ABSTRACT
The testing of concrete structures has posed many problems. Conventional ultrasonic transmission and pulse echo methods have limitations due to the nature and composition of concrete since they cause multiple reflections and non-direct ray paths. Alternative ultrasonic methods have been recently investigated that examine the shape of the waveform as it traverses through or over a complex material, the idea being not to located a single defect but to determine the overall mechanical properties within a certain region. These methods are known as Nonlinear Elastic Wave Spectroscopy (NEWS). Lacouture (Lacouture et al 2003) details a NEWS method to monitor the curing process of concrete, by means of transmitting and receiving an 8 kHz sine wave signal through the setting concrete. Van Den Abeele (Van Den Abeele et al 2001) outlines various NEWS techniques to measure micro-scale damage in building materials, including concrete. In one of the NEWS methods two different frequencies are transmitted into the material via two separate transducers and a third transducer is used as a receiver.
