Preliminary Investigation of a Test Method to Evaluate Bond Strength of Bituminous Tack Coats

摘要

It is generally recognized that a bituminous tack coat is beneficial for improving the bonding strength between two hot-mix asphalt layers. It is also qualitatively recognized that moisture on the surface of the tack coat can impede the bonding performance of the tack coat. Furthermore, varying tack coat application rates and aggregate interaction between hot-mix asphalt layers are also considered to have an effect on the bonding performance of the tack coat. In an effort to quantify the effects of moisture, tack coat application rate and aggregate interaction on bonding performance, a test apparatus and procedure were developed. Three field projects were also constructed and evaluated at various time intervals. Results indicate that water applied to the surface of the tack coat, representing rainwater, significantly reduced the shear strength of the specimens when compared to equivalent sections without water applied. Varying tack coat application rates within the range of 0.091 to 0.362 L/m2 had less of an effect on shear strengths. The use of a tack coat to increase bonding strength was more effective for fine graded mixtures compared to coarse graded mixtures. Aggregate gradations of the mixtures being bonded together played a critical role in the magnitude of the shear strengths achieved. Fine graded mixtures achieved significantly lower shear strengths than the coarse graded mixtures. A field project containing a milled interface achieved the greatest strengths of the projects tested. The single-operator standard deviation of the test procedure was determined to be 66.2 kPa.