Material Worlds

Engineers at ASU’s Advanced Pavements Laboratory want to understand how different materials behave under different conditions. Matt Witczak, a professor of civil and environmental engineering, leads the effort.

To get answers, ASU researchers test the performance characteristics of different pavement mixes. They use tests to study a variety of properties of the pavement material, including deformation at high temperatures and cracking at low temperatures.

Two major types of pavement exist, asphalt and concrete. Asphalt is a black byproduct of petroleum distillation. It can also occur naturally.

What people normally think of as asphalt is the mixture of asphalt with crushed gravel and sand, which is used for paving. Rubber is added to the mixture to produce asphalt rubber pavement. The amount of rubber varies, but in Arizona it usually makes up 20 percent of the asphalt weight, or approximately 2 percent of the total pavement mixture.

Cement is a powder of limestone and clay. It can be mixed with water and set or used as an ingredient in concrete. Concrete is a mixture of cement and sand, gravel, pebbles, broken stone or slag.

The amount of various components used can vary depending on the climate and traffic where the paving mixture will be used. A busy highway in snowy Flagstaff will have very different needs than a quiet, residential street in sunny Tempe.

“Laboratory testing of mixtures that are used in construction will identify inferior mixtures as well as predict the pavement performance,” says Kamil Kaloush, assistant professor of civil and environmental engineering. “If something were to go wrong in the first few years, we want to be able to trace it to a construction or a material problem. Understanding the material behavior in the laboratory will help us design and construct better performing pavements in the future.”

The lab’s results are stored in a database that can be used by other researchers and transportation agencies. Those results can help them to decide if asphalt rubber is the best material for a particular paving project. Despite only four years of work in this area, the ASU Advanced Pavements Laboratory received the 2002 Research Award from the Rubber Pavements Association.—Linley Erin Hall