Energy-Based Approach for Studying Fibre-Reinforced Concrete Subjected to Impact Loading

In general, concrete behaves differently when the load is applied at a different speed, i.e. concrete's mechanical parameters are strain-rate sensitive. There is a need for an experimental method that should meet several criteria such as removal or accurate description of boundary conditions, simplicity, affordability and reproducibility of the experiments. The main goal of this study is the design, assembly and optimisation of the experimental apparatus and procedure to carry out the impact testing. Using this apparatus, an experimental study was conducted. The main aspect of this experimental method is the elimination of rigid supports, which could negatively affect the obtained results. Measured data are acquired using specifically designed measuring devices and analysed using a computer script. Four concrete mixtures were examined ranging from high-strength concrete to ultra high-performance concrete. Quasi-static experiments were also carried out for comparison. A clear difference in quasi-static and impact performance of the materials was observed. Different trends for different compositions of the tested concrete specimens were apparent. Higher fibre content specimens generally showed higher strain-rate sensitivity and the highest strain-rate sensitivity was observed in combination with the two strongest concrete matrices. This was most probably related to fibre anchoring, as complete fibre pullout before premature matrix failure was critical. The newly designed measuring apparatus greatly improves the speed and precision of conducting the impact experiments. It can be successfully used for a relatively quick and simple comparison of materials when designing concretes for withstanding elevated strain-rate loading.