Each time Mija Hubler drives through Denver she notices bridges patched with concrete and thinks about how such structures can fail.

Hubler, an associate professor in CU Boulder’s Department of Civil, Environmental and Architectural Engineering, envisions a future where concrete cracks are repaired deep within to prevent such failures. She and her team of CU Boulder researchers and partners are developing technology that infuses concrete with self-repair capabilities found in living organisms. 

“Bridges are just patched again and again,” Hubler says. “My dream is to extend the structures’ lifetime by integrating this technology into new and aging construction.”

The project, "Reinforced Concrete Repair by an Evolving Visualized Internal Vascular Ecosystem (RC-REVIVE)" research team, has landed a $10 million grant from the Defense Advanced Research Projects Agency (DARPA) Biorestoration of Aged Concrete (BRACE) program, which draws inspiration from networks of filamentous fungi and human vascular systems. 

The idea is that networks of cracks in concrete can naturally provide a pathway to facilitate internal healing, similar to the veins in human bodies. Creating a biological network within a structure will allow the team to introduce nutrients and organisms for concrete self-repair.

Led by Hubler, the research team includes Associate Professor Wil Srubar, Associate Teaching Professor Chris Senseney and Assistant Professor Srikanth Madabhushi as well as four researchers from Drexel University and North Carolina State University.

Leveraging cracked networks to extend a concrete structure’s lifespan has never been done before, Hubler says. The team’s approach has the potential to transform the maintenance and durability of concrete structures, reducing long-term repair costs, she adds.

The project’s immediate goal is to enhance the longevity of Department of Defense structures and airfield pavements. If successful, the project will not only prevent new damage, but also shorten repair time, reduce maintenance costs and extend the life of infrastructure. 

The 4.5-year research effort consists of a strategic track, focusing on long-term solutions for large, heavy structures such as missile silos and naval piers, and a tactical track for improving rapid airfield damage repair.

Susan Glairon sat down with principal investigator Associate Professor Mija Hubler to find out more about the project.                                                                                                                                                                                                                               
Why is this project important to you?
I have been studying the long term deterioration of large reinforced concrete structures since I was a graduate student. Reinforced concrete structures not only cost dollars, but also lives, because they fall apart much earlier than expected.

This project combines my work developing new living materials for structural applications with my extensive background in studying the deterioration of existing reinforced concrete structures. It’s an exciting project because it merges those two areas.

What’s different about this project?
Compared to other projects I've worked on that utilized bio approaches for engineering applications, this project specifically focuses on vascularization. We draw inspiration from the idea that concrete crack networks naturally provide a pathway, similar to the veins in our bodies. By creating a biological pathway within the structure, we can introduce nutrients and organisms, enabling self-repair capabilities. 

The bacteria will repair cracks through mineral deposition.

Why is the proposed method a better way to repair concrete?
Currently we repair concrete after the damage has reached the surface, but typically the damage begins subsurface. Patching the broken surface is not actually repairing the system. Our method addresses the damage from within, allowing more effective and lasting repairs.

Why are you looking at a bio solution?
Researchers across all disciplines of engineering are realizing the importance of collaborations with biology and bioengineering. In this project, we're exploring a combination of organisms that are either available in the wild or engineered to fulfill a specific purpose. 

How do  these organisms survive?
It depends on which organism. For a photosynthetic organism, light may be sufficient. For non-photosynthetic organisms, additional stimulants can be incorporated into the material to encourage them to grow or respond. You can also promote the growth of certain organisms with an electric field through a current applied to the system. 

How many years might an organism be able to make repairs?
It depends on the organism. We are putting these organisms in an environment they don't like to live in. Concrete is not an ideal habitat for any organism, so we plan to engineer coating and other technologies to help the organisms live longer. Additionally, we might need to periodically check on the vascular system and provide it with additional nutrients to support the organism’s existence. Our approach shifts the focus from yearly surface repairs to monitoring the health of the vascular network.

Is the research focused on repairing existing concrete or is it to prevent cracks in new concrete as well?
The first two years of the project primarily focuses on developing a bio-based repair technique. After this initial stage, the team will explore two potential applications. One application involves the underground repair of aged, reinforced concrete, including filling existing cracks, and mitigating corrosion from rebars. The other application focuses on repairing extensively damaged airfields, which is different because when an airfield is damaged, it results in regions of missing material. So our technology will need to be incorporated into a new repair material that resembles fresh concrete. We have design metrics aimed at determining the capacity of repaired sections to accommodate aircraft landings. CU Boulder is leading both applications. 

How will you assess the longevity of internal repairs?
We will assess the mechanical and chemical condition of the concrete along with the effectiveness of the biological repair system. That information will be used by our modeling experts to develop a numerical model that predicts the structure’s lifetime.

Will this technology be used just for military applications, or will the research be used to improve civilian roads and bridges?
While DARPA projects are often inspired by military needs, most technologies initially developed for one purpose may be used for other purposes as well. Although the project intends to address an array of challenges faced by the military, the resulting product could be utilized for civilian infrastructure as well.