A common question for drivers everywhere in the U.S. is “How do potholes form?” If you live in a cold climate, we’ll hear about the freeze/thaw cycle that breaks down asphalt pavement. Check out the video below. It was created by the Minnesota Department of Transportation in a state with a cold climate indeed. What this video doesn’t address is how potholes form in hot climate states, like Texas, Louisiana and the like. Indeed, there are potholes there as well!
Asphalt is a flexible pavement and more likely to break down and form potholes. Concrete, on the other hands, is a rigid pavement and doesn’t break down into potholes. It cracks, but you rarely see a hole in concrete pavement. So how do potholes form? You can choose to watch the video or read the video transcript below.
Pothole video transcript:
Here’s a cross-section of a typical pavement. The weight of each vehicle bends the pavement slightly. Small cracks form, first on the bottom of the asphalt because that gets stretched the most. As the asphalt is fatigued, cracks also form on the top surface.
Now, water on the pavement from rain or melted snow gets into the cracks. When the temperature drops, the water freezes and expands making the cracks deeper and wider. With more precipitation, more freeze-thaw cycles, and the continued vehicle loading, sooner or later the cracks go all the way through the pavement.
Now, water can get underneath the surface. When this subsurface water freezes and expands, it pushes the pavement up and weakens it even more. When the ice melts and contracts, it leaves a space, so we have a weakened pavement layer over a cavity. All that’s needed now is a good-sized vehicle, and there’s your pothole.
Source: Minnesota Department of Transportation
You might want to check out Minnesota cities that are choosing to end potholes on their streets. Click on “Cities in Action” in the right-hand column to read about their projects.
The Spring Grove Herald editor in southeast Minnesota wrote a thoughtful newspaper column this month. It weighs the pros and cons of paving with concrete. The editor challenged local leaders to look at the whole picture when it comes to road construction projects. Concrete paving was placed on Fillmore County Road 1 in 2016 between Spring Valley and the Olmsted County line.
The newspaper column tapped into the case studies and facts on this Bye Bye Potholes website. We appreciate that he grasped that an investment in concrete is an investment for decades. And it eliminates the possibility of potholes.
Here’s an excerpt from that column and a jump over to the complete Spring Grove Herald column.
County highway should have smooth ride for decades
Before construction started in 2016 on Fillmore County Road 1 — Fillmore County’s busiest county state aid highway when it isn’t closed for road work — traveling that stretch of highway from Spring Valley to the Olmsted County line was rough, to put it mildly. The potholes had become so numerous that many people feared for the health of their vehicles and even their own health as they traveled the 12 miles of county highway.
However, potholes on that highway will be a thing of the past as Fillmore County is paving the road with concrete. It’s not the first Fillmore County highway to transition from the typical asphalt to concrete, but it is still rare for local roads to have a concrete surface.
The main reason for the lack of concrete thoroughfares is expense — at least upfront expense. As the potholes surface again this spring now that the snow and constant freezing is nearing an end, it is worth examining whether local governments are considering the whole picture when it comes to road construction.
New asphalt is cheaper than concrete, but asphalt roads can break down into potholes within three years on one extreme while new Minnesota concrete pavement designs are expected to last as long as 60 years with minimal maintenance on the other extreme. . . .
Is your city requiring both asphalt and concrete pavement bids when fixing or building streets? If not, the bigger question is, why not?
Elected officials say taxpayers are looking to get the biggest bang for their buck when it comes to the cost of government. That includes the cost of building and repairing streets.
For that reason alone, cities and counties should require bids for both asphalt and concrete pavements. And those bids should include a life cycle cost analysis for road construction or repair projects. Doing so helps them determine whether using asphalt or concrete materials is the more cost-effective, sustainable investment.
Life Cycle Cost Analysis
The life cycle cost analysis considers the pavement’s initial cost, as well as the projected maintenance and reconstruction costs over the life of the road. Ultimately, it helps answer the question: Which design alternative – asphalt or concrete – results in the lowest total cost over the life of the project?
According to a 2012 American Public Works Association report, getting both asphalt and concrete bids often lead to reduced cost and an increase in a projects’ sustainability rating.
The concrete industry itself acknowledges that its product often has a higher initial cost than asphalt, but points to life cycle cost analysis to show that concrete generally has a longer useful service life and fewer maintenance costs over the life of the project. Read more here.
But the cost is just one measure of sustainability. What about the environmental impact of a road project?
Another tool being used helps cities determine the societal cost of concrete and asphalt is the environmental life cycle assessment. This rating includes the environmental impacts of using concrete or asphalt.
These two tools provide two very different assessments. The life cycle costs analysis measures the cost-benefit ratio; the environmental life cycle assessment helps measure the environmental footprint of a road project. Yet both tools help determine whether concrete or asphalt materials give taxpayers the biggest bang for their buck.
We had some fun writing for this website in 2017. In addition to our case studies, which detail concrete road projects around the state, the posts ranged from one city’s fight against potholes to the dangers potholes pose for EMTs and paramedics as they race to the hospital.
Here are our Top picks for 2017. Take a look:
1. Worthington battling potholes on two fronts
Like many public works crews across Minnesota, Worthington city crews spend a lot of time filling potholes. Last spring, the Worthington Daily Globe reported that city crews spend a week of non-stop pothole filling to put a Band-Aid on the problem every spring and summer. But that’s not all. In its fight to reduce potholes, the city has begun to pave more streets with concrete. Read more.
2. How a Mustang is like a concrete street
Mustangs are not cheap cars, but they are well built and last a long time. In this blog post, Editor Renee McGivern likens her 2005 investment in a Mustang to city or county’s investments in concrete streets. Like her Mustang, she notes concrete may cost more than asphalt on the front end, but concrete streets are high performing and built to last. See the post.
3. Infographic makes it easy to see the cost of roads
This infographic compares the initial and “life cycle” costs of asphalt and concrete on a one-mile stretch of road. It includes the projected costs of potholes repairs, as well. The end result is that after 20 years, concrete costs a bit less. By the end of 40 years, the costs of maintaining that road will be fairly even. Check it out.
4. EMTs, paramedics know dangers of potholes
Add emergency medical technicians (EMTs) and paramedics to the list of folks who know the dangers of potholes. On the roads, it’s difficult for ambulance drivers – seeking the quickest way possible to an emergency call — to avoid the bumps, let alone pothole-riddled roads. Take a look.
In a previous post, we showed a spreadsheet of an analysis of the initial and “life cycle” costs of a one-mile stretch of road, comparing asphalt and concrete. Creating a visual of the comparison is very helpful, too. Here’s an infographic or visual view of that same spreadsheet. We added an estimate of potholes repairs to this as well. The end result is that after 20 years, concrete costs a bit less. We can predict that by the end of 40 years, the costs of maintaining that road will be fairly even.