Attenuation measurements in cement-based materials using laser ultrasonics

This research uses laser ultrasonic techniques to quantify the frequency-dependent attenuation losses of Rayleigh waves in cement-based materials; these materials are heterogeneous in nature, and this heterogeneity is seen at multiple length scales. As a result, ultrasonic waves that propagate in cement-based materials exhibit a high degree of (material) 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 tosses due to material heterogeneity. The high fidelity, large frequency bandwidth, and absolute, noncontact nature of laser ultrasonics makes this an ideal methodology to measure attenuation in these materials. This research uses a dual-probe, heterodyne interferometer to experimentally measure these attenuation losses las a function of frequency in three different materials: (1) aluminum; (2) mortar; and (3) granite. The aluminum results (aluminum is homogeneous at the wavelengths used here) 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 attenuation losses present in each material.