Fibre Reinforced Concrete: Optimization of fibre content and shear capacity of dapped-end beams
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Fibre reinforced concrete is a type of concrete which improves the fracture characteristics and structural behaviour through the fibres ability to bridge cracks: it offers a much more ductile response. Thus, the principal aim of this project has been to improve the current knowledge of the fresh and mechanical behaviour of fibre reinforced concrete. When casting FRC, the addition of fibres can substitute traditional reinforcement, which reduces the worker hours required and improves economic factors. Thereby, the goal has been to find a concrete where is possible to replace steel bars by the maximum amount of fibres possible. The goal is in the opposite way of the second objective of this project, which is to get a flowable concrete to improve the working environment at the construction or casting site. Hence, it was necessary to reach a meeting point between both goals. Thus, the experimental work of this project has consisted in the analysis of the response offered by different casting techniques and by different types of fibres: Dramix 65/60 RC BN, Dramix 5D, Dramix 65/35 3D BG, 13mm long straight fibres and 6mm long straight fibres. Each mix made was assessed according to fresh and mechanical properties. The first one by means of SF test, density, air content, LCPC-Box and 4C-Rheometer (yield stress and plastic viscosity). The second one by means of compressive strength test, three point flexural test and fibre counting. The best concrete result from the experimental work was used for a pre-design of a warehouse floor, made by hollow core elements and dapped-end beams. The design was carried out by using a strut-tie model for D-regions of dapped-end beams. Before using the S-T model, it was optimized using real shear capacities reported in an earlier project and theoretical ones calculated in the current project. The design of the beams was effectuated for both FRC as well as traditional RC. The aim was to find out the different steel bars required for each type of concrete, and in this manner to carry out an economical valuation comparing both. Thus, according to the concretes studied in this project, the overall conclusion of this thesis is that FRC cannot be used as a fully substitute of traditional reinforcement for dapped-end beams, but nonetheless, it contributes to a meaningful steel bars reduction. Its material cost is higher than traditional RC, but taking into account worker hours savings, electricity savings or company logistics, FRC can be economically beneficial.