Zero-emission cement refers to a type of cement manufactured with processes that minimize or eliminate the release of carbon dioxide (CO2) during its production. Cement production is traditionally a major contributor to greenhouse gas emissions, accounting for roughly 8% of global CO2 emissions. The bulk of these emissions come from two sources:
Calcination: When limestone (calcium carbonate) is heated to produce lime (calcium oxide), CO2 is released as a byproduct.
Fuel combustion: The high temperatures required for the process are usually achieved by burning fossil fuels.
Strategies for Achieving Zero Emission Cement
Alternative Materials:
Supplementary Cement Materials (SCMs) like fly ash, slag, and natural pozzolans can partially replace traditional Portland cement, reducing emissions.
Limestone Calcined Clay Cement (LC3), which combines calcined clay and limestone, uses less energy-intensive processes.
Development of geopolymer cements, which use industrial byproducts and alkali activation instead of limestone.
Innovative Processes:
Carbon Capture and Storage (CCS): Capturing the CO2 emissions from production and storing or repurposing them.
Electrification: Using renewable electricity for heating instead of fossil fuels.
Alternative Binders:
Products like magnesium-based cements, which can absorb CO₂ from the air during curing, resulting in net-negative emissions.
Recycling and Circular Economy:
Using recycled concrete and construction waste as raw materials.
Energy Efficiency and Renewable Energy:
Upgrading plants to improve efficiency and using renewable energy for operations.
Zero-emission cement is a critical innovation for achieving global climate goals, particularly in the construction industry, which relies heavily on cement for infrastructure development.
Zero-emission cement works by adopting processes and technologies that either prevent the release of carbon dioxide (CO2) during production or capture and utilize the emitted CO2. Here’s a breakdown of how different methods contribute to achieving zero emissions:
- Alternative Raw Materials
Instead of traditional limestone (CaCO₃), which releases CO₂ during calcination, alternative materials are used:
Supplementary Cementations Materials (SCMs):
Materials like fly ash, slag, or calcined clay replace a portion of Portland cement, reducing the amount of limestone required.
Magnesium Silicates:
Unlike limestone, magnesium silicates do not release CO2 during processing and can absorb CO2 during curing. - Carbon Capture and Storage (CCS)
This technology captures CO2 released during production and either stores it or uses it for other applications:
Capture:
CO2 is captured directly from the exhaust gases of kilns.
Storage:
The captured CO2 is compressed and stored underground in geological formations.
Utilization:
Captured CO₂ is injected into fresh concrete, where it reacts chemically to form stable calcium carbonate, becoming part of the concrete. - Electrification of Kilns
Traditional cement kilns burn fossil fuels for heat, emitting CO2. Electrifying the kilns and using renewable electricity eliminates these emissions.
Direct Electrification:
High-powered electric systems replace fossil-fuel combustion.
Renewable Energy:
Wind, solar, or hydropower provides the electricity needed for heating. - Alternative Cement Chemistries
Innovative chemicals reduce or eliminate emissions during production.
Limestone Calcined Clay Cement (LC3):
Combines limestone and calcined clay, which requires lower temperatures and emits less CO2.
Geopolymer Cement:
Uses industrial byproducts like fly ash or slag, activated by alkalis, instead of limestone.
Solidia Cement:
Utilizes a different chemical process that releases 30% less CO₂ and absorbs CO₂ during curing. - Recycling CO2 into Concrete
In processes like those developed by Carbon Cure, CO2 is injected into concrete during mixing.
The CO₂ reacts with calcium ions in the cement mix to form calcium carbonate.
This reaction permanently traps CO2 within the concrete, reducing the net emissions. - Energy Efficiency and Circular Economy
Energy Efficiency:
Advanced kiln designs and heat recovery systems reduce energy consumption.
Circular Economy:
Using recycled concrete aggregates and other industrial wastes reduces the need for virgin materials and energy-intensive processes.
Example of How It Works:
A plant producing zero-emission cement might:
Replace part of the limestone with calcined clay.
Electrify its kiln using renewable energy.
Capture the CO₂ from any remaining emissions and either store it underground or inject it into concrete.
Use recycled materials to minimize waste and raw material demand.
By combining these methods, the cement production process becomes significantly cleaner and closer to net-zero emissions.
The development of zero-emission cement involves contributions from researchers, companies, and organizations worldwide. While no single person or group “invented” the concept, significant progress has been made by several key players and innovators in the field. Here are some notable contributors:
Academic Researchers
Institutions like MIT, UC Berkeley, and ETH Zurich have been at the forefront of research into alternative bindings, supplementary cementation materials (SCMs), and carbon capture technologies in cement production.
Karen Scrivener and her team at EPFL (École Polytechnique Fédérale de Lausanne) in Switzerland are known for pioneering work on limestone calcined clay cement (LC3), which reduces emissions significantly.
Companies
Carbon Cure Technologies:
This Canadian company developed a method to inject captured CO2 into concrete during production, where it mineralizes and becomes a permanent part of the concrete.
Solidia Technologies:
Based in the U.S., Solidia produces cement that absorbs CO2 during curing, reducing emissions by up to 70%.
Calix:
An Australian company that uses electric-powered reactors to separate CO₂ during calcination, enabling carbon capture.
CEMEX and Heidelberg Materials:
These global cement giants are investing in carbon capture, utilization, and storage (CCUS) as well as low-carbon concrete products.
International Collaboration
The Global Cement and Concrete Association (GCCA):
This industry group is committed to achieving carbon neutrality by 2050 and funds research into zero-emission cement technologies.
Mission Innovation:
A global initiative of governments and organizations working to accelerate clean energy innovation, including sustainable building materials.
Early Pioneers in Carbon-Negative Concrete
Companies like Blue Planet Systems and Novacem have worked on carbon-negative technologies by using alternative raw materials and innovative curing methods.
The development of zero-emission cement is an ongoing global effort, driven by advances in materials science, chemical engineering, and climate policy.