OPTIMIZATION OF TACK COAT APPLICATION RATES AND CURING TIMES FOR ENHANCED INTERLAYER SHEAR STRENGTH IN MULTILAYER PAVEMENT

This study investigates the optimization of tack coat application rate and curing times to enhance interlayer shear strength in asphalt pavement structures. Two types of tack coat, CRS-1 and CRS-1P, were applied between the Asphalt Concrete–Wearing Course (AC-WC) and Asphalt Concrete–Binder Course (AC-BC) using PG 76 and Pen 60/70 binders. The Optimum Asphalt Content (OAC) was determined using the Marshall mix design method, followed by direct shear testing under tack coat application rates of 0.25, 0.35, and 0.45 L/m² and curing times ranging from 15 to 75 minutes. The results indicate that the maximum interlayer shear strength was achieved at an application rate of 0.35 L/m² and a curing time of 45 minutes. CRS-1P produced a higher peak shear strength (1.61 MPa) compared to CRS-1 (1.39 MPa). Excessive application rates and prolonged curing times reduced shear strength due to lubrication effects. Mechanistic analysis using BISAR 3.0 supported the experimental findings. These results highlight the importance of proper tack coat application to improve interlayer bonding performance in asphalt pavements.