Behaviour of Fibre-Reinforced Lightweight Self-Compacting Concrete Containing Recycled Brick Aggregate and Silica Fume

Abstract

Growing of the attention in sustainable construction materials has driven the advancement of lightweight self-compacting concrete (LWSCC), including recycled materials. The present study investigates the fresh and mechanical performance of LWSCC incorporating lightweight expanded clay aggregate (LECA) as coarse aggregate and with complete substitution of natural fine aggregate (NFA) by fine recycled brick aggregate (FRBA). Micro steel fibres (MSF) at 0.5% and 1% volume fractions and silica fume (SF) at 15% cement replacement were introduced. Five different mixes of LWSCC were prepared with the water-to-cement ratio fixed at 0.40. Fresh properties were evaluated using by utilization slump flow, T₅₀₀ time, and L-box tests, while mechanical properties were estimated after 28 days through compressive and splitting tensile strength tests. Dry density and water absorption were also measured in this experimental study. The results presented that full replacement of NFA with FRBA will reduce the strength by an average of 34% compared to the control mix with only NFA. However, incorporation of 0.5% and 1% micro steel fibres (MSF) led to developments in compressive strength of 15.7% and 26.0%, respectively, although the tensile strength improved in 39.1% and 63.4% related to the FRBA reference mix. Similarity, the addition of the silica fume (SF) at 15% resulted in enhancements of 9.4% and 7.4% in particular compressive and tensile strength, identifying it’s a positive effect on matrix densification and strength recovery in FRBA-based mixtures. All LWSCC mixes remained within acceptable limits of requirements of the structural lightweight concrete, with dry density below 1850 kg/m³. Water absorption increased with adding of FRBA but was significantly reduced with MSF and SF, reaching as low as 5.60%. All mixes satisfied EFNARC (2005) criteria for flowability, though MSF slightly increased viscosity. Combined use of the recycled aggregates, steel fibres, and silica fume was verified to be an effective approach for producing sustainable LWSCC with satisfactory strength and workability for practical applications.