Concrete is a material we encounter every day, from the sidewalks we walk on to the buildings we live and work in. It is an essential part of modern construction. However, the environmental impact of concrete production is staggering, contributing significantly to global carbon dioxide (CO2) emissions. In an innovative step towards a greener future, researchers at the University of Colorado Boulder, led by Wil Srubar, have developed a new type of concrete known as “living concrete.” This breakthrough uses bacteria to create concrete in a way that is not only sustainable but can also have a positive impact on the environment.
The Environmental Footprint of Traditional Concrete
Concrete is made primarily from cement, which, after water, is the second most-consumed material in the world. However, the production of cement is responsible for approximately 6% of global carbon dioxide emissions. The energy-intensive process of making cement involves heating limestone to create calcium oxide, which releases a significant amount of CO2. When mixed with water to form concrete, additional CO2 is produced during the curing process. As construction continues to grow globally, these emissions are expected to rise unless significant changes are made.
With the construction industry being one of the major contributors to environmental degradation, there is an urgent need for alternatives that reduce the carbon footprint of concrete production and use.
The Role of Bacteria in Concrete: A Step Towards Sustainability
While the idea of using bacteria in concrete is not entirely new, the recent developments in the field take it a step further. Previous studies have focused on using bacteria to help concrete repair itself by healing cracks as they form. These bacteria act as a self-healing mechanism, producing minerals that fill in gaps or cracks. However, the work done at the University of Colorado Boulder goes beyond this, exploring the potential of bacteria to create concrete that not only heals itself but is also more sustainable and carbon-positive.
The bacterium used in this research is Synechococcus, a type of Cyanobacteria, known for its ability to absorb carbon dioxide and release oxygen through the process of photosynthesis. This simple, yet powerful organism can contribute to making concrete a material that no longer harms the environment but instead contributes positively by absorbing CO2.
Synechococcus: The Bacterium Behind Living Concrete
Synechococcus belongs to the class of Cyanobacteria, which are among the oldest organisms on Earth. These bacteria are notable for their ability to harness sunlight, carbon dioxide, and other nutrients in the presence of chlorophyll. They then produce calcium carbonate, a compound commonly found in seashells and limestone, as a byproduct of their biological processes. This ability to absorb CO2 and convert it into a solid form of calcium carbonate directly addresses one of the key challenges of concrete production: its carbon emissions.
Cyanobacteria like Synechococcus can thrive in harsh conditions. They do not require a membrane-bound nucleus and can survive in environments with minimal nutrients or extreme temperatures, making them an ideal candidate for use in living concrete. Additionally, their process of reproduction—binary fission—means that one bacterium can multiply into two, allowing the concrete to grow and regenerate over time.
How Living Concrete is Made
To create living concrete, researchers at the University of Colorado Boulder combined Synechococcus bacteria with a mixture of gelatin, sand, and essential nutrients. This combination was placed into a mold, where the bacteria began to grow and perform their photosynthetic processes. Over time, the bacteria produced calcium carbonate crystals, which formed around the sand particles in the mixture. The result was a solid material with properties similar to traditional concrete.
The process is remarkably natural: the bacteria essentially “grow” the concrete. As the gelatin mixture cools, it solidifies, and the bacteria continue to work, creating a hard material capable of bearing loads. After the living concrete reaches a hardened state, it can be used just like regular concrete in construction. However, it differs in that it has the potential to continue growing if given the right conditions. By adding more sand and moisture, living concrete can generate new layers, creating more material from the same “parent” structure.
In one remarkable experiment, researchers were able to create eight new bricks from a single initial brick after three generations of growth. This regenerative ability sets living concrete apart from traditional materials, offering the possibility of self-replicating building materials that reduce the need for resource extraction.
The Advantages of Living Concrete
Living concrete offers several compelling advantages, especially in the context of sustainability and environmental impact:
- Carbon Capture and Oxygen Release: Unlike traditional concrete, which releases CO2 into the atmosphere, living concrete absorbs carbon dioxide and releases oxygen during the photosynthesis process. This makes it a carbon-negative material, helping to mitigate the very emissions caused by traditional cement production.
- Resource Efficiency: Living concrete has the potential to be produced in areas with limited resources. In remote or arid regions, such as deserts or even on other planets like Mars, where traditional construction materials might be difficult or costly to transport, living concrete could provide a solution. Its ability to grow and regenerate with minimal input makes it a promising material for off-world construction, potentially reducing the need for imported building supplies.
- Self-Sustaining Growth: One of the most exciting aspects of living concrete is its ability to continue growing as long as it is provided with the right conditions (sand, moisture, and nutrients). This means that structures could potentially “self-repair” or expand over time, reducing the need for constant maintenance or replacement.
Challenges and Limitations of Living Concrete
Despite its promise, living concrete is not without its challenges:
- Strength Limitations: While living concrete can replicate and grow, it still faces some limitations in terms of strength. For it to reach its maximum structural integrity, it must be thoroughly dried. This drying process can compromise the viability of the bacteria, which are no longer able to grow or reproduce in dry conditions.
- Environmental Conditions: Living concrete relies on certain environmental conditions, particularly humidity, to remain active and viable. In regions where moisture is scarce or where the temperature is too extreme, the bacteria may not survive, limiting the material’s global applicability.
- Strength Comparison: While living concrete can mimic some properties of traditional concrete, its strength is more comparable to that of mortar, which is weaker and not as durable. Further research and development are needed to improve the strength and performance of living concrete to make it a viable alternative to traditional building materials.
Conclusion: A Step Towards Sustainable Construction
Living concrete represents a groundbreaking advancement in sustainable building materials. By using bacteria to absorb carbon dioxide and produce a solid material, it offers a potential solution to the environmental challenges posed by the traditional concrete industry. Though there are still hurdles to overcome, such as improving the strength and viability of living concrete in diverse conditions, the concept holds great promise.
As the world increasingly looks for ways to combat climate change and reduce the environmental impact of construction, innovations like living concrete could help transform the way we build, offering a more sustainable and carbon-negative alternative to traditional materials. With continued research and development, living concrete could one day become a common building material, not just on Earth but also in places like deserts and even on Mars.