GFRC Backing vs Fiber Reinforced Concrete (FRC) Backing
June 27, 2024
The main difference between glass fiber reinforced concrete (GFRC) and fiber reinforced concrete (FRC) lies in the type and concentration of fibers used to reinforce the concrete mix.
Glass Fiber Reinforced Concrete (GFRC):
- Fibers Used: Contains alkaline resistant (AR) glass fibers with high zirconia content (minimum 16%) formulated to improve resistance to attack by aqueous alkaline solutions.
- Fiber Amount: 4.5% to 5.5% by weight
- Properties: Offers high tensile strength, flexibility, and resistance to cracking.
- Applications: Commonly used for architectural elements, decorative panels, façade cladding, and other non-structural components.
- Flexural Strength: 1,200 to 1,500 PSI (Limit of Proportionality for 5/8” coupon)
- Fibers Used: Primarily synthetic (e.g., polypropylene), or natural (e.g., cellulose).
- Fiber Amount: 1% or less by weight
- Properties: The specific properties depend on the type of fiber used. Generally, FRC improves the toughness, impact resistance, and durability of normal concrete.
- Applications: Used in a wide range of applications including pavements, industrial floors, precast products, and structural elements where enhanced durability and crack resistance are needed.
- Flexural Strength: 200 to 300 PSI (Limit of Proportionality for 5/8” coupon)
Fiber-reinforced concrete (FRC) is not suitable for architectural cladding applications due to its low flexural strengths, but some FRC manufacturers represent their material as GFRC, which puts projects at risk of critical material failures. Please see the photos below that show a “GFRC” skin next to a piece of Building Blocks GFRC.
Key differences to note:
- FRC skin is about ½” total thickness with a 1/8” poured face and 3/8” backing. Building Blocks GFRC is 1” thick with a 1/8” face and 7/8” structurally reinforced backing. Precast/Prestressed Concrete Institute (PCI) requires a minimum of 5/8” structurally reinforced backing.
- FRC skin has a single layer of polypropylene mesh pressed into the back of the panel. The polypropylene mat is a single reinforcing layer, acting in only two dimensions, not three dimensions like spray-up GFRC. Building Blocks GFRC is fabricated with a spray-up method and has a heterogeneous fiber distribution with a fiber content of 5% by weight. PCI requires a minimum of 4.5% fiberglass by weight.
- Require PCI Certification for the design and fabrication of the GFRC to ensure that you know what you are buying. The PCI search tool (https://www.pci.org/PCI/PCI/Directories/PCICertifiedPlants.aspx) allows you to search for certified plants and select Certification G.
- Require material test data for flexural testing per ASTM C947 for your GFRC with minimum required values of 800 psi (LOP not MOR).
- Require material samples specific for the project requirements that confirm color, texture and thickness.
- Require detailed proposal drawings listing all items to be provided by your GFRC fabricator, including skin thickness, anchors, framing, connection hardware, embeds, etc.