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This paper presents a comparison of pavement layer moduli determined from backcalculation with those measured in the laboratory on asphalt concrete (AC) and granular base materials. Deflection data and pavement materials obtained from two conventional flexible pavement structures were used. Pavement surface deflections were measured with a Falling Weight Deflectometer and were used in backcalculation analysis to determine pavement layer moduli. AC cores and granular materials from the base layer were taken for testing in the laboratory to determine resilient modulus in accordance with established ASTM testing procedures. The comparison of backcalculated and laboratory measured moduli for two pavement structures showed that for the AC surface layer the backcalculated moduli were generally lower than the laboratory measured at the same temperature; the difference was in a range of 20 to 30 percent. The backcalculated moduli also seemed to be less susceptible to temperature variation. For the base aggregate materials, the backcalculated moduli exhibited tendency of stress dependency similar to those measured in the laboratory. In the range where actual pavement stresses generally fall, a favorable comparison was observed, indicating that the modulus-stress relationship determined from backcalculation could be used in the analysis of nonlinear property of granular base materials.
Resilient modulus, backcalculation, asphalt concrete, aggregate base
Senior Engineer, Law PCS, Reno, Nevada