Understanding the mechanism of interaction of candidate soil stabilizing prototypes by using microscopy and spectroscopy techniques

Globally, there is a high demand for bio-based soil stabilizers required for improving the strength properties of weak in situ soil. Microbes and microbial components such as Bacillus spp. have gained interest as soil stabilizers due to their production of spores, bio-enzymes, and bio-polymers. However, the current approach for any microlevel assessment of bio-additives and in situ soil improvement is limited. This paper provides data for microstructural evaluation of stabilized soil material for the postulation of the mode of action. In this study, the microbonding effect (i.e., bio-based cementation, bio-clogging, and soil particle bio-coating) is successfully observed within the various stabilizing prototypes, obtained from a novel Bacillus spp. using advanced methods, namely field emission gun-scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that treated soil versus untreated soil properties are altered by the bio-additive/s stabilizing effect. These indicator tests provide data for further bio-stabilizer product prototype development and processes (i.e., improved products in terms of strength and moisture susceptibility). The use of microscopy and spectroscopy was sufficient for the preliminary selection of suitable candidates for soil stabilization.

Establishing miniaturised structural testing techniques to enable high-throughput screening of microorganisms and microbial components for unpaved road stabilisation application

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Development of miniaturised techniques to assess the structural properties of in-situ material.

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Structural criterion includes: abrasion, erosion, water absorption & compression load tests.

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Designed models consistent with industry, on a smaller scale using 3D printing technology.

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Development of methods for high-throughput screening of novel bio-based samples from Bacillus.

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Proof of Concept established on the use of bio-based stabilisers.

Roads are expensive to develop particularly in challenging environmental conditions, and a lack of understanding of the properties of soil can lead to poor design and premature failures contributing to costly maintenance. The construction industry is exploring new opportunities involving biological processes and products to modify the structural properties of the in situ material, in terms of strength, volume stability, durability and permeability. Through an integrative interdisciplinary approach several microorganisms and other existing bio-enzymatic products such as secondary metabolites, enzymes, endospores, and extracellular polymeric substances have been considered as possible alternatives to conventional methods for the development of sustainable road infrastructure. Limitations in the current state of technology to developing bio-based solutions include microorganism selection and the ability to evaluate derivative components in rapid structural tests that enhance the time to development of proper commercial products. This study focused on the testing of fermentation derived components of biological materials in a high-throughput manner, using miniaturised structural tests to validate screening and selection methodology. The methods tested included resistance to abrasion, resistance to erosion, water absorption and resistance to compression load. Unique miniaturised test equipment was successfully developed using computer-aided design (CAD) and 3D printing technologies. Effects were measured to enable the rapid evaluation of a target microorganism and for screening of biological components or fractions. Results obtained using a Bacillus isolate reported in the current study exhibit strength characteristics and can potentially be formulated as a product for soil stabilisation. This work forms the basis for in vitro selection methodology to enhance development of bio-based structural materials for application in the road sector.