Minnesota’s winters are among the fastest warming in the country. This warming trend is likely increasing the time during which winter temperatures are near freezing. As the number of freeze-thaw events goes up, so does the severity of pavement damage.
A MnDOT-funded study is looking at the impacts of climate change trends on Minnesota’s pavement systems. The goal is to understand the effects of changes in environmental conditions and help engineers design more sustainable pavement.
Data collection and analysis
In the first phase of this research, a multidisciplinary research team at Iowa State University did a comprehensive assessment of climate data in Minnesota.
Next, researchers defined the freeze-thaw cycle relevant to pavement damage. They studied the frost-susceptibility and freezing points of soils and pavements, moisture levels, and which temperatures (air, surface, pavement layer, or subsurface) are relevant in determining whether freezing and thawing will damage pavement.
Freeze-thaw events at different pavement layers were quantified using cells at MnROAD. Then, through detailed statistical analyses, the research team developed correlations between air, pavement, and subsurface temperatures during the freeze-thaw events.
No clear freeze-thaw increase, but more precipitation
The findings confirm changes in Minnesota’s climate. In the past 40 years statewide, days are one to two degrees Fahrenheit warmer and nights are two to five degrees Fahrenheit warmer, and the number of below-freezing days has decreased.
However, the researchers did not find an overall, clear increase in the number of freeze-thaw cycles as they and MnDOT might have expected. Rather, cycle quantity decreased at shallower pavement depths in early and late winter, and no trend was observed for the rest of the winter and in deeper pavement and subgrade levels. (They note that these results are applicable to the MnROAD location and may not be representative of the rest of the state.)
Freeze-thaw cycles using air temperatures were random throughout the decades analyzed, with most events occurring in early and late winter.
Also of significant interest, the team found an increase in precipitation of 0.5 to 1 inch both before and at the end of the cold season. More moisture can worsen heaving in the pavement and subgrade.
“Although researchers found that precipitation is increasing and this trend can potentially lead to more pavement deterioration, the good news is that warmer winters have actually decreased the number of freeze-thaw cycles, which means less pavement deterioration from that process,” says Raul Velasquez, geomechanics research engineer with MnDOT’s Office of Materials and Road Research and the project’s technical liaison.
“We are finding that the changes in climate—mainly increasing temperatures and precipitation—have more impact on the long-term performance of pavement infrastructures than do traffic loadings,” says Halil Ceylan, director of the Iowa State University Program for Sustainable Pavement Engineering and Research and the project’s principal investigator.
In the second phase of the study, the researchers will analyze the implications of increased precipitation and expand the exploration of climate impacts on pavement across the state. The result will be a moisture-induced vulnerability map for the pavement foundation of the entire road network.
Learn more:
- Effect of Warmer Minnesota Winters on Freeze-Thaw Cycles (MnDOT, July 2022)