GFRC Steel Building

When someone says fiberglass, we think of insulation or boats or Corvettes, but maybe we should think of concrete. Technically, fiberglass is simply very fine glass fibers. The material used to make boats or other products, although called fiberglass, is really glass fiber reinforced plastic-glass fibers in a polymer matrix. If, instead of the polymer, we use Portland cement and sand, the resulting material is glass fiber reinforced concrete--GFRC or sometimes GRC (the Brits call it grassfire reinforced concrete).

The problem with using glass fibers as reinforcement for concrete is that glass breaks down in an alkaline environment--and there's almost nothing more alkaline than concrete. You may have heard of concrete being damaged by alkali-silica reactivity (ASR) when there is reactive silica in the aggregate. Glass is primarily silica. The original GFRC in the 1940s rapidly lost strength as the glass was destroyed by the alkaline environment. In the 1970s alkali-resistant (AR) glass fibers were perfected by Owens-Corning and by Nippon Electric Glass (NEG) leading to a rapid increase in applications.

GFRC has been used for the past 30 years to produce many concrete products, especially thin architectural cladding panels, but also for ornamental concrete such as domes, statues, planters, and fountains. Recently, decorative concrete artisans have discovered the benefits of GFRC for decorative panels (such as fireplace surrounds), concrete countertops, and artificial rock work.

• Lighter weight: With GFRC, concrete can be cast in thinner sections and is therefore as much as 75% lighter than similar pieces cast with traditional concrete. According to Jeff Girard's blog post titled, "The Benefits of Using a GFRC Mix for Countertops", a concrete countertop can be 1-inch thick with GFRC rather than 2 inches thick when using conventional steel reinforcement . An artificial rock made with GFRC will weigh a small fraction of what a real rock of similar proportions would weigh, allowing for lighter foundations and reduced shipping cost.

• High strength: GFRC can have flexural strength as high as 4000 psi and it has a very high strength-to-weight ratio.

• Reinforcement: Since GFRC is reinforced internally, there is no need for other kinds of reinforcement, which can be difficult to place into complex shapes.

• Consolidation: For sprayed GFRC, no vibration is needed. For poured, GFRC, vibration or rollers are easy to use to achieve consolidation.

• Equipment: Expensive equipment is not needed for poured or vibrated GFRC with a face coat; for sprayed GFRC, equipment generally costs about $10,000.

• Toughness: GFRC doesn't crack easily-it can be cut without chipping.

• Surface finish: Because it is sprayed on, the surface has no bugholes or voids.

• Adaptability: Sprayed or poured into a mold, GFRC can adapt to nearly any complex shape, from rocks to fine ornamental details.

• Durability: According to ACI 544.1R-96, State of the Art Report on Fiber Reinforced Concrete, "The strength of fully-aged GFRC composites will decrease to about 40 percent of the initial strength prior to aging." Michael Driver, division manager with Nippon Electric Glass, a major manufacturer of AR glass fibers, disagrees. "There's never a durability issue. Water can't get in-there are no cracks-and that's a durable material. GFRC will outlast precast concrete, cast stone, even some natural stone." Durability has been increased through the use of low alkaline cements and pozzolans.

• Sustainable: Because it uses less cement than equivalent concrete and also often uses significant quantities of recycled materials (as a pozzolan), GFRC qualifies as sustainable.

• Cost: GFRC as a material, however, is much more expensive than conventional concrete on a pound-for-pound basis. But since the cross sections can be so much thinner, that cost is overcome in most decorative elements. "When you keep the thickness to about ¾ inch, the material cost is typically less than $2.00/square foot," said Driver. "Because of the high modulus of elasticity of the glass, it replaces all of the steel, but once you get into 4-inch slabs, the GFRC becomes cost prohibitive."

• "GFRC hasn't caught on like it could because of the mix design," said Driver. "When you have so much cement, your chemistry changes and you have a lot of variables to control. Many regular concrete guys have problems and end up disgruntled. It takes some time to become proficient with GFRC. There's a lot to know, a lot of variables. Training is key."