Deterioration of concrete in a hydroelectric concrete gravity dam and its characterisation

A hydroelectric concrete gravity dam in the Snowy Hydro network had shown signs of concrete distress in the form of cracking in some sections of the dam wall, and vertical movements in the wall, measured in routine surveys on the crest of the dam wall. Concrete elements of the associated power station had also shown some degree of distress in the form of cracking. Alkali-aggregate reaction (AAR) was considered among other mechanisms as a likely cause of cracking. In order to investigate the main causes of cracking of the various elements of the power station and the dam wall, core samples ranging in length from 0.3 m to 10 m were extracted and investigated for the presence of AAR, its extent, likelihood of continuing reaction, residual expansion potential, and effect on the strength of concrete. Results of the investigation showed that mild AAR was present in some sections of the wall of the power station but not in the floor, where drying shrinkage could have caused the cracking. Mild AAR was also present in sections of the dam wall with minor visible cracking, but it was stronger and more widespread in the badly cracked area. It was suggested that the walls of power station could be treated by appropriate surface coating to mitigate the progress of AAR, and the badly cracked portion of the dam wall be anchored to stabilise the vertical movement. Other portions of the dam wall did not appear to need treatment.