ABSTRACT
The roadbase is the most important structural layer of the road but any assessment of its structural condition is difficult because of its position in the road; consequently the mechanisms of roadbase deterioration are less clearly understood. Conventional wisdom based on laboratory studies considers fatigue cracking caused by repeated loading from traffic to be the major form of structural deterioration. This paper describes a study in which structural investigations were carried out on selected motorway sites and roadbase material was extracted for subsequent laboratory testing. The measured structural properties of the roadbase from the heavily trafficked near-side wheel path were compared with those of material from the lightly trafficked area, between the wheel tracks in the off-side lane, and with the overall condition of the motorway. The study provided no evidence that fatigue under repetitive traffic loading caused any weakening of the roadbase. The change in the measured residual life of the roadbase was related to material composition, with binder volume and increasing binder hardness with age being the most important variables. This work has important implications for the present criteria for pavement design and maintenance.
