Protective Performance and Microstructural Behavior of Asphalt and ‎Tar Coatings on Steel under Varying Chloride Concentrations ‎

Abstract

The present paper aims to undertake a comparison between the corrosion inhibition effects of asphalt and tar paints used on the surface of steel samples subjected to sodium chloride environments of different concentrations (0.5 M and 1.0 M). This was done by first coating the steel samples before subjecting them to sodium chloride environments for a period of 17 days. Measurements of the weight loss of samples after every 72 hours were made in order to estimate the corrosion rates. The gravimetric technique was employed in determining the corrosion rate in accordance with ASTM G31-21 standards. Other tests such as TDS and SEM were done to study salt concentration levels and microstructure alterations of surfaces. It is noted that there was a steady reduction in both salt concentration and corrosion rates as a result of iron oxide and hydroxides coating on the surface. Asphalt coatings showed a better level of protection against corrosion than tar coatings and untreated samples. The values of the corrosion rates were equal to 0.19 mm/year in 0.5 M NaCl solution and 0.36 mm/year in 1.0 M NaCl solution, while in the case of tar coatings they were equal to 0.28 and 0.52 mm/year correspondingly. SEM micrographs revealed that asphalt coating was dense, homogeneous, and tightly adhering to the surface with few defects, while tar coating was characterized by microcracks and porosities.