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Green construction: Reducing the carbon footprint of concrete
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Green construction: Reducing the carbon footprint of concrete

Cyclists passing a construction site in China

It is the second most commonly used substance on the planet, after water. It is an essential ingredient in modern cities. Depending on where you live, it supports everything from your roof to the dams and bridges that form essential infrastructure.

Concrete, a marvel material that has revolutionized construction and raised living standard across the globe, is one of the strongest drivers of global warming.

Global carbon dioxide emissions are dominated by the cement industry, which accounts for 8% of total global carbon dioxide emissions. This is more than twice as much as shipping or flying. If it were a country, its annual pollution would be only surpassed by the US or China.

Each year, cement is used to build homes, motorways, flood defenses, and other structures. As more people move to cities from poorer countries, cement’s use will increase. This is because they are able to afford the same quality housing and infrastructure as those living in wealther areas of the world. China, which produces more than half of the world’s cement, has poured more cement in the last few years between 2011 and 2013 than the US in the entire 20th Century.

“The fundamental problem is that [concrete]It is extremely carbon intensive, it’s a definite problem. Yet, we probably will continue using more of it,” stated Johanna Lehne from the Brussels-based climate think tank E3G.

Cyclists passing a construction site in China

China’s rapid expansion has been helped by a boom of concrete-powered construction.

Why climate-friendly concrete isn’t possible

Concrete is a simple material. Concrete is made from mixing inexpensive rocks, known as aggregates, with cement and water. These two substances react to create a binder which binds the components together.

Concrete is so dirty because cement is made. To heat rotating kilns above 1400 degrees Celsius, manufacturers use fossil fuels. This is what turns limestones and clays into clinker, the main component of cement. The majority of the CO2 is released when the limestone is broken down chemically.

Concrete production is an integral part of cement production so there is no way to eliminate concrete emissions. Lehne said cement presents a “fundamental technical challenge” unlike the power and transport sectors. Concrete lacks the equivalent to electric cars or wind turbines.

Air pollution from a coal plant in China

Cement kilns can be heated by burning coal

How to clean cement industry

The Global Cement and Concrete Association, which represents 80% of cement production in other countries and includes several Chinese manufacturers, published a roadmap to decarbonize the industry by 2050 in October 2021.

The plan to make concrete and cement more efficient is responsible for 40% of the savings. This includes heating kilns with no fossil fuels or replacing some clinker with scrap from steel and coal plants.

Nearly one quarter of the emissions reductions come from designing more efficient buildings, and extending their lifespans processes. This is something that the industry has little control over. This could mean that engineers and architects will retrofit old buildings, rather than knocking them down, and design new buildings to last longer. 

The last and most speculative of the savings comes from capturing carbon dioxide after it has been released. 

Pantheon in Rome, Italy

The Pantheon in Italy, made of Roman concrete, was built almost 2000 years ago

Can carbon capture technology make grey concrete green?

The technology to capture carbon dioxide is available, but it is not yet cost-effective and has not been tested at large scale. It is also still in its infancy in cement industry development. This means that the technology to capture carbon dioxide is still a work in progress and a key part of the industry’s future plans.

“In the next ten years we must make that technology mature, and prove the industrial scalability, and the commercial scalability, of the technology,” stated Thomas Guillot CEO of GCCA. He urged policymakers to work with investors and to coordinate the development of the infrastructure. It’s not an easy task.

The GCCA, which has asked for assistance from local governments and other players in the supply change, wants carbon capture technology to be applied at industrial scale in 10 cement factories by 2030. The first one is being built in Norway by Heidelberg Cement, a German concrete producer. It hopes to capture half of the CO2 that is emitted by the cement plant and store it permanently. The GCCA roadmap lists 29 carbon-capture projects at various stages of development at cement plants around the world.

Analysts have praised the roadmap’s realistic 2050 targets but also criticised its vague commitments to reduce emissions in the short-term. The GCCA members are yet to make specific commitments about how they will reduce pollution in the next decade. Guillot stated that details will be made later in the calendar year. “What we want to achieve is to actually live the talk, to transform commitments and global visions into action, local requirements into local requirements.” 

Workers installing concrete slabs at a construction site in Serbia

Recycled building waste could be injected with CO2 to make concrete aggregates.

Future solutions

There are small-scale solutions that have early signs of promise.

A pilot study conducted by Vattenfall, an energy company in Sweden, has shown that cement can be made technically from electricity. Researchers are also looking into how CO2 could possibly be injected into crushed concrete and used as an aggregate. One company in France managed to convert cement bypass dust into lightweight concrete using CO2 captured on site. 

Maarten van Roon is chief commercial officer of Carbon8 Systems, which developed the technology. He said that the cost of capturing carbon remains a barrier for cement producers. “We help eliminate a cost from the supply chain, which in turn helps us justify the expense of putting the innovation on-site.”

Concrete’s carbon footprint can be reduced by using sustainably sourced timber for construction. However, replacing concrete with timber on a large scale would place immense pressure on the planet’s forests.

Jorge de Brito, a professor of civil engineering at the University of Lisbon, Portugal, said that concrete has a large impact on the environment. He has published a study that compared green concrete alternatives. Concrete is the most commonly used material, so it has an impact.

Edited by Tamsin Walker

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