Damage evaluation in freezing and thawing test of concrete by elastic-wave methods

In the freezing and thawing test of concrete, elastic-wave methods are applied to estimate the frost damage nondestructively. Recently, two test methods are proposed in the RILEM recommendation. The alternative method A is based on the ultrasonic test, which measures the transmission time of the longitudinal wave (P wave), while the alternative method B measures the resonant frequencies of vibrations. With relation to these methods, evaluation of the frost damage by the elastic-wave methods is studied, focusing on the dynamic modulus of elasticity. The freezing and thawing tests were conducted by employing concrete samples after 1 year curing. As a result, the samples were not heavily damaged even after 300 cycles. Concerning the resonant frequencies of concrete samples, a three-dimensional analysis is performed by the boundary element method to identify actual vibration modes. It is clarified that an assumption of the one-dimensional resonant vibration is not applicable, resulting in a false discrepancy between the dynamic modulus and the static modulus of elasticity. It is found that relative modulus obtained from P-wave velocity is comparable to that from the tangential modulus of elasticity in the compression test, and is reasonably recommended to estimate the frost damage nondestructively.