Made from Ductal ultra-high-performance concrete, the custom-made lightweight spandrel panels on the Atrium, a commercial/retail building in Victoria, British Columbia, are only 3⁄4" thick.
Ductal is made from portland cement, silica fume (a byproduct of electric arc furnaces), silica flour, silica sand, water, and polycarboxolate high-range water reducers (superplasticizers) that help cement flow; Lafarge adds metal or polyvinyl alcohol fibers to provide structure. “All the materials in Ductal are standard products,” said Vic Perry, vice president and general manager at Lafarge North America. “It’s how we select them and put them together that makes Ductal work.” Lafarge controls the size, geometry, and orientation of all the materials “at the micro level,” in Perry’s words, to create a very dense matrix that can be formed into intricate shapes while maintaining its performance.
According to Perry, Ductal’s compressive strength is ten times higher than that of normal concrete, and its flexural strength is three to four times higher; he also says it has lower permeability and the same abrasion resistance as the highest-quality granite. With such low permeability, chlorides and water that degrade normal concrete have almost no effect on Ductal. At a test site along the Maine coast, samples of Ductal have been inundated with seawater twice a day and exposed to freeze-thaw cycles since 2006. A normal 3,000 psi concrete lasts only one year in these conditions, according to Perry, but the Ductal sample still has the same square edges, with virtually no chloride penetration or degradation. Based on the company’s calculations, he estimates Ductal’s lifespan to be a staggering 1,000 years.