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A nondestructive testing (NDT) method to detect internal cracks in concretestructures is presented. The method is based on the dynamic response of flawed concretestructures subjected to impact loading. The present method uses non-contacting devices forboth impact generation (a shock tube producing shock waves) and response monitoring(laser vibrometers measuring concrete surface velocity). Experimental and numerical(finite element) studies are carried out for concrete specimens containing artificial defects(penny-shaped cracks parallel to the free surface) with varying length and depth. It is seenthat the present method enables an effective detection of defects, particularly in the rangeof shallow defects.