Living concrete heals its own wounds

Smart concrete inspired by nature is the focus of new research published this month in the International Journal of Materials and Structural Integrity. Scientists from the USA and Turkey have tracked progress in this field and have projected future direction in research and development.

Many organisms, such as shellfish and some microbes, have the ability to assimilate calcium from their surroundings and use other materials including carbonates, phosphates, iron oxides, and sulfides to mineralize their cells and build exoskeletons. Among the minerals formed by calcium-using organisms are gypsum and calcite.

Civil engineer Paramita Mondal of the University of Illinois at Urbana-Champaign in Illinois working with colleagues there and at the University of Texas at Austin and Ozyegin University, Istanbul, Turkey, point out that interest in mimicking the biological mineralization process emerged from the idea of manufacturing a Portland cement that could be used to make self-healing concrete structures.

“Internal stresses, due to shrinkage, improper curing, temperature changes etc., may induce microscopic cracks which will continue to propagate upon the application of additional stresses, and these cracks can provide pathways for harmful chemicals to ingress, and lead to loss of strength and integrity,” the team explains. Conventional approaches to this problem usually involve embedding fibers in the concrete as it is setting to reduce the risk of fractures spreading. Repair methods involve the use of sealants and patches. No current preventative methods or treatment is wholly effective and cracks in concrete continue to be an issue for civil engineers worldwide whether constructing skyscrapers or building bridges.

Mondal and colleagues discuss the possibility of using microbes to brew an alternative to Portland cement for the fabrication of concrete that could remineralize when cracks form, healing its own wounds in other words and ensuring integrity of buildings, bridges and other concrete structures. There are many obstacles to be surmounted, such as engineering microbes that would remain viable within a smart concrete for many years rather than just months as has been seen in early research.

There is, however, one important advantage of such smart concrete in that the microbes would absorb carbon dioxide from the atmosphere in order to carry out the process of biomineralization. This could lead to a shift from one carbon footprint to the other in the emissions balance for global cement manufacture wherein currently carbon emissions are enormous and a major concern in the climate change debate.

Zhang, B., Bundur, Z.B., Mondal, P. and Ferron, R.D. (2015) ‘Use of biomineralisation in developing smart concrete inspired by nature’, Int. J. Materials and Structural Integrity, Vol. 9, Nos. 1/2/3, pp.39–60.

Author: David Bradley

Award-winning, freelance science writer based in Cambridge, England.