Effect of Notch and Tack Coat on the Interface Shear Performance between Asphalt Layers

In order to evaluate the important order and significance of the type of asphalt mixtures (A) on both sides of the interface of pavement surface course, the notch (B) in the interface, the tack coat (C), and the two-way interactions (AB, AC and BC) of the three factors that influence the interlayer shear strength, the orthogonal design was applied to make the test scheme. Three types of composite Marshall specimens were prepared by compaction method. The lower layer of specimens was 19 mm nominal maximum aggregate size (NMAS) dense-graded asphalt mixture (AC-20); and the upper layer was 13 mm NMAS dense-graded asphalt mixture (AC-13), AC-20, or 13 mm NMAS open-graded friction courses (OGFC-13), respectively. There were four treatments for the specimens interfaces, namely, neither notch nor tack coat (NNNT), no notch but tack coat (NNYT), no tack coat but notch (YNNT), and both notch and tack coat (YNYT). The interfaces of the specimens were directly sheared by the homemade interface shearing apparatus at 25℃. The results show that the average shear strength of the NNYT, YNNT, and YNYT interface is increased by 23.8%, 42.9%, and 53.9% respectively, compared with the average shear strength of the NNNT interface. By variance analysis, the effect of the three factors and their interactions on the shear bond strength can be ranked in a descending order as A, B, C, BC, AC, and AB. The A, B, C, and the interaction of BC are highly significant factors, and the interactions AB and AC are subordinate factors.