EFFECTS OF SOME BITUMEN COATING TREATMENTS ON THE CORROSION AND MECHANICAL BEHAVIOUR OF LOW CARBON STEEL

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Department of Engineering

ABSTRACT
The research work highlights the problem of corrosion of low carbon steel as a prime structural material in relation to the Nigerian economy. The work contributes to provide detailed analyses that can be used for sourcing, grading, modification and engineering coat-application of abundant bitumen resources in Nigeria to economically reduce corrosion of structural steelworks in the country?s petroleum-dependent economy that is subject to costly effects of corrosion. Low carbon steel rods and three bitumen samples were collected from different critical sources in Nigeria and characterized. Resistance to corrosion by various coating treatments of the bitumen samples and chemical fractions separated from them, and effects of treatment concentrations of sodium benzoate as a standard corrosion inhibitor on mechanical properties of the steel were separately experimentally investigated. Micro-structural make-ups of the coating treatments were also investigated through X-ray diffraction analysis. Analyses of the overall results indicated that bitumens from the sample sources are of high quality as per international standard (IS) for 60/70 and 80/100 penetration grade bitumen. Coattreating the steel with the bitumen samples in the range of 0.81 to 2.1mm coating thicknesses was found to produce appreciable corrosion inhibition of the steel and affected its mechanical properties. Within the coating thicknesses; resistance to tensile strength, fatigue strength, hardness, and impact strength deteriorations of the steel varied within different bands from 53.35 to 100%. Furthermore, the inhibition performance (IP) levels for the steel were found to vary with the bitumen samples and depended mainly on the asphaltene contents of the samples. By comparison with the coatings, sodium benzoate treatment concentrations in the range of 50 to 250ppm of the same test medium also produced appreciable good results with the highest inhibition efficiency of 27.4% at 250ppm concentration. Microstructurally, about 3.75 to 4.84% by weight of the coatings were found to consist of distinct mineral phases that varied in types and amounts with even bitumen from the same source.