Study of the propagation of Rayleigh waves in cement-based materials using laser ultrasonic techniques

The thrust of this research is to determine the feasibility of using laser ultrasonic techniques to experimentally characterize the propagation of Rayleigh surface waves in cement-based materials. Since cement-based materials are heterogeneous (multiphase) and consist of multiple length scales, ultrasonic waves propagating in these materials will exhibit material dispersion and attenuation losses. Physically, these attenuation losses are a combination of internal friction, such as the work done at material interfaces (ultrasonic absorption) and the scattering losses due to material heterogeneity.; The high fidelity, large frequency bandwidth, and absolute, non-contact nature of laser ultrasonics makes this an ideal methodology to study the propagation of Rayleigh waves in these materials. This research uses a dual-probe, heterodyne interferometer and a pulse laser source to experimentally measure attenuation losses (as a function of frequency) in cement-based materials.; First, a set of benchmark experiments are conducted to determine the feasibility, accuracy and repeatability of the proposed experimental procedure. This preliminary study examines three different material systems: aluminum, mortar and granite. The aluminum results (aluminum is homogeneous at these wavelengths) are used to demonstrate the fidelity of the laser ultrasonic measurement technique, while the mortar and granite results (both are heterogeneous at these wavelengths) are used to quantify the frequency-dependent attenuation losses present in each material. The experimental procedure uses a multi-station methodology, which utilizes the second probe to guarantee that all the waveforms are generated with the same (repeatable) source.; Next, a study is conducted that quantifies the effect of aggregate (scatterer) size on measured attenuation losses; this work studies five different material systems, each with a different dominant length-scale. This study quantifies the high level of variability present in a local volume of material and determines a reliable, global measure of frequency-dependent attenuation for each material system. The results of this study show that scattering losses are small compared to absorption losses and aggregate size is not the critical microstructural feature in determining attenuation losses.; The results of this thesis show that it is possible to measure attenuation losses and relate these values to the microstructure of the specific cement-based material being interrogated.