Flexible Concrete

Flexible concrete offers new solutions (Concrete Construction, December 2004) describes a highly ductile concrete produced under the trade name "Ductal". Flexible concrete differs from conventional reinforced concrete primarily in the absence of large aggregate in the concrete mix and the substitution of steel or organic fiber reinforcing for standard mild steel reinforcing.

The key to the behavior of the material is the creation of a highly regular matrix of fine aggregate interspersed with the reinforcing fiber in the concrete mix. The result is a material with greater strength and ductility than conventional reinforced concrete. Compressive strengths as high as 33,000 psi and flexural strengths as high as 7200 psi are claimed. Under extreme loading the material exhibits ductile behavior more similar to steel than conventional reinforced concrete. Ductile concrete also exhibits low porosity, reduced creep under sustained loading, and reduced drying shrinkage.

The high flexural strength of ductile concrete allows new possibilities for slender concrete elements. For example, curved concrete shell canopies for the a Calgary light rail transit station span 18 by 20 feet and are only 3/4 of an inch thick.

More Info:
Lafarge Ductal Home (click at top-right to view English version of site)
See also U-M researchers make bendable concrete (University of Michigan, May 4, 2005) press release for news of a similar developments at this university. Video links also included.