The most common cause of degradation and failure of reinforced concrete structures is chloride-induced corrosion of its embedded steel. This is a pervasive and urgent problem that requires immediate attention and public awareness.
An underlying concept of chloride threshold is widely used, and all existing models for predicting the corrosion performance of reinforced concrete structures exposed to chloride environments are based on this common theoretical concept.
In Applied physics examsfrom AIP Publishing, researchers from Switzerland, the United States, Canada and Norway are advocating for a paradigm shift in the science of predicting corrosion damage in reinforced concrete structures.
Just before the COVID-19 pandemic hit, the international group of scientists met and discussed the serious flaws in using the chloride threshold concept to predict corrosion. They say change is needed to meet the growing challenges of aging structures losing their functionality and potentially collapsing, greenhouse gas emissions and the economy in general.
“The corrosion of steel in concrete is a complex phenomenon,” said Ueli Angst, of ETH Zürich in Switzerland. “In the typically highly alkaline environment of concrete, where the pH can be above 13, steel is considered passive, which means that it is coated with a thin layer of protective oxides and its rate of corrosion is negligible.”
But concrete is porous, and when exposed to salts, such as seawater or road salts, chloride ions can eventually penetrate the concrete and reach the steel. At some point, the protective passive layer will be destroyed and corrosion can begin. Depending on actual exposure conditions, corrosion may occur at a faster or slower rate.
In reality, the corrosion of steel in concrete is a continuous process that is rarely separable into uncoupled sequential phases. Researchers say the focus should be on quantifying the time- and space-varying corrosion rate from the time the steel is placed in the concrete until it reaches the end of its life. its lifespan.
To achieve this, a multi-scale and multi-disciplinary approach combining scientific and practical contributions from materials science, corrosion science, cement/concrete research and structural engineering is required. Angst and his colleagues propose that scientific research move away from the chloride threshold concept.
“Despite enormous amounts of research, no clear chloride threshold could be found, and the influencing factors are complex,” said Burkan Isgor of Oregon State University. “Unfortunately, mainstream research is still searching for this threshold, which presents a major obstacle to the development of reliable corrosion prediction models.”
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Material provided by American Institute of Physics. Note: Content may be edited for style and length.