Glass Fiber Reinforced Concrete (GFRC)
GFRC was originally developed in the 1940s in Russia, but it wasn’t until the
1970’s that the current form came into widespread use in the US.
Commercially, GFRC is used to make large, lightweight panels, columns, and moldings profiles that are often used
as façades. GFRC systems are considered non-structural, in that they are designed to support their own weight.
The GFRC systems are considered lightweight because of the thinness of the material, not because GFRC concrete
has a significantly lower density than normal concrete.
Properties of GFRC
GFRC derives its strength from a high dosage of AR glass fibers and a high dosage of acrylic polymer. While
the compressive strength of GFRC can be quite high (due to low water to cement ratios and high cement contents), it is
the very high flexural and tensile strengths that make it superior to ordinary concrete. Essentially the high dose of fibers
carries the tensile loads and the high polymer content makes the concrete flexible without cracking.
While the structural properties of GFRC itself are superior to unreinforced concrete, properly designed fiberglass
rebar and fiberglass structural mesh reinforcing will significantly increase the strength of objects cast with either
ordinary concrete or GFRC.
GFRC does not replace reinforced concrete when true load carrying capacity is required. It’s best used for complex,
three-dimensional shells where loads are light. Applications, where GFRC makes the most sense, are fireplace surrounds,
columns, stone range hoods, molding profiles, and other similar elements. While the weight savings due to reduced
thickness is maintained, the effort of forming, mixing the lay-up GFRC system is more labor-intensive.
How the fibers work
GFRC uses alkali-resistant glass fibers as the principal tensile-load carrying member. The polymer and concrete matrix serves to bind the fibers together and transfer loads from one fiber to another via shear stresses through the matrix. The orientation of the fiber determines how effective that fiber resists the load.
Finally, the fiber needs to be stiff and strong enough to provide the necessary tensile strength. Glass fibers have long been the fiber of choice due to their physical properties and their relatively low cost.
The more random the orientation, the more fibers are needed to resist the load. That’s because on average, only a small fraction of randomly oriented fibers are oriented in the right direction.
There are three levels of reinforcement that are used in general concrete, including GFRC.