Discharge manhole with loss of integrity due to extensive H2S corrosion. Inspection found that a large portion of the interior of the structure was covered with an HDPE liner, which was protecting the manhole from the H2S gas. However, the liner did to fully extend the length of the manhole, leaving the base and the lower portions of the manhole walls exposed to the corrosive gases.
The city contracted with Underground Tech to restore the structural integrity of the discharge manhole and provide protection against further corrosion.
Cleaning and Prep Process:
Once the forced main was temporarily shut off and the structure properly ventilated, entry was made, and the cleaning process began. The first 2”-4” of the walls were completely deteriorated, H2S had turned the concrete to mud and in a few areas the reinforced steel in the precast manhole was exposed. All the degraded concrete was completely removed, after which the entire surface was thoroughly power washed with 5,000psi of water to remove any other loose or contaminated material. A termination cut was also made above the compromised area to allow for a place to terminate the liner per manufacture specifications.
Surface Rebuilding and Corrosion Protection:
Mainstay ML-72 Sprayable Microsilica Mortar was mixed and pumped down into the manhole where it was applied with a shotcrete nozzle. In order to restore the structural integrity and bring the final surface back to original, the restoration mortar was applied up to 5” thick in some spots. The mortar was then hand troweled and finished with a sponge to achieve a slightly textured surface.
For protection against further corrosion, Mainstay DS-5 100% Solids Epoxy was sprayed on the uncured mortar. The unique and essentially simultaneous application of the mortar and epoxy coating, resulted in a monolithic lining that is tightly bonded not only to the substrate, but also to each other.
Underground Tech was able to thoroughly restore the structural integrity of the discharge manhole and protect against further corrosion by utilizing the Mainstay Composite Liner.