For the first time ever, the chemical mechanism by which CO₂ injected during cement paste mixing has been captured in real time.
This provides a molecular-level explanation of how CO₂ mineralization works in manufacturing, unlocking the opportunity to optimize concrete mix designs, reducing cement while protecting strength. It represents an important step toward production of lower carbon concrete to meet market demand while also delivering operational savings.
The evidence was published in a peer-reviewed study in the Journal of the American Ceramic Society, co-authored by researchers at the Massachusetts Institute of Technology’s Masic Lab and CarbonCure Technologies. The team used advanced in situ Raman microspectroscopy — a technique capable of identifying individual chemical phases as they form at the micron scale, smaller than a human hair. Observing CO₂-activated cement hydration unfold hour-by-hour over 24 hours, the researchers uncovered the molecular sequence behind the early strength enhancing effects of CO₂ in cement, concrete’s key ingredient. Rather than disrupting the material’s chemistry, CO₂ in early-stage hydration creates a tightly-linked binder microstructure.
Phase mapping and spatial analysis of hydrate and carbonate reaction products.Journal Of The American Ceramic Society
What was Discovered
When CO₂ is injected into cement paste during mixing, the research team found it does not simply fill pore space with calcium carbonate particles, as previously theorized.
“The research findings provide the strongest experimental validation yet of carbon mineralization in concrete, explaining how carbon utilization technologies help producers reduce cement content and costs while delivering consistent, high-performing concrete,” says CarbonCure CEO Yuliya Kravtsov.
Adding, “This science reaches far beyond a lab setting. It’s been commercially proven by our real-world, worldwide application across more than 11 million loads in projects ranging from residential construction to complex high rise developments and infrastructure builds.”
When CO₂ is injected into cement paste during mixing, the research team found it does not simply fill pore space with calcium carbonate particles, as previously theorized. Instead, CO₂ triggers a fundamentally different three-stage hydration sequence:
In the initial “Mineralization” stage (within four hours of CO₂ injection), CO₂ rapidly forms nanosized calcium carbonate particles, temporarily diverting calcium from its usual role and allowing a smooth, evenly distributed silica gel network to develop.
In the second “Transition” stage (4-8 hours), once CO₂ is consumed, normal hydration resumes as calcium hydroxide reacts with the silica gel network to form evenly distributed calcium–silicate–hydrate (C–S–H), the material that gives cement its strength.
During the “Stabilization” stage (after ~8 hours), hydration continues in a conventional manner, filling in the structure and producing a more uniform, interconnected binder that sets faster and achieves about 13% higher early strength.
Critically, the study also provides the first direct visual evidence of early age CO₂ mineralization, with calcium carbonate particles remaining chemically stable over time, “permanently sequestered within the matrix.”
The study also provides the first direct visual evidence of early age CO₂ mineralization.
Commercial Application
Carbon utilization technologies represent one of the most commercially scalable, near-term pathways for reducing embodied carbon in the built environment. CarbonCure's carbon mineralization systems are currently deployed at hundreds of concrete plants in more than two dozen countries. To date, these plants have used CarbonCure in more than 20,000 distinct mix designs, treating 350 distinct cements, 200 supplementary cementitious materials and thousands of admixture combinations in concretes ranging from 10 MPa to 100 MPa. By permanently mineralizing CO₂ in concrete, CarbonCure's producer partners reduce cement content in their concrete mixes by an average of about 4-6 percent, while maintaining equivalent performance and meeting high performance project specifications.
"This is a breakthrough for the industry’s understanding of carbon mineralization," said Dean Forgeron, Chief Technology Officer at CarbonCure. "This paper shows that CO₂ mineralization does more than permanently store CO₂ in concrete. It actively influences binder microstructure from the earliest moments of hydration. Industry can now leverage this chemistry to improve cement efficiency and their profitability while delivering the same high-quality products and meeting even the most demanding project specifications.”
"With in situ Raman microspectroscopy, we were able to watch the chemistry of carbon mineralization happen in real time."
—Professor Admir Masic, Department of Civil and Environmental Engineering, MIT
A New Chemomechanical Framework
The study resolves a long-standing question in cement science about whether calcium carbonate particles formed during CO₂–activation serve as nucleation sites for strength-building CSH. The Raman imaging reveals that they do not. Instead, C–S–H forms where silica gel meets portlandite — not on carbonate surfaces. The carbonates just happen to be collocated with C-S-H because they get embedded within the silica gel as it develops. This reinterpretation means that CO₂’s early strength benefits primarily come from how efficiently silica gel forms, which producers can control through dosage and mixing parameters rather than simply producing more carbonates.
"For years, researchers have observed that CO₂-activated concrete is stronger at an early age, but the precise mechanism has remained elusive because the phases involved are transient and difficult to observe directly," said Professor Admir Masic, Department of Civil and Environmental Engineering, MIT, and corresponding author of the study.
Adding, "With in situ Raman microspectroscopy, we were able to watch the chemistry of carbon mineralization happen in real time. What we found is a highly ordered, beautifully orchestrated sequence: CO₂ creates a silica gel scaffolding across the material, and that structure becomes the template for a more interconnected binder. These insights provide the concrete industry a new framework for improving concrete performance through CO₂ mineralization.”
