Tack coats for asphalt paving

Poor bonding between two layers of hot mix asphalt (HMA) is the cause of many highway pavement problems. Normally, hot asphalt cements, emulsified asphalts or cutback asphalts are used as tack coat. The objective of this study was to evaluate the practice of using tack coat through controlled laboratory simple shear tests and determine the optimum application rate. The influences of tack coat types, application rates, viscosity and temperatures on the interface shear strength were examined. Test results indicated that latex modified asphalt emulsion has the highest interface bond strength. It was also found that applying low viscosity tack coat asphalt emulsion at two layers is more effective than a tack coat asphalt emulsion high viscosity one layer coat.