Nondestructive integrity analysis of multi-layer portland cement mortar slabs using spectral analysis of surface wave method

The SASW nondestructive test method was mainly developed and used in geotechnical engineering field such as examining the material properties of pavement systems, soil media, etc., under an infinite half-space condition. Active researches have been devoted to this area to understand the applicability and limitations of this method in recent decades. The current study is focusing on applying the SASW method in structural engineering field such as the single- and multi-layer cement mortar slab systems of finite thickness to understand the behavior of surface wave, mainly Rayleigh wave, together with resonant frequency test, impact-echo test, and cylinder test.; The SASW method consists of generation, measurement and processing of dispersive surface waves. The test can be implemented using the instrumentation of a small steel ball as an impact source, two vertical receivers and a recording device to analyze the behavior of the surface waves. One major advantage of the SASW method is that it requires only one side of access of the tested subject. This study is mainly interested in finding the surface wave velocity to correlate it with material properties and finding the shear wave velocity which can in turn be used to find the shear modulus and the modulus of elasticity based on the forward modeling.; The SASW method was used to analyze single-layer cement mortar slabs of different strengths to correlate their surface wave velocities to the compressive strengths. The detection of free boundaries was studied using the SASW method and linear spectrum analysis. To detect damages (delaminations) inside a slab, two two-layer slab systems, one with delamination and the other without delamination inside the slab, were examined and compared. The assessment of the accuracy of the compact dispersion curve and the theoretical dispersion curve were performed using two- and three-layer slab systems. The dispersive characteristics of multi-layer slab systems with finite thickness were studied using the SASW method. Numerical simulation using the finite element dynamic analysis was performed and the obtained accelerations and dispersion curves, etc., were compared with experimental results. Finally, a neural network was used to improve the drawbacks of the forward modeling in the SASW method.