Limestone powder enhances performance of 'green' concrete

September 4, 2013, National Institute of Standards and Technology

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, report researchers from the National Institute of Standards and Technology (NIST) and the Federal Highway Administration (FHWA).

The promising laboratory results suggest a path to greatly increasing the use of in concrete, leading to sizable reductions in greenhouse gas emissions, energy use, and landfill volumes. Global production of cement for concrete accounts for 5 to 8 percent of human-caused .

Currently, fly ash accounts, on average, for about 15 percent of the binder powders in the ready-made concrete used in the United States. 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," says NIST 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 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, 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, says 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.

Explore further: Experts propose research priorities for making concrete 'greener'

More information: Bentz, D., Tanesi, J. and Ardani, A. Ternary blends for controlling cost and carbon content, Concrete International, August 2013.

Related Stories

Recommended for you

Cryptocurrency rivals snap at Bitcoin's heels

January 14, 2018

Bitcoin may be the most famous cryptocurrency but, despite a dizzying rise, it's not the most lucrative one and far from alone in a universe that counts 1,400 rivals, and counting.

Top takeaways from Consumers Electronics Show

January 13, 2018

The 2018 Consumer Electronics Show, which concluded Friday in Las Vegas, drew some 4,000 exhibitors from dozens of countries and more than 170,000 attendees, showcased some of the latest from the technology world.

Finnish firm detects new Intel security flaw

January 12, 2018

A new security flaw has been found in Intel hardware which could enable hackers to access corporate laptops remotely, Finnish cybersecurity specialist F-Secure said on Friday.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.