When Elkem Materials began selling a white microsilica product as a filler for color-sensitive plastic products, the concrete industry seemed an unlikely market. Conventional dark gray silica fume matched the color of standard concrete when it was added to create high-strength mixes.
For the past decade, architects and designers have been using more colored concrete in high-performance applications. Artists who work with concrete also like the workability of silica fume mixes, which conform to detailed molds and remain more true to the artistic design. But the decorative concrete community has not been happy with the way the dark gray admixture affects their desired concrete colors. In response, Elkem introduced MicroWhite to the concrete market earlier this year.
By removing the carbon from conventional silica fume, the Pittsburg, Pa.-based silica products manufacturer created an ideal admixture for decorative applications requiring high-strength concrete. Silica fume often is used to produce ultra-high-performance concrete (UHPC) for bridge piles, girders, beams, and low-permeability concrete commonly found in bridge and parking decks. With the product, designers can create impact-resistant countertops and durable outdoor installations without sacrificing aesthetics.
Attractive and smart
Although the product became known for its white appearance, it also is attracting attention for being green. Using silica fume, a byproduct of producing silicon metal and alloys, diverts the waste material from landfills. The admixture can reduce concrete’s carbon footprint by replacing cement at a 4:1 ratio.
However, traditional silica fume also can contain up to 6% carbon content, as allowed by ASTM C1240. The fine, dark carbon particles also have a large surface area, which means the mixes require more water. Without the carbon, a MicroWhite mix requires less water. This is critical when producing UHPC, which typically specifies a water-cementitious material ratio less than 0.20.
The white silica fume is also ideal for “cool concrete” applications. Light-colored pavement keeps surrounding temperatures cooler by reflecting, rather than absorbing, the sun’s heat. Its higher albedo, or solar reflectance, can reduce the urban heat island effect in densely populated areas and ultimately help combat global warming.
MicroWhite’s most significant sustainable contribution may still be the green benefit silica fume always has provided: durability. Although it might not translate directly into points in a green rating system, the life cycle of a concrete building or infrastructure project relates directly to its sustainability.
“Our sustainable philosophy is to make concrete last for future generations,” says Tony Kojundic, Elkem’s business manager. “We haven’t been involved in any projects that aren’t going to be around for at least three generations. If you have to tear something down or repair it after 10 years, how sustainable is it?”
With color-friendly silica fume, artists and contractors can create decorative projects that showcase concrete’s versatility, and serve as lasting reminders that sustainable construction can also be beautiful.
For more information on the product in this article, visit www.elkem.com.