Expansive chemical reactions in dams and hydroelectric projects

The various forms of expansive reactions, including alkali–aggregate reactions and internal sulfate reactions, which may occur in the concrete in hydroelectric projects and dams are characterised. The effects of chemical expansion on different dam types and hydro-project structures and their vulnerabilities to it are identified. Preliminary estimates of strain and the timing of the development of critical issues for a sampling of known cases where data are available are presented in order to give some general indications of the magnitudes of the expansion strains that have been found to begin to cause critical operational or safety issues. The effectiveness of the current testing methods is reviewed. For dams where the expansions are continuing unabated, such as where alkali resupply is a factor, at present there is no known means to stop the reaction, and the focus is on long-term management of the expansion by slot cutting or other means to accommodate the effects. In only a very few cases has replacement become necessary due to expansive chemical reactions. Usually, the deterioration in key material properties is limited. The main concerns relate to the deformations that occur as a result of the expansion, causing cracking and/or equipment misalignment.