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Rock From The Road: Blog & Travelogue

April 27, 2016 –CNN's website is featuring a photo gallery of the "most spectacular bridges erected in recent years – and a few that could define the skylines of the...
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Prime-Time Products

Metso introduced a new cone crusher to the global market. The company said it designed the new HP5 with safety, simplicity and eco-efficiency in mind. Automatic settings, specialized maintenance tools,...
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Rock Stars

Brian Peters, E&S director at Mulzer Crushed Stone Inc., received the James E. Burch “Steward of the Environment Award” related to an environmental project at the company's Cape Sandy Quarry...
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Manufacturers in Focus

Global cement and minerals-processing company FLSmidth, and Kleemann, part of Wirtgen Group, have signed a long-term cooperation agreement on the supply of cone crushers for mobile applications in the construction...
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People on the Move

Kolberg-Pioneer Inc., Johnson Crushers International Inc. and Astec Mobile Screens Inc. promoted Ron Griess to North America Sales Director – East.
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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 1980-1989.
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Distributor News

ProCon JCB will be hosting an open house on Thursday, April 28 from 10 a.m. to 3 p.m. at the company’s headquarters, 461 Pioneer Place, Las Cruces, N.M. In addition to enjoying a free lunch, attendees will have the opportunity...
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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.