The present research examined effects of sisal-fiber length and content on Marshall, volumetric, and moisture-susceptibility properties of Sasobit-based WMA for a Type IIIA surface course. A total of nine fiber configurations, encompassing three lengths and three contents, were evaluated at the design asphalt content of the fiber-free WMA–Sasobit mixture. The configuration that satisfied all SCRB (2003) requirements while providing the highest Marshall stability was subjected to a separate Marshall mix design. Its properties were subsequently related with those of conventional hot-mix asphalt (HMA) and fiber-free WMA–Sasobit, while moisture susceptibility was evaluated according to AASHTO T283. The screening process identified a configuration of 0.3% sisal fiber measuring 9 mm in length as the optimal configuration, with an OAC of 4.7%. At this design condition, the mixture achieved a Marshall stability of 17.90 kN, which is numerically higher than those of WMA–Sasobit and HMA by 3.5% and 9.9%, respectively. The flow and volumetric properties of the substance in question satisfied all applicable SCRB limits. The mixture also exhibited a TSR of 84.4%, which is approximately three percentage points greater than those of both reference mixtures and above the specified minimum. The findings indicate that the laboratory-scale technical feasibility of the selected sisal-fiber configuration in Sasobit-based WMA at reduced production temperatures is demonstrated.
