Standards and product development activity have catapulted synthetic and steel fiber reinforcement to the forefront of concrete technology. Past action on standards, especially where synthetic reinforcing fibers are concerned, has moved at a snail's pace, most recently evidenced in the eight-year evolution of ASTM C 1399-98 Test Method for Obtaining Average Residual Strength of Fiber-Reinforced Concrete (Concrete Products, October 1998). The standard provides engineers and producers means of demonstrating that synthetic fibers — in dosages beyond the 1.5 lbs./yd. common in flatwork — have reinforcing potential and other beneficial functions in structural concrete.

ASTM Committee C 09 on Concrete and Concrete Aggregates has just announced formation of a task group to define synthetic fibers used in concrete. Chairing the group is SI Concrete Systems Business Development Manager Mel Galinat, who notes that a standard defining synthetic reinforcing fibers will 1) eliminate guesswork on product usage and performance; and 2) contribute to the evolution of a design methodology for specifying synthetic fibers in projects following ACI 318 Building Code Requirements for Structural Concrete guidelines.

Standardization of commercially available synthetic fibers is the first step toward ACI 318 recognition, Galinat affirms. From there, concrete practitioners will have a methodology to factor, for example, tensile properties fibers add to concrete. “The task group will cite fibers appropriate for concrete reinforcement made from synthetic filaments such as polyproylene, nylon and carbon,” Galinat explains. “While not excluding future innovations, it will limit the definition to current materials to simplify parameters needed for product standardization.” The result will be a list of prescriptive synthetic reinforcing fiber products that ACI 318 committee members can formally recognize, he adds.

“The lack of a design methodology has held up wider synthetic fiber usage in concrete for years,” Galinat contends. “The current methodology for reinforced concrete is based on the steel rebar's continuous reinforcing function and tensile strength characteristics. Synthetic and steel fibers impart discontinuous tensile reinforcement and perform synergistically with continuous reinforcement. For engineers, this requires a paradigm shift.”

The C 09 task group activity coincides with circulation of a design methodology for steel-fiber reinforced concrete proposed by RILEM, a European organization acting much like an ASTM counterpart. Galinat notes that principles of that methodology will be applicable to synthetic fiber reinforcement.

The push for standards recognizing performance characteristics achievable with fiber reinforcement is moving in lockstep with product development. Earlier this year, SI Concrete Systems rolled out its Novomesh e³ product — combining steel and synthetic fibers in mininum dosages of 24 lbs./yd. — for non-residential slabs requiring a higher level of secondary reinforcing. Bekaert Group, a Belgium company with a name in steel fiber comparable to SI's in synthetic fibers, has unveiled its own steel-polpropylene blend, Dramix Duo 150. Amid these innovations, carbon fiber, another synthetic product noted above, is emerging for commercial concrete at the hands of Conoco Cevolution (note Briefs, page 37).

With increasing recognition as a component in value-added concrete, fiber technology appears ready to clear hurdles that have kept it inching past the flatwork market.

e-mail: dmarsh@primediabusiness.com