Fibreglass as Rebar in Concrete
Glassfibre Reinforced Concrete—commonly referred to as GRC and GFRC—is, as the name suggests, concrete that is reinforced with fibreglass. But what can GFRC be used for? This building material can be used for many applications but is most commonly found in decorative architectural elements, such as facades, cladding, window sills, and similar features.
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The lightweight yet durable properties of fibreglass make GRC easy to model, which also makes it an excellent material for smaller, more intricate items, such as garden ornaments. It is not suitable for structural work; however, as fibreglass is not an appropriate reinforcement when strength is the primary desired attribute. That being said, GRC can give the appearance of structural work in some situations. One example of this would be decorated support pillars, where the pillar would be constructed from concrete that is reinforced with steel to provide adequate structural support. The outside of the pillar could then be styled using GRC to give a more aesthetically pleasing look.
What are the Advantages of Fibre Reinforced Concrete?
The main benefit of fibreglass reinforced concrete is the same benefit that any kind of reinforced concrete has, which is additional strength over standard concrete, which is already a strong material, to begin with. In addition to increasing strength, reinforcing concrete significantly reduces the risk of cracking. It also reduces the significance of cracking in concrete. When non-reinforced concrete cracks, it typically signals the beginning of the end for any structural item, as concrete is not a flexible material. With reinforcements, cracking is still an issue that needs resolving, but the reinforcement is still there to maintain structural integrity.
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It can also reduce the amount of concrete needed for a particular task since a higher level of strength can be achieved. The structural benefits of fibre reinforced concrete directly translate to cost savings, both in the initial construction and in longer-term maintenance.
Fibreglass, in particular, is a much lighter material than, for example, steel. So, while it is not as suitable for structural work as the more heavy-duty materials, is excellent for shaping and modelling, as it allows you to create the same look as concrete while using less material and, as a result, less weight and less expense.
How does Fibreglass Strengthen Concrete?
Concrete is a relatively brittle material in that it does not allow much flex before breaking. This is a problem for material like concrete, which is typically used in large structures that will be put under immense pressure. In these cases, the amount of force that would be involved in cracking concrete would mean very severe consequences were it to actually break.
The fibres are small and embedded into the concrete facing in all directions. This ensures the reinforcing effect of the fibre is effective regardless of the direction any forces are coming from.
For a simplified idea of how this process works, imagine a regular candle. You could easily snap the wax cylinder in half with a little pressure from your fingers. However, it is much more challenging to break the wick that runs through the middle. Fibre works in a similar way, only on a much smaller and more pervasive scale. Instead of one big wick through the centre, it is millions of tiny ones throughout the whole of the concrete.
How Much Stronger is Reinforced Concrete?
The first thing to understand about strength in this context is that there are different types of strength. For example, concrete is extremely strong when it comes to compression. That is, it would require a lot of force to crush a block of concrete. This is why it is such an excellent building material since the weight of the upper parts of the building will not be able to crush the lower parts of the building. Where concrete fails, however, is with tensile strength. If, for example, you had a concrete beam, and you supported that beam at either end and then applied force to the middle, it would not take much force (relatively speaking) to break the concrete. It is tensile strength where reinforcing improves the ability of concrete to withstand external forces.
It is also important to understand that there are different kinds of reinforcement (more on that shortly). The question is more complicated than “what can GRC be used for”, as GRC is not the only reinforcement that can be used. And the strength of your reinforced concrete comes down to the material you use. For example, concrete can be reinforced with rebar, which is essentially tough metal rods. Fibreglass does not offer the same strength as rebar, of course, but it is still a very effective material for adding tensile strength to concrete.
Where is Fibre Reinforced Concrete Used?
Fibre-reinforced concrete has many applications, especially in areas that need protection from plastic and drying shrinkage. Their superior durability and lower construction costs make them particularly suited for things like raised decks, such as mezzanine floors. They are also used for flooring in a lot of other cases, from driveways to runways. They are particularly popular for precast structures, like prefab walls.
Any large floored surface like a commercial warehouse, or parking structure, is also a prime example of where fibre reinforced concrete can shine. Really, the only areas where it is not suitable is for highly structural components, such as would be found in skyscrapers, and bridges.
What are the 4 Types of Concrete Reinforcement?
There are four main types of concrete reinforcement used to bolster the tensile strength of concrete;
Traditional Rebar
Briefly mentioned above, traditional rebar reinforcement involves strong metal rods being incorporated into the concrete. This is usually achieved by building a rebar framework first and pouring the concrete over it. The rebar is ridged to ensure the best possible bond with the concrete. It is typically rebar reinforcement that is used in structural concrete, such as tall buildings.
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Post-Tensioned Concrete
Post-tensioned concrete makes use of a series of cables around the concrete that are contained within ducts that keep them separate from the concrete itself. After the concrete has cured, the cables are drawn until they are under great tension.
Wire Mesh
Typically used in situations where concrete is being sprayed, such as during the construction of a pool. Indeed, this method is often referred to as pool mesh. The mesh acts in much the same way that rebar reinforcement does, albeit on a much smaller scale. The mesh is put in place first, and the concrete is then sprayed over it.
Fibre Reinforced Concrete
There is not much more to add that we don’t cover in this post, except to say that fibre reinforcement is not limited to fibreglass. It is also possible to use steel fibres to reinforce concrete, which offers greater strength over fibreglass.
What are the Disadvantages of GRC?
Though it is more a disadvantage of the concrete itself, it nevertheless applies to glass fibre reinforced concrete, but there is no ability to deform under strain. This means that, should there ever be sufficient force on the material, it will not bend under pressure, it will simply break. This can be a problem in structural concrete.
It is also more expensive than regular concrete, making it less practical when the structural benefits are not essential to the job at hand. Further adding to this is the fact that it is not a particularly friendly substance to mix and use. It is difficult to mix, and can easily fall apart if not applied properly. If you are not experienced yourself, you will likely need to hire a professional.
How Long will Reinforced Concrete Last?
When reinforced concrete first came onto the scene, engineers hoped, somewhat optimistically, that it would last for as much as a thousand years. Over a century has passed since then, and we now know that the timeframe is a much more modest fifty to a hundred years. Of course, many factors will affect this timeframe, such as the kinds of stresses the concrete is under, and the type of environment it is exposed to, but fifty to a hundred years a good ballpark figure.
Concrete can sometimes get a bit of a bad reputation due to the fact that ancient buildings—particularly those built by the Romans—are still standing as much as a thousand years after the empire that built them fell apart (in the case of the West Roman Empire). But it is worth noting that, while the concrete the Roman’s made does seem to last longer than the modern variant we now use, it would have been wholly unsuitable for the kinds of structures we build today, such as skyscrapers.
Why is Reinforced Concrete Better than Regular Concrete?
Simply put, reinforced concrete has considerably more tensile strength than concrete, allowing it to withstand a greater array of forces than it otherwise would. This increased tensile strength significantly reduces the amount of concrete that is needed to create structures, which in turn brings the cost of building those structures down. It also allows for much grander structures. For example, the higher a building gets, the more weight there is on the foundations. By using less of that heavy concrete, it allows the building to reach more height for the same weight.
