By Jose Vera Agullo, Head of the Concrete Group of ACCIONA’s Construction Business
Concrete has been in use for more than two millennia, dating back to when the Romans employed a similar material known as opus caementicium.
Its durability, versatility, and ease of transport make it difficult to replace, especially in large infrastructure projects like bridges and tunnels where it is essential.
However, the production of concrete has a significant drawback—its manufacturing process is carbon-intensive, particularly in the creation of clinker, a key ingredient.
The question arises: is it possible to produce a greener, more sustainable version of concrete? Progress in this field is already underway, with both experimental techniques and proven methods offering various ways to reduce emissions.
But what is precisely the clinker?
Clinker is a crucial element in cement production, and cement, in turn, is an essential component of concrete. It is produced by heating a precise mixture of raw materials—mainly limestone (calcium carbonate) and clay—at extremely high temperatures, typically between 1,400 and 1,500 degrees Celsius.
During the heating process in a rotary kiln, the raw materials undergo chemical reactions, producing small gray pellets or nodules known as clinker. These nodules contain the primary compounds that give cement its binding characteristics: calcium silicates and aluminates.
Once cooled, clinker is ground into a fine powder and mixed with a small amount of gypsum to create cement. Gypsum controls the cement’s setting time when it is combined with water. The most commonly used cement in construction is Portland cement, derived from this process.
Clinker production is responsible for significant carbon emissions. About one-third of CO₂ emissions stem from the extensive energy consumption during the calcination and grinding processes, while the remaining two-thirds result from the chemical decarbonation of limestone during production.
Some strategies to lower concrete’s carbon footprint
Several methods are currently being implemented to create low-emission green concrete. Alongside recycling initiatives, the following approaches are considered among the most impactful:
- Substitution of clinker with alternative materials: One of the most common solutions involves replacing clinker with materials such as fly ash or blast furnace slag. While this substitution is not complete, it significantly reduces emissions compared to traditional concrete. The complete elimination of clinker is possible through the use of geopolymers, though this technology remains in its early stages.
- Functional concretes that absorb carbon dioxide: Research is being conducted into concretes capable of absorbing CO₂ throughout their lifespan. This is achieved through compounds like mineral admixtures, which capture atmospheric carbon dioxide, or by injecting CO₂ into the concrete during production, allowing the gas to be stored within the material.
- Other actions that contribute to a net zero future: Below you can see the impact of each strategy. The interesting thing about the 22% you see in the image is that it depends on us as an engineering/construction company. And the 11% of the Efficiency in concrete production sometimes also depends on us. Other things depend more on the cement companies, like the biggest one is CCUS (carbon capture, use and storage) which is 36%.
