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Team Studies Concrete Moisture, Corrosion

Monday, November 28, 2016

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Sensing problems in concrete is the focus of ongoing research at North Carolina State University.

Researchers there have recently furthered their work with electrically conductive coatings that can sense problems in concrete, adding the capacity to sense corrosion-causing chemicals and moisture intrusion, and raising the possibility that the same technology could eventually be used on structural steel and other materials.

The team of engineers, headed up by Mohammad Pour-Ghaz, of the school’s Department of Civil, Construction, and Environmental Engineering, has been working for years on a “skin” that could use a process called electrical impedance tomography to identify structural issues in concrete before the human eye could see them.

EIT skin
Julie Williams Dixon, NCSU

The engineers use EIT to analyze the structural health of concrete by using electrodes on the conductive coating; through an algorithm, they can determine whether the skin is indicating discontinuity in the substrate.

The engineers use EIT to analyze the structural health of concrete by using electrodes on the conductive coating; through an algorithm, they can determine whether the skin is indicating discontinuity in the substrate. Pour-Ghaz and others published work on the topic in 2014, and an unrelated team at the University of Delaware recently published a new paper on a similar development.

The most recent news from Pour-Ghaz, working with NCSU’s Milad Hallaji, and the University of Eastern Finland’s Aku Seppanen, involves the addition of a secondary layer on the skin that could augment the technology with the ability to sense certain chemicals that might indicate problems.

Sensing Chlorides

The team’s research specifically involved a layer of copper nanomaterial that would react in the presence of chlorides, which cause corrosion in concrete. The new version of the “sensing skin” is made of the chemical-sensing layer, a buffer layer and the crack-sensing, conductive layer.

EIT skin imaging
Aku Seppanen

The team’s research specifically involved a layer of copper nanomaterial that would react in the presence of chlorides (indicated in the middle, copper layer, and translated into the small circle seen in the top left image). Cracks are indicated in the right image.

If the concrete structure itself is to be monitored for chlorides, the copper layer would be applied first to the substrate. If the goal is to monitor the air around the substrate for chlorides (or another chemical that the skin might be designed to detect), that layer would be applied to the outside, with the electrically conductive later applied first.

“We want people to be able to detect problems very early on,” Pour-Ghaz says. “And while this proof-of-concept looked at concrete, the technology—if properly applied—could be used on structural materials from metals to polymers.”

The corrosion-detection research was published in September in the journal Structural Health Monitoring.

EIT for Moisture Flow

Separate research from Pour-Ghaz, Hallaji and Seppanen, working with NCSU’s Reza Rashetnia and Danny Smyl, has recently looked at moisture intrusion, and whether EIT—the same technique used to sense cracks in concrete using the sensing skin—could also indicate whether and where moisture is flowing in the cracks.

Three separate papers published by the researchers this year—in Transport in Porous Media in August, in the International Journal of Heat and Mass Transfer in September, and in an upcoming December edition of Cement and Concrete Research—exhibit findings that EIT is a viable tool for analyzing moisture flow in concrete with noticeable cracks. The team says it has already been established that EIT can be used to measure moisture flow in undamaged concrete.

   

Tagged categories: Chlorides; Colleges and Universities; concrete; Corrosion; Cracks; Research

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