Monitoring internal swelling reactions in concrete dams

Abstract

Alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are the most common internal swelling reactions (ISR) in concrete dams. The swelling effects and concrete deterioration caused by ISR can be observed in several forms at the structural level, including relative movements between blocks, displacements and deformations, cracking, surface discoloration around the cracks, scaling or spalling as well as surface “pop-outs”. The detection and the assessment of these structural symptoms in large concrete dams is usually made through visual inspection and interpretation of the monitoring data, such as stress free strainmeters embedded in concrete, geodedic levelling, pendulums, rod extensometers and internal or external jointmeters. The strainmeters and the levelling data are also used for providing estimations of the dam concrete expansion. The Portuguese information system, designed to serve as a national database, has its own data structure and includes the monitoring systems data for large concrete dams of all structural types, including dams with over 60 years old. This information system is used by both the dam owners and the National Laboratory for Civil Engineering (LNEC) for dam safety assessment over the years. This work discusses the importance of the dam observed behaviour data provided by the monitoring system as a tool for ISR assessment. The progression of concrete expansion for several dams located in Portugal is presented. The presented observed results were based on data from stress free strainmeters, while others were calculated from geodetic levelling.