Zenith safely and successfully completed a complex fibre reinforced fibre (FRP) strengthening of a 213m high reinforced concrete chimney access platform at a refinery in Rotterdam, The Netherlands.

Following a detailed inspection, the concrete parapet wall proved to be in an unsafe condition. There were large areas of loose spalling concrete caused by corrosion to the embedded steel reinforcement. The extent of the corrosion observed during the initial inspection did not suggest that excessive section loss to the reinforcement had occurred, in so much that the structural integrity of the walkway and parapet wall was still sound. However, if it was left in this state, corrosion would continue to occur resulting in further spalling of the concrete and reducing the integrity of the structure.

A containment wrap was selected as a suitable repair method. The following scope of works was agreed with the client:

• Remove spalled concrete.
• Repair using a high build polymer modified concrete repair mortar.
• Clean all surfaces and apply fairing coat.
• Apply FRP glass sheets on a bi-directional layered system with a relatively low E value to wrap the parapet structure.
• As epoxy is susceptible to prolonged UV, an additional polyurethane coat should be applied.
• All products and systems for the protection and repair of concrete structure should be in accordance with the latest edition of BS EN 1504.
• The platform parapet wall sections to be encaptulated without altering the structural behaviour of the platform.

In conclusion the repair method allowed the following benefits:

• Long term stability to the concrete for the integrity of the structure
• Removed the need for exclusion zones at the base of the chimney
• Reduces future maintenance