Factors affecting the expansion and cracking of model bridge piles in seawater, and the effects of mechanical confinement.

Deterioration of some Australian bridge piles, submerged in seawater, has been attributed mainly to alkali-aggregate reaction (AAR) and delayed ettringite formation (DEF). Sixteen model piles were manufactured at 20 degrees celsius (ambient) or 85 degrees celsius (steamcuring), incorporating different aggregate types and cement sulphate contents, to clarify their influences on expansion under different exposure conditions. All piles containing reactive aggregate expanded significantly, being larger in the submerged portion of piles than in the dry portion. Higher cement sulphate content exacerbated the AAR expansion, due to DEF, only in the steam-cured piles. AAR was the only cause of expansion in ambient-cured piles. With non-reactive aggregate, DEF occurred rarely, only when high levels of temperature, alkali and sulphate were simultaneously present. Four cracked piles were repaired through confinement by carbon fibre reinforced polymer (CFRP) wrapping, or reinforced concrete jacketing. Extensive expansion results suggest that the confinement is only partially effective in reducing the expansion, which is continuing at lower but still deleterious levels. (a).