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  • Getting Out of the Sand Trap

    New Modular Wash Plant At GS Materials Produces Specialty Sand For Pinehurst Golf Club. By Mark S. Kuhar Read More
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    Fracking boom helps Arcilla Mining double production, and it relies on heavy iron and smart financing to keep material moving. By Mark S. Kuhar Read More
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Rock from the Road: Blog and Travelogue

article thumbnailAugust 27, 2014 – We need more mining engineers! The Society for Mining, Metallurgy & Exploration Inc. (SME) has submitted comments to the White House Office of Science and Technology Policy regarding its request for information about critical and strategic materials supply chains and their importance to American prosperity and national security. 

Prime-Time Products

article thumbnailTerex Minerals Processing Systems (MPS) launched the new MJ47 primary jaw crusher module, increasing the application capabilities and crushing capacity of its existing modular product range with their largest jaw module to date. The Terex MJ47 jaw crusher module is designed for large quarries or contractors that want a stationary type design...

Rock Stars

article thumbnailAndy Williams of Rogers Group, current president of the Indiana Mineral Aggregates Association, encouraged members to "re-emphasize our commitment to safety as the first priority in our business."
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Manufacturers in Focus

article thumbnailHOLT CAT, the Caterpillar equipment and engine dealer for South, Central, North and Northeast Texas, opened a new location in Edinburg, Texas.

People on the Move

article thumbnailPolaris Minerals Corp., which is focused on the development of quarries and the production of construction aggregates, announced the appointment of Scott Dryden as vice president of Business Development.

Latest Digital Issue

Off-Highway Diesel Prices


The national estimated average price-per-gallon for off-highway diesel fuel as of August 28 is $3.548. That is lower than the previous comparison price-per-gallon of $3.565.

 

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.