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Chip Enables Research on Real-Time Biocement Formation

Researchers from EPFL and the University of Lausanne have examined the characteristics of biocement formation using a chip that was initially created for environmental science. In some instances, this material could take the place of conventional cement binders in civil engineering.

Ariadni Elmaloglou, PhD student, and Dimitrios Terzis, one of her thesis supervisors. Image Credit: Alain Herzog / EPFL

The chip is the size of a credit card and has a flow channel engraved on its surface that is one meter long and only a hair thick. With the aid of time-lapse microscopy, researchers can inject a solution into one end of the channel and track its behavior over a period of several hours.

Environmental engineers have used similar chips to study biofilms and contaminants in drinking water, while medical scientists have used them to study how arteries become clogged or how a drug spreads into the bloodstream.

Now, researchers from the Faculty of Geosciences and Environment at the University of Lausanne (UNIL) and a team of civil engineers at EPFL’s Laboratory of Soil Mechanics (LMS) have repurposed the chip to comprehend the complex transport-reaction phenomena involved in the formation of new varieties of biocement.

Ariadni Elmaloglou, a PhD student, and Dimitrios Terzis, one of the thesis advisors at the Laboratory of Soil Mechanics (LMS) at EPFL, injected biocement solutions into microfluidic chips that resembled various types of sand to observe how the minerals formed and how the flow responded.

The primary components of biocement, calcium, urea, remained the same besides the sand types.

Thanks to the chip, we were able to observe variations in biocement mass distribution in the different mixtures. For instance, we could see where minerals were formed and which mixtures can lead to superior mechanical properties across the long flow path. Due to its miniaturized volumes, the chip enables us to perform multiple experiments with different mixtures in order to design efficient biocementation protocols.

Ariadni Elmaloglou, PhD student, Laboratory of Soil Mechanics, EPFL

Meter-Long Testing

The engineers’ findings were released in the Nature portfolio journal Scientific Reports. They conducted the first study to look at the formation of biocement over a meter in real-time, which is significant for many potential applications like crack repair, carbon storage, and soil remediation.

To promote a more in-depth investigation into this subject, all the data have been made available in an open-source format.

The LMS engineers have already begun the subsequent phase of their research in the interim.

The chip makes it easy for us to test biocements made with aggregates of recycled materials—like glass, plastic, or crushed concrete—rather than sand.

Dimitrios Terzis, Scientist, Soil Mechanics Laboratory, EPFL

These biocements could reduce or even completely transform the carbon footprint of the construction sector.

Terzis added, “The industry still relies heavily on concrete, even though the ingredients used to make it—especially sand—are getting harder to source. Our study shows that a cross-disciplinary approach can go a long way towards changing that. But we need to be open to methods from other research fields.

Inventing New Kinds of Biocement at EPFL

Dimitrios Terzis created a novel biocement using bacteria and urea for his PhD thesis at LMS. Instead of cement clinkers, calcium carbonate (CaCO3) crystals are used in the process to bind soil particles together.

The end result is a material that is bio-based, simple to use, durable, and reasonably affordable when compared to other binders like cement, lime, and industrial resins.

In particular, resins have the potential to become relatively unstable over time, contaminate the soil with microplastics or toxic materials, and raise the alkalinity of groundwater to levels that are too high. The EPFL-developed biocement can be made locally for a low cost and at room temperature with very little electricity needed.

Operators can modify the level of biocementation to suit their unique requirements. A sandstone-like result can be produced by adding very little CaCO3, and it is strong enough to withstand the shear stresses brought on by earthquakes that can cause soil liquefaction.

Other applications might be able to repair damaged foundations or assist with slope stabilization issues. A mixture that can be used as a building material or to waterproof soil is produced when more CaCO3 bio-minerals are added.

Terzis and Professor Lyesse Laloui established the EPFL startup MeduSoil in 2018 to commercialize their technology. Field trials have already been conducted by the company in both Switzerland and abroad.

The study received funding from the European Research Council Advanced Grant: Bio-mediated Geo-material Strengthening for engineering applications (BIOGEOS).

Journal Reference:

Elmaloglou, A., et al. (2022) Microfluidic study in a meter-long reactive path reveals how the medium’s structural heterogeneity shapes MICP-induced biocementation. Scientific Reports. doi:10.1038/s41598-022-24124-6.

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