Rock Products - The Leading Voice of the Aggregate Industries.
  • Loadout and Transportation

    While the bulk of an aggregates operation’s equipment and technology focus is the equipment down on the quarry floor, producers are also seeking the latest innovations for moving material and portable machinery out the front gate and up the highway. Here are some recent product launches focusing on trucks, tires, trailers, diagnostics and vehicle scales. Read More
  • Troubleshooting Conveyor Malfunctions

    Here are some common areas of concern with conveyor belts and how to quickly repair them while on the job. Read More
  • The Rock 100

    Top Crushed Stone Producers List Read More
  • Rock Products 120th Anniversary - Part 3

    In This Issue, We Cover The Years 1911-1920. Read More
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Rock from the Road: Blog and Travelogue

Thumbnail Sept. 29, 2015 – It is going to be tough medicine for Big Yellow. Caterpillar has announced significant restructuring and cost reduction actions that are expected to lower operating costs by about $1.5 billion annually once fully implemented, according to the company. These steps will begin in late 2015 and reflect recent, current and expected market conditions. For 2015, the company’s sales and...

Prime-Time Products

Thumbnail KPI-JCI and Astec Mobile Screens introduced the new-generation track-mounted GT125 Vanguard Jaw Crusher, which offers increased energy savings, reduced cost of operation and improved reliability.

Rock Stars

Thumbnail Charles F. Potts, chairman of the board of Indianapolis-based Heritage Construction & Materials, and past chairman (2008) of the American Road & Transportation Builders Association (ARTBA), is the 2014 recipient of the George S. Bartlett Award. It was presented to him Sept. 30 during ARTBA’s National Convention in Philadelphia.
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Manufacturers in Focus

Thumbnail Metso opened a new service center in Mesa, Ariz. The Mesa facility provides services for Metso's customers in the mining, aggregates and process industries. An official grand opening and open house event for the Mesa service center was held on Sept. 18, 2015.

People on the Move

Thumbnail Superior Industries Inc. named Mike Schultz its product manager for the company’s new crushing equipment product solutions. Schultz comes to Superior with two decades of past experience in the construction aggregates and metal mining industries.

120th Anniversary Celebration

Thumbnail 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 1920-1930.  
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The national estimated average price-per-gallon for off-highway diesel fuel as of Oct. 1 is $2.200. That is lower than the previous comparison price-per-gallon of $2.275.


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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.