Rock Products - The Leading Voice of the Aggregate Industries.
  • Summit's Hill Reaches the Peak

  • From Rocks to Gold

    A Special Rock Products Interview With Dave Turin Of The Hit Discovery Channel Television Series ‘Gold Rush.’ By Mark S. Kuhar Read More
  • Dealing with DPM

    Using Real-Time Diesel Particulate Matter Measurements to Optimize the Implementation of Administrative Controls. By James Noll, Larry Patts and Roy Grau   Read More
  • County Tyrone: Ireland's Crushing and Screening Mecca

    Northern Ireland is home to many quarries and manufacturers of equipment for the global aggregates industry. By Mark S. Kuhar   Read More
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Rock from the Road: Blog and Travelogue

article thumbnailApril 23, 2015 – The NSSGA Young Leaders annual conference is April 29-May 2 in Fort Lauderdale, Fla.

Prime-Time Products

article thumbnailCASE Construction Equipment introduced five new crawler excavators to the construction trade press at a special event at its Tomahawk, Wis., test facility: the CX210D, the CX250D, the CX250D Long Reach (LR), the CX300D and the CX350D. These new models are designed to provide significant operational gains, including cycle times up to 12 percent faster, improved responsiveness and multifunctional...

Rock Stars

article thumbnailRon DeFeo, chairman and chief executive officer of Terex Corp. is the sole recipient of the American Road & Transportation Builders Association’s (ARTBA) highest honor – the 2014 “ARTBA Award.” It was presented at an April 14 luncheon during the association’s Federal Issues Program in Washington, D.C.
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Manufacturers in Focus

article thumbnailSuperior Industries Inc. has officially completed its acquisition of Clemro Western Ltd., which was announced earlier this year. Based in Calgary, Alberta, Canada, the 30-year-old company is known for manufacturing jaw and cone crushers, incline and horizontal screens, and belt and grizzly feeders.

People on the Move

article thumbnailSuperior Industries Inc. has hired 36-year aggregate industry veteran Doug Lambert. In March, Lambert was appointed to a role as a sales and application engineer in the manufacturer’s new construction management division.  

Latest Digital Issue

The national estimated average price-per-gallon for off-highway diesel fuel as of April 21 is $2.521. That is lower than the previous comparison price-per-gallon of $2.574.

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.