For more than a century, concrete has been the foundation of our modern civilization’s infrastructure with a stoic permanence. But that strength comes at a cost. Concrete, and the cement that binds it, is one of the world’s dirtiest building materials, responsible for about 8 percent of global carbon dioxide emissions. If the cement industry were a nation, it would rank fourth in emissions, just behind China, the U.S., and India.

A new study, led by civil and environmental engineer Mehdi Khanzadeh at Temple University, proposes a method that could radically cut the carbon footprint of concrete, while making it stronger and more durable in the process. “If we can address limitations through the method we are proposing,” Khanzadeh said, “then we can open a much larger portion of our industry to implement carbonatable systems.”

From Carbon Source to Carbon Sink

Traditional concrete relies on a chemical reaction between cement and water, a chemical process known as hydration. But Khanzadeh’s research focuses on carbonatable concrete, an alternative material that reacts with carbon dioxide rather than water in a process called carbonation. This means the material can absorb CO₂ during curing, effectively trapping greenhouse gas inside walls and structures.

There’s a catch: carbonatable concrete doesn’t currently work well for large-scale construction. It’s mostly used for small non-structural units, like concrete masonry blocks (CMUs), because the CO₂ it absorbs only penetrates the surface. That shallow depth of carbonation limits its strength.

Khanzadeh has spent the last four years chipping away at this problem. Now, he believes he’s found a solution.

His new method, described in a paper published in ACS Sustainable Chemistry & Engineering, combines internal and external CO₂ curing, using a clever upgrade: enzyme-infused hydrogels embedded inside the concrete mix.

These tiny hydrogels carry an enzymatic solution that mimics processes seen in nature, specifically the catalytic behavior of the urease enzyme, which triggers the formation of calcium carbonate crystals. When CO₂ from the outside enters the concrete, it meets the enzymatic solution inside. The result is a cascade of crystallization reactions that push deeper into the material.

In lab tests, this method improved mechanical and durability performance by 80 to 100% compared to current carbonatable systems. Even more striking, calcium carbonate formation reached 15 times the amount observed in standard concrete blocks, approaching the theoretical maximum for this material.

Will It Scale Beyond the Lab?

Concrete’s ubiquity is both a curse and an opportunity. Any improvement to its carbon profile could have massive environmental benefits, but the barrier isn’t just chemistry. Practical challenges abound.

Khanzadeh knows this. “I try to keep in mind, even if this is successful, is it going to be applicable?” he said. “Is this material going to be scalable? This is especially important for something like concrete. We use it so much, so it needs to be accessible everywhere.”

So far, he has advanced from testing liquid solutions to pastes, mortars, and finally full-scale concrete systems. Each step involved rigorous performance evaluations. His team is now working on scaling up the technology to test for cost-effectiveness, material availability, and real-world feasibility.

The study remains in the proof-of-concept stage. Khanzadeh is cautious about overpromising. More testing is needed to evaluate the concrete’s long-term durability and determine whether it can be carbon-neutral or even carbon-negative.

But he’s optimistic. The breakthrough offers a new pathway for the construction industry, one that might reduce carbon emissions without compromising the strength or reliability that buildings demand.

A Greener Foundation

As governments and industries race to decarbonize, the pressure is mounting to clean up “hard-to-abate” sectors like construction. Innovations in materials, like carbon-storing concrete, could help close the emissions gap.

Other carbonatable systems have been explored before, but most struggle with uneven carbonation or require specialized facilities to produce. By tackling the depth-dependent limitation head-on, Khanzadeh’s internal-external CO₂ curing process offers scientific novelty paired with industrial promise.

His method enables concrete to do what it has always done best: hold firm, but now, with less guilt beneath its surface.

Whether this innovation will leap from the lab to the skyline remains to be seen. But for now, in a world still struggling to balance progress with sustainability, the humble block of concrete may have just found a new reason to exist.