Terrance Barkan, Founder and Executive Director of The Graphene Council, highlights the benefits of using graphene in cement and concrete mixes...
Global Cement (GC): What is graphene?
Terrance Barkan (TB): Graphene is the first 2D material to be isolated by humans. It was first produced at the University of Manchester in the UK by Professor Andre Geim and Professor Kostya Novoselov, in 2004. They received the Nobel Prize in Physics for isolating it in 2010.
Chemically-speaking, graphene is a single atomic layer of sp2 bonded carbon atoms in a lattice formation. It is 0.33nm thick. Graphene particles are usually sub-micron in length and breadth, but it is now even possible to produce it in sheets, like wallpaper.
GC: What are its properties?
TB: Due to the fact that graphene is so thin, its properties are no longer governed just by traditional physics. Instead, they are governed by quantum effects, which dominate at small dimensions. This means that the electron mobility is very high across the lattice, leading to near super-conductor resistance at room temperature and incredible thermal conductivity.
Graphene is also famously strong, again due to the sp2 carbon-to-carbon bonds. It is a crystal that has a 20% bending radius. This means we get strength with flexibility, rather than strength with brittleness. In cement mixtures, it can provide tensile and compressive strength at the same time.
GC: How is graphene produced?
TB: There are two main approaches: Chemical vapour deposition (CVD) is used to produce single layer graphene. This uses a carbon-bearing gas in a temperature and pressure-controlled chamber. It is infused to a metal surface, typically nickel or copper, to form a single layer lattice. This can be liberated from the substrate in a number of ways. CVD graphene is 97.2% transparent and is sold by the cm2. It is a cutting-edge material used for quantum electronics and solar panels, novel sensors and so on. A single gram of it could cover 2300m2, around half a soccer field. It’s a truly incredible material!
The other way to make graphene is to take graphite and exfoliate it down to 2 - 10 layers of crystal. Such particles are called nano-platelets and are also known as ‘bulk graphene.’ These are in the nanometer height range, with a high aspect ratio and generally appear as a black powder. This is the type of graphene that can be used in cement and concrete mixtures.
Layers | Description |
1 | CVD, Mono-layer or ‘Pristine’ Graphene |
1 - 3 | Very Few Layer Graphene (vFLG) |
2 - 5 | Few Layer Graphene (FLG) |
2 - 10 | Multi-Layer Graphene (MLG) |
>10 | Exfoliated graphite / Graphene Nanoplatelets (GNP) |
Above - Table 1: There are various types of graphene, defined by the number of layers.
GC: What are the effects when graphene is added to cement and concrete mixtures?
TB: Firstly, it acts as a nucleating agent, a bud for crystalisation. This leads to a faster cure and unleashes the existing strength within the cement, an effect that can be seen with other additives.
More interestingly, however, it imparts its excellent strength characteristics to the bulk material. This improves not only the compressive and flexural strength, but reduces the number of micro-cracks and reduces water penetration. Graphene has excellent barrier properties. Indeed, it is the most water-impermiable material ever discovered.
GC: How much graphene is required to have an effect?
TB: You do not need a lot of graphene to have a big effect on a cement or concrete mixture. On the convervative side, a 33g/t dose of graphene in a cement mixture leads to a 15 - 20% increase in compressive and flexural strength compared to the same material without graphene. Some claim 30 - 35% improvements and some, under perfect laboratory conditions, claim even greater improvements.
By doing so you can either achieve higher strength with the same amount of concrete (and cement and clinker). Alternatively, you can reduce the amount of concrete while retaining the same strength. In a high-rise building this would result in thinner columns and more space to sell.
If you have less cement in a building, you also have lower CO2 emissions. If you can improve perfomance by 25%, you can reduce the amount of cement by around 15%, which in turn lowers CO2 emissions by 15%. You would be very hard pressed to get these kinds of improvements with a low dose of a traditional supplementary cementitious material (SCM).
GC: What happens if you increase the dose?
TB: Adding more graphene is actually counterproductive. This is because it has a tendency to agglomerate back into larger particles with more and more layers due to physical interactions known as Van der Waal forces. This reduces the quantum effects and thus the benefits quite significantly.
GC: Are there any disadvantages of adding graphene to cement and concrete?
TB: As graphene is pure carbon, which is chemically inert in the cement mix, it does not affect other additives and other additives do not affect it. Under some conditions there may be a loss of workability. This is due to the high aspect ratio.
GC: The world has been tripped up before by ‘wonder materials’ with low aspect ratios, i.e.: asbestos. Is graphene safe to put in cement?
TB: All toxicological studies to date have confirmed that graphene is benign to humans. The morphology is different to asbestos in that asbestos is thin like a needle, whereas graphene is flat like a sheet. In fact, graphene is being looked at as a drug delivery vehicle and other healthcare-related applications inside the body.
GC: What are the cost implications of using 33g/t of graphene in a cement mixture?
TB: Many still have the perception that graphene is extremely expensive, but it has come a very long way in the past 15 years. For bulk graphene we are talking prices down to as low as US$50/kg, which is comparable to, or indeed lower than, other additives on the market. In an admixture, it adds around US$1/t to the final concrete material.
GC: Will prices for bulk graphene, continue to fall as production is scaled up?
TB: The production of bulk graphene will be scaled up in the future, but there is not much room for further reduction in price. This is because the raw material graphite costs US$1200 - 1500/t and you then have to factor in energy and costs to reduce it to the nano-scale. This is not an easy process and it is hard to maintain consistency and quality between batches. This is a skill-set that takes considerable expertise and investment to attain.
GC: How large can a batch of graphene be?
TB: It is hard to say, as each manufacturer uses a slightly different route. However, The Graphene Council has members that produce 1t/yr to 10t/yr or more. Once they have perfected their route, producers are able to scale up production quite quickly, simply by duplicating their production lines. It is not capital-intensive in terms of equipment once you have the in-house knowledge of how to produce the material.
GC: How widespread is the use of graphene in cement and concrete at present?
TB: At present this application represents cutting edge research and there is nobody using graphene commercially in cement yet. However, there have been some very interesting trials, including a German energy company that used the heat conduction properties of graphene-enriched concrete to dissipate heat from underground cables. It’s not just strength that users could benefit from.
One of the areas that will likely be among the first to benefit from graphene is the pre-cast concrete sector. This sector has close control over its mix. If you can cure faster, you can increase the throughput, while using less material per part. Lower weight benefits the handler and gives rise to lower CO2, and don’t forget the lower susceptibility to cracking.
The other applicable area is 3D printing, where a rapid cure is also very welcome. Graphene could offer thinner walls, less material and low water permeability for coastal or underwater applications. You can even tune graphene-containing materials to make them into sensors.
GC: What is the single largest barrier to the use of graphene in cement and concrete?
TB: I think the biggest barrier is a lack of awareness among users that the material is available and ready to go. There are tens of thousands of research papers, the benefits are clear, the cost is competitive, but the sector has been lacking in terms of drawing in attention from potential users. A lot of perceptions are out of date. The Graphene Council wants to change that, including via platforms such as Global Cement Magazine!
When a sector grabs hold of graphene, the benefits are clear. For example, the rubber sector now uses graphene to enhance a wide range of products. Traditionally, a tyre would have more grip if you make it softer. The trade-off is that you lose longevity because it wears rapidly. A harder compound will last longer but won’t be as grippy. Graphene, due to its compressive and flexural strength advantages, now allows better performance for tyres of all kinds. It is now a standard ingredient and the whole sector has raised its game.
It would be great to help the much larger cement and concrete sector realise a similar step change in performance. The easiest way to start would be through admixtures and water dispersion. To get it into the cement itself would require a fairly high level of involvement from the cement producers themeselves, and I encourage them to approach The Graphene Council, wherever they are in the world. Any producer that did this first would instantly produce a cement at a higher level across its entire product range. This is a big prize and one that should not be lost to admixture producers or concrete producers.
GC: How much graphene would the cement and concrete use, if it used it on a widespread basis?
TB: The Global Concrete Report 2018 shows that the top 25 companies produced 387.9Mm3, which is equivalent to 969.7Mt of concrete. This represents approximately 339.4Mt of cement. At a load factor of 0.02% graphene, this would translate through to 67,883t/yr of graphene.
GC: Could sourcing sufficient graphene be a barrier in itself?
TB: There are many graphene producers able to step up to the challenge of greater demand, so I don’t think that this will be a problem. Of course, the Graphene Council is ready and able to put them in contact with new markets as they arise.
GC: How long do you think it will be before graphene use really takes off in the cement sector?
TB: There will be some demonstration structures built over the next 12 months that should provide real-world examples of how graphene can help the sector. I think that, within five years, we should see a step change where the most innovative cement and concrete producers will be very much on board with graphene. They will make it hard for the wider industry to ignore this fantastic material.
GC: Thank you for your time today!
TB: Thank you for the opportunity.