Crumb Rubber as Partial Replacement of Coarse Aggregate in Asphaltic Concrete

Abstract

This paper presents the evaluation of the effects of crumb rubber on the characteristics of asphaltic concrete with a view to investigating its suitability as partial replacement of coarse aggregates in asphaltic concrete. The waste tyre was obtained from a dump site in Ede and the portion free from steel breeds was cut into smaller pieces and sieved to obtain crumb rubber passing through sieve 12.5mm and retained in 9.5 mm sieve. Asphaltic concrete materials and crumb rubber (CR) were characterized by carrying out particle size distribution, specific gravity, flakiness index, aggregate crushing value, and adsorption tests on the aggregates. Penetration, softening point, and flash point tests were also carried out on bitumen. Asphaltic concrete samples were prepared with partial replacement of coarse aggregate in the asphaltic concrete mix with crumb rubber at 0, 2, 4, 6, 8 and 10% by weight of the total mix. The samples were subjected to Marshall stability test and the values of stability, flow, air void (AV), voids in the mineral aggregate (VMA), and voids filled with bitumen (VFB) were obtained.

The results showed that the penetration, specific gravity and softening point of the bitumen were; 63.02 mm, 1.03 and 49.6  respectively; and the aggregate crushing value, flakiness index, elongation index, water absorption and specific gravity of the granite aggregate were; 23.8 %, 24.1 %, 28.8 %, 0.3 % and 2.74, respectively. The specific gravity of the crumb rubber was 1.10. The result of stability, flow, bulk density, voids filled (VFB), air voids (VA) and voids in mineral aggregate (VMA) of the asphaltic concrete without crumb rubber were; 12.65 kN, 3.41 mm, 2.36 g/cm³, 79.43 %, 3.94 % and 17.55 % respectively. However, the stability, flow, bulk density, voids filled (VFB), air voids (VA) and voids in mineral aggregate (VMA) of the asphaltic concrete at 2 % optimum crumb rubber were; 11.82 kN, 3.67 mm, 2.35g/cm³, 76.25 %, 4.63 %, and 18.15 %, respectively.The paper concluded that the properties of compacted asphaltic concrete for wearing course were satisfied at 2 % partial replacement of coarse aggregate with crumb rubber..

Keywords: Crumb rubber, Asphaltic Concrete, Asphaltic Concrete Properties