Proposta de otimização da distribuição das fibras em elementos de concreto moldado em camadas com base no ensaio indutivo

Abstract

Simple, unreinforced concrete presents a brittle behavior, with low tensile strength and low ductility, which led to the emergence of special concretes in order to supply its deficiencies, as is the case of fiber reinforced concrete (FRC), which has the proposal to improve the behavior of concrete in the Ultimate Limit State (ULE), since they minimize the limitation of low tensile strength of this composite. Among the different types of fibers, metallic fibers are highlighted because they have a greater modulus of elasticity than concrete, guaranteeing the composite greater ductility after cracking and even greater resistance to tensile stresses. In view of all the benefits, the use of steel fiber reinforced concrete (SFRC) in pavements, tunnel linings and even in flexural structural elements is an advantage and a reality in several countries. For the CRFA to be applied for structural purposes, a minimum mechanical performance must be achieved and tests with specific criteria are used to ensure that the design specifications are met by the current NBR 16938. However, since this behavior is influenced by the fiber content in the mixture and its dispersion, a non-destructive method that has been highlighted as an evaluation tool is the inductive method. This method is based on Faraday's Laws and on the variation of inductance measured in the specimen inserted in a coil. In Brazil, the fibers still have a high commercial value, and, adding the price of the additives necessary for the production of the mixture, the cost of CRFA can present a considerable increase in relation to conventional concrete. Focusing on an optimized use of CRFA, this work proposes the use of CRFA in tensioned zones of a beam under bending, correlating the orientation of the fibers in the specimen evidenced by the cracking result obtained through the inductive method. The analysis of the results shows that the use of layers guides the fibers in their optimal way, perpendicular to the crack, due to the reduction of its section, therefore, in addition to having a positive factor in reducing costs, the layered beams have the advantage of optimize the use of fibers by inducing an orientation in which they respond better to traction efforts.