The effect of high temperature on the mechanical properties of concrete reinforced by steel fibers with various aspect ratios has been investigated in this study. Concrete specimens were fabricated from four different concrete mixtures and cured for 28 days. After curing and natural drying, the specimens were annealed at a temperature of 500 °C for 3 h in an electric furnace. The compressive and tensile strengths as well as the elastic moduli of the produced specimens were determined. It was found that the mechanical properties (especially flexural toughness) of steel fiber-reinforced concrete were less affected by high temperature as compared to those of control concrete specimens. The flexural tensile strength of fiber-reinforced concrete measured after high-temperature treatment was almost equal to the value obtained for the reference concrete specimen at room temperature. It should be noted that the addition of steel fibers to concrete preserves its mechanical properties after exposure to a temperature of 500 °C due to fire for a period of up to 3 h, and thus is able to improve its high-temperature structural stability. The test results of this study indicate that the use of steel fibers in concrete-based materials significantly enhances their fire and hear-resistant characteristics.

This work reports the main conclusions of a study on the mechanical behavior of concrete under ISO 834 fire with different cooling methods. The aim of this research was to provide reliable data for the analysis of structures damaged by fire. The experimental program used cylindrical concrete test specimens subjected to ISO 834 heating in a furnace up to maximum gas temperatures of 400, 500, 600, 700, and 800 °C. The compressive strength was measured in three situations: (a) at the different temperature levels reached in the furnace; (b) after a natural cooling process; and (c) after aspersion with water at ambient temperature. The results indicate that the concrete residual compressive strength is fairly dependent on the maximum temperature reached in the furnace and revealed that concrete of a lower strength preserved relatively higher levels of strength. The cooling method significantly influenced the strength, albeit at a lower intensity. In all cases, the residual strength remained in the range of 38% to 67% of the strength at ambient temperature. The statistical analysis showed that the data obtained by the experimental program are significant and confirmed the influence of the conditions imposed on the residual strength.

The present study evaluated the mechanical behaviour of thin high-performance cementitious composite slabs reinforced with short steel fibres. For this purpose, slabs with 1%, 3% and 5% vol. of steel fibres were moulded using the slurry infiltration method. Fibres concentrated in the region subjected to traction during bending stresses. After curing for 28 days, all slabs underwent flexural testing. The slabs with 5% fibre showed significantly higher flexural strength, deflection and toughness compared to those of the control group without reinforcement. The dense fibre distribution, resulting from the production process, led to profiles with multiple random cracks in the region of failure of the slabs as the fibre content increased. The results of the statistical analysis showed the intensity of the correlation between the variables and revealed that the increase of the fibre content significantly influenced the parameters of mechanical behaviour (load, flexural strength, deflection, toughness and toughness factor). Images obtained by optical microscopy aided in understanding the fibre–matrix interface, showing the bonding surface between the constituents of the composite.

Resumo A proteção passiva contra incêndio (PPCI) é um campo de estudo aplicado à indústria da construção civil. Os resíduos de tijolos refratários contêm elementos que podem contribuir para as propriedades necessárias à PPCI. Diante disso, o trabalho desenvolveu uma argamassa com resíduos de tijolos refratários para utilização como PPCI. As 4 formulações propostas tiveram a resistência à compressão e flexão, densidade e porosidade aparente, condutividade térmica e variação linear avaliadas antes e após tratamento térmico a 600 °C e a 1100 °C. A densidade não apresentou significativas diferenças entre as formulações. A porosidade aumentou após o tratamento térmico. A mistura que apresentou maior contração a 1100 °C foi aquela com maior teor de gesso e todas as demais apresentaram valores de contração menores que o máximo permitido pela C195. A proporção que utilizou maior quantidade de gesso foi o que obteve a menor condutividade térmica. Portanto, conclui-se que a utilização do resíduo refratário é viável para PPCI, uma vez que atendem aos requisitos normativos.

Ultra-high-performance concrete (UHPC) exhibits enhanced characteristics compared to conventional concrete (CC), most notably its high compressive strength due to low porosity, a high fine content, and a low water-to-binder ratio (w/b). However, the toughness of UHPC remains an area requiring improvement. Incorporating high-modulus polyethylene fibers (HMPE) into UHPC is a promising alternative for enhancing the composite’s toughness. This study developed an optimized methodology for adding HMPE fibers to UHPC, comparing the performance of a reference UHPC (H0) with UHPC mixtures containing 0.10% and 0.15% HMPE fibers (H10 and H15). Workability, volume and mass variation, compressive and tensile strengths, toughness, and accelerated crack propagation were analyzed. Complementary analyses were performed using optical and scanning electron microscopy. Results demonstrated the feasibility of fiber insertion without composite expansion. The minimum normative compressive and tensile strengths required for classifying the composite as UHPC were achieved with fiber addition. Furthermore, reduced shrinkage and crack formation, as well as increased toughness, were observed, highlighting the potential of high-modulus fibers in ultra-high-performance matrices.