Effect of Filler Types (Crushed Stone, Gypsum and Lime Kiln-dust) on the Marshal Properties of Asphalt Concrete

Abstract

Roads are one of the country’s basic infrastructural facilities, which needs a precise engineering design to minimize the life cycle cost by achieving reliable in-service performance. For the paved road types, pavement structure design and mix design of asphalt concrete mixture including adequate structure with proper drainage system and durable raw materials are the major considerations to attain reliable pavement performance that is adequately strong, durable and resistive to fatigue, and permanent deformation by considering economical aspect. The HMA contains coarse aggregate, fine aggregate and mineral filler coated with a bitumen binder and air and the mechanical properties of bituminous road pavement depend decisively upon the properties of its filler-bitumen. Although Mineral filler plays a major role in filling voids of the mixture and on the modification of the asphalt concrete properties like stiffness of the asphalt mortar matrix, improving the rutting resistance of pavements, it needs high intention on the content of the mineral filler since the excessive use have also weaken the properties of the mixture. In Ethiopia, crushed stone from dust extractor is conventional filler material in almost all flexible pavement construction projects but deficiency of this mineral filler happens and leads to crush aggregate for that purpose, which increase the production cost and environmental deterioration of the area. The main objective of this thesis is therefore to investigate the effect of the filler types (crushed stone, lime kiln-dust, and gypsum) on the marshal properties of asphalt concrete and to analyze the cost breakdown for the production of hot mix asphalt with these different filler types. To evaluate the effect of these selected filler types marshal mix design was used and conducted the laboratory test for marshal stability, flow, air void, voids in mineral aggregate and voids filled with bitumen by preparing a total of 90 specimens compacted by marshal compactor by 75 blows on the upper and lower sides of the mold. From the marshal laboratory test, asphalt concrete with crushed stone, gypsum and limekiln dust attains all the requirements specified on the ERA manual. Comparing the filler types, mixture with crushed stone filler attains the highest stability (9.45KN) at 2% filler content. For the asphalt concrete mixture at 3% filler content, mixture with gypsum filler attains the highest stability (9.4KN). From the cost break down analysis for the production of 1m3 HMA, lime kiln-dust and gypsum lowers the production cost by 1.34% and 1.21% respectively with the comparison of HMA with crushed stone filler.