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Rock From The Road: Blog & Travelogue

July 7, 2016 – BZ Media LLC announced the second in its series of critical examinations of the hype and reality behind certain vertical commercial drone markets, “The Truth About...
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Prime-Time Products

A workhorse in mining and quarrying operations, the John Deere 870G LC production-class excavator follows in the footsteps of its G-Series counterparts with the addition of an EPA Final Tier...
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Manufacturers in Focus

Since 1968, ACS Industries has been in the business of providing attachments for large-scale earthmoving and construction equipment. In the aftermath of the recessionary economy of 2008 and 2009, the...
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People on the Move

Leon Luadzers – regional sales manager for Kolberg-Pioneer Inc. for 20 years – has retired effective June 30. He has held various positions with many aggregate-processing equipment manufacturing companies for...
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Rock Stars

Neal S. Berke, Ph.D., vice president of research at Tourney Consulting Group LLC in Kalamazoo, Mich., has received the Frank E. Richart Award from ASTM International Committee C09 on Concrete...
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120th Anniversary Celebration

In This Special Year-Long Series Celebrating Our 120th Year Publishing Milestone, Rock Products Presents A History Of The Aggregates Industry. In This Issue, We Cover The Years 2000-2009.
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Distributor News

During regional dealer meetings held in Savannah, Chicago, Las Vegas and Toronto, JCB North America presented its annual dealer awards to outstanding JCB dealerships in recognition of their exceptional efforts and achievements in 2015. Dealers of Excellence recipients were Northland...
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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.