Calliope River Railway Bridge, Gladstone QLD
The main-line railway bridge over Calliope River was built in the 1960's and consists of four river spans and six land spans. The river pier columns have deteriorated in the tidal environment over many years, despite reinforced concrete jackets being cast around the lower parts of each. Queensland Rail decided that a longer-term repair was required, with cathodic protection (CP) to prevent further corrosion of the reinforcement in the areas most at risk.
Marine and Civil Maintenance was awarded the contract in 2007 to remove the failed column jackets, carry out all the necessary concrete repairs, design and install a CP system to the lower columns and apply a protective silane coating to the upper superstructure. Extensive precautions were required to prevent debris from entering the river during the work.
Steel scaffolding was erected at the bridge piers to provide access to the full height of the bridge piers, and a suspended deck was used to provide access to the main spans.
After removing the concrete jackets, all damaged concrete beneath was removed from the columns by hydrodemolition and replaced with a formed structural repair mortar. As the bridge remained open to rail traffic, the reinstatement work was phased to avoid undue weakening of any pier.
Additional concrete repairs incorporating sacrificial anodes were undertaken on damaged parts of the superstructure that were outside the CP protection. Silane was applied to all areas of secondary exposure.
The CP design was carried out for MCM by Ian Godson & Associates. It required the installation of over one thousand
discrete anodes in the 16 concrete columns of the bridge, with permanent reference electrodes for monitoring and adjustment.
The CP system is powered by a transformer rectifier unit with 3 output zones. It was commissioned by MCM in July 2008.