A new concrete manhole was installed on a long residence sewer from Whangarei Heads back to the treatment plant. However the concrete was severely corroded in less than one year due to hydrogen sulphide gas attack. The contractor was issued with a notice to rectify and achieve a design life of 50 years. The sewer was already live and could not be taken out of service for more than a few hours at a time using plugs and turning off stream pump stations off, using the storage capacity of the network only.
Armatec supplied a FRP Liner to lower into the manhole and form a new manhole surface inside the existing one. The top of the manhole was removed, the liner fitted, and then the cavity between the FRP Liner and the old manhole was grouted. This was all done during daytime hours with the sewers plugged. At night time the plugs were removed and the sewer flowed as per normal, minimising disruption and costs.
The manhole now has an all fibreglass inside surface that is totally impervious to hydrogen sulphide attack. The expected life of the manhole is now in excess of 50 years.