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Feds: Prescriptive specs, fly ash thresholds hamper greening of concrete

Source: National Institute of Standards and Technology (NIST), Gaithersburg, Md.; CP staff

A new NIST report cites barriers to broader acceptance of concrete designed with 30 percent or higher fly ash binder, along with a need to allow practitioner pursuit of alternatives to prescriptive mix designs favoring portland cement.

“Measurement Science Needs for the Expanded Use of Green Concrete” is based on a 2012 workshop of representatives from industry, academia, plus state and federal government agencies. Among key factors participants noted for identifying whether concrete is considered green: amount of portland cement replacement materials; cement production processes and methods; plus, finished concrete performance and life cycle sustainability impacts.

 

“Performance specifications are integral to allowing green concrete to compete against standard concrete and other construction materials,” the report contends. “Current prescriptive specifications often constrain acceptance to traditional concrete mixtures, thus preventing alternative materials or mixture proportions with different but otherwise acceptable processing requirements or hardened characteristics from being used.

“Before broad acceptance of these materials can occur, overly-restrictive prescriptive specifications need to be overcome, and the performance of green concretes must be demonstrated to be either ordinary portland cement-equivalent or sufficient for the intended application.”

Part of the U.S. Department of Commerce, NIST prioritizes in “Measurement Science Needs for the Expanded Use of Green Concrete”  these topics for research:

  • Developing tools and metrics for quantifying the advantages and disadvantages of using different materials in concrete.
  • Developing and validating computer models that can predict the performance of green concrete mixtures, both during construction and over the long term.
  • Improving test methods for characterizing materials such as fly ash, glass, minerals, and other portland cement substitutes to determine whether they will perform as required in finished concrete.
  • Developing a more complete understanding of the water-driven chemical interactions that occur as industrial byproduct materials and other components are incorporated into concrete.

The report also highlights the importance of stakeholder education to increase industry awareness and understanding of alternative concrete mixtures’ performance and capabilities. Meeting challenges raised at the workshop will require what authors note is “measurement science for quantifying and ensuring the short and long-term performance of green concrete.” While many factors determine the overall energy and environmental impact of concrete, they add, reducing the amount of portland cement provides the biggest opportunity to address the latter challenge. Energy consumed in domestic portland cement production is equivalent to the amount of power used in 3 million home each year.

Representing concrete producers at the workshop were Lafarge North America Vice President, Product Performance Bruce Blair and Central Concrete Supply Business Development Engineer Ryan Henkensiefken. Industry peers joining them were Fred Kinney of Ceratech Inc.; Denise Silva of W.R. Grace; Hank Keiper of SEFA Group; Eric Koehler of Verifi LLC; plus American Coal Ash Association’s Thomas Adams, Portland Cement Association’s Steve Kosmatka and Silica Fume Association’s Tony Kojundic. Agency participants included Federal Highway Administration/Turner-Fairbank Highway Research Center’s Richard Meininger, formerly of National Ready Mixed Concrete Association and National Aggregates Association.

This workshop and report were commissioned by the NIST Inorganic Materials Group, Materials and Structural Systems Division. Participants authoring the report are Dale Bentz, Chiara Ferraris, Edward Garboczi, Nicos Martys, Kenneth Snyder and Paul Stutzman. The document is available as a free download.