The results of a 3-year pavement performance monitoring program with a primary focus on rutting are summarized. Pavement coring was conducted to determine the magnitude and cause of rutting in individual pavement layers. A pavement trench was excavated for further examination of pavement layers. Field data indicate that rutting was concentrated in steep uphill grade locations where heavy coal trucks travel at very slow speeds. Data from pavement cores and a pavement trench indicate that rutting in the large-stone mix may have been caused by insufficient direct stone-on-stone contact, which made the mixture susceptible to permanent deformation. Observations of the pavement trench at the location where the rutting was greatest (1.8 in) revealed no definite shear pattern within the cross section of the large-stone base layer. However, laboratory measurements indicated a significant reduction in the air voids content of the top 4 in of the pavement after 2 years of exposure to coal haul traffic loads. This significant reduction in air voids coupled with a lack of sufficient stone-on-stone contact contributed to the plastic behavior of thematerial. Pavement elevation data indicate that there has been an overall settlement of the roadway. The settlement may be attributed to consolidation of the subgrade and densification of the drainage blankets caused by upward migration of fines from the dense-graded aggregate into the open-graded No 57 layer and overall consolidation and penetration of particles along the interface between the two layers.
Samenvatting