The rail bridge over the Georges River at Como, south of Sydney, was constructed in 1972, and comprises seven 48 metre simply supported spans and carries two electrified and ballasted railway tracks. During routine underwater inspection of the precast, prestressed bridge piles in 2004, a significant proportion of the inspected piles exhibited vertical cracks. Railcorp (NSW) commissioned Arup in conjunction with ARRB Group to investigate and provide advice on the vertical edge-cracking in the piles. The investigation involved desktop structural analysis of the piles and laboratory investigation of concrete cores drilled from selected piles. The latter included petrographic examination, microstructural (SEM/EDX) investigation, chemical analyses, strength testing, and determination of residual expansion. The results showed that the load capacity of piles is in excess of the current operation loads. The main cause of the cracking was alkali-aggregate reaction, exacerbated by delayed ettringite formation. The residual expansion of the affected piles was found to be small. Consequently, further cracking in the future is considered unlikely, indicating that repair could be undertaken. In addition to the do not repair option, two repair options, namely, patch repair and steel or concrete jacketing are suggested to address the long-term durability of the structure. (a) For the covering entry of this conference, please see ITRD abstract no. E217099.
Samenvatting