Abstract
Test results are reported of the dynamic modulus (DM) elasticity and Poisson's ratio of concrete at early age by means of nondestructive evaluation. The DM was measured by a new test apparatus that includes a free-free boundary vibration chamber and a dynamic resonance measurement system with a fast Fourier transform analyzer. The measurement was conducted on concrete cylinder specimens. The DM and Poisson's ratio were calculated using the first 2 natural frequencies of a cylinder. The measured dynamic response showed good consistency and reproducibility. This method enables a measurement of progressive changes in the stiffness of the concrete without damaging the specimen and provides reliable values of DM. It is found that the age of concrete has a significant influence on resonance frequencies; herein, the resonance frequencies shift from lower to higher values in a regular pattern with the age of concrete.
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