An investigation was made to determine the location along the centerline of the axle of the maximum strain energy density, or work, in the pavement as defined by classical physics. The location is under the inside edge of either dual tire. The most influential strain was the shear component. The distribution of shear strains and stresses with depth through the full-depth asphaltic concrete and into the subgrade was investigated. Using Simpson's rule for an even number of increments, or using the trapezoidal rule, allows the summation of strain energy density calculated at various depths. This sum multiplied by a unit volume converts the strain energy density to work as defined by classical physics. The sum of work throughout the pavement structure provides a greater insight to the behavior of the pavement because all components of strain, or stress, are considered and the variation throughout the depth may be large according to the location within the tire print. The sum of strain energy density is much greater under the edge of the dual tire compared to that under the center of the dual tire, yet the magnitude of the strain energy density at the bottom of the asphaltic concrete may be nearly identical. For an 18-kip (80-kN) four-tired single axleload, the depth of maximum shear is approximately 35 to 40 percent of the thickness from the surface downward for a maximum pavement thickness of approximately 8 inches (203 mm); thereafter the depth of maximum shear moves toward the surface as the thickness increases. An investigation of shear stress indicated the maximum value was approximately 67 psi (0.46 GPa) due to an 18-kip (80-kN) single axleload and tire contact pressure of 80 psi (0.63 GPa). For an 80-kip (36-kN) tandem axleload and tire contact pressures of 100 psi (0.69 GPa), the shear stress increased o approximately 133 psi (0.92 GPa). As the tire contact pressures of 100 psi (o.69 GPa), the shear stress increased to approximately 133 psi (0.92 GPa). As the tire contact pressure increases, the shear stress may approach 200 psi (1.38 GPa).

Recommendations include eliminating any construction plane between the 1- to 4-inch (25– to 102–mm) depth from the surface and determining the shear resistance of the asphaltic concrete mix to insure that the mix can withstand a higher shear stress that is currently being obtained. Target values of shear stress have not been recommended for adoption because a limiting value has not been found in the literature.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, the Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.