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Na área da engenharia civil, o comportamento ao fogo de estruturas de betão armado é de primordial importância no contexto da segurança estrutural, dada a probabilidade elevada de ocorrerem colapsos locais ou globais, com impactos consideráveis ao nível de perdas humanas e de prejuízos económicos. Esta temática é de tal forma importante, que desde os anos 40 que se tem vindo a estudar a influência das altas temperaturas no desempenho mecânico e térmico do betão Neste artigo é feita uma recensão sobre as diferentes propriedades mecânicas, nomeadamente, resistência à compressão, à tração, à flexão e módulo de elasticidade, os parâmetros de que dependem e a relação entre os mesmos.

This 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.

Concrete is a heterogeneous material compounded of aggregates embedded in a cement paste matrix. The heterogeneity of concrete constituents can result in severe thermal damage at the cement pasteaggregate interface. When cement paste is exposed to high temperatures, different hydration products gradually lose water causing mass loss. This paper presents the results of an experimental investigation on the physical and chemical properties of a steel and polypropylene fibre high strength concretes at elevated temperatures. Several tests were carried out, such as thermal analysis (TGADTA), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Five concrete compositions with different steel fibres dosages and types were selected for the study: one without steel fibres, two with DRAMIX 3D steel fibres and two with DRAMIX 5D steel fibres (both with 45 and 75 kg/m3). All compositions had the same amount of polypropylene fibres (2 kg/m3). The temperatures levels tested were: 20, 200, 500, 800 and 1000 °C. These tests were performed with the purpose of evaluating the temperature effect on mineralogical changes that occurred in the hardened cement paste and its influence on compressive strength of these concretes at high temperatures.