THE USE OF A SINGLE-PARAMETER MODEL TO CHARACTERIZE THE CONDITION OF ASPHALT SURFACES

In this paper, a technique is presented for characterizing the condition of an asphalt surface by use of a single parameter. Comprehensive measurements of grazing incidence sound propagation over two asphalt surfaces, both before and after application of a sealant, are also presented. The measurements have been compared to predictions made using a theory that depends on a single parameter, the effective flow resistivity. The effective flow resistivity is considered here to account for the net effect of many physical factors, including the actual flow resistivity, tortuosity, and porosity of the surface. Grazing incidence sound propagation trials were performed using a broadband point source and a microphone placed directly on the asphalt surface. Measurements were made over distances between 0.1 m and 12.8 m, and over the frequency range of 1 kHz to 20 kHz. Effective flow resistivities for the surfaces were estimated by matching measured propagation results with parameterized theoretical predictions. It was found that estimates of the effective flow resistivity could be used to distinguish between asphalt surfaces having different surface treatments. It was thus concluded that flow resistivity estimates based on grazing incidence propagation trials may be used to monitor inter-site consistency and long term surface stability at a single site. The single-parameter theory was also found to reproduce the trends of the measured data; however, the estimates of the effective flow resistivity were seen to vary systematically with the distance and frequency ranges over which the theory and measurements were matched. Therefore, if the conditions of various asphalt surfaces are to be compared on the basis of effective flow resistivities inferred from grazing incidence propagation measurement, the frequency and distance range over which the theory is fitted to the measured data must be chosen consistently.