Abstract
Concrete sewer pipes can be deteriorated by sulfuric acid (H2SO4), which is created by the oxidation of hydrogen sulfide in the presence of certain bacteria inside the sewers. This process is called biocorrosion. In this paper, H2SO4 (i.e., chemical, non-biogenic) was used to study acid attack on concrete samples. The authors conducted experiments under different acid flows and concentrations, to account for the conditions prevailing in sewage networks exposed to flowing acidic waters. The effect of intermittent stormwater on the removal of protective layers was studied in addition to constant flow runs. Specimens’ erosion depth was measured with a Vernier micrometer. In addition, unconfined compression at an axial strain rate of 0.0016 mm/mm/min was used for the estimation of unconfined compressive strength and elastic modulus. Moreover, the formation of gypsum as a protective layer and its role in biocorrosion was discussed. From this study, it was concluded that although the utilization of constant flowrates of acidic waters represents an important indication of corrosion mechanism, intermittent sewage and water flows should be taken into account, corresponding to real conditions in sewage networks, and resulting into accelerated concrete corrosion. Stormwater in combined sewers could remove the protective gypsum layer, thus accelerating chemical corrosion; however, in the presence of biogenic H2SO4, the removal of gypsum by excess flows due to stormwater could have a positive effect on corrosion mitigation. Finally, for combined sewers, selected coatings should withstand the effect of stormwater and high-velocity water flow tests should be included in future studies.
Highlights
Sulfuric acid (H2SO4) generated from microbiological activities can deteriorate concrete sewers, in a process called biocorrosion or microbiologically induced corrosion (MIC)
As soon as gypsum is removed during chemical H2SO4 attack, new concrete surfaces are exposed to acid attack, resulting in progressive deterioration and corrosion rate increase
Few researchers have concluded that the removal of gypsum deposits by wastewater flows can enhance chemical corrosion [11], it should be taken into account that moisture and gypsum can be ideal conditions for biocorrosion to occur
Summary
Sulfuric acid (H2SO4) generated from microbiological activities can deteriorate concrete sewers, in a process called biocorrosion or microbiologically induced corrosion (MIC). The biogenic H2SO4 reacts with cementitious materials in concrete, resulting in structural failures of sewers [1,2]. Concrete sewer system biocorrosion problems in Greece have been recently assessed [3], while an ongoing national R&D project focuses on the development of an innovative active product, based on Mg(OH) and MgO [4], for the coating of the inner surfaces of concrete sewer network pipes to address corrosion problems [5,6]. Prior to the implementation of coating practices, a corrosion study of concrete samples should take place, in order to study deterioration of concrete due to sulfuric acid. Biogenic corrosion inside concrete sewers is a specific context of sulfate attack
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