Evaluation of compressive damage in concrete using ultrasonic nonlinear coda wave interferometry

Area of Science:

• Materials Science
• Civil Engineering
• Geophysics

Background:

• Concrete exhibits slow dynamics, a stiffness decrease and logarithmic recovery after mechanical stress, complicating damage assessment.
• Nonlinear coda wave interferometry (NCWI) is a technique sensitive to material nonlinearity, potentially useful for damage detection.
• Compressive stress in concrete induces nonlinear elastic effects that can be probed by wave propagation methods.

Purpose of the Study:

• To investigate the feasibility of nonlinear coda wave interferometry (NCWI) for evaluating compressive damage in concrete.
• To analyze the interference effects of compressive stress-induced slow dynamics on NCWI measurements.
• To establish a reliable indicator for concrete compressive damage using NCWI.

Main Methods:

• Experimental validation of NCWI on concrete specimens under varying compressive stress.
• Characterization of slow dynamics phenomena and its impact on wave propagation.
• Development and application of an efficient nonlinear level indicator (αdv/v).
• Comparative analysis using conventional coda wave interferometry (CWI) and direct wave interferometry (DWI).

Main Results:

• Slow dynamics in unloaded concrete significantly interfere with NCWI, exhibiting opposite dv/v changes compared to pump waves.
• After mitigating slow dynamics, the efficient nonlinear level (αdv/v) strongly correlates with compressive damage.
• The developed indicator (αdv/v) decreases proportionally with increasing compressive stress.
• NCWI demonstrated superiority over CWI and DWI in evaluating concrete compressive damage.

Conclusions:

• NCWI is a feasible and effective method for assessing compressive damage in concrete.
• Understanding and mitigating slow dynamics interference is crucial for accurate NCWI results.
• The efficient nonlinear level (αdv/v) serves as a reliable quantitative indicator for concrete damage evaluation.