Specific limitations
Over the past few decades, concrete has become the main material in construction, especially in densely populated urban environments. Thanks to its low cost, ease of use and scalability, concrete has gradually replaced bricks, stone and wood.
But it is not without problems.
Sustainability
First and foremost, it is far from a sustainable product in terms of resource consumption. It consumes so much sand that some people describe the world as ‘running out of sand’.
The production of cement is also an energy-intensive activity. Cement production is almost entirely powered by fossil fuels, resulting in cement production accounting for 8% of global carbon dioxide emissions.
This is comparable to the CO2 emissions of cars and lorries, which account for 10% of global emissions. Making concrete more sustainable would therefore have an impact comparable to turning all the world’s cars into electric vehicles and powering them with green energy alone.
Durability
If concrete buildings last for hundreds of years, we could at least assume that the sand consumption and CO2 emissions would be a one-off affair, and that the buildings would remain standing long after that.
But this is not the case. Today, reinforced concrete buildings make up the vast majority of the total building stock, with an average lifespan of only 50–100 years. Then they have to be completely destroyed, the rubble removed and buried somewhere, and the whole thing started again from scratch.
New concrete technology
Such high environmental costs and lack of durability mean that concrete needs to be improved. In theory, of course, we could simply go back to using stone, clay and wood as the basic building materials. However, the practicality and low cost of concrete make it hard to replace as the material of choice for architects.
Removing the steel
The culprit for the low durability of modern concrete is the steel reinforcement (rebar) inserted into it. The steel reinforcement provides an important structural advantage by fundamentally increasing the tensile strength (the ability to resist stretching or pulling) of the concrete.
The problem is that steel (which is mainly made of iron) will eventually rust. When it does, the steel expands, causing the surrounding concrete to crack. This is commonly known as concrete cancer, and it is the reason for the limited lifespan of reinforced concrete.
Graphene concrete
As we invent new materials, new solutions can be applied to concrete. By adding graphene, a special two-dimensional material, to concrete, Virginia University researchers have managed to improve the properties of concrete while making it more durable and reducing carbon emissions.
The paper, published in the Journal of Construction Engineering, is entitled ‘Rheological, mechanical, and environmental properties of printable graphene-reinforced cementitious composites with limestone and calcined clay.’
They focused on concrete used in 3D printing methods, and we were featured in ‘In North America, home ownership is more out of reach than ever – could 3D printing change that?’.
Graphene-reinforced LC2 concrete can reduce greenhouse gas emissions by around 31% compared to conventional printable concrete mixtures. This is because they don’t use steel (which itself produces significant carbon emissions during production), but rather graphene, which is made from pure carbon. So, at least in the reinforced part, this new concrete can capture carbon rather than emit it.
Although the cement part is also a carbon-intensive process, this is a good start.
And because graphene is more stable and does not oxidise (rust), this concrete should not cause concrete cancer. If the buildings that are eventually built last longer, then in the long term, emissions will be greatly reduced.