Impact-based Nonlinear Acoustic Testing for Characterizing Distributed Damage in Concrete
Nonlinear acoustic testing techniques have shown great potential for identification of volumetric microcracking and early damage in diverse materials. In this paper, we compare the results of two impact-based techniques: Impact-based Nonlinear Resonant Acoustic Spectroscopy (INRAS) and Dynamic Acousto-Elastic Testing (IDAET) in monitoring damage in concrete due to Alkali-Silica Reaction (ASR) and freeze-thaw (FT) cycles. Using an impact hammer as the large-strain (strain ~ 10-6 -10-5 ) source (instead of a piezoelectric ceramic or a shaker used in conventional testing) allows testing large samples and enables field transportability. INRAS gives a global measure of sample nonlinearity while IDAET provides a local but comprehensive picture of material nonlinear properties. We propose two new data processing approaches for a single-impact INRAS that while being simpler, yields similar results to those from other analyses. We then introduce IDAET and show how to extract both classical and non-classical nonlinear parameters from the test results. INRAS (various analysis approaches) and IDAET are used to monitor a set of concrete samples undergoing accelerated ASR and FT cycles. Nonlinear parameters extracted from the two tests show good agreement; all exhibiting far more sensitivity to distributed FT damage than standard resonance frequency measurements.