Characterization of asphalt concrete layer interfaces

A new constitutive model for the asphalt concrete layer interface is proposed. Direct shear tests at four levels of normal load and three temperatures were performed on two types of asphalt concrete layer interface: with and without a tack coat. The shear stress-displacement curves determined in these tests were used to derive the constitutive model, as the tangential and normal stresses at the interface are decoupled. In the proposed model, the shear stress and displacement are proportional until the shear stress equals the shear strength and the interface faits. After failure, a friction model may be used to represent the interface condition. Three parameters were considered to completely describe the interface behavior: the interface reaction modulus K, which is the slope of the shear stress-displacement curve; the shear strength Smax; and the friction coefficient after failure L For the interface with a tack coat, K and Smax are not affected by the normal stress level, but they are affected for the interface without a tack coat. All three parameters of the constitutive model are temperature dependent. A testing configuration for determining the shear fatigue behavior of the interface is also described. The fatigue tests indicated a linear increase of the permanent shear displacement with the number of load repetitions, the rate of increase being higher for higher stresses. The fatigue test can be used for a comparative evaluation of the durability of different types of interfaces.