Boulby Mine is located on a 490-acre(198-ha) site in North Yorkshire, situated on the north-east coast of the North York Moors National Park. It is operated by Cleveland Potash, a subsidiary of Israel Chemicals Limited (ICL) and is the world's first and only polyhalite mine. Polyhalite is a natural multi-nutrient fertiliser and a source of potassium, calcium, magnesium and sulfur. 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 which provides access to the UK's deepest mine to a depth of 1200m. The external elevation of the structure extends 45m above ground level and is 12.5m in diameter to the outer face with a 300mm-thick concrete wall. The structure is approximately 50 years old and needed structural refurbishment. Concrete Repairs Limited (CRL) was appointed as the principal contractor and structural refurbishment specialist, with the works commencing on-site in October 2020. Extensive survey works identified that significant areas of repair were required to both the external and internal faces of the 300mm-thick concrete wall. There were large areas of cracking and spalling to a depth of between 80 and 100mm, as a result of corrosion of the reinforcing bars. The effect of this was large volumes of concrete were delaminating from the structure and falling to the ground below, which if left unchecked would pose a significant safety hazard. From the client's perspective, one of the key obstacles to overcome on the project was to ensure that the man-riding shaft was kept operational while the internal repair works were carried out. In this respect, refurbishment was a much better option than demolition and renewal.
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