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Nondestructive pavement testing by way of dynamic deflection measurements with, for example, a falling weight deflectometer (FWD) is a widely accepted procedure the world over.
The measured deflection bowl can be used as an overall yardstick for the structural condition of the pavement. However, when the deflection bowl is used for the determination of the moduli, major errors can be made, especially when using backcalculation procedures. In the case of semirigid pavements (or, in general, of pavements where the modulus of the base is of the same order as the modulus of the upper layer), the deflection bowl does not provide all the information required for the separate calculation of the right moduli for the asphalt layer and the bound base layer.
It is recommended to determine the modulus of the asphalt layer or base layer by other (for example, laboratory) tests and to use this modulus as a fixed value in the backcalculation procedure. However, precautions should be taken if cracks are present in the layer(s).
falling weight deflectometer, backcalculation procedure, semirigid pavements, deflection bowl
Technical-scientific staff member, Ministry of Transport and Public Works, Delft,