2021
_NATURE ENVIRONMENT

_Bacterial Prevention

Tiny bacteria could soon be chipping in to keep roads from chipping away in the winter.

_Amir Yaghoob Farnam

Farnam is an assistant professor in the Department of Civil, Architectural and Environmental Engineering in the College of Engineering

_Christopher Sales

Sales is an associate professor in the Department of Civil, Architectural and Environmental Engineering in the College of Engineering.

_Caroline Schauer

Schauer is associate dean of research and faculty affairs and professor in the Department of Materials Science and Engineering in the College of Engineering.

Compounds like calcium chloride — commonly called “road salts” — are commonly used to prevent ice and snow on winter roads. But road salts also cause potholes and road surface deterioration, because the chemicals react to form an expansive compound called CAOXY — short for calcium oxychloride — that can break down concrete by generating internal expansions and distresses.

Three researchers in Drexel’s College of Engineering — Amir Yaghoob Farnam, Christopher Sales and Caroline Schauer — have discovered how mixing a bit of bacteria called Sporosarcina pasteurii into concrete can reduce the formation of CAOXY.

Over the past decade bacteria like S. pasteurii have been studied as a way to repair cracks in statues and concrete infrastructure, and, more recently, as an environmentally sustainable option for making bricks.

salty_consequence

Road salts damage concrete by forming a chemical, called CAOXY, that causes cracks to form and wedge apart. Adding bacteria to the mix could prevent CAOXY from forming.

But the Drexel researchers realized that one of the bacteria’s other talents might also be quite useful for preventing those cracks from forming in the first place.

To test their theory, Sales and Farnam made a series of concrete samples using the type of cement commonly used in roads and added a mixture of S. pasteurii with the nutrients they need to survive.

The concrete mixed with the bacteria experienced almost no deterioration after exposure to the calcium chloride. In addition, the levels of CAOXY were much lower in the bacteria-laden samples, as a result of the microbial-induced calcium carbonate precipitation. The presence of calcium carbonate suggests that the bacteria’s interaction could also be used to strengthen the road surface, though this application would require more research, according to the team.

“The bacteria are capable of changing the micro-environment around them to create conditions to heal micro-cracks in the concrete,” Sales concludes.