Winter weather's effect on pavements felt by motorists, agencies alike

Photo courtesy of WGN-TV, Chicago

Slightly more than a month into 2014, extremely cold temperatures and heavy snowfalls have shattered records throughout most of Illinois. This “polar vortex,” as it has been dubbed by meteorologists, has caused numerous school and business closings as frigid temperatures and blowing snow have made travel treacherous and, in some cases, impossible. But the effects of this extreme weather will be felt after the winds die down and temperatures rise as state and local agencies work to fill in potholes and repair cracks to keep roads in good working condition. 

Imad Al-Qadi, Founder Professor of Engineering at the University of Illinois at Urbana-Champaign and director of the Illinois Center for Transportation (ICT), explains that asphalt pavements are made of a skeleton of aggregate (rocks), which is held together by asphalt binder in a special design. In asphalt concrete, when there is excess moisture present, a complex thermodynamic, physiochemical, and mechanical process can separate binder separate from the aggregate and lose its adhesion, which is a process known as stripping. Freezing and thawing cycles accelerate this process significantly, possibly as a result of aggregate degradation. The presence of moisture, along with freezing and thawing, can also cause the binder to fail cohesively.

Stripping can lead to distress, resulting in raveling, which is the separation of aggregate and asphalt binder. This progresses to potholes. Al-Qadi adds that potholes could result from poor quality of paving material, improper mix design, and inadequate compaction, among other factors. During winter, such imperfections are manifested. In addition, the asphalt binder, which comprises around 5% by weight and 12% by volume of the mix, is viscoelastic. That means it’s soft at high temperatures and brittle at low temperatures. The brittleness of asphalt binder at low temperatures, like the ones experienced in January, can lead to asphalt cracks. These cracks appear in the pavement surface across the width of road at regular intervals. Older pavements, because they have aged, can be more brittle. These cracks start as hairlines, but they still allow water to enter, which accelerates the damage.

Al-Qadi notes that because of its viscoelastic nature, asphalt that has been cracked can sometimes heal itself as temperatures become warmer. However, sometimes it is necessary for crews to seal cracks to ensure motorist safety and protect pavement durability. He adds that asphalt binder is usually selected based on a region’s highest and lowest expected temperatures. For concrete pavements, freezing can lead to opening of joints, allowing debris and incompressible materials to enter and cause damage in the summer when the joints narrow. Also, moisture can enter the joints and cause erosion that results in slab movement and causes pavement damage.

The cold snap that hit Illinois the first weekend in January, which was then followed by severe thunderstorms and temperatures nearly 60 degrees warmer a few days later, caused significant stress changes in pavements, explains Al-Qadi. The combination of cold temperature cycles, moisture, and high traffic is a recipe for potential pavement distresses and development of potholes.

John Collins, Urbana public works operations manager, recently told the Champaign News-Gazette that the dramatic temperature changes are the biggest cause for pavement damage. He stated that his crews began filling in potholes as soon as possible along snow routes and then began addressing others they came across or that had been reported. Collins explained that certain routes in the area are maintained by the Illinois Department of Transportation (IDOT) and noted that potholes reported to Urbana public works on those routes are forwarded on to IDOT. Both Champaign and Urbana have web pages residents can use to submit information about potholes that need to be repaired, as do most other municipalities. IDOT has a pothole reporting hotline—the number to call is 1-800-452-IDOT.

In Chicago, crews are working seven days a week to respond to reports of potholes. A press release from the City of Chicago notes that in the first ten days of January, crews repaired 15,000 potholes across the city. Chicago residents can report pothole issues by phone, text, or smartphone app.

While road crews have been putting in extra effort to ensure that roads are safe and drivable this winter, ICT investigators have completed or are currently working on several IDOT-funded projects  aimed at making snowplow use safer and more efficient and making pavements more durable in extreme weather conditions. ICT/IDOT project R27-SP15, “Snowplow Simulator Training Study,” was completed in 2010. Another snowplow study, project R27-094, “Performance Evaluation of Snow & Ice Plows,” is under way.

In addition, ICT recently completed project R27-078, “Evaluating the Effects of Various Asphalt Binder Additives/Modifiers of Moisture Sensitivity in HMA,” which seeks to determine more effective methods for controlling moisture damage in hot-mix asphalt. This project was undertaken because IDOT identified a need to determine methods that are more effective in controlling moisture damage in hot-mix asphalt.

Snow Removal Effectiveness

In project R27-SP15, ICT investigator Thomas O’Rourke of the University of Illinois at Urbana-Champaign rated the effectiveness of IDOT’s snowplow simulator training. O’Rourke explains, “Snowplowing often occurs under treacherous and stressful conditions. Additionally, drivers often have to operate several plows and spreaders simultaneously. Opportunities to provide comprehensive training under real-world conditions are limited and are inherently hazardous, especially to novice drivers.” The purpose of this study was to determine the effectiveness of IDOT’s snowplow simulator and provide recommendations for improving it going forward. David Johnson, Maintenance Operations Engineer (now retired) for IDOT, chaired the Technical Review Panel for this project.

In project R27-094, ICT investigator Souhail Elhouar of Bradley University is currently evaluating various snow and ice removal trucks and types of blades. These trucks have been instrumented to measure scraping forces and shock acceleration with the ultimate goal of developing a comprehensive performance database that will assist IDOT in ensuring that its plowing operations are as efficient as possible. “As we have seen this year especially, clearing roadways of snow and ice efficiently is key to keeping the traveling public moving safely,” says Elhouar. This project was conducted under the direction of a Technical Review Panel chaired by Tim Peters, Snow and Ice Engineer at IDOT.

Preventing Potholes by Reducing Moisture Damage

Aside from determining how snowplows can be more efficient, ICT researchers investigated how pavement can be better constructed to prevent raveling or potholes. In project R27-078, Al-Qadi’s research team evaluated various additives and modifiers that can be mixed into asphalt to determine how they affect a pavement’s susceptibility to moisture. Al-Qadi explains, “The amount and type of moisture damage is affected by many different characteristics such as how the asphalt is processed, its specific composition, adherence to quality control measures, the amount and type of traffic on a pavement, environmental conditions, and aging of the pavement. The purpose of this research was to determine what can be done to develop more durable pavements that have less raveling or potholes using proper additives/modifiers.”

The Technical Review Panel that facilitated the moisture damage study was chaired by Jim Trepanier, the IDOT’s HMA Operations Engineer. Trepanier says that IDOT’S new quality control specifications, along with findings from the moisture damage study and three other  ICT/IDOT pavement performance projects (R27-079, “Designing, Producing, and Constructing Fine-Graded Hot-Mix Asphalt on Illinois Roadways,” and R27-100, “Best Practices for Implementation of Tack Coat: Part 1 and Part 2″) will aid in preventing moisture-related winter pavement failures of HMA.

Staying Safe This Winter

• When snowplows are out, be sure to give drivers as much space as possible to do their job.
• In inclement weather, ask yourself if it’s really necessary to make a trip. If the trip can’t be delayed, be sure to check IDOT’s state road conditions map to determine what road conditions are like. Be prepared in case you need to make an emergency stop or get stranded.
• Maintain your car and check it regularly to be sure it’s safe. It’s good to inspect tires frequently and check tire pressure. Check your vehicle’s owner’s manual to determine the ideal tire pressure.
• To avoid pothole damage to your vehicle, use common sense and be alert for potholes. If you spot an affected area, slow down (check your rearview mirror first for cars behind you).
• Beware of puddles in the road. These can mask potholes that have formed.
• If you do hit a pothole, make sure to have your vehicle’s alignment checked—especially if you find your car pulling left or right.