Developing Tack Coat Specification for Long-Lasting Composite Pavement Performance
Authors
De Jesus Moura, Geverson
Issue Date
2023
Type
Thesis
Language
Keywords
Alternative Title
Abstract
Pavements are constructed in multiple lifts to efficiently transfer traffic loads from the surface to the underlying layers. It is necessary to apply a tack coat material to ensure complete bonding during the construction of new pavements or rehabilitation processes. Otherwise, the pavement integrity may become compromised. The amount of tack coat and construction quality impact the pavement structure's performance and durability. The required quantity is influenced by factors such as the pavement surface type and condition, preparation of the layer, and appropriate construction practices. The bond strength between layers is also determined by the quality of tack coat and construction/application techniques employed.This research aimed to determine test methods and best practices to develop a specification for tack coat materials used in composite pavements, which can predict their performance in different environmental conditions, construction techniques, and pavement types. The focus was on tack coat properties related to bonding and durability.Establishing optimal tack coat specification thresholds required a comprehensive analysis of various rheological properties and an interlayer shear strength test. Rheological tests are fundamental in determining tack coat response to deformation and flow under different conditions. Additionally, interlayer shear strength tests evaluate the adhesive properties of the tack coat by measuring the required force to separate two pavement layers bonded with the tack coat. By correlating the results of rheological properties and interlayer shear strength test results, acceptable thresholds for bonding and durability performance were determined to improve the longevity of composite pavements.The commonly used parameters of penetration and softening point, for specifying tack coat materials, may not be sensitive enough to reflect the effects of polymer modification. However, the asphalt binder's high-temperature performance grading (PGH) proved to be a good alternative to evaluating tack coat bonding performance. The results suggest that using a tack coat material with a PGH equal to or higher than the binder used in asphalt concrete achieves comparable or better performance than the minimum laboratory-measured ISS of 40 psi required for satisfactory field-level tack coat efficiency based on past research.An aging index was estimated to assess the impact of aging on rheological properties of tack coat materials and make sure they will perform well throughout the pavement life. The results showed that all materials studied demonstrated good resistance to aging, with aging indexes below 4.0. This parameter was chosen based on a broader range of tack coat materials as part of the NCHRP Project 09-64.