Optimizing steel fiber reinforcement: effects of volume fraction and aspect ratio on fresh and hardened properties of self-compacting white concrete

Abstract White cement production has evolved to meet modern demands, and its use has increased significantly in recent years. Mineral additives and plasticizers enhance mechanical properties and improve resistance to temperature variations and corrosion. Steel fibers and their aspect ratios are key parameters that strongly influence the mechanical properties of self-compacted white concrete (SCWC). This study investigated the effects of steel fiber content and aspect ratio on the fresh and hardened properties of SCWC. Aspect ratios of 60, 70, and 80 were investigated. SCWC experimental mixes were technologically enhanced by employing 10% marble powder as a filler material together with a polycarboxylate superplasticizer, which met all SCWC requirements according to EFNARC guidelines, with a specified compressive strength of up to 30 MPa. The durability of the specimens was evaluated by subjecting them to a solution of ammonium sulfate [(NH 4 ) 2 SO 4 ] with a sulfate salt concentration of 2.0 g/l for 7, 28, and 90 days. Results showed a slump flow of 610–750 mm, T 500 times of 3.8–4.85 s, and compressive strength of up to 64.5 MPa in SCWC mixes (90 days, M15). Strength increased by 48.77% with 1.5% steel fibers, while acid-induced strength loss was minimal (1.06%). Tensile strength reached 6.36 MPa, and flexural strength attained a maximum of 9.3 MPa. The workability of SCWC was evaluated using slump flow, V-funnel, and L-box tests. Incorporating 10% marble powder improved flowability, whereas increasing steel fiber dosage and aspect ratio reduced workability due to fiber interlocking. However, steel fibers improved compressive strength (30–50 MPa) and enhanced sulfate resistance. Microstructural alterations were assessed using scanning electron microscopy over 28 days. Microstructural analyses confirmed denser matrices and C–S–H gel formation, demonstrating the effectiveness of marble powder and steel fibers under aggressive environmental conditions. These results verify the efficacy of marble powder and steel fibers in enhancing the strength, workability, and long-term durability of materials in the presence of harsh environmental conditions.