Lighter weight: With GRC, 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 GRC Mix for Countertops", a concrete countertop can be 1-inch thick with GRC rather than 2 inches thick when using conventional steel reinforcement . An artificial rock made with GRC 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: GRC can have flexural strength as high as 4000 psi and it has a very high strength-to-weight ratio.
Reinforcement: Since GRC is reinforced internally, there is no need for other kinds of reinforcement, which can be difficult to place into complex shapes.
Consolidation: For sprayed GRC, no vibration is needed. For poured, GRC, vibration or rollers are easy to use to achieve consolidation.
Equipment: Expensive equipment is not needed for poured or vibrated GRC with a face coat; for sprayed GRC, equipment generally costs about $10,000.
Toughness: GRC 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, GRC 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 GRC 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. GRC 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), GRC qualifies as sustainable.
Cost: GRC 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 GRC becomes cost prohibitive."
"GRC 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 GRC. There's a lot to know, a lot of variables. Training is key."
