TRINITY WHARF, CAIRNS PORT, QLD
Trinity Wharves 1-5 were constructed up to 90 years ago and they have a significant heritage value. Many of the concrete elements in the substructure have suffered considerable corrosion damage, and many types of repair have been carried out over the years. The most affected elements are the 2m deep primary beams and the square columns in the splash zone, although higher secondary beams and the slab are also damaged in places.
Cairns Port Authority has a long-term programme to maintain the structures and has awarded repair contracts in annual increments. The Authority has carried out extensive testing of the structures and is able to define the repair work in detail.
In 2002, Marine & Civil Maintenance won a contract to fully replace the bottom 900mm of selected beams, and about 2.1m of selected columns.
After installing access decks at each location and closing the area above to traffic, the selected beams and columns were completely cut away by hydrodemolition to the required height. The exposed reinforcement was often in very corroded condition or even completely absent, and frequently needed additional steel welded in place.
The structural elements were replaced with a high-quality concrete pumped to formwork. On stripping the forms, the exposed concrete was cured with water sprays and the area returned to normal traffic.
The first contract was completed in 2003 and MCM was successful in its tenders for further consecutive contracts in 2004 and 2005. Approximately 120 beams and 120 columns were replaced in these three contracts.
In 2006 MCM was awarded a contract to reinstate the upper secondary beams and the deck slab soffit. This involved hydrodemolition of the defective concrete and its replacement with proprietary gunite, sprayed by the dry mix method.