Can the Concrete Industry Really Go Carbon Neutral by 2050?

That's what the Global Cement and Concrete Association is promising, and it's a stretch.

A concrete bridge

 Getty Images

The problems with cement start with chemistry, and the formula CaCO3 + heat > CaO + CO2; you cook calcium carbonate at 1,450°C with lots of fossil fuel and you get clinker and lots of carbon dioxide. You then mix that with aggregate and water and you get concrete, the making of which is responsible for 8% of the greenhouse gases generated worldwide. This is why I tend to promote wood construction and bikes over concrete towers and big concrete highways; chemistry is tough.

That's why this pledge from the Global Cement and Concrete Association is so remarkable.

"Our Climate Ambition is our member companies’ commitment to drive down the CO2 footprint of their operations and products, and aspire to deliver society with carbon neutral concrete by 2050. We will work across the built environment value chain to deliver this aspiration in a circular economy, whole life context."

They have a concrete plan too, with an almost plausible strategy. Their document starts off on the wrong foot by claiming that "concrete is the world’s leading sustainable building material" but it gets better.

A concrete plan
A concrete plan. GCCA

You have to get through the PR fluff overselling the wonders of concrete:

"Concrete buildings and infrastructure can be transformative, helping to lift communities out of poverty through the building of safe schools, hospitals and homes, eliminating dirt floors, providing clean water and effective sanitation. These are critical elements."

They never once mention the sand and aggregate crisis, where so many of those homes and buildings are building built with materials that are illegally dredged. As Neil Tweedie asked in the Guardian:

 "Why buy expensive sand, sourced from licensed mines, when you can anchor your dredger in some remote estuary, blast the sand out of the riverbed with a water jet and suck it up? Or steal a beach? Or dismantle an entire island? Or whole groups of islands? This is what the “sand mafias” do. Criminal enterprises, their illegal mining operations in Asia, Africa and elsewhere, are protected by officials and police paid to look the other way – and powerful customers in the construction industry who prefer not to ask too many questions."

But back to the positive. They note that carbon neutrality can be achieved by cleaning up the fuel sources used to cook the limestone, including electric kilns. As for the 60% of the CO2 emissions that come from the chemistry, they remind us that it can be reabsorbed.


Roof of the Unite d'Habitation
I like concrete, I really do! Especially when it's old and recarbonated.  Lloyd Alter/ Marseille 2019
"Evidence shows that across the inventory of all concrete, an average of up to 25% of the process emissions emitted during cement manufacture is reabsorbed by concrete during its lifetime. This process can be enhanced through further application of best practice, with specific applications already achieving 100%." 

In the appendices they go into greater detail, and include demolition, which is not exactly great marketing:

"Another significant portion of concrete carbon uptake occurs when reinforced concrete structures are demolished, as the increased surface area and exposure to air accelerates the process. The amount of carbon uptake is even greater when stockpiles of crushed concrete are left exposed to the air before reuse." 

The other major problem with recarbonation is that it takes years, especially if you are including the demolition of the building in your analysis. 60% of the emissions come in one big burp at the beginning and then it takes the life (and death) of the building to re-absorb it? That sounds like wishful thinking.

Less Clinker Into Cement, Less Cement Into Concrete

The industry has had real success here, using fly ash, slag, recycled concrete fines and other materials that reduce the need for portland cement. "Manufacturing will be controlled digitally through data analysis and artificial intelligence, thus reaching higher product consistency and quality in applications."

CO2 Capture

Of course, they end up here, noting that "CO2 capture is still expensive today, but technology is improving and the significant number of demonstration facilities, currently being deployed in cement production, demonstrates the potential for significant cost reduction in the years ahead. "

Again, we are talking about 8% of the world's CO2 emissions coming from the manufacture of cement, and 60% of the CO2 presently coming from the chemistry, so that now represents 4.8% of emissions. That is a lot of CO2 to suck up. We have shown technologies like CarbonCure that can reabsorb some of the CO2, but many of the others out there are fantasies.

Celebrating Mass

SANAA's Zollverein School of Management and Design.
No insulation, solid concrete, geothermal heating in walls. credit: Lloyd Alter/ SANAA's Zollverein School of Management and Design

Finally, they go off the deep end by suggesting that concrete can make better buildings by contributing thermal mass.

"Zero-energy buildings will also be possible thanks to concrete. Concrete has the ability to absorb and later release thermal energy, due to its density and heat capacity. This property, known as thermal mass, makes concrete buildings more energy efficient: excess heat in summer is absorbed by the concrete during the day, and released with overnight ventilation, leading to less reliance on air conditioning. In winter, solar gains can be better taken advantage of thanks to concrete’s capacity to absorb heat, reducing heating needs. The thermal mass effect can be enhanced through the use of thermally activated building elements, i.e. heating or cooling delivered to a building through pipes embedded in the concrete elements." 

This is the "mass and glass" approach going back to the seventies, and outside of a few parts of the world with huge swings between day and night, has been pretty much discounted as not nearly as effective as good insulation, and will never get you to zero energy.

A Concrete Bridge Too Far?

In the end, the biggest problem with using concrete to lift people out of poverty and build houses without dirt floors, not to mention schools and hospitals, is that all of these ideas are really expensive. In many countries, you can't get the builders to even use legit sand, let alone cement made with clean electricity and then using carbon capture and storage.

In the video, you see people in the industry from all over the world, from China to India to South America, parts of the world where the vast majority of the concrete is being poured. China alone uses more concrete in three years than the USA does in a hundred. I am not sure that everyone in the industry is going to be willing to pay the price.

The Global Cement and Concrete Association has produced a grand plan and an ambitious commitment for going carbon neutral by 2050. The GCCA President says "there is a significant challenge involved in doing so," which is an understatement if I ever heard one.

In the end, I can't help thinking that it is a concrete bridge too far, that it's a grand plan for a distant future but that we have a serious problem right now, and I end up back where I started, promoting wood construction and bikes over concrete towers and big concrete highways. But I suppose I am not very realistic either.