Lab Spotlight

Cleaning Chemically Contaminated Concrete

concrete decon Sandia

In March 1995, members of a Japanese cult released the deadly nerve agent sarin into the Tokyo subway system, killing a dozen people and injuring a thousand more.

This leads to the question: What if a U.S. transportation hub was contaminated with a chemical agent? The hub might be shut down for weeks, which could have a substantial economic impact. Craig Tenney, a chemical engineer at Sandia National Laboratories, is looking for better ways to clean contaminated concrete and reduce that impact.

“We can’t just rip out and replace the affected concrete—that would be too expensive,” said Tenney. “We need to decontaminate it and make it safe. The public has to be confident enough to come back and use the affected facility.”

The project uses computer simulations to examine how chemical agents soak into and bind within concrete. Simulations allow researchers to glimpse details they can’t obtain experimentally. Researchers can expose a concrete block to a chemical, try to clean it, and then detect the remaining chemicals, but that doesn’t allow them to watch what is happening on the inside.

Concrete is chemically and physically complex. It’s also intricately spongy, and thus very difficult to clean. It may not look like it from the outside, but concrete is full of microscopic pores that allow a concrete structure to grab onto chemicals and sometimes “breathe” them back out. That means that even if the concrete surface is cleaned, dangerous chemicals from an event could still be hiding deep inside.

To design new decontamination methods and mixtures, Tenney said, he and his team need details of the chemical interactions that occur in concrete.

Building upon Sandia’s longstanding expertise in molecular-scale geochemical simulations, they modeled several long-lasting, oily chemical agents to see how they react and move within tiny water-loving concrete pores—where they spend their time and how they degrade.

Building on that knowledge and his expertise in atomic-scale models of chemical reactions, Chris O’Brien, a computational materials science postdoctoral researcher, looked at how chemical agents degrade in concrete, modeling an agent bound to several representative concrete environments to see how this interaction hastened or slowed the natural breakdown process.

The team has determined how strongly various agents stick to concrete pores and which ones clump together. The next step is to find ways to suggest better decontamination mixtures.

Tenney would like to team up with geochemists to look at the larger picture. Using what they learned from the nanoscale models, they would watch how chemical agents soak into larger bits of concrete, still smaller than a human hair. Once they understand the transport of chemical agents in concrete, they can suggest decontamination mixtures that would move similarly, following an agent to its hiding place within the porous concrete.

Computer models also allow Tenney’s team to screen and evaluate many different possible decontamination solutions more quickly than experiments. Eventually, the team hopes to validate these insights by testing new decontamination methods on concrete contaminated with sample chemicals.

Tenney said what they learn from the computational models could lead to more accurate field tests that accurately determine the areas impacted by an event and whether the cleaning was effective.

“It would be great from a scientific perspective to just understand what’s going on, but from an engineering point of view, it would also be darn nice if we could take that understanding, tailor our approach for decontamination and make it better,” said Tenney. “If the unfortunate (event) ever does happen, at least we (will be) prepared.”

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