NDE of two-layered mortar samples using high-frequency Rayleigh waves.

Area of Science:

• Civil Engineering
• Geophysics
• Materials Science

Background:

• Spectral Analysis of Surface Waves (SASW) images subsurface ground conditions using Rayleigh wave dispersion.
• SASW is adapted for civil engineering to detect subsurface damage in concrete structures.
• Damage involves a thin, porous surface layer, susceptible to aggressive agent penetration.

Purpose of the Study:

• To adapt the SASW technique for characterizing subsurface damage in concrete structures.
• To investigate the feasibility of using high-frequency Rayleigh waves for thin layer analysis.
• To validate signal processing methods on simulated and experimental data.

Main Methods:

• Generation of 0.5 MHz Rayleigh waves using the wedge method on two-layered mortar samples.
• Acquisition of phase velocity dispersion curves via broadband phase spectroscopy.
• Validation of signal processing with simulated data and comparison with Haskell's two-layered model.

Main Results:

• Measured dispersion curves generally align with theoretical predictions for a two-layered medium.
• High frequencies (hundreds of kHz) are required due to the thin damaged layer, leading to attenuation.
• A three-layered, visco-elastic model is suggested for improved accuracy.

Conclusions:

• SASW shows promise for detecting concrete cover damage.
• Accurate characterization requires advanced modeling, potentially a three-layered visco-elastic approach.
• Further refinement of SASW for thin layer damage assessment in civil structures is warranted.