Influence of asphalt tack coat materials on interface shear strength

Asphalt tack coat is a light application of asphalt, usually asphalt diluted with water. It is used to ensure a bond between the surface being paved and the overlying course. Normally, hot asphalt cements, emulsified asphalts, or cutback asphalts are used as tack coats. The objective of this study was to evaluate the practice of using tack coats through controlled laboratory simple shear tests and determine the optimum application rate. The influence of tack coat types, application rates, and test temperatures on the interface shear strength was examined. Four emulsions (CRS 2P, SS-1, CSS-1, and SS-1h) and two asphalt binders (PG 64-22 and PG 76-22M) were selected as tack coat materials. The residual application rates considered were 0.00 (0.00), 0.09 (0.02), 0.23 (0.05), 0.45 (0.1), and 0.9 (0.2) L/m(2) (gal/yd(2)). A simple shear test was performed to determine the shear strength at the interface at two test temperatures, 25degreesC (77degreesF) and 55degreesC (131degreesF). The results indicated that CRS-2P emulsion was the best tack coat type and 0.09 L/m(2) (0.02 gal/yd2) was the optimum application rate at which a maximum interface shear strength was measured for both test temperatures.