We literally live immersed in concrete. Modern cities rest on this gray substance that constitutes the invisible skeleton of our lifestyle: buildings, streets, sidewalks, bridges. It is cheap, durable, reliable. But behind this apparent solidity lies a huge problem. Cement is responsible for around 8% of global CO₂ emissions. An impressive fact: if it were a state, it would be the third largest emitter in the world, immediately after China and the United States.
For decades we have accepted this compromise as inevitable, almost as if it were the price to pay for modern civilization. Yet, according to some researchers, it is not at all certain that it has to be this way.
From air to stone
Professor Nima Rahbar, together with his team at the Worcester Polytechnic Institute (WPI), decided to question the entire cement production paradigm. The result is an innovative, economical, resistant and above all carbon negative material, capable of removing CO₂ from the atmosphere instead of releasing it.
To understand the scope of the discovery we must start from the traditional process. Producing cement requires extracting limestone, crushing it and firing it in kilns that reach 1,450 degrees Celsius. An energy-intensive operation that consumes enormous quantities of fossil fuels. Added to this is an inevitable chemical problem: when limestone is heated, it directly releases CO₂. On average, each ton of cement generates almost a ton of carbon dioxide.
The Rahbar team chose a completely different path, taking inspiration from nature. Bones, shells and solid biological structures form without extreme temperatures. The secret? Enzymes.
Building with enzymes
Enzymes are biological catalysts: proteins capable of accelerating chemical reactions that would otherwise take a very long time. In this specific case, WPI researchers used an enzyme called carbonic anhydrase, present in almost all living tissues, including red blood cells, where it helps our body transport carbon dioxide to the lungs.
In the laboratory, however, this enzyme changes jobs. It captures CO₂ from the air and makes it react with calcium, quickly generating calcium carbonate crystals, i.e. limestone. The fundamental difference is that this limestone is not extracted from the ground: it is “cultivated” directly between the grains of sand.
The process continues with the addition of sand and hydrochar, a carbon-rich material obtained from organic waste. Hydrochar functions as internal armor, comparable to steel rod in reinforced concrete. Everything is assembled using a technique called capillary suspension, which uses the same principle that makes a wet sandcastle stable: the liquid bridges between the grains hold the structure together until final solidification.
The result is Enzymatic Construction Material (ESM), a true biological cement that binds quickly, becomes solid in a few hours and traps carbon inside.
Resistance, water and exposure times
In the construction sector, innovation is not enough: only two fundamental factors count. Duration and costs. Labs are full of fascinating materials that don’t stand the test of the real world. According to the data provided by the researchers, the ESM holds all the cards in order. The compression tests speak for themselves: 25.8 MPa, a value that exceeds the 25 MPa threshold, considered the minimum standard for structural concrete used in residential and commercial buildings.
The behavior in the presence of water has also been carefully studied. Many biomaterials degrade rapidly with moisture, but thanks to the hydrochar structure, ESM maintains its shape and stability even after repeated exposure to water.
Another decisive advantage concerns timing. Traditional concrete takes up to 28 days to reach maximum strength. A long wait, which translates into costs and delays. ESM biological cement, on the other hand, reaches full strength in less than 24 hours. A detail that is anything but marginal, especially in emergency contexts or in areas affected by natural disasters, where rebuilding quickly means saving lives.
If the economic accounts still depend on the industrial scale, the environmental numbers are already very clear. Each cubic meter of traditional concrete produces on average 330 kilograms of CO₂. ESM, by contrast, absorbs 6.1 kilograms of CO₂ per cubic meter. The transition from +330 to -6 represents a radical turning point. In a world where the cost of carbon is increasingly monetized, a carbon negative material immediately becomes competitive from an economic point of view.
As Rahbar himself stated, cement is the most used construction material in the world, and its production weighs enormously on global emissions. ESM doesn’t just reduce impact: it actively captures carbon, offering a concrete, practical and scalable solution.
Sprayable, pourable and repairable
The WPI team designed the ESM with practical use in mind. It can be sprayed or poured into molds, adapting to existing building processes. Plus, it’s repairable, a huge plus for infrastructure maintenance, where cracks in traditional concrete are a costly and complex problem.
True, the construction industry is historically conservative. Companies and designers tend to trust what they know. But for the first time, there is a credible alternative to traditional concrete, capable of responding to structural needs and, at the same time, the climate crisis. The gray era of concrete may indeed have reached a turning point. And in its cracks, this time, something green might grow.
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