Alternative materials: Glass fiber reinforced concrete

Developed in the 1930s, Glass Fiber Reinforced Concrete, or GFRC, incorporates hydration products of cement or cement with sand and glass fibres. The first country to reinforce concrete with glass fibres was Russia. But the glass fibres were eroded by the highly alkaline portland cement matrix. Hence, the UK and other countries started developing alkali-resistant glass fibres. 

GFRC composes of portland cement, fine aggregate, water, acrylic copolymer, alkali-resistant glass fiber, reinforcement, and additives. 

These glass fibres are available in various forms like continuous rovings, chopped strand mats, cranette, wool, ropes, and woven fabric. A coating of an epoxy resin compound on the glass fiber protects it from an alkali attack from Portland cement. 

Advantages of GFRC | Glass Fiber Reinforced Concrete 

• As it composes of minerals, there is no way it burns. The nature of the concrete acts like a thermal regulator when exposed to flame. It protects other materials behind the GFRC from heat.
• It is relatively light in weight than traditional stone and terra cotta. 
• It is quick and easy to install.
• Casting can form any shape.
• It is available either with a cast in integral color or texture. 

Manufacturing Process of GFRC 

The glass fibres used in GFRC give this distinctive compound its strength. Alkali-resistant fibres act as the paramount tensile load carrying member while the polymer and concrete mix binds the fibres together. It helps in load transfer from one element to another. GFRC uses mainly two methods for casting, spray up and premix. 

Generally, items like the building cladding materials use the spray method, whereas smaller items use the premix method.  

Spray method 

This method is very similar to shotcrete, where the fluid concrete mixture is sprayed into the forms. The process uses a specialized gun to apply the concrete mix and to cut and spray long glass fibres from a continuous spool. 

The spray method GFRC creates a powerful product due to the high fiber load and long fiber length. 

Sprayed GRC is generally more vital than premix vibration cast GRC as spray method GRC usually has a lower water content than premix GRC.

Steps:

1. The high shear mixer takes in sand/cement in addition to the water and admixture to form a creamy slurry. A simple slump test kit could check the consistency of the slurry. 
2. The pump/spray unit then takes in the mix. The pump conveys the slurry at a regulated rate to the spray gun. At the spray gun, the fiber in the form of roving is cut at 32mm. It is then added to the slurry. An air supply from the compressor projects the two materials onto the mould.
3. The spraying of GFRC material forms thin layers until achieving the required thickness of 10-15mm. Simple hand rollers are used to compact the material between the layers. 
4. The product is left in the mold and covered with polythene to prevent moisture loss until the next day. The product is then demoulded
5.  After the demoulding, polythene covers the units, and the curing takes approximately seven days. 

Premix method | Glass Fiber Reinforced Concrete 

The premixing method mixes the shorter fibres into the concrete. It is either done through pouring or spraying. Premix tends to possess less power than the spray-up method since the fibres are short and placed more randomly throughout the mix. 

Steps:

1. Dry mixing of sand and cement takes place, and then water or admixture is added to the mix. The usage of a two-speed slurry/fibre blender creates a creamy slurry. After 1-2 minutes, there is a reduced speed and fibre, after which there is an addition of chopped strands slowly.
2. Once the mix is ready, pour it into moulds that vibrate using a vibrating table.
3. The product is left in the mold, and polythene covers it to prevent moisture loss until the next day.
4. After the demoulding, the products are curing under the polythene sheets to maintain moisture control for seven days. 

Hybrid Method

There is one final option to create GFRC, known as the hybrid method. It uses an inexpensive hopper gun that applies the face coat. Spraying of a thin face without fibres into the molds takes place. Later the packing of the backer mix by hand is done. Usage of this method is mainly for concrete countertop makers. 

Uses of Glass Fiber Reinforced Concrete

GFRC has restricted usage as it may suffer severe damage and loss of strength due to abrasion and impact forces generated during the movement of aggregates in a mixer. GFRC is used to build wall panels, repair works, and for industrial floors abroad. 

Properties of Glass Fiber Reinforced Concrete 

• Mechanical Strength: resistance is more significant than that steel.
• Lightweight: low weight ensures faster installation, less structural framing, and lower shipping costs.
• Electric Characteristics: even at low thickness, it is a good insulator.
• High Resistance: It is resistant to salt water and chemicals and is unaffected by acid rain.  
• Incombustibility: It is a mineral material GFRC is non-combustible. It does not support a flame. 
• Thermal Conductivity: Low thermal conductivity makes it highly useful in the building industry.
• High Durability: GFRC does not rot and remains unaffected by rodents and insects.

References:

1. “(PDF) Glass Fibre Reinforced Concrete (GFRC).” ResearchGate, www.researchgate.net/publication/322931740_Glass_Fibre_Reinforced_Concrete_GFRC.4
2. Admin. “How Is GFRC Made?” UP Ceilings, 29 Oct. 2019, www.upceilings.com/post/how-is-gfrc-made.
3. “GFRC – Stromberg Architectural Glass Fiber Reinforced Concrete.” Www.strombergarchitectural.com, www.strombergarchitectural.com/materials/gfrc.
4. https://www.facebook.com/TheConstructor. “Glass Fiber Reinforced Concrete (GFRC) – Properties and Applications.” The Constructor, 13 Oct. 2010, theconstructor.org/concrete/glass-fiber-reinforced-concrete/4773/.
5. “Innovative Glass Fiber Reinforced Concrete – an Impressive Science.” How to Civil, 25 July 2019, www.howtocivil.com/glass-fiber-reinforced-concrete-properties-and-applications/.