The increasing demand for sustainable infrastructure solutions has driven research into bio-based soil stabilization technologies, particularly for unpaved road construction in developing regions. This study investigates the microstructural interactions between novel Bacillus spp.-derived stabilizing prototypes and two distinct soil types—dolerite (low plasticity index, PI 4.46%) and weathered granite (medium plasticity, PI 7.70%)—using advanced field emission gun-scanning electron microscopy (FEG-SEM) and Fourier transform-infrared spectroscopy (FT-IR). The objective is to elucidate the mechanisms underlying bio-stabilization at the microscale, focusing on three key phenomena: biocementation, bio-clogging, and particle surface coating. By combining high-resolution imaging with molecular characterization, this work provides a comprehensive understanding of how microbial metabolites alter soil architecture and mechanical behavior.
Fermentation of Bacillus licheniformis was conducted in a 30 L bioreactor under controlled conditions (32°C, pH 6.8, dissolved oxygen ≥30% saturation), yielding four prototype fractions: whole broth from stationary phase (a), non-aqueous extract from vegetative cells (b₂), supernatant from sporulation phase (c), whole broth from spore phase (d), and non-aqueous fraction from spores (e₂). These were extracted using sequential aqueous and non-aqueous methods, with solvent recovery via rotary evaporation. The resulting extracts exhibited varying viscosities (23.80 cP for (a), 17.00 cP for (d), 24.20 cP for (b₂), and 22.20 cP for (e₂)), indicating differences in polymer concentration and molecular weight distribution. FT-IR analysis revealed that all fractions contained characteristic functional groups associated with proteins (amide I and II bands at 1650–1600 cm⁻¹ and 1550–1500 cm⁻¹), polysaccharides (C–O–C stretching at 1062 cm⁻¹), and carboxylate groups (asymmetric C=O stretch at 1716 cm⁻¹).CALB1 Antibody Autophagy Notably, the non-aqueous fractions (b₂ and e₂) displayed stronger aliphatic C–H stretches (2930–2850 cm⁻¹) and reduced hydroxyl intensity, suggesting higher hydrophobicity and greater molecular stability compared to their aqueous counterparts.CD36 Antibody Data Sheet
FEG-SEM analysis of untreated soils revealed distinct microstructures: dolerite exhibited a dispersed, irregular particle arrangement with visible pore networks, while weathered granite showed more organized, book-like stacking indicative of cohesive clay-rich aggregates.PMID:35260349 After treatment with the most effective prototypes—(a) whole broth and (b₂) non-aqueous extract—the microstructure transformed dramatically. In both soil types, new white crystalline deposits appeared on particle surfaces, filling interstitial voids and forming continuous surface coatings. These features corresponded to calcium carbonate precipitation and polymeric gel formation, consistent with biocementation. In dolerite samples treated with (b₂), extensive particle aggregation and network-like structures emerged, suggesting strong interparticle bonding through polymer bridging. Similarly, in weathered granite, the non-aqueous fraction induced a dense, interconnected matrix where particles were tightly packed and partially encased in a viscous film, demonstrating effective bio-clogging and surface encapsulation.
Quantitative image analysis using MIPARTM software confirmed significant reductions in pore space and increased particle cohesion. For dolerite treated with (b₂), average pore area decreased by 63% compared to untreated controls, while particle clustering increased by 48%. In weathered granite treated with (a), the mean particle size distribution shifted toward larger aggregates, confirming the role of hydrophilic polymers in promoting flocculation. Additionally, cross-sectional analysis revealed layered deposition patterns in (b₂)-treated specimens, indicating progressive surface coating during curing. These observations align with FT-IR data showing enhanced presence of glycosidic linkages (953–973 cm⁻¹) and stable amide bonds (1650 cm⁻¹) in stabilized samples, supporting the hypothesis of polymer-mediated structural reinforcement.
The results demonstrate that the mode of action differs significantly between aqueous and non-aqueous prototypes. Aqueous fractions (a and d) function primarily through hydration-driven swelling and electrostatic binding, promoting particle agglomeration via hydrogen bonding and ion exchange. Their effectiveness is limited in low-clay soils due to rapid leaching. In contrast, non-aqueous fractions (b₂ and e₂) act as durable, hydrophobic sealants that resist water intrusion, reduce permeability, and enhance mechanical strength through covalent bonding and physical entrapment. This dual mechanism—immediate surface sealing combined with long-term matrix development—makes them particularly suitable for high-traffic unpaved roads exposed to seasonal rainfall.
In conclusion, this study establishes a clear correlation between molecular composition, microstructural transformation, and macro-scale performance in bio-stabilized soils. The integration of FEG-SEM and FT-IR enables precise identification of stabilization mechanisms, allowing for rational selection and optimization of bio-additives. The findings support the development of tailored soil stabilizers based on soil type, climate, and intended application, paving the way for environmentally sustainable, cost-effective road construction solutions in resource-limited settings. Future work will focus on scaling up production, evaluating long-term durability under field conditions, and exploring synergistic combinations of bio-polymers for enhanced performance.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
