DecontaminationCleaning concrete contaminated with chemicals

Published 23 September 2016

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 to reduce that impact.

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 to 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.”

Sandia Lab says that the project, funded by Sandia’s Laboratory Directed Research & Development program, uses computer simulations to examine how chemical agents soak into and bind within concrete. The power of the simulations is that researchers can glimpse details they cannot obtain experimentally. Researchers can expose a concrete block to a chemical, try to clean it and then detect the remaining chemicals, but that does not allow them to watch what is happening on the inside, Tenney explained.

Decontaminating concrete is difficult because it is chemically and physically complex. Tenney said he and his team need details of the chemical interactions that occur in concrete so they can design new decontamination methods and mixtures.

Concrete’s nitty-gritty details
Concrete has been used since the Roman era and is everywhere: building foundations, sidewalks, even specialized underground seals and linings. But its ubiquity masks remarkable chemical complexity and physical intricacy, said Ed Matteo, a chemical engineer with expertise in cement durability.

Like a cake, the recipe for concrete can change depending on how spongy, or porous, it needs to be, but the major ingredients remain the same. Roasted and finely ground limestone and clay make up the “flour,” which is mixed with water to form the gluey “dough” called cement. Concrete is just cement with sand or gravel added to bulk up the mix. Other ingredients can be added to tweak properties, such as the time it takes to set.

On the chemical level, cement is made up of many minerals including aluminosilicates from clay, calcium oxide of quicklime and even potassium hydroxide from potash. But the most important component is amorphous calcium silicate hydrate, the “glue of the glue,” said Matteo. Cement loves