Microbiologically induced concrete corrosion in the cracked sewer pipe under sustained load

Microbiologically induced concrete corrosion (MICC) and stress crack are the most common structural defects in concrete sewer pipes. To investigate the microbial corrosion behavior of cracked concrete pipes under sustained loading, coupons with no load, 100% D-Load, and 120% D-Load were pre-adjusted to a suitable environment for acidophilic sulfur oxidizing bacteria (ASOB) colonization, and then placed together in a microbial chamber for 90-day accelerated corrosion. The corrosion variances of these coupons were compared in terms of surface morphology, crystalline violet staining, pH evolutions, crack width changes, as well as characterization results including Scanning Electron Microscope- Energy Dispersive Spectrometer (SEM-EDS) and X-ray Diffraction (XRD). It was found that the stress level slightly accelerates the pH drop on the coupon surface, positively correlates with the corrosion product content of the semi-corrosive layer, and causes stress-corrosion cracking of the semi-corrosive layer, but has little effect on corrosion loss. Stress-corrosion effects were only found in the semi-deteriorated layer of the stressed coupon, but no significant acceleration effect on corrosion rate was observed. This is explained by the fact that MICC is a non-diffusive corrosion where the semi-deteriorated layer is rather thin. Thus, cracking or not of the semi-deteriorated layer does not affect the corrosion rate. This study improves understanding of the service deterioration of sewage pipes.