Ultrasonic frequency-dependent amplitude attenuation characteristics technique for nondestructive evaluation of concrete

This paper presents a new ultrasonic method, frequency-dependent amplitude attenuation characteristics technique (FACT), for studying the effects of grain size and distributed microvoid damage upon the P-wave amplitude attenuation characteristics of concrete, while performing the contact-type, through-transmission nondestructive evaluation. It is demonstrated that the normalized amplitude attenuation characteristics under a wide range of exciting frequencies using the proposed FACT method are essentially not affected by the ultrasonic power amplifier system setting or the uncontrollable external disturbances, such as the concrete cylindrical surface contact conditions and forces. In addition, the proposed FACT methodology is significantly more sensitive on detecting the internal microstructural changes caused by distributed microvoid damage than the P-wave velocity method. Laboratory-cast concrete cylinders with various aggregate sizes are tested to demonstrate the grain size effects on the normalized P-wave amplitude attenuation profile. Furthermore, different volume fractions of small Styrofoam particles are mixed into laboratory-cast mortar and concrete cylinders to elucidate the effects of different degrees of controlled damage on the normalized P-wave amplitude attenuation characteristics. All ultrasonic amplitude measurements are obtained with a pair of broadband piezoelectric transducers with frequencies ranging from 100 to 1000 kHz. FACT is highly repeatable and consistent at the same material points and, therefore, appears promising for the nondestructive evaluation (NDE) of concrete.