Category Archives: Materials and Construction

MnROAD Breaks New Ground

In June, MnROAD, the only cold-weather accelerated pavement testing facility of its kind in North America, begins construction on its third phase of research since 1994, the first time MnDOT has rebuilt in partnership with other states.

Dozens of new experiments are planned along MnROAD’s test tracks in rural Albertville: the high-volume original Interstate-94 westbound (built in 1973), the mainline I-94 westbound (originally opened in 1994) and an adjacent low-volume road closed track.

Six states and numerous  industry partners recently formed the National Road Research Alliance (NRRA) to co-sponsor  the reconstruction.

NRRA-prioritized research will support state and local needs, including effective use of fiber-reinforced concrete, asphalt overlays of concrete pavements, cold central plant recycling and concrete partial depth repairs to name a few.

MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.
MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.

“The advantage of having these test  sections at MnROAD is we can take  bigger risks and push the envelope in terms of mix designs and layer thicknesses for both asphalt and concrete  layers that could not be done on a public roadway,” MnDOT Research Operations Engineer,   Dave Van Deusen said.

Forensic analysis of failed cells
Many old test cells will be dug up.  Before any reconstruction starts, however, each test section that is being reconstructed will receive a final forensic study. This allows researchers a look at each layer to see the distress that has occurred over the years—and make the final analysis of why it failed. There are always a lot of theories on the causes of what actually failed, but until the forensic is performed, there isn’t proof on what happened. These findings will help build longer-lasting pavements in the future.

The bid letting date for this year’s construction is April 28, but plans were made available for contractors on March 31. This should give the projects more exposure and generate more interest. Construction begins June 5 and continues until November 2017.

Focus Areas

  • HMA overlay and rehab of concrete and methods of enhancing compaction – States are looking for longer lasting HMA overlays of concrete. New mix designs were developed to promote long-term performance, including how reflective cracking effects can be minimized through design or other joint treatment.
  • Cold central plant recycling – Other states have used reclaimed asphalt pavement stockpiles into plant mix base course mixes (layers below the wear surface) to effectively recycle these materials in a controlled mix design. How can these layers best be used and what type of surface mix or chip seal can be placed on top?
  • Fiber reinforced concrete pavements – Nationally, states want to get a better understanding of the beneficial use of fibers in concrete pavement layers. Is it worth the cost? How can it be best used in both thin city streets and higher volume roadways? Can it be used in new construction and in concrete overlays? The research will provide the answers.
  • Long-term effects of diamond grinding – Each state has aggregates that have been used in concrete pavements that are considered reactive aggregates. Questions arise as to whether diamond grinding might accelerate deterioration in these pavements. What types of topical sealers can be used to treat the surface after the diamond grinding will also be tested.
  • Early opening strength to traffic – What effect does heavy traffic loading have on the long-term performance of full-depth concrete pavement, as well as fast–setting repairs? Test sections will be loaded by a pickup truck in one lane early enough to produce shallow ruts in the surface. In the other lane, a loaded 18-wheeler will travel over the new concrete immediately after it sets, and then sequentially every six hours up to 30 hours. The long-term effects of these early loadings will then be evaluated.
  • Optimizing the mix components for contractors – What effect do low-cementitious content mixes have on long-term performance and constructability of concrete pavements?  Two low cementitious content mixes will be studied to give agencies a better understanding of cost savings. Can these savings be achieved without significantly affecting long-term performance?
  • Compacted concrete pavement for local streets – Compacted concrete pavement is a form of roller compacted concrete that has a standard concrete pavement surface texture. The RCC industry has been successful in Michigan and Kansas constructing CCP pavement on local streets.  This research will determine if the texture that is accomplished is durable in harsh freeze-thaw climates.
  • Recycled aggregates in aggregate base and larger sub-base materials – States continue to look for effective ways to recycle materials into unbound bases. This research will add to MnROAD’s understanding of recycled bases and what seasonal strength values can be used for advanced mechanistic designs–and how they are affected by size/gradation.
  • Maintaining poor pavements– Road owners continually have less funding to maintain their roadway systems. What practices should be used for stabilizing both hot mix asphalt and Portland cement concrete roadways when longer-term repairs cannot be done due to funding levels?
  • Partial depth repair of concrete pavements – Agencies continually seek improved materials and methods for the repair of concrete pavements. In this study, up to 15 innovative concrete pavement repair materials will be evaluated on the concrete panels of the westbound I-94 bypass parallel to the MnROAD mainline.
  • Thin overlays-Experimenting with very thin overlays could provide a real benefit for a lot the roads currently out there. The premise is that with thin overlays, the ride can be smoother and the life of older roads can be extended.

“We don’t often get to reconstruct random roads these days, and when we do, we have much better specifications for low temperature cracking. By the same token, we have to maintain all those older roads built before we had performance grade binders,” said Dave Van Deusen, Materials and Road Research Lab principal engineer. “We will be doing this makeover on an original section of MnROAD built back in the 90’s.”

In one experiment, there is a head-to-head comparison of thin overlays on two sections of road. One section has a thick base and subbase under the asphalt. The other has a heavy asphalt top with very little base.

Van Deusen says if they can get an extra five years of life out of road using thin overlays, he would be pleased. Often, he admits, he is surprised by how long these “short-term” fixes actually last.

Stay up-to-date on construction by signing up for email alerts at mndot.gov/mnroad.  

Taconite byproduct reduces road wear from studded tires

In a recent project, the Alaska Department of Transportation (DOT) used a byproduct of Minnesota’s taconite mining industry for a section of the Alaska Glenn Highway.

The taconite byproduct—Mesabi sand—serves as the aggregate of a sand-seal treatment for a 4,600-foot stretch of the highway just north of Anchorage. Sand seals are an application of a sealer, usually an emulsion, immediately followed by a light covering of a fine aggregate (the sand).

“Our goal was to explore pavement preservation measures that extend pavement life and that also resist studded tire wear,” says Newton Bingham, central region materials engineer with the Alaska DOT. “Studded tires are allowed from mid-September until mid-April, and they cause rapid pavement wear.”

For the project, the Alaska DOT obtained sample pavement cores from the test area in 2014. Researchers then applied sand seals with two different hard aggregates—calcined bauxite and the Mesabi sand—to the surface of the cores to evaluate the effectiveness of each treatment.

Larry Zanko, senior research program manager of the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth, was the on-site representative for the taconite sand analysis. NRRI focuses on strategies to recover and utilize mineral-resource-based byproducts such as taconite and find potential beneficial end-uses for them.

“Taconite is one of the hardest natural aggregates,” he says. “Minnesota’s taconite mining industry generates tens of millions of tons of byproduct materials every year that could be used as pavement aggregate. Friction aggregates could be a higher-value niche for the industry.”

Testing of the sand-seals showed similar wear resistance for both types of aggregates. “We chose taconite sand since it is available from Minnesota as an industrial byproduct, whereas calcined bauxite sand has to be imported from nations on the Pacific Rim and costs more due to shipping,” Bingham says.

The Alaska DOT reports good performance to date on Glenn Highway and is funding ongoing pavement wear measurement.

NRRI researchers are also studying the use of taconite for other pavement applications. Funded by MnDOT, Zanko’s team developed (and later patented) a taconite compound for repairing pavement cracks and patching potholes (see an article the September 2016 Catalyst). The long-lasting patches reduce maintenance costs and traffic disruption. In continuing work funded by the Minnesota Local Road Research Board, researchers will refine the repair compound and develop and field-test a low-cost mechanized system for pavement and pothole repairs.

Thicker may not equal stronger when building concrete roadways

Transportation agencies have long placed high importance on the thickness of their concrete roadways, making it a major focus of control and inspection during construction. While it is commonly believed thicker concrete pavements last longer, there is little data to support this claim.

“One big reason for the lack of data on the relationship between concrete pavement thickness and performance is the destructive nature of these measurements,” says Lev Khazanovich, a former professor in the University of Minnesota’s Department of Civil, Environmental, and Geo- Engineering. “Concrete thickness is typically assessed by coring—a destructive, expensive, and time-consuming test that only offers widely spaced measurements of thickness.”

In a MnDOT-funded study, U of M researchers set out to fill this knowledge void by leveraging recent advances in the nondestructive testing of pavements that allow for large-scale, rapid collection of reliable measurements for pavement thickness and strength. They conducted four evaluations on three roadways in Minnesota using ultrasonic technology to collect more than 8,000 measurements in a dense survey pattern along with a continuous survey of observable distress.

“We found that both pavement thickness and stress measurements are highly variable, with a half-inch of variation in thickness about every 10 feet,” Khazanovich says. “Interestingly, three of the four surveys averaged less than design thickness, which is contrary to typical accounts of contractors building slightly thicker slabs in order to avoid compensation deductions.”

Data analysis showed that exceeding design thickness did not seem to increase or decrease pavement performance. However, a measurement of pavement strength and quality known as “shear wave velocity” did produce valuable findings. “A drop in the shear wave velocity strength measurement corresponded to an increase in observable pavement distresses such as cracking and crumbling,” Khazanovich explains. “This was especially apparent when we were able to easily identify locations of construction changes, where significant changes in shear wave velocity matched up with observable distress.”

The results of this study illustrate the importance of material quality control and uniformity during construction, since alterations in pavement strength and quality may significantly influence pavement performance. In addition, researchers say that despite inconclusive thickness results, it is still important that pavement has significant thickness to carry its intended traffic load over its service life. Finally, the study demonstrates that new methods of ultrasonic shear wave velocity testing are useful for identifying changes in construction and design that could lead to higher rates of pavement distress.

Partner States Get First Look at Minnesota Road Experiment

Walking along a half-mile segment of Co. Rd. 8 near Milaca last month, materials engineers from around the country got a first look at a shared test site for pavement preservation.

Nearly 60 one-tenth mile sections of Co. Rd. 8 and nearby Hwy 169 were recently treated with various combinations of fog seals, chip seals, crack seals, scrub seals and microsurfacing and a number of thin overlays. Data will be collected from these experimental test roads for three years and compared with the results of a similar experiment in Alabama, where the same test sections were also built on a low- and high-volume roadway, to see which techniques are the most effective for preserving road life.

“Evaluating pavement performance in both northern and southern climates will provide cost-effective solutions that can be implemented nationwide,” said Ben Worel, MnROAD operations engineer.

Photo of Barry Paye, Wisconsin DOT chief materials engineer; and Tim Clyne, MnDOT Metro District materials engineer.

From left, Barry Paye, Wisconsin DOT chief materials engineer, and Tim Clyne, MnDOT Metro District materials engineer, participate in a discussion about future road research needs. Photo by Shannon Fiecke

Nineteen states, which are co-funding the study through MnDOT’s road research facility (MnROAD), were in town Oct. 26-27 for a joint meeting with the National Center for Asphalt Technology in Auburn, Ala. In addition to touring test sections built this summer near Milaca and at MnROAD’s permanent test track in Albertville, the group reviewed preliminary research results and discussed ideas for new experiments.

MnROAD began two joint research efforts with NCAT last year to advance pavement engineering issues that affect both warm and cold climates. In addition to determining the life-extending benefits of different pavement preservation techniques, the partnership has also built test cells to evaluate which asphalt cracking prediction tests best predict future pavement performance. This second study will help state DOTs improve the quality of asphalt mixes, so roads hold up better through harsh winters, leading to less thermal cracking and fewer potholes.

Click here to learn more about the MnROAD-NCAT partnership.

MnDOT, Alabama center team up for national pavement research

The nation’s two largest pavement test tracks are planning their first-ever co-experiments.

The Minnesota Department of Transportation’s Road Research Facility (MnROAD) and the National Center for Asphalt Technology (NCAT) began discussing a formal partnership last year and have now asked states to join a pair of three-year research projects that will begin this summer.

Representatives of the test tracks are meeting next week in Minneapolis at the 19th Annual TERRA Pavement Conference. They said the partnership will develop a national hot mix asphalt cracking performance test and expand the scope of existing pavement preservation research at the NCAT facility in Auburn, Alabama, to  include northern test sections in Minnesota.

MnROAD plans to build test sections at its facility and also off-site on a low- and high-volume road, which may include concrete test sections if funding allows. These Minnesota test sections will supplement 25 test sections built by NCAT on an existing low-volume haul route in 2010 and an off-site high-volume test road planned for this summer in Alabama to assess the life-extending benefits of different pavement preservation methods. Both agencies have also been developing performance tests to predict the cracking potential of asphalt mixes, and they will now work together on that research as well.

“We will collect and analyze the data in similar ways, and I think we’ll have a greater appeal nationally, as we cover a range of climate conditions,” said MnROAD Operations Engineer Ben Worel.

Participation in the pavement preservation study is $120,000 per year for the initial research cycle, which will drop to $40,000 after three years; the cracking study will run three years at $210,000 per year.  Alabama will be the lead state for this effort.

State departments of transportation are asked for commitment letters this month if they are interested in joining either study, even if they do not have SP&R (State Planning and Research) dollars available at the time. Participating agencies will get to design the scope of the research and be kept advised of the ongoing findings, so they can benefit early from the project. Initial planning meetings will be done through a series of webinars in March and April of this year with participating agencies.

At a January 8 webinar, speakers said the research will help states determine how long pavement preservation treatments will last.

“Many DOTs have really well-designed and well-thought-out decision trees, where they can take pavement management data and end up with a rational selection of pavement alternatives. But the issue of extending pavement life is the really big unknown, because references provide a broad range of expected performance,”  NCAT Test Track Manager Buzz Powell said.

Another benefit is that states can learn how pavement treatments hold up in both hot and cold climates.

“It’s 14 degrees right now in Mississippi. It rains about every three days, freezes and then thaws,” said Mississippi Chief Engineer Mark McConnell. “So we need to know how pavement preservation is going to work in the north as well.”

For additional information, contact Ben Worel (ben.worel@state.mn.us) at MnROAD or Buzz Powell (buzz@auburn.edu) at NCAT.

mnroad_ncat
Aerial views of the pavement test tracks at MnROAD (left) and NCAT (right).

New Tool Measures Impact of Heavy Trucks

A new tool developed by the Local Road Research Board helps cities and counties assess how much increased heavy vehicle traffic affects local roads.

Researchers created an analysis method and corresponding spreadsheet tool that city and county engineers can use to calculate the impact of heavy vehicles on asphalt roads beyond what was planned in the original pavement design.

The information will help agencies optimize services, such as garbage collection, for the least amount of damage. It will also help agencies better plan roads in new developments, as well as redesign existing roads that are nearing the end of their lives.

Lack of Data

Heavy trucks cause local roads to deteriorate more quickly than passenger vehicles, but it is challenging to quantify the impacts, especially for areas where traffic was not forecast at the time a road was designed.

Many local engineers in Minnesota have requested information about the impact of heavy vehicles in light of new construction, commercial distribution facilities and hauling routes. This information is needed to assist in local road planning and maintenance.

Two Methods

In a newly completed study, investigators developed two methods for calculating heavy vehicle impact:

  • Calculate the additional bituminous material (and associated costs) that would have been required to construct the pavement had the heavy truck traffic been predicted when the pavement was designed.
  • Calculate the portion of a pavement’s design life, measured in equivalent single-axle loads (ESALs), consumed by unanticipated vehicles.

“Before this project, there wasn’t an easy way for an engineer to determine how much a specific truck was going to decrease the life of a road,” said  Deb Heiser, Engineering Director, City of St. Louis Park.

Whereas previous research has calculated the impact of extremely heavy vehicles over the short-term (typically the course of a construction project), this project calculates the impact of long-term increases in traffic from vehicles that are heavy, but still mostly within normal legal weight limits.

The tool can be used for a single street segment or an entire road network. Users can also compare current situations with proposed ones to evaluate the impact of potential changes in heavy traffic levels.

Related Resources

The 411 on Sign Management

A revised handbook offers Minnesota cities and counties the latest tips on how to meet new sign retroreflectivity requirements, as well as the 411 on sign maintenance and management – everything from knowing when it’s time to remove a sign to creating a budget for sign replacement.

The best practices guide – produced in conjunction with a new sign retroreflectivity study – also offers case studies from around the state.

“The life cycle of traffic signs, from installation to replacement, is a pretty complex issue and it can be a challenge to get your arms around,” said Tim Plath, Transportation Operations Engineer for the city of Eagan. “This handbook really boils it down into some basic concepts and also gives you the resources to dig deeper if necessary. It’s a good resource to have at your fingertips.”

2014RIC20-1

This handbook updates a previous version issued in 2010, to include new FHWA  retroreflectivity and maintenance and management requirements and deadlines.

“Maintenance/management of a large number of signs can potentially be an administrative and financial challenge for many local road authorities,” explained Sulmaan Khan, MnDOT Assistant Project Development Engineer.

Here’s a video demonstration of a sign life reflectometer (the Gamma 922), another resource MnDOT has available for local government agencies. Cities, townships or counties may borrow the reflectomer by contacting the Office of Materials and Road Research, (651) 366-5508.

Related Resources

Traffic Sign Maintenance/Management Handbook (PDF)

Traffic Sign Life Expectancy – Technical Summary (PDF) and Final Report (PDF)

Gamma 922 demonstration (video)

How roadside drainage ditches reduce pollution

Stormwater can pick up chemicals and sediments that pollute rivers and streams. Roadside drainage ditches, also known as swales, lessen this effect by absorbing water. But until recently, MnDOT didn’t know how to quantify this effect and incorporate it into pollution control mitigation measures.

In a recently completed study, researchers evaluated five Minnesota swales, measuring how well water flows through soil at up to 20 locations within each swale.

“There’s a big push in Minnesota, and probably everywhere, to do more infiltration,” Barbara Loida, MS4 Coordinator Engineer, MnDOT Metro District, said. “We know that our ditches are doing some of that, but we wanted to look at how much infiltration these ditches are providing.”

A key finding: grassed swales are significantly better at absorbing water than expected, which may reduce the need for other, more expensive stormwater management practices, such as ponds or infiltration basins.

This could save MnDOT and counties significant right-of-way and construction costs currently expended on more expensive stormwater management techniques. While swales were recognized in the Minnesota Pollution Control Agency’s new Minimal Impact Design Standards, there was a need to quantify the amount of water a swale can absorb so it could receive the appropriate MIDS credits.

Researchers also tested the ability of carbon, iron chips, steel wool and other materials to remove pollutants as ditch check filters—material put into swales to enhance removal of pollutants.

Gradations on a Modified Philip Dunne infiltrometer allow the measurement of stormwater infiltration.
Gradations on a Modified Philip Dunne infiltrometer allow the measurement of stormwater infiltration.
What’s Next?

A follow-up project, which the MPCA is participating in, will seek to clarify the impact of swale roughness on infiltration rates. The goal is a calculator for real-world infiltration rates that MnDOT and local agencies would be able to implement.

MPCA, MnDOT and the city of Roseville are also partnering on a project to install and test the effectiveness of ditch check filters in real-world locations.

Maintenance recommendations should help MnDOT and local agencies ensure that swales operate at maximum efficiency. These recommendations should continue to be revised as knowledge evolves.

Related Resources

*Editor’s note: This article was adapted from our upcoming edition of the Accelerator. Read the newsletter online, or sign up to receive by mail. 

Partnership planned for nation’s top pavement testing facilities

The nation’s two largest pavement testing centers are planning to partner in order to better leverage research performed at their cold and hot-weather facilities.

MnROAD, located in Albertville, Minnesota, and its southern U.S. equivalent, the National Center for Asphalt Technology in Auburn, Alabama, are full-scale test tracks that evaluate different types of pavement material under real-life conditions using semi-trailer truck and live interstate traffic.

Each facility has a history of evaluating the performance of pavement preservation treatments, including chip sealing, micro-surfacing, crack sealing and thin overlays. To address needs in both northern and southern climates, similar test sections would be developed at each facility to address national issues.

“By working together we can maximize the potential for each track,” said MnROAD Operations Engineer Ben Worel. “A closer relationship between NCAT and MnROAD is a logical progression in developing and evaluating new sustainable technologies, pavement systems and construction methods that lead to safer, quieter, lower-cost and longer-lasting roads.”

A test track at the National Center for Asphalt Technology in Alabama, MnROAD's hot-weather equivalent.
A test track at the National Center for Asphalt Technology in Alabama, MnROAD’s hot-weather equivalent.

The partnership idea was introduced to federal officials earlier this month at a national pavement performance conference in Minneapolis. Final details must still be worked out.

One of the workshops at the event discussed the proposed partnership between MnROAD and NCAT. Further talks are expected at the end of October.

“NCAT is thrilled about the opportunity for a partnership with MnROAD to address pavement research needs at a national level,” said NCAT Director Randy West. “Bringing NCAT and MnROAD results together will expand the climate base, loading distribution and other important pavement factors.”

Pavement conference

Pavement engineers from around the nation gathered Sept. 2 to 5 for the Midwestern Pavement Preservation Partnership forum and the SHRP2 R26 Workshop for the Preservation of High-Traffic-Volume Roadways, which featured tours of MnROAD, Minnesota’s cold weather pavement testing facility.

Conference participants also reviewed the latest preservation techniques being developed for high volume roads. MnROAD’s chip sealing study, which demonstrated that highways with an average daily traffic (ADT) of 58,000 can be successfully chip sealed, was especially attention-grabbing for agencies who don’t chip seal on roads with more than 2,000 ADT.

A national panel of speakers included Michael Trentacoste, director of the federal Turner-Fairbank Highway Research Center (pictured in top photo), who discussed Federal Highway Administration’s support of pavement preservation research and implementation.

With about 160 people in attendance over four days, MnDOT Materials Engineer Jerry Geib said the conference was successful in sharing the benefits of pavement preservation techniques with other state DOTs and federal highway officials who want adopt new practices to help alleviate budget constraints.

MnDOT saves time, money with new contracting method

Thanks to a flexible new contracting method, the cost and time of delivering small highway projects in Minnesota should go down.

The Minnesota Department of Transportation is now able to put road construction contractors on standby for certain types of projects, rather than bid each project individually, due to the adoption of Indefinite Delivery/Indefinite Quantity (IDIQ) contracts.

“IDIQ contracts give MnDOT more flexibility and the ability to get to the field quicker for work that we need repeated routinely, such as culvert repairs, overlays and seal coats,” said Kevin Kosobud, project development engineer with MnDOT’s Office of Construction and Innovative Contracting.

IDIQs also provide flexibility when needs are uncertain.  Contracts are often used for multiple small projects that are similar in scope, but difficult to quantify in cost and timing.

For instance, the state of Florida awards IDIQs for hurricane debris removal, activating and paying contractors only when a hurricane necessitates the service.

Although IDIQs showed great promise, MnDOT had to develop a framework to implement them.

The federal government has used IDIQ contracts since the 1980s, but only a small number of state DOTS have used them to procure construction services. No standard procedures existed for their use by state DOTs, and federal procedures are not always applicable at the state level.

MnDOT hired Iowa State University researchers to examine IDIQ usage across the country and develop implementation procedures for Minnesota. (Read a summary of their research here.)

Researchers examined contracting practices at 14 different transportation agencies to  recommend guidelines for Minnesota to follow, which allowed MnDOT to begin awarding IDIQ contracts in April 2013.

Case study analyses show clear benefits where IDIQ has been used: acceleration of the project delivery period, reduced construction costs and flexible delivery scheduling.

“IDIQs can help DOTs get better prices for routine services via an economy of scale, for instance, by awarding a contract for a larger number of culvert repairs rather than awarding a single contract for each repair,” explained Doug Gransberg, professor of construction engineering at the Iowa State University Institute of Transportation.

Agencies can award IDIQ contracts individually or collectively.

With a single-award contract, a single contractor is awarded task orders based on the pricing furnished in the initial bid package; multiple-award contracts determine a pool of qualified contractors who may subsequently bid on task orders.

*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.

Related Resources
  • Leveraging the Advantages of Indefinite Delivery/Indefinite Quantity Contracts – Technical Summary (1 MB, 2 pages); Final Report (expected Fall 2014)