Strength and resiliency were critical for New York's new 7 World Trade Center building. Detroit's Metropolitan Wayne County Airport needed smooth concrete runways that would resist alkali-silica reaction. And at the world's largest aquarium in Atlanta, the concrete had to be strong enough to hold 8 million gallons of water, and resist chloride and sulfate.
The common factor: slag cement.
If these high-profile projects are any indication, there is no slowdown in sight for slag cement. Slag cement shipments increased last year, for the 10th year in a row, according to the Slag Cement Association (SCA). Shipments reached a record in 2006, up 3.5% to 3.62 million metric tons (Click here to see bar chart showing the increase in slag cement and blended cement shipments).
Most slag cement is delivered as a separate material that is added, along with portland cement, during concrete batching operations. However, SCA credits growth since 2005 to the use of blended cement, which has increased almost 15 times from a decade ago.
Blended cement is a hydraulic cement made by intergrinding or blending portland cement with other materials. The cement producer delivers it in a ready-to-use form, which saves silo space. This flexibility and the overall availability of slag cement have fueled its popularity.
But its contribution to green building projects is arguably the greatest factor in its widespread acceptance. Slag and other industrial byproducts, such as fly ash and silica fume, cover the three environmental “R's” (Reduce, Reuse, Recycle), and lower the energy and greenhouse gas embodied in concrete.
“The green building movement is the biggest trend in our industry today,” says Jan Prusinski, executive director of the SCA. Producers realize that offering ‘green' concrete can set them apart.”
Transportation projects offer significant potential. After the SAFETEALU Act passed in 2005, Congress asked the EPA to prepare a report on industrial byproduct usage. When the report is completed next March, it is expected to reveal how byproducts are being used in federal projects and what more can be done.
The findings could lead to new federal legislation, further boosting the use of recycled materials. State DOT projects also represent a growth opportunity because not all states allow what the SCA calls “optimal levels” of slag in their specifications.
But more is not always better when it comes to recycled content. Problems can arise if producers use, or specifiers require, too much replacement material without fully understanding its properties. “You want to avoid byproduct replacement for replacement's sake,” says Prusinski.
This can diminish the energy and emissions reduction benefits of using recycled cementitious byproducts. “You have to look at each application and meet its special requirements,” he says.
This is where informed producers can fill an important niche. The SCA recognizes producers' efforts to educate customers as an important factor in the growth of slag cement usage. “Knowledgeable producers are key to explaining the best way to use byproducts because they know the materials more intimately than anyone,” says Prusinksi. “They can become the go-to guys for specifiers.”
The SCA provides various resources for producers regarding slag cement, including the “LEED-NC Guide: Using Slag Cement in Sustainable Construction,” at www.slagcement.org. For the full report and more, visit www.theconcreteproducer.com.
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