Mind & Matter


Perfecting the Use of Steel Slag in Concrete

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Steel slag being processed at a mill. Courtesy: Industrial Resources Council.


The increasing costs of material resources—coupled with the urgency of maintaining expansive infrastructure projects such as highways and bridges—have motivated scientists to investigate the repurposing of waste products in new materials at greater frequency. Fly ash, the byproduct of coal-based energy production, has now become a popular component for use in concrete. Another notable industrial waste product is steel furnace slag (SFS), a nonmetallic substance composed of calcium silicates and ferrites produced when steel is created in a furnace.

Steel furnace slag is a durable material that makes a desirable, angular aggregate for use in roadways and other construction projects. Although its history in civil engineering work dates back about 100 years, there is a general lack of knowledge regarding the durability and other critical properties of steel furnace slag, which can vary widely. For example, although steel furnace slag is typically stronger than typical concrete aggregate, air-cooled slag with low amorphous silica content is unsuitable for use in blended cement.

Researchers at the Slovenian National Building and Civil Engineering Institute have recently developed a method of ensuring the viability of steel furnace slag in future concrete construction. Noting that slag produced from the making of carbon steel has unpredictable properties, the scientists propose heating the slag above 1000 C in order  to ensure thermal stability. This irreversible process renders a substance with similar mechanical traits as conventional concrete.

Although one should question the development of another energy-hungry approach to material processing, the ability to offset a more energy-intensive substance such as Portland cement or replace virgin aggregate with a safe industrial byproduct deserves further scrutiny.




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About the Blogger

Blaine Brownell

thumbnail image Minnesota-based architect and author Blaine Brownell, AIA, is a self-defined materials researcher and sustainable building adviser. His "Product of the Week" emails and three volumes of Transmaterial (2006, 2008, 2010) provide designers with a steady flow of inspiration—a 21st-century Grammar of Ornament. Blaine has practiced architecture in Japan and the U.S. and has been published in more than 40 design, business, and science publications. The recipient of a Fulbright fellowship for 2006–07, he researched contemporary Japanese material innovations at the Tokyo University of Science. He currently teaches architecture and co-directs the M.S. in Sustainable Design program at the University of Minnesota. His book Matter in the Floating World was published by Princeton Architectural Press in 2011.