Deteriorated final settlement tank undergoes major refurbishment

Paul Boughton

A water utility company in Hampshire, UK, was experiencing severe erosion on the reinforced concrete walls of a final settlement tank. If left unchecked, this damage could have eventually led to the complete demolition and rebuilding of the tank wall. The company required a solution that would bypass this expensive and time-consuming procedure and not only repair the damaged substrate, but also protect it against any future damage.

During inspection by a Belzona engineer, it was found that erosion damage had occurred to the top of the reinforced concrete tank walls, resulting in the loss of the smooth wall cap. The damage had been caused progressively by the weight of the agitator arm, which is supported by a wheel travelling on a track on the top of the wall.

In addition to this, freeze-thaw damage had also occurred as a result of recent harsh winters. The culmination of damage had resulted in the formation of potholes which caused the wheel to become trapped. If left unrepaired, this eventually would have led to severe damage to the agitator motor, which would be extremely expensive to replace.

The conventional solution to this problem would be to remove the wheel rotating arm, demolish the existing reinforced concrete wall and rebuild it with concrete. This expensive solution would require the tank to be out of service for long periods of time and could potentially lead to sewage storage issues. The company required a solution that would avoid this expensive process while successfully repairing the settlement tank and fortifying the concrete substrate against future damage.

For the repair and resurfacing of the substrate, the company chose the non-porous, hard wearing epoxy repair composite, Belzona 4131 (Magma Screed). To prevent cracking on the movement joints, Belzona 2131 (D&A Fluid Elastomer), a flexible rubber material was further specified. The application would also incorporate Belzona Fungicidal Wash and Belzona 4911 (Magma TX Conditioner) to prepare and reconstitute the friable substrate prior to application.

Firstly, the interior and exterior walls of the tank were cleaned using the Belzona Fungicidal Wash in order to remove any mosses, lichens and other organic growth. This was then followed by grit blasting and mechanical preparation of the corroded metal and of the old concrete.

Once the substrate was thoroughly cleaned and prepared, Belzona 4911, a thixotropic resin conditioner specially designed to provide strong adhesion to masonry surfaces was then applied to condition the surface ready for the repair application.

Belzona 4131 was subsequently applied to repair and resurface general areas of the settlement tank. This material has been proven to exhibit excellent abrasion resistance. When tested in accordance with ASTM D4060 with a 1kg load the typical loss per 1,000 cycles is just 685mm³. This means once the Belzona system has cured, the tank walls will be able to withstand continuous impact caused by the weight of the agitator arm.

The movement joints were repaired using Belzona 2131, a fluid elastomeric resin that allows for a quick application by pouring. This flexible rubber material is ideal for joint reconstruction as its elasticity will respond sympathetically with the movement in the joints.

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