Asphalt-Bound or Cement-Bound Roadbase in Concrete Pavements

Plain Jointed Concrete Pavements (PJCP) are used on Swedish concrete roads. In the Swedish road construction specifications there are two alternatives for bound roadbases which can be used in concrete pavements. Generally a 150 mm thick cement-bound roadbase (CG) has been used. As an alternative a 100 mm thick asphalt-bound roadbase (AG) can be used. After 10 years of traffic exposure, damage in the form of cracks have started to appear on some sections of concrete roads where cement-bound gravel has been used as a roadbase. In Sweden there is a discussion about which kind of roadbase should to be used in concrete pavements. Therefore an investigation has been carried out on two sections of concrete roads with different kinds of roadbase. To investigate the stiffness of the concrete layer Falling Weight Deflectometer (FWD) has been used. Measurements show that the degree of deflection was depended on the temperature gradient in the concrete slab but also on the type of bound base-layer. An inspection was made on the condition of a concrete road approximately 10 years old. The inspection revealed only a few areas of damage on a section of road where the concrete layer was on an asphalt-bound roadbase. For the section of road where the roadbase is cement- bound gravel, cracks could be observed in several places. In some places, fine grained material had been pumped up in the longitudinal joint between the concrete slabs and the asphalt shoulder. The finegrained material probably comes from the cement-bound roadbase. This investigation shows that roadbase of AG appear to be a better alternative than CG roadbase in a concrete pavement. For the next concrete road to be built in Sweden in 2006, asphalt-bound roadbase will be used in the concrete pavement.