Anti-corrosion properties of magnesium oxide/magnesium hydroxide coatings for application on concrete surfaces (sewerage network pipes)

Abstract

The corrosion of concrete sewer pipes, mainly due to biogenic sulfuric acid (bio-corrosion), may lead to the degradation of sewerage system. The purpose of this study is to evaluate the corrosion protection that the combined magnesium oxide/magnesium hydroxide coatings can offer to concrete substrates. Four coatings with different proportions of magnesium oxide/magnesium hydroxide were prepared and applied as consumable coatings onto the surface of concrete specimens. Accelerated sulfuric acid spraying tests were used to simulate the acidic conditions, existing in most sewer pipes, and to trigger the consumption of protective coatings, due to their reaction with sulfuric acid. XRD analysis was used to evaluate the formation of gypsum, as the major corrosion product of concrete degradation. The coatings exhibited good adhesion onto the concrete substrate and their progressive consumption was confirmed by performing mass and thickness measurements. All coatings preserved the alkaline surface pH values (around 9–10) throughout the duration of acid spraying tests. The respective XRD semi-quantitative results indicated the small or zero formation of gypsum in the protected samples. Surface hardness and roughness values of the coated concrete specimens presented smaller variation, in respect to the uncoated concrete specimens. According to the results, magnesium oxide/magnesium hydroxide coatings can offer sufficient protection to concrete substrates against the sulfuric acid bio-corrosion.