, Professor, UMD-Civil Engineering
Eshan Dave, Assistant Professor, UMD-Civil Engineering
Low temperature cracking is the most prevalent pavement distress found in asphalt pavements in cold climates. As the temperature drops, the restrained pavement tries to shrink. Tensile stresses build to a critical point at which a crack is formed. Current specifications attempt to address this issue by requiring an asphalt binder with a certain low-temperature grade, i.e. xx-34. While this is a good start, it does not account for other factors such as hot mix asphalt (HMA) aggregate types & gradations, presence of recycled materials, and aggregate base and subgrade characteristics. Research has shown that binder tests alone are not sufficient to predict low temperature cracking performance in the field; testing asphalt mixtures at temperatures relevant to the climatic conditions for the pavement locations is necessary to obtain a reliable performance prediction. Furthermore, mixture testing techniques should be based on fracture mechanics rather than stiffness and strength. While still a point of debate, the pavement support conditions (base and subgrade) may also play an important role in extent of cracking and should be considered.
After 10 years of low-temperature cracking research, the Disk-Shaped Compact Tension (DCT) test emerged as the test to measure the fracture resistance of asphalt mixtures. The DCT test measures a mechanical property known as fracture energy. The Minnesota Department of Transportation (MnDOT) is nearing the end of the DCT Low-Temperature Fracture Testing Pilot Project, which implemented a trial specification on five asphalt paving projects in 2013. Preliminary results are promising, and the DCT Pilot study has identified the next steps for implementation.
The objectives of the research are to: 1) Assess DCT testing variability through round robin testing among selected consultants/MnDOT Verify and establish fracture energy criterion for asphalt concrete construction acceptance. This includes reviewing existing literature and data from MnDOT and other agencies. 2) Develop DCT testing and fracture energy specifications for asphalt mix acceptance. 3) If needed, provide support to MnDOT for implementing the DCT testing specification.