Researchers discovered that cement, historically pointed out as one of the major carbon emitters, actually has an unexpected facet.
According to a study by the Massachusetts Institute of Technology (MIT), urban infrastructures in the United States and Mexico absorb millions of tons of CO₂ each year.
The analysis, published in Proceedings of the National Academy of Sciences, revealed that cement can do this through a natural process of carbonation.
Thus, the finding challenges the traditional narrative about this ubiquitous construction material.
First national-scale measurement of CO₂ capture
The MIT team, led by Hessam AzariJafari and Randolph Kirchain, conducted the first measurement of carbon capture derived from the carbonation process in cement on a national scale.
Traditional global inventories offer very simplified estimates that are far from empirical reality.
The developed model integrated data bases of cement production, hundreds of urban building archetypes. It also included information on the life cycle of infrastructures.
The results showed strong figures: in the United States, the amount of CO₂ absorbed by cement in buildings and roads exceeded 6.5 million tons annually.
This figure is equivalent to 13% of the emissions generated by the manufacture of this material in that country.
In Mexico, absorption rose to 5 million tons per year, about 25% of the CO₂ emitted by the national cement industry.
How the study discovered this secret capacity of cement
To achieve a rigorous estimate, the MIT team refined existing methodologies. Additionally, they left behind the generic factors that tend to overestimate or underestimate the true capture capacity.
The model considered:
- the diversity of cement products (from concrete to mortar and blocks);
- the geometry of streets and houses, and;
- the type of environmental exposure of each structure.
AzariJafari explained that “the carbon capture depends on variables that until now had not been taken into account in sufficient detail”.
He added that not only should “the type of cement be considered, but also the design, climate, location, and auxiliary materials such as mortar”.
The researcher noted that in the same city, two buildings can show differences of up to five times in their CO₂ absorption rate depending on these nuances.
Mexico vs United States: different construction practices
The comparative analysis between the two countries allowed for a revealing interpretation. Mexico uses approximately half the cement that United States does, but manages to capture three-quarters of the carbon absorbed by its northern neighbor.
The central reason lies in the higher proportion of mortar (looser and more porous) and the tradition of mixing cement on-site. These characteristics accelerate the chemical capture reaction.
The MIT warned that indiscriminately promoting carbonation can have side effects.
The exposure of structures to air increases the risk of corrosion of the reinforcing steel in reinforced concrete.
Design and maintenance strategies are required to maximize carbon absorption without reducing the lifespan of infrastructures.
Randolph Kirchain, one of the study’s directors, detailed the strategies to enhance capture:
- Increase the surface exposed to air
- Choose less dense mixes
- Opt for waffle type structural designs
- Avoid massive use of paint and coatings
However, each decision must be weighed against the possible impact on the durability of the material.
What this “power” of cement means for environmental policies
The work of MIT left a central warning for the sector and regulatory bodies.
Many national and international inventories overestimate carbon capture by applying generic factors disconnected from local empirical reality.
AzariJafari emphasized “the need to update environmental reporting systems to reflect the diversity of contexts and technologies”.
This approach can be replicated worldwide, adding data bases of buildings with national statistics and advanced modeling.
Cement, which until now was seen only as a major emitter, becomes a strategic tool within the roadmap for global decarbonization.
The conclusions of the MIT study represent a shift in the narrative about cement and its relationship with carbon.
Optimizing building design, refining reporting methods, and understanding the capture potential at the urban level are emerging as central priorities for the sector.
