The effect of a tack coat on the bond between asphalt concrete layers was investigated, and then new tack coat materials were developed for airport pavements. The following conclusions were obtained.
(1)Failure of the surface course considered herein will occur in the following manner: first, separation between the layers of the surface course occurs because of insufficient adhesion at the interface. Flexural or tensile failure of the surface course then follows.
(2)The strength at the interface of the layers in the surface course is different due to differences in the interval between wearing course and surface course construction.
(3)Tack coat will be effective to ensure the bond if the cure is sufficient.
(4)Water in the emulsified asphalt will evaporate fully by curing either for one hour in the daytime or for six hours at night.
(5)When dirt adheres to the interface, widely used cationic tack coat material, PK-4, will not be effective to adhere the layers if the sufficient cure is not ensured.
(6)The newly-developed, rubberized emulsified asphalt with higher penetration gives higher shear strength at the interface. This is effective in preventing the failure of the asphalt layers in summer.