Noncontact surface wave testing of pavements using microphones.

Pavements are constructed using several layers of materials, and their durability depends mainly on the stiffness modulus and thickness of these strata. Surface wave testing is an effective tool to measure the stiffness and thickness of pavement layers. However, measurements are still based on spot testing with fixed receivers and source. The typical large size of pavements and the cost of closing down roads to make stationary testing makes these measurements impractical. We present experiments where a multichannel array of microphones and an automatic source are attached on a small trolley so that measurements can be taken almost continuously while moving. Measurements on asphalt or concrete pavement layers are based on supersonic leaky air-coupled surface waves. We also demonstrate that the same approach can be applied to softer granular pavement layers utilizing the seismic-to-acoustic coupling in poroelastic materials. Results show that microphones can be successfully used to measure correct surface wave dispersion curves even while moving along the surface. This opens up the possibility for faster on-the-fly surface wave testing of pavement layers since surface contact is no longer required. The theoretical background along with experimental results of the application to nondestructive testing of pavements will be presented