Assessment of bond condition using the Leutner shear test

Pavement structures comprise several layers of different materials. The overall strength and stiffness of the pavement depends not only on the strength and stiffness of each individual layer, but also on the bond between them. Should the bond at an interface be inadequate, the strains throughout the pavement may increase (under trafficking) and its life may consequently be reduced. This paper investigates the use of the Leutner test to measure bond condition between surfacing and binder course materials and binder course and base materials. A range of bond conditions have been investigated. Results show that, for a particular combination of materials, there is an approximate linear relationship between interface shear strength and corresponding shear displacement that is independent of the bond condition. Results also indicate that, for HRA/20DBM, SMA/20DBM and 20DBM/28DBM combinations, the type and quantity of tack coat commonly applied in practice are sufficient to approach maximum attainable bond strength. For the 20DBM/28DBM combination a much reduced interface shear strength occurred if tack coat was not used, but extra tack coat appeared to compensate to some extent for the presence of dirt. In the 20DBM/CBM combination, it proved impossible to achieve a good bond, reflecting common experience on site.