Flexural performance of reinforced concrete beams with recycled aggregates and steel fibres

The presence of mortar makes recycled aggregate (RA) a heterogeneous material compared to its parallel homogeneous natural aggregate (NA). Consequently, the mix proportioning method most suitable for RA reuse for structural applications has long been debated. This study presents an unconventional mix proportioning method involving recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and steel fibres (SF) for recycled aggregate concrete production. The equivalent mortar volume (EMV) mix proportioning technique developed for concrete containing RCA is extended to incorporate RFA and SF. Five different mixes were formulated using both conventional and the extended EMV mix design methods, to study the flexural behaviour of reinforced concrete beams produced with RA and SF. The results showed that the load bearing capacity of the beam of the mix containing 100% RA and 1% SF prepared using the conventional method, increased by up to 13% and 8% compared to similar mix without SF and the reference mix, respectively. The unconventional beam containing 60% RA showed equal load resistance of 63kN as the reference beam made entirely of NA. Additionally, the unconventional beam had the fewest cracks, least crack width, and visually, the least deflection at the fracture when compared to the other beams with or without SF. This study shows that the extended EMV mix proportioning technique is adequate and offsets the need for SF addition in concrete containing RA.