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  • AGG1 2015 Preview

    The Aggregates Industry's Big Show of the Year Puts the 'More' in Baltimore. By Mark S. Kuhar   Read More
  • Boosting Throughput

    An Ontario Quarry Increases Production Capacity And Plant Uptime With Anti-Pegging Screen Media Solutions. By Carol Wasson Read More
  • A Need to Feed

    Edwards Sand And Gravel Relies On Vibratory Feeders To Keep Material Moving At Its Pennsylvania Quarry. By Mark S. Kuhar Read More
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Rock from the Road: Blog and Travelogue

article thumbnailFebruary 24, 2015 – Aggregates industry professionals who want to see the latest product innovations – and discover the latest industry best practices – are headed to the 2015 AGG1 exhibition in Baltimore, March 17-19. Show organizers tell me that:

Prime-Time Products

article thumbnailVolvo Construction Equipment is showing a number of products at booth 1814. The Volvo L250H wheel loader is designed for two-pass loading of finished aggregate product into tri-axle on-highway trucks for up to 30 percent more truckloads per day compared to competitive loaders, which require three passes. With the excellent visibility and ergonomic design of the Volvo Care Cab, you can be sure your...

Rock Stars

article thumbnailFormer U.S. Transportation Secretary Ray LaHood, appearing on 60 MINUTES, said that many of the roads and bridges we drive on every day are “on life support.”
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Manufacturers in Focus

article thumbnailStockpile Reports, an online service that delivers accurate stockpile volume, tonnage and pile locations using an Apple iPhone device, Aerial, Walking Wheel, GPS or Laser data was awarded a contract for stockpile measurements from the TxDOT beginning in 2015.

People on the Move

article thumbnailBridgestone Commercial, a division of Bridgestone Americas Tire Operations (BATO), announced the appointment of a new president in the commercial tire division. As president, Commercial OTR, Taylor Cole will be responsible for leading Bridgestone’s North American commercial and strategic direction. Cole will be instrumental in harnessing resources for continued growth of the division,...

Latest Digital Issue

The national estimated average price-per-gallon for off-highway diesel fuel as of Feb. 10 is $2.571. That is lower than the previous comparison price-per-gallon of $2.589.

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.