Preparing regular concrete scientists replaced ordinary water with water concentrate of bacteria Bacillus cohnii, which survived in the pores of cement stone. The cured concrete was tested for compression until it cracked, then researchers observed how the bacteria fixed the gaps restoring the strength of the concrete. The engineers of the Polytechnic Institute of Far Eastern Federal University (FEFU), together with colleagues from Russia, India, and Saudi Arabia, reported the results in ‘Sustainability’ journal.
During the experiment, the bacteria activated when they gained access to oxygen and moisture, which occurred after the concrete cracked under the pressure of the setup. The ‘awakened’ bacteria completely repaired fissures with a width of 0.2 to 0.6 mm within 28 days. The microorganisms released a calcium carbonate that crystallized under the influence of moisture. After 28 days of self-healing experimental concrete slabs retrieved their original compressive strength. In the renewed concrete, the bacteria ‘fell asleep’ again.
Spores of Bacillus cohnii are capable of staying alive in concrete for up to two hundred years and, theoretically, can extend the lifespan of the structure for the same period. This is almost 4 times more than the 50-70 years of conventional concrete service life.
Self-healing concrete is most relevant for construction in seismically risky areas, where small fissures appear in buildings after earthquakes of a modest magnitude, and in areas with high humidity and high rainfall where a lot of oblique rain falls on the vertical surfaces of buildings. Bacteria in concrete fill the pores of the cement stone making them smaller so less water gets inside the concrete structure.