Microbially induced carbonate precipitation (MICP) technology offers an innovative approach for the solidification and stabilization of heavy metal-contaminated soils; However, the mechanical strength and long-term stability of this remediation method have not been thoroughly investigated. This study introduces an innovative curing and stabilization technique using MICP-activated MgO to address the geotechnical challenges posed by zinc ion-contaminated soils. To investigate the effect of zinc ions on soil and the optimal efficacy of MICP-activated MgO in curing zinc contamination, experiments were conducted on zinc-contaminated soils with varying zinc ion concentrations (0.05%, 0.1%, 0.5%, 1.0%), dry densities (1.35, 1.4, 1.45, 1.5 g/cm³), and activated MgO admixtures (1%, 2%, 5%, 10%). The effectiveness of MICP-activated MgO was evaluated through macroscopic analysis and stability tests, including unconfined compressive strength tests, direct shear tests, and the Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that zinc ions disrupted soil particle cementation, enlarged inter-particle pores, and significantly reduced both unconfined compressive strength and shear strength. The optimal dosage of MICP-activated MgO for curing zinc-contaminated soil was determined to be 10%, resulting in an unconfined compressive strength of 1.196 MPa and a Zn²⁺ leaching concentration of 0.1414 mg/L. The combined actions of MICP-activated MgO facilitated the formation of alkaline magnesium carbonate, calcium carbonate, and magnesium hydroxide. These compounds filled the inter-particle pores of zinc-contaminated soil, encapsulating and co-precipitating zinc ions, thereby enhancing the soil's strength and stability. These findings establish a theoretical foundation for the engineering application of MICP-activated MgO in the remediation of zinc-contaminated soils.

The BS EN 1504-2:2004 groups surface treatments into three types: impregnations, hydrophobic impregnations, and surface applied corrosion inhibitors. Impregnations reduce surface porosity by filling concrete pores, while hydrophobic impregnations create a water-repellent surface without filling pores. Surface applied corrosion inhibitors form a protective film on the rebar surface. Impregnation strengthens the surface by blocking pores with reaction products that reduce ingress of aggressive agents. Hydrophobic impregnation produces a hydrophobic and water-repellent surface that inhibits water penetration while allowing concrete to breathe. Corrosion inhibitors migrate to the steel surface and form a mono-molecular film, preventing further corrosion. In this study accelerated corrosion test was used for determination of the effectiveness of each category in offering corrosion protection by subjecting concrete specimens coated with these surface treatments to accelerated corrosion conditions that is intended to induce corrosion in the embedded rebars. This paper presents test results for the performance of these three surface treatments on grade G30 and G40 concretes. Results show that hydrophobic agents are more effective than traditional impregnates in reducing water absorption and chloride penetration.

Bio-inspired root pile (abbreviated as root pile) is a new type of bio-inspired foundation, which has a broad application prospect in the development and construction of China's South China Sea area due to its good bearing characteristics such as pullout bearing capacity. The effect of root buried depth on the uplift bearing characteristics of root piles is analyzed through the model test of uplift bearing of root piles with different root buried depths in coral sand foundation. The results show that increasing the root buried depth can improve the ability of the root pile to control the uplift displacement, and there exists an optimal buried depth or range of buried depths that can effectively improve the pile foundation's uplift bearing capacity and control the ultimate displacement. The attenuation of axial force at the root is in the form of a step; with the increase of root buried depth, the maximum value of lateral friction resistance develops from the lower part of the pile body without root to the upper part of the pile body without root. The range of the bearing ratio of the root section of the pile with root buried depth of 260 mm, 340 mm and 420 mm is 12.33%-15.68%, 9.98%-17.82% and 7.61%-21.65%, respectively; the smaller the root buried depth is, the higher is the ratio of the bearing ratio of the root section at the beginning of loading, and the bigger the root buried depth is, the bigger is the ratio of the root's final bearing ratio. The change of soil pressure around the pile increases and then decreases, and the densest point of soil compacting moves upward with the increase of root buried depth. The research results provide scientific basis for the design of root pile buried depth and root arrangement in actual projects.

Conventional techniques for soil erosion control often rely on the use of cementing additives and coating agents to improve shear strength, minimize particle movement, and increase soil water repellency. These chemical agents, however, involve energy intensive production and treatment processes and can cause significant environmental impacts. Recent studies have demonstrated that fungal mycelium (a root-like three-dimensional structure of fungi) can extend through soil pores and secrete strong hydrophobic compounds, binding soil particles together and increasing soil water repellency at the soil surface. This study investigated the effect of fungal mycelium on the erosion resistance of a low plasticity silt for potential soil erosion mitigation. Water dripping tests were conducted on untreated and fungal-treated specimens under various conditions, including different fungal growth durations, void ratios, water dripping rates, and desiccation condition. Untreated specimen exhibited a 45% soil mass loss and 10.5 mm of erosion depth after one hour of water dripping. In contrast, fungal-treated specimens showed no loss of soil mass and 4-5 mm of erosion depths after four hours of water dripping. Furthermore, fungal mycelium remained effective in erosion resistance even after 30 days of desiccation at 60 °C.

There is a growing need for sustainable ground improvement, stabilization and remediation, as well as ways to maintain infrastructure. This is resulting in a rise of nature-based solutions, bio-based ground improvement techniques, bio-inspired methods, a “build-with-nature” approach. Shallow soil layers have historically been disregarded by geotechnical engineers due to unwanted characteristics, an overall lack of familiarity with the evolution of their properties in time, and/or theoretical framework for interpretation. Recent research in unsaturated soil mechanics, the characterization of organic soils, and understanding of organic matter transformation processes has improved understanding and modelling capabilities of shallow soil layers. However, soil biota (bacteria, fungi, algae, protists, soil fauna and plants) must also be considered. In this perspective, we summarize the effects of soil biota presence and activity on soil mechanical and hydraulic properties, explore their underlying mechanisms, and discuss how they can be utilized in implementing bio-based solutions. Additionally, we examine the applications and limitations of these bio-based solutions.

Ureolysis and denitrification are the two major microbial metabolic pathways commonly used in Microbially induced calcite precipitation (MICP) for geoengineering applications. Although ureolysis is generally the more efficient pathway, the denitrification pathway has gained more attention recently because a diverse group of bacteria can precipitate calcite via denitrification, and no harmful byproduct is generated provided that the reduction of nitrate to nitrogen gas is complete. There are, however, many environmental factors that could inhibit or reduce the efficiency of the denitrification process in soil. Some examples of these factors include salinity, pH, temperature, biodiversity (abundance and species of denitrifiers and competitors), water stress (extreme wet-dry conditions), degree of saturation (anaerobic vs. aerobic conditions), high heavy metal content (e.g., mine tailings), and shortage of dissolved carbon sources. In this paper, the denitrification process, the denitrification inhibitors, and the mechanisms involved in their inhibition of the denitrification process are discussed in detail. This investigation indicates that although general optimum conditions can be formulated for MICP through denitrification, significant adjustments may be necessary if inhibitory conditions are anticipated. It was also shown that when inhibitors are expected, it is crucial to investigate not only the amount of precipitated calcium carbonate but also the N2O/N2 gase ratio to ensure the complete reduction of nitrate to nitrogen gas and prevent the release of byproducts (especially N2O) into the environment. Finally, the implications of the inhibitory factors on the field application of denitrification MICP treatment for different geotechnical projects are discussed.

With the advancement of technology, the demand for environmentally friendly energy sources is increasing. Currently, the most commercially successful lithium-ion batteries cannot meet future demands due to their relatively low theoretical energy density. In contrast, lithium-sulfur batteries and metal-air batteries possess exceptionally high theoretical energy densities, making them the most promising candidates for next-generation batteries. However, several challenges remain before these batteries can be commercially viable on a large scale. Wood-derived materials, being abundant, environmentally friendly, biodegradable, and possessing unique hierarchical porous structures and excellent mechanical properties, present a remarkable potential for use in binder-free self-supporting electrodes and thick electrodes. These attributes offer a promising solution to the challenges faced by lithium-sulfur and metal-air batteries. This review highlights the application of wood-derived materials in next-generation high-performance batteries, specifically lithium-sulfur and metal-air batteries. It discusses the role of the hierarchical porous structures of wood-derived materials and outlines the challenges associated with their use. Additionally, it provides insights and ideas for future research directions in this area.

Tree root-soil interaction is important for problems such as uprooting of trees subjected to wind loads or the stability of vegetated slopes. This paper examines the stability of laterally loaded trees (e.g., subjected to wind) and introduces a novel methodology for characterizing the uprooting capacity of tree root-soil systems. The novelty of the methodology originates from the coupling between the Space Colonization Algorithm (SCA) for the geometry characterization of the root system with an efficient Finite Element Method(FEM) model. Each tree is unique, and finding a generalized model would need to account for multiple scenarios involving different a priori uncertain tree root geometries and soil types. The proposed methodology allows for the assessment of uncertain root geometries and their effects on the mechanical response of the root-soil system, thanks to the stochastic nature of the SCA. It introduces a competitive growth algorithm that models root branch expansion in the soil as a dynamic and stochastic process. The study captures the mechanical response of a tree root system with a 3D FEM model by using an elastoplastic mechanical model for the soil, while the roots are modeled with elastoplastic embedded beams. The proposed model enables the identification of the locations of root breakage and soil failure paths in multiple scenarios. Model outputs allow quantitative investigation into the relationship between root system geometry and the root-soil system uprooting capacity and base stiffness.