The existing lining in the effluent pits had broken down and was no longer protecting the concrete from the aggressive chemicals present within the site effluent. It appeared that previously a polyurethane cementitious system had been used, which was unusual as these materials are not normally deemed suitable for an immersion environment.
All defective areas were made good by the application of Remmers Betofix concrete repair materials.
When lining buried concrete tanks/pits a key consideration is the risk of osmosis. The concrete acts as a semi permeable membrane, which if ground water is present can lead to osmotic blistering in the new tank lining.
To mitigate this, we proposed the application of Aquron 2000 waterproofing treatment. This Colloid Silicate penetrates up to 200mm into the concrete that is being treated and forms a hydrogel, that prevents the transmission of moisture, thus significantly reducing the risk of osmosis.
This strategy was vindicated as during the works we experienced water ingress around pipe penetrations and between the joints in the concrete rings. To resolve this we conducted resin injection works using Normet Tampur 150 initially.
Around the pipes further sealing works were undertaken by breaking out a recess prior to filling using Remmers Stopaq swellable sealant. This works by expanding when it contacts moisture, forming a pressure seal that can withstand ground water pressure.
To ensure the Stopaq material was retained in place as it expands a fillet detail was formed around the pipe using Remmers Betofix mortars.
Prior to tank lining application a cementitious fairing coat was applied throughout the pit to fill blow holes in the concrete – these cannot be filled with coatings alone! The same material was used to form a fillet detail at the floor/wall interface to isolate the point of greatest potential movement from the tank lining.
This was allowed to cure and hydrate naturally prior to the introduction of heating and dehumidification to ensure the correct climatic conditions for coating application. The climatic conditions were tested and recorded and moisture content of the concrete checked also.
Because of the aggressive chemicals that the pit could contain we had proposed the application of a glass flake reinforced vinyl ester tank lining from Chemco International . These materials offer some of the highest levels of chemical resistance for polymeric linings, however they are very rigid systems.
Therefore to give better protection against any cracking in the concrete, glass fibre matting was incorporated into the highly damp tolerant epoxy primer. This was fully saturated and broadcast with a quartz aggregate to act as a bonding bridge between the two different resin technologies.
Chemco RB332 was then spray applied to a thickness of 1000 microns per coat to give a total thickness of 2mm. Even with the relatively small size of the project spray application was elected as this allows greater coating film build in shorter durations.
As per our standard tank lining quality assurance the new tank lining was checked for porosity using a DC holiday spark tester and any pin holes marked and made good. In chemically demanding environments a single pin hole is a point of failure that will allow aggressive chemicals to attack the concrete again.
For maximum chemical resistance and to aid curing Chemco RB300 TC was applied by method of brush and roller. Once initial cure had completed heating was introduced to post cure the lining and allow a shorter return to service to align with the clients shutdown period.
The additional water stopping works that evolved through the project meant that at short notice our team had to work weekends so that the project duration did not exceed the shutdown period which would have meant significant costs for our client through loss of production.
