Rock Products - The Leading Voice of the Aggregate Industries.
  • Beyond Assessment:

    Helmet-CAM Technology Influencing Dust Exposure Awareness and Response. By Emily J. Haas and Andrew B. Cecala   Read More
  • A Better Blend

    A.F. Gelhar Diversifies to Produce Silica Sand for Use as Frac Sand. By Mark S. Kuhar   Read More
  • Focus on Frac

    Low Oil Prices Have Taken Their Toll, But Frac Sand Production Continues and There Are Positive Signals Ahead. By Mark S. Kuhar Read More
  • Rock Products 120th Anniversary

    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 1940-1949. Read More
  • 1
  • 2
  • 3
  • 4

Rock From The Road: Blog & Travelogue

Clinton Calls for Infrastructure Investment

Nov. 30, 2015 – There has been very little serious talk on the presidential campaign trail about infrastructure spending. But Hillary Clinton's campaign said recently she would allocate $250 billion...
Read All

Prime-Time Products

Terex Washing Systems Launches AggreStac Range

Terex Washing Systems (TWS) has enhanced its product portfolio with the announcement of the Terex AggreStac conveyor range of equipment. The launch took place as part of TWS Global Distributor...
Read All

Rock Stars

Charlie Potts

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...
Read All

Manufacturers in Focus

Liebherr Hosts Sales Seminar

More than 170 sales professionals, dealers, Liebherr representatives, customers and special guests gathered at Liebherr Construction Equipment's 2015 Sales Seminar and Open House held Nov. 2-6 at the Liebherr Construction...
Read All

People on the Move

ALLU Group Names Chavez President, CEO

ALLU Group Inc. announced that Edgar J. Chavez will take over as president and CEO, replacing Mardi Ohanessian who will be retiring at the end of 2015.
Read All

120th Anniversary Celebration

Rock Products 120th Anniversary - Part 5

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 1940-1949.
Read All

Off-Highway Diesel Prices

The national estimated average price-per-gallon for off-highway diesel fuel as of Nov. 24 is $2.185. That is lower than the previous comparison price-per-gallon of $2.218.
Read All

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.