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Rock from the Road: Blog and Travelogue

article thumbnailDec, 17, 2014 – The U.S. aggregates industry faces a challenging year in 2015. Aggregates producers are looking ahead with anticipation to improved market conditions, driven by the resurgence in residential housing and increased activity from state DOTs, however, many questions remain.

Prime-Time Products

article thumbnailSuperior Industries Inc. reported that its washing fines recovery system was granted patent protection from the United States Patent and Trademark Office.

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 thumbnailA global innovator in bulk material handling is celebrating 70 years of designing high-quality equipment and accessories, serving customers in a wide range of industries around the world.  Along with spearheading efforts in safety and education, Martin Engineering has had a profound impact on efficient operations in coal, cement, aggregate, biomass and other industries across six continents.  This has...

People on the Move

article thumbnailSuperior Industries hired 20-year industry veteran Jason Adams as general manager of the company’s construction management division.

Latest Digital Issue

The national estimated average price-per-gallon for off-highway diesel fuel as of Dec. 3 is $3.336. That is lower than the previous comparison price-per-gallon of $3.421.

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.