Institute for Transportation

Many concrete pavement mixtures in the United States are still developed based on standard, prescriptive “recipes.” These methods can be overly conservative as far as defining, for example, minimum strengths, maximum water-to-cement ratios, and minimum cement content. Such requirements often have no direct correlation to optimizing desired pavement performance. Plus, prescriptive approaches may result in other problems, like using more cementitious materials than necessary.

There is another approach. Performance engineered mixtures, or PEMs, are designed and proportioned to optimize readily available materials, minimize the use of reactive materials, provide workable mixtures that set “on cue,” and result in pavements that perform as desired within the unique parameters and desired characteristics of individual pavement projects.

The knowledge and technologies to develop PEMs are largely available. But their use has yet to become standard practice.

“It’s not that complicated,” says Peter Taylor, director of the National Concrete Pavement Technology Center (CP Tech Center) at the Institute for Transportation, who is leading PEM training efforts. He emphasizes three guiding principles for PEMs:

• Choose an aggregate system that minimizes paste content requirements
• Select a paste system based on desired performance characteristics of the pavement
• Proportion the paste volume at 1.5 to 2 times more than voids between aggregates

Staff from the CP Tech Center are spreading the word about PEMs through workshops and other training activities across the country. In addition, Taylor has developed a spreadsheet tool for applying PEM principles.

“A focus on performance engineering will lead to a profound change in the way mixtures are proportioned in the future,” says Taylor.

For more information contact Peter Taylor, CP Tech Center director, ptaylor@iastate.edu

This aritcle is part of the CTRE EnRoute 2014 Year-at-a-Glance series. Download the full document (.pdf).