Binder Draindown Control in Open-Graded Bituminous Concrete Mixes Using Chemically Treated Natural Pineapple Fiber

ABSTRACT

Open-graded bituminous concrete (OGBC) mixtures require a relatively high asphalt binder content to achieve adequate aggregate coating, making them particularly susceptible to binder draindown during production, transportation, and placement. Although cellulose fibers are commonly used to mitigate this problem, the growing demand for sustainable pavement materials has motivated the search for renewable alternatives. This study investigates the potential of agro-waste-derived pineapple fiber as a stabilizing additive for OGBC mixtures incorporating VG40 and polymer-modified bitumen (PMB). To improve the compatibility of the fiber with the asphalt binder, natural pineapple fiber (NPF) was chemically modified using alkali (NaOH) and potassium permanganate (KMnO4) treatments. The alkali treatment parameters, including chemical concentration, treatment temperature, and soaking duration, were optimized using response surface methodology (RSM). The chemical and morphological modifications induced by the treatment were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. Subsequently, untreated and treated fibers were incorporated into OGBC mixtures and evaluated in terms of binder absorption, binder draindown, moisture susceptibility, and rutting resistance using the Hamburg wheel tracking test. A correlation analysis between binder absorption and draindown, together with a comparative cost assessment, was also carried out. The results showed that alkali treatment substantially improved the binder absorption capacity of pineapple fiber, resulting in lower binder draindown and enhanced moisture and rutting resistance compared with untreated pineapple fiber and conventional cellulose fiber. Among the investigated mixtures, alkali-treated NPF combined with PMB consistently exhibited the best overall performance. Furthermore, the cost analysis indicated that treated pineapple fiber offers a more economical alternative to conventional cellulose fiber and maintains superior engineering performance. Overall, the findings demonstrate that chemically treated pineapple fiber provides a technically effective, economically viable, and environmentally sustainable solution for improving the performance of OGBC mixes.