Silver Bullets, Grey Cement and Green Futures
07 February 2023
When we think about what causes climate change, immediately visions of billowing smoke from power stations fill our minds. When we think about how to combat that, we turn our thoughts to solar panels and wind turbines. We’ve grown – and for good reason – to associate climate change with energy production. Energy production and associated fossil fuel use are without doubt the major contributing factors to our climate decline. This impact hasn’t gone unnoticed however, with multiple non-emitting means of energy production available to us, should we choose to use them. The choice of using them is a challenge entirely on its own, however on a systems level we have solved the power generation problem. That’s a wonderful thing, but there’s harder challenges ahead.
What isn’t given as much consideration is what we do about the carbon dioxide we have to produce. Let me turn your attention to cement, the most utilised material on earth after water. Cement and concrete are ubiquitous with construction, with almost every development making use of it in some fashion. It’s easy to produce, simple to use, mouldable to almost any form and – crucially – cheap. It cannot be understated that the mass uptake of cement revolutionised the way we construct. We can now build faster, cheaper, and more creatively than ever possible without it. For those outside of the construction sphere, this concept is often missed. In terms of impact on humanity, concrete stands shoulder-to-shoulder with agriculture, germ theory, and the internet. However, while cement has elevated the human condition, its production is wreaking havoc on our world and there’s no real alternative like we have in power generation.
Just how polluting is cement? Very. Roughly 5-8% of the worlds CO2 output comes from the manufacture of cement – or about enough to rank it the 3rd biggest producer of CO2 if it were a country. It gets worse: using less isn’t an option. Increasing global urbanisation and economic growth have pushed our demand for concrete to historic levels. Furthermore, our green ambitions for the future will need new infrastructure – and lots of it. Every hydroelectric dam for green energy, every cobalt mine for electric car batteries, all of it, present increase demand for cement.
Cement Production Crash Course: Cement is produced in a 4-stage process. One of these stages involves heating up the ingredients in a kiln to 1400 C. The process of heating up the kiln is very energy intensive and normally comes from natural gas. Once the kiln is heated, a chemical reaction (calcination) takes place that breaks down calcium carbonate into calcium oxide (the cement you want) and CO2 (the gas you don’t want).
So, what do we do? One solution is to heat the kilns using renewable sources of energy, and yes, that's effective in reducing some of cements carbon impact. However, only around 30% of the CO2 from cement production comes from the heating of the kiln, with the rest coming from the chemical reaction taking place, and clean-cut solutions to this are harder to find. That’s not to say that there aren’t solutions. Materials science has produced cement alternatives that require less energy to process, as well as alternatives such as AshCrete – which uses recycled industrial waste in place of a portion of the required cement. There’s certainly a great deal of promise, however the technology isn’t adoptable at scale currently; concrete alternatives are currently only able to meet a small amount of our total concrete demand and generally tied to the production of another material which presents economic and logistical challenges.
In my view, a more suitable solution can be found in carbon capture technology. Carbon capture is an umbrella term that refers to technologies that trap carbon released at certain stages of industrial processes, preventing them being released into the atmosphere. Under most circumstances, it’s likely a poor application of our energy. This approach focuses on treating the symptom rather than the disease, and in a world that craves the status quo, is precisely what we need to move away from.
However, for some very specific situations, like the world of cement production, some carbon capture technologies make a great deal of sense. Of the carbon capture technologies, there are many viable solutions, with calcium looping and direct capture showing great promise. What I’d like to focus on however, is amine scrubbing. Amine scrubbing, sees the gas produced during heating pushed through organic compounds called amines. This binds the carbon to the amines allowing the resultant amine-carbon mixture to be taken away from the site and disposed of underground or used in industry rather than pumped into the atmosphere. It’s a technology that is well understood and proven to work in other industries, with commercial viability due to its ease of implementation – often simply requiring an addition to the existing production plant rather than a redesign. The importance of ease of implementation really can’t be stressed enough here. A significant amount (circa 40%) of the operating costs for cement production are fixed (don’t fall when you make less cement), meaning any disruption to the production process has dire financial ramifications, highlighting the importance of a solution that is easy to integrate.
As much as we would love a silver bullet solution, it doesn’t exist. Not carbon capture, not alternative substrates, not one of them can solve this issue. This is because the problem of cement is multifactorial, it demands multiple solutions at every step of the process. Moving to use of alternative substrates, more advanced processing of those substrates, as well as carbon capture technology, it’s all necessary to solve this puzzle. It’s harder solving problems this way. It requires a lot more thought and a lot more moving parts, and often your reward for finding that solution isn’t revolutionary carbon neutral cement that sees Nobel Prizes awarded and powerful hands shook. Instead, it’s 7.5% less polluting cement here, coupled with 10% more energy efficient production there, and so on until you have the makings of a new method. It’s not easy but it works, and we need what works.
In closing, there’s an important allegory to be found in the dusty world of cement. We often get lost in the idea of a green future populated by ethereal beings who live in a world free of hardship and worry. However, I find this thinking harmful. By crafting illusions of a perfect future, we distract ourselves from the imperfect present, and in so doing we make ourselves blind to solutions. We cannot wait for scientific breakthroughs to give us, get out of jail free cards. Instead, we must be implementing the best options we have right now and working to find better ones every day. One small improvement at a time.