Transverse cracking and tenting are significant problems for asphalt pavements, especially in colder climates where the asphalt layer contracts during winter conditions. While the impacts of frost on roads are generally known, more data is needed about treatments to mitigate tenting and the influence of base layers on tenting behavior. This project examined the effectiveness of pavement treatment options and identified primary causes of tenting to help state and local engineers limit future tenting.
Tenting occurs on roads when ice expands in the subsurface materials, causing the asphalt at the edges of a crack to move upward. This movement creates a tent-like peak in the road’s surface, which reduces ride quality, increases safety risks and accelerates pavement deterioration and pothole formation.
This project investigated the effectiveness of available pavement treatment options to identify the primary causes of tenting and mitigate tenting and road roughness. To assist state and local engineers with road designs and maintenance, investigators developed a method to classify base materials by frost susceptibility and created decision trees for selecting the best pavement treatment option for distressed roads.
What Did We Do?
This project conducted in-depth fieldwork, comprehensive laboratory testing and pavement performance data analysis to meet its goals. Fieldwork measured the extent of tenting on six roads in St. Louis County, while analysis of pavement roughness data from eight MnDOT districts determined the effectiveness of pavement treatment options on improving road roughness.
International Roughness Index (IRI) data was used as the primary roughness indicator, with values measured immediately before and after each treatment. The percentage change in IRI indicated the effectiveness of each treatment.
“The guidance and standards developed in this work will be of value to state and local engineers as they design and maintain roads that limit tenting,” said Matthew Hemmila, Engineering deputy director, St. Louis County.
MnDOT Class 5 aggregate samples from local plants and road sections experiencing tenting were evaluated in the laboratory for gradation, hydraulic conductivity, moisture–density relationships and frost heave potential. The results were used to develop a course void/fine void (CV/FV) index that correlates aggregate void structure with susceptibility to frost to offer guidance for selecting base materials for road designs.
Investigators also created decision trees that engineers can use for mitigating the effects of frost heaving in base materials and for selecting the most effective treatment to reduce tenting on distressed pavements.
What Did We Learn?
Fieldwork results confirmed that tenting is a localized distress caused by moisture seeping into the subsurface layer and the presence of fine particles at the interface of the surface and subsurface layers.
This distress often increases with traffic volume, independent of the thickness of the surface layer. Importantly, tenting does not completely disappear in summer as the intruding fines create permanent uplift or a depression occurs along the transverse crack, indicating the tenting will affect pavement roughness throughout the year.
Investigators identified the base layer CV/FV index as the best predictor of frost performance, demonstrating that the overall distribution of voids within the pavement is more significant than the extent of fine particle content. Higher CV/FV indexes correlate with higher permeability and frost susceptibility, whereas an index less than 0.88 showed better resistance.
Analysis of pavement roughness results found that IRI improvement is primarily a function of pavement type and maintenance method. Microsurfacing is often the most effective option for mitigating road roughness, particularly on bituminous over aggregate base and bituminous over bituminous layer pavements.
Project findings led to decision trees for three scenarios:
- Selecting a pavement treatment to decrease road roughness and tenting on existing pavement.
- Selecting between a localized or comprehensive pavement treatment to decrease road roughness and tenting.
- Selecting a CV/FV ratio based on road condition.
What’s Next?
Study results recommend using the CV/FV index and new decision trees. For new pavement construction, findings suggest that road designers should select base materials with a target CV/FV index of less than 0.88 to limit potential tenting to less than 2.5 mm. However, further research and field validation are needed to identify optimal CV/FV ranges for design use.
Crossroads 