Standard Test Method for Non-Contact Measurement of Resonant Frequencies of Concrete Cylinders

Importancia y uso:

5.1 While this test method serves a similar purpose as Test Method C215, attachment of a vibration sensor to the cylinder is not required, and requirements for preparing and supporting the specimen for testing are different. Smartphones or tablet computers can perform the required data acquisition, signal analysis, display, and result storage functions. Therefore, this test method does not require expensive instrumentation nor extensive specimen preparation. The specimen is not damaged and can be tested repeatedly over time to track the development of material properties.

5.2 This test method requires that the cylinder be allowed to vibrate freely without constraint. This is accomplished by supporting the cylinder on a soft material, such as a sponge foam pad or folded towel. The mode of vibration is influenced by where the cylinder is struck with the impactor. For transverse vibration, the cylinder is struck at its mid length and perpendicular to the length axis. For longitudinal vibration, the cylinder is struck perpendicular to one of its end faces. A misaligned impact may excite multiple modes of vibration.

5.3 For a given concrete mixture, the resonant frequency at the time of testing depends on the actual cylinder dimensions. Variations in dimensions of cylinders made from the same concrete mixture can result in significant variations in the measured frequencies, even though the concrete mixture is the same. If the actual cylinder dimensions differ from the nominal dimensions by more than 1 mm [0.05 in.], the measured dimensions are used to normalize the measured resonant frequency to the frequency of a cylinder with the nominal dimensions (Section 9).

5.4 The measured resonant frequency for the longitudinal or transverse mode of vibration can be used along with the mass and dimensions of the cylinder to estimate the dynamic elastic modulus as described in Test Methods C215 and E1876.

5.5 As concrete matures, material properties such as the elastic modulus will change, and so will the resonant frequency. Therefore, resonant frequencies for specimens of a given size and shape can be used as indicators of changes in mechanical properties of a given concrete mixture. A relationship can be developed between resonant frequencies and compressive strength of a given concrete mixture as described in Appendix X2.

5.6 The principle of the test method and examples of how resonant frequencies of test specimens are related to compressive strength are described in Booth, et al.

Subcomité:

C09.64

Volúmen:

04.02

Palabras clave:

acoustic resonance; cylinder; frequency analysis; fundamental frequency; impact response; impulse excitation; modes of vibration; nondestructive testing;