July 20, 2024

New Self-Healing Concrete System Utilizes Bacteria-Infused Fibers

In a groundbreaking development, researchers from Drexel University’s College of Engineering have created a new method to improve the durability of concrete. By turning reinforcing fibers into a living tissue system, the research team aims to produce concrete structures capable of repairing their own cracks. This innovative approach involves embedding a grid of polymer fibers called BioFibers within concrete structures. These fibers are encased in a bacteria-laden hydrogel, as well as a protective, damage-responsive shell. The BioFibers can improve the durability of the concrete, prevent crack propagation, and enable self-healing.

The research team’s findings, recently published in the journal Construction and Building Materials, demonstrate how this method draws inspiration from nature to enhance building materials. Amir Farnam, an associate professor in the College of Engineering and leader of the research team, emphasizes the significant impact this development could have on the construction industry. Aging concrete structures often suffer from damage, reducing their lifespan and requiring costly repairs. Farnam envisions a future where concrete structures can heal themselves, similar to how our skin and tissues naturally repair damage through a fibrous structure infused with self-healing fluid.

Extending the lifespan of concrete is not only beneficial for the building sector but also important for reducing greenhouse gas emissions worldwide. The process of producing concrete ingredients, which involves burning minerals like limestone, clay, or shale at high temperatures, currently accounts for 8% of global greenhouse gas emissions. Concrete structures can degrade within 50 years, depending on environmental conditions. With constant replacements and increasing demand for new buildings, concrete is the most consumed and sought-after building material globally.

By developing concrete that can last longer and self-heal, the contribution of concrete to global warming can be significantly reduced, along with long-term infrastructure repair costs. Recognizing the potential, the U.S. Department of Energy has initiated efforts to improve concrete production. In the past decade, Drexel University has been at the forefront of research to enhance the sustainability and durability of concrete. Farnam’s lab is participating in a Department of Defense initiative aimed at fortifying aging structures.

The concept of bio-self-healing cementitious composites has been nurtured within the Advanced Infrastructure Materials Lab at Drexel University. Mohammad Houshmand, a doctoral candidate in Farnam’s lab and the lead author of the research, highlights the interdisciplinary nature of the BioFiber project. The endeavor brings together expertise from civil engineering, biology, chemistry, and materials science to pioneer the development of a multifunctional self-healing BioFiber technology.

The inspiration for creating BioFibers came from the self-healing capability of skin tissue and the role of the vasculature system in aiding organisms in healing wounds. The research team developed a biological technique to enable self-repair in concrete infrastructure through biomineralizing bacteria. Collaborating with various research teams within the College of Engineering, the group identified Lysinibacillus sphaericus bacteria as a bio-healing agent for the fiber. This bacteria, commonly found in soil, can drive microbial-induced calcium carbonate precipitation, forming a stone-like material that stabilizes and hardens to repair exposed cracks in concrete.

The bacteria can survive harsh conditions by forming an endospore inside the concrete, remaining dormant until activated. Caroline Schauer, the Margaret C. Burns Chair in Engineering, describes the strength of this research as a result of the diverse expertise of the team members. The selection of the right combination of bacteria, hydrogel, and polymer coating was critical to the functionality of BioFiber. While drawing inspiration from nature is one thing, accomplishing an application composed of biological ingredients that coexist in a functional structure required a multifaceted team of experts.

To assemble the BioFiber, the team coated a polymer fiber core capable of stabilizing and supporting concrete structures with an endospore-laden hydrogel. The entire assembly was encased in a damage-responsive polymer shell, resembling the structure of skin tissues. Placed in a grid pattern throughout the concrete during pouring, the BioFiber acts as a reinforcing support agent. It reveals its true abilities when a crack penetrates the concrete and pierces the fiber’s outer polymer shell.

As water finds its way into the crack, it reaches the hydrogel within the BioFiber, causing it to expand and push out of the shell toward the crack’s surface. Simultaneously, the bacteria are activated from their endospore form in the presence of carbon and nutrients. Reacting with the calcium in the concrete, the bacteria produce calcium carbonate, which fills the crack and acts as a cementing material, repairing it completely.

The healing time depends on the size of the crack and the activity of the bacteria, an area the research team is studying. However, initial indications suggest that the bacteria could complete the repair process within one to two days.

Farnam emphasizes that there is still work to be done in understanding the kinetics of self-repair. However, the findings suggest that this method is a viable means of preventing crack formation, stabilizing existing cracks, and repairing them without external intervention. BioFiber holds the potential to create “living” concrete infrastructure, significantly extending its lifespan and reducing the need for expensive repairs or replacements in the future.

1. Source: Coherent Market Insights, Public sources, Desk research
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