With a little electricity, sand collects, which can help protect the coast.

The texture of wet sand on the coast can be changed by passing electricity through it. A solid rock layer is then formed. This “natural cement” could perhaps be used against coastal erosion, Researchers write From Northwestern University in the United States in the scientific journal Nature, Earth and Environment Communicationswho tested it in their laboratory.

Coastal erosion is a growing problem as sea levels rise due to climate change. Until now, construction or cement injections have been the main ways to combat coastal erosion. New, more effective and affordable ways to preserve disappearing lands are being sought. The way mollusks make their shells using minerals from seawater inspired the Northwestern method.

minerals in seawater

The structure of the sand changes because electricity increases the pH of the water between the pores of the sand. This triggers chemical reactions. Minerals in the seawater then combine with the existing sand. The researchers used 2 to 4 volts, and after a few days they observed the formation of a solid layer containing calcium carbonate, magnesium hydroxide and hydromagnesite, the same materials found in mollusk shells.

The longer the current continues to flow, the more solid the layer becomes. Even after the flow stops, the rock layer remains. But the change does not have to be permanent; the reaction can also be reversed, causing the layer to break apart again.

“This method is new for use with sand, but electricity has been used for some time to protect steel that comes into contact with seawater from rusting,” says Stefan Jansen, environmental chemist and microbiologist at the Deltares Knowledge Institute. “This happens with windmills, for example, and there too we see that a hard chalky crust forms around the steel.”

A little chlorine

“The tricky point is that some chlorine is also formed in the reaction,” says Jansen. “Chlorine is very reactive and can therefore have unpleasant side effects. For use in steel, extensive research has been done on how to prevent chlorine formation, namely by keeping the voltage within a certain frequency range. It may be possible to prevent it, but researchers easily ignore it. If they also start experimenting outside the laboratory, this needs attention.”

“It’s an elegant approach, but I doubt it’s suitable for large-scale coastal defense,” Jansen says. “I’m not an environmental scientist, but what does turning sand into a solid layer do to the life of the soil that relies on loose sand? I envision more targeted applications, like supporting wind turbine foundations or coastal defense structures, for example. You might even be able to patch cracks with it, like you would plug a hole.”

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