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An experimental pavement approximately 200 m (650 ft) long was constructed in May of 1978 consisting of a 19-mm (0.75-in.) triple surface treatment over a 460-mm (18 in.) crushed-stone base. By 1985 the pavement had been subjected to about 1.4 million equivalent 80 kN (18 kip) American Association of State Highway and Transportation Officials (AASHTO) single-axle loads neglecting front axle effects. The straight segment of the pavement had a present serviceability rating of 3.0 to 3.5 in 1985. About 6.5% surface cracking had developed mostly within the last two years (1984 to 1985). The pavement is constructed on a clayey and sandy silt subgrade which is relatively dry and has a field California bearing ratio (CBR) of 10. The crushed stone base is well graded, has a maximum aggregate size of 30 mm (1.5 in.), and contains less than 2.0% fines. Field tests performed on the pavement included static plate load tests, Benkelman beam, surface strain measurements, and falling weight deflectometer (FWD) tests.
Using the AASHTO design method, a base course layer coefficient for the upper 305 mm (12 in.) was backcalculated to be 0.18, and 0.16 for the remaining stone base. The elastic modulus of the base was backfigured from the FWD test results to be 406 MN/m2 (59 ksi) using the Waterways Experiment Station (WES) approach; other methods of backcalculation gave widely varying results. The elastic moduli of the base and subgrade depend upon the test method and also the mean stress and shearing strain to which the material is subjected. Because of the difference in loading conditions, the elastic modulus of the base will be somewhat lower under a dual-wheel, 80-kN (18-kip) axle loading than under the single, 40-kN (9-kip) FWD test loading.
field investigations, pavements, pavement design, pavement condition, performance evaluation, performance
Georgia Institute of Technology, Atlanta, GA
Subsurface Investigations, Inc., Charlotte, NC
Waterways Experiment Station, Vicksburg, MS
Vulcan Materials Company, Birmingham, AL