Client – Wesfarmers Resources
Consultant – Infracorr Consultant
Contractor – Freyssinet / Marine &civil joint venture
Date – 2011
An 85m diameter x 3m high mine thickener tank situated in the Bowen Basin West of Mackay North Queensland was suffering from severe chloride attack resulting in corrosion to reinforcing steel due to periodic exposure to water and coal dust.
The Launder wall of the 30-year-old Tank was showing signs of fatigue with extensive areas of delaminated concrete and on further inspection isolated areas of the lower wall and launder soffit showed deterioration requiring corrosion control.
Infracorr Consulting was contracted to perform a condition assessment on the external walls of the structure, the assessment detected reinforcement corrosion to 100% of the outer walls.
The recommendation and remedial design selected the Hybrid corrosion control system, as it provided a low-disruption option and long term solution to the corrosion problem.
The Hybrid system could be installed in discrete drilled holes, minimising the work required to protect the structure. The external launder walls were a minimum 100mm in thickness restricting conventional methods of corrosion control.
Challenges included electrical continuity; reinforcement bars were required to be wielded in place around the circumference of the tank to ensure continuity was made.
The hydro-demolition/dry-process gunite concrete backfill techniques were successful in completing the concrete repairs within the 2-week shutdown, thus allowing the tank to be put back in, service in accordance with Wesfarmers program.
Specialist Remediation contractors were chosen because of their experience and highly trained technicians to install the system. The project was completed on time and within budget.
The hybrid system was chosen as the most practical corrosion system, only loose or delaminated concrete was removed. The Hybrid system has been designed to allow regular and cost-effective remote monitoring of its performance from anywhere where there is Internet access.
Monitoring thus far indicates that the Hybrid system is protecting the reinforcement as the design intended.
The expected design life of the concrete walls is 30 years.