Detecting the reinforced concrete beam/column joints by ultrasonic wave and impact-echo methods

This paper used an ultrasonic wave method and an impact-echo method to measure pressure wave velocities in full scale columns,block specimens with different thickness,cruciform specimens,and beam/column joints by obliquely placing transducers on the opposite faces.The results were then compared with those by direct measurement using an ultrasonic device to evaluate the accuracy of oblique measurement.The feasibility of quality evaluation for the concrete at the beam/column joint using the measured pressure wave velocities by oblique measurement was discussed.The test results showed that,the measured wave velocity went down sharply when the wave receiver deviated more than 40 cm for the measurement on a 40 cm width full scale column by the ultrasonic wave method.However,the measured wave velocity would begin to go down when the wave receiver deviated more than 70 cm using a 3 mm diameter steel ball as the impacting wave source by the impact-echo method.Using a 6 mm diameter steel ball,the deviation distance could reach up to 100 cm.Using a 9 mm diameter steel ball or a small hammer,the measured wave velocity would not go down even when the deviation distance was up to 300 cm.All test results on the specimens showed that,the wave velocity measured by the ultrasonic wave method basically went down when the deviation distance of the receiver increased,but the wave velocity measured by the impact-echo method was not affected.When compared with ultrasonic direct measurement,the wave velocity errors of the impact-echo method were well within ±3%.