Use of Rayleigh wave methods to detect near surface concrete damage: Fid-Bau Portal

Use of Rayleigh wave methods to detect near surface concrete damage

Wardany, R. Al / Rhazi, J. / Ballivy, G. / Gallias, J.L. / Saleh, K.

Massive concrete structures, like dams, are often subjected to aggressive attacks. Weathering actions, temperature variation, chemical attacks, abrasion and other degradation processes, can act simultaneously on the concrete surface and minimise its durability. The maintenance and rehabilitation of the near surface damaged concrete zone, require a good evaluation of its degradation depth. The use of Rayleigh waves in non invasive methods, appear to be a promising approach for the determination of concrete stiffness profile. Based on the SASW method, advances in the determination of more robust resultant dispersion curve using a limited number of sensors (six accelerometers) were presented in this paper. This way of analysis aims to make easy test setup and to give more reliable results: there is no need to inverse the source position and to change the distance between receivers as required for the SASW test setup. Accuracy of this approach was approved to test concrete homogeneity and to detect poor surface concrete quality, voids, and horizontally cracking planes on concrete volumes. A new multistation Rayleigh wave method was developed in this study for concrete non destructive testing. The method considers a 2D-FFT transformation of the wavefield energy from the time-space plane to the frequency-wavenumber domain to identify existing Rayleigh wave modes. The extracted fundamental mode will be inverted using forward modeling to determine the appropriate shear wave velocity profile. This technique may be used when there is multimode propagation of Rayleigh waves through layered system. Comparison of the experimental and theoretical dispersion curve shows excellent agreement and reliable model. The proposed new method demonstrates high potential to characterize concrete stratification and determine thicknesses ever if variations in Young modulus profile are small.