Characterizing the Performance of Stone Matrix Asphalt Mixtures Comprising Waste Steel Fibers

The increasing demand for sustainable and durable asphalt pavements presents significant challenges to the road construction industry, necessitating materials that can withstand harsh environmental conditions and heavy traffic loads. Integrating recycled materials alongside innovative reinforcement techniques has emerged as a promising approach to enhance pavement performance while promoting environmental stewardship. This study evaluates the feasibility and effectiveness of incorporating waste steel fibers (WSF) as a sustainable reinforcement to enhance the mechanical properties of Stone Mastic Asphalt (SMA) mixtures, which are selected for their rich mortar structure and high rutting resistance. This study evaluated the effects of including WSF at varying dosages (1.25%, 2.5%, 3.75%, and 5% by weight of asphalt binder) into SMA mixtures designed using the Balanced Mix Design (BMD) methodology. Comprehensive laboratory testing assessed key parameters such as Cracking Tolerance Index (CT-Index), Cracking Resistance Index (CRI), Toughness Index (TI), Flexibility Index (FI), Strain Tolerance ( ε ), indirect tensile strength (ITS), and Cantabro loss, drain down, durability indices [tensile strength ratio (TSR)], and volumetric properties. Results indicate that an optimal binder content of 6.2% for SMA is required to achieve balanced resistance to rutting, cracking, and durability requirements. Adding WSF with an optimal performance of approximately 3.75% WSF significantly improves SMA mixtures. These enhancements represent actual laboratory measured enhancements in the mechanical performance of the modified SMA mixtures compared to the unmodified SMA mixtures by enhancing CT-Index (15.6%–67.8 %), TI (54.9%–‍80.3%), CRI (19.4%–17.5%), strain tolerance (14.8%–21.2%), and ITS (24.5%–0%). Low fiber dosages may reduce flexibility or CRI due to insufficient bridging, whereas higher dosages ( > 3.75 % ) show diminished returns from fiber clustering. Fibers effectively enhance energy dissipation and improve tensile stress distribution and durability, reducing cracking susceptibility in flexible pavements. These findings highlight the viability of WSF as a sustainable and efficient reinforcement material capable of substantially enhancing the longevity and resilience of flexible asphalt pavements.