Bridges

A concrete dam structure constructed around 70 years ago, was originally identified to be affected by Alkali-Aggregate Reaction (AAR) in 2002, and at the time some chemical, mechanical and microstructural properties of concrete in various parts of the dam were determined. Observation of concrete conditions since 2002 showed increased vertical movement of dam crest, associated with increased extent of visual cracking in 2020. Although the residual expansion was measured to be small in 2002, the concrete suffered extensive cracking, indicating that the results of this test need more careful interpretation. Results of microstructural tests showed stronger manifestation of AAR in the concrete at a microstructural level, and greater adverse effects on the mechanical properties of concrete over the intervening 18 years. Moreover, much greater amounts of ettringite were detected in some locations in the 2020 investigation. Compared to the test data available from the original onsite concrete trials at the time of construction, and those of 2002, progress of AAR has caused some 20% reduction in compressive strength and 50% reduction in the static elastic modulus of concrete. The extent of horizontal cracking in the dam was also more significant in 2020 than in 2002. With respect to remediation/ maintenance of the dam, vertical post-tensioning and anchoring of the dam wall is considered a practical method of confinement and suppression the AAR-induced expansion and cracking