Self-healing Cement

Mo Li is out to transform the cement industry which creates 8% of the world's carbon emissions. Li has created concrete that can heal itself and a process to produce cement with clean energy. Find out more about her concrete innovations in this episode. Mo Li is a Professor and Chair of the Department of Civil and Environmental Engineering at UC Irvine.

TRANSCRIPT:

[sound of crane]

NATALIE TSO, HOST:

That's the sound of a crane in a three-story high lab where they test pillars of cement for earthquake resilience. Concrete is the second most used substance on Earth, after water. And the cement industry creates 8% of the world's carbon emissions. That's why it needs an overhaul. And Mo Li is leading the way. She's a professor and chair of the Department of Civil and Environmental Engineering at UC Irvine.

Li wants to make concrete greener and smarter. One of her innovations is making it more like the human body — to be self-healing.

MO LI: So self-healing concrete is a concept that how about we transform concrete from a brittle material to a ductile material like metal? But the physics is concrete cannot just be stretched like metal. In order for concrete to be stretched without failure, we designed this very unique damage process into concrete, kind of like a seashell. It actually forms many, many small, tiny cracks hardly seen to human eye.

TSO: She explains how she designed her concrete to sense damage and heal its own cracks.

LI: To make self-healing happen, we also need to design the chemical composition in the concrete so that once you have a crack, the healing process got naturally actuated. The crack surface will have chemicals exposed to the air and water, and then chemical reaction started. It formed the new ingredients in the crack that fills the crack.

TSO: Li is working with California's Department of Transportation. Her lab has already created a concrete bridge slab that has healed itself.

LI: So we tested the full scale bridge slab 30 feet long, create the damage. We put it outside in the field conditions, and we proved the cracks are gone.

TSO: This technology could have a major impact on the cement industry.

LI: We don't need to keep, repair and maintain a concrete bridge deck or pavement. So overall, in terms of life cycle, it becomes more, more sustainable because we end up using less material.

TSO: Li is a national leader in self-healing materials, but that's not the only innovation happening in her lab. She also wants to recycle concrete

LI: To make concrete, we need to take everything from the earth. Cement you need to take limestone, clay from earth. To make concrete, we not only need cement, we also need sand and rocks. We take all of them from Earth as well. And then we use some water and we use small amount of chemicals. Because a huge volume is involved, there's limited resources on Earth.

TSO: But recycling concrete is not easy.

LI: It sounds fascinating, but the main challenge is like turning something old into the baby again. So it's against time, against nature Because when cement turns into concrete, there's chemical process there. How do we reverse it? So we can imagine we can crush concrete first, old concrete from demolition site, and then with the smaller pieces, we first ball it into particles. Then we analyze those particles and find out the status composition.

[sound of ball mill machine]

TSO: That's the sound of the planetary ball mill machine, which helps turn old concrete into powder. The ball mill enables them to control the size of the particles. Then the lab analyzes the powder for its properties and how to reuse it.

LI: With that understanding, we can do our magic — the chemical process, electrochemical process. We extract the mineral we want from the old concrete like calcium. We can extract other things like silica. Once we have the process to extract those ingredients out of it, and then we can see how we can return it into a fresh cement. So that's really a cradle to cradle approach.

TSO: Her lab has been working with companies like Mitsubishi who supply raw materials.

LI: We want to turn it into higher performance materials. So that is the main philosophy we have that is different from the other type of recycling — smartly redesigned into something even better.

TSO: Another breakthrough she's made is electrifying the production process of cement so it doesn't use fossil fuels. She and her partner, UCI Professor Iryna Zenyuk, created an electrochemical process powered by clean energy that greatly reduces carbon emissions.

They're working with industry to bring their greener process to market. Li’s vision is to transform the cement industry.

LI: My ultimate dream is to create a building, a built environment that is more durable, more sustainable and more bea