The modern world is held together not by romantic notions of trust or community — although they help — but by thick gray goo.
Concrete is the second-most consumed material on the planet after water. Strong, cheap and resilient, it is made everywhere and used for pretty much everything. From hospitals and bridges to dams and pavements, if it is infrastructure, you will probably need concrete for it.
However, because the world uses about 30 billion tonnes of the stuff every year — a number that is expected to grow as large swathes of the Global South urbanize — it also accounts for a chunky percentage of humanity’s carbon footprint. About 8 percent of global emissions come from cement production — the binding agent within concrete is the source of most of its emissions — which is more than twice aviation’s contributions.
A pathway exists to reduce the climate impacts of this vital construction product, but there are plenty of trip hazards en route.
To understand how to reduce concrete emissions, we need a quick lesson on cement. Portland cement — the most common type, developed in the early 19th century — is made predominantly of a substance called clinker. Limestone and clay are ground up and fed into a very long rotating kiln heated to about 1,450°C. Clinker emerges on the other side. These marble-sized balls are crushed and mixed with additives like gypsum to create the cement. Adding water and aggregates such as sand and stones gives you concrete. Together, the chemical reaction inside the kiln and the fuel used for heat produces the bulk of the carbon pollution.
So how can we decarbonize something so ubiquitous?
The Global Cement and Concrete Association, an industry group representing 80 percent of global cement volume outside of China, has published a road map to net zero emissions by 2050. A bunch of levers need to be pulled, such as carbon capture and storage, more efficient usage, decarbonization of electricity and new fuels for clinker production.
The most accessible method so far has been substituting some of the clinker in the concrete mix for other materials, namely fly ash and ground-granulated blast-furnace slag, which are waste products from coal-fired power plants and steelmaking. Being able to swap a fraction of the carbon-intensive clinker for a cheaper waste product has been a boon environmentally and economically.
You might rightly notice a problem, though. The UK just shut down its last coal-fired power plant, while the country’s blast furnaces are being replaced by electric arc furnaces. If we are to limit the global temperature rise to less than 2°C, then the rest of the world will need to follow — meaning the green transition will eventually make these materials scarce.
The association anticipated this decline in its road map. For now, there is enough ash stockpiled to keep the industry going for some time, Claude Lorea, innovation and environmental, social and governance director at the Global Cement and Concrete Association, tells me, but there is a new clinker substitute in town that is becoming very fashionable: Calcined clay.
It is made by heating kaolin clay, or kaolinite, to about 700°C. When combined with raw limestone and clinker, it can create a strong cement, which the industry is calling LC3, with up to 40 percent lower carbon emissions.
Investment into scaling up is already being made: Heidelberg Materials AG is building a plant to produce calcined clays in Ghana while also assessing the suitability of other locations.
Cost is the obvious challenge. Unlike industrial byproducts, the clay needs processing with heat. If it is coupled with carbon capture for the remaining clinker, it is sure to be pricier. The association is keen to establish a carbon price, which ought to help boost the competitiveness of products like LC3.
Then there are the apparent logistical challenges in increasing the production of a new variety of cement. We only generated an estimated 45 million tonnes of kaolinite in 2021. If all cement made today used this clay, then we would need to extract 1.6 billion tonnes a year.
Yet it is red tape that might hold LC3 back from widespread adoption — or at least slow down its rollout.
Understandably, there are tight regulations around the resources used in infrastructure. When a material is holding up bridges and skyscrapers, safety is paramount.
As writer and climate strategist Michael Barnard points out, there are roughly 22,000 municipalities and counties in the US alone, of which as many as 15,000 are estimated to have their own building codes or significant modifications to templates. The thought of getting all of those updated to accept a new low-carbon material gives me a headache.
Around the world, many building codes are prescriptive, meaning they list acceptable raw ingredients and recipes. LC3 has been shown to be 10 percent stronger at 90 days compared with conventional cement, so the problem is more bureaucratic than anything else. Switching regulations to performance-based specifications would enable the faster and more flexible adoption of new technologies without sacrificing safety.
After all, LC3 is not the only new type of cement hitting the market. Other innovative solutions are springing up to solve the concrete problem. Some are experimenting with a basalt-based product, while others are looking at recycling methods or finding ways to replace clinker altogether.
Building codes should be updated now to be flexible enough to apply to a range of existing and emerging products. If they meet certain performance thresholds, they should be allowed. It might be migraine inducing, but it will ensure we do not waste time wading through red tape later.
Lara Williams is a Bloomberg Opinion columnist covering climate change. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
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