The effect of a tack coat on the bond between asphalt concretelayers was investigated. First, the stresses at the interfacecaused by aircraft loads were calculated. Second, the effect ofusing a tack coat was evaluated by examining samples taken fromin-service airport pavements. Third, laboratory tests were conductedto investigate how bonding characteristics were influenced bydirt adhering to the existing surfaces. Finally, measures to ensuresufficient bonding were developed.

The following conclusions were obtained. The interval betweenthe construction of the wearing and binder coarses influencesthe bond strength: the strength decreases as the interval increasesbecause dirt accumulates on the binder course. Adhesion betweenthe courses can be improved by applying a tack coat. The curingtime of the tack coat, however, also influences the strength,and the strength after one hour of curing is much less than thatafter 24 hours of curing. However, satisfactory strength can beobtained by using a newly developed tack coat. In addition, thestructural integrity of the surface course can be ensured by introducinga thick lift construction procedure.