Mechanistic interpretation of nondestructive pavement testing deflections

A method is proposed for the backcalculation of material properties in flexible pavements based on the interpretation of surface deflection measurements. ILLI-PAVE, a stress-dependent finite element pavement model, was used to generate data for developing algorithms and nomographs for deflection basin interpretation. Twenty four different flexible pavement sections throughout the State of Illinois were studied. Deflections were measured using the Benkelman Beam, the IDOT Road Rater, the Falling Weight Deflectometer, and an accelerometer to measure deflections under moving trucks. Loading mode effects on pavement response were investigated. The factors controlling the pavement response to different loading modes are identified and explained. Correlations between different devices are developed. Good agreement is achieved between backcalculated material properties and laboratory determined properties. Agreement is also obtained between measured and predicted deflection basins. The backcalculated parameters derived from the proposed evaluation procedure can be used as inputs for asphalt concrete overlay design. (FHWA)