Durability planning for concrete on the Ross River Bridge, Townsville

Abstract

The Ross River Bridge in Townsville is currently under construction and will be located in an aggressive environment at the river's mouth. A durability plan was developed prior to construction in order to determine appropriate concrete design and construction practices to achieve the required design life of 100 years. Possible deterioration mechanisms investigated included: chloride ingress; carbonation; alkali-aggregate reaction (AAR); sulphate attack; acid sulphate soil degradation; atmospheric corrosion and corrosion of pile casings due to sulphate reducing bacteria. This paper outlines the approach undertaken to ensure that the bridge design met the required life. The results of mathematical modelling of chloride ingress and carbonation are presented based as both deterministic and probabilistic approaches. The concrete mix design was adjusted to address AAR and sulphate attack and appropriate testing was incorporated into the project specifi cations. The design approach outlined resulted in some durability requirements exceeding those nominated in AS5100.5 such as increased cover requirements and the need for stainless steel reinforcement.