HARD DUTY

While it’s an integral ingredient of the world’s built habitat, cement is also responsible for large amounts of carbon dioxide emissions. However, new technology is making it stronger – and easier on the environment

HARD DUTY

Researchers at Germany’s University of Applied Sciences Potsdam released a video last September, showing the cumulative volumes of carbon dioxide (CO2) since the mid- 1700s. Rather than using charts and graphs, they portrayed those greenhouse gas volumes as geographically specific 3D skyscrapers, soaring from the Earth’s surface into space.

The visualisation starts with a small white lump emerging out of London at the start of the Industrial Revolution (around 1760), with more dots following around Europe, then Asia and then the US where, in the early 1900s, CO2 emissions burst into the heavens around New York, Chicago and southern California. By the time we reach the present day, there are CO2-representative sky- scrapers looming across the world, with particularly high bars in the US, China and Europe, where CO2 emissions are currently the highest.

‘Our aim was to make the relationship between CO2 emissions and global warming comprehensible to the general public,’ the research team behind the video said in a statement. ‘Essential to our film is the concept of an emissions budget. At the 2015 UN Climate Conference in Paris, it was agreed to keep global warming to well below 2°C. In order to achieve this goal, we can only emit a limited amount of CO2 into the atmosphere. Ultimately, we have to reduce the CO2 emissions to zero.’

It’s an unusual – and eye-catching – way of representing global carbon emissions, yet the visual keys are also wholly appropriate, given that skyscrapers (that is, the homes we live in, the buildings we work in) are made using cement, which is a significant part of the CO2 problem.

In a blog post for the US-based sustainability research organisation the Rocky Mountain Institute (RMI), senior fellow Robert ‘Hutch’ Hutchinson writes: ‘Globally we produce over 4 billion metric tons of Portland cement per year – the key ingredient in concrete and (which is) responsible for the majority of its CO2 footprint – driving over 5% of total anthropomorphic CO2.’ Hutchinson cites RMI research that found that ‘to have a chance of significantly shrinking the industry footprint and meeting our Paris Agreement goals, revolutionary thinking and significant disruption is needed’.

Of course, finding a viable alternative to cement is no easy task – simply because the world needs and uses so much of the stuff. It’s the most flexible, cheap and universally used building material on the planet, Hutchinson points out. ‘The only thing we use more of globally is water.’

The problem there is that standard Portland cement cannot be made without releasing significant amounts of CO2. This is done either through burning fuel to produce the high kiln temperatures required, or through a calcining chemical reaction that occurs when the limestone is heated. Even at the most efficient cement plants, 60% or more of the CO2 released comes from this unavoidable chemical reaction.

Complicating matters even further, total Portland cement volume makes up about 20% of concrete by weight, with the other main ingredients being sand, water and aggregate. The global volume of Portland cement has, according to RMI’s estimates, more than tripled in the last 20 years, at an annual growth rate of nearly 6%. Much of that growth has been in China (as the Potsdam video shows) but other developing regions such as India, Turkey, Indonesia and large parts of Africa will soon take over as infrastructure projects increase. What’s more, although construction teams can partially substitute Portland cement with natural or waste materials (including limestone, rice hulls and certain kinds of fly ash), Portland cement is so carefully standardised that it seems all but impossible, for now, to find any specific substitute. The challenge then is not necessarily to replace cement, but rather to find ways of making it carbon-neutral or (to meet those Paris goals) carbon-negative.

US firm CarbonCure recently took a huge step towards that goal when it demonstrated the world’s first integrated CO2 capture and utilisation from cement for concrete production. The project saw the first successful collection of cement kiln CO2 for subsequent utilisation downstream in concrete production and construction. Building on that, CarbonCure teamed up with compressed industrial gases distributor Roberts Oxygen Company to supply that CO2 to the concrete industry in Pennsylvania, Delaware and New Jersey.

According to Scott van Pelt, VP of sales at Roberts Oxygen, CarbonCure Technology presents a fantastic new approach to CO2 utilisation. ‘The introduction of CO2 into concrete production chemically converts and permanently captures the CO2, which is positive for the environment.’ There’s also a strong environmental and business case for it: the Global CO2 Initiative estimates a potential $400 billion market opportunity for CO2 utilisation products in the concrete sector alone; while the Cement Sustainability Initiative – a global effort by 24 major cement producers, who produce 30% of the world’s cement – has calculated that carbon capture utilisation and storage technologies will be required to achieve 440 of the 790 megatons of annual CO2 reductions needed to meet the sector’s greenhouse gas targets.

Meanwhile, researchers at Purdue University in the US are moving into the testing phase of their studies into whether concrete can be made stronger by infusing it with microscopic-sized nanocrystals from wood. The research team has been working with cellulose nanocrystals, by-products generated by the paper, bio-energy, agriculture and pulp industries, to find the best mixture to strengthen concrete. Their test case will take them out of the lab and into the real world, building a bridge using that nanocrystal-infused concrete.

‘Simply getting out there where people can actually drive on it … is a huge step because you can’t just say it’s a lab curiosity at that point. It has real-world implications,’ says Jeffrey Youngblood, materials engineering professor.

The Purdue team’s idea is simple in principle: by creating stronger cement, construction teams can use thinner, lighter concrete while retaining the same durability and load-bearing properties as traditional cement. They can also use less of it – which will reduce costs and CO2 emissions.

Elsewhere, Australian engineering firm Fiber-con worked with researchers from Queensland’s James Cook University to develop a new method for replacing steel mesh used in concrete reinforcement with recycled plastic. ‘Plastic fibres in concrete have been around for 20 years,’ Fibercon CEO Mark Combe told the media. ‘What is new about our product is that it is 100% recycled. The intention is to do something to give back, to close the cycle of useless waste.’

On the other side of the world, in England, researchers at the University of Exeter published research into graphene-reinforced concrete, which meets British and European construction standards while offering greater strength, water-resistance and durability. The study showed that introducing graphene can reduce concrete’s CO2 emissions by about 50%. ‘This groundbreaking research is important as it can be applied to large-scale manufacturing and construction,’ writes lead study author Dimitar Dimov. ‘The industry has to be modernised by incorporating not only off-site manufacturing, but innovative new materials as well.’

Those solutions – and there are many more like them – look inside the product, at the composition of the concrete itself. Add something in here, take something out there, replace something else in another place… But what if the ‘revolutionary thinking’ and ‘significant disruption’ that Hutchinson wrote about came not only in how we make cement, but also how we use it on the building site?

For decades, the construction industry has been using the same approach: Portland cement is mixed with sand, water is added to produce a slurry, the slurry is poured into metal or wooden forms where it sets, and the forms are removed. It’s a slow, labour-intensive and expensive process.

‘We’ve actually made tremendous progress in recent years, coming up with new types of concrete with improved properties, but we are still stuck [with] working with forms, which account for most of the labour and the cost,’ Henri van Damme of the Massachusetts Institute of Technology-French National Centre for Scientific Research joint research said ahead of a meeting at Tennessee’s Vanderbilt University in 2015. During that meeting at Vanderbilt, researchers put forward the idea of replacing the existing Portland cement technology with 3D printing.

Two years later, in October 2017, a team from the Netherlands’ Eindhoven University of Technology used 3D-printing technology to build a small bicycle bridge.

The bridge itself is just 8m long and 3.5m wide, but the technology behind it suggests an exciting way forward for the cement industry. The bridge has about 800 3D-printed layers of reinforced, pre-stressed concrete – and, because of 3D printing’s precision technology, it used (and wasted) far less concrete than traditional construction methods.

The same Eindhoven team is now working on a series of five 3D-printed concrete houses. The first house, which will be ready for occupation in early 2019, will be a single-storey home; the other four will be multi-storey homes, with the fifth and final building slated to be printed and built entirely on site.

Could 3D printing – combined with better, stronger concrete – be the disruption the industry has been looking for? Suddenly, that Potsdam video starts to look like it may need a re-edit.

By Mark van Dijk
Images: Unsplash, Gallo/Getty Images

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