Diffuse ultrasound monitoring of stress and damage development on a 15-ton concrete beam

Abstract

This paper describes the use of an ultrasonic imaging technique (Locadiff) for the Non-Destructive Testing & Evaluation of a concrete structure. By combining coda wave interferometry and a sensitivity kernel for diffuse waves, Locadiff can monitor the elastic and structural properties of a heterogeneous material with a high sensitivity, and can map changes of these properties over time when a perturbation occurs in the bulk of the material. The applicability of the technique to life-size concrete structures is demonstrated through the monitoring of a 15-ton reinforced concrete beam subject to a four-point bending test causing cracking. The experimental results show that Locadiff achieved to (1) detect and locate the cracking zones in the core of the concrete beam at an early stage by mapping the changes in the concrete's micro-structure; (2) monitor the internal stress level in both temporal and spatial domains by mapping the variation in velocity caused by the acousto-elastic effect. The mechanical behavior of the concrete structure is also studied using conventional techniques such as acoustic emission, vibrating wire extensometers, and digital image correlation. The performances of the Locadiff technique in the detection of early stage cracking are assessed and discussed.

Three-dimensional in-situ imaging of cracks in concrete using diffuse ultrasound

“…Their locations are in good agreement with observations made onsite at the outer surface (Fig. 1c), within a spatial uncertainty that corresponds to the Note that a data exclusion criterion was introduced based on the resolution index of the inverted model 16 . A resolution index reported by Vergely et al 22 is calculated to evaluate the quality of the inverted model: the more this index is close to one, the better the inverted model corresponds to the expected one 23 .…”

“…std m is determined using the L-curve method so as to determine the best trade-off between the regularization of the model and the data fitting 21 . For more technical considerations about the inversion approach, the reader is invited to refer to previous works 16 .…”

Detecting damage events in concrete using diffuse ultrasound structural health monitoring during strong environmental variations

“…These sensitivity kernels can be used in inversion procedures, such as the LOCADIFF algorithm, for locating local changes to the material. [7][8][9][10][11] In concrete, one issue with CWI and ultrasonic methods in general is the high attenuation of highfrequency waves, caused by both scattering and intrinsic absorption. This attenuation, combined with often noisy environments for civil structures, means that the transducers cannot be separated by large distance before the signal-to-noise ratio (SNR) decreases below useful levels.…”

Monitoring Local Changes in Granite Rock Under Biaxial Test: A Spatiotemporal Imaging Application With Diffuse Waves

“…We find that the maximum value of scattering cross‐section σ reaches 4 m 2 /m 3 . This number has to be compared to previous works during mechanical experiments using intact concrete (Larose, Obermann, et al, ; Zhang et al, ) that found structural changes of the order of (0.1 ∼ 1 m 2 /m 3 ) for cracks developing in concrete. In the case of granite, there exists no specific experiment to compare to, so it is hard to discriminate which part of σ is due to reversible microdeformation and which part of σ is due to irreversible damage/microcracking developments.…”

“…Recently, a time‐lapse differential tomography technique named Locadiff (Larose et al, ) was developed to explore spatiotemporal changes based on analytical diffuse sensitive kernels together with a linearized inversion technique. Although Locadiff is still an ongoing project, the performance of this method was assessed through numerical studies (Pacheco & Snieder, ; Planès et al, ) and applied to imaging velocity changes and structural changes both in seismology (Obermann et al, , ) and in nondestructive testing and evaluation (Larose, Obermann, et al, ; Zhang et al, ). Using another inversion procedure, it even showed a potential to image high‐resolution subwavelength (∼1/15 λ , λ = 0.75 mm) changes (Xie et al, ).…”