Rock Products - The Leading Voice of the Aggregate Industries.
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Rock From The Road: Blog & Travelogue

Nov. 11, 2016 – Academy Blasting is offering its popular "Mechanics of Rock Blasting" course to Rock Products' readers at a special 10 percent discount.
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Prime-Time Products

Superior Industries Inc. launched a new Attrition Mill within its line of washing and classifying machinery. The new machine provides an efficient solution for sand applications including disintegration of conglomerates,...
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Manufacturers in Focus

The Association of Equipment Manufacturers (AEM) announced its 2017 officers as well as those elected to the AEM board of directors and AG and CE sector boards.
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People on the Move

Chaney Enterprises announced the promotion of Francis H. (Hall) Chaney III, to president. Previously executive vice president, Chaney assumes responsibility for all aspects of the Gambrills, Md.-based concrete manufacturer, aggregate...
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Rock Stars

John Malinowski, Baldor Electric Co.’s senior director of industry affairs, received the MS’16 award at the 2016 Motor Summit in Zurich, Switzerland. The MS’16 award recognizes his contributions in making...
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Distributor News

Terramac, a leading manufacturer of innovative rubber track crawler carriers, expanded its representation in the North American market to include Kirby-Smith Machinery, Inc. as part of its dealer network. Kirby-Smith will represent the versatile Terramac product line in Oklahoma.
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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.