Synergistic effect on concrete corrosion control in sewer environment achieved by applying surface washing on calcium nitrite admixed concrete

Microbially influenced concrete corrosion (MICC) is often the major cause for the structure-failure in sewers. To mitigate the MICC, surface washing was considered as a cost efficient approach, however its effect is temporary and limited due to the fast re-establishment of sulfide oxidizing microorganisms (SOMs). Recently calcium nitrite admixed concrete was found as a promising approach to mitigate MICC. In this study, we hypothesize that applying a single surface washing on calcium nitrite admixed concrete would yield synergistic and effective control of MICC in sewers. The corrosion development and re-establishment after high-pressure washing on concrete coupons without calcium nitrite and with 1% (N1) and 4% (N4) (by the weight of cement) of calcium nitrite was investigated by exposing these coupons in a pilot-scale gravity sewer system for sixteen months. The corrosion process was monitored by measuring surface pH, corrosion product composition, corrosion loss and the microbial community. With one wash, the corrosion loss reduced by 45% and 58% in N1 and N4 coupons, respectively. The corrosion mitigation effect of surface washing for coupons without calcium nitrite was negligible. The combined application of surface washing and calcium nitrite admixed concrete showed synergetic effects and promising efficiency in MICC mitigation.