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Advances in Biocement Technology Could Revolutionize Construction

The integration of biocement-producing bacteria in construction and repair processes presents a promising advancement for the industry. However, the challenge lies in cultivating these microbes at construction sites. Recent findings published in ACS Applied Materials & Interfaces highlight a new freeze-drying technique that could facilitate the use of these bacteria, potentially enabling construction crews to utilize a convenient powder to create tiles, mend oil wells, or reinforce the ground for temporary roads or camps.

Soil stabilization and the repair of concrete are pressing issues within civil engineering. Research has increasingly focused on a specific bacterium known as Sporosarcina pasteurii, which has the ability to synthesize a calcium-based mineral termed biocement. This microorganism decomposes urea, resulting in the formation of ammonium and carbonate, and when calcium is introduced, the outcome is calcium carbonate. This compound effectively binds sand and soil particles together or fills in cracks in damaged concrete structures. Traditionally, cultivating these bacteria for biocement has required sophisticated equipment and expertise on site. Thus, Maneesh Gupta and his research team sought to create a shelf-stable version of S. pasteurii that construction workers could easily use.

Inspired by the freeze-drying methods utilized in fertilizer production, Gupta’s team experimented with various solutions to determine how well the bacteria could endure freezing. Their research revealed that sucrose provided the best protection for the microbes compared to other substances. After undergoing freezing, the bacteria were desiccated and packaged in resealable plastic bags. Notably, the sucrose-enriched S. pasteurii demonstrated its viability for a minimum of three months.

Additional laboratory experiments confirmed that the freeze-dried bacteria could effectively bond sand within 3D-printed cylindrical molds. For these tests, the researchers utilized two types of sand: play sand, commonly found in children’s sandboxes, and naturally sourced sandy soil. Spraying a solution of calcium chloride and urea onto the columns allowed the bacteria to produce biocement. Notably, the biocement derived from play sand exhibited greater strength than that produced from the natural soil. Most samples could be extracted from the play sand molds, while biocement within PVC pipes containing natural sandy soil remained intact. The exposure to higher concentrations of calcium chloride and urea further enhanced the strength of the biocement in both sand types.

In practical field applications, researchers applied the freeze-dried bacteria to 3-foot by 3-foot (approximately 1-meter by 1-meter) plots and treated them with urea and calcium chloride. Within just 24 hours, the upper 3 inches (7.6 centimeters) of soil displayed enhanced strength, demonstrating the potential for rapid application in the field.

While further research is necessary, this study marks a significant breakthrough, demonstrating that freeze-dried S. pasteurii can remain viable and effectively produce biocement. This innovation could pave the way for its application in real-world construction scenarios.

The study received funding from the U.S. Air Force Laboratory Seedlings for Disruptive Capabilities Program.

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