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IN THE MISSION IMPOSSIBLE MOVIES, secret agent Ethan Hunt tells people he’s a traffic engineer with the Virginia Department of Transportation, an answer so boring that nobody follows up to ask what he actually does.

Real transportation engineers recognize the stereotype.

“You do tend to tell people you work in infrastructure and leave it at that,” said Professor John Harvey, director of the UC Pavement Research Center.

In fact there are plenty of reasons to care about pavement. Tough commute? Imagine driving it on roads of dirt or gravel. If you are driving on roads that have already missed their freshness date for maintenance or rehabilitation, you can feel it every day.

Rapid, reliable transportation is vital to the economy and to modern life. Keeping California’s tens of thousands of miles of roads, from state highways to suburban streets to bike and walking paths, in good condition is an enormous and expensive task. For most local governments, roads are very likely the most expensive single asset they own.

If you are driving on roads that have already missed their freshness date for maintenance or rehabilitation, you can feel it every day.

There’s also a complicated environmental angle. Rough roads lead to lower fuel efficiency, shorter vehicle life, more freight and crop damage, all of which have environmental impacts in addition to cost increases. Just making asphalt and concrete produces environmental impacts in energy, water use and carbon dioxide emissions. And roads of course alter the environment they pass through.

Spend some time talking to pavement scientists and you can even find yourself turning into a bit of a pavement geek. Who knew there’s so much science in such everyday stuff?

History

Pavement research began at UC Berkeley in 1948 when state legislation established the Institute for Transportation Studies. It was established as a separate program in pavement testing in 1994, at the Richmond Field Station. In 2002, Harvey moved to the �鶹��ý Department of Civil and Environmental Engineering and in 2008, with support from the California Department of Transportation, established a lab on campus including space for stretches of “test road.”

The center is one of a handful of advanced labs in the world carrying out scientific research on road materials, with the goal of making roads that are cheaper and faster to build and maintain, longer lasting and that reduce environmental impacts throughout their life cycle, for example by using recycled road materials. Most of the center’s work is funded by the California Department of Transportation (in 2017 the department renewed the center’s three-year grant).

“If it involves pavement, we’re doing research on it,” Harvey said. “If it’s an engineered surface in contact with the ground, it’s pavement, and that’s us.”

Working on a university campus has advantages over being a standalone government lab, Harvey said. There is the rigorous academic culture, a research arc from fundamental science through development to implementation, and easier interactions with potential collaborators in other disciplines.

At the same time, the center is helping to train a new generation of civil engineers. About 12 graduate students at a time are working at or with the center, and there are about a half dozen visiting professors and graduate students from around the world each year.  

The terroir of asphalt and concrete

Your basic road material is a mix of hard aggregate material (crushed rock) glued together with a binder, usually asphalt or cement. Asphalt mixes can be spread hot and harden as they cool in place, providing a smooth yet resilient surface to drive on. Cement is mixed with water creating a chemical reaction that builds a smooth and long-lasting material. People have been paving roads this way since the 19th century.

Yet within that simple summary is a great deal of complexity. What is the aggregate made of? What size are the pieces? What exactly is in the binder?

Asphalt is a naturally occurring crude oil product: its properties vary depending on where it comes from — asphalt from the Bakersfield area, for example, behaves rather differently as a binder to that from coastal California. California refineries also import oil for asphalt from other states and countries, all of it with slightly different properties. To put it in �鶹��ý terms, you might say that asphalt has terroir.

“You can taste and smell the difference,” Harvey said.

“Asphalt is one of those things where the more you know, the more you realize you don’t know.”

One project at the lab is testing the composition of different asphalts to understand how this affects their quality and properties as binders.

“Asphalt is one of those things where the more you know, the more you realize you don’t know,” said David Jones, associate director of the center.

Engineers try to use asphalt blends suitable for conditions. This mixing used to be done empirically, adjusting the blend until it was right. Center researchers want to put that on a more scientific basis by identifying the critical properties that determine how materials will react to water and traffic. Then they want to move that knowledge into practice in materials design and construction quality control.

 

“The idea is that you can test a sample of asphalt, model its properties and then work out how to blend it and construct it for the optimal result,” Jones said.

Just like wine, the properties of pavement depend on how you treat the raw materials.

“It’s not just the grapes, but how you treat the grapes,” Harvey said. “You can engineer your way out of poor raw materials as long as you understand their properties, measure them and then account for them in your design.”

Just like wine, the properties of pavement depend on how you treat the raw materials.

Concrete materials and pavement structures are designed to meet performance requirements and also the demands of the California traveling public to limit construction windows and the resulting traffic delays, Harvey said. California pioneered the use of concrete that can be placed at night and opened to truck traffic by the next morning, gaining strength within two to four hours. Center researchers are working with Caltrans on ways to place thinner concrete slabs on existing pavement, engineering the interface between the new and old pavement to reduce cost and construction time.

Cement production for roads and construction makes a significant contribution to greenhouse gas emissions worldwide, consuming energy and fresh water. Sabbie Miller, assistant professor in the Department of Civil and Environmental Engineering, is researching ways to reduce cement’s carbon footprint by making it more efficiently, using it more effectively or replacing it all together.

Recycled roads

Once pavement is laid down, it has to withstand years of car and truck traffic as well as the effects of heat, cold, rain and depending on location, snow and ice. Asphalt surfaces become brittle over time and more prone to damage. By better understanding the properties of road materials, engineers could better predict how fast roads will wear and schedule repairs before damage becomes advanced and costly.

Another area of research is to develop new, rapid methods to resurface roads. Replacing worn-out road once involved breaking up the pavement, hauling it away and laying completely new material. New techniques rely instead on grinding up the old road on site and turning it into at least part of the aggregate for the new road, stabilized with a dash of cement sometimes mixed with foamed asphalt (asphalt bubbles). This recycling of asphalt pavement is faster and generates less waste material than older methods of road repair.

A California state law calls for the Department of Transportation to use asphalt containing recycled tire rubber  in a large percentage of its asphalt materials . The Pavement Research Center is working with Caltrans and industry to evaluate the properties of new kinds of mixes using tire rubber crumbs and how best to use them in different applications. Based on this research, they will develop draft specifications for Caltrans to use.

Heavy wear

So how do these new mixes and additives perform in practice? The rubber hits the experimental road outside the center’s lab on the experimental test track.

The center has two Heavy Vehicle Simulators, machines that roll wheels back and forth over pavement, simulating 20 years of truck traffic in a few months. Researchers can lay down a stretch of experimental pavement, embedded with instruments, and observe the results as simulated years of wear rack up.