A new method of testing low-temperature cracking in asphalt pavement shows promise for design, quality control and quality assurance. Test results produced by the new method, which is faster and less expensive than the previous method, match well with results from the older method.Continue reading Evaluating Cracking Resistance Test Methods for Asphalt Pavements
Adding graphite nanoplatelets (GNP) to asphalt binders and applying the methodology developed in a new MnDOT study could provide a cost-effective approach to reducing cold-weather cracking and increasing the durability of Minnesota pavements.
“This project gives MnDOT a low-cost way to incorporate the latest nanotechnologies into our asphalt mixtures, reducing cold-weather cracking and increasing the durability of Minnesota pavements,” said Shongtao Dai, Research Operations Engineer, MnDOT Office of Materials and Road Research.
What Was Our Goal?
The objective of this project was to develop a cost-effective method to determine the optimum mix design of GNP-reinforced asphalt binders and mixtures. This method would predict the fracture behavior of these materials using a combination of simple laboratory testing and computer modeling.
What Did We Do?
Researchers developed a method for determining the quantity of GNP to add to an asphalt binder to achieve optimal asphalt mixture performance. The method used a computer model to predict the low-temperature fracture behavior of mixtures based on bending beam rheometer (BBR) tests on fine aggregate mixtures. This test applies a load to the center of a thin, rectangular specimen that has been cooled to a low temperature while its edges rest on two elevated supports, and then measures how the specimen bends over time. The results of this test determine the stiffness of materials and their ability to relax the stresses of contraction.
The BBR test is simpler, less expensive and less labor-intensive than the more accurate semicircular bend (SCB) test, which measures fracture resistance—the way cracks in a material form—by loading a semicircular sample from its apex. However, the SCB test can determine the properties of all the particles within a mixture; the BBR test can only evaluate the mechanical properties of coarse aggregates. To obtain the accuracy of the SCB test without the labor and expense, the computer model developed by researchers in this study uses BBR results as inputs to simulate SCB tests and infer the properties of fine aggregates.
What Did We Learn?
Researchers validated their computer model by comparing its results with those of actual SCB tests. They found that the model was able to predict the results of SCB tests for both conventional and GNP-modified mixtures. By performing only a BBR test on the fine aggregates mixture and inputting the results into the computer model, researchers obtained a reasonable prediction of the fracture response of the final asphalt mixtures.
In turn, the model showed that using GNP in asphalt binders can significantly improve the strength and fracture resistance of a mixture compared to mixtures with unmodified asphalt binders. The model can be used as a design tool to determine what percentage of GNP is needed to achieve the necessary tensile strength for a target value of fracture energy.
Using GNP in asphalt binders, in combination with the methodology developed in this project, could potentially provide MnDOT with a cost-effective approach to improving the cold-weather performance of Minnesota pavements, preventing cracking and increasing pavement durability. MnDOT will continue to evaluate the use of GNP in its asphalt mixes.
This post pertains to Report 2018-02, “A Mechanistic Design Approach for Graphite Nanoplatelet (GNP) Reinforced Asphalt Mixtures for Low-Temperature Applications.” Further GNP research is underway. Find related projects at MnDOT.gov/research.
As the first big snow and ice storms sweep through parts of Minnesota today, we’d like to remind you of some of our great winter weather research studies. Here’s a list of some of this winter-related research from MnDOT and the Local Road Research Board:
Living snow fences
Living snow fences are trees, shrubs, native grasses, wildflowers, or rows of corn crops located along roads or around communities and farmsteads. These living barriers trap snow as it blows across fields, piling it up before it reaches a road, waterway, farmstead or community. Through multiple research efforts, MnDOT continues to advance its practices for living snow fences. Willow plants, which are which are inexpensive and fast-growing, are a new form of snow fence. MnDOT has also developed a tool that allows the agency to better offer a competitive payment to farmers.
- Evaluating the Cost and Benefits of Living Snow Fences
- Web-Based Preventative Blowing and Drifting Snow Control Calculator Decision Tool
- Assessing the Use of Shrub-Willows for Living Snow Fences in Minnesota
- Expanding the Adoption of Blowing and Drifting Snow Control Treatments on Private Lands
According to recent studies, researchers believe Minnesota could eliminate salt usage on low-volume local roads by switching to permeable pavements. Permeable pavements — pavements that allow water to seep through them — have been studied in some Minnesota cities, and a research project is currently underway to further investigate how much salt reduction can be expected.
- Permeable Pavements in Cold Climates: State of the Art and Cold Climate Case Studies
- Permeable Pavement for Road Salt Reduction
Traffic recovery during winter storms
MnDOT’s Metro District developed a way to automatically determine when to stop plowing a highway after a snow storm. The method involves measuring traffic flow to determine when road conditions have recovered. Current practice calls for maintenance workers to visually inspect traffic lanes. The automated technique could potentially be more accurate and save time and costs.
Salt and other deicing chemicals
Minnesota winters are no joke, and Minnesotans still need to get wherever they’re going despite harsh snow and ice conditions. That’s why MnDOT is constantly researching new and improved versions of salt and other deicing chemicals to keep roads safe at the least amount of damage to lakes, rivers and groundwater.
- Roadway Salt Best Management Practices
- Chloride Free Snow and Ice Control Material
- Salt Brine Blending to Optimize Deicing and Anti-Icing Performance and Cost Effectiveness Phase III
- Study of De-Icing Salt Accumulation and Transport Through A Watershed
A couple years ago, MnDOT snowplow operators in southwestern Minnesota invented an experimental plow that uses the wind to cast snow from the road without impeding traffic or the operator’s view. This winter, MnDOT intends to test multiple types of snowplow blades as part of a larger research project comparing types of deicers.
While a lot of research has been done on the plow itself, MnDOT hasn’t forgotten to invest in research to improve in-cabin snowplow technology as well. Some of the great technology recently developed to assist snowplow drivers, includes a driver assist application that a MnDOT plow driver used last winter to navigate a storm and rescue stranded motorists. The agency is also studying equipment factors that can cause fatigue in snowplow operators.
- Driver Assistive Systems for Rural Applications: A Path to Deployment
- Synthesis on GPS/AVL Equipment Used for Winter Maintenance
When the snow melts every spring, the damage salt does to roadside grass is obvious. That’s why researchers have spent years looking into developing and implementing salt-tolerant grasses on roadside settings. The result of this effort has been the introduction and use of salt-tolerant sod and seed mixtures that are made up primarily of fine fescue species. MnDOT is also studying how chlorides are transported within watersheds in order to better focus efforts to reduce deicer usage in areas where it will have the biggest environmental impact.
- Developing Salt-Tolerant Sod Mixtures for Use as Roadside Turf in Minnesota
- Best Management Practices for Establishment of Salt-Tolerant Grasses on Roadsides
- Expanding the Success of Salt-Tolerant Roadside Turfgrasses Through Innovation and Education
- Regional Optimization of Roadside Turfgrass Seed Mixtures
Cold-weather cracking prediction test
MnDOT has developed a test that can tell whether a contractor’s proposed asphalt mix will cause the road to crack in the winter. Building roads using better asphalt mixes leads to less cracking and fewer potholes. The test is expected to save the state about $2 million per year.
- DCT Low Temperature Fracture Testing Pilot Project
- Optimizing Cold In-Place Recycling (CIR) Applications Through Fracture Energy Performance Testing
- Disc Shaped Compact Tension (DCT) Specifications Development for Asphalt Pavement
Pedestrian snow removal
It’s not all about cars and trucks. Minnesotans still ride bikes and walk in the winter. That why MnDOT assembled a comprehensive review of existing practices and policies from other states, as well as a summary of valuable publications that could be referenced while developing a new policy.
Maintenance Decision Making
MnDOT research led to the development of a Maintenance Decision Support System and related components provide real-time, route-specific information to snow plow drivers, as well as recommended salt application levels. These recommendations have reduced chemical usage while still achieving performance targets for snow and ice clearance.