Effect of Aggregate Size on Attenuation of Rayleigh Surface Waves in CementBased Materials

This research uses laser ultrasonic techniques to study the effect of aggregate size on the attenuation of Rayleigh surface waves in cement-based materials. The random, multiphase, and heterogeneous nature of cement-based materials causes a high degree of material attenuation in the ultrasonic waves that propagate in these materials. Physically, these attenuation losses are due to a combination of absorption and the scattering losses due to material heterogeneity. Laser ultrasonics is an ideal methodology to measure attenuation in these materials because of its high fidelity, large frequency bandwidth, and absolute, noncontact nature. To investigate the effect of aggregate size on attenuation, this research uses a dual-probe, heterodyne interferometer to experimentally measure attenuation losses (as a function of frequency) in five different material systems (each with a different microstructure). These experimental results show that absorption, not scattering from the aggregate, is the dominant attenuation mechanism present in cement-based materials. As a result, aggregate size does not dominate attenuation.