Tack coat materials, which are typically emulsified bituminous products, are used to provide a sufficient bond between asphalt concrete (AC) layers/lifts. Owing to construction limitations and severe temperature variations in cold regions, agencies are investigating the use of fast curing and non-tracking emulsions as tack coat materials. The objective of this study is to evaluate the performance of various tack coat products in cold climates. Several tack coat products were installed during a field study in Saskatchewan, Canada. The tack coat products included slow setting, medium setting, and three proprietary fast curing/non-tracking emulsions. Core samples were collected three weeks after construction to evaluate the initial interlayer shear strength (ISS) for typical construction conditions in cold regions. Although the ISS values for all of the products, except one SS-1 section, varied in a narrow range, this does not indicate that all products will have a similar long-term performance. The modes of failure for the bond strength samples were classified into two types according to the shape and location of the failure surface: type A and type B. Failure type B indicates that the tack coat material can successfully provide sufficient bond strength to make the two AC lifts behave as one thick homogenous layer. The results showed that the failure mode should be included as an evaluation criterion in addition to ISS. The results showed that the energy required to reach peak shear stress is a comprehensive parameter that should also be considered when evaluating tack coat materials.
Experimental evaluation of cohesive and adhesive bond strength and fracture energy of bitumen-aggregate systems