Sustainable Utilization of Shredded Polypropylene Fibers in Pavement Subgrade and Binder Course Applications

Abstract

This study investigates the use of randomly distributed shredded polypropylene fibers to strengthen both flexible pavement subgrade soils and asphalt course. For subgrade stabilization, fiber dosages from 0% to 2.0% by dry weight of soil were evaluated. For binder course modification, polypropylene fibers were added at 0% to 12% by weight of bitumen to assess improvements in mix performance. Incorporating polypropylene fibers increased the unconfined compressive strength of the soil, with peak performance at 1.25% by dry weight. At this optimum dosage, the 28-day UCS was 78% higher than that of the unreinforced control. Soaked CBR peaked at 9.9% with 1.25% polypropylene fiber, a 209% increase over the control. The fibers improve performance through tensile reinforcement and lateral confinement, reducing deformation and effectively controlling swell in expansive soils. After 12 wet–dry cycles, UCS retention peaked at 88% with 1.25% polypropylene fiber, versus 52% for unreinforced soil. Marshall Stability increased up to 10% polypropylene fiber, as the 3D fiber network bridged micro cracks and improved tensile resistance. This dosage gave optimum performance by bitumen weight, achieving peak stability while maintaining acceptable flow and favorable volumetric properties. Both dry and wet Indirect Tensile Strength peaked at 10% polypropylene fibers, rising from 950 to 1180 kPa and 741 to 1050 kPa, respectively. TSR also increased from 78.0% to 89.0%, confirming improved moisture resistance. Using shredded polypropylene fibers at layer-specific optimum dosages, 1.25% for subgrade soil and 10% for the asphalt binder course offers a technically viable and sustainable strategy for pavement upgrade. The utilization of shredded polypropylene fibers promotes sustainable pavement construction by converting plastic waste into a value-added resource while reducing dependence on conventional pavement materials and contributing to improved resource efficiency.