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  • Forging Forward

    Crusher Helps Riverside Sand Diversify and Nail a New Market Niche. By Mark S. Kuhar   Read More
  • What a Rush

    On The Set of Gold Rush, Product Placement and Productivity Go Hand in Hand. By Jimmy Siler Read More
  • Here Comes The Helmet-CAM

    A Recent Advance In Technology Can Improve How Mine Operators Investigate And Assess Respirable Dust. By Andrew B. Cecala and Andrew D. O’Brien   Read More
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Rock from the Road: Blog and Travelogue

article thumbnailOct. 29, 2014 – I am blogging live this week from Peoria, Ill., where Caterpillar is holding a product exhibition for members of the trade press.

Prime-Time Products

article thumbnailContiTech has developed the steel cable conveyor belt STAHLCORD Barrier for less conveyor belt damage and a long service life in opencast mining. With its new sturdy steel transverse reinforcement in the top cover, the conveyor belt is two to three times more resistant to impact breaks than conventional steel cord conveyor belts without transverse reinforcement, the company said. “These...

Rock Stars

article thumbnailThe Association of Equipment Manufacturers (AEM) announced that Jonathan Egge, a technical sales specialist at Kolberg-Pioneer Inc. (KPI-JCI and Astec Mobile Screens), won the I Make America custom-painted Harley-Davidson motorcycle. Egge’s name was chosen from among thousands of Americans who were entered for a chance to win the bike when they signed up as I Make America campaign supporters...
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Manufacturers in Focus

article thumbnailYokohama Tire Corp. (YTC) announced  it is relocating its corporate headquarters from Fullerton, Calif., to nearby Santa Ana, Calif. to accommodate business growth. The move is expected to take place in November.

People on the Move

article thumbnailTerex Construction appointed Gary Dennis as vice president and general manager of Terex Construction Americas and Global Aftermarket. In support of Terex Construction’s continued focus on customer responsiveness and process improvement, Dennis will work with the company’s teams in Southaven, Miss., and Rothenburg, Germany, to ensure that Terex Construction Americas is well-positioned to meet...

Latest Digital Issue

The national estimated average price-per-gallon for off-highway diesel fuel as of Oct. 7 is $3.473. That is lower than the previous comparison price-per-gallon of $3.508.

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.