net zero emissions

Cement and Steel—Nine Steps to Net Zero Emissions

Cement and steel are essential components of buildings, cars, dams, bridges, and skyscrapers. But these industries are among the most polluting on the planet. Cement production generates 2.3 billion tons of CO2 every year, and steel production releases about 2.6 billion tons of CO2 every year, accounting for 6.5% and 7.0% of global CO2 emissions respectively.

Concrete is the second most consumed product on earth, after clean water. CO2 is released from the carbon-intensive production of cement and steel, as well as from the high temperatures generated by burning fossil fuels in the manufacturing process. There is therefore an urgent need for cleaner ways to make and use cement and steel. The world must reach net-zero carbon emissions by 2050, against a backdrop of growing industrial demand and soaring energy prices. Infrastructure, technology transfer and financial risk reduction mechanisms must be put in place to allow low-emission heavy industry to flourish.

1. Use the latest technology

Ensuring production plants are equipped with the best available technology can reap immediate benefits. Improving the way industrial plants are insulated can save 26% of energy; better boilers can reduce energy requirements by up to 10%; and using heat exchangers can reduce the power requirements of refining processes by 25%. Today, the most efficient cement plants can only save 0.04% of energy per year through technology upgrades. Much more needs to be done.

2. Reduce dosage

The same project can use less steel and cement. Small but significant reforms to building codes and the education of architects, engineers, and contractors could reduce cement demand by 26% and steel demand by 24%, according to the International Energy Agency. Today, many building codes rely on over-designing systems for safety reasons. This margin would be greatly reduced if modern materials and computer modeling were used to simplify the design and use only the necessary resources. For specific uses, alternative materials with a smaller carbon footprint, such as aluminum, may replace steel in some products, including cars. Professionals will have to change their practices and retrain.

3. Reshape the steel production process

Carbon is a core material in traditional steel production. Coke (extracted from coal) fuels blast furnaces where iron ore is reduced to metallic iron at temperatures up to 2300°C. The combustion of coke produces CO, which reduces the ore into iron and CO2. The molten iron is then refined into steel, typically in coal-fired furnaces, a process that emits approximately 1,800 kg of CO2 per ton of steel produced.

There are other substances available that can be used to reduce ores. About 5% of the world’s steel is produced through the “direct reduced iron” (DRI) process, which does not require coke and typically uses hydrogen and CO (from methane or coal). By using methane-derived gas and renewable electricity to power electric furnaces, such steel plants emit about 700 kg of CO2 per ton of steel produced, 61% less than coke-based steel plants.

Moreover, using only hydrogen for DRI can reduce CO2 emissions to 50 kg or less per ton of steel, a 97% reduction. Companies in Europe, China and Australia are piloting such plants, with some planning to open them in 2025 or 2026. The challenge with this approach is that the process requires large amounts of hydrogen.

Producing all steel in this way would mean almost tripling global hydrogen production from 60 million tons per year to about 135 million tons. Most cheap hydrogen currently comes from natural gas, which releases CO2. Another greener option – splitting water using electrolysers – costs about 2.5 times as much. As more factories are built, costs should come down.

There are other options worth checking out, too. In 2004, the Ultra-Low CO2 Steelmaking Alliance, composed of 48 companies and organizations in 15 European countries, evaluated these options. Jamshedpur, India-based Tata Steel set up a pilot plant in the Netherlands in 2010 for an advanced steelmaking process that was still based on coal but was streamlined to make carbon capture easier . Now the falling price of green hydrogen, produced using renewable energy, is luring Tata groups towards hydrogen-based DRI.

4. Reshape the cement production process

The production of Portland cement (the most common cement) begins with the calcination of limestone, which is heated to temperatures above 850°C to form lime and CO2. Lime is mixed with sand and clay in a kiln at 1450°C to make clinker. Mix some other ingredients to make cement. Approximately 60% of the emissions from a high-quality plant come from the calcination reaction, with most of the remainder coming from burning fuel. In total, an average factory produces 800 kg CO2 per ton of cement produced, while a high-quality factory produces 600 kg CO2 per ton of cement produced.

Today, cement can be made without limestone. For example, magnesium oxychloride cement (called sorel) has been around since 1867 but has not been commercialized due to its low water resistance. Dozens of different types of cement are being researched. However, for their use in construction, building codes, designs and practices must change to take into account the different strengths and properties of these materials. This will take more than ten years.

Another option is to replace some of the clinker with more sustainable materials. Common ones include blast furnace slag and ash from coal-fired power plants. But as fossil fuels are phased out, these materials will become scarce. Researchers are investigating other options, including recycled iron produced from electric furnaces and slag extracted from DRI electric furnace steel processing.

Limestone calcined clay cement (LC3) is a good example. Its performance is similar to that of ordinary Portland cement and it is close to commercialization. Up to half of the clinker can be replaced. Several companies have already integrated LC3 technology into their net-zero strategies, including France’s LafargeHolcim and Germany’s HeidelbergCement.

5. Change fuel

For steel, it is recommended to replace coal and coke with charcoal or other forms of biomass. But there are challenges. Growing biomass for energy can conflict with agricultural land needs, and not all biomass harvests are sustainable. Charcoal is less strong than coke and cannot support the layers of material in a blast furnace. As mentioned above, rethinking the steel processing process is a better solution.

For cement, however, municipal solid waste – or carefully sorted garbage – can be used as an alternative fuel: the high temperatures in the kiln can incinerate the waste’s toxic materials, and the ash can be incorporated into the clinker. Mexico’s Cemex’s cement plant in the UK derives up to 57% of its energy from these alternative fuels, while UK company Hanson’s alternative fuel consumption is 52%. This strategy should be encouraged, including through the adoption of corresponding regulations at the national level.

6. Carbon capture

CCS – which absorbs and stores CO2 underground – is critical to reducing emissions from cement production and is also important for steel.

CCS is relatively advanced in some other industries. Equinor, the Norwegian national oil company, has been operating CCS projects since the late 1990s, absorbing about 1 million tons of CO2 every year. But this technology is not yet fully utilized; only 0.1% of global emissions are currently captured and stored. Only a few steel and cement plants are experimenting with CCS. For example, a modern DRI steel plant in Abu Dhabi has been using CCS since 2016. CCS must scale up quickly.

7. Storing CO2 in Concrete

Adding CO2 can make concrete stronger. If CO2 accounts for only 1.3% of the weight of concrete, the material’s hardness can be increased by about 10%. This will reduce the amount of cement required in the structure and net emissions by approximately 5%.

Optimizing carbon capture in concrete is an active area of research. Leaders like Dartmouth, Canada’s CarbonCure are already injecting CO2 into concrete at scale: they have reportedly delivered nearly 2 million truckloads of CarbonCure concrete, consuming 132,000 tons of CO2.

Both cement and concrete absorb CO2 from the air by converting calcium-based components into limestone. The potential there is huge: in theory, about half of the CO2 emissions from the cement manufacturing process could be reabsorbed. But these materials must be ground down at the end of their service life to make the concrete particles smaller for better CO2 diffusion. This is expensive and requires energy.

8. Recycle steel

Steel can be recycled efficiently using electric arc furnaces. Today, a quarter of steel production is based on recycled scrap. Global recycling production is expected to double by 2050, reducing emissions by 20-25% compared to today (depending on how electricity is generated).

However, it is not yet possible to recycle steel indefinitely. Toxic substances—harmful compounds (especially copper)—can build up. Their accumulation can be slowed by better sorting scrap and redesigning products to make copper wires easier to remove.

9. Subsidy changes

In short, the potential of these eight steps is enormous. However, further economic hurdles must be overcome if low-carbon heavy industry is to reach the scale of million-tonne production per year.