Nine footprints

“If the cement industry were a country, it would be the third largest emitter in the world– behind China and the US.”

Motivated by breathing ash-filled air over recent summers and other ecological horrors, I’ve been taking steps to educate myself on the impact we as a species, and I, specifically, have on our endangered earthly climate.

Starting with the climate impact of concrete, the age-old, humble and assertive material I’ve come to appreciate. Learning techniques from the ancients has helped me adapt it to my art practice.

Here's a little fact soup I've dredged up in recent years, starting with a few definitions:

• If you’re not hiding from the news in your broom closet, you’ve come across the term “carbon footprint.” And you know it basically means how much carbon, usually measured in tons, is being emitted by a given activity or machine. A complementary idea is “ecological footprint,” which measures how much capacity we need from nature to sustain our needs. In other words, how much land area and carbon-exchanging flora we need to neutralize those emissions.

• Also, I'm compelled to clear up one muddle: concrete is not cement. In case you’re interested: o Concrete consists of a filler and a binder, which is a paste of cement and water. o Cement is made by burning limestone and clay together at around 1,500 degrees Celsius, then grinding it to powder. o Water, when mixed with cement, causes the hydration process, a chemical reaction in which the compounds in cement form chemical bonds that bind the aggregate and harden the concrete. o Aggregates are the filler, sand and gravel in construction, held together by the cement paste. They add strength and stability and help prevent cracking. In my art practice, I use cotton fabric as the aggregate because cotton fibers, being hollow, are absorbent, and the fiber’s surface is rough nanocrystals, microscopic clusters of atoms.

I read the 2018 report[1] by Chatham House, a British think tank, that compared the cement industry to a country. As the key component of concrete, it's the most widely used construction material in the world. Each year, more than 4 billion tons of cement are produced, accounting for about 8% of global CO₂ emissions, behind only China at 29%, and the US at 14%.

• For perspective, when considering CO₂ emissions per person: China's levels are less than half those of the United States.

• If it’s hard to envision that scale, consider that three tons of CO2 are sent into the atmosphere for every person on earth, every year. That’s right, all 7.8 billion of us, and counting.

A couple of other relevant facts from the report:

• Concrete is expected to play a vital role in the expansion of the built environment, especially in emerging economies. On a ‘business as usual’ trajectory, global cement production is set to increase to over 5 billion tons each year over the next thirty years. And that’s just for buildings; it doesn’t include the use of concrete in infrastructure projects.[2]

• To bring the cement sector in line with the Paris Agreement on climate change, its annual emissions will need to fall by at least 16% by 2030—that’s if assumptions about the contribution from carbon capture and storage (CCS) technologies don’t prove to be too optimistic.

• To bring the cement sector in line with the Paris Agreement on climate change, its annual emissions will need to fall by at least 16% by 2030—that’s if assumptions about the contribution from carbon capture and storage (CCS) technologies don’t prove to be too optimistic.[4]

So, I promised footprints!

Why recite the problematic stats if you're not going to cite some solutions? The following facts relate to buildings, which humans have constructed since our species first discovered the benefits of shelter. Together, we face the challenge now of decoupling economic growth from carbon emissions. Innovation in sustainable building materials will have to be an essential contributor to this.

Here are nine common building materials, ranked from lowest to highest in their carbon footprints.

1. Rammed earth: 48kg embodied carbon per m³ (cubic meter)

Ranking the lowest in carbon footprint, averaging 48kg embodied carbon[5] per cubic meter, is an ancient technique that uses natural raw materials such as earth, chalk, lime, and sometimes gravel (and, historically, some even used animal blood as a stabilizer). With its sustainability and its unique aesthetic, rammed earth has made a comeback in modern buildings.

2. Softwood timber: 110kg embodied carbon per m³

Softwood timber, often used in residential buildings, comes from gymnosperm trees, conifers, while hardwood is from angiosperm trees like oaks and maples (though in both groups there’s a wide variation in actual wood hardness). Because softwood t on average 110kg embodied carbon per m³, it’s an especially responsible choice.

3. Cross laminated timber: 219kg embodied carbon per m³

It’s made by stacking several layers of dried lumber, laying the grain in opposing directions, then bonded with adhesives to produce a rectangular panel. Averaging about 219kg embodied carbon per m³ in emissions, CLT is commonly used in large scale buildings. It’s lightweight, very strong and easy to install. It also has effective acoustic, fire, seismic and thermal properties.

4. Stone: 237kg embodied carbon per m³.

The pyramids of Egypt. The Megalithic Temples of Malta. The Great Stupa at Sanchi in India. The Great Wall of China. One of the oldest building materials on earth, stone requires basically no manufacturing as it is building-ready in its raw state. Stone emits about 237kg embodied carbon per m³.

5. Clay brick: 345kg embodied carbon per m³

Another ancient building material, clay brick is very easy to produce: just mix clay and water. It’s also strong, non-combustible and durable in any weather. Like stone, many clay brick structures built centuries ago still stand. It averages 345kg embodied carbon per m³.

6. Reinforced concrete: 635kg embodied carbon per m³

Half of all the world’s buildings are made from concrete because it’s the ideal construction material: it’s strong and cheap. It’s also resistant to fire and pests like termites and rot. By itself, it has low tensile strength (resistance to breaking under tension) so it’s usually reinforced by steel bars. But with an average of 635kg embodied carbon per m³ during production, the cement industry has come to the center of the climate change debate, especially since the publication of the Chatham House report.[5] Furthermore, unlike alternative materials, concrete has no recycling potential—each new project needs new concrete.

7. Glass: 3,600kg embodied carbon per m³

Glass exists in nearly every building on the planet. It’s manufactured by applying intense heat to sand or quartz. It admits light, of course, so it’s essential for the well-being of a building’s occupants, and it’s weather and fire resistant. But on average its production has 3,600kg embodied carbon per m³. Glass with a low emissivity (low-e) coating lowers a building’s energy use, though it’s more expensive in construction.

8. Steel: 12,090kg of embodied carbon per m³

The amount of CO2 emissions from steel manufacturing is almost double the amount of steel created: 1.85 tons of carbon per 1 ton of steel.[6] More than half of the world’s demand for steel comes from the construction industry. It’s affordable and strong, but has an extraordinarily high 12,090kg of embodied carbon per m³ from burning fossil fuels in production. Making steel has a number of other impacts too, including wastewater contaminants, hazardous waste and solid wastes.

9. Aluminum: 18,009kg of embodied carbon per m³

It’s considered a critical construction material for its high strength to weight ratio, ease of use, low transportation cost and low maintenance. It’s also an abundantly available natural resource. However, it has 18,009kg of embodied carbon per m³ on average, both in direct process emissions from aluminum electrolysis and oxidation of the carbon anode; and indirect emissions from consumption of electricity used for smelting.

From my reading, it appears that the industries involved in producing these materials are researching carbon-reducing processes and components, to one degree or another. The Cement Sustainability Initiative, for example, is an effort by 24 leading cement producers, with operations in more than 100 countries. They say they’ve “integrated sustainable development into their business strategies and operations, as they seek strong financial performance with an equally strong commitment to social and environmental responsibility.” They are tracking the carbon dioxide emissions of each firm and have committed to reduce, by 2050, their global direct CO2 emissions by 24%.[7]

But let’s speak on an individual level. Being honest, I know I can do much more to reduce my own carbon footprint than driving a hybrid car, boycotting beef, minimizing single-use plastics and repurposing my cottage cheese tubs. While I figure that out, I’m testing alternatives to using Portland cement in my art, and that’s less than a drop in the old bucket. But it’s a symbolic gesture, and I’m working on it.

[1] Chatham House, Johanna Lehne and Felix Preston, 2018, “Making Concrete Change: Innovation in Low-carbon Cement and Concrete,” https://www.chathamhouse.org/2018/06/making-concrete-change-innovation-low-carbon-cement-and-concrete, June 2018. [2] Ibid. [3] “List of countries by carbon dioxide emissions,” World fossil carbon dioxide emissions 1970 to 2018, Wikipedia, https://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions, 2018. [4] Chatham House, Johanna Lehne and Felix Preston, 2018, “Making Concrete Change: Innovation in Low-carbon Cement and Concrete,” https://www.chathamhouse.org/2018/06/making-concrete-change-innovation-low-carbon-cement-and-concrete, June 2018. [5] Ibid. [6] Carbon Clean, “Cleaning Up The Steel Industry: Reducing CO2 Emissions with CCUS,” https://www.carbonclean.com/blog/steel-co2-emissions, January 2021. [7] The World Business Council for Sustainable Development (WBCSD), “Cement Sustainability Initiative,”http://docs.wbcsd.org/2009/06/CementIndustryEnergyAndCO2Performance.pdf, 2009.

Other resources:

• Maikel Kuijpers, The Correspondent, “Concrete is one of the most polluting materials in the world. Here’s how we can make it sustainable.,” https://thecorrespondent.com/678/concrete-is-one-of-the-most-polluting-materials-in-the-world-heres-how-we-can-make-it-sustainable, September 2020.

• Pliteq, “Nine building materials and their shocking carbon footprints that will surprise you,” https://pliteq.com/news/building-vs-carbon-footprint/, January 2022.

© 2022 Su Cummings. All rights reserved.

Image credits:

• Masthead image: Mcshane on Unsplash. Creative Commons Attribution-NonCommercial 3.0 Unported License.

• Graph: Historical annual CO₂ emissions for the top six countries and confederations, Wikipedia: Tomastvivlaren - Own work