Comparison of Moduli of Kansas Superpave Asphalt Mixes

Abstract

Currently, hot-mix asphalt (HMA) mixture design and pavement structural design are not fully integrated, although Superpave® asphalt mixture design is somewhat project specific. The objective of this study was to compare elastic moduli assumed during structural design of pavements with the backcalculated moduli of HMA layers obtained from the falling weight deflectometer (FWD) tests and the dynamic modulus values measured in the laboratory. Five newly built Superpave pavements, designed by using the 1993 AASHTO Design Guide, were selected as study sites in this research. Deflection data were collected with a Dynatest 8000 FWD on a 1,000-ft test section at each site. The HMA layer moduli were then backcalculated by using an elastic-layer analysis program. Full depth cores were taken from each section and tested in the laboratory for dynamic moduli. The results showed that backcalculated and laboratory moduli were somewhat comparable for all practical purposes. The laboratory dynamic moduli increased with the loading frequency, indicating the need for consideration of vehicle speeds in the HMA pavement structural design. HMA design moduli, assumed by the Kansas Department of Transportation during pavement structural design, are lower than both backcalculated and laboratory dynamic moduli. Thus, current HMA design moduli are achievable in the field through Superpave mixture design, despite the fact that the pavement structural design and mix design processes are not integrated.