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 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.
Another approach is performance-engineered mixtures (PEMs). PEMs are designed and proportioned to optimize readily available materials; minimize the use of reactive materials; and provide workable mixtures that set “on cue”. PEMs result in pavements that perform 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 ISCP Board Director Peter Taylor, Director-National Concrete Pavement Technology Center (CP Tech Center)—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
CP Tech Center Staff are spreading the word about PEMs through workshops and other training activities across the United States. 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, please contact Peter Taylor: E-mail: ptaylor@iastate.edu
ISCP would like to thank CPAM and CTRE “EnRoute 2014 Year-at-a-Glance” (page 20) for this article.
For the full “EnRoute 2014 Year-at-a-Glance” PDF document, please click here.