Street Rules: The little-known story of pavement

CEDAR RAPIDS - For a product that draws hundreds of millions of dollars from public coffers, pavement gets little attention aside from when the ride is rocky or a bike tire catches a crack.

'A lot of people don't know the difference between asphalt and concrete or concrete and cement,” said Peter Taylor, associate director at the National Concrete Pavement Technology Center at Iowa State University. 'It's just the hard stuff you drive on and get irritated with when the ride's not comfortable.”

Research, new technology, weather fluctuations, heavier vehicle loads, and a fierce rivalry between asphalt and concrete test engineers as they try to produce a product that - if all goes well - the public will hardly notice.

'It's constantly changing,” said Doug Wilson, Cedar Rapids capital improvement project manager. 'You want to stay on top of those changes so we can maximize our taxpayer dollars.”

Cedar Rapids is conducting condition ratings on all the streets across the city as part of redoing its 10-year street capital improvement plan, Wilson said. A preliminary report is due at the end of October and a final product in January, Wilson said.

The pavement discussion starts with the ever-sticky debate between asphalt and concrete, which those in the middle try hard to navigate diplomatically.

'We use both,” said Chris Brakke, a pavement design engineer with the Iowa Department of Transportation. 'It comes down to life-cycle costs: how long do they both last and what's the cost associated with rehabilitation? You can build either one to perform under similar conditions.”

Concrete is a mixture of cement, crushed rock, water, an aggregate such as sand or gravel, and a binder such as burnt lime.

Asphalt, or bitumen, is a form of petroleum used as a binder when mixed with an aggregate.

'Concrete comes from a chemical process where the water reacts with Portland cement,” Brakke said. 'With HMA (hot mix asphalt) once the pieces of pavement are put together, it's more of a physical process of cooling and stiffening.”

Concrete is rigid so it distributes loads more evenly, whereas asphalt is more flexible so the load is more concentrated, he said.

Both sides tout why their product is better.

'Concrete's hallmark is durability and strength,” said John Cunningham, vice president of Iowa Concrete Pavement Association. 'I think especially in Iowa, one of the biggest benefits is it's an Iowa product. All the parts found here in Iowa.”

Bill Rosener is a counterpoint as executive vice president of the Asphalt Paving Association of Iowa.

'Asphalt's advantage is the smoothness of our ride, better fuel mileage and less wear and tear on your vehicle, and how quick it sets,” Rosener said. 'The speed of construction is a huge advantage. As soon as you get the roller on the road, you can turn traffic loose.”

Iowa and the Midwest in general pose environmental challenges for pavement engineers.

The temperature this year swung from negative 20 degrees in February to greater than 100 in July and August, mean the pavement must withstand the cracking that occurs in the cold as well as rutting under high temperatures.

More challenging is what's known as freeze-thaw cycles. For example, the temperature warmed from 4 degrees on Jan. 18 to 42 degrees on Jan. 19.

'Other parts of the country get freeze-thaw, but the Midwest is the part of the country where we get the extremes - the very cold, deep frost, and then the thaw and moisture,” Brakke said. 'We also have to deal with high temperatures that are hard on asphalt.”

Iowa's soil also complicates matters for pavement because it holds water rather than letting it run through. Engineers work hard to get water away from the pavement, so it doesn't freeze, crack and cause potholes.

'Iowa has the best topsoil in country, but it is not great for laying roads,” Rosener said.

Researchers such as Taylor at Iowa State, and Hosin David Lee, a civil and environmental engineering professor at University of Iowa, are on the front lines of new technology designed to better handle the weather and heavy traffic, use recycled products, and improve stormwater drainage.

Later this week, a product Lee developed in a lab in UI's Seaman Center for Engineering will be used to pave Third Avenue in Cedar Rapids. Lee developed a polymer for a 'warm mix asphalt,” which allows the asphalt to become flexible at a lower temperature than traditional hot mix asphalt products.

In Cedar Rapids, the city relies more on concrete, which has held up to weather and travel demands, Wilson said. But, the city takes bids from asphalt companies as well, and uses asphalt to extend the life of roads.

'We are always looking at alternate technologies,” Wilson said. 'We are constantly training and looking for answers to get the pavement to last longer.”