Desulfurated ash-based solidified soil with gradient-adjustable strength density and construction method thereof

Abstract

The application discloses a desulfurization ash-based solidified soil with gradient-adjustable strength and density and a construction method thereof, and belongs to the technical field of solid waste resource utilization and geotechnical engineering materials. The solidified soil is formed by layering and pouring a desulfurization ash-based slurry to form a continuous gradient distribution structure along the depth direction, and the slurry comprises, in mass fractions, 100 parts of desulfurization ash, 10-45 parts of composite cementing material, 2-15 parts of excitation control component, 0-10 parts of pore adjusting component and 30-80 parts of mixing water. The matched construction method controls the layering interval and interface treatment to ensure the cementing continuity and integrity between the gradient layers. The application can improve the resource utilization rate of the desulfurization ash, and solves the problems that the traditional homogeneous solidified soil cannot meet the differentiated functional requirements at different depths in engineering and the weak combination between the layered filling layers.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and geotechnical engineering materials technology. Specifically, this invention relates to a desulfurized ash-based solidified soil that achieves continuous gradient changes in strength and density along the construction depth through the synergistic effect of chemical activation and physical porosity regulation, as well as a construction method for the solidified soil. Background Technology

[0002] Coal-fired power plants generate a large amount of desulfurization ash during flue gas desulfurization. This industrial byproduct contains calcium sulfate and potentially active silica-alumina components, possessing potential for resource utilization. Using desulfurization ash as an engineering fill material can both dispose of large quantities of solid waste and reduce engineering construction costs, thus attracting widespread attention in related research.

[0003] Chinese patent CN111116117B discloses a chemically activated desulfurized ash-based foamed lightweight soil. This technical solution uses desulfurized ash, cement, and mineral powder as raw materials, and prepares a material with a dry density of 500–1200 kg / m³ through alkali activation and foam introduction. 3 The solution involves lightweight soil within a certain range. However, the product prepared by this technical solution is a single homogeneous material with uniform overall properties, making it impossible to achieve differentiated performance configurations for different depth zones within the same structure according to engineering requirements.

[0004] Chinese patent CN112982051B discloses a construction device and method for EPS foam particle mixed lightweight soil subgrade. This technical solution uses EPS particles, cement, fly ash, and other materials to prepare mixed lightweight soil layers of different densities, forming a layered structure with decreasing density from bottom to top. Although this solution proposes the concept of layered filling, the different layers use independent material systems with significantly different properties. These different materials exhibit significant differences in elastic modulus, shrinkage rate, and hydration reaction characteristics, making it highly susceptible to stress concentration at the interlayer interfaces, leading to interlayer separation, slippage, or cracking.

[0005] Furthermore, Chinese patent application CN117534384A discloses a foamed lightweight soil composition for backfilling abutments under high water level conditions. This document mentions forming a functional layer structure with gradually varying strength through casting. However, each functional layer still uses a composition with different basic proportions, failing to achieve a gradient transition of performance through continuous control within the same material system. Moreover, it lacks a corresponding interlayer bonding strengthening process, making it difficult to fundamentally solve the problem of weak interlayer bonding.

[0006] In engineering practices such as load-reducing backfilling of soft soil foundations, deep foundation pit backfilling, and roadbed filling, structures exhibit significant stress differences along their depth: the bottom region requires lightweight materials to achieve load reduction and water isolation, the middle region needs appropriate strength and deformation compatibility, and the top region requires higher strength and stiffness to meet load-bearing and load diffusion requirements. Existing technologies have failed to provide a solidified soil material and its construction method that can achieve a gradient functional adaptation from lightweight load reduction to high load-bearing capacity within the same material system through continuous control of component ratios.

[0007] Therefore, providing a solidified soil material and its supporting construction technology that uses bulk solid waste desulfurization ash as the main raw material, achieves continuous gradient changes in physical and mechanical properties through component adjustment within the same cementing system, and has tight interlayer bonding and natural transition is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The primary objective of this invention is to provide a desulfurized ash-based solidified soil with adjustable strength and density, in order to solve the problems of existing desulfurized ash-based solidified soil products having a single function and being unable to achieve performance gradient adaptation within the same structure, as well as the problems of weak interlayer bonding and stress concentration caused by the layering of different materials.

[0009] Based on this, the second objective of the present invention is to provide a construction method for the above-mentioned desulfurized ash-based solidified soil.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Option 1: A desulfurized ash-based solidified soil with adjustable strength and density, wherein the solidified soil is formed by layering or filling desulfurized ash-based solidification slurry or mixture into shape, and forms a continuous gradient distribution structure along the construction depth; the desulfurized ash-based solidification slurry comprises, by mass parts: Desulfurization ash: 100 parts; Composite cementitious material: 10-45 parts; Activation and regulation components: 2–15 parts; Pore ​​conditioning component: 0–10 parts; Mixing water: 30-80 parts; By synergistically adjusting the types and / or proportions of the composite cementitious material, the activation and regulation components, and the pore regulation components, different layers of the solidified soil can obtain differentiated wet density and compressive strength.

[0011] Furthermore, the continuous gradient distribution structure includes, in order from bottom to top or top to bottom: a Level I lightweight load-reducing layer, a Level II transition buffer layer, and a Level III high-strength load-bearing layer.

[0012] Furthermore, the wet density of the Class I lightweight load-reducing layer is 500–750 kg / m³.3 The 28-day compressive strength is 0.5–1.5 MPa; the wet density of the Class II transition buffer layer is 750–1050 kg / m³. 3 The 28-day compressive strength is 1.5–3.0 MPa; the wet density of the Class III high-strength load-bearing layer is 1050–1350 kg / m³. 3 The 28-day compressive strength is 3.0–6.0 MPa.

[0013] Furthermore, the desulfurization ash is one or a combination of several of the following: semi-dry desulfurization ash, circulating fluidized bed desulfurization ash, and wet desulfurization by-product ash.

[0014] Furthermore, the composite cementitious material is one or a combination of several of the following: cement, slag powder, steel slag powder, fly ash, and desulfurized gypsum.

[0015] Furthermore, the excitation regulating component is one or a combination of several of sodium hydroxide, water glass, calcium oxide, and sodium sulfate.

[0016] Furthermore, the pore-regulating component is one or a combination of several of EPS particles, pre-formed foam, foaming agent, and foam stabilizer.

[0017] Furthermore, the solidified soil also includes 0 to 8 parts by mass of a functional regulating component; the functional regulating component is one or a combination of several of hydroxypropyl methylcellulose, polypropylene fiber, and lignocellulose.

[0018] Option 2: A construction method for the above-mentioned desulfurized ash-based solidified soil, comprising the following steps: S1. Base treatment: Clean, level and compact the base of the construction area; S2. Raw material pretreatment: The desulfurization ash is dried and ground to ensure that the residue on a 45μm square-hole sieve is no more than 15%; the foaming porosity conditioning component is pre-foamed to obtain a density of 50-70 kg / m³. 3 Stable pre-fabricated foam with a half-life greater than 30 min; S3. Base material preparation: According to the design ratio of the bottom layer, desulfurization ash, composite cementitious materials and functional control components are put into the mixer and dry-mixed evenly; then, mixing water with pre-dissolved activation control components is added and wet-mixed to form a uniform base material slurry; finally, pore adjustment components are added under low-speed stirring, and after stirring evenly, the slurry required for the current construction layer is obtained. S4. Gradient Parameter Adjustment: After completing one layer of pouring, by changing the type and / or dosage of the composite cementitious material, the type and / or dosage of the activation and regulation components, and the type and / or dosage of the porosity adjustment components in the layer to be poured, the activation degree of the cementitious reaction and the bulk density are linked and controlled; so that the absolute value of the design wet density difference between adjacent pouring layers is controlled within 150-300 kg / m³.3 .

[0019] S5. Layered pouring: Pour the slurry layer by layer from bottom to top. The thickness of each layer should be controlled at 50-80cm. The pouring time interval between adjacent layers should be controlled at 20-90 minutes so that the lower layer of slurry has initially lost its fluidity but is still in the active reaction stage.

[0020] S6. Interlayer transition treatment: Before pouring the upper layer of grout, roughen the surface of the lower layer of grout to form a rough surface with a depth of 5-15mm; and / or after the upper layer of grout is poured, use an immersion vibrator to vibrate the interface area to a depth of 10-20cm through the interface, so that the cementitious components of the upper and lower layers of grout can penetrate and interweave at the interface.

[0021] S7. Curing and shaping: After all the pouring is completed, the exposed surface shall be covered and kept moist for curing for no less than 7 days; or the soil shall be covered and naturally cured after the solidified soil has set.

[0022] Compared with the prior art, the present invention has the following substantial features and significant progress: (1) For the first time, this invention achieves a continuous gradient change of solidified soil material from lightweight and low strength to high strength and density through the synergistic effect of chemical activation and physical pore regulation in a unified cementing system with desulfurization ash as the main component. This overcomes the problems of interlayer incompatibility and abrupt stiffness change caused by the traditional method of stacking different types of materials.

[0023] (2) The present invention clearly constructs a three-layer functional gradient structure of "lightweight load reduction - transition buffer - high strength load bearing", which enables the material properties to be precisely matched with the stress requirements along the construction depth, which can significantly reduce the stress concentration inside the structure and improve the overall stability and durability of the engineering structure.

[0024] (3) The construction method of the present invention ensures that the cementitious components of different performance grades of slurry penetrate and interweave in the interlayer area by controlling the interlayer time interval and interface treatment process, forming an interface transition zone that is microscopically interconnected and macroscopically continuously and gradually changing, effectively solving the problem of weak interlayer surfaces in layered construction.

[0025] (4) This invention increases the resource utilization rate of industrial waste desulfurization ash to over 65%, while reducing the overall material cost by 20-35% compared to traditional solutions, thus achieving a balance between environmental and economic benefits. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1This is a schematic cross-sectional view of the gradient layered structure of the desulfurized ash-based solidified soil prepared in an embodiment of the present invention.

[0028] In the diagram: 1-base layer; 2-Class I lightweight load-reducing layer; 3-Class II transition buffer layer; 4-Class III high-strength load-bearing layer. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0030] The strength and density gradient adjustable desulfurized ash-based solidified soil constructed in this invention achieves the linkage adjustment of the amount of cementitious phase generated and the volume density of the solidified product through the synergistic effect of "chemical activation degree regulation" and "physical porosity regulation" within the same material system, thereby forming a functional gradient structure with continuously changing physical and mechanical properties along the construction depth direction.

[0031] Specifically, the technical solution of this invention mainly includes the following three aspects: First, the chemical activation and regulation mechanism. Although desulfurization ash contains potentially active aluminosilicate components, its own hydration activity is very low, making it difficult to use directly as a cementing material. This invention introduces activation and regulation components to increase the alkalinity of the liquid phase and introduce active factors such as sulfate ions, thereby disrupting the stable network structure of aluminosilicate glass in auxiliary cementing materials such as desulfurization ash and slag. This promotes the depolymerization and dissolution of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, resulting in the formation of cementing products such as hydrated calcium silicate (CSH) gel and ettringite. Among these, CSH gel is the main source of strength, while the needle-like crystals of ettringite can fill pores and enhance the framework structure. This invention achieves precise control over the activation degree of the cementing reaction and the amount of cementing products generated by differentially configuring the activation and regulation components and the types and amounts of composite cementing materials in different layers, thus regulating the strength development of each layer from a chemical perspective.

[0032] Second, the physical porosity control mechanism. This invention, by differentially introducing porosity-regulating components into different layers, forms uniformly distributed closed pores or lightweight fillers in the slurry, thereby physically controlling the material's bulk density. As porosity increases, the material's density decreases, reducing its weight and meeting the lightweight requirements of the bottom load-reducing layer; conversely, as porosity decreases, the material's density increases, enhancing its strength and meeting the mechanical performance requirements of the top load-bearing layer. More importantly, changes in the dosage of the porosity-regulating components directly lead to a systematic alteration of the material's internal pore structure characteristics (such as porosity, pore size distribution, and pore connectivity), thereby affecting the material's density, strength, permeability, and deformation modulus.

[0033] Third, the synergistic mechanism of chemical-physical dual regulation. This invention implements the aforementioned chemical activation and physical porosity regulation synergistically within a unified desulfurized ash-based cementitious system. Through extensive creative work, the inventors have determined that in the process of solidified soil strength formation, the amount of cementitious products generated and the pore structure are two interrelated yet relatively independent variables. By independently or jointly regulating these two variables, continuous regulation of material density and strength can be achieved over a wide range. For example, for a Class I lightweight load-reducing layer, this invention simultaneously employs a lower dosage of cementitious materials and activators (reducing the amount of cementitious products generated) and a higher dosage of pore-regulating components (increasing porosity), minimizing density while ensuring basic strength; for a Class III high-strength load-bearing layer, a higher dosage of cementitious materials and activators and an extremely low or even zero dosage of pore-regulating components are simultaneously employed to achieve high strength and high density. The parameters of the Class II transition buffer layer fall between these two.

[0034] Based on the above technical mechanism, the present invention provides a desulfurized ash-based solidified soil with gradient adjustable strength and density, wherein the slurry comprises, by mass parts: 100 parts of desulfurization ash; 10-45 parts of composite cementitious material; 2–15 parts of the stimulation and regulation component; 0-10 parts of porosity conditioning component; Mixing water 30-80 parts; Functional regulatory components: 0-8 parts.

[0035] The components of the above-mentioned formula exhibit a close synergistic relationship, which is key to achieving the technical objective of this invention. This is explained in detail below: The desulfurization ash in the formulation of this invention is the main component and skeleton material of the solidified soil of this invention. In this invention, the desulfurization ash is selected from one or a mixture of several of the following: semi-dry desulfurization ash, circulating fluidized bed desulfurization ash, and wet desulfurization by-product ash. Semi-dry desulfurization ash and circulating fluidized bed desulfurization ash usually contain components such as CaSO3, CaSO4, Ca(OH)2, and free calcium oxide, and have certain hydration activity potential; wet desulfurization by-product ash is mainly composed of CaSO4·2H2O (gypsum dihydrate).

[0036] This invention fixes the dosage of desulfurization ash at 100 parts by mass, using it as the calculation benchmark for the dosage of other components. Setting desulfurization ash as the benchmark component maximizes the utilization rate of industrial solid waste (reaching over 65%) and ensures that different batches and performance grades of solidified soil products have a unified chemical basis system. This is a prerequisite for achieving chemical compatibility and cementation continuity among layers in the gradient structure. Before use, the desulfurization ash should undergo drying and grinding pretreatment to ensure that its residue on a 45μm square-hole sieve is no more than 15%. This aims to increase its specific surface area and reactivity while ensuring the uniformity of the slurry.

[0037] The main function of the composite cementitious material in the formulation of this invention is to work synergistically with the activation and regulation components to generate cementitious products through hydration and pozzolanic reaction, thereby providing a strength skeleton for the solidified soil.

[0038] In this invention, the composite cementitious material is selected from one or a mixture of several of silicate cement, slag powder, steel slag powder, fly ash, and desulfurized gypsum.

[0039] The mass fraction of the composite cementitious material ranges from 10 to 45 parts (based on 100 parts of desulfurization ash). This range is determined based on the following considerations: When the amount of composite cementitious material is less than 10 parts, regardless of the increase in the activating and regulating components, the total amount of cementing products generated in the system is insufficient to effectively bind the desulfurization ash particles. The final product's 28-day compressive strength is unlikely to meet the minimum engineering requirement of 0.5 MPa, and its water stability is extremely poor. When the amount of composite cementitious material exceeds 45 parts, the relative proportion of desulfurization ash decreases, the solid waste utilization rate declines, and the material cost increases significantly. Simultaneously, excessive cementation reaction leads to excessively high heat of hydration and chemical shrinkage, increasing the risk of cracking between the gradient structure layers due to shrinkage differences. The preferred range for the amount of composite cementitious material is 15 to 35 parts.

[0040] The core function of the activation and regulation component in the formulation of this invention is to provide an alkaline environment and specific ions to activate the reactivity of potentially active silica-alumina components in desulfurization ash and composite cementitious materials. In this invention, the activation and regulation component is selected from one or a combination of several of sodium hydroxide (NaOH), water glass (sodium silicate), calcium oxide (CaO), and sodium sulfate (Na2SO4). Among them, sodium hydroxide and water glass mainly provide OH... - The liquid phase alkalinity is increased to promote the depolymerization of the aluminosilicate glass; calcium oxide introduces active calcium ions while providing alkalinity; sodium sulfate mainly provides SO4. 2- It promotes the directional formation of ettringite.

[0041] The mass fraction of this activation and regulation component ranges from 2 to 15 parts. This range is determined based on the following considerations: When the amount of the activation and regulation component is less than 2 parts, the alkalinity of the liquid phase is insufficient, making it difficult to effectively activate the activity of potential active components such as desulfurization ash and slag. This results in a low rate and extent of gelation reaction, slow strength development, and insufficient final strength. When the amount of the activation and regulation component exceeds 15 parts, excessively high alkalinity may lead to an overly rapid and uncontrolled reaction, causing the slurry to lose its workability in a short period of time, affecting the casting and construction. In addition, excessive alkali metal ions may remain in the pore solution and may react with CO2 in the air later to form carbonates, causing volume changes and strength reduction. The preferred dosage range of the activation and regulation component is 3 to 10 parts.

[0042] The main function of the pore-regulating component in the formulation of this invention is to introduce stable closed pores into the slurry or replace part of the volume with lightweight particles, thereby reducing the wet density and weight of the material. In this invention, the pore-regulating component is selected from one or a combination of EPS particles, pre-formed foam, foaming agent, and foam stabilizer. The pre-formed foam is a foam group with controllable density and a long half-life pre-formed by mechanical foaming of a foaming agent solution. This invention preferentially uses pre-formed foam prepared with animal protein-based foaming agents, with a density controlled at 50–70 kg / m³. 3 It has a half-life of more than 30 minutes.

[0043] The mass fraction of this porosity-regulating component ranges from 0 to 10 parts. This range is determined based on the following considerations: when the porosity-regulating component dosage is 0 parts, corresponding to a Class III high-strength load-bearing layer, the material reaches a dense state with the highest density and strength. As the dosage increases, the material density and strength gradually decrease. When the dosage exceeds 10 parts, excessive pores lead to excessively thin pore walls, a sharp increase in the proportion of interconnected pores, excessive fragmentation of the cementitious skeleton, and a sharp drop in strength (e.g., 28-day compressive strength drops below 0.6 MPa), resulting in loss of structural stability and making it difficult to meet the minimum mechanical performance requirements of engineering projects. This invention achieves a wet density of 500–1350 kg / m³ by precisely controlling the dosage of the porosity-regulating component within the range of 0–10 parts. 3 Continuous adjustment within the range.

[0044] The mixing water in the formula of this invention is an essential medium for the hydration reaction of the cementitious materials, and also provides the workability required for slurry construction. In this invention, the mass fraction of the mixing water ranges from 30 to 80 parts. If the water content is too low, the slurry will be too dry and thick, making it difficult to mix evenly and cast, and the cementitious materials will not be fully hydrated; if the water content is too high, the slurry will segregate and bleed, increasing the porosity of the hardened body and reducing its strength and durability. In actual construction, the specific amount of water needs to be determined comprehensively based on the water requirement of the desulfurization ash, the type of cementitious materials, and the dosage of porosity regulating components, with the criterion being to achieve a uniform, pumpable, or castable slurry.

[0045] The functional regulating components in the formulation of this invention are additives that help optimize the workability of the slurry and the mechanical properties of the hardened body. In this invention, the functional regulating components are selected from one or a combination of several of hydroxypropyl methylcellulose (HPMC), polypropylene fiber, and lignocellulose. HPMC mainly functions as a thickener and water retainer, improving the cohesiveness and homogeneity of the slurry, and is particularly helpful for the stable and uniform dispersion of pre-formed foam. Polypropylene fiber, through its three-dimensional random distribution, acts as a micro-reinforcement and crack-resistant agent in the hardened body. Especially in the interlayer transition zone, the fiber can bridge the upper and lower matrix layers, improving the interlayer shear and crack resistance.

[0046] The mass fraction range of this functional control component is 0 to 8 parts. When the dosage exceeds 8 parts, excessive HPMC will cause the slurry to become too viscous, difficult to stir, and the air entrainment to become uncontrollable; excessive polypropylene fiber will cause fiber clumping and uneven dispersion, which will lead to internal defects. The preferred dosage of the functional control component is 0.3 to 5 parts.

[0047] In view of the above-mentioned desulfurized ash-based solidified soil formulation with adjustable strength and density, the present invention also provides a corresponding preparation process for desulfurized ash-based solidified soil.

[0048] The preparation process includes the following steps: S1, Basic treatment.

[0049] The specific implementation plan for this step is as follows: Remove loose soil, debris, and standing water from the surface of the base layer in the construction area, and compact or level the base layer. If necessary, a layer of geotextile or sand cushion can be laid as an isolation layer. The purpose of this step is to provide a stable and flat construction base for the upper gradient structure, and to prevent uneven settlement of the base layer or mud from contaminating the solidified soil underlying material.

[0050] S2. Raw material pretreatment.

[0051] This step involves two parallel sub-processing flows: Sub-step S2-1 (Desulfurization ash pretreatment): The desulfurization ash is dried in a drying equipment at 105-110℃ until constant weight, and then ground by ball mill or vertical mill so that the fineness of the treated desulfurization ash reaches a sieve residue of no more than 15% on a 45μm square hole sieve.

[0052] In this treatment step, drying eliminates the influence of free water in the desulfurization ash on subsequent water-cement ratio control; grinding increases the specific surface area of ​​the desulfurization ash, breaks down the inert coating layer on the particle surface, exposes fresh reaction surfaces, and improves its reactivity. In addition, grinding can improve the particle size distribution of the desulfurization ash, which is beneficial to the uniformity and density of the slurry.

[0053] Sub-step S2-2 (Foam Pretreatment): When using pre-made foam as the pore-conditioning component, dilute the foaming agent (such as animal protein foaming agent) according to the recommended ratio, and then foam it using a mechanical foaming machine to obtain a density of 50-70 kg / m³. 3 Uniform and fine pre-made foam with a half-life greater than 30 minutes. Pre-made foam must be used immediately after preparation to avoid prolonged standing, which can lead to foam drainage and defoaming.

[0054] In this process, pre-formed foam technology can precisely control the density and stability of the foam. Compared with foaming directly in the slurry, the introduction of pre-formed foam can more accurately control the porosity and distribution in the solidified soil, and avoids the problem of reduced foaming efficiency that may be caused by direct contact between the foaming agent and the highly alkaline slurry.

[0055] S3, Base Material Preparation.

[0056] This step is the core of material preparation and is divided into three stages based on the order of material input: The first stage (dry mixing): The pre-weighed desulfurization ash, composite cementitious materials (cement, slag powder, steel slag powder, etc.), and solid fibers or powdered additives from the functional control components are added to a forced mixer and dry-mixed at 200-400 rpm for 2-4 minutes to ensure thorough and uniform mixing of all solid components. This dry mixing stage avoids uneven localized hydration reactions of the powder components upon contact with water; simultaneously, the dry mixing process helps to initially disperse lightweight components such as polypropylene fibers in the powder, reducing the risk of fiber clumping during subsequent wet mixing.

[0057] The second stage (wet mixing activation): The activation and regulating components (such as sodium hydroxide, water glass, etc.) are pre-dissolved in all or most of the mixing water to form an activation liquid. While the mixer is running continuously, the activation liquid is slowly added to the dry mix, the speed is increased to 250-350 rpm, and stirring is continued for 3-5 minutes to obtain a uniform base slurry. In this stage, the activation and regulating components are pre-dissolved in water before being added, ensuring the instantaneous uniform distribution of alkalinity and active ions in the slurry, avoiding uneven reaction or the "alkali-aggregate reaction" effect caused by local enrichment of solid activator particles; the stirring process also achieves further homogenization of the materials and partial initiation of the gelation reaction, and the slurry begins to develop a certain degree of cohesion.

[0058] The third stage (pore adjustment): Reduce the stirring speed to a low level of 50-100 rpm and add the pore-conditioning component according to the designed dosage. If it is pre-prepared foam, add the pre-prepared foam slowly in batches to the slurry, stirring at low speed for 60-120 seconds until the foam is evenly distributed; if it is EPS particles, stir until the particles are evenly suspended after adding the foam. In this stage, the pore-conditioning component must be added under low-speed stirring conditions. High-speed stirring will cause a large number of foams to break or EPS particles to break, resulting in uncontrolled introduction of pores and failure to achieve the target density. At the same time, the cohesive slurry formed in the wet-mixing activation stage provides a good suspension and bearing environment for the foam or lightweight particles, which helps to stabilize and evenly disperse the pore-conditioning component.

[0059] S4, Gradient parameter tuning.

[0060] This step is crucial for constructing the gradient structure. After preparing the grout for the current layer and pouring it in step S3, the mix proportions for the next layer to be poured need to be adjusted. Specific adjustments include: adjusting the type and / or amount of composite cementitious materials (e.g., changing from slag powder as the main component to a mixture of slag powder and cement with an increased total amount), adjusting the type and / or amount of activation and regulation components (e.g., changing from sodium hydroxide to a mixture of sodium hydroxide and water glass with an increased concentration), and adjusting the type and / or amount of pore-regulating components (e.g., reducing the amount of pre-formed foam or completely eliminating foam).

[0061] Furthermore, the principle for mixing here is to control the absolute value of the difference in design wet density between adjacent pouring layers within 150–300 kg / m³. 3 Based on this range of control: if the density difference between adjacent layers is too small, too many layers are needed to achieve the overall performance transition, increasing construction complexity and time; if the density difference between adjacent layers is too large, the interlayer performance will change significantly, easily forming a stiffness abrupt interface, weakening the continuous transition advantage of the gradient structure.

[0062] S5. Layered pouring.

[0063] The implementation plan for this step is as follows: The prepared grout is poured into the construction area layer by layer from bottom to top using a pump or chute. The thickness of each layer is controlled to be 50–80 cm. This thickness range balances construction efficiency and interlayer bonding quality: a thickness less than 50 cm results in too many construction layers, a long construction period, and high costs; a thickness greater than 80 cm may cause segregation within a single layer of grout, and the lower layer's own weight pressure may cause the precast foam to be compressed and deformed, leading to distortion of the designed density.

[0064] The pouring time interval between adjacent layers should be controlled between 20 and 90 minutes. This time interval is based on the setting and hardening characteristics of the desulfurized ash-based cementitious system: if the interval is too short (less than 20 minutes), the lower layer of slurry is still in a flowing state, and the upper layer of slurry will erode the surface of the lower layer when poured, resulting in mixed layers and blurred interfaces, and failing to form a clear gradient stratification; if the interval is too long (more than 90 minutes), the lower layer of slurry has tended to be fully set, and effective penetration and chemical bonding of cementitious components cannot occur between the upper and lower layers of slurry, and the interface will become a weak "cold joint". Within the suitable interval of 20 to 90 minutes, the lower layer of slurry has initially lost its fluidity (plastic state) but is still in the active hydration reaction period. When the upper layer of slurry is poured at this time, the cementitious components of the upper and lower layers of slurry can diffuse and penetrate each other at the interface, forming an interface transition zone with a certain thickness and gradual properties.

[0065] S6. Interlayer transition processing.

[0066] To further enhance the quality of interlayer bonding, this invention designs an interlayer transition processing step. This step includes two processing methods that can be used individually or in combination: Method 1 (Surface Roughening): Before pouring the upper layer of slurry, the surface of the lower layer of slurry is manually roughened using a toothed rake or similar tool to form a rough surface with a depth of 5-15 mm. The purpose of this rough surface is to increase the specific surface area of ​​the contact between the upper and lower layers, providing mechanical interlocking; to break up any floating slurry layer or bleed film that may form on the surface of the lower layer of slurry, exposing fresh, active slurry, which is beneficial for chemical bonding between the upper and lower layers.

[0067] Method Two (Interface Vibration): After the upper layer of grout is poured, a short, light vibration is applied to the interface area using an immersion vibrator. The vibrator should penetrate the interface to a depth of 10-20 cm. The purpose of this vibration is to allow for localized, moderate mixing and interpenetration of the upper and lower grout layers at the interface through mechanical vibration, eliminating air bubbles and voids that may have been trapped during pouring, and further enhancing the continuity and overall cementitious integrity of the interface. It is crucial to ensure that the vibration is "short and light" to avoid over-vibration that could damage the layered structure or cause excessive foam dissipation.

[0068] S7, Curing and Shaping The implementation plan for this step is as follows: After all pouring is completed, the exposed top surface of the solidified soil should be promptly covered and kept moist for curing. This can be done by covering with plastic film or geotextile and regularly sprinkling water, with a curing time of no less than 7 days. For backfilling projects, backfilling can be carried out directly after the solidified soil has set (generally 24-72 hours after pouring), utilizing the backfill to achieve natural moisture retention and curing. Sufficient curing is a necessary condition to ensure the continuous hydration and full strength development of the cementitious material, especially for desulfurized ash-based systems containing a large number of potentially active components, where continuous moisture retention and curing contributes more significantly to the later strength.

[0069] In the desulfurized ash-based solidified soil preparation scheme with gradient adjustable strength and density formed by the above steps, S1 provides a stable base for the entire structure; S2 provides qualified active raw materials and stable porous media for S3; the three stages of dry mixing-wet mixing activation-pore adjustment in S3 cannot be reversed, and they respectively realize the functions of uniform mixing, reaction initiation and pore construction, and the product of the previous stage is the basis for the next stage; the cyclical cooperation of S4 and S5 realizes the gradual construction from the bottom layer to the top layer; S6 strengthens the interlayer interface formed in S5; and S7 ensures the continuous development of strength and stable performance of the overall structure after construction.

[0070] The desulfurized ash-based solidified soil prepared based on the aforementioned material formulation and preparation process exhibits the following characteristics: Figure 1 The gradient hierarchical structure features are shown.

[0071] See Figure 1 The diagram shows a cross-sectional structure of the solidified soil of the present invention. The structure includes, from bottom to top (or from top to bottom according to engineering requirements): a Class I lightweight load-reducing layer 2, a Class II transition buffer layer 3, and a Class III high-strength bearing layer 4. The above three layers are constructed on the base layer 1.

[0072] This gradient structure has the following outstanding performance characteristics: (1) Gradual density variation: From the first-level layer to the third-level layer, the wet density of the material is between 500 and 1350 kg / m³. 3 The density increases gradually over a wide range, with smooth transitions between adjacent layers and no abrupt density transitions.

[0073] (2) Gradual strength characteristics: The 28-day compressive strength of the material gradually transitions from 0.5 to 1.5 MPa in the first-level layer to 3.0 to 6.0 MPa in the third-level layer, realizing a continuous performance spectrum from low strength and lightweight to high strength and dense.

[0074] (3) Interlayer continuity: Thanks to the unified desulfurized ash-based cementitious system and the "plastic composite" construction process, there is no diametrically separated macroscopic interface between adjacent layers. Instead, a transition zone of several centimeters thick cementitious components is formed at the microscopic scale. Within this transition zone, physical and mechanical parameters such as density, strength, and porosity are continuously and gradually distributed, thereby effectively eliminating the weak surface of "cold joints" in traditional layered construction.

[0075] (4) Functional adaptability characteristics: The bottom Class I layer has low density and light weight, which can significantly reduce the additional load on the soft soil foundation below, and play the role of load reduction and water isolation; the middle Class II layer has appropriate strength and deformation coordination ability, and can serve as a transition buffer between the upper and lower layers to absorb differential deformation; the top Class III layer has high strength and good density, and can withstand the traffic load or structural load above, and effectively diffuse stress.

[0076] The aforementioned structural features enable the solidified soil product of this invention to have comprehensive performance advantages that traditional homogeneous filling materials cannot match in engineering scenarios such as soft soil foundation backfilling, deep foundation pit backfilling, bridge abutment backfilling, and roadbed widening, which are sensitive to differential settlement and have high requirements for load reduction.

[0077] The technical solution and its effects of the present invention will be further illustrated below through specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0078] <Raw Material Preparation> The main raw material sources and pretreatment methods used in the following embodiments and comparative examples are as follows: The desulfurization ash was taken from a semi-dry flue gas desulfurization unit of a coal-fired power plant. Its main chemical components are CaSO4, Ca(OH)2, and a small amount of active silicon-aluminum components. Before use, it was dried in an oven at 105℃ for 24 hours and then ground in a ball mill until the residue on a 45μm square hole sieve was 12%.

[0079] The blast furnace slag powder is S95 grade granulated blast furnace slag powder with a specific surface area ≥400m². 2 / kg.

[0080] The steel slag powder was taken from the converter slag of a steel company, and its specific surface area after grinding was 420 m². 2 / kg.

[0081] The cement is P·O 42.5 grade ordinary Portland cement.

[0082] Sodium hydroxide is industrial-grade caustic soda flakes with a purity of ≥98%.

[0083] Water glass is liquid sodium water glass with a modulus of 2.8 and a solid content of approximately 40%.

[0084] Calcium oxide is industrial-grade quicklime powder with an effective CaO content of ≥90%.

[0085] Pre-formed foam is prepared by diluting animal protein foaming agent 30 times and then using a mechanical foaming machine, with the foam density controlled at 60±5 kg / m³. 3 The half-life is greater than 30 minutes.

[0086] HPMC (hydroxypropyl methylcellulose) has a viscosity specification of 100,000 mPa·s.

[0087] The polypropylene fiber is 6 mm in length and approximately 30 μm in diameter.

[0088] <Examples and Comparative Examples> Example 1 (Class I Lightweight Load Reduction Layer) This embodiment is used to prepare and verify the performance of the first-order lightweight load-reducing layer in a gradient system.

[0089] Formula (parts by weight): 100 parts desulfurization ash, 15 parts slag powder, 8 parts cement, 2 parts sodium hydroxide, 5 parts pre-made foam, 55 parts mixing water, and 0.3 parts HPMC.

[0090] Preparation process: Desulfurization ash, slag powder, cement, and HPMC are added to a forced mixer and dry-mixed at 300 rpm for 3 minutes. Sodium hydroxide is dissolved in the mixing water to form an activating liquid, which is slowly added to the mixer and wet-mixed at 250 rpm for 4 minutes to obtain a uniform base slurry. The mixing speed is reduced to 80 rpm, pre-made foam is added, and mixing continues for 90 seconds until the foam is evenly distributed. The resulting slurry is poured into a 300mm×300mm×300mm cubic mold, the surface is smoothed, and cured in a standard curing room at 20±2℃ and relative humidity ≥95% until the specified age for performance testing.

[0091] Example 2 (Level II Transition Buffer Layer) This embodiment is used to prepare and verify the performance of the Level II transition buffer layer in a gradient system.

[0092] Formula (parts by weight): 100 parts desulfurization ash, 20 parts slag powder, 8 parts steel slag powder, 12 parts cement, 3 parts water glass, 3 parts precast foam, 48 parts mixing water, and 0.2 parts polypropylene fiber.

[0093] Preparation process: Desulfurization ash, slag powder, steel slag powder, cement, and polypropylene fiber are added to a mixer and dry-mixed at 320 rpm for 4 minutes. Water glass is dissolved in a portion of the mixing water and slowly added to the mixer, with the remaining mixing water added. The mixture is then wet-mixed at 280 rpm for 5 minutes. The mixing speed is reduced to 70 rpm, pre-made foam is added, and mixing continues for 120 seconds until homogeneous. Molding and curing conditions are the same as in Example 1.

[0094] Example 3 (Level III High-Strength Load-Bearing Layer) This embodiment is used to prepare and verify the performance of the Class III high-strength load-bearing layer in a gradient system.

[0095] Formula (parts by weight): 100 parts desulfurization ash, 25 parts slag powder, 12 parts steel slag powder, 18 parts cement, 4 parts calcium oxide, 1 part precast foam, 40 parts mixing water, and 0.2 parts HPMC.

[0096] Preparation process: Desulfurization ash, slag powder, steel slag powder, and cement are added to a mixer and dry-mixed at 350 rpm for 4 minutes; calcium oxide is added and dry-mixed for another 2 minutes. Mixing water is added and stirred at 300 rpm for 5 minutes to form a uniform slurry. The stirring speed is reduced to 60 rpm, pre-made foam is added, and stirring is continued for 60 seconds until uniform. Molding and curing conditions are the same as in Example 1.

[0097] Example 4 (Integral Casting of Gradient Structure) This embodiment is used to verify the complete gradient structure construction method and product performance.

[0098] In a vertical mold with dimensions of 300mm×300mm×900mm, a three-layer gradient structure is formed by pouring the material layer by layer from bottom to top.

[0099] S1 Base Treatment: Lay a layer of needle-punched nonwoven geotextile at the bottom of the mold to simulate the base layer.

[0100] Preparation of S2-S3 base material: Prepare the Grade I slurry according to the formula in Example 1, pour it into the bottom of the mold, and pour to a thickness of 60cm. Smooth the surface and let it stand.

[0101] S4 gradient parameter adjustment: After standing for 60 minutes, prepare the second-level slurry according to the formulation of Example 2.

[0102] S5 layer pouring and S6 layer transition treatment: The Class II grout is poured on top of the Class I layer to a thickness of 15cm; a micro vibrator is used to lightly vibrate the interface area to a depth of about 10cm through the interface. After standing for 30 minutes, the Class III grout is prepared according to the formula of Example 3, poured to a thickness of 15cm, and the interface is vibrated.

[0103] S7 curing: After pouring, cover the top surface with plastic film and cure in a standard curing room for 28 days.

[0104] After curing, core samples were taken from the specimens by drilling, and cylindrical core samples were continuously cut from different locations along the height direction for density and strength testing.

[0105] Comparative Example 1 (homogeneous and uniformly proportioned) This comparative model simulates a traditional homogeneous solidified soil solution.

[0106] Formula (parts by weight): 100 parts desulfurization ash, 18 parts slag powder, 10 parts cement, 3 parts precast foam, and 50 parts mixing water. No activation or functional control components are added.

[0107] Preparation process: Dry mix all dry powder materials, then add water and mix thoroughly. Add pre-made foam and mix well. Pour the mixture into a 300mm×300mm×900mm mold in one go. Curing conditions are the same as in Example 4.

[0108] Comparative Example 2 (Excessive Foam) This comparative example is used to verify the negative impact of excessive pore conditioning components on performance.

[0109] Formulation (parts by weight): Based on the formulation of Example 1, the pre-made foam is increased to 12 parts, while the remaining components and amounts remain unchanged. The preparation and curing processes are the same as in Example 1.

[0110] Comparative Example 3 (Insufficient cementitious material) This comparative example is used to verify the negative impact of insufficient composite cementitious material dosage on performance.

[0111] Formula (parts by weight): Based on the formula of Example 1, the total amount of slag powder and cement is reduced to 6 parts (4 parts slag powder and 2 parts cement), while the remaining components and their amounts remain unchanged. The preparation and curing processes are the same as in Example 1.

[0112] Comparative Example 4 (without interlayer treatment) This comparative example is used to verify the necessity of the interlayer transition processing step of the present invention.

[0113] The formulation and layering scheme are the same as in Example 4, but the interface roughening and vibration treatment in step S6 are omitted during construction. The Level II and Level III layers are directly poured on the already settled surface of the lower layer. The curing conditions are the same as in Example 4.

[0114] <Performance Testing and Results> The following performance indicators were tested on the samples obtained from each embodiment and comparative example: wet density (referring to JG / T 266 "Foamed Concrete"), 28-day compressive strength (referring to GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"), and interlaminar shear strength (for the gradient specimens of Example 4 and Comparative Example 4, core samples were drilled along the interlaminar interface for direct shear tests). The test results are summarized in Table 1.

[0115] Table 1

[0116] <Comprehensive Performance Analysis> Based on the analysis of the above test results, the following conclusions can be drawn: (1) The test results of Examples 1 to 3 show that the material formulation system of the present invention can prepare wet density of 620 kg / m³ by adjusting the type and amount of cementitious material, the type and amount of activator, and the amount of pore-regulating component in a unified desulfurization ash-based master system. 3 Strength 1.12 MPa, wet density 905 kg / m³ 3 Strength 2.47 MPa, wet density 1225 kg / m³ 3 The product range, with three performance levels including a strength of 4.85 MPa, fully covers the performance requirements from "lightweight load reduction" and "transition buffer" to "high-strength load bearing." This verifies that the core mechanism of "synergistic performance gradient achieved through chemical activation regulation and physical porosity regulation" in the technical solution of this invention is feasible and effective.

[0117] (2) The test results of Example 4 further demonstrate that the layered pouring and interlayer transition treatment construction method proposed in this invention can integrate the above three different performance grades of slurry into an integral structure with continuous gradient variation characteristics. The density and strength of each layer are basically consistent with those of the single layer preparation, and there is no performance degradation due to layered construction. The interlayer shear strength of Example 4 (0.48 MPa) is significantly higher than that of Comparative Example 1 (0.22 MPa) and Comparative Example 4 (0.25 MPa), which fully proves that the "time interval control" in step S5 and the "interlayer transition treatment" in step S6 of the construction method of this invention have significant and substantial technical effects on improving the interlayer bonding quality. When the upper layer is poured within an interval of 20 to 90 minutes, the lower layer of slurry is still in the hydration active period, and a transition zone of continuous penetration and chemical bonding of cementitious components can be formed between the upper and lower layers, rather than simple physical superposition.

[0118] (3) The test results of Comparative Examples 2 and 3 verified the scientific and technical rationality of the dosage range of each component in this invention. Comparative Example 2 increased the porosity adjustment component to 12 parts, exceeding the upper limit of 10 parts in this invention, resulting in a decrease in density to 410 kg / m³. 3 The strength dropped sharply to 0.58 MPa, and the structure became excessively porous, rendering it unusable. In Comparative Example 3, the cementitious material was reduced to 6 parts (total 8 parts, also below the lower limit of 10 parts in this invention), resulting in a 28-day strength of only 0.73 MPa, which failed to meet the load-bearing requirements. These two comparative examples demonstrate, from the opposite perspective, that the mixing ratio range set in this invention is a necessary technical boundary to ensure the engineering applicability of the product.

[0119] (4) The comparison between Comparative Example 4 and Example 4 strongly demonstrates the indispensability of the "interlayer transition treatment" step in the construction method of the present invention. Comparative Example 4 omits the interface roughening and vibration treatment. Although the strength of each layer is comparable to that of Example 4, its interlayer shear strength is only 0.25 MPa, close to the level of the homogeneous specimen of Comparative Example 1 (0.22 MPa), and far lower than the 0.48 MPa of Example 4. This shows that the uniformity of material formulation and the control of time intervals alone are insufficient to form a sufficiently strong interlayer bond; Step S6 of the present invention, by increasing interface roughness and mechanical penetration, is a key technical means to achieve a high-strength continuous transition between layers.

[0120] In summary, the desulfurized ash-based solidified soil with gradient adjustable strength and density provided by this invention, through the original technical route of "component synergistic regulation + gradient construction process", successfully solves the common industry problems of single performance of existing desulfurized ash-based solidified soil and weak interlayer bonding in traditional layered filling. Its technical solution has significant creative and industrial application value.

[0121] 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 illustrative of the 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 present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A desulfurized ash-based solidified soil with gradient adjustable strength and density, characterized in that, The solidified soil is formed by layering or filling desulfurized ash-based solidification slurry or mixture into shape, and forms a continuous gradient distribution structure along the depth direction of the structure; the desulfurized ash-based solidification slurry comprises, by mass parts: Desulfurization ash: 100 parts; Composite cementitious material: 10-45 parts; Activation and regulation components: 2–15 parts; Pore ​​conditioning component: 0–10 parts; Mixing water: 30-80 parts; By synergistically adjusting the types and / or proportions of the composite cementitious material, the activation and regulation components, and the pore regulation components, different layers of the solidified soil can obtain differentiated wet density and compressive strength.

2. The desulfurized ash-based solidified soil according to claim 1, characterized in that, The continuous gradient distribution structure includes, in order from bottom to top or top to bottom: a Level I lightweight load-reducing layer, a Level II transition buffer layer, and a Level III high-strength load-bearing layer.

3. The desulfurized ash-based solidified soil according to claim 2, characterized in that: The wet density of the Class I lightweight load-reducing layer is 500–750 kg / m³. 3 The 28-day compressive strength is 0.5–1.5 MPa; the wet density of the Class II transition buffer layer is 750–1050 kg / m³. 3 The 28-day compressive strength is 1.5–3.0 MPa; the wet density of the Class III high-strength load-bearing layer is 1050–1350 kg / m³. 3 The 28-day compressive strength is 3.0–6.0 MPa.

4. The desulfurized ash-based solidified soil according to claim 1, characterized in that, The desulfurization ash is one or a combination of several of the following: semi-dry desulfurization ash, circulating fluidized bed desulfurization ash, and wet desulfurization by-product ash.

5. The desulfurized ash-based solidified soil according to claim 1, characterized in that, The composite cementitious material is one or a combination of several of the following: cement, slag powder, steel slag powder, fly ash, and desulfurized gypsum.

6. The desulfurized ash-based solidified soil according to claim 1, characterized in that, The excitation and regulation components are one or a combination of several of sodium hydroxide, water glass, calcium oxide, and sodium sulfate.

7. The desulfurized ash-based solidified soil according to claim 1, characterized in that, The pore-regulating component is one or a combination of EPS particles, pre-formed foam, foaming agent, and foam stabilizer.

8. The desulfurized ash-based solidified soil according to any one of claims 1 to 7, characterized in that, The desulfurized ash-based curing slurry also includes 0-8 parts by weight of a functional regulating component; the functional regulating component is one or a combination of several of hydroxypropyl methylcellulose, polypropylene fiber, and lignocellulose.

9. A construction method for desulfurized ash-based solidified soil as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Base treatment: Clean, level and compact the base layer of the construction area; S2. Raw material pretreatment: The desulfurization ash is dried and ground to ensure that the residue on a 45μm square-hole sieve is no more than 15%; the foaming porosity conditioning component is pre-foamed to obtain a density of 50-70 kg / m³. 3 Stable pre-fabricated foam with a half-life greater than 30 min; S3. Base material preparation: According to the bottom layer design ratio, dry mix the desulfurization ash, composite cementitious materials and functional control components evenly; add mixing water pre-dissolved with activation control components, and wet mix to form a uniform base material slurry; Add the pore-conditioning component under low-speed stirring and stir evenly to obtain the slurry required for the current construction layer. S4. Gradient Parameter Adjustment: After completing one layer of pouring, the activation degree of the cementitious reaction and the bulk density are adjusted by changing the type and / or dosage of the composite cementitious material, activation and regulation components, and porosity regulating components in the layer to be poured, so that the absolute value of the design wet density difference between adjacent pouring layers is controlled within 150-300 kg / m³. 3 ; S5. Layered pouring: Pour the concrete layer by layer from bottom to top, with the thickness of each layer controlled at 50-80cm; control the time interval between two adjacent layers to be 20-90 minutes. S6. Interlayer transition treatment: roughen the surface of the lower layer of slurry before pouring the upper layer of slurry, and / or insert vibration in the interface area after pouring the upper layer of slurry, so that the cementitious components of the upper and lower layers of slurry can penetrate and interweave at the interface. S7. Curing and Shaping: After all the pouring is completed, the exposed surfaces are covered with moisture-retaining materials or covered with soil for natural curing.

10. The construction method according to claim 9, characterized in that: In step S6, the rough surface formed by the roughening treatment has a depth of 5-15 mm; the vibration depth of the immersion vibrator is 10-20 cm through the interface.

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