Low-carbon durable chemically-improved soil skeleton slope protection material and construction method

Abstract

The invention relates to a low-carbon durable chemically-improved soil skeleton slope protection material and a construction method thereof, and belongs to the technical field of railway roadbed slope protection engineering. The material takes engineering spoil as a main raw material, and cement, lime, fly ash, water and a composite additive are matched, so that solid waste resource utilization is realized, and carbon emission is reduced. Cement or lime is selected as a main modifier according to the soil property, so that the strength and durability are improved. During construction, a wet spraying process is adopted, the materials and the accelerator are mixed and then directly sprayed into a foundation trench for forming, formwork erecting is not needed, and the construction efficiency is high. The formed framework is tightly combined with the slope surface, the integrality and the impermeability are excellent, freeze thawing, dry-wet circulation and water and soil loss can be effectively resisted, and the method is suitable for protection and reinforcement of various soil slopes.

Description

TECHNICAL FIELD

[0001] The present application relates to a material and its forming method, in particular to a low-carbon durable chemical improved soil skeleton revetment material and its construction method, belonging to the technical field of railway subgrade slope protection engineering. BACKGROUND

[0002] Skeleton revetment is an important structure of railway subgrade soil slope protection engineering. It forms overall constraint to the slope surface through rigid skeleton, effectively disperses slope stress, prevents soil slope from shallow collapse and other diseases under the action of train dynamic load and dry-wet and freeze-thaw cycle, ensures long-term stability of subgrade, and avoids major safety risks such as track deformation and line interruption caused by slope instability.

[0003] The existing skeleton revetment mainly adopts cast-in-place or prefabricated concrete form: the cast-in-place concrete skeleton has problems such as complicated process and low construction efficiency; while the prefabricated concrete skeleton has problems such as weak combination of concrete skeleton and original soil layer, poor overall performance, difficulty in matching standard parts with terrain, and high cost of special-shaped customization. In addition, the production process of concrete has large carbon emission, which is not conducive to the advantages of green railway in the process of engineering construction.

[0004] For example, the construction method of the concrete arch skeleton revetment disclosed in CN 111119204A optimizes the design of the integrated skeleton formwork connection and position control, reduces the difficulty of setting up the formwork, but still has problems such as complicated construction process and time-consuming and labor-intensive operation.

[0005] CN 104846834A and CN 117364807A disclose a prefabricated skeleton structure and a construction method. By modularizing and standardizing the slope protection skeleton, batch prefabrication and standard installation are realized, the construction process is reduced, and the rapid construction of the skeleton revetment structure is realized, but there are still problems such as poor overall performance of the structure, high requirements for the flatness of the slope surface and the groove, etc.

[0006] CN 116023078A discloses a method for preparing flowable solidified soil from engineering waste slag. The engineering waste slag is resourcefully utilized to prepare flowable solidified soil, which is used for various backfilling and pouring engineering, and meets the green, low-carbon and sustainable development strategy, but the durability of the material and its construction performance in slope protection engineering are unknown.

[0007] Therefore, there is an urgent need for a low-carbon and durable skeleton revetment material, as well as an economical and efficient construction method with excellent structural performance. SUMMARY

[0008] In view of the deficiencies in the prior art, the purpose of the present application is to provide a solid waste-based low-carbon durable skeleton revetment material, which makes full use of engineering spoil (slag) and reduces carbon emissions while ensuring that the material has certain strength and durability. Another purpose of the present application is to provide a skeleton revetment construction method to improve construction efficiency and the overall integrity of the structure.

[0009] A low-carbon durable chemically improved soil skeleton revetment material, characterized by being composed of the following raw materials in parts by mass: engineering spoil 100-150 parts, cement 3-15 parts, lime 3-15 parts, fly ash 10-50 parts, water 10-20 parts, and composite admixture 1-3 parts.

[0010] Preferably, the engineering spoil is one or more of fine sand, silt, clay, or red-bed mudstone, and the maximum particle size is not greater than 15 mm.

[0011] Preferably, when the plasticity index of the engineering spoil is less than 12 and the sulfate content is less than 0.25%, cement is used as the main modifier; when the plasticity index is greater than 12 and the sulfate content is less than 0.8%, lime is used as the main modifier.

[0012] Preferably, the cement strength grade is 32.5 or 42.5, and the lime is first-class building calcium quicklime powder with a CaO+MgO content of not less than 80%.

[0013] Preferably, the fly ash has a fineness of not greater than 20%, a SO3 content of not greater than 3%, and a loss on ignition of not greater than 8%, and is used in combination with cement or lime.

[0014] Preferably, the composite admixture includes a surfactant, a polyol, active silicon dioxide, a carbonate, and a sulfate.

[0015] The present application also discloses a construction method for the low-carbon durable chemically improved soil skeleton revetment material as described above, comprising the following steps: (1) Side slope pretreatment, removing loose soil and vegetation on the slope surface; (2) Measuring and setting out, trimming the slope surface according to the design drawings; (3) Excavating the foundation trench according to the skeleton layout; (4) Mixing the chemically improved soil with the accelerating agent at the spray head to obtain wet-sprayed chemically improved soil material; (5) Spraying the chemically improved soil in the foundation trench layer by layer from bottom to top to form a skeleton beam, with a spraying thickness of 30-50 mm for each layer, and thickening the spraying at the edge of the skeleton to form a water retaining edge at the end; (6) Shaping after spraying and forming, covering the geotextile and watering for 7-14 days for curing.

[0016] Preferably, the accelerator is an alkali-free accelerator with an initial setting time of 1-5 minutes, a final setting time of 5-12 minutes, and a dosage of 3%-5% of the cement dosage.

[0017] Preferably, the skeleton beam is formed in one step by wet spraying, without the need for formwork.

[0018] The present invention also discloses the application of a low-carbon, durable, chemically modified soil skeleton slope protection material as described above in railway subgrade slope protection engineering. Beneficial effects

[0019] (1) Chemically improve a large amount of waste soil (silty sand, silt and other sandy soils, as well as special soils such as cohesive soil and mudstone with high water content) in railway engineering construction to replace concrete for the skeleton slope protection, thereby expanding the scope of intensive utilization of engineering waste soil and reducing carbon emissions.

[0020] (2) As a roadbed slope protection project, the skeleton slope protection is exposed to the complex external environment for a long time and needs to have good environmental stability and durability. The addition of composite amendments improves the water stability and frost resistance of chemically improved soil.

[0021] (3) The sprayed frame slope protection method does not require formwork, which improves construction efficiency. Moreover, the chemically improved soil has good contact with the original soil layer of the slope, which improves impermeability and integrity, and can effectively prevent soil erosion on the slope and enhance slope stability. Detailed Implementation

[0022] The low-carbon, durable, chemically modified soil skeleton slope protection material provided by this invention is based on the transformation of "waste (engineering spoil)" into "high-performance engineering materials" through specific component selection and synergistic proportions. The selection of each component has a clear purpose and is irreplaceable: 1. Construction waste soil (100-150 parts): Basic aggregate and matrix. As the main framework and filling matrix of the material, it is key to realizing the resource utilization of solid waste, reducing carbon emissions and material costs. Its physical properties (particle size, plasticity) determine the selection of the subsequent cementitious system. Without it, the core principles of "low carbon" and "solid waste utilization" of this invention are lost, reverting to traditional concrete or cement-stabilized soil, failing to solve the problems of construction waste soil disposal and high carbon emissions.

[0023] 2. Cement (3-15 parts) and lime (3-15 parts): main binder and modifier.

[0024] Cement: The primary hydraulic binder that provides early and late strength. It reacts rapidly and develops strength quickly in soils with low plasticity and low sulfate content.

[0025] Lime: For highly plastic soils (such as clay soils and mudstones), lime can effectively reduce the soil plasticity index, improve compaction, and provide long-term strength through ion exchange, flocculation, and pozzolanic reaction. At the same time, lime has better tolerance to a certain amount of sulfate in the soil.

[0026] Both materials are indispensable, but the emphasis varies depending on the soil type. Using only cement to treat highly plastic soil can easily lead to cracking and poor durability; using only lime to treat sandy soil results in insufficient early strength to meet the requirements for rapid strength formation in slope protection. Combining the two provides a "menu-style" cementitious solution adaptable to different soil types.

[0027] 3. Fly ash (10-50 parts): An auxiliary binder and micro-aggregate, its functions include: ① Morphological effect: Its micro-bead morphology acts as a lubricant, improving the workability of the mixture and facilitating spraying. ② Pozzolanic effect: It reacts with Ca(OH)2 produced by the hydration of cement and lime to form hydrated calcium silicate with cementitious properties, increasing later-stage strength and density. ③ Micro-aggregate filling effect: It fills the pores between soil particles and binders, improving the material's impermeability and durability.

[0028] Without fly ash, the workability of materials (especially the balance between fluidity and cohesion required for spraying) deteriorates, and later strength growth and durability (such as resistance to sulfate attack) are also reduced. It is a key "bridge" connecting coarse-grained soil and fine-grained cementitious materials.

[0029] 4. Water (10-20 parts): Reaction medium and workability regulator. It provides the necessary conditions for the hydration reaction of cement and lime and the pozzolanic reaction of fly ash, while adjusting the moisture content of the mixture to achieve a consistency suitable for mixing and spraying. Insufficient water results in incomplete reaction, making the material dry and unsuitable for spraying; excessive water leads to slurry segregation, decreased strength, increased shrinkage, and easy flow during spraying, making stable formation on slopes impossible.

[0030] 5. Composite admixtures (1-3 parts): Performance-oriented enhancers, their functions are as follows: Surfactants / polyols: Improve the material's affinity for water, enhancing its resistance to water erosion and water stability. Activated silica: As a highly active component, it can accelerate early reactions and improve early strength. Carbonates / sulfates: Can regulate the type and crystallization rate of hydration products, helping to improve the material's freeze-thaw resistance and shrinkage resistance. Without these admixtures, the material is merely ordinary improved soil, and its durability (water stability, frost resistance) under long-term exposure to wet-dry and freeze-thaw cycles cannot be guaranteed, making it difficult to meet the requirements for long-term service of the framework slope protection.

[0031] In summary, the above six components constitute a complementary system that collectively achieves the four major goals of "solid waste utilization, low carbon emissions, durability, and sprayability." The absence of any one of these components will result in shortcomings in the system's environmental friendliness, adaptability, workability, or durability, failing to fully address the problems identified in the background section.

[0032] The following specific examples and comparative examples illustrate the influence of different mix proportions on material properties and verify the effectiveness of the scope defined in claim 1. In all tests, the excavated soil was represented by silt with a plasticity index (Ip) of 8 (sulfate content 0.1%) and clay with an Ip of 18 (sulfate content 0.5%). Performance tests included 7-day unconfined compressive strength (UCS, MPa), 28-day UCS, freeze-thaw cycle resistance (F15, mass loss rate %), and workability evaluation.

[0033] Examples 1-4 (for silty soil, Ip=8, using cement as the main binder)

[0034]

[0035] Conclusion: Example 2 (10 parts cement, 5 parts lime, 20 parts fly ash) achieved the best balance in terms of strength, durability, and workability. Example 1 had the highest strength but a large amount of cement, resulting in slightly lower economic efficiency; Example 3 (5 parts cement) had relatively low strength and insufficient durability; Example 4 (50 parts fly ash) showed slightly slower early strength development, and the material's excessive stickiness affected construction efficiency. This demonstrates that the part ratio range of claim 1 is reasonable in a silty soil system.

[0036] Examples 5-8 (for clay, Ip=18, using lime as the main binder)

[0037]

[0038] Conclusion: Examples 6 and 8 (approximately 10 parts lime and 30 parts fly ash) exhibit good overall performance. Example 5 (15 parts lime) has too low early strength, which is not conducive to rapid protection; Example 7 (15 parts fly ash) has poor material integrity and poor durability. This demonstrates that the part range of claim 1 is also effective in highly plastic clay systems, and emphasizes the synergistic importance of lime and sufficient fly ash.

[0039] Comparative Examples 1-4 (used to verify the effects of missing components or imbalanced proportions)

[0040] in conclusion: Comparative Example 1: The lack of fly ash resulted in poor workability and a loose structure, leading to a sharp decline in freeze-thaw resistance and durability, which could not meet the requirements for long-term exposure.

[0041] Comparative Example 2: In the absence of composite additives, the water stability and antifreeze properties of the material deteriorated significantly, verifying the key role of this component in improving durability.

[0042] Comparative Example 3: The amount of cement used far exceeded the scope of the claims. Although the strength was high, the shrinkage and cracking were severe, the durability was reduced, and the carbon emissions and economic efficiency deteriorated.

[0043] Comparative Example 4: Excessive water usage caused the material to fail to form, lose strength, and ultimately fail completely.

[0044] Based on the above embodiments and comparative examples, it can be seen that: 1. Necessity of Components: The technical solution includes six components, each with its own function, forming a complete system. The absence of any one component (such as in Comparative Examples 1 and 2) will lead to fatal defects in the material's durability, workability, or environmental friendliness.

[0045] 2. Rationality of Proportioning Range: The mass fraction range of each raw material specified in the technical solution (100-150 parts of excavated soil, 3-15 parts of cement, 3-15 parts of lime, 10-50 parts of fly ash, 10-20 parts of water, and 1-3 parts of composite admixture) is an effective window obtained through extensive experimental optimization. Within this range (as in Examples 2, 6, and 8), the material can simultaneously meet the following requirements: low carbon emissions and solid waste utilization: extensive use of excavated soil. Strength requirements: 7-day strength can reach above 1.2 MPa, and 28-day strength can reach 2.0-4.5 MPa, meeting the stress requirements of the slope protection framework. Excellent durability: good resistance to freeze-thaw cycles (mass loss rate <5%), and good water stability. Good workability: suitable for wet spraying process, and can firmly adhere to the slope trench in one step.

[0046] 3. Addressing Background Technical Issues: This mix design successfully transforms unusable engineering waste soil into reliable slope protection material, replacing high-carbon-emission concrete. Its wet-spraying molding method eliminates the need for formwork, improving construction efficiency, and ensures tight bonding with the original soil layer and good overall integrity. Therefore, this technical solution effectively solves a series of technical problems raised in the background technology, such as "high carbon emissions from concrete," "poor integrity of precast components," "complex construction procedures," and "lack of consideration for slope durability in existing solidified soil."

[0047] Based on the above specific implementation methods and experimental verification, this invention provides a specific low-carbon durable chemically modified soil material formulation and a matching wet spray molding process, forming a complete and synergistic technical solution that systematically solves many problems pointed out in the background art: At the materials level, this invention creatively selects and defines a synergistic system and its proportion range of "engineering waste soil - cement / lime - fly ash - composite admixture". This system not only realizes the large-scale and resource-based utilization of engineering waste soil, fundamentally reducing the carbon footprint of material production, but also endows the improved soil with sufficient early and late strength, excellent water stability, freeze-thaw resistance and drying shrinkage resistance through the adaptive selection of cementitious materials (cement / lime) and the refined compatibility of functional components (fly ash, composite admixture). This enables the improved soil to meet the durability requirements of long-term exposure to harsh environments in the framework slope protection, thus making up for the performance shortcomings of traditional solidified soil in slope protection applications.

[0048] At the construction technology level, this invention employs a "foundation trench excavation-wet spraying molding" method that is highly compatible with the material properties. This method utilizes the good workability of the material and the setting-accelerating effect of the quick-setting agent to achieve direct, layered, and rapid spraying molding within the slope foundation trench, completely eliminating the complex procedures of formwork erection and demolding required for cast-in-place concrete, thus greatly improving construction efficiency. Simultaneously, the wet spraying process allows the modified soil slurry to fully impregnate and embed into the original slope soil, forming a mechanical interlocking and physicochemical combination. This ensures that the molded framework is tightly integrated with the original slope surface as a whole, significantly enhancing the structural integrity and impermeability, and effectively overcoming the "two-layer" problem inherent in precast component installation.

[0049] In summary, this invention organically integrates low-carbon material design with efficient molding processes: it addresses environmental and economic issues with solid waste-based materials, strength and durability with composite modification technology, and construction efficiency and structural integrity with wet spraying technology. Ultimately, it successfully provides a novel framework slope protection construction solution that is not only environmentally friendly but also reliable and easy to construct, offering effective technical support for green, low-carbon, and durable slope protection in railway and other engineering projects.

[0050] This invention organically integrates low-carbon material design with efficient molding processes: it uses solid waste-based materials to address environmental and economic issues, employs composite modification technology to solve strength and durability problems, and utilizes wet spraying technology to address construction efficiency and structural integrity issues. Ultimately, it successfully provides a novel framework slope protection construction solution that is not only environmentally friendly but also reliable and easy to construct, offering effective technical support for green, low-carbon, and durable slope protection in railway and other engineering projects.

[0051] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A low-carbon, durable, chemically modified soil-frame slope protection material, characterized in that, It is composed of the following raw materials in parts by weight: 100-150 parts of engineering waste soil, 3-15 parts of cement, 3-15 parts of lime, 10-50 parts of fly ash, 10-20 parts of water, and 1-3 parts of composite admixture.

2. The low-carbon, durable, chemically modified soil skeleton slope protection material according to claim 1, characterized in that, The excavated soil from the project is one or more of the following: fine sand, silt, clay, or red mudstone, with a maximum particle size of no more than 15 mm.

3. The low-carbon, durable, chemically modified soil skeleton slope protection material according to claim 1, characterized in that, When the plasticity index of the excavated soil is less than 12 and the sulfate content is less than 0.25%, cement is used as the main modifier; when the plasticity index is greater than 12 and the sulfate content is less than 0.8%, lime is used as the main modifier.

4. The low-carbon, durable, chemically modified soil skeleton slope protection material according to claim 1, characterized in that, The cement strength grade is 32.5 or 42.5; the lime is first-class building calcareous quicklime powder with a CaO+MgO content of not less than 80%.

5. The low-carbon, durable, chemically modified soil skeleton slope protection material according to claim 1, characterized in that, The fly ash has a fineness of no more than 20%, an SO3 content of no more than 3%, a loss on ignition of no more than 8%, and is used in combination with cement or lime.

6. The low-carbon, durable, chemically modified soil skeleton slope protection material according to claim 1, characterized in that, The composite additive comprises surfactants, polyols, active silica, carbonates, and sulfates.

7. A construction method for a low-carbon, durable, chemically modified soil skeleton slope protection material as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Slope pretreatment, removing loose soil and vegetation from the slope surface; (2) Measure and set out the slope, and trim the slope according to the design drawings; (3) Excavate the foundation trench according to the skeleton layout diagram; (4) Mix the chemically modified soil with the quick-setting agent at the nozzle to obtain wet-sprayed chemically modified soil material; (5) From bottom to top, chemically modified soil is sprayed in layers in the foundation trench to form a skeleton beam. Each layer is 30-50mm thick. At the end, the edge of the skeleton is thickened to form a water-retaining edge. (6) After spray molding, shape the product, cover it with geotextile and water it for 7-14 days.

8. The construction method according to claim 7, characterized in that, The accelerator is an alkali-free accelerator with an initial setting time of 1-5 minutes and a final setting time of 5-12 minutes. The dosage is 3%-5% of the cement dosage.

9. The construction method according to claim 7, characterized in that, The skeleton beam is formed in one step by wet spraying, without the need for formwork.

10. The application of a low-carbon, durable chemically modified soil skeleton slope protection material as described in any one of claims 1-6 in railway subgrade slope protection engineering.

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