An Investigation of Pump-Induced Conditioning in NCWI of Concrete

Coda Wave Interferometry (CWI) is a highly sensitive ultrasonic method for damage detection, but it often fails to see elastic nonlinearities such as closed cracks. Nonlinear Coda Wave Interferometry (NCWI) addresses this by using a high-amplitude, low-frequency pump to transiently open closed cracks, allowing their detection using high-frequency CWI probes. Despite the successful implementation of NCWI for damage monitoring in concrete, the impact of ‘non-equilibrium dynamics’ on NCWI measurements remains unexplored. In particular, conditioning effects induced by the pump could significantly influence the results, yet these effects have not been systematically studied; this is the gap addressed by this study through a series of controlled experiments conducted inside an environmental chamber. By accounting for this critical phenomenon, this work aims to enhance the reliability and accuracy of NCWI techniques, paving the way for its widespread applications in structural health monitoring.