Cement and concrete
Cement and concrete

Cement and concrete

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Meeting the Paris agreement is not possible without reducing emissions from cement production: cement is responsible for 8% of global GHG emissions and production is increasing.
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A lack of innovation isn't the problem: Alternatives to high GHG emitting cement are already available, it is regulations that have been slowing down widespread adoption.
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Industry standards favor high emitting cement: A new cement might be just as strong as Portland, but it won't show in the tests because it takes longer to develop those properties and all concrete is tested at 28 days (where portland cement is at full strength).

Cement

Cement, a binder material used in the construction industry, is responsible for 8% of global GHG emissions. Global production of cement was 5.17 billion tonnes in 2020 (up from 1.6 billion in 2000) and is expected to hit 6.08 billion tonnes by 2026.

"All the plastic produced over the past 60 years amounts to 8bn tonnes. The cement industry pumps out more than that every two years." - The Guardian, 2019

It is estimated that every 1000 kg of cement produced emits between 730-990 kg of CO2.

More than half of cement emissions come from clinker production. Clinker is the binding agent in cement and is produced by heating limestone and clay until they liquefy (1400°C-1500°C). This process is so emissions heavy because the heated limestone itself releases CO2.

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Clinker emissions = 50% CO2 released from limestone + 40% burning fuels to heat limestone + 10% mining and transportation.

Concrete

The most common use of cement is to make concrete, which is the 2nd most used material in the world (#1 is water). About 10 billion tons of concrete are produced every year and the most commonly used cement is Portland Cement, and concrete is rated by the amount of clinker contained within the cement, with the highest rating (for the strongest cement) at 95% clinker and 5% additives. Lower ratings contain less clinker.

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Modified from: How concrete is made

Clinker can be replaced, either fully or partially, with certain types of rock dust and industrial by-products. There has been resistance from the construction sector due to safety concerns (not technically proven to be as strong) and pricing (high cost to switch equipment and materials).

Regulations

Regulations based on Portland cement clinker properties are preventing the widespread growth of lower-emission alternatives.

  • Tests used to determine concrete strength are not always appropriate for alternative clinkers and cement. Concrete is tested for strength at 28 days but alternatives can take longer to develop the same strength and durability characteristics. (According to concrete expert)
  • Europe
    • There are regulations on the type of cement that must be used based on the environment it will be used in (temperature, water exposure, etc) and the type of structure.
      • Eurocode 2 specifies the technical requirements of concrete structures in Europe.
  • United States
    • In 2021, California became the 1st US state to pass a law requiring cement carbon emissions to be cut. The goal is to reduce emissions per ton by 40% below 2019 levels by 2035.
    • 5 firms control 43% of cement manufacturing and 5 of the 11 committee positions at the ASTM Cement Committee (develops cement standards) are held by reps from large cement corporations.
    • There are some concerns over the types of investments going to novel cement companies and that large tech and oil companies are putting themselves in a position to monopolize and regulators have been called on to step in and keep the industry competitive.

Reducing emissions

The cement industry is already at maximum energy efficiency, and so emission reductions will need to come from other areas. If the world were to reduce the clinker-to-cement ratio, it could save 364 million tonnes of CO2 from being emitted, but this isn't the only way to reduce emissions from cement.

  • The Global Cement and Concrete Association (GCCA) released a roadmap in Oct 2021, pledging to reach net-zero emissions in concrete production by 2050. The GCCA represents 80% of cement manufacturers outside of China (55% of all cement production happens in China).
    • Under this proposal, 36% of CO2 savings will come from carbon capture and storage in cement plants and only 9% from using clinker substitutions and alternative cement.
    • Aiming for 20% in CO2 reduction from cement production by 2030.
  • The Portland Cement Association (PCA) has called for cement and concrete specifications in the US that have performance specifications (built for the usage demands of the building) rather than prescriptive.
    • Ex: A high-rise building won’t be occupied for 8-months, so they could use a 56-day blend rather than the 28-day blend (allowing for blended cement and clinker substitutes).
    • The PCA is led by dominant cement corporations and promotes Portland cement through extensive lobbying.
  • The Netherlands is a good example of successfully using clinker composites. Most of the cement used there is less than 64% clinker and they have been incorporating slag into concrete production since the 1920s, mainly in marine environments. Regulations around industrial waste disposal have encouraged collaboration between waste producers and cement companies.

Clinker substitutes (for blended cement)*

  • Slag: Byproduct of the steel industry that can replace 70-80% of clinker in concrete.
  • Fly ash: Byproduct of the coal industry that can replace up to 25% of clinker in concrete. As coal use goes down, this supply will too.
  • Pozzolans: silicate-based materials like volcanic rocks and ceramic residues; can replace up to 40% of traditional portland cement in concrete.
  • Alkali-activated binder technologies (AAM): aka geo-polymers. Regional availability is limited due to the required materials. Generally not used in structural applications. Has the potential to be chemically superior to Portland cement (resistant to sulfate and acid attack, higher fire resistance, protect steel from corrosion).
  • Calcined clay + ground limestone: Inexpensive and widely available, can be sourced locally, but calcined clay still requires heating (about 800 deg versus 1400 needed for clinker) and the grinding process for limestone is very energy-intensive.
  • Agriculture and aquaculture waste: Needs more research, but the ash produced from burning this waste for fuel is a potential clinker substitute due to high silica content. Candidates: rice husks, corn cobs, wood, shells (oyster, mussel, and even eggshell).

Non-clinker alternatives (novel cement)*

  • Super sulfated cement: Contains 75%+ industrial waste and can be made without clinker. Resistant to a form of concrete degradation known as "sulfate attack" where sulfate in water causes leaching of calcium hydroxide from limestone-based cement.
  • Magnesium-based: Uses carbon-free magnesium silicates. Possible to even absorb CO2 (yielding net negative emissions). Still in the R&D phase. One company tried to commercialize it (Novacem) but they ran out of funding in 2012.
  • Biocement: Microorganisms precipitate calcium carbonate that binds grains of sand together creating a solid mass.

Alternatives to the alternatives*

  • Carbon capture and storage: CO2 is released from limestone during clinker production, no matter the energy source. A project in Norway is capturing CO2 and shipping it to offshore underground storage; they anticipate being 100% carbon neutral by 2024.
  • Carbon negative aggregates: Captured CO2 is converted into a solid product and used in place of rocks or sand in concrete.
  • Alternative fuels: 70% of global cement is produced using coal, and another 24% using oil and natural gas.
  • Performance optimization: Designing concrete around its function can reduce the amount of cement, clinker, or even total concrete necessary to perform.
  • Self-healing concrete: Certain bacteria, chemicals, nanomaterials, and even fungi can be used to allow concrete to self-repair cracks (reducing the need to repair and replace).

*This is a small snapshot of some of the alternatives available. They don't necessarily address the climate impact we've outlined above and it is not a comprehensive list or a suggested list of solutions. If you've come across any great alternative solutions that aren't listed here, and are addressing the climate impact explored above, please feel free to get in touch.

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Last updated: Oct 2022