A pedestrian bridge in Sherbrooke, Quebec, served as a North American pilot application of reactive powder concrete technology similar to that behind Lafarge's Ductal material. The structure has an open-web space truss design whose diagonals consist of thin-walled RPC-filled tubes. St. Marie, Quebec-based Beton Boulduc prepared the truss members and six 10-meter match cast segments they support. Steel on the bridge is limited to the truss tubes and segments' post-tensioning strand.

Lafarge Group unveiled Ductal for the European market at the 1999 Batimat trade fair in Paris — demonstrating that with a little prestressing strand and thin structural profile, the product could more than “carry its weight.” Reston, Va.-based Lafarge Corp. timed Ductal's roll out on this side of the Atlantic with World of Concrete 2001.

With World of Concrete 2001 in Las Vegas as a backdrop, Lafarge Corp. announced plans on February 28 to market Ductal, a proprietary, cement-based composite material exhibiting a compressive strength range — 26,000 to 33,000 psi — unlike any commercial formulation North American concrete producers and practitioners have observed. The announcement followed the signing of a production and marketing licensing agreement with a European consortium of which Paris-based Lafarge Group is a part.

Ductal is classified a reactive powder concrete. Its mix design includes oil well cement, precipitated silica, silica fume, superplasticizers and metallic or organic fibers. The latter serve as primary reinforcement and can preclude the use of conventional rebar, particularly in architectural panels and other thin profile, low load-bearing conditions where weight reduction is sought. Conventional wire strand and prestressing equip Ductal members for structural applications. Lafarge officials note that the material's uniqueness is owed to a combination of compressive and flexural strength, plus a high resistance to abrasion and corrosive elements.

Preliminary market development of Ductal will be centered on precast applications in the Western Region of Lafarge Canada, based in Calgary. That region has North America's largest concentration of plants using high-intensity, twin shaft mixers. While conventional equipment can be used with longer mix cycles, Lafarge officials find the high intensity units better suited for achieving the mix consistency necessary to yield product with super high compressive strength and other performance features.

In addition to twin shaft units' mixing energy, the controlled setting of a precast operation is more conducive than a job site for the level of curing required to reach strength and durability levels. Product specifications state that Ductal cured at 70°F should achieve compressive strength exceeding a) 15,000 psi 24 hours after initial set; and b) 26,000 psi at 28 days. Strength development up to 33,000 psi can be reached in four days with curing at 195°F after final set.

Mix materials can be provided in bulk; early on, however, Lafarge will ship Ductal preblended in 50-lb. bags and 1,500-lb. “bigbags.” The mix technology was developed by Lafarge Group and two French construction and engineering concerns, Bouygues S.A. and Rhodia S.A. They are members of a consortium that licenses Ductal production and marketing worldwide. Lafarge's French unit was the first licensee, entering an agreement in 1999.

Spearheading the Ductal development in North America will be Lafarge Vice President and General Manager Andy Radler, P.E., operating out of Calgary. In a World of Concrete press gathering, he explained that cost savings from the product can be significant because it makes for a faster construction process and generates labor and material savings. Radler also noted that the special nature of Ductal and its custom applications are prompting Lafarge to treat it as product group separate from cement and construction materials.