Layer Characteristics Affecting Interlayer Shear Resistance in Flexible Pavements

The evaluation of interlayer shear resistance is important to better understand how multi-layered pavements behave under traffic conditions. This paper focuses on the characterization of the interlayer shear behavior in flexible pavements through experimental investigation and analysis of two parameters that affect interlayer bonding: the influence of air void content of the two mixes in contact and the contact surface roughness of double-layered asphalt concrete specimens. Two different shear test devices (LPDS and ASTRA equipments) were used to evaluate interlayer resistance, whereas air void content and roughness characteristics at the interface were measured by using both traditional and innovative techniques. In particular, a non-destructive method, the X-ray Computer Tomography (CT), was used to investigate interlayer air void content and interlayer roughness after compaction of the upper layer. The results were able to show that air void content influences interlayer shear resistance in a non-linear way. As far as contact surface roughness is concerned, profile comb, laser profilometer and X-ray CT were used and further elaborated with advanced techniques such as fractal theory and spectral analysis. The results showed how higher macro-texture leads to an increase in LPDS and ASTRA interlayer shear resistance.