Alligator Cracking on Bibi New Test Road and Fatigue Test Results for Asphalt Mixtures in the Laboratory

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This study describes fatigue failure characteristics of asphalt mixture and asphalt-layer design. We conducted long-term performance measurements on Bibi New Test Road and a four-point bending fatigue test in the lab. The test road was constructed in 1990 as part of National Highway 36 in Hokkaido, Japan. The test road consists of eight sections with a different total thickness of asphalt-layer and a different asphalt mixture at the bottom asphalt layer. It was subjected to a daily average of 2,441 repetitions of a 49-kN equivalent wheel load. Alligator cracking first appeared in 2001. The study and its results follow.
1) Fatigue cracking was observed on the four sections whose bottom asphalt layer is of coarse-graded asphalt concrete Type B(poor asphalt type). Fatigue cracking did not appear in
the sections whose total asphalt-layer thickness was the same as the sections with cracking but whose bottom asphalt layer was coarse-graded asphalt concrete Type A (normal type) or
dense-graded asphalt concrete, which demonstrates that cracking resistance differs according to the fatigue failure characteristics of mixture used for the bottom layer of asphalt concrete.
2) The four-point bending fatigue test revealed that the number of loadings to reach fatigue failure of different asphalt mixtures differed by a statistically significant degree. The lab test
results agree well with the results observed at Bibi New Test Road.
3) To reduce life-cycle cost, the bottom asphalt layer must incorporate an asphalt mixture with a high fatigue-failure resistance.