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Concrete Waterproofing Coatings for Ashton Water Treatment Works

Around 24 tonnes of materials have been provided by Flexcrete for an impressive refurbishment project at Ashford Water Treatment Works (WTW) near Cannington in Somerset. Ashford WTW is one of Wessex Water’s showcase facilities and incorporates an education centre on-site for visits from local schoolchildren.

We worked alongside specialist concrete coatings system contractor Ultimate Coatings Limited to deliver a long-lasting solution. The concrete water tanks at Ashford WTW had deteriorated over time due to chemical attack from the treatment process. The reinforced concrete substrate was showing extensive signs of erosion, resulting in 20mm losses of concrete in some areas. A well proven concrete repair and protection solution was sought and Flexcrete and Ultimate Coatings Limited collaborated to provide a system designed to last at least 20 years before first maintenance is required.

Wessex Water supplies 1.3 million people in the South West of England with around 284 million litres of water daily. The company treats 475 million litres of sewage every single day and operates 110 Water Treatment Works, 340 Service Reservoirs and Water Towers and 405 Sewage Treatment Works. It is recognised by water industry regulator Ofwat as one of the most efficient water and sewerage companies in England and Wales.

All areas were first high pressure jet washed by Ultimate Coatings Limited to remove the weak concrete before rendering. The whole surface was then overcoated with two 1mm spray applied coats of Flexcrete Cementitious Coating 851. A highly advanced, two component, waterborne cementitious modified polymer coating, 851 provides an effective barrier against the effects of aggressive acid gases, moisture and chlorides, and also has greatly enhanced chemical resistance. It forms a hard, highly alkaline coating for the protection and structural waterproofing of concrete, resisting positive and negative pressure under a 100 metre head, and is approved under Regulation 31(4)(a) for use in contact with drinking water. It is also CE marked in accordance with BS EN 1504 Part 2, the pan European standard for concrete repair, and is approved by the British Board of Agrément (BBA).

A 2mm coating of Cementitious Coating 851 provides equivalent cover to 100mm of good quality concrete and being cement based, it chemically reacts with the substrate to form an integral part and will have a design life to match that of the concrete to which it is applied. As it is water-based, it exhibits minimal hazard during application and is non-toxic when cured.

Such is the chloride resistance of Cementitious Coating 851 that Flexcrete has received official confirmation it will resist chloride penetration for at least 24 years. In 1988, a 2mm thick film of Cementitious Coating 851 was applied to a concrete slice and sealed in a chloride ion diffusion cell in the laboratory at the VINCI Construction Technology Centre and it is still going strong some 24 years (8750 days) later. Tests recently carried out show that the barrier properties of 851 are such that a steady state of flux of chloride ions through the coated concrete has not been attained after a test period spanning 24 years, whereas the control concrete achieved this in just 28 days.

The application of Cementitious Coating 851 at Ashford WTW will prevent further chemical attack to the concrete. The slab was also cleaned and primed using Flexcrete Polymer Admixture 850 to prevent any outgassing before a single 2mm spray coat of Cementitious Coating 851 was applied.

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