Concrete reinforced with steel forms the skeleton of many buildings and bridges. But any cracks in its gritty exterior make it vulnerable: "Water is the culprit for concrete because it enters the cracks and it brings aggressive chemicals with it," says Henk Jonkers of Delft University of Technology in Delft, the Netherlands. These chemicals degrade both concrete and steel.
Jonkers thinks the solution is to fight nature with nature: he suggests combating water degradation by packing the concrete with bacteria that use water and calcium lactate "food" to make calcite, a natural cement.
Unfortunately, most organisms keel over in a pH above 10, which is typical of concrete. To find bacteria that are happy in such an alkaline environment, Jonkers and his colleagues looked to soda lakes in Russia and Egypt where the pH of the water is naturally high – and found that some strains of Bacillus thrived there.
Moreover, the bacteria can take on a dormant spore state for long periods – up to 50 years, according to Jonkers – without food or water. He compares them to seeds waiting for water to germinate.
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