INSIGHTS Can We ‘Grow’ Living Concrete Alternatives? By Rollin J. Jones, Sarah L. Williams, and Wil V. Srubar III, Ph.D. oncrete has been used for thousands than 0.5% of the initial bacterial inoculum of years. Today, it is the most utilized has been shown to last more than 30 days. constructionC material in the world. Modern The Future concrete is so ubiquitous because of its unmatched compressive strength, fresh-state Led by Professors Wil Srubar, Sherri Cook, Jeff malleability, and long-term durability, as well as Cameron, and Mija Hubler at the University the global availability of raw material resources. of Colorado Boulder, the interdisciplinary The use of concrete is not without its draw- research team ‘grew’ portland cement-free backs. Cement production alone is responsible concrete materials instead. In one of the for 8% of global carbon dioxide (CO2) emis- approaches, researchers engineered a concrete- sions. Numerous efforts within the cement like material with an internal environment and concrete industry have targeted reductions more suitable for microbes. In these living in the environmental footprint of concrete. building materials (LBMs), photosynthetic Strategies such as the use of supplementary marine cyanobacteria capable of MICP were cementitious materials, like fly ash, slag, cal- encapsulated in a biocompatible, hydrogel- Sample of a ‘grown’ living building material (LBM). cined clay, and other natural pozzolans, reduce sand matrix. It was demonstrated that the embodied carbon and increase the service life minerals produced by the bacteria signifi- Initial Conclusions of concrete materials. While companies such cantly improved the mechanical properties as Blue Planet and Minus Materials aim to of the materials compared to bricks without The research efforts are only beginning to produce aggregates from CO2, we are a long cyanobacteria. scratch the surface of possibilities. Other way off from achieving carbon neutrality for The result was a ‘grown’ composite material living organisms, for example, could impart cement and concrete products. with a compressive strength (f´c) of approxi- a myriad of biological functionalities, like At the University of Colorado Boulder, an mately 500 psi – on par with a low-strength bioluminescence. Different bacteria species interdisciplinary team of researchers took inspi- cementitious mortar and higher than that of or co-cultures of bacteria could work together ration from nature to address the fundamental adobe brick. Microbial viability within these in a multifunctional way to self-regenerate, challenge of producing a carbon-neutral – or materials substantially exceeds that of traditional self-heal, and/or sense and respond to external even carbon-storing – concrete. They asked, self-healing concrete. Nine percent of the initial stimuli, such as light, heat, pressure, and mag- “Is it possible to ‘grow’ a concrete alternative inoculum survived for 30 days in the cyanobac- netism. If nature can do it, living materials instead? If so, could we keep it alive?” terial mortar. These mortars represent a new can be engineered to do it, too. materials paradigm, in which microorganisms Considering the challenges humans will face in Self-Healing Bioconcrete can participate in material manufacturing and the 2020s and beyond – climate change, disaster An interesting crossover between biotechnol- persist within the resultant material, thereby resilience, infrastructure, and space exploration ogy and concrete has been occurring over the imparting a biological functionality to an oth- – we should look to the power of biology and past few decades. Self-healing concrete materi- erwise inert structural material. living materials at the building scale to help als, which utilize microbially induced calcium solve some of the most critical environmental Other Biological Functions carbonate precipitation (MICP), originated crises of our time. By doing so, we could harness at the Delft University of Technology in the Maximizing long-term microbial viability the ability of living organisms to create materi- Netherlands and have since been the focus opens the door for a multitude of biological als that would help us build more sustainable of extensive research worldwide. Self-healing functions to be engineered into structural communities – both on earth and beyond – that concrete, in principle, is concrete designed materials, like carbon sequestration, chemi- better blur the boundaries and bring to seal its own cracks. Bacteria capable of cal sensing and signaling, self-healing, and harmony to the built environment MICP are mixed into concrete along with self-regeneration. In the University’s semi- and natural world.■ the nutrients required for survival. As cracks nal work, successive self-regeneration was form, the bacteria produce calcium carbonate explored. Researchers took one brick, split it Rollin J. Jones is a Ph.D. student in the Civil, minerals, which subsequently fill the cracks. into two, fed it fresh nutrients, and effectively Environmental, and Architectural Engineering This self-sealing approach could be particu- ‘grew’ two new bricks from one parent genera- department at the University of Colorado Boulder. ([email protected]) larly effective for preventing further exposure tion. This was accomplished two subsequent and subsequent corrosion of rebar, which is times so that one parent resulted in eight Sarah L. Williams is a Ph.D. student in the detrimental to the longevity of reinforced living child bricks. This study demonstrated Materials Science and Engineering Program at concrete structures. that the manufacture of building materials the University of Colorado Boulder. ([email protected]) While MICP is an effective crack-repair does not have to be limited to making one method for concrete, the local environment steel beam or one concrete mix at a time. In Wil V. Srubar III is an Associate Professor at the within concrete is very harsh. It does not take the future, the manufacture of materials will University of Colorado Boulder and Principal long for most bacteria to lose their ability to be possible exponentially by harnessing the Investigator of the Living Materials Laboratory. reproduce and produce minerals. In fact, less exponential growth of bacteria. ([email protected]) STRUCTURE magazine JUNE 2021 57.