Climate change is a real issue, and today’s latest in materials science post is about a concrete strategy to combat greenhouse gas emissions. Today we are talking about an innovation that was inspired by nature to combat climate change. It involves the incorporation of carbon dioxide ingesting bacteria into concrete to create a carbon dioxide scrubbing concrete.
Implications of Climate Change and Carbon Dioxide Scrubbing
Climate change is one of the impending challenges that society has to address. With the rise of manufacturing and the increased release of carbon dioxide and other greenhouse gases, the earth’s overall temperature is rising. That means oceans are warming at alarming rates, glaciers and ice caps are melting, and weather events are a lot more extreme. These reasons and so many more make climate change a critical issue that society needs to develop strategies to combat. Today’s post is about a group of researchers looking for concrete solutions to this problem.
These researchers took bacteria and mixed it into the raw materials of concrete to make a new material that captures and stores carbon dioxide. If you want to learn a little bit more about concrete as a material and how these researchers developed this new concrete stay tuned.
What is Concrete and How is it Made?
Before we talk about this carbon dioxide scrubbing concrete’s specifics, let’s talk shortly about what concrete is and how it is made. Concrete is a composite material, which means that it is not just made up of one thing. It is actually a combination of several materials to give it its properties. The materials that make up concrete include sand and rocks, which are the reinforcing material, and then a binder to hold it all together, called cement. Cement is made out of a ceramic material called limestone or calcium carbonate, a rock type. It is cooked at really high temperatures to turn it into lime, calcium oxide.
Annual Concrete Production
This composite made of sand, rocks, and cement is actually one of the world’s most abundant materials, second only to water. About 10 billion cubic meters of concrete are produced each year. For context, making a single high rise building can take up to 40,000 cubic meters of concrete. The total annual concrete production equates to 250,000 high rises. Of course, that is not the only thing concrete is used for, but it just gives you an idea of how much concrete is made and used each year.
Carbon Dioxide Production from Concrete
And with all of that concrete being produced comes carbon dioxide production as a byproduct of the manufacturing process. The release of carbon dioxide accounts for more than 5% of the carbon dioxide released into the air each year. Specifically going back to the cement when cooked at those high temperatures, one of the byproducts of the chemical reaction is CO2. Additionally, the kilns, like ovens used to cook the material, need to be heated, and often fossil fuels are used to heat the materials.
Understanding Inherent Carbon Dioxide Scrubbing Properties of Concrete
However, concrete does not only emit carbon dioxide. It also has the ability to absorb some. In 2016 a group of researchers used computational modeling to determine how much carbon dioxide is absorbed by concrete each year. Computational modeling is a technique used by researchers to create a math equation to estimate something. These are very complex math equations developed using data that is present already or generated from experiments. Specifically for the study, we talked about these scientists who went worldwide and gathered information about concrete usage. Then they used that information in combination with a process called carbonation to determine how many greenhouse gases the world’s concrete absorbs.
Carbonation in Concrete
Carbonation is a process where carbon dioxide enters the tine holes in concrete and interacts with all of the chemicals and water trapped in the concrete. When the carbon dioxide interacts with the chemicals or water, it converts it to other chemicals like water or calcium carbonate.
Through their study, the researchers determined that the existing concrete in the world absorbs a little more than 40% of the concrete produced during cement manufacturing. This means that there is still 60% of the greenhouse gases produced from cement manufacturing. The other 95% of greenhouse gases produced from other cars and manufacturing activities still need to be addressed.
How the Carbon Dioxide Scrubbing Concrete is Made
So enter the carbon dioxide scrubbing concrete that a group of researchers developed at UC Boulder. A material scientist at the university of colorado Boulder named Wil Srubar developed concrete that contains bacteria that can pull the carbon dioxide out of the air into the concrete and then use it to grow and produce a mineral that toughens the concrete. This is a perfect example of using nature in engineering. The bacterial they used is called cyanobacteria, and it is commonly referred to as blue-green algae. Cyanobacteria has the ability to produce oxygen and has actually played a huge role in the composition of the atmosphere. Like huge as in we can breathe on Earth because of the oxygen cyanobacteria produces.
Mechanism of Carbon Dioxide Scrubbing
Using a process called photosynthesis and biomineralization, the cyanobacteria take in the carbon dioxide. With the by-products produced, calcium carbonate can form in the concrete when interacting with the other chemicals. This process allows the concrete the researchers developed to absorb carbon dioxide and convert it to strengthen the concrete.
Self-Healing and Regenerating Concrete
In addition to making the concrete stronger, it also gives the concrete the ability to reproduce. That’s right; you heard me this concrete could make baby concrete and even grand and great-grand baby concrete. The calcium carbonate that the cyanobacteria produce is a critical ingredient in cement, the concrete binder. Hence, the researchers could spill the concrete and then grow new concrete bricks. In their laboratory experiments, they split the bricks a total of 3 times. From the original brick, they were able to make 8 bricks.
Limitations of the Living Bacteria
Although this is a really cool innovation, there are some limitations. The other bacteria and microbes that the cyanobacteria would be exposed to in the real world is one challenge. If the concrete comes in contact with a bacteria that is stronger or grows faster than the cyanobacteria, it could be overrun. If the cyanobacteria are eliminated the concrete’s ability to capture and store carbon dioxide. Additionally, the bacteria needs specific conditions to grow and thrive. Specifically, it needs humidity to survive, so this concrete would not work very well in drier environments. Despite these challenges, it is exciting to see scientists looking to nature for inspiration to solve global challenges.