Agradeço de coração a todos que ajudaram nesse longo caminho, minha família, meus colegas, todos que foram imprescindíveis para a conclusão deste trabalho. Agradeço à CAPES, pela concessão da bolsa. Agradeço do fundo do coração ao meu professor orientador Antônio Carlos, pela oportunidade e honra de receber a sua brilhante orientação durante todo período do meu trabalho.

Vegetable fibres have been shown to be promising as reinforcement in composites because they are abundant, renewable, and low cost. However, the fibre-matrix interaction can be damaged by dimensional variation of vegetable fibres, due to moisture variations. The alkaline medium of cementitious matrix is aggressive to natural fibres, compromising their durability. The aim of this study was to modify sisal fibres (Agave sisalana) by esterification with acyl chlorides to improve their stability and compatibility with the cementitious matrix in order to optimize the performance and durability of composites. The esterified fibres were characterized by moisture absorption, tensile tests, Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM) and the composites by bending tests and SEM. The results showed that esterification changed both the morphology and physical properties of sisal fibres. The composite produced using esterified fibres with octanoyl chloride maintained the properties of 28 to 90 days of age, which represented an improvement in the fibre stability compared to natural fibre composite.

This paper proposes an adjusted function for estimating the punching shear load-carrying capacity of concrete flat slabs without shear reinforcement according to the Brazilian standard code. The Adjusted function considers the influence of the steel fiber content. Data from 68 steel fiber reinforced concrete slabs (SFRC slabs) were used, simulating the connection of flat slabs with square section columns. These slabs were obtained from a study conducted by 14 different researchers. The parameters used for the adjusted function were the fiber content and the compressive strength of the concrete. The adjusted function was obtained by curve-fitting. The result from the adjusted function shows a relation in the order of 1.3 between the experimental rupture load and the calculated load, a value close to that already obtained by the normative text when the calculation is for conventional concrete. This shows that the proposal presented here keeps the same level of security with a confidence index of 96% in comparison with other authors’ models presented in this study.