Mechanical and Impact Performance of Lightweight Self-Compacting Concrete Incorporating Two types of lightweight Aggregate, Crumb Rubber, and Steel Fibers

Abstract This study examined the effects of the amount and particles size of Crumb Rubber (CMR), surface treatment with NaOH, and inclusion of micro hook-end steel fiber (MSF) on the performance of lightweight self-compacting concrete (LWSCC). Two types of lightweight aggregates (Lightweight Expanded Clay Aggregate (LECA) and Artificial Attapulgite Aggregate (ATG)) were used as coarse aggregates, with CMR (two particle sizes: 1–3 mm and 3–5 mm) replacing natural sand at a volume percentage of 10–30%. A portion of the rubber was surface treated with NaOH, and 0.5% MSF was added to some mixtures. The findings revealed that the ATG-based mixtures exhibited acceptable mechanical properties, with approximately 11% and 21% higher compressive strength and modulus of elasticity than the LECA-based mixtures, respectively for structural lightweight concrete application. The strength decreased by 35% with an increase in the CMR content, whereas the impact ductility improved notably (up to 83%). Finer rubber particles exhibited better performance. While NaOH treatment partly recovered strength and improved ductility, the addition of MSF boosted the impact resistance and improved the tensile and flexural strengths by up to 29%. All mixtures met the EFNARC standard requirements for fresh properties, proving that ATG-based LWSCC with CMR and steel fibers provides a more impact-resistant, structurally sound, and sustainable solution for structural applications.