Boulby Mine, UK

THE PROJECT

Boulby Mine is a 200-hectare site located south-east of the village of Boulby in North Yorkshire, England. It is run by Cleveland Potash, a subsidiary of ICL, and is the world’s ‘first and only Polyhalite mine’. The main shaft building is a cast in situ concrete structure with primary and secondary steel reinforcement. It houses a steel sheave wheel and supporting structure that provides access to the UK’s deepest mine. The external elevation of the structure extends 45 metres above ground level and is 12.5m in diameter to the outer face. When one of the man riding shafts needed refurbishing, the client contacted CRL (Concrete Repairs Ltd) as Principal Contractor. Corrosion from sulphides from mined material, high internal humidity levels, and the salty coastal environment had caused significant areas of the 300mm thick wall to crack and spall to an average depth of 80-100mm on both faces. Areas of the concrete had delaminated and fallen to the ground, presenting a significant safety hazard. One of the key obstacles to overcome was to facilitate the requirement to keep the shaft operational during the internal works. Having worked closely alongside Fosroc for many projects, CRL contacted the specification team for technical product advice.

THE SOLUTION

Scaffolding was erected by CRL’s scaffolding sub-contractor and the steelwork was refurbished. More than 1500 sacrificial anodes were then incorporated with the concrete repairs to slow down the corrosion of reinforcement and prolong its life. Fosroc specified Renderoc HBS concrete repair mortar (R4) due to its high strength, high build properties, which are specifically engineered for vertical and overhead repair work. Renderoc DS was then applied using a dry spray technique. This product is ideal for covering large areas quickly and economically, with low rebound and high resistance to attack from carbon dioxide. The structure was thoroughly cleaned to remove all surface contaminants prior to the two layers of anti-carbonation coatings to help protect from future corrosion problems.

THE BENEFITS

After the application to the structure of the Renderoc DS over 3500m2 of anti-carbonation coatings were applied to the structure. Due the excellent surface finish that was achieved by using Renderoc DS savings in product volumes and application time were achieved. Overall, the restoration approach offered estimated savings of 92% in the volume of concrete required, 96.49% in the volume of steel required. The total emissions savings from materials was an estimated 93.79%. The cost savings to the client, the ability to maintain operations and the environmental benefits make this an excellent example of a sustainable construction project.