Asphalt rutting is a major permanent degradation issue caused by the high temperature and the cyclic load of vehicles along roadways. In this work, a highway slow lane within a tunnel was affected by a relevant deformation in a relatively short time. The investigation focused on a 200 m road distance. Benkelman deflection tests on the road surface, measurements of the depth of the road deformation, particle-size distribution of the road base, Proctor and CBR tests were performed. The unbinded underground material matched the required limits. Moreover, a concrete basement with a thickness up to 60 cm was present between the upper bituminous layers and the unbinded sub-base. The concrete increased the stiffness of the whole pavement system. The road base exhibited a good bearing capacity, while the reason for the rutting needed to be found in the middle and lower bituminous layers, in spite of the wide curvature of the permanent deformation.
Keywords : asphalt, rutting, highway tunnel, pavement.