Materials and Construction

New test could help asphalt pavements survive winter intact

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If there was ever a winter that demonstrated what cold weather can do to asphalt pavements, last one was it. But future winters may wreak less havoc on Minnesota roadways, thanks to a new asphalt mixture test in the final stages of evaluation by MnDOT’s Office of Materials and Road Research (OMRR).

Developed through a decade-long multi-state research project, the Disc-shaped Compact Tension (DCT) test evaluates the low-temperature performance of asphalt mixes. (See a video about the project that helped develop the DCT test below.)

For the first time, engineers will be able to predict how well a contractor’s proposed asphalt mix will hold up under harsh Minnesota winters.

“Performance testing is assuring that we’re getting what we’re paying for,” explained MnDOT Research Project Engineer Luke Johanneck.

Low-temperature cracking is the most prevalent form of distress found in asphalt pavements in cold climates. As the temperature drops, the pavement tries to shrink, creating cracks that allow water to seep in and eventually lead to pavement deterioration.

Until now, engineers have typically evaluated the individual components (such as amount of crushed aggregate and asphalt binder grade) and volumetric properties (such as air voids and asphalt content) of an asphalt mix, not how the final product performs in low temperature.

“It’s like baking a cake,” explained MnDOT Bituminous Engineer John Garrity. “Our current system says put in a half-cup of oil, two eggs and cake mix. Rather than just looking just at those individual components, taste the cake to see how good it is.”

Created by researchers at the University of Illinois, the DCT test applies tension to an asphalt mixture sample to determine its thermal fracture resistance. The test was determined to be the best of several methods looked at in another research study, conducted by the University of Minnesota with assistance from neighboring state universities.

The Disc-Shaped Compact Tension Test measures the fracture energy of asphalt mixture lab or field specimens, which can be used in performance‐type specifications to control various forms of cracking.
The test measures the fracture energy of asphalt mixture lab or field specimens, which can be used in performance specifications to control various forms of cracking.

The Office of Materials and Road Research is conducting pilot tests to become more familiar with the DCT test and to educate road contractors, who may eventually be required to use the test in Minnesota.

“This is very new to a lot of people that have been in the business for a long time,” Johanneck said.

Last summer, OMRR asked five contractors to submit asphalt mixes for testing. If a mix didn’t pass, the contractor was given suggestions for how to modify their recipe to better resist thermal cracking. This summer, OMRR plans to collect asphalt mixes from around the state to see how they measure up against a set of performance targets that were developed in the pooled fund study.

“We envision this at some point being part of our standard bid specifications,” Garrity said.

Those with a professional interest in the subject might be interested in a new video from MnDOT Research Services & Library (below) that demonstrates how to do the sample preparation for the DCT test.

Research Studies

Current DCT Test Implementation Project (2014) Pooling Our Research: Designing Asphalt Pavements That Resist Cracking at Low Temperatures (March 2013 Technical Summary) Synthesis of Performance Testing of Asphalt Concrete (September 2011) Investigation of Low Temperature Cracking in Asphalt Pavements National Pooled Fund Study 776 (2007 report)

Related Videos

Frost Damage in Pavement: Causes and Cures (full-length) Frost Damage in Pavement: Causes and Cures (short version)

Traffic and Safety

New Roadway Safety Institute focuses on user-centered solutions for multiple modes

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The new Roadway Safety Institute, a $10.4 million regional University Transportation Center (UTC) established in late 2013, will conduct a range of research, education, and technology transfer initiatives related to transportation safety. Led by the University of Minnesota, the two-year consortium will develop and implement user-centered safety solutions across multiple modes.

The Institute will be a focal point for safety-related work in the region, which includes Minnesota, Illinois, Indiana, Michigan, Ohio, and Wisconsin. Other consortium members are the University of Akron, University of Illinois at Urbana-Champaign, Southern Illinois University Edwardsville, and Western Michigan University.

Max Donath, professor of mechanical engineering at the U of M, serves as the new Institute’s director. In this month’s issue of the CTS newsletter, Catalyst, Donath shared his vision for the Institute.

According to Donath, the Institute will focus on addressing regional traffic safety priorities, educating the public, and attracting more professionals to the safety workforce by connecting with students.

Research topics will focus on two key areas, Donath said: high-risk road users and traffic safety system approaches. The goal of this work is to prevent the crashes that lead to fatalities and injuries on the region’s roads.

One unique Institute effort will involve working with American Indian communities in the region to explore and address the unusually high number of motor vehicle crash fatalities on tribal lands.  “Our research will work to better understand why this is happening and to develop more effective solutions,” Donath said.

Read the full Q&A in the April issue of Catalyst.

Bridges and Structures

High-Tech Inspections to Keep Minnesota’s Timber Bridges Safe

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Across Minnesota, hundreds of wooden bridges are reaching the end of their lifespan, but counties don’t know which ones to repair and which ones to replace.

In 2010, a timber bridge partially collapsed in Nobles County, heightening concerns about the state of inspections statewide.

“A lot of it right now is just visual and sounding the wood – striking it with a hammer and interpreting dull or hollow sounds,” said MnDOT State Aid Bridge Engineer David Conkel.

Timber bridges are at a critical point in Minnesota, not only because of the sheer number built in the 1950s and 1960s, but because it’s difficult to judge their structural soundness without advanced equipment.

While current inspection methods adequately identify areas of advanced decay, they do a poor job of detecting early decay or internal deterioration, especially in the timber substructure.

MnDOT and the Local Road Research Board have partnered to develop better inspection and repair methods on behalf of Minnesota counties. Training will be held in May and June for county inspectors. [Register here]

The most troublesome area of decay on a timber bridge are in the pilings, which usually have contact with the water. The drying and wetting of the water causes rot to form.
The most troublesome area of decay on a timber bridge are in the pilings, which usually have contact with the water. The drying and wetting of the water causes rot to form.

Identifying internal deterioration early is essential because once significant rot is noted, a timber bridge can slip into a severe condition within just two to three years.

Early bridge makers treated timber bridge elements with creosote to prevent decay from fungi and insect damage. However, because it was typically applied to the shell, a good external condition may hide severe internal deterioration.

“The timber bridge elements typically decay from the inside out due to the lack of preservative in the center of the timber,” explained Matt Hemmila, St. Louis County Bridge Engineer. “The outside will look okay, but the inside may be highly deteriorated.”

Better Inspection

Resistance microdrills and stress wave timers are two proven inspection tools that counties can use to see past the surface of a timber bridge and identify the actual amount and area of internal rot. But Minnesota counties have lacked this equipment and the training.

“These tools will enable us to identify the bad bridges before the decay shows up visually– but it will also tell us which bridges are still good so we can allocate the funds we have to replace the worst bridges,” Hemmila said.

A stress wave timer (video above) locates bad areas on a bridge by using probes to measure the time it takes for sound to travel through the material. A decayed piling will have a time that is more than double that of a sound piling.

A resistance microdrill (video below) can then be used to determine how much good wood is left in a piling or timber element by drilling a bit into the wood and measuring the resistance.

MnDOT and the LRRB are developing a customized inspection manual and standardized inspection protocols, which can be integrated into the state’s bridge data management software.

“Good inspections can catch potential problems early and possibly avoid emergency closures or load postings,” Conkel said. “It enhances safety while also helping stretch available funding for bridge repair and replacement.”

Baby Boomers

Minnesota has one of the highest concentrations of timber bridges in the country — 1,600 (down from 1,970 in 2001), more than half built before 1971.

These bridges typically start experiencing issues in their substructure when they reach 40 to 60 years old, with decay usually occurring where the piling meets the ground or water line – a perfect environment of air and moisture for rot to thrive and propagate.

Unfortunately, some bridges were unwisely built on the pilings of former bridges.

“Well-maintained, well-designed and well-treated bridges can last a long time, equivalent to other materials,” said Brian Brashaw, director of Wood Materials and Manufacturing Program at the University of Minnesota-Duluth.

Age of Minnesota's Timber BridgesBecause bridge engineers have been unable to fully assess the internal cross-sections of timber bridges, they have been very conservative when assessing timber bridges, Brashaw said, resulting in load limit reductions and bridge replacements.

“The use of advanced techniques will take the guess work out of the equation, allowing for better decision-making on which bridges need repair or replacement now,” Brashaw said.

With no formal national or state guidance, MnDOT and the Local Road Research Board undertook a research project to identify state-of-the-art inspection practices and marry those techniques with the needs of Minnesota county engineers.

“We don’t have enough money to just replace all the timber bridges, so we want to provide county engineers with more advanced inspection tools so they can determine how much decay there is in the piling, and other susceptible areas,” Conkel said.

A second LRRB project, led by Iowa State University, is advancing the development of cost-effective repair techniques that counties can use to lengthen a bridge’s service life.

“We can’t build them fast enough, so we have to find a way to make them last longer so we can catch up,” Hemmila said.

Upcoming courses (see flyer) *

May 14: SE Minnesota – Register Here for Welch, MN

May 15: SW Minnesota – Register Here for Windom, MN

June 23: NE Minnesota – Register Here for Aitkin, MN

June 24: NW Minnesota – Register Here for Bemidji, MN

 

*All classes 9:00 a.m. to 3:30 p.m.

Bicycling, Policy and Planning, Research

Bike to Work Day: progress in Minnesota, but miles to go

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By Greg Lindsey

This blog post by University of Minnesota Professor Greg Lindsey was originally posted on the CTS Conversations blog.

April 9 is national Bike to Work Day, a day to celebrate those who choose bicycling as their principal mode of transportation for commuting, and a time to encourage more people to consider this healthy, efficient transportation option. Minnesota has much to celebrate in terms of bicycle commuting. Bike-Walk Twin Cities and Transit for Livable Communities are wrapping up the National Non-Motorized Pilot Program, a federally funded program to demonstrate the potential to increase biking and walking through focused investment in infrastructure and other interventions. Bicycle commuting rates in Minneapolis have climbed to 4.5%, and Minneapolis now ranks 20th in the nation in bicycle commute share. This is a noteworthy achievement, especially considering our notorious winter weather. These achievements, along with others such as the success of Nice Ride, our pioneering bike share program, have contributed to Minneapolis being named America’s most bike-friendly city by Bicycling Magazine. Celebration of these achievements – which represent hard work by hundreds of individuals and thousands of commuters – certainly is warranted.

But we only need look across municipal boundaries to know we had better put more energy into encouraging bicycling than into celebration. Bicycle commute rates in St. Paul remain below 2% less than half the Minneapolis rate, and rates in most suburban, exurban, and rural communities remain even lower. And the story remains essentially the same for all types of bicycle trips. Jessi Schoner, a doctoral candidate in the Department of Civil Engineering, is analyzing non-motorized mode shares for all trips recorded the Metropolitan Council’s recent Travel Behavior Inventory. Her analyses show that bicycling remains an urban phenomenon, with the share of all trips taken by bicycling highest in Minneapolis, followed by St. Paul, and then suburban and outlying communities. Why is this so? Better infrastructure no doubt is part of the reason, but there likely are other reasons, including housing patterns, access to employment, socio-demographic factors, and culture. Additional research is needed.

But this leads to additional reasons to be optimistic this Bike to Work Day: the commitments made by the Minnesota Department of Transportation (MnDOT) to foster multi-modal transportation systems and the agency’s investments in research to increase understanding of bicycle traffic patterns. In 2013, as part of the Minnesota Bicycle and Pedestrian Counting Initiative, MnDOT funded the installation of the state’s first two automated, continuous in-street bicycle counters. These counters, which monitor bicycle traffic around the clock, 365 days per year, will provide new insights into the bicycle traffic volumes and their daily and seasonal patterns. While bicycle traffic monitoring in Minnesota is only in its infancy, it represents progress towards establishing the evidence base we need to determine how to make bicycling safer and to invest in bicycle infrastructure.

And so celebrate this Bike to Work Day and thank your fellow Minnesotans for all they have accomplished. But also take time to reflect on the work that needs to be done to improve opportunities for cycling throughout the state, for we have miles to go.

Greg Lindsey is a professor at the University of Minnesota Humphrey School of Public Affairs. His areas of specialty include environmental planning, policy, and management. His current research involves studies of the relationship between the built environment and physical activity, specifically factors that affect the use of pedestrian and cycling infrastructure. Lindsey presented some of his bicycle and pedestrian data collection research at the 2014 Minnesota Transportation Conference held March 4-6.

Environment, Maintenance Operations

Deicing treatments tested at Valleyfair, Canterbury Park

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Excalibur and the High Roller may be closed for the season, but Valleyfair Amusement Park still has one attraction open for the season: a driving track for Minnesota snowplow drivers.

MnDOT-funded researchers are studying the effects of weather and vehicle traffic on different deicing treatments in the parking lots of Valleyfair and Canterbury Park in Shakopee, Minn.

It’s been a busy winter, but each week MnDOT Metro District snowplow drivers make one last stop before heading home, to apply different combinations of salt and anti-icing chemicals to nine 1,000-foot driving lanes. They also drive over each lane multiple times to test the effect of traffic.

“We’re running trucks up to 30 miles per hour with different speeds, wind conditions, traffic conditions and pre-wetting chemicals,” said Steve Druschel, a researcher with the Minnesota State University, Mankato. “Each lane is its own experimental unit.”

Professor Steve Druschel speaks with MnDOT snowplow driver John Hokkanen.
Professor Steve Druschel speaks with MnDOT snowplow driver John Hokkanen.

Professor Druschel’s students will review more than 17,000 photos from time-lapsed cameras to document how the snow melted in each experimental run.

“The influence of factors like pavement type and age, traffic volume, truck proportion, weather conditions and sun presence will be assessed to evaluate which techniques have special advantages for certain situations or roadways,” said Maintenance Research and Training Engineer Tom Peters.

In 2010, Druschel tested 25 anti-icing compounds in 1,500 different combinations in a laboratory to study the effectiveness of different deicers.

“Public work superintendents commented, ‘Great work. It looks good, except it’s all in the lab. Beakers aren’t what people drive on,’ ” Druschel said. “So we’re taking it from the two-inch ice cup to the real world in phase two of this study.”

With rock salt prices quadrupled, finding the most cost-effective methods of treatment is important.

This latest research will help determine the best times for applying anti-icing treatments and examine whether certain chemicals — such as a pre-storm liquid treatment that costs twice as much — melt enough snow to be worth the extra cost.

Test runs in Shakopee are strictly experimental, but in Mankato students are analyzing how real-world salting treatments are working on the North Star Bridge.

An article in the Mankato Free Press tells how Druschel’s team is collecting road melt runoff and documenting bridge traffic. (Big trucks, for instance, squeeze more water out of the snow.)

MnDOT snowplow driver John Hokkanen makes a test run at the research site at Canterbury Park. (Photo by Nick Busse)
MnDOT snowplow driver John Hokkanen makes a test run at the research site at Canterbury Park. (Photo by Nick Busse)

Students plan to use time-lapsed photos, along with weather data and snowplow records, to determine what chemical treatments worked best – and when.

With the multi-pronged research project, Druschel hopes to put definitiveness to what some snowplow drivers have already tried in the field.

“The key to it is not so much that we’re so smart and we have a better idea or are inventing something new,” he said. “We’re just trying to enhance what they are already doing.”

Helpful resources

Salt Brine Blending to Optimize Deicing and Anti-Icing Performance –Technical Summary (PDF, 1 MB, 2 pages) and Final Report (PDF, 11 MB, 151 pages) (previous study) 

 

Pedestrian, Traffic and Safety

Smartphone app guides blind pedestrians through work zones (updated)

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Each year, approximately 17 percent of road construction work zone fatalities nationwide are pedestrians.

At special risk are the visually impaired, who rely on walking and public transportation to get around.

A major challenge  for them is crossing the street — which is even more difficult if an intersection is torn up.

MnDOT has invested significant effort to accommodate pedestrians, particularly those with disabilities, in temporary traffic control situations. This includes requiring temporary curb ramps and alternative routes when a sidewalk is closed.

Researchers, funded by MnDOT, have now developed a cell phone application to guide blind pedestrians around a work-zone.

Illustration of Bluetooth beaconplacement at decision points around a work zone.
Illustration of Bluetooth beacon placement at decision points around a work zone.

Building on previous work to provide geometric and signal timing information to visually impaired pedestrians at signalized intersections, the smartphone-based navigation system alerts users to upcoming work zones and describes how to navigate such intersections safely.

The smartphone application uses GPS and Bluetooth technologies to determine a user’s location. Once a work zone is detected, the smartphone vibrates and announces a corresponding audible message. The user can tap the smartphone to repeat the message, if needed.

The federal government strongly encourages states to provide either audible warnings or tactile maps at work zones where visually impaired pedestrians are expected to be impacted.

“The smartphone application is a step in that direction,” said MnDOT technical liaison Ken Johnson. “It’s a way to see if this type of way-finding device would work.”

Since smartphone use is still limited, the state is also interested in special equipment that could relay the audible warnings at affected work zones.

“However, smartphone use is increasing in the general population, as well as with persons with disabilities, and there will likely be a day when it will be rare to not have a smartphone and this tool could meet road agency needs,” Johnson said.

Before developing the smartphone application, researchers surveyed 10 visually impaired people about their experiences at work zones and what types of information would be helpful in bypass or routing instructions.

The University of Minnesota research team, led by Chen-Fu Liao, tested the smartphone application by attaching four Bluetooth beacons to light posts near a construction site in St. Paul.

Additional research is now needed to conduct experiments with visually impaired users and evaluate system reliability and usefulness.

*Update 4/29/2014: Check out this story from KSTP on the app.

More information

Development of a Navigation System Using Smartphone and Bluetooth Technologies to Help the Visually Impaired Navigate Work Zones Safely — Final Report (PDF, 1 MB, 86 pages)

Environment, Materials and Construction

Flume research simulates Red River flooding to test road protections

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Flooding in the Red River Valley is an almost annual occurrence, and the cost to roads, property and lives is huge.

Highway 1 gets torn up year after year, only to be rebuilt in time for next year’s flood, joke residents in the little town of Oslo, which becomes an island whenever the roads close.

While not much can be done to prevent swollen farm fields from overflowing, what if a road embankment itself could be bolstered to prevent physical damage to the underlying structure of the road?

“We can’t just raise the road because it would create backwater upstream,” explained JT Anderson, Assistant District 2 Engineer. “Our best bet is to let the water over-top the road and try to protect the road when it does.”

Researchers have built a flume inside the University of Minnesota’s St. Anthony Falls Laboratory to test six methods of embankment protection specific to the needs of towns like Oslo.

“It is not uncommon for one over-topping site to have a half-mile long stretch of road being damaged,” said university research engineer Craig Taylor. “One road being protected should cover the cost of the study and the cost of deploying the erosion control product for that road.”

Nationally, research of this kind has mostly been restricted to high-intensity flooding.

“Those really high-depth, short duration events, you can only protect an embankment with concrete and boulders,” Taylor said. “With longer duration, low-depth floods, we may be able to protect roads with soft armoring, like reinforced vegetation.”

The damage in northern Minnesota has been the worst on east-west roads, where the river flow runs perpendicular to the center of the road, causing the road to act like a dam and the water to jump at the edges.

“It eventually eats through that road embankment and makes the road collapse,” Anderson explained.

Researchers will examine how a cross-section of a road holds up under various erosion control methods at different levels and speeds of water-flow.

The damage from flooding was less in 2010 after engineers added rocks and vegetation to the side of Highway 9, near Ada.
The damage from flooding was less in 2010 after engineers added rocks to the side of Highway 9, near Ada, Minn.

One test will be to slow the flow of water by covering the road shoulder with a rubberized membrane and temporary water-filled tubes.

Permanent schemes — such as turf reinforcement mats and rocks — will also be tested.

“These methods have been deployed in the field, but you never really know under which conditions they survived or failed,” Taylor said.

In the Red River Valley, MnDOT engineers have tried a combination of vegetation and boulders, as well as concrete blocks covered with topsoil, to protect highways. Flattening a slope is another option.

“I expect that a single erosion protection technique will not cover every situation our road embankments may be exposed to at any given location,” Anderson said.  “Rather, I expect we would look at using several different techniques in concert to develop an effective erosion protection system for the expected velocities.”

Policy and Planning, Research

Funding highway projects with value capture could speed project completion

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There’s broad agreement that the U.S. transportation system cannot continue to be funded with existing financing and revenue-generation methods. What’s unclear, however, is how to pay for highway projects in the future. The current transportation funding system emphasizes user fees, but there is growing interest in alternative funding strategies. One promising strategy is value capture, which aims to recover the value of benefits received by property owners and developers as a result of infrastructure improvements.

In recent years, University of Minnesota researchers have helped lead the way in value capture research with a series of reports identifying value capture strategies. In a newly published study, the research team applied their previous work to a real-world scenario, with impressive results.

The new research, sponsored by the Minnesota Department of Transportation, focused on the planned development of Trunk Highway 610 (TH 610) in Maple Grove, Minnesota—a stretch of planned state highway delayed for years by state transportation funding shortages. Researchers set out to discover how the value of the enhanced accessibility provided by the planned improvements could be predicted and captured to help fund the project’s completion.

To accomplish their goal, researchers first defined a study area of about 10 square miles surrounding the unfinished highway segment. Then, they modeled property values based on five factors using parcel-level data. This model was designed to isolate the so-called “highway premium” by controlling for other factors that affect land value including water views, open space, railroads, transit stops, and existing highway exits. Using this model, researchers found significant evidence that the completion of the highway could lead to an over $17 million increase in property value.

Researchers expect these findings to have significant benefits for the TH 610 project and beyond.

Read the full article in the March issue of Catalyst.

Photo courtesy of SRF Consulting Group, Inc.

Traffic and Safety

Warning system could protect drivers from traffic ‘shock waves’

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Two summers ago, the Minnesota Department of Transportation installed electronic message boards on parts of Interstates 35W and 94 to help warn drivers of crashes and to recommend speed levels during periods of high congestion.

Now, MnDOT would like to use the devices — officially known as Intelligent Lane Control Signs (ILCS) — to advise drivers of sudden stopping or slowing of traffic.  Many crashes occur when drivers cannot react quickly enough to these changes.

The Minnesota Traffic Observatory (shown in the feature photo above) is developing a warning system to detect such problematic traffic patterns and issue automatic advisories to drivers.

Shock waves on I-94

A section of I-94 in downtown Minneapolis, where southbound I-35W and westbound I-94 converge, may have the highest crash rate in the state.

As shown in the video above, vehicles constantly slow down and speed up here during rush hour, which causes a ripple effect called “shock waves.”

“There’s a crash every two days,” said University of Minnesota researcher John Hourdos, whose students watched over a year’s worth of video footage to document every accident and near accident. “They’re not severe crashes — no one has died for as long as I can remember, and most happen at slow speeds — but they cause a lot of delays for the traveling public.”

When statistics were still being kept, this section of I-94 had the highest number of accidents in the state, with approximately 150 crashes and 400 near crashes observed in 2003.

Researchers developed a program 10 years ago to detect “shock wave” patterns in the traffic, but they couldn’t develop a practical solution until the state invested in electronic message boards.

The University of Minnesota deployed cameras and sensors on three downtown rooftops in 2002 to observe traffic patterns.  They provide seamless coverage of the entire area, allowing researchers to watch vehicles from the moment they enter and exit the area. MnDOT has added additional cameras and detectors to watch over this roadway section. For the past year, the combined efforts of MnDOT and the university have provided data from 26 cameras and 12 traffic sensors for the two-mile section that includes the high-crash frequency location.

Thanks to the message boards, Hourdos and his team can now create an automated system to warn drivers when conditions for “shock waves” are greatest, using an algorithm he developed in the previous study.

Traffic monitoring equipment on a rooftop
From downtown Minneapolis rooftops, traffic monitoring equipment detect shockwaves on Interstate 94.

Crosstown interchange 

A newer problem that researchers hope to tackle is the lineup of cars on I-35W southbound during rush hour at the newly reconstructed Crosstown interchange.

Although two lanes of traffic are provided for eastbound Highway 62 at the I-35W/62 split, these vehicles must later converge into one lane, due to the Portland Avenue exit. This causes a back-up on the 62 ramp that stretches back to 35W.

Hourdos said developing an algorithm to detect these queues is a different problem than what goes on with I-94, since there is a constant stoppage of cars and no rolling shockwaves.

“Combining the two methodologies will form a more robust solution and a single implementable driver warning system,” Hourdos said.

Researchers might target other problems areas should the state  install additional ILCS message boards elsewhere in the Twin Cities.

Minnesota's transportation research blog