X-Ray Computed Tomography Observations Of Low-Noise Mixes

In recent years, low-noise mixes have met with considerable success, as they provide an effective response to a well-identified problem and produced effects that are directly perceptible by residents. The design of mixes that reduce rolling noise is based on the presence of a high voids content. At the same time, there is a tendency to reduce the maximum particle size (D) without sacrificing skidding resistance which remains excellent even in the case of mixes with 0/4 mm aggregate. The focus of conventional mix design tools is on mechanical characteristics which is generally combined, in the case of lownoise mixes, with a measurement of absorption capacities. These methods provide only an overview of the product and knowledge of the voids content, but are unable to characterize the morphology of the voids. Computed tomography can reveal this morphology in detail. This observation technique was tested on ten different mixes. After a brief presentation of the technique and the information it can provide the paper describes the tested mixes and analyzes them in terms of their acoustic performance and the detailed characteristics of their void space.