Effect of Surface Characteristics on Bonding Properties of Bituminous Tack Coat

Abstract

The evaluation of the influence of surface characteristics on the bonding properties at the interlayer is important to understand better how multi-layered pavements behave under traffic conditions. Three double-layered systems were prepared with dense, porous asphalt concrete and stone mastic asphalt mixtures. The direct shear test was used to measure the bond properties provided by tack coat, whereas the surface characteristics were measured by traditional techniques. Variables included surface type, curing time, curing temperature, emulsion type, and residual application rate. For a given value of applied normal stress, the interface between the dense-graded asphalt mixtures resulted in higher peak shear strength than that between the open- and gap-graded mixtures. An increase in mean texture depth and film thickness led to a decrease in the peak shear strength and the reaction tangential modulus. The surface characteristics were shown to play a key role in interlayer bonding. Curing time was an important factor, indicating that paving could be performed right after the emulsion was broken. Increasing the residual application rate increased shear strength up to a point, then shear strength decreased gradually. The use of tack coat increased the interface bond strength, and an optimum residual application rate existed, at which the shear resistance reached a maximum value. The bonding properties at elevated temperatures were more associated with the surface characteristics than at lower temperatures.