A Concrete Revolution

It is the material that symbolises modernity: ubiquitous, durable, and affordable. However, it is also one of the most polluting materials in the world. A pillar of global development, it is responsible for 7% of global CO2 emissions.

It is the concrete of the future evolving to become sustainable and durable, capable of self-repair by sequestering carbon dioxide from the atmosphere.

Concrete is a key material in the construction of the built environment. Along with its main binder, cement, it is the essential building material that provides society with its foundations. Infrastructure, buildings, water and energy networks – without this material, the growth of modern societies would be unthinkable.

Its intrinsic properties, such as durability, resilience to climate and natural disasters, affordability, widespread availability, and versatility, underpin its extensive use. It is no coincidence that, according to a UNOPS (United Nations Office for Project Services) report, the built environment supports society in achieving 92% of the 169 targets of the 17 UN Sustainable Development Goals.

This figure considers all aspects of the built environment (infrastructure for water, waste, energy, transport, and digital communications; buildings and structures) and highlights the central role of the cement sector in achieving most of the Sustainable Development Goals.

However, the increased concrete production results in higher CO2 emissions into the atmosphere, at least until this trend is reversed through innovation and research.

The aim is not only to reduce emissions, but to produce concrete that absorbs more CO2 than it emits – a goal that no longer seems so unattainable.

A new generation of concrete is emerging, thanks to studies conducted in the United States. Professor Mehdi Khanzadeh, an engineer at Temple University, has developed an innovative method called “internal-external CO₂ curing,” which significantly increases the depth of carbonation in concrete. Traditional concrete uses cement, a key ingredient that emits significant amounts of CO₂ when limestone is heated to produce clinker. With this method, CO₂ is incorporated and reacts with other compounds in the concrete to form stable carbonates, which enhance the material’s durability and strength.

According to the study, mechanical performance and durability can improve by 80% to 100% compared to existing technologies. This qualitative leap could make these concretes suitable for beams, columns, and load-bearing structures, overcoming the limitations that have so far confined them to non-structural elements.

Another line of research comes from Northwestern University. The team, led by researcher Alessandro Rotta Loria, has developed a process inspired by the natural formation of coral and mollusc shells. By combining electricity, seawater, and carbon dioxide, they obtained solid minerals such as calcium carbonate and magnesium hydroxide, capable of storing up to 50% of their weight in CO₂. These materials can replace sand and natural aggregates in concrete formulations, helping to reduce the impact of mining activities in rivers, seas, and mountains.

Furthermore, the process produces hydrogen as a by-product, a clean energy source that can potentially be reused in the production cycle. The innovative aspect is clear: transforming CO₂ into sustainable building components directly near industrial plants, taking advantage of the proximity to coastlines. This approach could pave the way for carbon-negative buildings that absorb carbon dioxide rather than emit it, while simultaneously reducing pressure on ecosystems by reducing the use of sand and natural aggregates.

Other research is also exploring complementary solutions. For example, a study published in Science examines the permanent trapping of tonnes of CO2 not only in cement but also in other building materials.

It also analyses the possibility of adding biochar, a substance produced by controlled heating (pyrolysis) of biomass. The aim is to permanently store the carbon dioxide that plants have absorbed and converted into stable carbon-based compounds throughout their lifetimes. Using the same principle, biomass fibres could be used to produce bricks, asphalt, plastic, and other building materials.

The most promising materials identified are cement, asphalt, and bricks, especially given their widespread global use. One challenge this technology may face is the supply of raw materials. The distribution of mineral oxides capable of reacting with carbon dioxide to form stable carbonates is not uniform worldwide.

Some are pushing innovation even further. At the University of Colorado, a team of researchers has developed a “living” concrete based on cyanobacteria’s (algae’s) photosynthetic ability. This material is not only self-repairing but also capable of reproducing: by breaking a brick in half, the bacteria migrate and “grow” two new bricks using sand as nourishment. It is literally a “mother” brick that generates “daughter” bricks.

If these innovations pass the technical and environmental validation phases, we could see the introduction of a new construction standard: an active concrete that contributes to the fight against climate change without sacrificing the strength and reliability that make it the most widely used material in the world.

Alice Masili