Assessment of Waste Tyre Rubber as Aggregate Modifier in Asphalt Pavement Mixes for Low-Volume Roads in Oyo State

This study assesses the use of crumb rubber derived from waste vehicle tyres as a modifier for aggregate and binder in asphalt pavement mixes designed for low-volume roads in Oyo State, South West Nigeria. Nigeria generates significant quantities of end-of-life tyres that are predominantly disposed of through open burning, creating severe health and environmental hazards, while road infrastructure in rural Oyo State suffers from premature rutting and cracking under tropical conditions. Crumb rubber is produced by ambient temperature grinding of collected waste tyres, sieved to particle sizes below 2 mm, and incorporated into asphalt mixes at 0, 3, 5, 7, and 10 weight percent of bitumen (wet process) and as fine aggregate replacement at 0, 5, 10, and 15 percent (dry process). Marshall mix design, stiffness modulus, and indirect tensile strength are evaluated. Rutting resistance is measured by the wheel tracking test at 60 degrees Celsius. Results show that wet process crumb rubber at 5 percent improves stiffness and rutting resistance relative to control mixes without reducing workability below acceptable levels. Dry process incorporation at 10 percent provides acceptable mechanical properties with greater rubber utilisation per batch. Economic analysis indicates a 12 percent reduction in bitumen material cost at the optimal wet process dosage. Keywords: crumb rubber, asphalt pavement, waste tyres, Marshall mix design, Oyo State.