Glass-fibre Reinforced Concrete (GRC) is the generic term for a high-strength composite stone made with cement mortar (primarily a mixture of cement and sand) reinforced with bundled strands of fibreglass filaments. GRC differs from what most people refer to as ‘fibreglass’ in that cement mortar is used instead of a plastic resin (e.g. polyester) for encapsulating the fibreglass strands.
Unreinforced concrete is strong in compression but weak in tension. This is why reinforcement is added. Precast concrete is typically reinforced with steel, but precast concrete products are very heavy because of their overall thickness.
Adding glassfibres overcomes this weight problem while dramatically increasing the tensile strength of concrete. The glassfibre strands in the cement-sand mortar (3-5% by weight depending on the process) reduce product weight because of the much thinner but stronger wall sections. GRC products are typically only 20-25% of the weight of traditional precast concrete products. This lightweight feature of GRC also makes it safer and easier to handle on site, and reduces loads on structures when installed.
The advantages and benefits of Glass-fibre reinforced concrete
GRC combines the high strength of glass fibre with the rigidity of concrete. The resulting composite is a tough, rigid material that has a strength-to-weight ratio superior to most other commonly-used building products.
Other advantages and benefits of GRC include:
- Mouldable – GRC can be moulded to accurately reproduce almost any small or large shape (eg. curves, patterns, reliefs, etc).
- Colour – GRC products can be manufactured using different cements (eg. white, off-white, grey) that can be coloured with mineral oxides.
- Impact resistant – GRC products are highly durable. They will not shatter upon impact, and any localized damage can usually be repaired.
- Weather-proof – GRC will not rust or rot, it needs no painting, and because it doesn’t contain reinforcing steel it won’t develop ‘concrete cancer’.
- Water resistant – G RC is virtually impermeable to water thus making it ideal for products such as planters and water-features. Usually no additional waterproofing is required.
- Chemical resistant – the high density and high cement content of GRC give it a higher chemical resistance than other cement based materials.
- Fire resistant – GRC does not burn or emit smoke when exposed to fire. This gives architects and designers greater flexibility in specifying components to satisfy fire performance requirements.
The main constituents of GRC are based on the naturally occurring earth oxides that are used in the manufacture of cement and glass fibres. These are not generally regarded as pollutants.
The reduced weight of GRC compared to steel reinforced concrete products provides environmental benefits. An assessment carried out as part of a UK government-DETR/Concrete Industry Alliance ‘Partners in Technology’ project compared two precast concrete and GRC products that fulfil the same function. The results show that GRC has a lower environmental impact (around 40% less).
The main reasons for the reduced environmental impact of GRC compared to traditional precast concrete are:
- reduced cement usage per product
- reduced transport costs
All of these advantages and benefits make GRC an ideal material for the manufacture of planters, planter boxes, street furniture, architectural mouldings and panels.