Precast concrete piles used in 1983 in the construction of a bridge in the North Eastern region of NSW have shown severe longitudinal cracking. Considering the salty nature of the tidal river water in which the bridge is constructed, the risk of corrosion of reinforcement steel could be significant. A preliminary investigation, undertaken on a spare pile left at the construction site since 1983, showed that although the aggregate was susceptible to alkali-aggregate reaction (AAR), no significant signs of AAR were observed in cores taken from this pile. Indications of delayed or secondary ettringite formation were noted in the concrete cores, but this was not associated with any noticeable cracking of the spare pile, and this mechanism could not be related to the cracking of the piles under service conditions. Consequently, concrete cores were taken from the submerged piles, and a severe case of AAR has been identified in these piles, which appears to be associated with ettringite formation. Evidence of sea water interaction with the AAR products has also been seen in some of the piles. AAR has been suggested as the main cause of the cracking. Although the chloride content of the cover concrete is high, there was no sign of corrosion of reinforcement in the cores because of oxygen starvation of the submerged piles. (A)
Abstract