ASSESSMENT OF BITUMEN MODIFIED WITH RUBBER FOR FLEXIBLE PAVEMENT

This study investigates the viability of using Crumb Rubber-Modified Bitumen (CRMB) to enhance the performance of asphalt pavements mix, while concurrently addressing the environmental issue of waste tire disposal. The primary aim was to evaluate the effect of varying crumb rubber (CR) content on the properties of hot mix asphalt (HMA) and to determine an optimal dosage. The research employed a laboratory-based experimental methodology. Conventional aggregates, 60/70 penetration grade bitumen, and fine crumb rubber were used. The Optimum Bitumen Content (OBC) was first determined as 6.0% for the control mix. Subsequently, asphalt mixtures were produced by replacing a portion of the cement filler with CR at percentages of 2%, 4%, 6%, 8%, and 10% by total mix weight. The performance of these mixtures was assessed using the Marshall Stability test, with results evaluated against the Nigerian General Specifications for Roads and Bridges (1997). Key findings indicate that all CR-modified mixes exceeded the minimum stability requirement of 3.5 kN. The study identified 6% CR as the optimum content. This mix uniquely satisfied all specified criteria: a stability of 9.316 kN, a flow of 3.7 mm, air voids (Vv) of 3.34%, and voids filled with bitumen (VFB) of 78.83%. Mixes with lower (2%) or higher (8%, 10%) CR content failed to meet the required volumetric standards, primarily related to air void content. The study concludes that the incorporation of 6% fine crumb rubber as a filler substitute in HMA is a technically viable and promising modification for flexible pavement construction.