Nonlinear Elasticity in Concrete Structures: Toward In-Situ Methods for Integrity Assessment

Abstract

Decades of research on small-scale concrete specimens—such as cores and beams—have demonstrated that concrete, a highly heterogeneous material, exhibits elastic nonlinear effects, namely the stress- and time-dependence of its elastic properties. These nonlinear effects are highly sensitive to the presence of heterogeneities, even at the milli- or nanoscale. Prior studies have proposed leveraging these nonlinear elastic effects as a nondestructive testing method for detecting small-scale damage in concrete structures. However, formalizing such techniques for real-world applications requires transferring knowledge from controlled laboratory conditions to field settings. This research extends the study of nonlinear elastic effects to a full-scale concrete structure under field conditions. Specifically, it investigates the presence of classical and nonclassical nonlinear elastic behaviours—the acoustoelastic effect and Slow Dynamics, respectively—and their relationship with the relative integrity level of a concrete test bridge. Through an experiment conducted to measure vibrations across multiple frequency bands, this work demonstrates that soft microstructures—associated with varying levels of structural integrity—can be identified using nondestructive, wavefield-based measurement techniques. These findings contribute to the investigations for the development of in-situ methods for early-stage damage detection in existing and new concrete infrastructure.