With regard to the DWPA test, the appropriate evaluation index still requires further discussion.
However, the DWPA test provides more severe test conditions, which means that direct application to the calculation method in Chinese standard may cause error.
According to the calculation results shown in Table 4, we found [C.sub.DWPA] to be smaller than the dynamic stability of the Chinese standard rutting test, as the weight of the test wheels (0.78 kN for the Chinese standard rutting test total axle load) was smaller than that of the DWPA test.
After referring to the Chinese specification , we preliminary determined the rutting performance evaluation standard for the DWPA test: 60[degrees]C for the test temperature, 2.5 kN for the axle load, and 0.7 MPa for the tire pressure.
With reference to the APA test, the total deformation for the evaluation standard of the DWPA criteria we chose was as follows: after 2000 repetitions, the rut depth did not exceed 10 mm, or after 8000 repetitions, the rut depth did not exceed 15 mm.
The previous analysis revealed that deformation slope and total deformation indexes could be used as evaluation index of DWPA rutting test.
Five rutting indexes were used for the grey relational analysis in this research, namely, the rut depth index of the APA test, the depth index of the Chinese standard rutting test, the dynamic stability index, the depth index of the DWPA test, and the dynamic stability index [C.sub.DWPA].
According to Table 6, we found good correlation degree among DWPA rut depth index, APA rut depth, and rut depth of the Chinese standard rutting test.
From Formula (5), the correlation orders of DWPA rutting depth index with the other three indicators were 0.7736 (2000 repetitions) and 0.7741 (8000 repetitions) and the correlation orders of [C.sub.DWPA] with the other three indicators were 0.8162.
Therefore, the criteria for DWPA rutting test are as follows: the [C.sub.DWPA] index of the material is calculated from the rut depth of 2000 and 8000 repetitions at a test temperature of 60[degrees]C, the axle load is 2.5 kN, and the tire pressure is 0.7 MPa.
We preliminary established a corresponding rutting performance evaluation standard for DWPA test.
Compared to other rutting test methods, the DWPA test provides more rutting information.