Concrete base

Anthony King

The first graphene-enhanced concrete slab has been laid down in a UK commercial setting in a joint venture by Nationwide Engineering and the University of Manchester. Adding graphene strengthened the concrete by around 30%, according to construction firm Nationwide Engineering in Amesbury, UK, which put down the slab in summer 2021.

The graphene-enhanced Concretene meant 30% less material was used without any steel reinforcement, which Nationwide Engineering estimates will save 10-20% on costs for customers. Concrete manufacture generates around 8% of global CO₂ emissions, so reducing the amount used can reduce emissions substantially. Importantly, the new concrete could be laid down as usual.

Only small quantities of graphene, which is made of a single layer of carbon atoms, need to be added to concrete to boost its strength. ‘Many of the improvements we see are due to its small size and geometry’ says Paul Lambert, visiting professor at the Centre for Infrastructure Management at Sheffield Hallam University, UK. Portland cement concrete is a complex mix of sand, cement, stone and special additives.

Liquid concrete sets into its solid form through chemical reactions termed hydration and gelation, where the water and cement react to form a paste that hardens over time. The added graphene modifies the nature of hydration as the cement sets.

Once water is added, it starts to produce a mesh of interlinking fibres of calcium silicate hydrates. ‘Anything that can be done to improve this crystal growth and its interlinking is of interest,’ says Lambert. ‘Graphene because of its size, and possibly aided by its geometry, encourages more effective crystal growth and a denser matrix.’ Typically, there will be pockets of strength and weakness in this mesh, but graphene can also make this mesh less patchy and more uniform.

Civil engineering is one of the most conservative disciplines and wary about changes, for good reason. If you get it wrong, people may die. It’s very carefully regulated.
Paul Lambert Centre for Infrastructure Management, Sheffield Hallam University, UK

A denser structure boosts strength and makes it less permeable to water, which can bring in chlorides, for example, that can initiate corrosion of steel if present for reinforcement. Graphene also seems to offer some micro-enforcement to the system, which appears to influence not just strength but also improved flexural performance, adds Lambert.

The initial use of Concretene was for a floor slab in a new gym owned and run by military veterans in Amesbury, Wiltshire. However, the adoption by industry of graphene in concrete is likely to be slow and cautious. ‘Civil engineering is one of the most conservative disciplines and wary about changes, for good reason,’ says Lambert. ‘If you get it wrong, people may die. It’s very carefully regulated.’

This view is shared by others. ‘There’s a reluctance to take on any new innovative products in construction,’ says Gareth Whittleston, lecturer in civil engineering at the University of Salford, UK. Nonetheless, UK science and industry is ‘ahead of the curve’ in the use of graphene in concrete, he says, adding that a lot of companies and universities are trying to protect their IP and their products. ‘There’s a barrier to information, especially in the UK,’ says Whittelston.

A big announcement for graphene in concrete was that graphene-reinforced 3D printed concrete will be used for the HS2 high-speed railway in the UK. The project is expected to use 19.7m t of concrete, generating around 5m t of CO₂. Network Rail has promised to reduce CO₂ emissions by 11% over the next four years, and graphene can help it get to this destination.

‘It has been said that if concrete was a country, it would be the third worst polluter,’ Lambert notes. ‘What they tend to ignore is that reinforced concrete is the most widely used material in the world.’ The aim with graphene is to strengthen it, so that less concrete can be used for the same purpose. ‘It is not there to solve an immediate problem, but it can help achieve zero carbon footprint emissions in structures in the longer term,’ Lambert says. Less than 1% of graphene is added.

The usual way to strengthen concrete is to reinforce it with steel, which has the upside of giving it ductility – this means it is somewhat predictable in overload conditions, as it will yield before breaking. ‘Ultra-high performance concrete gives strengths around 150MPa, whereas most ordinary concrete you walk on or lean against is probably 30-40MPa,’ says Lambert.

One issue with steel inside concrete is that it can tend to corrode. Lambert says graphene, although chemically inert, can be conducting and therefore it could aggravate corrosion. ‘It wouldn’t cause corrosion,’ notes Lambert. ‘I’m not trying to cause scare mongering. It’s just something that needs to be looked at.’

The initial reported uses of graphene in the UK are without steel. ‘We use steel reinforcing bars to improve flexural and tensile strength of concrete, and graphene improves those properties,’ says Whittleston. Another way to strengthen concrete is to add carbon steel fibres.

Lambert suggests that it may take decades before graphene is widely used as an additive to concrete. ‘Partly because of the desire to see a track record for any new material and partly because of the need to ramp up production,’ he explains. He sees parallels in the slow take-up of stainless steel for reinforcement of concrete, an excellent material that is under-used, often for practical supply constraints. ‘You can get reinforcements in small quantities, at high cost, and in a limited range of sizes,’ Lambert says.

The use of graphene in concrete in large infrastructure projects, such as the HS2 railway line, may scrunch up the timeline for concrete with graphene, admits Lambert. In September 2021, it was reported that graphene would be used to improve new asphalt that would be laid along a stretch of Northumberland motorway in the north of England. National Highways said that it hopes adding graphene into the surfacing mix will make the asphalt stronger and less likely to be affected by sunlight, meaning fewer road repairs. Nationwide says its graphene concrete will be used in London tunnels, with proof-of-concept trials due in Spring 2022.

Such announcements push Whittleston towards an optimistic view on the future for graphene concrete. A lot of countries are producing graphene now, he says, and ‘supply to demand shouldn’t be an issue’.

Image credit: Hybrid Images/Science Photo Library