This disk shows a composite material in which a chemical reaction helped to “heal” small fissures.
Delft University of Technology This disk shows a composite material in which a chemical reaction helped to “heal” small fissures.

For the past several years, academies and laboratories have been trying to figure out how to reduce the damage to buildings caused by cracks in concrete.

There have been numerous approaches to this problem, including a form of concrete, developed in 2009 by the University of Michigan’s Advanced Civil Engineering-Materials Research Lab, which uses microfibers that allow the concrete to bend. The dry concrete absorbs moisture from the air and softens to fill tiny cracks (no wider than 150 micrometers) with calcium carbonate material.

In 2010, a student at the University of Rhode Island embedded a microencapsulated sodium silicate healing agent into concrete. When tiny cracks form, the capsules rupture and release the healing agent that reacts with calcium hydroxide naturally present in the concrete to form a compound to heal cracks and block pores. The drawback is that the gel created takes week to harden.

Last year it was reported that Dr. Alan Richardson of the University of Northumbria in Great Britain was using ground-borne bacteria—grown on a nutrient concoction of yeast, minerals, and urea and added to concrete—to create calcite, a crystalline form of natural calcium carbonate. The calcite blocked the concrete’s pores, keeping out water and other damaging substances to prolong the life of the concrete.

Delft University of Technology in The Netherlands also made headlines in 2012 when, after seven years of research, it unveiled “bio-concrete,” a material that contains granules of bacterial spores and calcium lactate, a nutrient needed to keep the spores alive. The spores activate upon contact with rainwater (one of the major causes of concrete fissures), and can fill cracks to within 0.5 millimeters in width.

For the past two years, Delft’s researchers have blogged about their progress, and have presented findings to science and business audiences in Germany and South Korea.

In an email response to questions from BUILDER, Erik Schlangen, a professor of experimental micromechanics at Delft’s department of civil engineering and geosciences, says there are still some “small problems concerning mass production” to solve, as well as “dealing with certification issues” that will require showing long-term functionality via accelerated heat tests. His team plans to conduct larger field trials over the next two years.

Delft University and the University of Ghent also are taking the lead on a European Commission–funded project with 13 research groups to find a common procedure for producing self-healing concrete.

According to Schlangen, if bio-concrete can be produced at a price that is within 15 percent to 20 percent of conventional concrete, he believes “it will be a valuable material.”