Steel Fibre Reinforced Rubcrete under Impact Loading: A Review of Mechanical Behaviour, Energy Absorption and Sustainable Applications

The growing volume of construction and demolition waste and the continuous depletion of natural aggregates have increased interest in sustainable concrete incorporating recycled materials. Rubcrete, developed by replacing conventional aggregates with recycled coarse aggregate or rubber-based particles, provides environmental benefits but often exhibits reduced workability, compressive strength, stiffness, and interfacial bonding. Steel fibres have therefore been introduced to improve crack control, tensile capacity, post-cracking behaviour, toughness, and impact resistance. This review examines published studies on recycled aggregate concrete, rubberized concrete, steel fibre reinforced concrete, and their combined behaviour under static, flexural, fatigue, and repeated impact loading. Particular attention is given to fibre geometry, dosage, aggregate replacement level, surface treatment, test methods, energy absorption, fracture behaviour, and failure mechanisms. The literature shows that increasing recycled or rubber aggregate content commonly reduces mechanical strength, whereas moderate replacement can improve ductility and energy dissipation. Hooked-end, crimped, and mixed-aspect-ratio steel fibres delay crack propagation and substantially increase first-crack resistance, ultimate impact resistance, fracture energy, and residual load-carrying capacity. However, excessive fibre content may reduce workability and cause fibre balling. The review identifies a need for standardized impact-testing procedures and systematic optimization of recycled aggregate content, fibre dosage, durability, and long-term structural performance.