Hybrid fibre-reinforced concrete under repeated loading

Fibre-reinforced concrete containing several volume fractions in different ratios of two types of fibre—polypropylene and steel—were tested under repeated loading. The mechanical properties of speciments—cubes 150 mm × 150 mm × 150 mm (for compressive strength), prisms 100 mm × 100 × 400 mm (for flexural strength) and short cylinders 150 mm long and 60 mm in diameter (for impact strength)—have been experimentally investigated before and after cyclic loading after a curing of 28 days. Mix proportions were design according to DIN 1045 with maximum aggregate size 8 mm and grading curve B8. Portland cement PC 40 in the amount of 450 kg m −3 was applied and the water-to-cement ratio was 0.55. The workability of mixes was measured by the Vebe method and regulated by the plasticizing admixture Ligoplast Na. The maximum hybrid fibre volume fraction (polypropylene + steel) was 1.0%. The dynamic forces generated in a Schenck testing machine with a frequency of 16 Hz had a sinusoidal waveform varying between 0.7 and 0.1 of the static mechanical characteristics. The number of cycles in all tests was 10 5. The residual MOR in the static four-point bending test and working force-deflection diagram were also obtained. The impact properties after repeated loading in compression were tested by means of the falling-weight test. Relationships between the composition of fibre composites with different amounts of polypylene (0.2, 0.3 and 0.5 vol.%) and steel fibre content (0.5, 0.7 and 0.8 vol.%) were obtained and the technological properties of the mixes as well.