Engineering and Chemical Characterization of Natural Bitumen Resources from Nigeria

Abstract

High demand for good engineering materials that are not harmful to human and environment for sustainable roads has necessitated this study with the aim of evaluating the quality and grade of natural bitumen and their impact on health and the environment. Engineering and chemical properties of bitumen in Agbabu and its environs were evaluated for their suitability in road pavement construction. Raw samples of natural bitumen were collected in Agbagbu, Mile 2 and Mulekangbo, Ondo State, Nigeria. The engineering properties involves the analysis of the bitumen penetration, flash and fire points, water content, loss on heating and specific gravity. The chemical evaluation includes the analysis of heavy metals by the use of Atomic Absorption Spectroscopy (AAS) and the analysis of Poly Aromatic Hydrocarbons (PAHs) involves the use of Gas Chromatography/Mass Spectrometer (GCMS). Based on the penetration values, Agbabu and Mulekangbo bitumen sample, fall within 200/300 penetration grade and are classified as temperature susceptible bitumen, while the samples of Mile 2 fall within 100/150 penetration grade and are classified as conventional paving bitumen. Thus, Agbabu and Mulekangbo bitumen can only be used in the temperate regions of the world, while Mile 2 bitumen can best be applied in the tropics, after they must have been upgraded by modifiers. The results of AAS indicate a high concentration of iron in all the samples of the locations in the decreasing order of Fe<Zn<Cu<Mn<Pb<Ni. For Agbabu bitumen sample, the concentration indicates Fe (509 mg/kg), Zn (16 mg/kg), Cu (14.00 mg/kg), Pb (1.00 mg/kg), Ni, Cd and Mn are negligible, Mile 2 bitumen sample indicates Fe (8605.00 mg/kg), Zn (36.00 mg/kg), Cu (35.00 mg/kg) Mn (27.00 mg/kg), Ni and Cd are negligible; for Mulekangbo bitumen sample: Fe (8905.00 mg/kg), Zn (48.00 mg/kg), Cu (39.00 mg/kg),  Mn (37.00 mg/kg), Pb (7.00 mg/kg), Mn (37.00 mg/kg), Ni (1.01mg/kg) and Cd is negligible. Metals like Pb, Ni, Cd, even though present in small concentration can cause environmental hazard. The GCMS analysis revealed high percentage of PAHs such as Chrysene, Pyrene, Fluorene, Phenanthrene and Anthracene in Mulekangbo bitumen sample, while Agbabu and Mile 2 bitumen samples indicate low percentage of the target PAHs. The PAHs present in bitumen sample of Mulekangbo can be carcinogenic and mutagenic, thus, exposure to these compounds can pose health/environmental risks. This study recommends clean technology during refining process to remove hazardous PAHs from the bitumen to prevent human and environmental health challenges during utilization.