It consists of two parts, viz., the mechanical ionic pulse velocity method and the ultrasonic pulse velocity method.
The mechanical sonic pulse velocity method consists of measuring the time of travel of longitudinal or compressive waves generated by a single impact hammer blow or repeated blows. The ultrasonic pulse velocity method consists of measuring the time of travel of electronically generated mechanical pulses through the concrete. Of these two, the ultrasonic pulse velocity has gained popularity throughout the world.
The pull velocity methods have been used to evaluate the quality of concrete, concrete strength, durability, Modulus of Elasticity, detection of water, etc.
High pulse velocity readings in concrete are indicative of concrete of good quality. Table 8.15 gives the pulse velocity range of quality of concrete (Leslie and Chessman, 1949, reported by Shetty, 2006).
Table 8.15 Suggested pulse velocity for concrete
Pulse velocity techniques have been used successfully for the detection of cracks. This is possible only when the width of the crack is of considerable depth and of appreciable width. The basic principle in such a situation to detect the crack of the depth is that no signal will be received at the receiving transducers, the pulse will pass around the end of the crack and signal is received at the transducers. However, the pulse would have travelled a distance longer than the straight line path upon which pulse velocity computations are made. The difference in the velocity of pulse is used to estimate the path length and therefore the crack depth. Figure 8.9 illustrates the principle of crack detection.
Figure 8.9 Pulse velocity technique
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