Dynamics-based testing to localize macro cracking due to alkali-silica reaction in concrete

Reliable methodologies that help diagnose flaws in structural components of nuclear power plants play a crucial role in a plant's operational and maintenance decision process. In this work, we focus on degradation in concrete structures caused by the alkali-silica reaction (ASR): a chemical reaction between the cement and certain aggregates containing amorphous silica. In the presence of water, the ASR gel, formed as a byproduct of the ASR, expands and leads to diffused cracking. We investigate the suitability of a novel dynamics-based method, namely vibro-acoustic modulation (VAM), for the detection and localization of cracks caused by the ASR. In a VAM test, the structural component is excited using two frequencies. The frequency modulation (and hence the nonlinear structural behavior) appears as sidebands around the higher (probing) frequency in the power spectral density (PSD) of the measured response in the neighborhood of the damage zone. A map of the magnitude of such sidebands can be used to detect and localize the damage. Previously, VAM has successfully been used for detection and localization of near-surface delamination in thin composite plates [l]. However, its applicability for detection and localization of cracks in thick concrete walls and slabs has not been studied. We conduct laboratory experiments on a cement slab containing four pockets of reactive aggregates placed at known locations, and show that VAM-based testing with optimized test parameters and suitable sensor density can potentially be used to detect and localize cracks in thick concrete structures.