Interlayer bonding of binder, base and subbase layers of asphalt pavements: Long-term performance

With bond testing of asphalt layers becoming a more important topic as well as in research as in every day pavement construction, the question of long term behaviour of bonding properties has come up. In recent research it has been shown that the bonding properties between surface and binder courses seem to improve with time considering that the surface course does not show distress phenomena and that the traffic volume does not exceed the traffic considered for pavement design. That bond failure is not only a question of the top layers is a well known fact; therefore the long term properties of the lower layers are also of interest. The paper focuses on the effect of long term behaviour of bonding properties of the lower pavement layers (binder or base and subbase courses) presenting the results of an extensive Swiss study. The study compares the bonding properties determined with the layer parallel shear test (LPDS) according to Leutner of high volume roads after a 9–13 years period. It was found that for rehabilitations or old constructions an improvement cannot be expected and especially in case of old constructions seems to depend on their service life. For the bond between lower layers decreases of shear force values down to 50% are possible.