Precast, prestressed concrete bridge piles, submerged in tidal water, have exhibited significant cracking and delamination. A large portion of the pile (including the prestressing wires and the steel reinforcement bars) had completely disappeared, leaving only one prestressing wire in that portion. Examination of the affected concrete by several techniques revealed a strong case of alkali-aggregate reaction (AAR), and exhibited a large residual AAR expansion. There was also strong evidence of delayed ettringite formation (DEF), which very probably contributed to the cracking, and indicated that the pile was overheated in the production process. The hydrated cement paste was significantly altered due to interaction with seawater. Similar AAR- and DEF-affected piles in another bridge exhibited delamination of cover concrete at the position of the prestressing wires. In addition, Freidel's salt was noted to have formed in some locations with the same morphological features as DEF. Both the cement paste and AAR products appeared to have been altered by exposure to seawater. This paper describes the characterisation of the damaged piles and discusses the reactions that may be involved in the expansion and deterioration of AAR-affected concrete under marine exposure conditions. (a) For the covering entry of this conference, please see ITRD abstract no. 0612AR242E.
Samenvatting