Rock Products - The Leading Voice of the Aggregate Industries.
  • Rock Products 120th Anniversary - Part 2

    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 1911-1920.   Read More
  • Maximizing ROI With Operator Training

    How To Identify And Implement Practical Cost Improvements At Your Operation. By Chris Connolly   Read More
  • A Productive Solution

    New Birmingham Inc.’s New Excavator Helps Increase Cycle Times and Production. By Mark S. Kuhar   Read More
  • Saving for the Future

    Lakeview Sand and Gravel Invests in Two New Loaders to Reduce Operating Costs. By Mark S. Kuhar   Read More
  • Focus on Loading & Hauling

    The Latest Developments in Loading and Hauling Technology From the Industry’s Top Manufacturers. By Mark S. Kuhar and Josephine Smith   Read More
  • Rock Products 120th Anniversary - Part 1

    In This Special Year-Long Series Celebrating Our 120th-Year Milestone, Rock Products Presents A History Of The Aggregates Industry. In This Issue, We Cover The Years 1896-1901.   Read More
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Rock from the Road: Blog and Travelogue

article thumbnailAug. 28, 2015 – Maybe it should have been called "Take a Senator to Work Day." In its ongoing push for congressional action on a multi-year surface transportation reauthorization, the North Carolina Aggregates Association helped organize a tour for Republican Sen. Thom Tillis.

Prime-Time Products

article thumbnailScreen Machine Industries has added a new cone crusher model to its current equipment line. The model CXT Cone Crusher is the latest example of Screen Machine Industries innovation, according to the company.

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 thumbnailFor years, McLanahan Corp. has serviced customers throughout Latin America using a team of international sales people and a representative network in the area. Market growth has increased the demand for a team based in this region, which is why McLanahan is opening a new location in Santiago, Chile.

People on the Move

article thumbnailPatrick Dunne joined the National Stone, Sand & Gravel Association (NSSGA) as director of communications, and will lead the day-to-day communications efforts for the association.  

120th Anniversary Celebration

article thumbnailIn 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 1911-1920.  
More inAnniversary  
The national estimated average price-per-gallon for off-highway diesel fuel as of Sept. 2 is $2.275. That is lower than the previous comparison price-per-gallon of $2.320.

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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.