Similarly to VicRoads’ coastal concrete structures, QSL’s port assets degrade in the aggressive maritime environment.
For QSL this is exacerbated by them being located in the Tropics as well. The wharves and associated infrastructure at Lucinda, Bundaberg and Cairns are under threat of chloride attack, in addition to damage from tropical storms and cyclones.
“Correct interpretation of observations and testing is essential to a correct diagnosis and prognosis of the problem, and thus enable appropriate corrective measures to be taken,” Andrews-Phaedonos said.
The traditional method of concrete repair is to remove the cracked, delaminated and spalling concrete to a depth of 20-30mm behind the reinforcing bars to fully expose the rusted material and remove the contaminated concrete from the steel. All the corrosion affected material is then removed and the steel treated or replaced, after which specialist repair concrete mortars are applied and the surface made good. A modern development is for the repair mortars to be polymer modified to improve adhesion and resist further ingress of contaminants. Coatings are commonly used in combination with patch repairs to reduce further entry of carbonation or chlorides.
Edelman said that when the QSL jetty at Lucinda was built there was an issue with alkali silica reaction (ASR) causing cracking of the concrete. Chlorides have penetrated the concrete and caused premature corrosion of the reinforcing steel on parts of the structure. In some highly exposed parts of the structure this corrosion has caused extensive damage where elements have had to be repaired or replaced. However, in large sections of the jetty structure, the chlorides in the concrete have not yet reached a concentration where corrosion has initiated.
“The chloride concentrations have been monitored over many years and they are slowly increasing,” Edelman said. To counter this, QSL has started a program to apply an impregnating silane coating to the underside of the 5.7 kilometre length of the jetty to prevent further ingress of chlorides. “By putting this relatively inexpensive protection in place now, we can extend the life of the structure,” stated Edelman. “If we wait another 10 or 15 years the chlorides levels will have increased, corrosion will have started and it will be too late.” “The square-metre cost of a simple protective coating like silane is as little as 1/100th the cost of a concrete patch repair, but it is only effective before corrosion starts”.