Enhancing mechanical properties of concrete material with fibres of different materials

Fibre reinforced cementitious composites are highly effective for construction due to their enhanced concrete properties. Materials such as steel fibre have been used extensively to reinforce concrete because of their excellent mechanical properties. Academic researchers have comprehensively discussed the impact and challenges of fibre reinforcement to obtain optimal properties in the resultant concrete. Most researchers have reported the mechanical performance of fibre- reinforced concrete (FRC) under static loads. Concrete with fibre reinforcement is stronger and more ductile than concrete without reinforcement. Significant efforts have been made to demonstrate the properties and enhancements of concrete after reinforcing it with different types and shapes of fibres. However, the optimization in the reinforcement process is still unanswered. No academic study in the literature now available can pinpoint the ideal fibre type, quantity, shape, and, more crucially, the overall technical viability of the reinforcement. After performing the optimization, researchers considered how these optimizations could affect the crack resistance or properties under dynamic loads with different temperatures. However, a comprehensive analysis is still missing that can explain the crack resistance performance of FRC under dynamic loads at relatively high temperatures. The main aim of this thesis is to investigate the mechanical behaviour of concrete structures under thermo-mechanical dynamic loads about reinforcing fibres of different weight ratios. This study uses parametric analysis in accordance with extensive mechanical tests to identify the optimal shape, size, and percentage of fibres. The design variables for optimization are divided into input and output parameters. The input parameters are the influences of the type, length, and percentage of fibres on concrete performance, including samples of fresh and mechanical concrete properties, to search for the most effective relation of fibre dose and dimension to optimize the combined responses of workability, splitting tensile strength, flexural strength, and compressive strength. The current work also proposes the Khan Khalel model, which can predict the desirable compressive and flexural strengths for any given values of key fibre parameters. Statistical tools are used to develop and validate the model with numerical results. The proposed model is easy to use but predicts compressive and flexural strengths with errors under 6% and 15%, respectively. This error primarily represents the assumption made for the input of fibre material during model development. It is based on the elastic modulus of the material and hence neglects the plastic behaviour of the fibre. A possible modification in the model for considering the plastic behaviour of fibre will be considered as future work. Finally, this study analyses the efficacy of FRC beams for crack resistance under coupled loads, i.e., dynamic loads at relatively high temperatures. Cantilever FRC beams are tested on a modal exciter in a band heater to expose the beams to bending loads at different temperature values. The variation in the dynamic response parameters of the beam, including modal amplitude and frequency, is discussed and compared with experimental results for regular and reinforced concrete beams. The stress intensity factor and displacement amplitude characteristics show that the steel FRC specimens have excellent ductile behaviour and higher crack resistance than ordinary concrete samples.