Interface layer tack coat optimization

Interface bonding is a key factor affecting pavement performance life. This study focused on optimizing in situ tack coat application rate and field installation. The objective was to validate the laboratory-determined optimum residual application rate and evaluate the field performance of tack coat materials. The parameters analyzed included two cleaning methods (broom and air blast), two paving procedures (spray paver and conventional paving with use of a distributor and a regular paver), tack coat type (SS-1h, SS-1hp, and SS-1vh), and existing pavement surface. Projects were conducted on I-80 and Illinois Route 98. Cores were tested by using the interface shear test device. A life-cycle cost analysis that considered construction materials and paving methods was performed. Results showed similar bond strength for both cleaning methods; however, air-blast cleaning reduced the required optimum residual application rate. The resulting interface bond strength was similar when using either of the paving procedures considered. SS-1vh, a nontrack tack coat, performed better than any other material studied. Identification of the optimum tack coat application rate will help ensure cost-effective and efficient tack coat application in the field.