Detection of Concrete Damage Using Ultrasonic Pulse Velocity Method

This paper investigates the efficiency of Ultrasonic Pulse Velocity (UPV) method in detecting cracks and flaws inside the concrete. A series of concrete beams and slab specimens were cast and damaged to simulate the different mechanisms possible in a reinforced concrete deck due to mechanical loading. Two types of simulated cracks, namely, cracks perpendicular and cracks parallel to axis of beam were induced without actually breaking the beam. An ideal vertical crack was simulated by introducing a cut perpendicular to the axis of the beam using a diamond tipped concrete cutter and a real crack was simulated by inserting a thin sheet of plastic while casting the beam. Horizontal cracks were simulated using lower acoustic impedance materials like thermocole and polyvinyl chloride inserted at a known distance while casting the specimen. Materials with less acoustic impedance as compared to that of concrete have good reflectivity and hence would simulate the damage accurately. The results indicate that the pulse velocity method can be used effectively to measure the crack depth of vertical cracks. The depths can be measured with high degree of accuracy, if the distance between the transducers is maintained between 100 200 mm. However, for horizontal cracks, this method does not prove to be accurate and effective in measuring the location of cracks. But within a distance of 100-200 mm between the transducers, the depth of the horizontal cracks can be estimated to a reasonable degree of accuracy. Hence, the distance between the transducers plays a vital role in the accuracy of depth measurement. This is because, if the distance between the transducers is less than 100 mm, then the surface wave reaches the receiver before the reflected compression waves and leads to lower values of depth. Also, if the depth is more than 200 mm, there are possibilities of multiple reflections and hence there is an error in measurement.