Shane Underwood is an associate professor of Civil Engineering in the North Carolina State University Civil, Construction and Environmental Engineering Department. His expertise is in the field of pavements and materials, and his current research focuses on the use of bottom-up, model-based investigations of asphalt concrete and its constituent materials as well as the use of top-down systems studies to identify needs and knowledge gaps that the bottom-up investigations can inform. His goal is to analyze pavements that are truly sustainable in the short-term and over the product lifecyle.

Observing Change through Time

His interest in pavement materials started with realizations that through time, engineers have made certain implicit assumptions about the way things will be in the future based on how things have been in the past. He looked at two or three different areas where this didn’t seem to hold, so he started his research work about three or four years ago.

“We started seeing a lot of articles and discussions around climate change and especially extreme events,” says Underwood. “We started this work to try and get a handle on how some of these factors could contribute to pavement engineering.”

He notes that it’s easy to overlay where climates are going to change with where infrastructure is located and see where they intersect, but when engineering and delivering pavements and infrastructure, there are many more factors—local factors—that go into how those materials and pavements are delivered.

Research Goals and Techniques

When starting their research, the team looked at climate records from the U.S. Historical Climate Network going back to 1966 to extract air temperatures at different places across the United States. They then analyzed the data using sets of equations that have been developed through engineering practice and other research projects.

“We borrowed the equations that relate air temperatures to actual pavement temperatures, and those pavement temperatures are the basis for selecting the type or grade of asphalt cement used in pavements,” notes Underwood. “How would future temperature changes affect the grade choices that would be made based on following those equations and current practices in selecting materials?”

The research team, based at Arizona State University, didn’t create independent climate modeling; they extracted a set of 38 different climate models from two different possible future scenarios: one that posits a relatively mild change and increase in temperature; and one that proposes that the temperature changes will be more substantial.

From those climate models, they repeated the process of using grade selection and looked at different time windows in 30-year increments up until the end of the century.

Regional Results

In their results, they noted that the impact of climate change—estimates of cost—was regionally specific. They saw greater impact in two particular regions: the southeast and the Ohio Valley, which roughly corresponds to the Midwest. They also found that states with large infrastructure networks, regardless of where they’re located, tend to have higher impacts, such as Texas, Illinois, Florida and others.

Although not climatologists and reluctant to make climate connections, Underwood and the research team reached some engineering conclusions.

“There is a link in how we design and deliver infrastructure in the future where things seem less certain than they once were,” says Underwood. “Assuming that the future will look exactly like the past can have major economic consequences.”

Underwood adds an important note that infrastructure is delivered with multi-decade perspectives and must be looked at over the long term.

“We design roads for 20 years; other pieces of infrastructure are designed for even longer periods of time,” he says. “So when engineers design the infrastructure we rely on, they may not have been considering the possibility of such large and extreme events as the hurricanes we’ve recently seen.”