Red clay roadbed reinforcing material based on waste biomass as well as preparation method and application of red clay roadbed reinforcing material

Abstract

The invention discloses a red clay roadbed reinforcing material based on waste biomass, a preparation method and application, the reinforcing material takes waste biomass as a raw material, the material realizes resource utilization of the waste biomass, biomass charcoal is prepared through a pyrolysis process, the biomass charcoal is mixed with pretreated plant fiber according to a certain proportion, and the mixture is prepared into a mixture; and finally, uniformly stirring by adopting a double-shaft forced stirrer. Wherein the preparation process of the biomass charcoal comprises the following steps: under the protection of inert gas, firstly, carrying out drying and high-temperature pyrolysis on waste biomass, and then grinding into fine particles; the plant fibers are cut into short fibers before being mixed, and the performance of the plant fibers is enhanced through alkali liquor spraying treatment. The environment-friendly composite reinforcing material is prepared from the waste biomass, the mechanical property and durability of the red clay roadbed are remarkably improved through the optimal proportion and treatment process of the biomass charcoal and the plant fibers, and the composite reinforcing material has an ecological restoration function and is suitable for green road construction in a complex environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of road engineering, and particularly relates to a red clay subgrade reinforcing material based on waste biomass, a preparation method and application. BACKGROUND

[0002] Red clay is widely distributed in southern China and other regions, but its engineering properties are poor, with low water permeability, easy swelling when wet, and easy shrinkage after drying, which makes it unable to be directly used as a filling material for road subgrade. Traditional red clay subgrade reinforcement methods usually use cement or lime for treatment, however, these methods have problems such as large resource consumption, high cost, and environmental impact. First, the production of cement and lime requires a large amount of energy and is accompanied by high carbon emissions, which does not meet the current green and low-carbon development requirements. Second, the construction area of red clay subgrade is often located in complex environment / rainy areas, and excessive use of cement or lime may damage the soil structure, reduce the ecological function of the soil, and affect the vegetation recovery. In addition, the transportation cost of cement and lime is high, especially in complex environment / rainy areas, long-distance transportation not only increases the construction cost, but also may cause environmental pollution along the way due to spilling and dust.

[0003] Therefore, using waste biomass as a composite reinforcing material is gradually becoming an important development direction for future research and engineering application. By applying biomass charcoal and plant fiber composite materials to the reinforcement of red clay subgrade, not only can the resource utilization of waste biomass be realized and the environmental disposal pressure be reduced, but also the engineering mechanical properties of red clay can be effectively improved, and the stability and bearing capacity of the soil body can be improved, thereby providing a new path for soil reinforcement that is both economical and environmentally friendly. However, there are still some technical bottlenecks in the synergistic mechanism of biomass charcoal and plant fiber, material ratio optimization, strengthening and toughening effect, and long-term environmental adaptability. Therefore, further research and development of high-efficiency, low-cost, and good ecological compatibility of composite subgrade reinforcing materials and processes have important theoretical value and practical significance for promoting the development of road construction towards green and sustainable direction. SUMMARY

[0004] The purpose of the present application is to provide a red clay subgrade reinforcing material based on waste biomass, which can enhance the strength and stability of red clay subgrade, reduce construction cost, and reduce environmental pollution.

[0005] The second purpose of the present application is to provide a preparation method of a red clay subgrade reinforcing material based on waste biomass.

[0006] The third purpose of the present application is to provide an application of a red clay subgrade reinforcing material based on waste biomass.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is a preparation method of a red clay subgrade reinforcing material based on waste biomass, which is specifically performed according to the following steps:

[0008] First, waste biomass is used as a raw material to prepare biomass charcoal through pyrolysis, and the biomass charcoal is mixed with plant fibers, and a double-shaft forced stirrer is used to uniformly stir the mixture to obtain the red clay subgrade reinforcing material.

[0009] Further, the mass fraction of the biomass charcoal is 30% to 50%, and the mass fraction of the plant fibers is 50% to 70%.

[0010] Further, the plant fibers include a mixture of one or more of rice straw and wheat straw; and the biomass charcoal pyrolysis process specifically includes: first, drying the waste biomass under inert gas protection, with the temperature controlled at 150 to 200 DEG C and the duration being 25 to 35 minutes; then, continuously heating to 600 to 800 DEG C under inert gas protection for 40 to 50 minutes; the waste biomass includes a mixture of one or more of branches, leaves, tree bark, and weeds; after pyrolysis, the waste biomass is ground to a particle size of 0.15 to 0.6 mm; and inert gas protection is applied during the pyrolysis process.

[0011] Further, before being mixed with the biomass charcoal, the plant fibers are cut into short fibers of 10 to 20 mm, and then an alkali treatment is performed by spraying a NaOH solution with a concentration of 0.5 to 1 mol / L on the plant fibers, with the mass ratio of the fibers to the solution being 1:(9 to 11).

[0012] A red clay subgrade reinforcing material is prepared by the above preparation method.

[0013] Further, the reinforcing material is used for reinforcing the red clay subgrade.

[0014] Further, the specific method for using the reinforcing material to reinforce the red clay subgrade includes:

[0015] S1, selecting a construction area, determining a construction subzone according to the length and width of the subgrade, and controlling the length of each subzone to be 50 to 100 meters;

[0016] S2, removing weeds, trees and other obstacles in the construction area, appropriately loosening the subgrade, and making the surface flat;

[0017] S3, uniformly laying the reinforcing material on the surface of the subgrade, with the laying thickness controlled to be within 30 cm;

[0018] S4, pyrolysis treatment is performed on the laid waste biomass composite reinforcement material using a mobile pyrolysis device, then the reinforcement material is compacted using a compactor, and finally the reinforcement material is cured.

[0019] Further, the curing process in S4 includes:

[0020] S401, the laid reinforcement material is cured for 28 days through natural curing;

[0021] S402, after the curing is completed, quality detection is performed on the roadbed to check the compressive strength, shear strength and permeability of the reinforcement layer;

[0022] S403, the drainage system of the roadbed is checked to ensure that the dewatering can be smoothly discharged.

[0023] Further, the requirement for the compressive strength in S402 is that the unconfined compressive strength is greater than or equal to 1.2 MPa;

[0024] the requirement for the shear strength is that the internal friction angle φ is greater than or equal to 25° and the cohesion c is greater than or equal to 35 kPa;

[0025] the requirement for the permeability is that the permeability coefficient is between 1x10 -5 ~ 5x10 -6 cm / s, and the material pH value is between 6.5-7.8.

[0026] Compared with the prior art, the present application has the beneficial effects that: the present application is based on waste biomass resources (such as branches, leaves, barks and weeds, etc.), and a composite red clay roadbed reinforcing material is prepared by resource utilization, effectively avoiding the high energy consumption and high carbon emission problems caused by the traditional cement and lime reinforcing methods, and meeting the development trend of green transportation and ecological environmental protection. The material of the present application is composed of biomass charcoal and plant fiber optimized by ratio, and under the optimal process parameters that the biomass charcoal accounts for 40%, the plant fiber length is 20 mm and the NaOH concentration is 0.7 mol / L, the unconfined compressive strength of the prepared reinforced soil body can reach 1.47 MPa, which is more than 320% higher than that of the original red clay, the cohesion reaches 58.9 kPa, and the internal friction angle exceeds 28°, which significantly improves the bearing capacity and shear resistance of the red clay. Durability test shows that the strength retention rate is higher than 78% after 15 dry-wet cycles, the elastic modulus retention rate is more than 76.5% after 10 freeze-thaw cycles, and the pH value is stable at neutral (7.0) after 360 days of natural exposure, which shows good environmental adaptability and long-term stability, and is suitable for variable climate and terrain conditions. From the microstructure, the microporous structure of the biomass charcoal and the plant fiber treated by alkali form a spatial cross-linking network, which significantly improves the integrity and water stability of the soil structure, and also helps to increase the soil organic matter content, promote vegetation recovery, and realize the dual functions of engineering reinforcement and ecological restoration. In terms of construction, the material can be locally sourced, and combined with a mobile pyrolysis device to realize on-site preparation and laying, fully adapting to complex environment / rainy area construction, reducing transportation cost, and having good engineering application prospect and promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0028] Figure 1 is a waste biomass composite reinforced layer roadbed structure profile;

[0029] Figure 2 is a biomass charcoal preparation process flow chart. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely in the following combined with the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] This embodiment provides a red clay roadbed reinforcement material based on waste biomass. Specifically, it is a waste biomass composite reinforcement material suitable for red clay roadbeds. It uses waste biomass (such as branches, leaves, bark, weeds, etc.) as raw materials, prepares biochar through pyrolysis, and mixes it with natural plant fibers (such as rice straw, wheat straw, etc.) to form a highly efficient waste biomass composite reinforcement material.

[0032] In some specific embodiments, the biochar content in the reinforcing material is 30%-50% by mass, with the optimal proportion being 35% ± 2%; while the plant fiber content is 50%-70% by mass.

[0033] In some possible implementations, to ensure optimized material performance, the biochar raw material (waste biomass) is ground to a particle size range of 0.15-0.6 mm after pyrolysis and carbonization at 600-800℃, ensuring good bonding with plant fibers.

[0034] In some possible embodiments, the plant fibers are short fibers with a length of 10-20 mm, and then sprayed with NaOH solution (concentration 0.5-1 mol / L). The fibers are impregnated with the solution at a mass ratio of 1:9 to 11 to undergo alkali treatment modification, which gives them better strength and adhesion.

[0035] In some specific implementation methods, such as Figure 2 The pyrolysis process of biochar is as follows: First, the biomass raw material is dried at a temperature controlled at 150-200℃ for 30 minutes ± 5 minutes under inert gas protection. Then, the carbonization stage begins, with the temperature raised to 600-800℃ for 45 minutes ± 5 minutes under inert gas protection. Finally, cooling is performed naturally within a closed system. This series of controlled processes ensures that the biochar meets the desired performance requirements.

[0036] This embodiment also provides an application of a reinforcement material for red clay roadbeds, specifically a reinforcement method for red clay roadbeds, including the following steps:

[0037] Preliminary preparations: Select a flat construction area with good drainage, clear debris from the site and conduct a geological survey to ensure that the roadbed surface is flat, the roadbed length is controlled between 50 and 100 meters, the roadbed surface is clean and the thickness is not less than 20 cm.

[0038] Preparation and mixing of waste biomass composite reinforcement material: biomass charcoal accounts for 30%-50%, the best ratio is 35%±2%; plant fiber accounts for 50%-70%; biomass charcoal particle size is controlled within 0.15-0.6mm, plant fiber length is 10-20mm, and alkali treatment concentration is 0.5-1mol / L NaOH solution. In the pyrolysis step of biomass charcoal, the temperature is controlled within 600-800℃, and the carbonization is carried out under the protection of inert gas for 40-50 minutes, and then natural cooling. This process can ensure the stability and mechanical properties of biomass charcoal. In terms of plant fiber, 0.5-1.0mol / L NaOH solution is used for spraying treatment, and the treated fiber has better adhesion, which ensures good combination with biomass charcoal.

[0039] Subgrade reinforcement treatment and material laying: the mixed reinforcement material is evenly laid on the surface of the subgrade, and the laying thickness is controlled within 30cm; the reinforcement layer needs to be compacted to more than 95% density to ensure that the material and soil are fully combined.

[0040] Later maintenance: the reinforcement material is solidified for 28 days, and the original state of the reinforcement layer is maintained during this period to ensure strength and stability; the compressive strength should be more than 1.2MPa. Regularly check the compressive strength (≥1.2MPa), shear strength and permeability of the subgrade, and the drainage slope should be not less than 2% to ensure smooth drainage of water and avoid water accumulation affecting the stability of the subgrade.

[0041] Next, the specific construction method of the present application will be described in detail in combination with examples.

[0042] An ecological reinforcement method and construction process suitable for red clay subgrade, including S1 preliminary preparation, S2 preparation and mixing of waste biomass composite reinforcement material, S3 subgrade reinforcement treatment and material laying, and S4 later maintenance of four stages.

[0043] In some embodiments, the specific implementation process of the step S1 preliminary preparation is:

[0044] S11 Select construction area: according to the actual situation of the red clay subgrade, select an area with flat terrain and good drainage for construction. According to the length and width of the subgrade, determine the construction partition, and the length of each partition is controlled within 50-100 meters to gradually complete the reinforcement work.

[0045] S12 Clean the site: remove weeds, trees and other obstacles in the construction area to ensure that the surface of the subgrade is clean and flat, facilitating subsequent construction.

[0046] S13 Geological survey and analysis: conduct detailed geological survey to ensure that the distribution range and characteristics of the red clay subgrade meet the construction requirements, analyze the water content, compactness and other physical properties of the red clay, and provide data support for subsequent construction.

[0047] In some embodiments, the step S2 of preparing and mixing the waste biomass composite reinforcing material is implemented as follows:

[0048] S21 Preparation of biomass charcoal: Selecting waste biomass such as branches, leaves, and tree bark or their mixture, and subjecting it to pyrolysis treatment. The waste biomass is heated to 600-800°C for carbonization pyrolysis and ground to a particle size range of 0.15-0.6 mm. This process is carried out under the protection of inert gas (nitrogen or argon) to prevent excessive oxidation reaction and ensure the efficiency and stability of the biomass charcoal. By controlling the temperature and treatment time, the carbonization stage is ensured to last for 45 minutes in a limited oxygen environment, and finally cooled in a closed system through a natural cooling process to obtain high-quality biomass charcoal.

[0049] S22 Treatment of plant fibers: Selecting a mixture of natural plant fibers such as rice straw and wheat straw, and cutting them into short fibers of 10-20 mm. Use a NaOH solution with a concentration of 0.5-1 mol / L to spray the plant fibers for alkali treatment modification to improve their strength and adhesion, ensuring good bonding effect with the biomass charcoal.

[0050] In some possible implementations, the plant fibers can also be single wheat straw or rice straw, or other plant fibers.

[0051] S23 Preparation of mixed materials: Mix the biomass charcoal and plant fibers in a ratio of 30%-50%, with the optimal ratio being 35%±2% biomass charcoal and 50%-70% plant fibers to ensure the optimized performance of both. Use a double-shaft forced mixer to uniformly stir the mixture to ensure the stability and uniformity of the materials.

[0052] In some embodiments, the step S3 of subgrade reinforcing treatment and material laying is implemented as follows:

[0053] S31 Soil preparation: After cleaning the surface of the subgrade, loosen the subgrade properly to make the surface flat for uniform laying of the reinforcing material later.

[0054] S32 Laying of waste biomass composite reinforcing material: Lay the mixed waste biomass composite reinforcing material evenly on the surface of the subgrade, with the laying thickness controlled within 30 cm to ensure uniform distribution of the material and avoid accumulation or voids.

[0055] S33 Reinforcement and Compaction: Using a mobile pyrolysis device, the laid waste biomass composite reinforcement material is subjected to pyrolysis treatment, optimizing the chemical structure of the biochar and plant fibers, making them have higher strength and stability. Subsequently, a compactor is used to compact the reinforced material to ensure its full integration with the roadbed soil, increasing the compactness and stability of the reinforced layer.

[0056] In some embodiments, the specific implementation process of the step S4 post-curing is as follows:

[0057] S41 Solidification Treatment: The laid reinforced material needs to be solidified for 28 days through natural curing to achieve optimal strength and stability. During the curing period, ensure that the reinforced layer is not disturbed by external factors and maintain its original state.

[0058] S42 Quality Inspection: After solidification, the roadbed is subjected to quality inspection to check the compressive strength, shear strength, and permeability of the reinforced layer to ensure compliance with design requirements.

[0059] S43 Drainage System Inspection: Inspect the drainage system of the roadbed to ensure that the water can be smoothly drained to avoid water accumulation affecting the stability of the roadbed. By opening drainage ditches and setting appropriate drainage slopes, ensure the waterproof effect of the roadbed.

[0060] The ecological reinforcement layer composed of the reinforced material of the present embodiment is as shown in Figure 1 .

[0061] In the present embodiment, the unconfined compressive strength of the material of the present embodiment is ≥1.2 MPa (28 days curing), ensuring that the reinforced layer can withstand construction and long-term load; Direct shear performance and interfacial adhesion of biomass charcoal and plant fiber composite material: The direct shear strength requires that the internal friction angle φ ≥ 25° and the cohesion c ≥ 35 kPa, ensuring its shear stability.

[0062] Durability performance and environmental adaptability test of biomass charcoal and plant fiber composite material: The permeability coefficient is controlled between 1×10 -5 and 5×10 -6 cm / s, the pH value of the material is required to be between 6.5-7.8, maintaining neutral improvement, avoiding negative impact on the surrounding soil environment. Through freeze-thaw cycle test, wet heat aging test, etc., the long-term stability and durability of the material in harsh environments are verified.

[0063] Experimental Example 1

[0064] Experimental purpose: This experiment aims to determine the effect of NaOH solution concentration on the modification of plant fibers, and to evaluate the mechanical properties, interfacial bonding, and environmental adaptability of the fibers under different treatment concentrations.

[0065] Experimental Design: A single-factor, five-level experimental design was adopted, with other parameters fixed (treatment time 30 minutes, temperature 25℃). A blank control group (CK1) was included, with no NaOH solution added (water). The experimental design is shown in Table 1.

[0066] Table 1 Experimental design of the effect of NaOH concentration on fiber properties

[0067]

[0068] Experimental steps:

[0069] (1) Sample preparation: Take the same batch of rice straw fibers and cut them to a length of 15±2 mm; prepare NaOH solutions (0.3 / 0.5 / 0.7 / 1.0 / 1.2 mol / L) according to the concentration gradient; impregnate the fibers and solutions at a mass ratio of 1:10, and treat with constant temperature shaking at 25℃ for 30 minutes; rinse with deionized water until neutral, and dry at 60℃ to constant weight.

[0070] (2) Performance testing: Tensile strength: using a universal testing machine (GB / T 14337), clamping distance 50mm, tensile rate 10mm / min; Interfacial adhesion: prepared fiber-biochar composite sample, and determined by pull-out test (GB / T50123); Mass loss rate: calculated the change in fiber dry weight before and after treatment; Surface morphology: observed the surface modification effect of fiber using scanning electron microscopy (SEM).

[0071] Experimental results: The experimental results are shown in Table 2.

[0072] Table 2 Effect of NaOH concentration on fiber properties

[0073]

[0074] Experimental Conclusion: The results show that when the NaOH solution concentration is 0.7 ± 0.05 mol / L, the tensile strength of the fiber reaches a peak of 182 MPa, which is 91.6% higher than that of the untreated group (CK1); at this concentration, the interfacial adhesion between the fiber and biochar reaches 1.35 N / mm². 2 This significantly improved the bonding performance of the material; the mass loss rate was controlled at 15.8%, within an acceptable range, ensuring efficient material utilization. Excessively high concentrations (above 1.0 mol / L) led to a decrease in fiber strength and bonding force, while the mass loss rate increased significantly, indicating that excessive corrosion adversely affected the fiber structure, and that higher NaOH solution concentrations do not necessarily equate to better performance in traditional processes. After neutralization, the treated wastewater had a pH of 7.2 ± 0.3, meeting environmental emission requirements and reducing treatment costs by 37%.

[0075] Experiment Example 2

[0076] Experimental Objective: This experiment aims to investigate the effect of different biochar-to-plant fiber ratios on the unconfined compressive strength of roadbed reinforcement materials. By comparing different biochar contents, plant fiber lengths, and ratios, the material formulation can be optimized to obtain the best compressive strength and stability, ensuring its effective application in practical roadbed reinforcement.

[0077] Experimental Design: An orthogonal array design was used, with three parallel samples prepared for each group. A blank control group (CK2: unreinforced red clay) was set up. The experimental design is shown in Table 3. The evaluation indicators included compressive strength and water stability coefficient.

[0078] Table 3 Experimental Design for Unconfined Compressive Strength Test

[0079] Factor Level 1 Level 2 Level 3 A: Biomass char ratio 30％ 40％ 50％ B: Pyrolysis temperature 600℃ 700℃ 800℃ C: Fiber length 10 mm 15 mm 20 mm

[0080] Experimental steps:

[0081] (1) Material preparation: Collect cedar tree branches and pyrolyze them at different temperatures to prepare biochar (grind to 0.15-0.6 mm); treat rice straw fiber with 0.75 mol / L NaOH for 30 minutes and then cut it to the target length; mix biochar, fiber and red clay according to the ratio (control the optimal moisture content at 15±2%); compact and shape in layers (Φ50×100 mm cylinder), each layer is compacted 15 times.

[0082] (2) Sample curing: After the sample preparation is completed, it is placed in a standard constant temperature and humidity curing chamber for 7 days at a temperature of 20±2℃ and a curing humidity of ≥90%.

[0083] (3) Performance test: Unconfined compressive strength: cylindrical specimen according to GB / T 50123 standard; Water stability: compressive strength is tested after immersion in water for 7 days, and the water stability coefficient is calculated (r = saturated strength / standard strength).

[0084] Experimental results: Unconfined compressive strength test data (28-day curing) are shown in Table 4.

[0085] Table 4 Unconfined compressive strength test data (after 28 days of curing)

[0086]

[0087]

[0088] Experimental conclusions: The results above show that when the biochar content is 40%, the pyrolysis temperature is 700℃, and the fiber length is 20mm (Group 5), the compressive strength reaches 1.47MPa, which is 320% higher than CK2, and the cohesion is 150% higher; the increase in pyrolysis temperature significantly improves the material strength (the microporous structure is most developed at 700℃); the water stability coefficient is 85.6% (meeting the requirements for long-term service of roadbed).

[0089] Experimental Example 3

[0090] Experimental Objective: This experiment aims to study the direct shear properties of biochar and plant fiber composite materials and their interfacial adhesion to soil. By using different proportions of biochar, plant fiber lengths and ratios, the shear strength and interfacial adhesion of the reinforcement material are optimized, and the practical application effect of this material in the reinforcement of red clay subgrade is further verified.

[0091] Experimental Design: A single-factor experimental design was used, with other parameters fixed, to explore the effects of different biochar ratios, plant fiber lengths, and proportions on the shear strength of the composite material. The experiment consisted of three different experimental schemes:

[0092] The optimal biochar ratio (40%) and plant fiber length (20 mm) were determined by different NaOH solution concentrations (0.5 mol / L, 0.7 mol / L, and 1.0 mol / L).

[0093] The optimal NaOH solution concentration (0.7 mol / L) and biochar ratio (40%), and different plant fiber lengths (10 mm, 15 mm, 20 mm);

[0094] The optimal plant fiber length (20 mm) and optimal NaOH solution concentration (0.7 mol / L) were determined by different biochar ratios (30%, 40%, and 50%).

[0095] Direct shearing experiments were conducted under a vertical pressure of 200 kPa in the above three cases.

[0096] Table 5 Single-factor experimental design matrix

[0097]

[0098]

[0099] Experimental steps:

[0100] (1) Material preparation: Fir waste was pyrolyzed at 700℃ (drying at 200℃ / 30min, carbonizing at 700℃ / 45min) and then ground to 0.15-0.6mm. Rice straw was cut to the target length and then sprayed with NaOH solution for 30min (0.7mol / L for Group 1 and Group 3).

[0101] (2) Sample molding: Mix materials according to the specified ratio (red clay moisture content 15±2%). Use a ring cutter method for layered compaction (Φ...

[0102] (61.8×20mm), single layer compacted 8 times.

[0103] (3) Curing conditions: constant temperature and humidity for 28 days (20±2℃, humidity ≥90%).

[0104] (4) Test method: Direct shear test: ZJ type direct shear apparatus, vertical pressure gradient loading, shear rate 0.8mm / min (GB / T 50123).

[0105] Experimental results: The data from the single-factor experiment are shown in Table 6.

[0106] Table 6 Key data from the single-factor experiment

[0107]

[0108] Experimental conclusion:

[0109] (1) Optimal parameter verification: NaOH concentration: 0.7 mol / L treatment increased the fiber-biochar interface adhesion by 175.4% (compared to untreated); Fiber length: 20 mm fibers form a continuous reinforced network through three-dimensional interweaving, with a shear strength of 153.2 kPa; Biochar content: 40% microporous structure is the most developed.

[0110] (2) Quantification of technical advantages: The optimal combination (40% biochar + 20mm fiber + 0.7mol / L) has a shear strength that is 89.7% higher than that of traditional lime soil. The experimental results meet the requirements of the "Specifications for Design of Highway Subgrade" JTG D30-2015.

[0111] Experiment Example 4

[0112] Experimental Objective: This experiment aims to evaluate the performance degradation characteristics of biochar and plant fiber composite materials under wet-dry cycles, freeze-thaw cycles, and long-term exposure, verify their engineering applicability under complex climatic conditions, and ensure that they can maintain high strength, stability, and ecological adaptability during long-term use, thus meeting the durability requirements of roadbed reinforcement.

[0113] Experimental Design: The experimental design is shown in Table 7, with blank control groups (CK3, CK4, CK5). The blank control group (CK3) used unreinforced red clay, the blank control group (CK4) used traditional lime-reinforced soil, and the blank control group (CK5) used pure biochar material. In the experiment, the moisture content of the red clay in all samples was 15±2%. After 28 days of standard curing, durability tests were conducted to simulate wet-dry cycles, freeze-thaw cycles, and long-term exposure conditions.

[0114] Key parameters: Baseline group: 40% biochar + 20mm fiber + 0.7mol / L NaOH treatment; Curing conditions: Durability test was conducted after 28 days of standard curing.

[0115] Table 7 Experimental Design for Durability of Biochar and Plant Fiber Composite Materials

[0116]

[0117] Experimental steps:

[0118] (1) Sample preparation: The composite material (red clay with a moisture content of 15±2%) was prepared and molded into Φ50×100mm cylinders (unconfined compressive strength) and 50×50×50mm cubes (freeze-thaw test).

[0119] (2) Durability test: wet-dry cycle: 12h saturation (20℃ water bath) → 12h drying (55℃) is one cycle; freeze-thaw cycle: -20℃ freezing for 12h → 25℃ water bath thawing for 12h is one cycle; natural exposure: simulated environment (annual average rainfall of 1200mm, temperature difference of -15~35℃).

[0120] (3) Performance testing: Mechanical properties: triaxial test (confining pressure 50-300kPa), ultrasonic test (wave velocity and porosity correlation); Chemical stability: ICP-MS detection of heavy metal leaching (GB 5085.3); Ecological indicators: soil microbial activity detection (ATP bioluminescence method).

[0121] Experimental results: Key durability data comparisons are shown in Table 8.

[0122] Table 8 Comparison of Key Durability Data

[0123]

[0124]

[0125] Experimental conclusion:

[0126] (1) In the wet-dry cycle and freeze-thaw cycle tests, the compressive strength of the composite material was retained at over 75% after 15 wet-dry cycles, which is significantly higher than the less than 50% of that of traditional lime-reinforced soil; in the freeze-thaw cycle, the elastic modulus of the composite material was retained at 76.5%, which is also better than that of traditional materials (48.3%). This indicates that the biochar and plant fiber composite material has good anti-attenuation properties.

[0127] (2) Regarding the mass loss rate, the composite material had a mass loss of 4.5% after 15 wet-dry cycles, which was significantly lower than that of the traditional material (>15%), indicating that the composite material had stronger stability. The mass loss rate after freeze-thaw cycles also showed good performance, further demonstrating the durability of the material.

[0128] (3) In the long-term exposure experiment, the pH value of the composite material was stable between 6.8 and 7.5, which met the requirements of ecological restoration, while the pH value of the traditional material fluctuated greatly and did not meet the requirements of ecological stability.

[0129] (4) In microscopic analysis, the porosity increase of the composite material is 34.2% lower than that of the traditional material, and the interfacial adhesion decreases less, proving that the combination of biochar and plant fiber effectively enhances the structural stability of the material.

[0130] (5) Taking into account compressive strength, mass loss rate, pH value and microstructure stability, the optimal ratio is 40% biochar and 20mm plant fiber, which is modified by treatment with 0.7mol / L NaOH and exhibits the best performance. This ratio not only improves the mechanical properties and stability of the material, but also ensures its long-term durability under complex climatic conditions.

[0131] Experimental Examples 1-4 of this invention used orthogonal experiments, single-factor variable analysis, and long-term environmental simulation methods to verify the technical advantages of biochar-plant fiber composite materials in the reinforcement of red clay subgrades. The key conclusions are as follows:

[0132] (1) Material composition:

[0133] Biochar: 40% (by mass), pyrolyzed in three stages at 700℃ (drying at 200℃ for 30 min, carbonizing at 700℃ for 45 min, and then naturally cooled), and ground to 0.15-0.6 mm.

[0134] Plant fiber: 60% (by weight) of rice straw fiber, cut to 20mm and modified with 0.7mol / L NaOH.

[0135] (2) Construction process:

[0136] Paving thickness: ≤300mm / layer, compaction degree ≥93%.

[0137] Solidification treatment: On-site activation using a mobile pyrolysis unit (processing capacity 2-3t / h).

[0138] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0139] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a red clay roadbed reinforcement material based on waste biomass, characterized in that, Please follow these steps: First, waste biomass is used as raw material to prepare biochar through pyrolysis, which is then mixed with plant fiber. The mixture is then uniformly stirred using a twin-shaft forced mixer to obtain a reinforcement material for red clay roadbed.

2. The method for preparing a red clay roadbed reinforcement material based on waste biomass according to claim 1, characterized in that, The biochar accounts for 30% to 50% of the total mass, and the plant fiber accounts for 50% to 70% of the total mass.

3. The method for preparing a red clay roadbed reinforcement material based on waste biomass according to claim 1, characterized in that, The plant fiber includes one or more of rice straw and wheat straw; the biochar pyrolysis process specifically involves: firstly, drying the waste biomass under inert gas protection at a temperature controlled at 150–200°C for 25–35 minutes; then, continuing to heat to 600–800°C under inert gas protection for 40–50 minutes; the waste biomass includes one or more of branches, leaves, bark, and weeds; after pyrolysis, grinding to particles with a diameter of 0.15–0.6 mm; inert gas protection is applied during the pyrolysis process.

4. The method for preparing a red clay roadbed reinforcement material based on waste biomass according to claim 1, characterized in that, Before mixing the plant fiber with biochar, it is first cut into short fibers of 10-20 mm, and then sprayed with a NaOH solution with a concentration of 0.5-1 mol / L. The mass ratio of the fiber to the solution is 1:(9-11), and the plant fiber is modified by alkali treatment.

5. A red clay roadbed reinforcement material based on waste biomass, characterized in that, The material is prepared according to any one of the methods for preparing reinforcement materials for waste biomass red clay roadbeds as described in claims 1 to 4.

6. The application of a red clay subgrade reinforcement material based on waste biomass as described in claim 5, characterized in that, The reinforcement material is used for reinforcing red clay roadbeds.

7. The application of a red clay roadbed reinforcement material based on waste biomass as described in claim 6, characterized in that, The specific method for using the aforementioned reinforcing material to reinforce red clay roadbeds is as follows: S1. Select the construction area and determine the construction zones according to the length and width of the roadbed. The length of each zone should be controlled between 50 and 100 meters. S2. Clear weeds, trees and other obstacles from the construction area, and loosen the roadbed appropriately to make its surface flat; S3. Spread the reinforcement material evenly on the roadbed surface, and control the thickness of the material to within 30cm. S4. Use a mobile pyrolysis device to pyrolyze the laid waste biomass composite reinforcement material, then use a compactor to compact the reinforcement material, and finally cure the reinforcement material.

8. The application of a red clay subgrade reinforcement material based on waste biomass according to claim 7, characterized in that, The maintenance process in S4 includes: S401. The reinforcement material after laying shall be cured naturally for 28 days. S402. After curing, conduct quality testing on the roadbed to check the compressive strength, shear strength, and permeability of the reinforced layer; S403. Inspect the roadbed drainage system to ensure that rainwater can be discharged smoothly.

9. The application of a red clay subgrade reinforcement material based on waste biomass as described in claim 8, characterized in that, The compressive strength requirement for S402 is: unconfined compressive strength ≥ 1.2 MPa; The shear strength requirements are: internal friction angle φ≥25°, cohesion c≥35kPa; The permeability requirement is: a permeability coefficient of 1×10⁻⁶. -5 ~5×10 -6 The material's speed is between cm / s and its pH value is between 6.5 and 7.8.

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