NONDESTRUCTIVE TESTING OF CONCRETE STRUCTURES USING THE RAYLEIGH-WAVEDISPERSION METHOD

This paper presents the Rayleigh wave dispersion method, which shows g reat potential for nondestructive testing (NDT) of concrete structures . Its application allows both the determination of stiffness profiles within a structural element and monitoring of concrete curing as a fun ction of time and depth. The method constitutes on improvement over co nventional stress-wave techniques used in NDT of concrete structures t hat are capable of determining only average wave velocity along a spec ific path. Thus, conventional methods can neither evaluate changes in material qualities (e.g., stiffness) with depth, nor the position of d efects within a layered section. This novel method also called the spe ctral analysis of surface waves (SASW) method is based on the generati on of low-amplitude Rayleigh waves at a broad range of frequencies fro m which shear wave velocities and elastic moduli profiles are determin ed. The method was developed primarily for determining stiffness profi les and thicknesses of ''larger'' layered systems that satisfy conditi ons for an infinite half-space, such as layered soils. Nevertheless, t he method has already been successfully used in flexible pavements and concrete elements satisfying conditions for an infinite half-space, s uch as concrete tunnel liners. This suggests that the SASW method coul d be successfully employed for Nor of other concrete elements. The goa l of the reported research was to evaluate if this method could be use d for NDT of concrete structural elements that do not satisfy conditio ns for an infinite half-space. Presented in this paper are basic conce pts of the SASW method results of a nondestructive evaluation of a mod el concrete wall using the SASW method and directions for future resea rch.