Experimental Evaluation of Notch and Tack Coat that Influences the Bond Strength at the Interface between Asphalt Mixture Layers

Abstract

The interlayer bond between two layers of hot mix asphalt (HMA) plays an important role in the performance of asphalt pavement structures. Three types of HMA cylindrical specimens were prepared with compaction method, which were composed of two layers. The material of the lower layer was 19mm nominal maximum aggregate size (NMAS) dense-graded asphalt mixture (AC-20), and the upper layer was 13mm NMAS dense-graded asphalt mixture (AC-13), AC-20 or 13mm NMAS open-graded friction courses (OGFC-13) respectively. There were four cases for the interfaces of the specimens, such as, neither notch nor tack coat, no notch but tack coat, no tack coat but notch, and both notch and tack coat. The tack coat was cationic emulsified asphalt PC-3, the application rate of which was the optimum content of the corresponding structure. The notch was square and lay in the lower layer, the geometry size of which was fixed. Then the interfaces of the specimens were directly sheared by the homemade interface shearing instrument at room temperature. Shear strength can characterize the bond strength. Results showed that the HMA composition on both sides of the interface had the greatest effect on the interface bond strength of the three factors in this study. The notch or tack coat increased the interface bond strength respectively, but the effect of the notch was more evident than tack coat. The improvement of bond strength from notch or tack coat was equivalent for the interface composed of AC-20 and AC-20, but for the interface formed by AC-13 and AC-20, or OGFC-13 and AC-20, the notch was much better. Joint use of notch and tack coat had larger effect on the interface bond strength than either of the two factors for the interface formed by AC-20 and AC-20, or OGFC-13 and AC-20. But for the interface formed by AC-13 and AC-20, the joint use of notch and tack coat had almost the same effect on the interface bond strength as the notch. Keyword: asphalt mix, interface bond, notch, tack coat