Effect of single and hybrid incorporation of steel, polypropylene and polyethylene terephthalate fibres on the properties of concrete under static and impact loading

The effects of single and hybrid use of steel fibres (STF), polypropylene fibres (PPF) and polyethylene terephthalate fibres (PETF) on the static and impact properties of concrete were comprehensively evaluated. The concretes were evaluated and compared according to different properties, including static properties (unit weight, compressive strength, flexural strength, splitting tensile strength, fracture energy and flexural toughness), microstructural properties, impact performance and cost. In addition, the overall performances of the tested mixtures were comparatively assessed using desirability function (DF) analysis. The performed tests and analyses showed that STF had a positive effect on the compressive strength of concrete, the PPF and PETF had a negative effect. On the other hand, the fibres, especially STF, led to remarkable increases in the splitting tensile strength, flexural strength, flexural toughness, fracture energy and impact performance of the concrete. It was found that under static and impact loads, fibres were successful at shifting the brittle behaviour of concrete into more ductile behaviour. Scanning electron microscopy analysis revealed that the STF had better adherence with the surrounding cement paste than the PPF and PETF. It was concluded from the DF analysis that concrete containing 1% STF showed the best overall performance of all the tested concrete mixtures.