Concrete may seem strong and permanent, but it can be surprisingly vulnerable to the elements. Now researchers at Drexel University have demonstrated a type of self-healing concrete embedded with “BioFibers” that use bacteria to patch up cracks as they form.
You don’t get to be crowned the world’s most-used building material without doing a few things right – concrete is easy to make, strong and, under ideal conditions, durable for long periods. But of course, the real world rarely plays to ideals, so concrete is exposed to constant weathering that can cause cracks. That’s when the real trouble starts, as temperature fluctuations force the cracks wider while moisture triggers various processes that can eat away at the concrete.
As such, concrete structures need constant maintenance, which can be costly and inconvenient, as well as increasing the (already large) environmental footprint of making the stuff. Finding ways to slow that deterioration could save a lot of headaches.
That’s where Drexel’s BioFiber comes in. These polymer fibers not only act as physical reinforcements, but they have an important double life as a self-healing mechanism. The fibers are coated with a layer of hydrogel that contains endospores – dormant forms of bacteria that can withstand extreme environments, then revive themselves when things become more comfortable. The hydrogel layer is then coated with a thin polymer shell.
BioFiber concrete can be used like any other, but its secret superpower only becomes apparent later, when and if it cracks. When water reaches the BioFiber, the hydrogel will expand and bust out of its shell, pushing up towards the surface. In the process, the slumbering bacteria are woken, and they begin feeding on carbon and calcium from the concrete around them. This produces calcium carbonate, a cementing material that fills and patches up the crack.
“This is an exciting development for the ongoing efforts to improve building materials using inspiration from nature,” said Amir Farnam, lead researcher on the team. “We are seeing every day that our aging concrete structures are experiencing damage which lowers their functional life and requires critical repairs that are costly. Imagine, they can heal themselves? In our skin, our tissue does it naturally through multilayer fibrous structure infused with our self-healing fluid – blood. These BioFibers mimic this concept and use stone-making bacteria to create damage-responsive living self-healing concrete.”
While the healing time may vary, the team says BioFiber seems to be able to patch up cracks in as little as a day or two. Previous studies have made self-healing concrete infused with bacteria, but one of the main challenges was in how to keep the microbes alive long-term, while the concrete is intact. Using the dormant endospores encased in hydrogel, beneath a protective polymer shell, could be the answer.
There’s still plenty of work left to do, but the researchers say that BioFiber concrete could eventually help reduce maintenance requirements of buildings, as well as the CO2 emissions from concrete production.
The research was published in the journal Construction and Building Materials.
Source: Drexel University
