Monitoring the water saturation and damage in reinforced concrete subjected to alkali-silica reaction gradient by non-destructive testing

Alkali silica reaction (ASR) is a harmful swelling pathology in concrete influenced by various factors such as moisture levels and stress conditions. In order to evaluate ASR-damaged structures, it is essential to characterize in situ water saturation gradients and to quantify the influence of reinforcement on ASR-induced damage. This research aims to assess the capability of different non-destructive testing (NDT) methods to evaluate moisture gradients in the context of ASR as well as the damage arising from expansion gradients in presence of reinforcement. Plain and reinforced concrete specimens were cast using both reactive and control composition. After curing, the specimens were fully, half-immersed and quarter-immersed in water at 38 °C to monitor the effects of ASR under varying water saturation conditions. The physicochemical conditions were characterized using permittivity tests. Expansion and damage were monitored through two-dimensional length change measurements, linear vibration analysis, acoustic emission (AE) and crack observations. This paper proposes an original method involving AE monitoring during mechanical loading following expansion. The linear vibration method was found to correlate the extent of damage with average expansion, regardless of the moisture gradient or presence of reinforcement. The acoustic emission during mechanical loading, along with crack observation techniques, effectively localized damage resulting from moisture gradients and reinforcement effects. The discussion highlights the complementary nature of these two techniques for monitoring the damage in both plain and reinforced concrete subjected to ASR.