We use over 4 billion metric tons of cement each year, and almost 3 billion metric tons of CO2 are emitted to manufacture it. And yet, we cannot do without this material.
This is how companies are working to reduce its environmental impact. It is undoubtedly one of the most familiar presences for us all. It was beside us in the hospital, when we were born. It was with us on the first day of school, almost certainly on our first day at work or when we took our first flight. Concrete is perhaps the distinctive mark of the Anthropocene. A few years ago, The Guardian called it "the most destructive material on Earth." And yet Vaclav Smil, a member of the Canadian Academy of Science, estimates that if the floors of the world’s poorest homes were made from cement instead of earth, parasitic diseases would decrease by 80 percent.
Concrete is the most consumed material in the world, and according to the Zurich Polytechnic, something like 900 billion metric tons of it have been cast since the beginning of the industrial revolution (the equivalent of pouring a 1-meter layer of concrete on the entirety of Iraq).
Concrete is perhaps the distinctive mark of the Anthropocene.
The effects of this on ecosystems are not difficult to imagine. In recent times, global production of cement (which, as we will see, is not the same thing as concrete) is just over 4 billion metric tons per year (it was less than 2 billion in 1995). China is the largest producer with 2,200 million metric tons. In a business-as-usual scenario, according to the U.K.’s Royal Institute of International Affairs (Chatham House), global cement production, driven by growing urbanization and infrastructure projects in less economically developed countries, is set to reach 5 billion metric tons per year within the next three decades.
What is cement?
But let’s start at the beginning. Early forms of cement were already in use in ancient times — you may remember learning in school about the mix of lime mortar and pozzolana the Romans used for the opus caementitium to build their aqueducts. The modern variant was created in 1824 when Englishman Joseph Aspdin patented Portland cement, on which almost all current types of cement are based. What is cement? In essence, it is a binder that activates when united with water (a hydraulic binder).
It can be made from marls, limestones, or clays, heated to 2,642 degrees (the temperature of lava), which leads to calcination, the breaking down of limestone into calcium oxide and carbon dioxide. The resulting material is known as clinker, which is ground down and mixed with chalk, becoming cement. Between calcination and energy use, the production of one metric ton of cement results in the approximate emission of 1 metric ton of CO2 into the atmosphere. The addition of sand and gravel (known as aggregates) to cement produces concrete. One cubic meter of concrete requires about 300 kilograms of cement, one cubic meter of aggregates and 120 liters of water.
From raw materials to water: the consumption of the cement industry
The construction sector is responsible for the consumption of about 50 percent of all raw materials extracted globally, amounting to 42 billion metric tons per year (the weight of a mountain made from 14 billion Land Rover Discovery SUVs).
One metric ton of CO2 for each metric ton of cement is far from what might be called a climate-friendly activity. In fact, the cement industry is responsible for about 5-9 percent (depending on the estimate) of total anthropogenic emissions, just below the chemical industry and more impactful than metalworking or aviation. "With its 2.8 billion metric tons, if the cement industry were a country it would be the third largest dioxide emitter in the world, behind the United States and China," states The Guardian. Despite diminishing energy consumption, fueling the kilns so that they reach almost 2,732 degrees requires more or less 5 percent of global energy consumption.
Looking at the production process more closely, we can focus on water: almost 500 liters are needed per metric ton of clinker. According to a study published in Nature, this accounts for 9 percent of global industrial water use. "The water requirements are enormous, and particularly burdensome in those regions of Earth that are not blessed with an abundance of fresh water," says Christian Meyer of Columbia University. "The concrete industry uses about 1 billion cubic meters of water each year."
With its 2.8 billion metric tons, if the cement industry were a country, it would be the third largest dioxide emitter in the world.
And when products made from cement (buildings) reach their end-of-life, they become a primary source of waste: in Europe, they account for over one-third of all waste produced, about 500 million metric tons.
Innovation in cement
It is impossible to overlook the great benefits of this material: it is versatile, cheap, extremely resistant, has a very long useful life, and is 100 percent recyclable. However, with such a calling card the global concrete industry is inevitably set to be one of the most important fronts in the ecological transition and the fight against climate change.
As we will see, companies are making moves. However, Johanna Lehne of Chatham House, co-author with Felix Preston of a report on low-carbon innovation in cement, notes a useful caveat: "The sector is dominated by a handful of major producers which are cautious about pioneering new products that challenge their existing business models. And, in the absence of a strong carbon-pricing signal, there is little short-term economic incentive to make changes."
We can try to provide a quick but obviously not exhaustive overview of the initiatives at play. They will be presented in alphabetical order.
Reducing carbon emissions
C for carbon dioxide. If half of emissions can be ascribed to the chemical reactions between the materials that make up the clinker, the first solution could be to replace these materials and reduce the amount of clinker in cement and concrete. Part of the clinker’s raw materials is already being replaced with production waste from other manufacturing sectors, which have the same chemical and physical properties. These include ash from coal power plants and blast furnace slag from steel production, both good examples of industrial symbiosis.
"In Europe today, approximately 5 percent of the raw materials used in the production of clinker, some 9 million metric tons per year, is made up of recycled materials and ash from combustion processes," claims Nikos Nikolakakos, environment and resources manager at Cembureau, the European cement producers association (which also includes Turkey, Switzerland, Norway and the U.K., reaching 6 percent of global production).
Fifty carbon capture and storage plants have been completed worldwide, all pilot plants, two linked to cement works.
Within the same sector, the EU’s ReActiv program (Industrial Residue Activation for Sustainable Cement Production) was launched to connect the cement and aluminium supply chains, deploying bauxite residues (aluminium production by-products) in cement manufacturing, thus reducing calcination waste and CO2 emissions.
Vertua, a range of low-carbon concrete products (up to 70 percent less, according to the manufacturer) made by Mexican multinational Cemex, is being used in the construction of HS2, the U.K.’s high-speed railway. The rate of clinker in Cemex cement has fallen from 85.5 percent in 1990 to 77 percent today.
Tom Schuler, former CEO of Solida Technologies, spoke in a TED Conference about innovation in this company, which recently received almost $80 million from several investment funds. "We use less limestone and we fire the kiln at a lower temperature, resulting in up to a 30 percent reduction in CO2 emissions."
Solida Technologies cement "does not react with water but hardens when coming into contact with the CO2 captured in other industrial systems. The chemical reaction that is triggered ‘breaks’ the carbon dioxide to produce limestone." In essence, instead of emitting CO2, this cement — so far used only for prefabricated products — absorbs the greenhouse gas, reducing emissions by up to 70 percent and saving considerable amounts of water.
A similar solution is offered by Canadian firm CarbonCure, which injects carbon dioxide, which has been chemically converted into a mineral, into concrete.
Capturing CO2
The solutions mentioned here, while extremely interesting, are still niche. They have promising applications but are still not accessible to large swathes of the market. Thus, to cut down emissions, manufacturing companies are focusing on Carbon Capture and Storage (CCS).
"The reduction of CO2 emissions by adopting carbon capture and storage or capture and reuse technology in the production of cement is becoming an interesting and active area of research," explains Paulo Monteiro of the University of California at Berkeley. "However, it is still uneconomical." This is because CCS is still not widespread on an industrial scale.
According to the Global CCS Institute, 50 carbon capture and storage plants have been completed worldwide, all pilot plants, two linked to cement works. Of these 50, according to statistics provider Statista, 26 were operational in 2020. Most big players in the sector focus on CCS: from China National Building Materials (CNBM), the world’s largest producer, to LafargeHolcim, which announced four pilot projects in 2020 alone, and to Dalmia Group in India.
There are also several European projects on this very interesting front, not only for the cement industry. LEILAC 1 (Low Emissions Intensity Lime & Cement) and LEILAC 2 brought together Calix (Australian manufacturer of sustainable technology for industry) and HeidelbergCement (the world’s fourth-largest producer of cement) to create a pilot plant at the Hannover cement works. With a capacity of 100,000 metric tons per year, the aim is to prove that it is possible to create capture and storage technology at an industrial scale that is low-cost, scalable, replicable and applicable to existing sites.
In December 2020, German company HeidelbergCement also obtained public funding to create a carbon capture plant, which should become operational in 2024, at the Norcem cement works in Brevik, Norway. The goal is to capture 1.8 million metric tons of carbon dioxide per year, thanks to a mixture of water and amine solvents. This will then be stored under the North Sea (in depleted Equinor oil wells).
Saving energy and reducing fossil fuels
Next, we come to E for energy. While half of climate-altering emissions are due to calcination, the other half are linked to energy use, especially those of kilns, largely powered by fossil fuels. One solution would be electrification, but this would be hard to implement given the very high temperatures at which the kilns need to operate.
However, attempts have been made. In Sweden, Cementa (a subsidiary of HeidelbergCement) collaborated with energy company Vattenfall on a project called CemZero, aimed at electrifying production. Having demonstrated technical feasibility, the research is advancing through three projects in collaboration with several universities and companies: heat transfer to plasma in rotating kilns, direct capture of carbon from calcination and electrified production once again. HeatNeutral is a startup that, in collaboration with LafargeHolcim, develops kilns that require less fuel than traditional ones with equivalent power output.
Once again, however, we are discussing niche experiences and pilot programs. In the meantime, companies are aiming to replace traditional fuels with non-recyclable waste, with the support of the European Union. This avoids having to import and burn fossil fuels and reduce the amount of waste sent to landfills. "In the EU, in 2018, the sector replaced 48 percent of its consumption of fossil fuels," notes Nikolakakos, "with non-fuels derived from non-recyclable waste, saving approximately 7.8 million metric tons of carbon."
According to the companies, this is also a circular economy. So long as — we would like to add — it does not reduce recycling commitments. Kilns aside, electrification and energy efficiency are more within reach: LafargeHolcim, for example, is investing in Waste Heat Recovery (WHR) technology that harnesses the heat from kilns to make electricity.
Recycling raw materials and extending concrete’s life
R for raw materials. While it may be difficult to replace the materials used to make clinker, the same cannot be said for concrete aggregates. And, as in all supply chains, the reduction of natural extraction is obtained through recycling.
Mobbot, another startup chosen by LafargeHolcim via its open innovation platform, works on integrating recycled materials in 3D printing processes, which are more efficient in the use of materials compared to traditional casting. "Concrete debris is probably the most important candidate for reuse in new concrete," explains Christian Meyer. "Using such debris to produce new concrete conserves natural resources and reduces valuable landfill capacity at the same time."
Columbia University has carried out studies on the use of post-consumer glass and recycled carpet fibers as aggregates. "Since carpet fibers are typically made of nylon, recycled fibers have been shown to improve some mechanical properties of concrete," the researcher clarifies. Several universities have carried out research on other waste materials that may be useful, including wood, used tires, plastic, paper mill residues, and also agricultural waste such as bagasse ash, cork, peanut shells and rice husk ash.
Since a product’s environmental footprint should be assessed throughout its entire lifecycle, extending concrete’s already long life could contribute to relieving its environmental impact. An interesting example is the various studies carried out on the inclusion of bacteria in concrete that help activate processes (carbonate precipitation) with self-repairing, anti-crack effects.
Recycling water
Finally, W for water. "The recycling of water can be easily done in practice, and it is already a legal requirement in some countries," says Meyer. More often, in industrial settings, companies resort to closed systems that recycle the water used in manufacturing processes and to wash machinery. This also has self-evident economic benefits.
LafargeHolcim, the third global producer of cement and one of the most innovative players in the sector, reduced the freshwater required for each tonne of cement by 9 percent in 2020 compared to the previous year. Sometimes, the solutions implemented are as simple as they are effective: at the Italcementi facility in Matera, Italy (part of HeidelbergCement Group), tanks are used to collect and store rainwater for use.
Towards sustainable concrete
So far, we have focused on the several phases of the production process. However, it is clear that sustainability also relates to the use phase. Here, some innovative products can have positive effects on the environment compared to traditional cement. One example, increasingly found in manufacturers’ catalogs, is pervious concrete, which allows water to pass through without altering the water cycle. This limits the waterproofing of the soil and, in cities, it contributes to reducing the heat island effect.
Another example is Italcementi’s i.active Biodynamic, a cement mortar made from 80 percent recycled aggregates derived from Carrara marble processing scraps. In the version used to clad the Italy Pavilion at Expo 2015 in Milan, for example, the mortar also contained TX Active. This photocatalytic principle, patented by Italcementi, uses light to accelerate natural oxidation processes that aid a quicker decomposition of environmental pollutants (micro-dusts, nitrogen oxides), preventing them from building up.
However, we are learning that technological innovation alone is not enough to bring about the ecological transition. Public institutions have tried to play their part: from China, whose 13th five-year plan aims to reduce the thermal energy intensity of production, to Europe’s Emission Trading Scheme and regulations on energy efficiency.
But evidently, this is not enough, if "reactions" from the market are not triggered. "Government and the major concrete-consuming companies should grow the market for low-carbon building materials," reflects Johanna Lehne. In particular, "this will entail incorporating metrics on ‘embodied carbon’, the emissions released during production."
