, the maximum temperature that the concrete was subjected to and the loading level on the residual mechanical properties of calcareous and granite aggregate concretes. The properties studied were the residual compressive, tensile, splitting and flexural strengths and modulus of elasticity. Four levels of temperature; 20, 300, 500 and 700ºC; two loading levels (0.3f and 0.7fcd) and two cooling processes (cooling in the air and by water jet) were tested. The high temperatures attained and the sudden cooling down process on the concrete showed a negative effect on its residual mechanical properties. This effect was more notorious on the residual compression strength than in the other mechanical properties
- Compressive strength at high temperatures of a concrete made with recycled tire textile and steel fibersPublication . Santos, C.C.; Rodrigues, João PauloThis paper presents the results of a research work on the evaluation of the compressive strength at high temperatures of a concrete made with recycled tire steel and textile fibers. It was considered five different concrete compositions, with a water/cement ratio (W/C = 0.43), differ only in the type and amount of fibers. The compositions with smaller amounts of textile fibers were those that gave better results. The compositions with steel fibers showed a less explosive rupture showing the effectiveness of this type of fibers in the spalling and cracking control.
- Concreto com agregados reciclados de borracha de pneu: resistência à compressão a altas temperaturasPublication . Santos, C.C.; Rodrigues, João PauloA sustentabilidade é uma preocupação para a indústria da construção civil, uma vez que é responsável pelo consumo de uma grande quantidade de recursos naturais e por impactos ambientais. Assim, a utilização de agregados reciclados em substituição dos agregados naturais mostra-se benéfica ao minimizar os impactos ambientais, o consumo de recursos naturais e na redução de alguns problemas urbanos associados à acumulação de lixo. Neste contexto, o trabalho de investigação desenvolvido teve como objetivo o estudo da utilização de agregados reciclados de borracha de pneu na composição do concreto, contribuindo com uma alternativa sustentável para o problema do depósito de pneus após a sua vida útil. O trabalho laboratorial realizado compreendeu ensaios de resistência à compressão do concreto. Estudaram-se três composições de concreto, uma composição de referência, uma composição com uma taxa de substituição de 15% e outra com taxa de substituição de 30% de agregados naturais por agregados reciclados de borracha de pneu usados. Os diferentes provetes de concreto foram submetidos a vários níveis de carregamento (0,15fcd; 0,3fcd e 0,7fcd) e a diferentes níveis de temperatura (20, 300, 500 e 700ºC). Os resultados obtidos permitiram verificar que o aumento da percentagem de agregados de borracha reciclados de pneu inserido no concreto conduz a um aumento do controlo de fendilhação e minimiza o surgimento de fissuração de origem térmica.
- Inflence of the cooling process on the residual mechanical properties of ordinary concretePublication . Santos, C.C.; Rodrigues, João Paulo; Coelho, António LeçaThe concrete structures have usually good behavior in fire. However, when the fire is severe and of long duration the concrete elements may lose partial or totally their load bearing capacity. This phenomenon can be aggravated by the extinction process of the fire used that causes quite always high thermal stresses and cracking in concrete. With the aim to clarify the effect of the cooling process on the mechanical properties of the concrete a research program was carried out in the University of Coimbra. The concrete specimens were heated up to different temperature levels (300, 500 and 700ºC) and after a period of stabilization they were cooled down. Two processes of cooling were tested, cooling on the air (intending to simulate the natural extinction of the fire) and cooling by water jet (intending to simulate the action of the firemen in fire combat). During the heating / cooling process the specimens were subjected to a constant compressive load (0.3fcd and 0.7fcd) in way to simulate the real situation of the concrete when in a structural member. The specimens after the heating / cooling process and at room temperature were then tested in compression, allowing determining the residual compression strength of the concrete.
- Influência das elevadas temperaturas e as propriedades mecânicas residuais do concreto normalPublication . Santos, C.C.; Rodrigues, João PauloO concreto, de um modo geral, apresenta um bom comportamento em situação de incêndio quando comparado com o aço, todavia em função da temperatura ocorrem algumas transformações químicas e físicas que podem comprometer esse desempenho. Apesar das alterações das propriedades mecânicas e térmicas do concreto quando sujeito a temperaturas elevadas e após situação de incêndio já terem sido avaliadas em vários estudos, ainda é um campo aberto onde é necessário muita investigação. O presente artigo apresenta os resultados de um estudo experimental sobre a avaliação das propriedades mecânicas residuais de concretos normais após incêndio. Para o efeito foram selecionados agregados graníticos e agregados calcários, dado serem os agregados mais utilizados na construção civil em Portugal e em muitos outros países. Os parâmetros testados foram: o nível de carregamento (0,3fcd e 0,7fcd); o processo de arrefecimento (arrefecimento ao ar e arrefecimento por jato de água) e o nível máximo de temperatura atingida (20, 300, 500 e 700ºC). As propriedades mecânicas estudadas foram a resistência à compressão residual, resistência à tração direta e resistência à tração por compressão diametral, resistência à flexão, módulo de elasticidade e coeficiente de Poisson. As temperaturas atingidas e o arrefecimento rápido do concreto apresentaram um efeito negativo sobre as propriedades mecânicas residuais. Este efeito foi mais notório na resistência à compressão residual do que nas restantes propriedades mecânicas estudadas.
- Compressive strength at high-temperatures of concretes made with textile and steel recycled fibersPublication . Santos, C.C.; Rodrigues, João Paulo; Caetano, HugoThis paper presents the results of an experimental research on the ambient and high-temperature compressive strength of concretes made with steel or textile fibers from recycled tires. The studied compositions included a reference (RC), two textile fibers (TF) and two steel fibers (SF) concretes. The other aggregates were crushed ones and natural sand and the cement content 400kg/m3 for a water/cement ratio of 0.31. The specimens were tested in compression for different levels of temperature (20, 300, 500 and 700ºC). The specimens were heated, under loading, inside a tubular furnace accomplished to a tensile/compression machine. During the heating, the specimens were subjected to a constant loading level of 0.5fcd. The results of this experimental program showed that steel and textile fibers are a good solution in the compressive behavior of the concrete regarding to cracking control. However, some difficulties in the concrete preparation were experienced as the mixing of fibers.