Scientists from the Polytechnic Institute of the Far Eastern Federal University (FEFU) (Vladivostok, Russia), in collaboration with colleagues from Russia, India, and Saudi Arabia, recently developed a concrete material that independently seals cracks and restores strength. This self-healing concrete is particularly useful for construction projects in seismically hazardous areas where small cracks appear in structures, as well as areas with high humidity and high rainfall.
“Concrete remains the world's number one structural material because it is cheap, durable and versatile,” says Roman Fedyuk, an engineering professor at FEFU. “However, any concrete can crack over time as a result of various external factors, including moisture and repetitive freezing/thawing cycles, of which in the Far East, for example, [there are] more than a hundred per year. When concrete cracked, this is an almost irreversible process that can endanger the entire structure,”
“What we have done within the framework of our experiment is in line with international trends in construction, where there is a demand for such ‘living’ materials that have the ability to self-diagnose and self-heal,” adds Fedyuk. “Thanks to them, technically complex and expensive repair procedures can be avoided or reduced.”
The scientific team made its self-healing concrete with an aqueous concentrate containing the bacteria Bacillus cohnii, as well as calcium carbonate (CaCO3) to fill in any resulting damages. Once the concrete mixture finished curing, the team tested the compressive strength of the material. Once the concrete cracked under pressure, they observed that the microorganisms inside the Bacillus cohnii were activated. Accessing oxygen and moisture through the cracks, the “awakened” bacteria successfully healed cracks with a 0.2-0.6 mm (0.007-0.023 in) width within 28 days by releasing the CaCO3 that crystallized under the influence of water.
After the concrete slabs returned to its original compressive strength, the bacteria “fell asleep” once more. According to FEFU, Bacillus cohnii spores can live in concrete for up to 200 years and, in theory, can extend the life of structures for the same period. This is almost four times longer than the 50-70 years of service life of conventional concrete.
Scientists grew Bacillus cohnii samples in labs using a simple agar substrate and culture medium, which forces the bacteria to survive in cement stone pores in order to release the desired chemical "repair" composition. The team assessed crack repair at the microscopic level and examined the chemical composition of the repair agent using electron microscopy and X-ray images.
The FEFU scientific team plans to develop reinforced concrete whose properties are further enhanced with the help of different types of bacteria, which will speed up the process of material recovery. The full results of the current FEFU-led study were published in Sustainability and can be read here.
Source: FEFU Press Service, www.dvfu.ru/news.