Nondestructive evaluation of steel-concrete composite structure using high-frequency ultrasonic guided wave

Steel-concrete modular construction is increasingly used in nuclear structure construction. Conventional nondestructive testing methods are not able to detect internal concrete defects because the thick concrete wall is covered by steel plates. An ultrasonic guided method is proposed to detect honeycombs and voids around cross tie bars by using the tie bar as the waveguide. Guided wave dispersion curves are analyzed for the two-layer system (tie bar embedded in concrete). The high order longitudinal mode L(0,8) is selected as the working mode due to its lowest attenuation. Ultrasonic attenuations were measured on naked bars and bars embedded in concrete. Material damping coefficients of the steel bar were calibrated on the naked bar. Three tie bars with different bonding conditions in concrete (solid, with honeycomb and void) were tested at early age, 7 days and 110 days. The experimental results demonstrate that ultrasonic guided wave attenuation can be used to identify internal defect and evaluate the tie bar/concrete bonding condition at both early and late ages.