Effects of Asphalt Mixture Type on Asphalt Pavement Interlayer Shear Properties

Abstract

This study compares the interlayer shear properties of pavement layers composed of different asphalt mixture types. Two dense asphalt mixtures (one surface mixture with Tennessee designation of D mix and another binder course mixture with Tennessee designation of BM mix) and one open-graded friction course (OGFC) mixture were selected for the comparison. The direct shear test was conducted with and without normal stress to assess the shear strength and shear stiffness at different tack coat application rates. Results show that at .2-MPa normal stress, the specimens composed of two dense mixtures gave higher shear properties than those with OGFC as the upper layer. This is due to the fact that the noncontact area between the OGFC and the underlying layer compromised the bonding between the two layers. Among the samples composed of two dense layers, the D-BM specimens showed a higher interlayer shear resistance resulting from a larger interlayer roughness caused by a better aggregate interlock between D and BM mixtures. This indicates an upper layer with a small nominal maximum aggregate size (NMAS) and an underlying layer with a large NMAS could provide a better bonding. For specimens composed of OGFC and a dense mixture (D or BM), at the optimal tack coat application rate, OGFC-BM showed a better shear performance than OGFC-D, due to the double effects of a larger interface contact area and a larger interface roughness than OGFC-D.