Method for filling soil by using highly-doped fly ash and alkali-activated material

Abstract

The invention discloses a method for filling soil by using highly-doped fly ash and an alkali-activated material. According to the method, the fly ash and a small amount of alkali activator and water are utilized and matched with a rolling process to be used for soil filling and land reclamation, the use amount of the fly ash reaches 70% or above, and the technical problems that in a traditional fly ash treatment method, the fly ash mixing amount is low, and the utilization rate is low are solved; secondly, the coal ash is used in the method and does not need to be matched with a fixed cementing material system of cement, so that carbon emission and raw material cost are reduced; and by combining a physical rolling process, the requirements of land reclamation engineering on foundation bearing capacity, settlement control and vegetation planting are met after a soil filling layer is formed, clay and loam which are used in a large amount in a traditional soil filling and land reclamation method can be replaced, and high economical efficiency and practicability are achieved. The method can be used in the engineering fields of mining area repair, road subgrade, building foundation and the like.

Description

Technical Field

[0001] This invention belongs to the field of solid waste utilization technology, and in particular relates to a method for backfilling soil using high-volume fly ash and alkali-activated materials. Background Technology

[0002] With the continuous development of industrialization, the amount of industrial waste generated is increasing dramatically. The lack of sorting and treatment of this industrial solid waste can cause serious environmental pollution. Traditional treatment methods, such as landfill and dumping, not only occupy a large amount of land resources but may also lead to secondary pollution. Furthermore, with the acceleration of urbanization and the scarcity of land resources, land reclamation has become an important means of expanding usable land. Traditional land reclamation methods mostly use natural soil and rock materials such as clay and sand, which have problems such as ecological damage from resource extraction, high transportation costs, and a significant supply-demand imbalance. To solve these two problems, researchers have begun to explore new technologies that combine industrial solid waste with land reclamation, which can both improve the utilization rate of industrial solid waste and meet the environmental requirements of land reclamation.

[0003] Fly ash is the largest solid waste produced by the thermal power generation industry, with annual emissions exceeding 600 million tons in my country. Fly ash can also combine with sulfur dioxide, nitrogen oxides, and other pollutants, further exacerbating environmental damage, making its resource utilization as solid waste an urgent priority. Simultaneously, my country faces a shortage of land resources. Problems such as surface subsidence, wetland degradation, and desertification following mining operations are reducing usable land, necessitating low-cost, eco-friendly land reclamation solutions.

[0004] Currently, there are few ways to utilize fly ash as a resource, resulting in low utilization rates. Furthermore, existing land reclamation technologies also face technical bottlenecks, specifically as follows: 1. In existing technologies, land reclamation mainly uses clay and loam as raw materials, and fly ash is used as filler. Its content usually does not exceed 50%, which fails to give full play to its potential activity and results in low fly ash disposal efficiency.

[0005] 2. Fly ash usually needs to be mixed with silicate cementitious materials such as cement. Cement accounts for a high proportion of the cost, and the production of cement will increase carbon emissions (approximately 0.8 tons of CO2 are emitted for every ton of cement produced), thus failing to achieve true environmental friendliness.

[0006] 3. Low-volume fly ash fill lacks a cementing system and relies solely on physical compaction, resulting in low early strength and poor water stability after molding. The unconfined compressive strength is generally below 0.3 MPa, which easily leads to engineering problems such as shrinkage cracking and insufficient bearing capacity, making it difficult to meet the requirements of land reclamation projects for foundation bearing capacity, settlement control, and vegetation planting.

[0007] 4. Unmodified fly ash has a high pH value of 10-12 and lacks the porous structure and nutrient carriers required for plant growth. When plants are planted directly in it, the survival rate is less than 30%.

[0008] 5. Existing land reclamation technologies typically rely on large amounts of high-quality clay, resulting in high raw material prices and transportation costs. Some technologies require the addition of cement, lime, and other binding materials, which not only increases costs but also easily leads to soil compaction and inhibits plant growth.

[0009] 6. Existing technologies are usually only applicable to a single scenario, such as reclamation after mining, and have not formed a general land reclamation solution that takes into account "high solid waste content, strength stability and ecological compatibility". Summary of the Invention

[0010] To solve the above-mentioned technical problems, the present invention provides a method for backfilling soil using high-volume fly ash and alkali-activated materials.

[0011] The present invention is achieved through the following technical solutions.

[0012] This invention provides a method for backfilling soil using materials with high fly ash content and alkali activation, comprising the following steps: A1: The fly ash is dried and screened sequentially; A2: Alkali-activated materials are prepared by mixing alkaline components and auxiliary admixtures; A3: After the fly ash treated by A1 is dry-mixed evenly with the alkali-activated material, water is added to the dry mixture for wet mixing to obtain a compactable mixture. A compaction test is performed on the compactable mixture to determine the optimal moisture content at the maximum dry density of the compactable mixture. A4: Clean the construction area, spread the compactable mixture in layers in the construction area, level the area while spreading, and then compact the compactable mixture in layers to complete the backfilling. A5: Curing of the compacted fill area.

[0013] Preferably, in A1, the material is dried to a moisture content of ≤1.0% and sieved through a 0.9mm sieve, and in A2, the mass ratio of alkali component to auxiliary admixture is 1~3:1~2.

[0014] Preferably, the alkali component includes one or more of water glass, sodium hydroxide, and sodium carbonate, and the mass ratio of water glass, sodium hydroxide, and sodium carbonate is 1~3:1~2:1. The auxiliary admixture is one or more of slag powder, steel slag powder, and metakaolin.

[0015] Preferably, the mass ratio of the fly ash to the alkali-activated material in the dry mixture is 70~80:10~15.

[0016] Preferably, the fly ash and alkali-activated material are dry-mixed in a mixer with a rotation speed of 45~48 r / min for 3~5 minutes to obtain a mixed dry material.

[0017] Preferably, water is added to the obtained dry mixture, and the mixture is stirred in a mixer with a speed of 45~48 r / min for 5~8 minutes. After stirring, the mixture is allowed to stand for 10~20 minutes to obtain a compressible mixture.

[0018] Preferably, the mass of water in A3 is 10-15% of the total mass of the mixed dry materials and water.

[0019] Preferably, the compactable mixture in A4 is laid in layers with a thickness of 20-30cm per layer. If the construction area is a soft soil foundation, a 10-15cm thick graded sand and gravel cushion layer needs to be laid in advance and compacted to a compaction degree of ≥95%.

[0020] Preferably, after the leveled and compactable mixture in A4 is layered, it is compacted in layers using a vibratory roller with an excitation force ≥30kN. The compaction method is to first perform static compaction twice, then vibratory compaction once or twice, and finally static compaction once. This compaction method is repeated for each layer of compactable mixture 3 to 5 times to ensure that the compaction degree of each layer of compactable mixture is ≥93%. During compaction, the moisture content of each layer of compactable mixture is continuously monitored. If the real-time moisture content is lower than the optimum moisture content, water is sprayed or added to control the real-time moisture content within the range of ±2% of the optimum moisture content.

[0021] Preferably, the curing steps in A5 include: covering the surface of the backfill area with geotextile and carrying out natural curing or steam curing. During natural curing, the temperature of the backfill area is controlled to be no lower than 5°C, and the natural curing time is 7 to 14 days; the steam curing temperature is 40 to 60°C, and the curing time is 45 to 50 hours.

[0022] The beneficial effects of this invention are as follows: 1. Environmental Value: Maximizes solid waste resource utilization efficiency and reduces ecological pollution. Fly ash content ≥70%, per 1000m³ 3 The backfill can absorb 1200-1500 tons of fly ash, and one 100,000 m³... 3 Medium-sized projects can dispose of 120,000 to 150,000 tons of fly ash, significantly reducing dust and groundwater pollution caused by open-air fly ash storage. They can replace traditional cement and clay raw materials, reducing emissions per 1000m³ of fly ash. 3 Filling with fly ash reduces cement consumption by 300-500 tons, corresponding to a reduction of CO2 emissions of 240-400 tons. The heavy metal leaching concentration of the finished fly ash fill meets environmental protection requirements, with no secondary pollution, achieving waste-to-waste treatment.

[0023] 2. Project Value: Stable strength and controllable settlement, meeting the core requirements for land reclamation. 28-day unconfined compressive strength ≥1.2MPa, 90-day strength loss ≤10%, ensuring consistent and durable strength. Meets the load-bearing requirements for vegetation planting and light greening projects such as lawns, shrubs, and small landscapes, preventing later settlement and cracking; compaction degree ≥93%, settlement rate ≤3%, strong stability. The formed land can be directly used for greening and ecological restoration without additional reinforcement. Utilizing conventional vibratory rollers, the layered paving and compaction process is simple, shortening the construction cycle by 20%~30% compared to traditional land reclamation, adapting to complex field operating environments, and offering high construction efficiency.

[0024] 3. Ecological Value: Integrating land reclamation with vegetation creation promotes ecological restoration. Significantly improved vegetation adaptability: Optimized design with a pH of 8.0-9.5 and porosity of 15-25%, combined with functional additives such as water-retaining agents and biochar, ensures a survival rate of ≥85% for common greening plants such as alfalfa, sea buckthorn, and bermudagrass, exceeding the survival rate of existing fly ash fill by more than 50%. It can be directly used for mine reclamation, wetland restoration, desertification control, and coastal mudflat transformation, adapting to multiple ecological scenarios and achieving greening through land reclamation. The fill substrate has no risk of compaction, allowing plant roots to grow normally and forming a stable surface vegetation cover, further enhancing land stability and achieving ecological cycles and long-term ecological sustainability.

[0025] 4. Economic Value: Significantly reduces land reclamation costs and has the potential for large-scale promotion. Fly ash is an industrial solid waste, and its procurement cost is far lower than that of clay and cement. The amount of composite alkali-activated material used is only 5-20%, and the overall raw material cost is 30-50% lower than that of traditional clay fill. No special equipment is required; conventional compaction equipment used in road and construction projects can be reused, reducing equipment investment. The maintenance process is simple, requiring no expensive maintenance materials, resulting in low overall construction costs. A single project can simultaneously achieve "solid waste disposal, land expansion, and ecological restoration," resulting in significant and high comprehensive economic benefits. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0027] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0028] Example 1: like Figure 1 As shown, a method for backfilling soil using high-volume fly ash and alkali-activated materials includes the following steps: A1: The fly ash is dried and screened to remove impurities in sequence; A2: Alkali-activated materials are prepared by mixing alkaline components and auxiliary admixtures. Alkali-activated materials must be stored in a sealed container. A3: After the fly ash treated by A1 is dry-mixed with the alkali-activated material, a dry mixture is obtained. Water is added to the dry mixture for wet mixing to obtain a compactable mixture. A portion of the compactable mixture is taken for a compaction test to determine the optimal moisture content at the maximum dry density of the compactable mixture. A4: Clean the construction area, spread the compactable mixture in layers in the construction area, and level it with a bulldozer at the same time. During the spreading process, avoid the material from being exposed to the sun and losing water or getting rained on and clumping. After leveling the compactable mixture in layers, use a vibratory roller to compact the layers to complete the backfilling. A5: Curing of the compacted fill area.

[0029] The fly ash is Class F, Grade II ash produced by a power plant, containing SiO2, Al2O3, Fe2O3, and CaO, with a content exceeding 90%, and a specific surface area of ​​360 m². 2 / kg.

[0030] The A1 component is dried to a moisture content of ≤1.0% and sieved through a 0.9mm sieve. The mass ratio of the alkali component to the auxiliary admixture in the A2 component is 1:1.

[0031] The alkaline components are water glass, sodium hydroxide, and sodium carbonate, with a mass ratio of 2:1:1. The activity of fly ash is activated by OH⁻ ions in the alkaline components. The auxiliary admixture is slag powder, which can supplement the calcium components in the composite and optimize the structure of hydration products.

[0032] The mass percentage of the dry-mixed fly ash and alkali-activated material is 75%:12%.

[0033] The fly ash and alkali-activated material are dry-mixed in a mixer at a speed of 47 r / min for 4 minutes to obtain a mixed dry material, ensuring that all components are mixed evenly and that the mixed dry material is free from local lumps or segregation.

[0034] Water is added to the obtained dry mixture, and the mixture is stirred for 7 minutes in a mixer at a speed of 46 r / min to form a uniform, compressible material. After stirring, the mixture is allowed to stand for 15 minutes to allow the alkali-activated material to come into full contact with the fly ash, initiate the early hydration reaction, improve the subsequent molding strength, and obtain a compressible mixture.

[0035] The mass of water in A3 is 13% of the total mass of the mixed dry materials and water.

[0036] The compactable mixture in A4 is laid in layers, with each layer having a thickness of 25cm. If the construction area is a soft soil foundation, a 12cm thick graded sand and gravel cushion layer needs to be laid in advance and compacted to a compaction degree of ≥95% to avoid settlement in the later stage.

[0037] In section A4, the surface weeds, humus, and construction waste in the construction area are cleaned to eliminate the impact of impurities on the hydration reaction and compaction. After the leveled and compactable mixture in layer A4 is layered, it is compacted using a vibratory roller with a vibration force ≥30kN. The compaction method involves two static passes, followed by two vibratory passes, and finally one static pass, ensuring that the surface is free of obvious wheel tracks and cracks. This "static-dynamic-static" compaction sequence ensures a tighter bond between the particles in each layer of compactable mixture, reducing large gaps caused by irregular particle shapes. Each layer of compactable mixture is compacted four times to achieve a compaction degree ≥93% for each layer. The moisture content of each layer is continuously monitored during compaction. If the real-time moisture content is lower than the optimum moisture content, water is applied or added to control the real-time moisture content within ±2% of the optimum moisture content to ensure effective compaction. This layered paving and compaction method contributes to the overall porosity uniformity and mechanical stability of the fill, preventing a situation where the upper layer of fill is compacted while the lower layer is loose, thus avoiding local instability. Real-time monitoring and adjustment of moisture content can ensure that the compaction effect is maintained at around the maximum dry density, achieving the optimal compaction effect.

[0038] The curing steps in A5 include: covering the surface of the fill area with geotextile to retain moisture and maintain moisture, and carrying out natural curing or steam curing. During natural curing, the temperature of the fill area should be controlled not to be lower than 5°C. Too low a temperature will affect the hydration activity of fly ash and alkali-activated materials. Natural curing is 10 days. The time can be appropriately shortened as the temperature rises, but too short a time will lead to insufficient development of fly ash activity. During this period, the curing time can be appropriately shortened as the temperature rises, but it should not be less than 7 days. Keep the surface moist during the curing period. A moist state helps the growth of hydration activity and the development of strength. Avoid strong wind erosion or rain erosion, which will affect the curing effect. Example 2: like Figure 1 As shown, a method for backfilling soil using high-volume fly ash and alkali-activated materials includes the following steps: A1: The fly ash is dried and screened to remove impurities in sequence; A2: Alkali-activated materials are prepared by mixing alkaline components and auxiliary admixtures. Alkali-activated materials must be stored in a sealed container. A3: After the fly ash treated by A1 is dry-mixed with the alkali-activated material, a dry mixture is obtained. Water is added to the dry mixture for wet mixing to obtain a compactable mixture. A portion of the compactable mixture is taken for a compaction test to determine the optimal moisture content at the maximum dry density of the compactable mixture. A4: Clean the construction area, spread the compactable mixture in layers in the construction area, and level it with a bulldozer at the same time. During the spreading process, avoid the material from being exposed to the sun and losing water or getting rained on and clumping. After leveling the compactable mixture in layers, use a vibratory roller to compact the layers to complete the backfilling. A5: Curing of the compacted fill area.

[0039] The fly ash is Class F, Grade II ash produced by a power plant, containing SiO2, Al2O3, Fe2O3, and CaO, with a content exceeding 90%, and a specific surface area of ​​360 m². 2 / kg.

[0040] The A1 component is dried to a moisture content of ≤1.0% and sieved through a 0.9mm sieve. The mass ratio of alkali component to auxiliary admixture in the A2 component is 2:1.

[0041] The alkaline component is water glass and sodium carbonate, and the mass ratio of water glass, sodium hydroxide and sodium carbonate is 1:1. The activity of fly ash is activated by OH⁻ ions in the alkaline component. The auxiliary admixture is steel slag powder, which can supplement the calcium component in the composite and optimize the structure of hydration products.

[0042] The mass percentage of the dry-mixed fly ash and alkali-activated material is 70%:15%.

[0043] The fly ash and alkali-activated material are dry-mixed in a mixer at a speed of 45 r / min for 3 to 5 minutes to obtain a mixed dry material, ensuring that all components are mixed evenly and that the mixed dry material is free from local lumps or segregation.

[0044] Water is added to the obtained dry mixture, and the mixture is stirred for 5 minutes in a mixer at a speed of 45 r / min to form a uniform, compressible material. After stirring, the mixture is allowed to stand for 10 minutes to allow the alkali-activated material to come into full contact with the fly ash, initiate the early hydration reaction, improve the subsequent molding strength, and obtain a compressible mixture.

[0045] The mass of water in A3 is 15% of the total mass of the mixed dry materials and water.

[0046] The compactable mixture in A4 is laid in layers, with each layer having a thickness of 20cm. If the construction area is a soft soil foundation, a 10cm thick graded sand and gravel cushion layer needs to be laid in advance and compacted to a compaction degree of ≥95% to avoid settlement in the later stage.

[0047] In section A4, the surface weeds, humus, and construction waste in the construction area are cleaned to eliminate the impact of impurities on the hydration reaction and compaction. After the leveled and compactable mixture in A4 is layered, it is compacted in layers using a vibratory roller with a vibration force ≥30kN. The compaction method involves two static passes, followed by one vibratory pass, and finally one static pass, ensuring that the surface is free of obvious wheel tracks and cracks. This "static-dynamic-static" compaction sequence ensures a tighter bond between the particles in each layer of compactable mixture, reducing large gaps caused by irregular particle shapes. Each layer of compactable mixture is compacted three times to achieve a compaction degree ≥93% for each layer. The moisture content of each layer is continuously monitored during compaction. If the real-time moisture content is lower than the optimum moisture content, water is applied or added to control the real-time moisture content within ±2% of the optimum moisture content to ensure effective compaction. This layered paving and compaction method contributes to the overall porosity uniformity and mechanical stability of the fill, preventing a situation where the upper layer of fill is compacted while the lower layer is loose, thus avoiding local instability. Real-time monitoring and adjustment of moisture content can ensure that the compaction effect is maintained at around the maximum dry density, achieving the optimal compaction effect.

[0048] The curing steps in A5 include: covering the surface of the fill area with geotextile to retain moisture and maintain moisture, and carrying out natural curing or steam curing. During natural curing, the temperature of the fill area should be controlled to be no lower than 5°C. Too low a temperature will affect the hydration activity of fly ash and alkali-activated materials. Natural curing is 14 days. The time can be appropriately shortened as the temperature rises, but too short a time will lead to insufficient development of fly ash activity. During this period, the curing time can be appropriately shortened as the temperature rises, but it should not be less than 7 days. Keep the surface moist during the curing period. Moistness helps the growth of hydration activity and strength development. Avoid strong wind erosion or rainstorm erosion, which will affect the curing effect. Example 3: like Figure 1 As shown, a method for backfilling soil using high-volume fly ash and alkali-activated materials includes the following steps: A1: The fly ash is dried and screened to remove impurities in sequence; A2: Alkali-activated materials are prepared by mixing alkaline components and auxiliary admixtures. Alkali-activated materials must be stored in a sealed container. A3: After the fly ash treated by A1 is dry-mixed with the alkali-activated material, a dry mixture is obtained. Water is added to the dry mixture for wet mixing to obtain a compactable mixture. A portion of the compactable mixture is taken for a compaction test to determine the optimal moisture content at the maximum dry density of the compactable mixture. A4: Clean the construction area, spread the compactable mixture in layers in the construction area, and level it with a bulldozer at the same time. During the spreading process, avoid the material from being exposed to the sun and losing water or getting rained on and clumping. After leveling the compactable mixture in layers, use a vibratory roller to compact the layers to complete the backfilling. A5: Curing of the compacted fill area.

[0049] The fly ash is Class F, Grade II ash produced by a power plant, containing SiO2, Al2O3, Fe2O3, and CaO, with a content exceeding 90%, and a specific surface area of ​​360 m². 2 / kg.

[0050] The A1 component is dried to a moisture content of ≤1.0% and sieved through a 0.9mm sieve. The mass ratio of alkali component to auxiliary admixture in the A2 component is 3:2.

[0051] The alkaline component consists of water glass and sodium hydroxide, with a mass ratio of water glass to sodium hydroxide of 1:2. The activity of fly ash is activated by OH⁻ ions in the alkaline component. The auxiliary admixture is metakaolin, which can supplement the calcium component in the composite and optimize the structure of hydration products.

[0052] The mass percentage of the dry-mixed fly ash and alkali-activated material is 80%:10%.

[0053] The fly ash and alkali-activated material are dry-mixed in a mixer at a speed of 48 r / min for 5 minutes to obtain a mixed dry material, ensuring that all components are mixed evenly and that the mixed dry material is free from local lumps or segregation.

[0054] Water is added to the obtained dry mixture, and the mixture is stirred for 8 minutes in a mixer at a speed of 48 r / min to form a uniform, compressible material. After stirring, the mixture is allowed to stand for 20 minutes to allow the alkali-activated material to come into full contact with the fly ash, initiate the early hydration reaction, improve the subsequent molding strength, and obtain a compressible mixture.

[0055] The mass of water in A3 is 10% of the total mass of the mixed dry materials and water.

[0056] The compactable mixture in A4 is laid in layers with each layer having a thickness of 30cm. If the construction area is a soft soil foundation, a 15cm thick graded sand and gravel cushion layer needs to be laid in advance and compacted to a compaction degree of ≥95% to avoid settlement in the later stage.

[0057] In section A4, the surface weeds, humus, and construction waste in the construction area are cleaned to eliminate the impact of impurities on the hydration reaction and compaction. After the leveled and compactable mixture in layer A4 is layered, it is compacted using a vibratory roller with a vibration force ≥30kN. The compaction method involves two static passes, followed by two vibratory passes, and finally one static pass, ensuring that the surface is free of obvious wheel tracks and cracks. This "static-dynamic-static" compaction sequence ensures a tighter bond between the particles in each layer of compactable mixture, reducing large gaps caused by irregular particle shapes. This compaction method is repeated five times for each layer of compactable mixture, resulting in a compaction degree of ≥93% for each layer. During compaction, the moisture content of each layer of compactable mixture is continuously monitored. If the real-time moisture content is lower than the optimum moisture content, water is sprayed or added to control the real-time moisture content within ±2% of the optimum moisture content to ensure the compaction effect. The above-mentioned layered paving and compaction are beneficial to the overall porosity uniformity and mechanical stability of the fill, avoiding a situation where the upper layer of fill is compacted while the lower layer is loose, which could lead to local instability. Real-time monitoring and adjustment of moisture content can ensure that the compaction effect is maintained at around the maximum dry density, achieving the optimal compaction effect.

[0058] The curing steps in A5 include: covering the surface of the fill area with geotextile to retain moisture and maintain moisture, steam curing, and during natural curing, controlling the temperature of the fill area to be no lower than 5°C. Too low a temperature will affect the hydration activity of fly ash and alkali-activated materials. The steam curing temperature is controlled in the range of 40~60°C, and the curing time is controlled in the range of 45~50 minutes. Steam curing can shorten the construction period. In Examples 1-3: 1. The alkali content in the alkali component of the alkali activating material is controlled at 8-12% of the mass of the fly ash component to ensure the alkali activation efficiency and the volume stability of the hydration combination products. 2. The water-cement ratio can be adjusted according to the activity of fly ash. The higher the activity of fly ash, the lower the water-cement ratio can be. 3. The ambient temperature during construction should be controlled within the range of 5~35℃. If there is rain, strong wind or other severe weather, construction should be suspended in order to control the moisture content of the compactable mixture and ensure the filling effect. The compaction degree of each layer of the compactable mixture should reach more than 93% to avoid excessive porosity of the fill due to insufficient compaction, which would affect the strength and water stability.

[0059] 4. After the maintenance is completed, remove the geotextile and other surface coverings. Plants that are tolerant of poor soil and mild salinity, such as alfalfa, sea buckthorn, bermudagrass, and ryegrass, can be planted directly on the fill surface. After planting, water appropriately and let the roots settle to reduce the erosion of the fill by rainwater.

[0060] The performance of the fill layers prepared in Examples 1-3 was tested. The testing specifications and standards referred to were: "Construction Quality Acceptance Standard for Building Foundation Engineering" (GB 50202-2018), "Land Reclamation Quality Control Standard" (TD / T 1036-2013), "Standard for Geotechnical Testing Methods" (GB / T50123-2019), and "Specifications for Highway Geotechnical Testing" (JTG 3430-2020).

[0061] The technical indicators of the fly ash-filled land reclamation product were tested, including compaction degree, 7d / 28d / 90d unconfined compressive strength, permeability coefficient, compression modulus, pH value, electrical conductivity, and plant survival rate. The results are as follows: Compaction degree: 93~95%, meets the requirements; Unconfined compressive strength: 1.7~2.1MPa at 7d, 2.8~3.0MPa at 28d, and 3.4~4.1MPa at 90d, meeting the requirements; Permeability coefficient: 5.4 × 10 -5 ~3.7×10 -6 cm / s, which meets the requirements; Compression modulus: 74~115MPa, meets the requirements; pH value: 8.2~8.8, meets the requirements; Electrical conductivity: 1.3~2.1 mS / cm, meets the requirements; Planting status: After the soil layer maintenance in Examples 1-3 was completed, 50 alfalfa seedlings were transplanted. After 3 months, the number of surviving seedlings was greater than 45, and the survival rate was greater than 90%. The surviving alfalfa seedlings were dug up and their root systems were observed, and they were growing well.

[0062] Performance testing showed that the fly ash backfilling and land reclamation results met the requirements of the "Construction Quality Acceptance Standard for Building Foundation Engineering" (GB 50202-2018) and the "Land Reclamation Quality Control Standard" (TD / T 1036-2013).

Claims

1. A method for backfilling soil using materials with high fly ash content and alkali activation, characterized in that, Includes the following steps: A1: The fly ash is dried and screened sequentially; A2: Alkali-activated materials are prepared by mixing alkaline components and auxiliary admixtures; A3: After the fly ash treated by A1 is dry-mixed evenly with the alkali-activated material, water is added to the dry mixture for wet mixing to obtain a compactable mixture. A compaction test is performed on the compactable mixture to determine the optimal moisture content at the maximum dry density of the compactable mixture. A4: Clean the construction area, spread the compactable mixture in layers in the construction area, level the area while spreading, and then compact the compactable mixture in layers to complete the backfilling. A5: Curing of the compacted fill area.

2. The method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The A1 component is dried to a moisture content of ≤1.0% and sieved through a 0.9mm sieve. The mass ratio of the alkali component to the auxiliary admixture in the A2 component is 1~3:1~2.

3. The method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The alkaline component includes one or more of water glass, sodium hydroxide, and sodium carbonate, and the mass ratio of water glass, sodium hydroxide, and sodium carbonate is 1~3:1~2:

1. The auxiliary admixture is one or more of slag powder, steel slag powder, and metakaolin.

4. The method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The mass ratio of the dry-mixed fly ash to the alkali-activated material is 70~80:10~15.

5. A method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The fly ash and alkali-activated material are dry-mixed in a mixer with a speed of 45~48 r / min for 3~5 minutes to obtain a mixed dry material.

6. The method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: Add water to the obtained dry mixture and stir for 5 to 8 minutes in a mixer with a speed of 45 to 48 r / min. After stirring, let the mixture stand for 10 to 20 minutes to obtain a compactable mixture.

7. A method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The mass of water in A3 is 10-15% of the total mass of the mixed dry materials and water.

8. A method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The compactable mixture in A4 is laid in layers, with each layer having a thickness of 20-30cm. If the construction area is a soft soil foundation, a 10-15cm thick graded sand and gravel cushion layer needs to be laid in advance and compacted to a compaction degree of ≥95%.

9. A method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: After the leveled and compactable mixture in A4 is layered, it is compacted in layers using a vibratory roller with an excitation force of ≥30kN. The compaction method is to first perform two static compactions, then one to two vibratory compactions, and finally one static compaction. This compaction method is repeated for each layer of compactable mixture 3 to 5 times to ensure that the compaction degree of each layer of compactable mixture is ≥93%. During compaction, the moisture content of each layer of compactable mixture is continuously monitored. If the real-time moisture content is lower than the optimum moisture content, water is sprayed or added to control the real-time moisture content within the range of ±2% of the optimum moisture content.

10. A method for backfilling soil using high-volume fly ash and alkali-activated materials as described in claim 1, characterized in that: The curing steps in A5 include: covering the surface of the backfill area with geotextile and carrying out natural curing or steam curing. During natural curing, the temperature of the backfill area is controlled to be no lower than 5°C, and the natural curing time is 7 to 14 days; the steam curing temperature is 40 to 60°C, and the curing time is 45 to 50 hours.

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