Assessment of alkali-aggregate reaction in three bridges and its implications for maintenance of the structures

Alkali-aggregate reaction (AAR) can cause damage to concrete structures, which can vary from serious reductions in structural capacity to less serious maintenance problems, or minor durability effects. New cases of AAR continue to be discovered in different concrete structures in Australia, and exhibit different visual effects. The affected concrete needs to be characterised in order to determine the extent of damage caused by AAR, and to establish appropriate rehabilitation strategies. Recently, three bridges were diagnosed with AAR and were characterised using petrography, scanning electron microscopy, measurement of residual alkali content and residual expansion potential, compressive strength and elastic modulus. The results show that AAR has impacted the three bridges differently, and the paper discusses the consequences of AAR and appropriate treatments for each case.