Dynamic Property Determination for Early-Age Concrete

This paper reports the test results of the dynamic modulus of elasticity and Poisson's ratio of concrete at early age by means of nondestructive evaluation. The dynamic modulus 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 (FFT) analyzer. The measurement was conducted on concrete cylinder specimens. The dynamic modulus and Poisson's ratio were calculated using the first two natural frequencies of a cylinder. The measured dynamic response showed very 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 dynamic modulus. 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.