Partial Replacement of Blended Corncob Ash and Saw Dust Ash as a Filler Material in Hot Mix Asphalt

Abstract

The government of Ethiopia has allocated a huge amount of resources to upgrade the existing road network nationwide. In connection to this, in Ethiopia, most of the trunk, link roads and some economically sensitive area roads are constructed and rehabilitated using asphalt concrete. In the construction of highway pavements, one of the main problems is insufficient amount of crushed stone dust from crushing of aggregates. Crushed stone dust is the most commonly used filler for hot mix asphalt construction in Ethiopia. Hence, it is important to see alternative mineral filler materials that could be replaced crushed stone dust partially or if it is possible fully. Thus, this study was conducted with this intention. The objective of this research is partial replacement of blended corncob ash and saw dust ash as mineral filler in hot mix asphalt. Materials needed are aggregates, bitumen, crushed stone dust, corncob ash and saw dust ash. For all the materials quality test was done. to determine OBC and OFC three different gradations were prepared by varying amount of crushed stone dust (4.5%, 5.5% and 6.5% by weight of aggregates) with five different bitumen contents (4%, 4.5%, 5%, 5.5% and 6% by weight of total mix). The OBC and OFC at different values of crushed stone dust filler was selected based on NAPA (National Asphalt Pavement Association) curve plotting method. The replacement ratio of blended corncob ash and saw dust ash was 10 % (by weight of optimum filler content) by trial and error method. According to the laboratory quality test results compared with the standard specification all the materials satisfied the criteria. Based on the results of Marshall Stability test 5.5% crushed stone dust and 5% bitumen content were OFC and OBC respectively. The potential of blended corncob ash and saw dust ash to be replaced crushed stone dust was 50% (by weight of OFC) after 50 % it cannot satisfied the standard requirements. To determine the optimum replacement ratio of BCSA it was based on Marshall Property test result values of maximum stability, maximum bulk density and air voids (VA, %) within the allowed range of specification. The values at 40% BCSA (by weight of OFC) replacement were stability of 10.06 KN, Bulk-Density of 2.375gm/cm 3 and Air void (VA) of 4% which were the best when compared to other percentage replacement ratio values. Hence 40% (by weight of OFC) is adopted as the optimum replacement ratio of blended corncob ash and saw dust ash