What's the difference between GFRC and Precast?
When looking for architectural prefabricated concrete, there are two types of mixes you’ll come across: conventional concrete (precast) and Glass Fiber Reinforced Concrete (GFRC). Which one’s the better choice for your next project? Knowing the advantages and history of each will help influence this decision.
Conventional concrete is made roughly the same way today as it was decades ago: a simple mix of sand, pea gravel (or other stone aggregate), Portland cement, and water which can be used to pour formed stone like curbs, sidewalks, and facade panels, and more. However, when it comes to the architectural precast industry, conventional concrete is not the standard it used to be and is being taken over rapidly by GFRC.
GFRC is essentially a high-performance special concrete mix. Per its name, it includes glass fiber in its concrete mix, which gives it enhanced structural properties over conventional concrete. Traditional precast would generally require some type of steel rebar reinforcement to achieve an equivalent level of strength. Apart from fiberglass, the mix for GFRC also includes cement, acrylic polymer, fine sand aggregate, and other performance admixtures.
GFRC is also both a more elastic and more dense cementitious material than precast concrete. The ratio of cement to sand for GFRC is 1:1, compared to 1:6 for precast concrete. The addition of glass-fibers to reinforce the skin results in significantly higher flexural and impact strength than precast, as well as lower permeability to water and air.
GFRC can be used for a curtain wall (non load-bearing) exterior cladding. In cases where panels are required to supply structural support to the building, precast panels are a better choice.
Why GFRC is quickly replacing traditional precast for architectural applications:
Because GFRC can be made with 50% of the thickness of traditional precast, it is automatically 50% the weight. Because GFRC does not use stone or as much sand, which are denser and heavier than cement, the weight savings is even greater.
Precast is typically made 1.5″ thick and weighs 17-19 pounds per square foot. 3/4″ thick GFRC weighs 6-9 pounds per square foot.
The effective minimum thickness for precast is 1.5″ because of the required strength and the steel reinforcing. GFRC’s practical thickness is only about 1/4″.
GFRC also has a high strength to weight ratio – making it cost effective for higher elevation applications.
Less Expensive Installation
Two strong men can handle a 300 pound slab. Not so when you approach 500 or more pounds.
For example, trying to install a 18-foot long precast panel at 675 pounds you would need either special equipment or 5 or more people to handle the load, at risk to their backs and their safety.
GFRC reduces the number of employees and the labor costs needed for your business. There is also less building structure needed, and less erection equipment and yard management.
Shorter Lead Time
Because GFRC has high early strength, in part provided by the fibers, it can be demolded quickly. Most GFRC projects can be removed from the molds in 24 hours. In general, traditional precast projects should stay in the molds at least a couple of days.
Since most profiles are custom, removing parts faster leads to significant savings in manufacturing lead times without raising cost (for example by making more molds). For large projects with a lot of parts, these time savings can shave weeks off the schedule.
Because of GFRC’s strength and toughness, it can take a lot more abuse before it cracks. GFRC can even bend. It's also much more durable compared to other exterior products such as stucco or EIFS.
No Additional Reinforcement
For most projects, the GFRC itself provides all the reinforcement needed, via the AR glass fibers in the backer coat. Some applications require the addition of AR glass scrim, but this is thin and easy to place between layers of backer.
Complex Profiles and Pieces
If you can build the mold for it, you can make it out of GFRC. We have used many clever strategies to build molds to create almost and 3D shape desired. If it can't be achieved in one piece, we can use multiple molds to create the part and find creative ways to hide the seam.
For more information on how to use GRC on your architectural project, reach out to UP Ceilings today: