Case Studies of Concrete Repair and Strengthening of Coal Storage Silos in Eastern Australia

Two 3000 tonne and one 5000 tonne capacity reinforced concrete coal silos in the Hunter Valley, New South Wales, Australia were deteriorated. The storage silos are a critical asset necessary to facilitate the efficient delivery of coal. Serious concrete deterioration of the silos and corrosion to external post-tensioned cables had the potential to catastrophically interrupt the supply chain. A risk and structural assessment of the silos was undertaken and a condition investigation completed. The structural assessment established that the enhancement of hoop tensile strengths is considered paramount and their effect needs to be restored. Further strengthening of the silo walls was also required in the regions close to the ring beam levels.

The condition investigation (diagnostic survey) identified that concrete compressive strengths were considered adequate and reinforcement corrosion activity was concentrated at external crack locations generally greater than 0.5mm wide due to the depth of carbonation and low cover areas.

A remedial option scenario analysis was conducted for each silo, to provide a serviceable strengthening solution. Each solution used either carbon fibre laminates (CFL) and or post tensioned cables, all externally applied. In both cases where delaminated (drummy) zones of concrete were present or where concrete had severely spalled (internally and externally) they were repaired with a sprayed repair mortar. An elastomeric anti-carbonation coating system was then applied to external silo concrete surfaces.

The capacity of the silos has been fully restored, service life has been extended to the required 25 and 20 years respectively with safety having also been returned at each of the sites.