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Wet well lining and concrete repair

Concrete repair materials manufactured by Flexcrete Technologies Limited, part of AkzoNobel, have been chosen to restore the structural integrity of a wet well in the Colchester area, enabling it to be rapidly returned to normal service.

The refurbishment project was carried out by specialist contractor CSC Services on behalf of Anglian Water which supplies water and water recycling services to more than six million domestic customers from Grimsby to Milton Keynes. The wet well stores sewage underground and required maintenance and cleaning in order to avoid future blockages, as concrete is highly susceptible to erosion from bacteria found in domestic sewage. Bacterial organisms oxidise gasses in the atmosphere and produce sulphuric acid which readily attacks concrete.

As is the case with many wet wells, the wet well was difficult to access and problems were caused by vegetation growth and root ingress. Upon initial inspection, tree roots were found to be entering the well through joints and pipe entry. Ring joints and grout holes were leaking and there were holes to the base and cracks to the wall. Between 5-10mm of concrete had been lost from the walls and soffit areas.

CSC Services was commissioned to remove all vegetation and reline the wet well in order to prevent future blockage problems and to ensure structural integrity was retained. A Flexcrete repair and protection system was chosen due to its outstanding track record of use in wastewater applications. CSC Services initially inserted pipe access bungs into the wet well and set up over-pumping to an intermediate bulk container. Confined space entry was then established whereby CSC Services entered the wet well via a secure ladder with operatives attached to the rescue winch cable. Once the atmosphere was tested and forced ventilation was set up, the tree roots were cut out and removed. The concrete substrate was prepared using high pressure water jetting and grinding equipment.

Trusted Protection for Wastewater Applications

All joints, grout holes, cracks and voids were sealed using Monomix HD – a high strength, waterproof, class R4 structural repair mortar which has outstanding abrasion resistance, is easily trowellable, has excellent low sag properties and can be applied up to thicknesses of 80mm in a single application. The high bond strength of Monomix HD exceeds the tensile strength of concrete and its dense matrix offers low permeability to water, even at 10 bar pressure, and very high diffusion resistance to acid gasses and chloride ions.

Monolevel 844SP – a waterproof, engineering quality fairing coat – was then applied to bring the concrete back to profile prior to the application of two 1mm coats of Cemprotec E942, an innovative, two component, water-based cementitious coating that benefits from modification with both a thermoplastic polymer as well as an epoxy resin to provide a hard-wearing surface with greatly enhanced chemical and abrasion resistance. The product exhibits excellent resistance to sulphuric acid attack and is very versatile with the ability to be applied to both concrete and ferrous metals without a primer. It has a long track record of successful use in digester tanks where the most onerous conditions are found. Just 24 hours after application of Cemprotec E942, a physical check was made to ensure that the coating was fully cured and bungs were removed before the wet well was returned to normal service.

The Project Engineer for Anglian Water said: “The finished product looks like a brand new install and I was highly impressed with the level of detail provided on this job. The works were carried out within just three days, allowing the wet well to be put back into normal operation extremely quickly. Thanks for a great job.”