The CO2 Mammoth Beneath Our Feet

Save for a few moderate sceptics to keep us questioning – and a handful of unfortunate fringe entities that would benefit from sweeping it under the rug – the world is resolved to keep Earth habitable. CO2 emissions have been receiving the attention they deserve, and along the way we’ve had to ask some difficult questions.

Food, Energy, Transportation, and Deforestation are the usual suspects; both altering the atmosphere and inhibiting the planet’s natural balancing act.

The next area to be promoted from subject-specialist to the public list of concerns is Infrastructure. Most notable in that is the wonderful construction favourite: Concrete.

Cement alone contributes around 8% of the global CO2 emissions – significantly higher than aviation fuel (2.5%). It stands to reason that a large proportion of this comes from more recently developing countries; economically advanced countries have already been through this period of high infrastructure growth and emission.

There’s Just so Much of it

Concrete serves purposes that no other substance currently can. It’s affordable, convenient, safe to use, easy to transport, and durable. It can be used to create otherwise impossible dams and reservoirs, hold buildings firm, and even form the buildings themselves.

It’s no wonder that it has been so widespread for generations, and no surprise that concretes of different composition stretch far back throughout human history.

There is so much of it. All of the following issues are only really an obstacle because of the scale we’re talking about. And while the growth of concrete consumption has started to level out, we’re not showing any signs of making any less each year. Nor should we, really.

This is actually more of a blessing than it first seems. With one large and fundamentally universal material to improve, advances in Concrete are also affected by that scale. Every tiny change to a single bucket makes a huge difference to the world.

So how does CO2 come into this?

The process of creating and using Portland Cement Concrete is far more colourful than the end result.

The cement itself is the main source. Two primary ingredients are necessary: usually limestone and clay, with additive impurities. The first obvious cost is the cost of extraction: quarrying for those resources, and the equipment used to do it.

Next is the key area for improvement: processing those materials. Over 50% of cement emissions comes from a specific process: the production of ‘clinker’. Clinker is made in a high temperature kiln from clay and limestone, soon to be ground down and cut with something else, like gypsum, to create cement powder.

Aside from the emissions associated with firing the kiln itself, chemistry plays a much larger role.

Limestone is predominantly calcite: ‘Calcium Carbonate’ or CaCO3. During calcination in that kiln, carbon dioxide (CO2) is driven off, leaving calcium oxide (CaO) aka ‘lime’ in the clinker.

So to create cement by this process, huge amounts of CO2 is simply in the way of what it really needs: lime.

The industry needs – and is well underway in looking for – solutions. Replacing clinker, developing alternative cements, and capturing byproduct CO2 at the source alone would be enough to make a huge difference.

Cement continues to hide in plain sight publicly, but if it does not keep up with other CO2 emission advancements, it might not hide for very long.