Acoustic emission activation protocols for alkali-silica reaction damage assessment in concrete

As existing concrete structures age, several degradation phenomena can endanger their structural safety. A severe threat to the integrity of concrete is posed by the alkali-silica reaction, which starts internally by the formation and swelling of a hydrophilic gel and eventually leads to concrete cracking. The acoustic emission technique can be applied to monitor ongoing damage caused by degradation processes. However, due to the working principle of the technique, only active damage can be detected. This paper investigates damage activation protocols to assess already existing damage in a limited timeframe. Small concrete samples that were deteriorated up to a target damage level in an accelerated way are investigated. Several activation protocols such as changing the moisture content, applying temperature fluctuations, and heating the samples with a heat lamp are applied and analyzed. It is found that changing the moisture content is most promising in terms of AE activation, its ability to distinguish damaged and undamaged samples, and allow damage localization.