The cement industry produces huge emissions of carbon dioxide (CO2) annually. These emissions are not sustainable. They ramp up global warming and do untold damage to the planet’s oceans and biosphere. In this article, we explain how cement is made, how its CO2 emissions are generated and what new technologies exist to reduce them.
- Cement: A Critical Ingredient of Concrete
- What is Concrete Made Of?
- What is Cement Exactly?
- How is Cement Made?
- When Was Portland Cement First Made?
- Why is Cement Bad for Climate Change?
- Which Countries Have the Highest Cement Emissions?
- Why Does Cement Production Cause So Many CO2 Emissions?
- Other Environmental Impacts
- How to Reduce Emissions From Cement Production
- New Roadmap for the Industry
- What New Cement Technologies Are Being Developed?
- How Much Can Cement Emissions Be Reduced?
- New Urban Designs
- The Power of the Cement & Concrete Industry
Cement: A Critical Ingredient of Concrete
Cement is the key component of concrete, which is the world’s most consumed material after water. How much concrete is made? At present, the world produces 10 billion tons annually. 1 More than twice as much concrete is used in construction than all other building materials put together. 2
For example, concrete is the go-to building material for almost every sort of major structure you can think of, including dams, bridges, towers, flyovers, skyscrapers, multi-storey car parks, apartment blocks, pavements, motorways, runways, and monuments.
In the oceans, concrete accounts for more than 70 percent of marine infrastructure, including harbors, ports, breakwaters and other coastal defence structures. In China, for instance, approximately 60 percent of its coastline is concreted. In the United States, an estimated 14,000 miles of coastline is covered in concrete. The 55km-long Hong Kong to Macau sea bridge, which opened in October 2018 at a cost of $20bn, contains a staggering one million tonnes of concrete. 3
What is Concrete Made Of?
Concrete is a relatively simple mix of ingredients. But it’s the cement that binds them together and gives concrete its durability and structural qualities.
Main Components of Concrete
Aggregates 60-75 percent
Water 14-21 percent
Cement 7-15 percent
Air up to 8 percent
Basically, concrete is made up of two components: aggregates and paste. The paste consists of portland cement and water, which binds with aggregates (sand, gravel & crushed stone or rocks). The paste coats the surface of the fine (small) and coarse (larger) aggregates. As a result of a chemical reaction known as ‘hydration’, the paste hardens and becomes stronger, forming the rock-like mass we call concrete.
Concrete is malleable when newly mixed; strong and durable when it hardens. These two characteristics are the reason it is embraced by architects, structural engineers, and building companies around the globe.
The presence of cement is critical. According to Felix Preston, co-author of a heavyweight report produced by UK think-tank Chatham House “building without concrete, although it is possible, is challenging.” 1
What is Cement Exactly?
Basically, it’s a fine powder consisting of limestone, clay, and other materials. The industry standard is a type known as ‘Portland cement’. This was invented in the early 19th century and named after a building stone widely used in England at the time. It is used in 98 percent of concrete globally today, with more than 4 billion tonnes produced annually.
Cement’s main function is to act as a binder: that is, a substance used in construction that sets, hardens, and effectively ‘glues’ other materials (sand, gravel, small rocks) together.
How is Cement Made?
Portland cement is made by crushing and combining the following materials: (Note: formulas can vary significantly):
|Iron Oxide (Fe2O3)||3%|
|Calcium Sulfate (CaSO4)||3%|
It is the process of making “clinker” – the key constituent of cement – that emits the largest amount of CO2 in cement-making.
• Raw material rocks, mainly limestone and clays, are quarried and crushed to about 3 inches in size.
• The remains are combined with other ingredients including iron ore or fly ash, then milled and combined.
• The mix is fed into huge, cylindrical kilns and heated to about 1,482°C (2,700°F).
• The process of “calcination” splits the material into calcium oxide and carbon dioxide.
• In the process a new substance is created, known as clinker.
• The clinker is cooled, finely ground and mixed with a small quantity of gypsum and limestone.
The finished cement can now be transported to ready-mix concrete companies to be used in a variety of construction projects. 5
Although most cement is made using the dry process, some kilns in the US use a wet process. The two processes are basically the same, except that in the wet process the raw materials are milled and combined along with water before being fed into the kiln.
When Was Portland Cement First Made?
The first portland cement was made about 1824 by Joseph Aspdin. He called it portland cement because the mortar it yielded resembled “the best Portland stone” – the finest building stone in use in England at the time. However, the patent he registered does not describe the product recognised as Portland cement today, but rather a prototype.
Aspdin’s product was improved upon by in the late 1840s by Isaac Charles Johnson whose superior and cheaper product is credited with being the first real portland cement. Thereafter, its manufacture spread rapidly across Europe and North America.
Why is Cement Bad for Climate Change?
Cement is bad for climate change because of the staggeringly high CO2 emissions released during its manufacture. In total, more than 4.1 billion tonnes of cement are produced annually, accounting for about 8 per cent of global CO2 emissions. 6 This is more that any country produces except for China or the United States. Among all materials, only fossil fuels emit more greenhouse gas.
Man-made emissions of CO2 into the atmosphere emanate from three main sources: (a) combustion of fossil fuels, (b) deforestation and other land-use changes, and (c) carbonate decomposition. Cement is the largest source of emissions from the decomposition of carbonates. But it wasn’t until just after World War II that the production of cement accelerated rapidly around the world.
Since 1990, global production has almost quadrupled, with Asia and China accounting for the bulk of growth. China, for example, used more cement in the three years 2011, 2012 and 2013, than the US did in the entire 20th Century. 7
What’s more, cement use is set to rise further due to increasing global demand driven by rapid urbanisation and economic development. With Chinese consumption now slackening, most future growth in construction is set to take place in the emerging markets of South East Asia and sub-Saharan Africa.
According to think-tank Chatham House, the floor area of the world’s buildings is forecast to double in the next 40 years, requiring a 25 percent increase in cement production by 2030. Another reason why scientists are now saying that our climate plan can’t cope and that stronger measures are needed.
Which Countries Have the Highest Cement Emissions?
China is the world’s largest cement manufacturer & CO2 emitter by a huge margin, as the following table shows:
|Country||Cement Output. Million tonnes/year|
Why Does Cement Production Cause So Many CO2 Emissions?
So where do these emissions come from? There are two main sources. The first is the chemical reaction involved in the production of clinker, as carbonates (mostly calcium carbonate, found in limestone) are decomposed into oxides (mostly lime, CaO) and CO2 by the addition of heat. Roughly half of the emissions from cement manufacture come from this chemical reaction. 1
Which is why such emissions are thought to be so difficult to cut. If the CO2 is released as a result of a chemical process, it can’t be reduced by changing the fuel used, or by increasing efficiency. The only way to reduce these ‘process emissions’, is either by changing the chemicals used in the production of clinker, or by reducing the amount of clinker per tonne of concrete.
The second source of CO2 emissions is the burning of fossil fuels to heat the kiln to 1,480°C. This accounts for another 40 percent of emissions. The final 10 percent of emissions come from fossil fuel energy used to mine and transport the raw materials.
According to the latest estimates, the 4.1 billion tonnes of cement produced annually account for roughly 8 percent of all man-made CO2 emissions. 9
Other Environmental Impacts
As well as ramping up the greenhouse effect through its enormous emissions of carbon dioxide, cement manufacture damages the environment and its ecosystems in a number of other ways.
• Setting up quarries for raw materials defaces the landscape.
• Quarrying machinery causes airborne pollution in the form of dust, gases and noise. 10
• Movement of heavy lorries to and from the quarry causes damage to the local countryside.
• In some circumstances, kilns can release gases and dust rich in volatile heavy metals, such as thallium, cadmium and mercury.
How to Reduce Emissions From Cement Production
The concrete industry has made clear, albeit insufficient, progress in its energy use and emissions. By burning biomass or waste instead of coal and by using more efficient kilns, cement production is less energy-intensive per tonne than it used to be. In fact, average CO2 emissions per tonne have fallen by 18 percent over the last few decades. 1
However, these improvements are not being applied worldwide. Global average energy use per tonne of cement is still about 20 percent higher than production in certain companies using best available technologies. And as a whole, the industry’s emissions have risen significantly in recent decades and are forecast to rise further.
Unfortunately, since the bulk of CO2 emissions arise from the clinker process, replacing fossil fuels with alternative fuels or raising plants’ energy efficiency, is not sufficient. What the cement sector needs to focus on, is how to reduce clinker-related emissions: one that uses (a) new recipes for clinker, or (b) new cements that use less clinker or that emit less CO2.
Progress is being made here, too, although not fast enough. In addition to cements consisting of 100 percent clinker, there are now number of ‘composite’ or ‘high-blend’ cements, in which some of the clinker is replaced by fly ash, ground slag, or limestone.
These alternative raw materials do help to reduce CO2 emissions, but since they also affect the cement’s properties, it is only feasible for a limited number of end-uses. Also, the availability of certain alternative materials like fly ash – a by-product of coal-burning and one of the most widely-used clinker substitutes – is decreasing as more coal-fired power plants are closing down.
Overall, according to the International Energy Agency (IEA), the CO2 emission rate of cement has changed little since 2014, as energy efficiency improvements have been offset by a slight increase in the clinker-per-tonne ratio.
For more industrial gases, see: F-Gases: Fluorinated Greenhouse Gases.
New Roadmap for the Industry
In 2018, the concrete and cement industry set up a new lobby group representing more than one third of global cement production capacity, known as The Global Cement and Concrete Association (GCCA). According to its chief executive Benjamin Sporton, the fact the organisation now exists, is a demonstration of the commitment of the industry to climate action and sustainability. The GCCA plans to publish a set of sustainability guidelines, to be followed by its membership.
In 2019 the GCCA collaborated with the IEA and the Cement Sustainability Initiative (CSI) to release a new low-carbon roadmap. The roadmap proposes four strategies to reduce emissions, three of which have been pursued with insufficient success: namely, improved energy efficiency, alternative fuels and lower clinker ratios.
For example, the roadmap proposes an average global clinker ratio of 0.60 by 2050, down from 0.65. According to think-tank Chatham House, fulfilling such a target would require 40 percent more clinker substitutes by 2050 than today, at a time when sources of traditional substitutes – such as fly ash and blast-furnace slag – are dwindling.
Granulated blast-furnace slag (GGBFS) is the by-product of an iron blast furnace. When finely ground, it acts as a type of hydraulic cement which can be used to replace a portion of portland cement. 11
Despite these problems, it’s possible that a new generation of ‘bio-cements’ will produce a winner. One basic type of bio-cement is formed with sand, or other forms of aggregate, to which is added bacteria and urea. The urea acts on the bacteria to make it secrete calcite – a type of calcium carbonate – gluing the mixture together into a solid material rather like limestone. Bio-cements typically have around 33 percent of the CO2 emissions of normal concrete.
The fourth area involves “innovative technologies”, which is basically carbon capture and storage (CCS). CCS is a common sense climate change mitigation strategy that, in theory at least, can be applied to many different industrial sectors hampered by high levels of greenhouse gas emissions. However, like the power generation sector, the cement industry has been reluctant to commit to the costs involved.
As it happens, the world’s first full-scale carbon capture and storage (CCS) facility for cement production is about to come on stream at the Brevik cement plant in Norway. The plant, owned by Norcem, employs CCS technology developed by Aker Solutions and is capable of capturing up to 400,000 tonnes of CO2 a year. However, it doesn’t come cheap. Building the full-scale CCS system and operating it for five years is estimated to cost $1 billion.
Despite the fact that carbon capture and storage technology has not been used commercially in the cement industry, the IEA/CSI roadmap assumes that CCS will attain commercial-scale deployment by the end of this decade.
What New Cement Technologies Are Being Developed?
Here is a short summary of a number of alternative technologies and their stages of development.
Development of New Cement Technologies
|Research||– Magnesium-based cements|
– Ground-glass pozzolan as part-substitute for cement
|Pilot||Cements based on carbonation of calcium silicates|
– CO2-rich synthetic limestone
– Injection of liquid CO2 into concrete during mixing
– Bio-concrete bricks made by trillions of bacteria
– Carbon capture technology
|Calera, Solidia Cement|
– Blue Planet
– CarbonCure Technologies
– Aker Solutions/ Norcem
|Demo||– BYF clinkers (type of CSA clinkers)|
– Low carbonate clinkers with pre-hydrated calcium silicates
|Lehigh Cement (Heidelberg)|
|Commercialized||– Cements with reduced clinker content|
– Geopolymers and alkali-activated binders
– Belite-rich Portland clinkers (BPC)
– Belitic clinkers with ye’elimite (CSA)
|L3K, LC3, CEMX, Ecocem|
bannahCEM, Zeobond cement
How Much Can Cement Emissions Be Reduced?
No one knows. The IPCC have great faith in carbon capture and storage technologies, as do the authors of the IEA/CSI roadmap. Clearly, neither authority is troubled by the costs involved. New cement formulations appear more feasible although this approach may benefit more specialist end-use applications.
Effects of Possible Mitigation Strategies on Cement-related CO2 Emissions
|New Cements||90-100 percent|
|Clinker Substitution||70-90 percent|
|Alternative Fuels||40 percent|
|Energy Efficiency||4-8 percent|
New Urban Designs
A new form of urban climate-proof infrastructure known as “sponge cities” is gaining in popularity around the world. Pioneered (ironically) in China, a sponge city is designed to combat urban flooding and (to a lesser extent) the urban heat island effect.
The sponge city concept replaces concrete in numerous spaces with plants, grasses and shrubs, in order to absorb rainfall and reduce run-off. Increased shade and transpiration from extra tree-planting helps to produce a cooling effect. Air pollution from CO2 and acid rain is also reduced.
Green building or green construction is a growing global trend. It emphasizes constructing buildings which cause minimum damage to people and the environment. The aim, for example, is to avoid the destruction of ecosystems due to deforestation or mining in the extraction of raw materials. And to avoid waste, water and air pollution in the manufacturing process of building materials, including cement.
If the production of cement can become carbon neutral, concrete does have some advantages. The light colour of concrete surfaces has a higher albedo than asphalt surfaces, reducing the urban heat island effect. And porous concrete allows water to permeate into the ground, improving drainage.
The Power of the Cement & Concrete Industry
For some years, the cement sector has been considered too difficult to decarbonise, along with other industries including aviation and steel. As a result, the industry has faced less political and commercial pressure than the fossil fuel and power generation industries.
In addition, control of large parts of the cement sector remains in the hands of a small number of major corporations.
Add to this, the fact that cement is a must-have material for all developing countries, their economies and their governments – thus encouraging cosy relations between suppliers and government buyers – and you can see why radical changes in production to reduce the industry’s carbon footprint, may not be uppermost on the agenda of most cement multinationals.
- “Making Concrete Change: Innovation in Low-carbon Cement and Concrete.” Chatham House.
- Source: World Business Council for Sustainable Development
- “The world’s growing concrete coasts.” BBC Future Planet.
- “8 Main Cement Ingredients & Their Functions.”
- “How Portland Cement is Made.”
- “Why Cement is a Major Contributor to Climate Change.” Chatham House.
- Source: US Geological Survey statistics. See: “How did China use more cement between 2011 and 2013 than the US used in the entire 20th century?”
- “The Cement Industry and Global Climate Change: Current and Potential Future Cement Industry CO2 Emissions.” Mahasenan, N. & Smith, S. & Humphreys, K. (2003). Greenhouse Gas Control Technologies – 6th International Conference. 995-1000
- “Global CO2 emissions from cement production, 1928–2018.” Robbie M. Andrew. Earth Syst. Sci. Data, 11, 1675–1710, 2019.
- See for example: “Concrete: the most destructive material on Earth.” Jonathan Watts. The Guardian.
- “What is Slag Cement?”