'Super concrete' made with fungus can heal itself if it cracks

As concrete deteriorates over time, even the smallest cracks can pose a major threat to the stability of a structure.

But, a new type of self-healing concrete could put an end to the problem for good, all thanks to fungi.

By mixing in nutrients and a type of fungus called Trichoderma reesei, any cracking in the concrete would cause the production of calcium carbonate, as the activity ‘ wakes up’ the dormant fungus and spurs spore growth.

‘ Without proper treatment, cracks tend to progress further and eventually require costly repair,’ said Congrui Jin, assistant professor of mechanical engineering at Binghamton University.

‘If micro-cracks expand and reach the steel reinforcement, not only the concrete will be attacked, but also the reinforcement will be corroded, as it is exposed to water, oxygen, possibly CO2 and chlorides, leading to structural failure.’

As the researchers note, small, unseen cracks can pose a serious threat; in a nuclear power plant, for example, concrete might be used for radiation shielding.

Even replacing the aging concrete only acts as a short-term solution, according to Jin.

Eventually, the cracks will reappear.

To find a permanent solution, the researcher turned to biological inspiration.

‘ This idea was originally inspired by the miraculous ability of the human body to heal itself of cuts, bruises, and broken bones,’ said Jin.

‘For the damaged skins and tissues, the host will take in nutrients that can produce new substitutes to heal the damaged parts.’

This process, the researchers found, can be obtained using the fungus Trichoderma reesei.

When mixed with concrete, the fungus will remain dormant – but, once the first crack appears, spore growth begins.

‘The fungal spores, together with nutrients, will be placed into the concrete matrix during the mixing process,’ Jin said.

‘When cracking occurs, water and oxygen will find their way in. With enough water and oxygen, the dormant fungal spores will germinate, grow and precipitate calcium carbonate to heal the cracks,’ said Jin.

‘ When the cracks are completely filled and ultimately no more water or oxygen can enter inside, the fungi will again form spores.

‘As the environmental conditions become favourable in later stages, the spores could be awakened again.’

The researchers are now working to see how well the fungus will survive in the concrete environment.

With some adjustments, however, they expect it will prove an effective solution.

‘ There are still significant challenges to bring an efficient self-healing product to the concrete market,’ said Jin.

‘In my opinion, further investigation in alternative microor- ganisms such as fungi and yeasts for the application of self-concrete becomes of potential great importance.’