Nondestructive electrical conductivity test detects alkali-silica reaction in concrete

May 4, 2022, 9:30AMNuclear News
Alkali-silica reaction was confirmed at the Seabrook nuclear power plant in 2010. (Photo: NextEra Energy Resources)

Concrete structures built to last for decades, including reactor containment buildings and other nuclear power plant structures, are subject to the alkali-silica reaction (ASR), a reaction between alkali ions found in cement and silica, the two main components of concrete. The reaction forms a gel that absorbs water and expands over time, causing a buildup of pressure within the concrete that can eventually lead to cracking and deterioration.

Researchers at Argonne National Laboratory have successfully used electrochemical impedance spectroscopy (EIS) to detect ASR in the lab and believe it could be used for cost-effective, nondestructive testing at nuclear power plants.

Monitoring reactor concrete: Identifying and, if necessary, monitoring and mitigating ASR within nuclear plant structures is critical to the safety and relicensing of facilities for long-term operation. ASR was detected at NextEra Energy’s Seabrook nuclear plant in New Hampshire in 2010 using the conventional technique of extracting and examining concrete cores from potentially affected regions of the structure.

“All existing reactors in the United States are decades old, having mostly been built between 1970 and 1990,” said Argonne scientist Alexander Heifetz. “Accelerated testing of concrete mixes for ASR were less accurate in those times than they are today. These structures are getting into the zone where problems caused by ASR typically develop.”

Heifetz and his research team have discovered that EIS, which measures electrical conduction, could be used to detect ASR nondestructively.

How it works: Electrical conduction in concrete occurs via networks of pores that form during curing and contain ionic fluids. The gel that forms from ASR spreads to fill the gaps in these pore networks. The researchers believed that ASR could affect the ionic fluids within the pores, as well as the connectivity of the pore networks, changing the concrete’s electric conduction, which they could measure through EIS. While EIS has been used to indirectly measure the mechanical properties of concrete, this is the first time it has been used for nondestructive detection of ASR, according to Argonne.

“We basically found a way to characterize a material’s property based on its current conduction, and in the end, we see there is a correlation between the conduction and the presence and progression of ASR,” Heifetz said.

In the lab: Heifetz and his colleagues developed accelerated ASR in samples of concrete that were affected by ASR to varying degrees, and then used EIS to calculate the electrical resistance of the concrete.

“We have the potential to develop this into a technique that can be used on actual structures,” Heifetz said. “We’re working with industry to see if this approach can work on a greater range of geological samples than those used in our study, to hopefully advance its application.”

The research was funded by Argonne’s Laboratory Directed Research and Development Program and was published in the journal IEEE Transactions on Instrumentation and Measurement.

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