Drop-Weight Impact Response of Self-Compacting Concrete Slabs Reinforced with Industrial, Recycled and Hybrid Steel Fibres

This study compares the drop-weight impact response of self-compacting concrete (SCC) slabs with industrial (ISF), recycled tyre-derived (RSF), and hybrid ISF–RSF steel-fibre reinforcement. Four 1200 × 1200 × 100 mm slabs were tested at 28 days: plain SCC and slabs containing 90 kg/m3 ISF, 90 kg/m3 RSF, or 45 kg/m3 of each. A 105 kg projectile was released from 4.0 m (nominal potential energy 4.12 kJ). Damage, mean underside deflection, contact force and local acceleration were recorded. The plain slab perforated and developed rear-face scabbing; none of the fibre-reinforced slabs exhibited these failure modes under the investigated condition. The ISF slab showed the smallest peak and terminal residual average deflections, while the hybrid slab exhibited the largest peak and the RSF slab the largest terminal residual deflection. Peak contact forces were 285.83, 256.52 and 258.00 kN for ISF, hybrid and RSF, compared with 110.00 kN for plain SCC. Because one slab represented each mixture and matrix compositions varied, the comparisons are descriptive and do not isolate fibre-type effects or establish energy-absorption capacities or design values.