The Basics of Glass Fiber Reinforced Concrete (GFRC)
Glass Fiber Reinforced Concrete (GFRC), also known as
Glassfibre Reinforced Concrete (GRC), is a versatile engineered material
composed of cement, aggregate, polymer, and fibers. This amalgamation creates a
remarkably lightweight yet incredibly robust substance. GFRC is renowned for
its exceptional flexural strength, making it an ideal choice for a myriad of
interior and exterior applications such as wall cladding, fire pits,
countertops, furniture, and more.
Understanding GFRC Mix Composition
One of the distinctive features of GFRC is its unique mix
composition when compared to traditional concrete. The key components in a GFRC
mix include:
1. High Cement Proportion: GFRC mixes typically consist of
an equal ratio of cement to sand, which is relatively high compared to
conventional concrete mixes.
2. Glass Fiber Reinforcement: Instead of utilizing steel for
reinforcement, GFRC employs glass fibers as the primary reinforcement material.
These fibers significantly contribute to the material's remarkable strength and
durability.
3. Polymer Resin: An acrylic polymer resin is added to the
mix to enhance the material's strength, act as a curing aid, and provide
numerous other benefits.
4. Additional Components: Many GFRC mixes may also include
pozzolans, defoamers, and shrinkage reducers to further enhance their
properties.
Basic GFRC Mix Design
Here's a breakdown of the basic components in a typical GFRC
mix design:
·
Cement: 18.5 lbs (8 kg)
·
Alto-Pozz: 4.5 lbs (2 kg)
·
Sand (#30 sieve preferred): 23 lbs (10 kg)
·
Water: 6-6.5 lbs (3-3.5 kg)
·
KongKrete Polymer: 2.3 lbs (1 kg)
·
PVA Fibers 8mm (face coat only): 85 grams
·
¾” (19mm) AR Glass Fibers (Backer Coats only):
2.6 lbs (1.1 kg)
·
Optimum 380 Superplasticizer: 23-42 mL
·
C-64 Defoamer (optional): 5-10 mL
It's important to note that this information provides only a
fundamental understanding of the GFRC mix design process. There are various
factors and variables that can influence the final outcome, and therefore,
independent practice and testing are crucial.
The GFRC Process Overview
The GFRC fabrication process involves several key steps to
ensure the material's proper composition and successful casting. Let's delve
into the process:
A. Prepare Supplies & Equipment
1. Ensure all necessary equipment and tools are set up and
ready for use.
2. Prepare the casting forms by cleaning and applying a
release agent. Remove any caulk or residue, cover screw heads with tape, and
complete other necessary preparations.
3. Cut and prepare any foam, scrim, or inlays that will be
included in the project.
B. Calculate Recipe & Materials Needed
1. Determine the batches for the face and backer coats based
on your project's requirements. Use a mix calculator for accurate measurements.
2. Decide on the total number of batches to be mixed,
considering factors like job size, ambient temperature, the type of mixing
equipment, and the working time. Avoid mixing more material than can be used
within 20 minutes.
C. Mixing
1. Begin with the Mist Coat (Face Coat) by mixing one batch
using a handheld mixer to create a thin, milkshake-like consistency. Add
plasticizer as needed to maintain the desired texture.
2. For the Backer Coat, mix one batch with fibers for the
initial backer coat. Dispense only half of the mix into a bucket, ensuring it
can be used before it begins to set. Adjust the consistency based on your
preference, with thinner mixes being easier to work with and achieving better
consolidation.
3. Follow these steps for mixing:
·
Add mix water and polymer to the mixing bucket.
·
Dry blend sand, pigment, cement, and pozzolan
(PVA fibers for the face mix) in a separate bucket.
·
Add approximately 80% of the dry blended
material to the water and mix on low speed until well blended. For backer
coats, add AR Glass fibers after thoroughly mixing and blend them in on low
speed.
·
Repeat for subsequent and final backer coats.
·
Mix on high speed for 1-2 minutes to shear the
mix until it reaches a loose, smooth consistency, similar to a milkshake.
·
Add the remaining dry blended material and mix
on low until well blended. Adjust the consistency with plasticizer if
necessary.
D. Casting
1. Start with the Mist Coat:
·
Fill the hopper gun about halfway.
·
Set the air pressure to around 90 PSI and
regulate it at the gun to achieve the desired results (usually around 45 PSI at
the gun).
·
Test spray in an area away from the forms to ensure
the gun is operating correctly.
·
Begin spraying from a corner, working outward,
concentrating on edges first and then open areas. Clear any sand rebound that
accumulates and ensure the material looks wet when applied.
·
Do not allow the mist coat to dry; it should
remain soft to promote proper bonding.
2. Backer Coat Options:
- You can apply the
backer coat with a backer coat gun, maintaining a higher air pressure (100+
PSI) and spraying an even, thin layer over the surface. Use chip brushes and
compaction rollers to ensure proper consolidation.
- Alternatively,
you can apply the backer coat by hand, taking care not to push it through the
mist coat. Use chip brushes and compaction rollers to achieve the desired
thickness and proper consolidation.
3. Make sure to address any corners, edges, and open areas
thoroughly. It's crucial to avoid any gaps or air pockets between layers, and
reinforcing fibers should be correctly oriented to maximize strength.
E. Curing
1. Gently clean excess cement from the forms.
2. Mist the concrete surface with water and cover it with
plastic to ensure wet curing for at least 24 hours (or 36 hours in cooler
temperatures). The plastic should fully enclose the mold and be secured to
retain moisture.
3. Enhance curing by using moving blankets, foam sheets, or
other means to maintain heat and minimize gaps between the mold and plastic.
It's vital to keep the surface hydrated for the first 24-36 hours.
F. Demolding
1. You can demold GFRC as soon as 24-36 hours after casting,
provided the concrete is at room temperature. Be cautious when handling the material,
as it is still relatively soft. Faster curing can be achieved with accelerators
and heat.
2. Once removed from the mold, place the casting on stickers
or shims to allow air movement on all sides of the concrete for even curing.
3. Avoid placing any objects on top of fresh concrete, as
this could cause "ghosting."
G. Slurry Coat (Optional)
1. If necessary, create a slurry coat using the following
recipe:
·
Dry Ingredients: Cement (320 grams), Alto-Pozz
(80 grams), Microspheres (up to 60 grams).
·
Wet Ingredients: Mix 1 part KongKrete Polymer
with 3-4 parts water.
2. Mix only the amount of slurry that you can use within 15
minutes. If it hardens, you can add Optimum plasticizer to extend working time.
3. Dampen the surface lightly and spread the slurry into
voids, ensuring it is packed thoroughly. Use hand tools, a grout float, sponge,
or any suitable equipment to achieve this.
In conclusion, understanding the basics of Glass Fiber
Reinforced Concrete (GFRC) is essential for those looking to work with this
innovative construction material. By following the process of preparation,
mixing, casting, curing, demolding, and optionally applying a slurry coat, you
can create a wide range of durable and visually appealing projects, from
countertops and wall cladding to furniture and fire pits. Remember that
practice, experimentation, and meticulous attention to detail are key to
mastering the art of working with GFRC.
.png)
