Surface rainfall erosion resistance and freeze-thaw durability of bio-cemented and polymer-modified loess slopes

Biopolymer-enzyme-induced carbonate precipitation (EICP) for the green solidification/stabilization of graphite tailings: Mechanical, leaching, and microstructural characterization

The rapidly increasing global demand for graphite has increased the generation of graphite tailings. However, graphite tailings are rich in harmful substances, such as heavy metals, which pose serious threats to the environment and human health. Traditional recycling methods of graphite tailings face challenges, including high costs, substantial CO2 emissions, and limited effectiveness in heavy-metal stabilization, which inhibit their environmental sustainability in large-scale applications. In this study, a novel ecofriendly strategy was proposed for the green solidification and stabilization (S/S) of graphite tailings. Chitosan (CTS), a biopolymer, was introduced during the enzyme-induced carbonate precipitation (EICP) of graphite tailings. The potential of CTS-EICP in binding the loose particle structure of graphite tailings and inhibiting the release of heavy-metal pollutants was discussed from dual dimensions of mechanical strength and environmental effects. Results revealed that the unconfined compressive strength (UCS), split tensile strength (STS), and calcium carbonate generation rate of CTS-EICP-treated graphite tailings significantly improved compared with those of EICP-treated tailings. The effects were optimal when the CTS content was 0.15 %, reaching 897.8 kPa, 258.1 kPa, and 8.03 %, respectively. After CTS-EICP treatment, the pH of the tailing leachate stabilized at 7.90-8.26 and the fixation rate of heavy-metal ions was 92.61 %-100 %. CTS promoted the formation of carbonate crystals via urease stabilization mechanism, which were embedded in the three-dimensional network formed via the crosslinking of CTS molecules and yielded a multilayer composite barrier structure of "tailings-CTS-carbonate-CTS-tailings." CTS-EICP provided a new perspective for employing biopolymer-EICP synergistic remediation interactions in multidimensional green S/S of heavy metal-containing tailings.

Classification of additives and their influence mechanisms in improving the performance of biologically induced carbonate precipitation

Microbial/enzyme induced carbonate precipitation (MICP/EICP) is one of the hot topics in the field of civil engineering, environmental engineering in recent years, primarily attributed to its environmental friendliness and low energy consumption. However, how to enhance its economic and technical feasibility to ensure its stable and high-performance is still a significant challenge. This paper systematically explores the strategic incorporation of additives as a promising approach to enhance the efficiency and controllability of MICP/EICP process. An overview of MICP and EICP, including a comparison between them, is first compiled. According to the characteristics of various additives and the regulatory requirements, they are classified into the following categories: organic macromolecular additives, inorganic additives, biological additives and others. It then highlights the potential of additives to impact the mineralization dynamic process and the underlying mechanisms of their involvement in the reaction, such as providing nucleation sites, enhancing bioactivity, altering the properties of the calcium carbonate product, and reducing by-products. Whereas these additives either possess outstanding biocompatibility, specific functional groups, or particular viscosity, can work synergistically with MICP/EICP, they still have some intrinsic limits that need to be addressed. Therefore, future perspectives in additive-modified MICP/EICP systems are discussed in-depth. These insights establish a theoretical framework for additive selection tailored to specific MICP/EICP applications, making the incorporation of additives a powerful tool in the future to improve mineralization outcomes in different application scenarios.

Effect of Bio-Cementation Level and Rainfall Intensity on Surface Erosion Resistance of Biotreated Slope Using PEICP Method

Biomineralization technology is a promising method for soil cementation, enhancing its mechanical properties. However, its application in mitigating slope surface erosion caused by rainfall has not been fully explored. This study experimentally examined the feasibility of using plant-based enzyme-induced carbonate precipitation (PEICP) to reduce slope surface rainfall erosion through simulated rainfall tests. The effects of biotreatment cycles (N) and rainfall intensity (Ri) on erosion resistance were evaluated. The results demonstrated that increasing the biotreatment cycles improved the bio-cementation level, as evidenced by enhanced surface strength, increased calcium carbonate content (CCC) and thicker crust layers. Specifically, as the biotreatment cycles (N) increased from 2 to 6, the crust layer thickness expanded from 5.2 mm to 15.7 mm, with surface strength rising from 38.3 kPa to 244.3 kPa. Likewise, the CCC increased significantly from 1.09% to 5.32%, further reinforcing the soil structure and enhancing erosion resistance. Slopes treated with six biotreatment cycles exhibited optimal erosion resistance across rainfall intensities ranging from 45 to 100 mm/h. Compared to untreated slopes, biotreated slopes showed significant reductions in soil loss, with a decrease to below 10% at N = 4 and near-complete erosion resistance at N = 6. These findings highlight the potential of PEICP technology for improving slope stability under rainfall conditions.

Influence of biopolymers on geotechnical properties and erosion resistance of colliery spoil dumps

Conventional chemical soil binders used on colliery spoil (CS i.e., the material that lies above a coal seam) dumps to mitigate wind and water erosion are facing significant scrutiny due to potential environmental and stability risks. These binders can cause toxicity and leaching, which may harm human health and safety. Using biopolymers would be a new and eco-friendly method that can improve the erosion stability of CS dumps. This article investigates the behaviour of three distinct biopolymers: Agar gum (AG), Guar gum (GG), and Xanthan gum (XG). These biopolymers were used to stabilize CS. The surface charges of these biopolymers vary. XG is anionic, while GG and AG are non-ionic. The study found that biopolymer-treated CS improved in both index and geotechnical properties. This improvement is due to the biopolymers' high viscosity, ability to aggregate, adsorption capabilities, and the formation of cross-linking bonds. The effectiveness of the improvement contrasts on the concentration and type of the biopolymer used. Furthermore, the biopolymer-treated CS were tested for stability against wind and water erosion through various tests, such as pinhole, surface resistance, cylindrical dispersion, and water retention tests. The results showed that even a small amount, 0.5% concentration of biopolymer solution can increase adhesion effects of CS. Moreover, microscopic analysis using a scanning electron microscope (SEM) showed how the structure of the soil changed after being treated with biopolymers. These changes were correlated to improve the geotechnical properties of CS soil. The long chains of biopolymers interacted with the soil to cause these changes. Finally, a leachate analysis was inculcated to measure the effectiveness of untreated and biopolymer-treated CS soil comparatively.

Exploration of ureolytic airborne bacteria for biocementation applications from different climate zones in Japan

The present study investigated the ureolytic airborne bacteria for microbial induced carbonate precipitation (MICP) applications, seeking resilient strains in order to address the problems of bacterial survivability and adaptability in biocementation treatment and to contribute a robust approach that can effectively stabilize diverse soils. Since the airborne bacteria tend to survive in dynamic environments, they are believed to possess remarkable adaptability in harsh conditions, thus holding great potential for engineering applications. Samplings across diverse climatic zones revealed that approximately 10-20% of the isolates were ureolytic bacteria in each sampling site. A series of characterization tests were conducted on selected strains to study the temperature dependency of urease activity. The results revealed that many of these isolates are unique in many aspects. For instance, some trains of Glutamicibacter sp. were found to precipitate extra-large calcium carbonate crystals that could be beneficial in the cementation of coarse soils. This study stands out from previous research on standard ureolytic bacteria by focusing on the exploration of airborne bacteria. The findings demonstrate that a significant number of ureolytic airborne bacteria have great potential, suggesting that the air can serve as a bacterial isolation source for MICP applications.

Effectiveness of microbial-induced carbonate precipitation for mitigating the hydraulic erosion of the riverbank

Soil erosion and riverbank degradation pose major threats to ecosystem health and sustainable development of human society. The seemingly effective hard revetment structures have often overlooked the self-purification capacity of rivers. This study experimentally explored the effectiveness of microbial-induced carbonate precipitation (MICP) for mitigating the hydraulic erosion of riverbanks and permeability characteristics of bio-revetment. Erosion tests of MICP-treated sandy soil using the premixing-infiltration technique were conducted with a modified Erosion Function Apparatus (EFA). The erosion resistance of microbially premixed sandy soil did not exhibit the anticipated enhancement due to the limited quantity and ineffective cementation of CaCO3 from the single-time premixed treatment. The erosion rate of the MICP-treated natural sand increased exponentially with the escalation of the flow shear stress. The critical shear stress for the sand treated with premixing and four rounds of infiltration increased by 105.9 times, and the erodibility coefficient decreased by 99.9% compared to the untreated group. This notable enhancement was attributed to the accumulation of effectively cemented CaCO3 from repeated infiltrative consolidation treatments. A generalized power functional model was established to describe the relationship between the critical shear stress and CaCO3 content. The permeability of the revetment was characterized to delineate the connectivity between the aquatic and terrestrial environments. The scanning electron microscopy (SEM) analysis revealed that sand particles and effectively cemented CaCO3 at their contact points formed a skeleton-like structure, creating a novel sand-based material with both water permeability and erosion resistant. This bio-cementation method offers an innovative perspective for mitigating riverbank degradation.

Application of Sporosarcina pasteurii for the biomineralization of calcite in the treatment of waste concrete fines

In this study, we explored and described various parameters of microbially induced calcite precipitation (MICP) using the alkaliphilic bacterium Sporosarcina pasteurii DSM 33, which exhibits ureolytic activity, to stabilize and strengthen waste concrete fines (WCF). Bacterial cell concentration, single and repeated addition of bacterial suspension, and pH adjustment were tested in stage 1 of the experimental agenda in order to tune parameters for sample preparation in stage 2 focused on the effect of MICP treatment duration (14, 30, 60, and 90 days). Two types of WCF materials differing in their physicochemical properties were used for the stabilization. The results of the EDS and XRD analyses confirmed the presence of CaCO3 crystals, which increased by about 10-12% over time, affecting the porosity, compactness, and strength of the formed composites. The XRD results also indicated that the WCF properties significantly influence the formation of the type of CaCO3 crystals, supported also by microscopy observations. This study highlights the potential of MICP technology to make concrete recycling more sustainable, aligning with the concept of a circular economy; however, the interplay between the WCF materials of various properties and bacterial activity must be further scrutinized.

Preparation and performance evaluation of an efficient microbial dust suppressant for dust control in disturbed areas of blast piles in open-pit coal mines

Open-pit coal mining creates large rock piles as a result of removing overlying strata. When disturbed by loading operations and wind, these rock piles release considerable dust, leading to significant environmental pollution. This study aims to develop an environmentally friendly and cost-effective method for dust control in disturbed areas of open-pit coal mines, using Sporosarcina pasteurii as a microbial dust suppressant to explore its potential application and development. Laboratory experiments were conducted to simulate the growth characteristics of Sporosarcina pasteurii in the microenvironment of blast pile dust. The effectiveness of the microbial dust suppressant was evaluated under conditions of impact disturbance and rainfall erosion through wind and rain erosion tests. Results showed that under optimal conditions, the wind erosion resistance of treated samples improved significantly, with an increase of 98.24%, 86.99%, 64.08%, and 40.98% after 1, 2, 3, and 4 impact disturbances, respectively. Additionally, rain erosion resistance improved by 75.55% after 35 min of simulated rainfall. The growth conditions of Sporosarcina pasteurii in blast pile dust leachate were similar to those in sterile water, demonstrating robust growth and consistent urease activity of 7.78 mmol L⁻1 min⁻1 after 24 h. The mineralization product was calcite-type CaCO3 with uneven particle sizes. This work confirms the feasibility of microbial dust suppressants for managing dust in disturbed areas of open-pit coal mine blast piles, offering a promising approach for dust control in such environments.

Water retention property and microscopic mechanism of shallow soil in inner dump improved by fly ash and polyacrylamide

Improving the water retention property of shallow soil in the inner dump is the key step in the sustainable development of mines. In recent years, the use of fly ash to improve the structure of the inner dump and polyacrylamide as an additive to enhance water retention was an effective method. The article used a physical model test, filter paper method, and microstructure analysis method to compare and analyze the water retention property and microstructure of slope-improved soil with different fly ash and polyacrylamide content. The results show that the combined use of fly ash and polyacrylamide improved the water retention property of the amended soil. Fly ash and polyacrylamide had a greater effect on the low suction stage of the amended soil. Polyacrylamide reacted with water and bound soil particles to form aggregates, and the structural unit bodies were a block structure. Fly ash was non-sticky and was a matrix of fine particles, which weakened the bonding effect of polyacrylamide, and reduced the aggregates of soil particles, and the structural unit bodies were a flocculated structure of aggregates mixed with matrix. This, in turn, enhanced the capillary action and improved the water retention performance of the improved soil. In addition, polyacrylamide could connect water molecules, further enhancing the water retention property of the improved soil. The combined use of fly ash and polyacrylamide improved the available water content of improved soil, providing a viable and sustainable solution for improving the comprehensive utilization of fly ash, and laid the foundation for land reclamation at the inner dump.

Impact of soil density on biomineralization using EICP and MICP techniques for earthen sites consolidation

Enzyme-induced calcium carbonate precipitation (EICP) and microbially-induced calcium carbonate precipitation (MICP) techniques represent emerging trends in soil stabilization. However, the impact of soil density on biomineralization, particularly in historical earthen sites, remains unclear. This study compares the consolidation effects of EICP and MICP on cylindrical samples (10 cm × 5 cm) with three densities (1.5 g/cm3, 1.6 g/cm3, and 1.7 g/cm3) derived from the soil near the UNESCO World Cultural Heritage Site of Suoyang Ancient City, Gansu Province, China. Results showed that calcium carbonate production increased across all densities through bio-cementation, with higher densities producing more calcium carbonate. MICP-treated specimens exhibited larger increases in calcium carbonate production compared to those treated with EICP. Specimens with a density of 1.7 g/cm³ showed a wave velocity increase of 3.26% (EICP) and 7.13% (MICP), and an unconfined compressive strength increase of 8% (EICP) and 26% (MICP). These strength increases correlated with the generation of calcium carbonate. The findings suggest that biomineralization can be effectively utilized for in situ consolidation of earthen sites, emphasizing the importance of considering soil density in biologically-based conservation technologies. Furthermore, MICP shows potential advantages over EICP in providing stronger, compatible and more sustainable soil reinforcement.

Application of New Polymer Soil Amendment in Ecological Restoration of High-Steep Rocky Slope in Seasonally Frozen Soil Areas

In seasonally frozen soil areas, high-steep rocky slopes resulting from open-pit mining and slope cutting during road construction undergo slow natural restoration, making ecological restoration generally challenging. In order to improve the problems of external soil attachment and long-term vegetation growth in the ecological restoration of high-steep rocky slopes in seasonally frozen areas, this study conducted a series of experiments through the combined application of polyacrylamide (PAM) and carboxymethyl cellulose (CMC) to assess the effects of soil amendments on soil shear strength, water stability, freeze-thaw resistance, erosion resistance, and vegetation growth. This study showed that the addition of PAM-CMC significantly increased the shear resistance and cohesion of the soil, as well as improving the water stability, freeze-thaw resistance, and erosion resistance, but the internal friction angle of the soil was not significantly increased after reaching a certain content. Moderate amounts of PAM-CMC can extend the survival of vegetation, but overuse may cause soil hardening and inhibit vegetation growth by limiting air permeability. It was observed by a scanning electron microscope (SEM) that the gel membrane formed by PAM-CMC helped to "bridge" and bind the soil particles. After discussion and analysis, the optimum application rate of PAM-CMC was 3%, which not only improved the soil structure but also ensured the growth of vegetation in the later stage under the optimum application rate. Field application studies have shown that 3% PAM-CMC-amended soil stably attaches to high-steep rocky slopes, with stable vegetation growth, and continues to grow after five months of freeze-thaw action, with no need for manual maintenance after one year.

Experimental test and mechanism analysis of soil crust erosion resistance of rammed earth Great Wall in rainy season

Rammed earth is a kind of cleaning material, widely used in all kinds of buildings in the world. The Great Wall of ancient China is a typical world cultural site built from rammed earth. The rammed earth Great Wall of Shanhaiguan is close to Bohai Bay, which has suffered from long-term erosion by rain, causing a series of problems such as soil loss, collapse and gully flushing. The protection materials of the rammed earth site have always puzzled scholars. However, during the rainy season, it was found that some of the walls at Xiaowan Gouge and Nantuzhuang Gouge in the Shanhaiguan Great Wall had unwashed traces, the soil surface of the walls was intact, and the anti-erosion ability of the walls was significantly higher than that of other places. In order to explore the reasons for its strong anti-erosion ability in the natural state of rammed earth wall, guide the protection of rammed earth Great Wall, and carry out different experimental tests to explore its anti-erosion reasons and internal mechanisms. Firstly, the characteristics of rammed soil were understood through the composition test of rammed soil, and the indoor and outdoor erosion test was carried out to determine that the anti-erosion reason was the protection of gray-green soil crust. The property and composition of soil crust were determined through the immersion test and genome sequencing. Finally, the protection mechanism of soil crust was analyzed by scanning electron microscopy.

State-of-the-art review of soil erosion control by MICP and EICP techniques: Problems, applications, and prospects

In recent years, the application of microbially induced calcite precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) techniques have been extensively studied to mitigate soil erosion, yielding substantial achievements in this regard. This paper presents a comprehensive review of the recent progress in erosion control by MICP and EICP techniques. To further discuss the effectiveness of erosion mitigation in-depth, the estimation methods and characterization of erosion resistance were initially compiled. Moreover, factors affecting the erosion resistance of MICP/EICP-treated soil were expounded, spanning from soil properties to treatment protocols and environmental conditions. The development of optimization and upscaling in erosion mitigation via MICP/EICP was also included in this review. In addition, this review discussed the limitations and correspondingly proposed prospective applications of erosion control via the MICP/EICP approach. The current review presents up-to-date information on the research activities for improving erosion resistance by MICP/EICP, aiming at providing insights for interdisciplinary researchers and guidance for promoting this method to further applications in erosion mitigation.

Soil microbial improvement using enriched vinasse as a new abundant waste

This study proposes the use of vinasse, an inexpensive and readily available waste biopolymer, as a fundamental component of a waste culture medium that can enhance the effectiveness and cost-efficiency of the microbial-induced calcite precipitation (MICP) method for sustainable soil improvement. Vinasse enriched with urea, sodium caseinate, or whey protein concentrate is employed to optimize bacterial growth and urease activity of Sporosarcina pasteurii (S. pasteurii) bacterium. The best culture medium is analyzed using Taguchi design of experiments (TDOE) and statistical analysis, considering the concentration of vinasse and urea as effective parameters during growth time. To test the best culture medium for bio-treated soil, direct shear tests were performed on loose and bio-treated sand. The results demonstrate a substantial cost reduction from $0.455 to $0.005 per liter when using the new culture medium (vinasse and urea) compared to the conventional Nutrient Broth (NB) culture medium. Additionally, the new medium enhances soil shear strength, increasing the friction angle by 2.5 degrees and cohesion to 20.7 kPa compared to the conventional medium. Furthermore, the recycling of vinasse as a waste product can promote the progress of a circular economy and reduce environmental pollution. As ground improvement is essential for many construction projects, especially those that require high shear strength or are built on loose soil, this study provides a promising approach to achieving cost-effective and sustainable soil microbial improvement using enriched vinasse.

Effect of surfactant on urease-producing flora from waste activated sludge using microbially induced calcite precipitation technology to suppress coal dust

The wettability of microbially induced calcite precipitation (MICP) is a challenge in dust suppression. Herein, the tolerance of urease-producing flora to surfactants was investigated. The optimal tolerance concentrations of the urease-producing flora to sodium dodecylbenzene sulfonate (SDBS, anionic surfactant), alkyl polyglycoside (APG, non-ionic surfactant), and cocamidopropyl betaine (CAB, zwitterionic surfactant), and were 0.2%, 0.1%, and 0.05%. The cetyltrimethylammonium bromide (CTAB, cationic surfactant) inhibited urease production by urease-producing flora. The mineralization products of SDBS, APG, and CAB treatments were all transformed into calcite. The wind resistance test showed that the mass loss of all samples is less than 0.1%. The rain resistance and hardness tests showed that 0.2% SBDS had the best effect, followed by 0.1% APG and 0.05% CAB, and finally, No surfactants. Microbiome analysis showed that the abundance of Sporosarcina and Unclassified_bacillaceae reduced, and the intense competition between Paenalcaligenes and Sporosarcina are essential reasons for reducing urease activity. SDBS and APG could reduce the pathogenic risk of microbial dust suppressants. This study will facilitate the practical application of microbial dust suppressants.

Wind erosion control using alkali-activated slag cement: Experimental investigation and microstructural analysis

This paper aims to mitigate wind erosion of soil by employing alkali-activated slag. Wind tunnel tests were conducted on soil samples treated with varying percentages of slag at different wind speeds (7, 14, 21, and 28 m/s) and under a sand bombardment condition. In the absence of saltating particles, the erodibility ratios of the alkali-activated slag-treated samples with weight percentages of 1%, 2%, 4%, and 6% to the untreated sample at the highest wind speed (i.e., 28 m/s) correspond to 0.19%, 0.10%, 0.08%, and 0.06%, respectively. Moreover, in the presence of saltating particle bombardment, these samples exhibited erodibility reductions of 98.5%, 98.8%, 99.4%, and 99.6% compared to the untreated sample. The strength of the formed crusts, determined by penetrometer tests, increased significantly for the treated samples, ranging from 1300 to 6500 times greater than the untreated sample. The complementary analysis using x-ray diffraction and field emission scanning electron microscopy revealed the formation of albite and anorthite crystals along with the formation of calcium aluminosilicate hydrate, sodium aluminosilicate hydrate, and calcium silicate hydrate gels in the cementation process. Overall, the study highlights the effectiveness of alkali-activated slag in forming strong crusts that provide substantial protection against wind erosion, resulting in a significant decrease in wind erodibility.

Assessment of the Composition Effect of a Bio-Cementation Solution on the Efficiency of Microbially Induced Calcite Precipitation Processes in Loose Sandy Soil

Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H2NCONH2, C6H10CaO6, CaCl2, MgCl2). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated.

A State-of-the-Art Review of Organic Polymer Modifiers for Slope Eco-Engineering

In slope ecological restoration projects, reinforcing soil and promoting vegetation growth are essential measures. Guest soil spraying technology can be used to backfill modified soil and vegetation seeds onto the slope surface, resulting in successful ecological restoration. The use of organic polymer modifiers to reinforce soil has several benefits, such as high strength, effective results, and low pollution levels. Organic polymer soil modifiers can be divided into two categories: synthetic polymer modifiers and biopolymer modifiers. This paper provides a thorough review of the properties and interaction mechanisms of two types of polymer modifiers in soil consolidation. The properties of organic polymer modifiers make them applicable in soil and vegetation engineering on slopes. These modifiers can enhance soil mechanics, infiltration, and erosion resistance and promote vegetation growth. Therefore, the suitability of organic polymer modifiers for soil and vegetation engineering on slopes is demonstrated by their properties and potential for improvement in key areas. Furthermore, challenges and future prospects for slope protection technology using organic polymer modifiers are suggested.

Study of the disintegration of loess modified with fly ash and Roadyes

The disintegration property of loess is the wetting and subsequent disintegration of loess in water, which is generally an important index for resistance to erosion and disintegration of wet loess slopes and foundations. In this study, a disintegration instrument is developed in this laboratory and used to study the disintegration properties of fly ash-modified loess in foundations and Roadyes-modified loess in subgrades. Disintegration tests are used to compare samples of loess modified with different amounts of fly ash and Roadyes, different water contents and different dry densities; the influence of fly ash and Roadyes content on the disintegration of modified loess is analyzed. The differences in disintegration properties between the pure loess and modified loess are compared to explore the evolution of disintegration properties of modified loess and the optimal incorporation levels of fly ash and Roadyes. The experimental results show that the incorporation of fly ash reduces the disintegration of loess, while the incorporation of Roadyes likewise decreases the disintegration of loess. The disintegration of the loess modified with the two curing agents is better than that of the pure loess and loess mixed with a single curing agent; the optimal incorporation levels are 15% fly ash and 0.5‰ Roadyes. Comparing the evolution of the disintegration curves of samples of loess with different modifications shows is a linear relationship between time and amount of disintegration for pure loess and Roadyes-modified loess. Thus, a linear disintegration model is established in which the parameter P is the disintegration rate. According to the exponential relationship between time and amount of disintegration of fly ash-modified loess and loess modified with both fly ash and Roadyes, an exponential disintegration model is established in which the water stability parameter Q affects the strong and weak disintegration of the modified loess. The relationship between the water stability of the loess (modified with added fly ash and Roadyes) in water and the initial water content and dry density is analyzed. The water stability of the loess first increases and then decreases with increasing initial water content and gradually increases with increasing dry density. When the sample density is the maximum dry density, the sample has the best water stability. These research results provide a basis for the application of loess modified with added fly ash and Roadyes.

Comparison of Solidification Characteristics between Polymer-Cured and Bio-Cured Fly Ash in the Laboratory

Fly ash (FA) usually causes air and soil pollution due to wind erosion. However, most FA field surface stabilization technologies have long construction periods, poor curing effects, and secondary pollution. Therefore, there is an urgent need to develop an efficient and environmentally friendly curing technology. Polyacrylamide (PAM) is an environmental macromolecular chemical material for soil improvement, and Enzyme Induced Carbonate Precipitation (EICP) is a new friendly bio-reinforced soil technology. This study attempted to use chemical, biological, and chemical-biological composite treatment solutions to solidify FA, and the curing effect was evaluated by testing indicators, such as unconfined compressive strength (UCS), wind erosion rate (WER), and agglomerate particle size. The results showed that due to the viscosity increase in the treatment solution, with the increase in PAM concentration, the UCS of the cured samples increased first (from 41.3 kPa to 376.1 kPa) and then decreased slightly (from 376.1 kPa to 367.3 kPa), while the wind erosion rate of the cured samples decreased first (from 39.567 mg/(m²·min) to 3.014 mg/(m²·min)) and then increased slightly (from 3.014 mg/(m²·min) to 3.427 mg/(m²·min)). Scanning electron microscopy (SEM) indicated that the network structure formed by PAM between the FA particles improved the physical structure of the sample. On the other hand, PAM increased the nucleation sites for EICP. Due to the stable and dense spatial structure formed by the "bridging" effect of PAM and the cementation of CaCO₃ crystals, the mechanical strength, wind erosion resistance, water stability, and frost resistance of the samples cured by PAM-EICP were increased significantly. The research will provide curing application experience and a theoretical basis for FA in wind erosion areas.

Mechanical properties and mechanism of soil treated with nano-aqueous adhesive (NAA)

The loose structure and low mechanical strength of the surface soil make it vulnerable to damage under erosion conditions. Slope ecological protection is one of the effective methods to improve the stability of slope soil. Although it has been proved that polymer modified materials can effectively improve the soil properties and the environmental protection effect of slope, so far, the improvement mechanism has not been fully understood, especially the chemical mechanism of the material on the enhancement of soil mechanical properties is not clear. In the present study, the effects of nano-aqueous adhesive (NAA) on unconfined compressive strength, shear strength and aggregate characteristics of soil were studied by a series of laboratory experiments. The results show that NAA can increase the strength, aggregate number and stability of the soil, to effectively improve the stability of surface soil. In addition, through infrared spectroscopy and SEM test, it was found that NAA molecules were mainly distributed in the interlayer position of flaky clay minerals, mainly connected with clay minerals through hydrogen bonds, thereby effectively enhancing the cohesion of soil particles.

Model Test Study on the Enhancement of Ecological Self-Repairing Ability of Surface Slope Soil by New Polymer Composites

Plant-based ecological protection is one of the effective methods to improve the stability of slope soils. However, plants need a stable growth environment and water supply. Although it has been demonstrated that polymer materials can effectively enhance the stability and water retention of soils, their improvement mechanism and long-term effects are yet to be clear. In this paper, we use a new polymer composite material (ADNB), an optimized compound of nano-aqueous binder (NAB) and super absorption resin (SAR), to conduct outdoor model tests to study the effects of different ADNB ratios on soil compactness, biochemical properties, and plant growth at longer time scales, and to explore its action law and mechanism of enhancing the ecological self-repairing ability of surface slope soil. The results show that ADNB can effectively improve the soil structure, increase the compactness of the soil, increase the organic matter content, microbial population and available nutrient content in the soil, thus promoting plant growth. The adsorption and agglomeration effect of the NAB in ADNB on soil particles and its degradation in natural environment can be observed by SEM. In summary, ADNB can not only effectively enhance the ecological self-repairing ability of surface slope soil, but also has good environmental friendliness and can be completely degraded under natural conditions without additional adverse effects on soil and environment.