As mentioned earlier, an acceleration transducer can be used for the purpose of this test. As an alternative, the average can be determined and used. The reflected echoes are then recorded for each individual impact. The distance between the impact location and the sensor should be no larger than 300 mm. Several impacts are applied to the top of the pile. The integrity testing should be performed no sooner than 7 days after casting or after concrete strength achieves at least 3/4 of its design strength, whichever occurs earlier. The location of the sensor should be selected away from the edges of the pile. At the minimum, an acceleration transducer should have an Analog to Digital Converter with 12-bit resolution and a Sample Frequency of at least 25 KHz. Acceleration, velocity, or displacement transducers can be used for this purpose. Motion transducers should be capable of detecting and recording the reflected echoes over the pile top. An impactor (usually a hand-held hammer) is used for impacting pile head the impact should be applied axially with the pile. To do so, a couplant material should be used to attach the acceleration sensor the pile head. The acceleration sensor should be placed on concrete firmly. This step is very important because the connection between the sensor and concrete should be solid. The pile head surface should be accessible, above water, and clean of loose concrete, soil or other foreign materials resulting from construction. Initially all types of contamination should be removed to reach a solid and sound concrete surface.
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