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Rock From The Road: Blog & Travelogue

April 21, 2017 – The National Stone, Sand and Gravel Association (NSSGA) celebrated 25 years of the Young Leaders Annual Meeting at Wild Horse Pass in Chandler, Ariz. Industry professionals...
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Prime-Time Products

ASGCO added a semi-ceramic option to their pulley lagging product line, featuring 40 percent coverage. With this newest addition, customers have a choice between full-ceramic coverage with the Arrowhead Ceramic...
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Manufacturers in Focus

The grand opening of Polydeck’s newest remote facility, the South Texas Distribution Center (DC) in San Antonio, was held on Friday, April 7.
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People on the Move

Jonathan Fippinger will join Crisp Industries as its new North Texas sales representative, according to the company. He will replace Greg Venghaus, a long-time Crisp employee who passed away suddenly...
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Rock Stars

Douglas D. R. Palmore, senior vice president of customer and technical services at Luck Companies, was named the 2017 recipient of the Barry K. Wendt Memorial Commitment Award from the...
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Distributor News

Superior Industries Inc., a U.S.-based manufacturer and global supplier of bulk material processing and handling systems, announced Grant Aggregate as a new distributor of Superior components products. Officially a distributor since Jan. 1, 2017, Grant Aggregate will market, stock and...
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Resource Center

Limestone Cited as Benefit to Green Concrete


By Mark S. Kuhar

Adding limestone powder to “green” concrete mixtures – those containing substantial amounts of fly ash, a byproduct of coal-burning power plants – can significantly improve performance, according to researchers from the national Institute for Standards and technology (NIST) and the Federal Highway Administration (FHWA).

The promising laboratory results suggest a path to greatly increasing the use of fly ash in concrete, leading to sizable reductions in greenhouse gas emissions, energy use, construction costs and landfill volumes. Global production of cement for concrete accounts for 5 to 8 percent of human-caused greenhouse gas emissions, according to NIST.

Currently, fly ash accounts, on average, for about 15 percent of the binder powders in the ready-made concrete used in the U.S. To produce a more green concrete, NIST is researching new material combinations and procedures that could help the industry use fly ash to routinely replace 40 to 50 percent of the ordinary portland cement (OPC), the main binding and hardening agent in concrete.

Because of delays in setting times and questions about its strength in the first few days after application that both “impact its constructability,” said NIST chemical engineer Dale Bentz, “green concrete has been a tough sell in large parts of the construction industry.” However, Bentz and his FHWA colleagues found that a “judicious combination of fine limestone powder” can help to put these concerns to rest.

So-called high-volume fly ash “ternary” mixtures (including some limestone) that replace between 40 percent and 60 percent of the cement portion not only set at rates comparable to those for typical concrete, but also were superior in terms of key properties.

Initially, the strength of the green concrete mixtures after 28 days slightly lagged that of concrete without any fly ash. However, the team was able to tweak their fly ash-limestone-OPC mixture to overcome the gap, primarily by lowering the water-to-powder ratio and switching to a different standard composition of OPC (ASTM Type III).

Today, global production of OPC totals about 3.5 billion metric tons (3.85 billion tons) annually. Generation of each ton of OPC emits about a ton of carbon dioxide into the atmosphere.

Greater use of high-volume fly ash mixtures could significantly reduce this environmental burden and, at the same time, reduce costs for concrete construction, said Bentz.

For Bentz and his team, the next research challenge is to test their limestone-enhanced mixtures in the field, where curing conditions can vary. A later report will be issued with additional findings.