Laboratory assessment of highways asphalt bitumen in southwest of Nigeria

This paper reports laboratory tests conducted while evaluating some properties of bitumen used in the production of hot mixed-hot laid asphalt of three different asphalt plants in southwest of Nigeria. The bitumen properties investigated included determination of the purity or contamination of the bitumen sample. Determination of the temperature at which bitumen sample used will attain standard fluidity for the purpose of mixing with aggregate. The bitumen properties also investigated included determination of the sample grade at the temperature of 25°C and 60°C. These properties were investigated through Solubility, Softening Point, Penetration and Saybolt Viscosity tests respectively. Although all the three asphalt plants samples passed the Softening Point and the Solubility tests but could not satisfy the specification values set up as standards for Penetration and Saybolt Viscosity tests. Southwest of Nigeria is in the tropical region and the standard specification values for Penetration test should be AC 60/70 but the results obtained are of about AC 85/100 that is meant for temperate climate regions. It is pertinent to note that the harder the grade of bitumen, the lower the penetration value and the better its use for the production of quality asphalt in tropical region. The significance of this study is that results of experiments on bitumen samples from the three selected asphalt plants in southwest of Nigeria are unsatisfactory when related to the expected standard approved grades of both Penetration and Saybolt Viscosity tests. Unsatisfactory results from Penetration and Saybolt Viscosity tests as shown in this study could significantly affect the performance of asphalt leading to the premature failure of flexible pavements as presently prominent in southwest of Nigeria.