OPTIMUM BITUMEN CONTENT FOR BITUMINIOUS CONCRETE – AN ALTERNATIVE APPROACH FOR ESTIMATION

The major parameter in design of hot mix asphalt (HMA) widely used in flexible pavements as base course and surfacing course all over the world, is to find out the optimum bitumen content (OBC) required in achieving the desired objective. Bitumen is a costly material and needs to be designed very carefully to achieve the desired objectives, namely structural strength, skidding resistance, resistance to oxidation, impermeability of HMA. The traditional method of mix design is a lengthy cumbersome process. In this paper an alternative method is suggested to find out the OBC from the physical properties of aggregate used in a particular type of HMA (Bituminous Concrete) with a particular grade of bitumen (Viscosity Grade - 30). In this method, bitumen need for different purposes of HMA have been calculated and added together for calculating the OBC. Forty-five samples collected both from State Highways and National Highways, geographically spread in different parts of Odisha, India are analysed. OBC calculated by alternative method developed from the simple physical property of the aggregate used such as gradation, elongation and flakiness and water absorption/ porosity for a particular type of HMA and specific grade of bitumen. The results of alternative method are comparable with the actual consumption of the bitumen obtained from extraction test.