Category Archives: Materials and Construction

New test could help asphalt pavements survive winter intact

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)

Flume research simulates Red River flooding to test road protections

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.”

Innovative pavement textures reduce noise, improve fuel economy

What if something as simple as changing the texture of the pavements we drive on could not only increase safety, but also reduce noise pollution and boost our vehicles’ fuel economy?

It’s possible, according to the latest research from MnROAD, the state’s one-of-a-kind pavement research facility. In a new report, investigators detail how quieter pavement textures, such as those applied by grinding grooves into pavements with diamond-coated saw blades (see the photo above), may also reduce rolling resistance — the force that resists a tire as it moves across the pavement’s surface.

The potential benefits to the public are significant. A 10-percent reduction in rolling resistance could reduce the U.S. public’s fuel consumption by 2–3 percent, eliminate up to $12.5 billion in fuel costs each year (as well as cutting carbon emissions). Add on the cost savings from reducing noise pollution (building noise barriers along highways can cost as much as $3 million per mile), and it’s clearly a win-win situation.

In the study, researchers used an innovative line-laser profiler to develop three-dimensional representations of test pavement surface textures. They then investigated the relationship between these surface characteristics and data on rolling resistance that was collected during a 2011 study using a special test trailer developed by researchers in Poland. This year, the same trailer will be used to conduct a second round of rolling resistance measurements at MnROAD.

The research is related to an ongoing pooled-fund study on concrete pavement surface characteristics. The goal is to produce data that will allow MnDOT to identify ideal ranges for surface characteristics that improve pavements’ quietness and ride quality while keeping them safe and durable.

Learn more
Researchers relied on rolling resistance data from a study conducted in 2011 with a test trailer developed by the Technical University of Gdańsk, Poland. This was the first time such measurements were taken in the United States.
Researchers relied on rolling resistance data from a study conducted in 2011 with a test trailer developed by the Technical University of Gdańsk, Poland. This was the first time such measurements were taken in the United States.

MnROAD earns concrete pavement association award

Staff from MnROAD, the Minnesota Department of Transportation’s cold weather road research facility in Albertville, Minn., were presented with the Marlin J. Knutson Award for Technical Achievement by the American Concrete Pavement Association in December.

The award cites the facility’s well-deserved reputation for being a place where both agency and industry ideas are put to the test. This award was presented as a tribute to the agency’s commitment to learning and putting ideas into practice.

The Marlin J. Knutson Award for Technical Achievement is presented to an individual or group who has made significant contributions to advance the development and implementation of technical innovations and best practices in the design and construction of concrete pavements.

(far right) Gerald Voigt, ACPA president and CEO, presented MnDOT with the Marlin J. Knutson Award for Technical Achievement during a ceremony in December. Receiving the award are (from left) Luke Johanneck, Bernard Izevbekhai, Roger Olson, Tom Burnham, Glenn Engstrom, Maureen Jensen and Sue Mulvihill. (Photo courtesy of the ACPA)
(Far right) Gerald Voigt, ACPA president and CEO, presented MnDOT with the Marlin J. Knutson Award for Technical Achievement. Receiving the award are (from left) Luke Johanneck, Bernard Izevbekhai, Roger Olson, Tom Burnham, Glenn Engstrom, Maureen Jensen and Sue Mulvihill. (Photo courtesy of the ACPA)

“MnROAD is helping to make roads last longer, perform better, cost less, construct faster, and have minimal impact on the environment,” said Gerald Voigt, ACPA president and CEO. “It is a model for other agencies to follow.”

MnROAD is a pavement test track initially constructed between 1991-1993. It uses various research materials and pavements and finds ways to make roads last longer, perform better, cost less to build and maintain, be built faster and have minimal impact on the environment. MnROAD consists of two unique road segments located next to Interstate 94.

Staff from the MnROAD facility in Albertville were recognized during the ACPA’s Distinguished Service and Recognition Awards ceremony in December. (Photo by David Gonzalez)
Staff from the MnROAD facility in Albertville were recognized during the ACPA’s Distinguished Service and Recognition Awards ceremony in December. (Photo by David Gonzalez)

This article, authored by Rich Kemp, originally appeared in Newsline, MnDOT’s employee newsletter. 

LRRB research showcased at pavement and dust control conferences

The Transportation Engineering and Road Research Alliance and Road Dust Institute conferences are being jointly held this week in Minneapolis. Among the many research topics being presented are several recently completed studies funded by the Minnesota Local Road Research Board.

The LRRB, which celebrates its 55th anniversary this year, is one of only two statewide organizations in the United States that fund transportation-related research projects and education on behalf of local governments.  In honor of the TERRA and dust control events, we thought we’d take the opportunity to highlight a few of the latest pavement and dust control-related research projects from the LRRB.  If you’re at TERRA today, be sure to stop by their booth and check out their latest research results, videos and more.

Recycled Asphalt Pavement: Study of High-RAP Asphalt Mixture on Minnesota County Roads 

This report summarizes the field performance of local roads containing recycled asphalt pavement (RAP), associated field and laboratory work with asphalt activation, and design and performance testing of high-RAP bituminous mixtures. Conclusions include:
• Transverse cracking performance of county highways averaging 20 to 26 percent RAP was improved when PG 52-34 binder was used.
• Coarse aggregates from plant mixing achieved a more uniform coating and were subjected to less abrasion than those from laboratory mixing.
• IDT critical temperature results showed that the addition of RAP significantly increased the critical temperature, predicting less crack resistance.

Research using Waste Shingles for Stabilization or Dust Control for Gravel Roads and Shoulder

Minnesota generates more than 200,000 tons of shingle waste each year. While a small portion of recycled asphalt shingle waste (RAS) can be incorporated into hot-mix asphalt (HMA) pavement mixtures, there is still a lot of waste left over, prompting MnDOT to investigate other potential uses. Alternative options include improving the performance and quality of gravel surfacing and reducing dust by replacing common additives such as calcium chlorides with RAS. This will remove valuable RAS materials from the waste stream, supplement the use of more expensive materials, and improve the performance of local roads.

Aggregate Roads Dust Control: A Brief Synthesis of Current Practices

More than half of our local roadways are gravel roads, making them a vital part of our transportation system. To help control the dust on gravel roads, the Minnesota LRRB has developed a new guidebook, which summarizes a variety dust suppressants, their effectiveness, and impacts.

More than half of our local roadways are gravel roads, making them a vital part of our transportation system. One of the drawbacks and biggest complaints about gravel roads is the dust they produce when vehicles drive over them.  Residents that live on gravel roads deal with the dust that settles on their homes, yards, and parked cars. Dust can also have adverse effects on air quality and the environment. To help control the dust on gravel roads, the Minnesota LRRB has developed this new guidebook, which summarizes a variety dust suppressants, their effectiveness and impacts.

CTS fall research seminars begin September 26

This fall, CTS will offer five research seminars on transportation topics ranging from resilient communities to asphalt at low temperatures.

Seminars will be held every Thursday from September 26 through October 31 (except Oct. 17) on the U of M campus in Minneapolis. You can either attend in person or watch the live webcast of each seminar. Additional information is available on the CTS website.

Seminar schedule:

Geotextile research at MnROAD

Geotextiles are synthetic polymer materials used to improve the performance of roadways. As discussed in this 2011 technical summary, geotextiles facilitate filtration and water drainage, improve the integrity and functioning of base materials, and provide a stable construction platform over soft or wet soils. These improvements can benefit both the cost-efficiency and longevity of pavements.

Geosynthetic materials have been used throughout Minnesota, and can be found in both reconstructed and new roadway projects. The use of geotextiles as a separator layer under concrete overlays, however, has had limited documentation in Minnesota and other cold weather climates. MnROAD‘s recent dedication of several test cells to this purpose will determine the performance of this application of geotextiles, with the goal of improving its applications on other Minnesota roadways.

The new test sections, designated as Cells 140 and 240, consist of a very thin, 3-inch concrete overlay over an existing 7-inch concrete pavement constructed 20 years ago. Some unique features of the design include the use of a fiber-reinforced concrete mix, two different thicknesses of the nonwoven geotextile, and the use of a special type of glue, rather than nails, to fasten it to the existing concrete before paving.

The fabric and fiber used in the concrete mix were supplied through a public-private partnership with Propex Geotextile Systems. The results of this study, along with other unbonded overlays constructed at MnROAD and around the country, will be incorporated into a new national pooled fund project — TPF 5-(269) — led by MnDOT. This project will develop an improved mechanistic design procedure for unbonded overlays.

A second application being demonstrated at MnROAD is the use of a geosynthetic drainage system under several dowel bar baskets in new concrete pavement test section. Minnesota has historically used a dense-graded base layer under concrete pavements to provide a stable foundation and construction platform. However, this material drains very slowly, and traps moisture within the joints, leading eventually to significant distress (See Effect of Drainage on the Performance of Concrete Pavement Joints in Minnesota.) This application will compare the use of the geotextile drainage material placed under both sealed and unsealed joints, as well as a control joint without the drainage material.

Permeable pavements could protect the environment, save taxpayer dollars

KSTP has a nice story today on the Minnesota Department of Transportation’s ongoing research into permeable pavements at the MnROAD research facility. (The video isn’t embeddable on WordPress, but you can find a direct link here.)

Permeable pavements (also known as “porous” or “pervious” pavements) are designed to allow water to pass through roadways and infiltrate directly into the underlying aggregate and soil. Their primary effect is to reduce stormwater runoff, which carries harmful materials from the road’s surface out into waterways. Of course, reducing runoff also mitigates the need for the kinds of costly drainage structures that are normally required to manage stormwater. Permeable pavements also reduce noise and mitigate the potential for hydroplaning, among other documented benefits.

These types of pavements are already used in some areas in Minnesota — mainly in parking lots and city streets — and MnDOT has been studying their potential use for full-depth roadway pavements. As the video indicates, so far the results have been encouraging. (You can read more about MnDOT’s ongoing research on the MnROAD website.)

As a side note, the amount of water these pavements can absorb is quite impressive. Last month, we posted a new Local Road Research Board video on stormwater management. In one scene, a public works crew dumps what appears to be several hundred gallons of water onto a permeable pavement and watch as it disappears almost instantaneously. (Watch the clip here.)

Here are the results of some recent permeable pavement studies here in Minnesota:

Construction kickoff at MnROAD, the state’s high-tech road research facility (updated)

*Editor’s note: This article was updated 6/11/13 with additional information provided by MnROAD engineers.

You’re probably aware that MnDOT recently kicked off its 2013 construction season, comprising $1.1 billion in new transportation investments in more than 300 projects across Minnesota. What you might not know is that another MnDOT construction season has begun at MnROAD, the department’s unique, high-tech pavement test facility located near Albertville, Minn.

MnROAD serves as a proving ground for innovative pavement designs, equipment and construction techniques that help transportation professionals all over the world strengthen roads, cut costs, and reduce construction times. It has a two test tracks — a 3.5- mile mainline carrying “live” traffic and a 2.5-mile closed-loop, low-volume roadway — that are used for state, university and private industry pavement research. These tracks are made up of dozens of individual “cells,” which are unique stretches of pavement each representing several research projects.

This summer, several test cells are being torn up and repaved. Cell 40, a 20-year-old concrete pavement, will receive an innovative 3-inch thick unbonded concrete overlay.  To increase the capacity of such a thin overlay , a fiber-reinforced concrete mixture will be used.  To separate and cushion the thin overlay from the existing concrete, two different thicknesses of nonwoven geotextile fabric will be laid.  This will help MnROAD researchers to understand how much cushioning is needed, as well as the drainage capacity of each fabric.  Fabric interlayers are gaining popularity as an alternative to asphalt interlayers.

Thin concrete overlays of asphalt, commonly known as whitetoppings, will also be used to reconstruct Cells 60-63.  Similar to Cell 40, fiber reinforced concrete will be used to test its benefit in supplementing load transfer at joints and across cracks.  Pavement built with this material will be strengthened by the fiber, prolonging a road’s lifespan, and potentially allowing for thinner concrete pavements.  Findings from Cells 40 and 60-63 support the ongoing development of improved design procedures for concrete overlays.

Cell 13 reconstruction is using recycled concrete aggregate provided by the contractor’s stockpile from other pavement projects. The concrete from the stockpile will be included in the concrete mix — a new practice to understand how to better recycle paving materials and ascertain the cost and benefits of this practice. Cell 13 will also be testing two innovative types of preformed joint sealants, and several joints drained by geotextile drains.

Construction updates are available on the MnROAD website as well as information regarding current research projects.

Image from MnROAD's 2013 construction kickoff.
Removing concrete in MnROAD Cell 13.