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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.
- 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.