Investigation of Low Temperature Cracking in Asphalt Pavements–Phase II (TPF-5/132)

Low temperature cracking is the most prevalent distress found in asphalt pavements built in cold climates. As the temperature drops, the restrained pavement tries to shrink, causing tensile stresses to build up until they reach a critical point at which a crack is formed. The current Superpave specification attempts to address this issue by specifying a limiting low temperature for the asphalt binder. The specification does a reasonable job predicting performance of conventional asphalt cements, but this does not hold true for polymer-modified asphalt binders that are manufactured to reach the very cold temperature grades needed in cold climates. Currently the low temperature specification considers only the asphalt binder. Specifications must be developed for the asphalt mixture as well.

A comprehensive research effort is in progress by a team led by Dr. Mihai Marasteanu at the University of Minnesota. This project is a unique partnership between the Minnesota Department of Transportation and four universities: the University of Minnesota, Michigan Technological University, the University of Illinois at Urbana-Champagne, and the University of Wisconsin at Madison. The goal of the current project is to evaluate different laboratory procedures, material properties, and pavement features in order to develop an optimal system for selecting materials that resist cracking at low temperatures. There is a critical need to validate the findings of this experimental work with field data. To this end, two sections will be constructed at MnROAD. MnROAD provides a unique combination of instrumentation, regular performance monitoring, controlled traffic applications, researcher expertise, and a safe work environment that makes it an ideal location for this study.

The research in this field study builds on previous research in the area of low temperature cracking performed in Minnesota and around the country. The next step is to validate the new models and laboratory test methods with field performance tests at MnROAD. The models being developed for top-down cracking and reflective cracking may be of some use for modeling thermal cracking. New asphalt materials, including modified PG binders, can be tested according to the principles developed in past research. Finally, upgrades to the AASHTO 2002 Design Guide could be proposed based on new innovations in modeling.

The main objective of this study is to validate the laboratory test procedures, models, and pavement design procedures that come out of Phase I of this study. This will be accomplished by monitoring two new test sections at the Minnesota Road Research Facility (MnROAD). Phase I was aimed at developing a fracture mechanics-based specification for a better selection of asphalt binders and mixtures with respect to their resistance to crack formation and propagation. This fracture mechanics approach will also be used to investigate the detrimental effects of aging and moisture on the fracture resistance of asphalt materials.