Concrete fails and has a huge carbon footprint

Due to its enormous carbon footprint, concrete is at the center of many materials research studies: how to make products more climate-friendly, how industry can reduce its carbon dioxide emissions by 2050, how to use less concrete in general.

Concrete accounts for between 6% and 10% of all CO2 emissions, and now a team of international scientists, from Norway and Switzerland, as well as Canada and the United States, have a different idea on how to reduce the need for concrete in bridges and buildings. They hope they can hang on longer and stay where they are.

What they are asking for is a better and more accurate way to assess the fatigue and risk of failure of the steel present in the concrete used to build bridges and other structures. Better prediction of corrosion damage would lead to better safety, but it would also mean that some structures could stay in service longer because they no they must be replaced.

Like trees, they would continue to sequester their carbon inputs while avoiding any catastrophe.

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Chlorine-induced corrosion is the most common cause of structural failure, such as the collapse of a bridge in Pittsburgh in January or the catastrophic loss of the Champlain South Towers last year in Miami. Therefore, almost all existing prediction models used to assess concrete structures are based on this concept.

“The corrosion of steel in concrete is a complex phenomenon,” says Ueli Angst, material durability specialist at ETH Zürich in Switzerland. “In the generally very alkaline environment of concrete, where the pH can be above 13, the steel is considered passive, that is, it is covered with a thin layer of protective oxides and that its corrosion rate is negligible.”

However, concrete is porous. When exposed to salts, such as seawater or road salts, chloride ions can slowly work their way through the concrete, eventually reaching the steel. “At some point, the passive protective layer will be destroyed and corrosion can begin,” the researchers explain. “Depending on actual exposure conditions, corrosion may occur at a faster or slower rate.”

A New Way to Evaluate Concrete

What the researchers propose in their paper recently published in Applied Physics Review is a “time and space” approach that better considers the real context of the structure. Local data on relative humidity, temperature, precipitation or water splash, integrated with existing data on chlorides and other measurements, would provide greater accuracy.

“For many geographic regions of the world, high-quality meteorological data are available to describe exposure conditions,” the paper’s authors said. “To link these macroscopic exposure data to the microclimate on the site for specific situations,” they add, they must rely on “state-of-the-art surveillance systems, possibly supported by machine learning algorithms.”

Digital sensor systems could continuously monitor humidity, chlorides and pH while the bridge is standing. According to the authors, this would shift the focus to the mechanisms and factors that control the entire lifespan of a structure and advance the existing use of machine learning.

It would also change materials research, even as climate change heralds an accelerated challenge with humidity and associated exposures calling for moving away from the limits of chloride-based assessments.

“Despite extensive research, no clear threshold for chloride could be found, and the influencing factors are complex,” says Burkan Isgor of Oregon State University. “Unfortunately, mainstream research is still searching for this threshold, which presents a significant obstacle to the development of reliable corrosion prediction models.”

By Lauren Fagan. Articles in English

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