Geophysics: Impact Echo Concrete Testing
Impact-Echo (IE) surveys are performed in general accordance with ASTM International (ASTM) C1383, “Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method.” The purpose of IE Testing is to nondestructively detect presence of concrete flaws, such as voids, delamination cracks, asperities, or honeycombing.
The Impact-Echo instrument includes an IE scanner that is connected to a field computer for digital data collection, processing, and storage.
The IE test head sensor is held on the surface of the concrete while a relatively light weight hammer is used to impact the top of slab concrete surface. The hammer strike generates a compressional velocity wave that is transmitted through the concrete near the scanner. The generated time domain compressional wave is processed using a Fast Fourier Transform (FFT) to obtain a peak frequency in the frequency domain, which corresponds to the depth or thickness of the concrete. If multiple frequency peaks are obtained, possible concrete flaws or anomalies may be present, such as cracking, voids, honeycombing, and/or delaminations of the concrete. The frequency peaks and their associated amplitudes are evaluated in the frequency domain to evaluate the depth and nature of the possible concrete flaw. In general, low amplitude and high frequency flaws may potentially indicate a concrete flaw. As with any geophysical method, the detection and interpretation of an anomalous object is a function of the size, depth, and geometry of the object.