Science & Nature

Jun 1, 2017

A technological leap

Buildings and structures that can, by magic, completely regenerate the cracks caused by pressure, changes in temperature or humidity? What was a science fiction scenario only a few years ago is already a reality thanks to the invention of the Dutch microbiologist Hendrik "Henk" Marius Jonkers.

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The world of technology does not stop, it is made, in every field of human activity, gradually and occasionally by means of significant leaps. The construction business is no exception and this is the story of one such jump.

Concrete is the most commonly used building material in the world. In Europe, it is found in more than 70% of buildings and structures. It is also one of the most durable, yet it is not indestructible.

The formation of cracks in the concrete allows the infiltration of salts and water that can fall down flooding the bases of the buildings or get to corrode the structures of steel in its interior to the point of collapsing them. This is the reason why quantities of steel are used in excess of those needed to support the buildings, which serve to prevent the growth of cracks and the consequences of their formation.

Jonkers, a researcher at the Technical University of Delft, was questioned in 2006 by his colleague Eric Schlagen, a specialist in concrete, about the possibility of using bacteria to enable the material to self-repair properties. The scientist accepted the issue as a challenge and set out to create a revolution in the way we build, creating an entire program of bio-sustainable civil engineering research for the development of new building materials.

Noting that 8% of human CO2 emissions are due to cement production, mutilation of natural landscapes and destruction of raw materials, the microbiologist, following the bionic approximation, referred the issue to the Nature, seeking an approach to self-renewal and self-regeneration.

What is Bio-concrete?

Bio-concrete, a mixture of traditional concrete with what they called the "repair agent" - colonies of alkaline bacteria (living in extremely alkaline environments such as concrete), called bacillus pseudofirmus, which produce calcite (calcium carbonate) and may, in addition to surviving the cement mixer, wait years to carry out its restoration work. This bacillus can remain in a kind of lethargy for decades, without food or oxygen until it is animated by them, that is, when there is a crack in the concrete, the moisture and air that enters it awakens the bacteria that rupture the capsules where are found, begin to reproduce and produce the calcite that will fill the open space. The repair process takes about 3 weeks. After the crack is closed, the bacteria return to their previous state. This state of numbness can last up to 200 years.

To produce the calcite, the bacillus needs a food source. Jonkers started by trying sugar but this substance softened and weakened the concrete. Later the team of scientists opted for calcium lactate, placed next to the bacteria, inside biodegradable plastic capsules. Calcite is therefore the product of calcium lactate digestion combined with carbonate ions.

Advantages and obstacles

According to Jonkers, bio-concrete can repair cracks up to 8 millimetres in width, which, while seeming little, can ensure an exponential increase in building life and thus dramatically reduce maintenance costs. This type of repair may be particularly suitable for buried concrete structures that are difficult to access or in old buildings with many cracks that can collapse through low magnitude earthquakes. The main obstacle to the development of this product is one of economic origin. Despite the obvious savings in repairs (only 6.8 billion dollars are spent annually in Europe), the cost difference for ordinary concrete is 40%.

For this reason, researchers are now working on improving the method of encapsulating the food in order to optimize its distribution to the bacteria and, thereby, reduce production costs by 50%.

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