Interlayer bond testing using a model material

Bond problems between asphalt layers are attracting more attention due to the continuous refinement of pavement design methodologies. However, research nowadays is mainly focussing on the practical evaluation of specific pavement material types and tack coat materials. In this paper, the influence of aggregate interlock combining different aggregate sizes on the shear strength between two layers is evaluated. Using a model material composed of idealized aggregates represented by steel balls and 10/20 penetration graded bitumen, this study is investigating the question on how the ball size and/or a combination of different ball sizes influence interlayer shear strength and shear stiffness. Shear bond testing was done using the Layer Parallel Shear Test (LPDS) with two different test speeds as well as a Shear Box with varying normal stress.

► We investigated the shear behaviour using a model material.
► The model material consisted of two steel ball sizes and hard penetration binder.
► LPDS testing determined a clear shear stress ranking for different steel ball combinations.
► The test ranking was in agreement with a calculated simple geometrical evaluation.