Stabilization of open graded asphalt friction course mixes with plant-based natural fibers

Abstract

Open-graded asphalt friction course (OGAFC) is a bituminous wearing course designed and constructed to allow rapid surface water drainage, eliminate splashes and sprays, offer enhanced skid resistance, and reduce glazing, particularly during wet weather. However, draindown is one of the challenges that is often observed with OGAFC mixes. Draindown refers to the phenomenon in which asphalt binder and mastics extricate from the mix under gravity, especially at high temperatures experienced during the production, storage, transportation, and construction phases. The occurrence of draindown have an adverse impact on the functional and structural performance of OGAFC mixes. In addition to the use of stiffer grades of binder, stabilization via fiber addition is quite often practiced to restrict draindown in OGAFC mixes. With a focus on adopting sustainable and environmentally friendly materials and technologies.in pavement engineering, this study investigates the use of two plant-based natural fibers, namely sisal fiber (SIF) generated from the leaves of the sisal (Agave sisalana) plant and sunnhemp fiber (SHF) obtained from the bast of the sunn hemp (Crotalaria juncea) plant, as stabilizing additives in OGAFC mixes to combat the issue of draindown. The effectiveness of the two natural fibers in resolving the binder draindown issues of OGAFC mixtures was evaluated across a variety of domains, including fiber lengths (3, 6, 9, and 12 mm); fiber dosages (0.15, 0.30, and 0.45%); binder dosages (5.5, 6.0, and 6.5%); binder types (unmodified and polymer modified binder); and thermal conditioning time intervals (30, 60, 90, 120, 150, and 180 min). A fiber length of 9 mm and fiber dosage of 0.45% exhibited optimum performance, and SHF yielded marginally better efficacy in controlling draindown than SIF. Statistical analysis using analysis of variance (ANOVA) revealed that binder content, fiber dosage, fiber length, and time interval significantly impact draindown characteristics of OGAFC mixes.