Análise da influência do teor e do comprimento de fibras de carbono e do consumo de cimento nas propriedades de concretos de ultra-alto desempenho

Abstract

Ultra-high-performance concrete (UHPC) is characterized by high mechanical strength, low porosity, and enhanced durability. However, in the absence of fibers, it exhibits a brittle response under loading, making the incorporation of fibrous reinforcement necessary to improve ductility and energy absorption capacity. Thus, this study evaluated the interaction between carbon fibers and the UHPC matrix, as well as their influence on the mechanical properties, toughness, and electrical properties of the composite, considering a constant water-to-binder ratio of 0.23 for all mixtures. The research comprised the physical and chemical characterization of the constituent materials, followed by the definition of a central composite rotatable design for statistical experimental planning. Subsequently, the packing density of fine materials was optimized using the modified Andreassen and Andersen particle packing model. The optimized mixtures were produced and evaluated in both fresh and hardened states. The composite properties were investigated at different curing ages, according to the requirements of each test. At 28 days, compressive strength, flexural tensile strength, total porosity by absorption, and electrical resistivity were evaluated. At 56 days, compressive strength, flexural tensile strength, electrical resistivity, and modulus of elasticity were determined. The results of the experimental design enabled the development of response surfaces and the identification of statistically significant variables, highlighting cement content as the main governing factor for the mechanical properties within the studied domain. The results demonstrate that it is possible to produce ultra-high-performance concrete with low cement consumption (500 and 550 kg/m³), contributing to the advancement of knowledge on UHPC mixture design. Complementary mixtures with higher carbon fiber content indicated that increasing the fiber content significantly improves the tensile strength and toughness of the composite. The mixture containing 3.7% carbon fibers exhibited outstanding overall performance, combining high mechanical strength with enhanced energy absorption capacity, demonstrating the potential of carbon fibers to produce UHPC with improved mechanical properties.