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  • Right Up The Road: ConExpo-Con/Agg 2017

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Rock From The Road: Blog & Travelogue

Feb. 27, 2017 – Going to ConExpo-Con/Agg? If you are a frac sand producer, don’t miss a special Rock Products-sponsored seminar: Frac Sand: How Technology and Market Dynamics Will Drive...
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Prime-Time Products

Rhino Hyde polyurethane wear products, being shown in booth C33229, are manufactured using formulations based on more than 40 years of application experience.
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Manufacturers in Focus

In 2015, Maximus North America set the "gold standard" for the mobile crushing and screening industry by introducing the Irish-based Maximus Crushing and Screening product line into North America. This...
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People on the Move

Mississippi Lime Co. promoted Blake Dell to director of business planning and development.
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Rock Stars

Mark Savit, senior counsel in Husch Blackwell’s Energy & Natural Resources group, and long-time Rock Products law columnist, was named the 2016 recipient of the President’s Citation Award from the...
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Distributor News

Terex Trucks announced a partnership with ICP (International Construction Parts) to distribute and support its articulated dump trucks in Costa Rica. Strengthening its capacity to aid customers in the Americas, the manufacturer’s collaboration with ICP will ensure that the requirements...
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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.