Effect of using blends of rice husk and corn cob ash as fillers on the performance of bituminous mixtures.

Abstract

This study investigates the use of blended agricultural waste specifically rice husk ash (RHA) and corn cob ash (CCA) as a partial replacement for conventional stone dust filler in asphalt mixtures for the wearing coarse in areas with normal loading conditions. The primary aim was to evaluate the impact of these bio-ash blends on the mechanical and volumetric properties of hot mix asphalt (HMA), focusing on stability, flow, bulk density, air voids, and moisture susceptibility. Granite aggregates and 60/70 penetration grade bitumen were used, while the RHA and CCA were incinerated separately and blended in specified ratios. In the experimental setup, stone filler was replaced with blended ash at 0%, 50%, and 100% levels. Additionally, within each total ash composition, the proportions of CCA and RHA were varied at 0%, 50%, and 100% to assess their individual and combined effects. The optimum bitumen content for each variation of total ash blend in the mix was determined and it was found to be 4.5%, 5.5% and 6% for 0% ash, 50% ash and 100% ash respectively while considering 50% CCA and 50% RHA. Laboratory tests revealed that the optimal blend having 50% RHA + 50% CCA with 50% stone filler replacement exhibited the most desirable performance with Marshall stability of 11,672 N, flow value of 3 mm, air voids of 4.2%, ITS of 352 kPa, and ITSR of 98.7%, all meeting standard specifications (AASHTO T 245, 2015). In contrast, mixtures with 100% CCA failed to meet minimum requirements, showing inadequate Marshall Stability (6,451 N) and ITSR (79.4%). Similarly, mixes with 100% RHA exceeded the maximum allowable air voids 7.4%, despite achieving high stability of 13,626 N and acceptable flow 2.8 mm. The study concludes that a 50:50 blend of RHA and CCA with 50% stone filler can be used as an effective filler in asphalt mixtures, offering a cost-effective and environmentally sustainable alternative to traditional materials. This research supports Uganda’s drive toward greener infrastructure by reducing dependence on non-renewable quarry materials while improving road construction sustainability.