A clean water agent waste residue-magnesium-aluminum ternary synergistic flow state solidified soil for bridge head backfilling and a preparation method thereof

Abstract

The application discloses a kind of water purifying agent waste residue-magnesium-aluminum ternary synergistic flow state solidified soil for bridge head backfill and preparation method, the flow state solidified soil includes: soil material, water purifying agent waste residue, aluminate cement, active magnesium oxide, magnesium sulfate heptahydrate, water-resistant modifier, reinforcing modifier and additional water.The application constructs water purifying agent waste residue-aluminate cement-magnesium sulphoaluminate cement three synergistic excitation mechanism, utilizes the chemical synergistic effect of aluminate cement and water purifying agent waste residue in magnesium sulphoaluminate cement environment, in combination with water-resistant modifier and reinforcing modifier, in situ induced magnesium-aluminum-calcium-based composite crystalline network.The network is inserted and wrapped in the interface transition zone between waste residue micro-particles and matrix, effectively repairs the crystal defects of traditional magnesium cement, significantly enhances the water resistance and chemical stability of the material, improves its strength retention rate in long-term immersion environment, ensures that backfill body has excellent long-term durability when bearing road load.

Description

Technical Field

[0001] This invention belongs to the field of building materials and road engineering technology, specifically relating to a fluidized solidified soil for bridge abutment backfilling, based on a synergistic activation mechanism of water purification agent waste residue, aluminate cement, and magnesium sulfate oxysulfate cement, and its preparation method. This invention constructs a composite cementitious system using aluminate cement, active magnesium oxide, and magnesium sulfate solids, optimizing the performance of a magnesium matrix containing water purification agent waste residue and with magnesium sulfate oxysulfate cement hydration products as its core, to obtain a backfill material with high fluidity, self-compacting properties, and high durability. Background Technology

[0002] Bridge abutment slab settlement is a long-standing quality defect in highway engineering. Its core cause lies in the fact that the backfill area behind bridge abutments is typically a narrow, irregularly shaped, and confined space, making it prone to compaction dead zones during mechanical compaction with traditional backfill materials. While fluidized bed fillers can solve the self-leveling filling problem, conventional fluidized bed fillers usually require a high water-cement ratio to achieve high fluidity. In the later stages of hardening, the consumption and discharge of free water, accompanied by strong capillary drainage stress, leads to significant drying shrinkage of the material, causing the backfill to detach from the abutment, forming seepage cavities and inducing differential settlement. Furthermore, unlike traditional backfill materials that prioritize lightweight and high strength, bridge abutment backfill projects face more demanding construction and service environments. The slurry must maintain a high fluidity of over 160mm while possessing extremely strong anti-segregation capabilities to support long-distance pumping, and must also have extremely low post-construction settlement rates and good resistance to water erosion. Meanwhile, existing fluid materials that incorporate large amounts of industrial solid waste often suffer from performance degradation due to weak interfacial bonding between solid waste particles and the cementitious matrix, as well as a loose crystalline structure, under long-term groundwater seepage or repeated dynamic loads.

[0003] Water treatment agent waste residue is an industrial solid waste generated during the production of polyaluminum chloride water treatment agents. It is rich in highly chemically active metal hydroxides and aluminate components, and its high specific surface area endows it with the ability to participate in the gelation reaction as an active filler. Traditional magnesium cement has the characteristics of rapid hardening, early strength, low carbon and environmental protection. However, if a large amount of water treatment agent waste residue containing chloride ions is directly added to the magnesium cement system to prepare backfill material, the following technical problems will arise: First, the introduction of a large amount of chloride ions will make the product stability in the magnesium cement matrix worse, and the crystal skeleton is easily disintegrated due to the dissolution of chloride ions, which will lead to a serious decrease in strength and significant volume fluctuations in the later stage. Second, the interface transition zone between water treatment agent waste residue particles and magnesium matrix often has problems of insufficient bonding force and high porosity, making it difficult for the erosion resistance and water resistance of the large-volume solid waste system to meet the technical requirements of long-term chemical stability and zero differential settlement for bridge abutment backfilling projects.

[0004] Therefore, how to construct a high-performance fluid backfill material that integrates "high flowability and self-compacting properties, long-term volume stability and high resistance to softening" while ensuring the quality of waste residue from large-volume water purification agents has become the core technical bottleneck in solving the problem of bridge approach slab settlement on highways. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention constructs a ternary synergistic mechanism based on "water treatment agent waste residue-aluminate cement-magnesium oxysulfate cement," achieving chemical reactivation and high-performance utilization of industrial solid waste with large admixture amounts. In this system, aluminate cement acts as an inducing agent, and its hydration releases calcium and aluminum components (such as Ca) 2+ The magnesium ions (including aluminate ions) first combine with the active aluminum (i.e., the highly chemically active amorphous aluminum component in the waste residue) and free chloride ions in the water purification agent waste residue to form initial microcrystals rich in calcium and aluminum elements. These microcrystals further induce magnesium ions in the matrix to combine with the aluminum components in the waste residue (including active aluminum and aluminum mineral components that gradually participate in the reaction through synergistic activation) to construct a three-dimensional cross-linked magnesium-aluminum-calcium-based composite crystalline network (containing a water-like double hydroxide structure). This crystalline network has a three-dimensional cross-linked structure, interpenetrating and wrapping the interface transition zone between the waste residue microparticles and the matrix, transforming the easily hydrolyzed metastable phase (the structurally unstable intermediate products and amorphous phases formed during the hydration of magnesium oxysulfate cement that are easily decomposed by water) into a dense, erosion-resistant network structure. This crystalline network fundamentally solves the problems of poor water resistance of traditional magnesium cement and strength reduction caused by large amounts of waste residue.

[0006] To achieve the above objectives, the technical solution of the present invention is to provide a fluidized solidified soil for bridge abutment backfilling, which is a ternary synergistic mixture of water purification agent waste residue, aluminate cement, and magnesium sulfate heptahydrate cement. The components, by weight, include: soil material (100 parts by dry weight), 70-100 parts of water purification agent waste residue, 5-15 parts of aluminate cement, 30-55 parts of active magnesium oxide, 25-50 parts of magnesium sulfate heptahydrate, 1-5 parts of water-resistant modifier, 1-3 parts of reinforcing modifier, and added water; the molar ratio (water-sulfur ratio) of total mixing water to sulfur in magnesium sulfate heptahydrate is (18.0-29.5):1, and the total mixing water includes added water, inherent moisture in the soil material, and crystal water in magnesium sulfate heptahydrate.

[0007] Preferably, the molar ratio (water-sulfur ratio) of total water in the mixture to sulfur in magnesium sulfate heptahydrate is (21.5-29.5):1.

[0008] Furthermore, the soil material is cohesive soil, high-moisture silty soil, silt, sandy soil, or construction waste soil from the construction site. Before on-site preparation, the soil material needs to be crushed and sieved through a 10mm standard sieve to remove large-sized lumps and impurities. The plasticity index of the soil material should be 7-18, and the dry density should not be less than 1.5g / cm³. Before mixing, its natural moisture content needs to be measured in real time, and the actual amount of added water should be adjusted accordingly to ensure that the total water content of the system meets the technical requirement of a water-sulfur ratio within the range of 18.0-29.5:1. The soil material of this invention, through synergistic reaction with modifiers and aluminate cement, effectively utilizes soil particles as fine aggregate to construct a suspended structure. Utilizing the physical filling and surface charge adsorption between soil particles and cementitious components, the homogeneity and anti-bleeding properties of the slurry are significantly improved, providing stable physical space support for the growth of magnesium-aluminum-calcium-based composite crystalline networks.

[0009] Furthermore, the waste residue from the water purification agent is an aluminum-containing industrial waste residue generated during the preparation of polyaluminum chloride water purification agent, which is dried and ground for later use; the pH value is 6-8, and the D... 50 The median particle size is 0.045-0.09 mm, and the residue on a 0.075 mm standard sieve is less than 15%.

[0010] Furthermore, the aluminate cement is CA-50 type aluminate cement, wherein the alumina (Al2O3) content is 50%-60% and the specific surface area is 300-500m² / kg; the activity of the active magnesium oxide is above 60% and the specific surface area is 300-500m² / kg.

[0011] Furthermore, the water-resistant modifier is nano-silica with an average particle size of 20-50 nm. Its technical function lies in utilizing the extremely high chemical activity and surface hydroxyl groups of nano-silica to undergo a pozzolanic reaction and coordination bonding with magnesium and aluminum ions in the matrix under alkaline conditions, generating in-situ magnesium silicate (MSH) gel and composite aluminosilicate phases with higher stability. These newly formed phases synergistically crosslink with the magnesium-aluminum-calcium-based composite crystalline phase, directionally inducing hydration products to grow tightly on the surface of water purification agent waste and soil particles, constructing a high-bonding-strength interfacial transition zone. Combined with the micro-skeleton filling effect of nano-silica, it can refine the internal pores of the hardened body from both chemical modification and physical filling aspects, blocking water penetration channels and fundamentally improving the strength retention rate of the backfill under long-term immersion conditions.

[0012] Furthermore, the reinforcing modifier is sodium hexametaphosphate, with an effective component content ≥95.0%. As a dispersion and complexation regulating component, it significantly improves the dispersion uniformity of water purification agent waste and soil particles in the slurry through electrorepulsion effect during the slurry stage, reduces the slurry yield stress, and ensures high fluidity. At the same time, sodium hexametaphosphate can regulate the supersaturation of ions in the system, induce the synergistic hydration of aluminate cement and magnesium oxysulfate cement, and promote the transformation of hydration products from disordered accumulation to a dense cross-network structure, thereby improving the early and late strength of the hardened body.

[0013] Furthermore, the molar ratio (oxygen-sulfur ratio) of oxygen in active magnesium oxide to sulfur in magnesium sulfate heptahydrate is (5.5-7.8):1.

[0014] The oxygen-sulfur ratio determines the amount of main crystalline phase formed in magnesium oxysulfate cement, while the water-sulfur ratio is a scientifically defined limit on the total amount of mixing water. By controlling the ionic strength of the liquid phase reaction environment (i.e., the liquid medium composed of mixing water and soluble ions), the rheological threshold of the slurry and the microstructure density of the hardened body are directly determined. Within the ranges of 5.5-7.8 for the oxygen-sulfur ratio and 18.0-29.5 for the water-sulfur ratio, the coupling effect of the two specific molar ratios ensures that the system maintains high fluidity while in-situ inducing the growth of a magnesium-aluminum-calcium-based composite crystalline phase with reinforcing properties, rather than allowing for disordered precipitation in the slurry. Simultaneously, this precise ratio matching enables dynamic adjustment of setting time under different temperature and humidity conditions, thus balancing the dual requirements of high fluidity for pumping construction and early strength development.

[0015] In the specific system constructed in this invention, waste residue from water treatment agents, aluminate cement, and magnesium oxysulfate cement together constitute a synergistic activation mechanism. This invention utilizes the calcium and aluminum components released during the early hydration of aluminate cement as reactive centers, in situ inducing a co-precipitation reaction between the active aluminum components (and free chloride ions) in the waste residue from water treatment agents and the magnesium oxysulfate cement matrix. This transforms the traditional metastable phase into a magnesium-aluminate-calcium-based composite crystalline network with higher chemical stability, and captures and preferentially fixes chloride ions within the interlayer structure of layered double hydroxides (LDHs). This microscopic repair mechanism essentially utilizes the chemical potential differences among the three components to induce ion recombination, microscopically repairing the interfacial defects caused by the waste residue particles and significantly enhancing the system's erosion resistance. Furthermore, the combined intervention of the waste residue from water treatment agents and aluminate cement regulates the ion supersaturation within the magnesium oxysulfate system, promoting the transformation of the hydration products from a single magnesium salt phase to a multi-element ternary synergistic composite phase. This transformation not only achieves tight filling of pores in physical space but also, chemically, achieves in-situ lattice fixation of ions. The synergistic microscopic mechanism of these three factors manifests macroscopically as a significant improvement in material strength and volume stability, which has been confirmed by the experimental data of this invention.

[0016] The industrial preparation process of the fluidized soil containing water purification agent waste residue described in this invention is as follows: S1. Preparation of the reinforcing and modifying solution: Dissolve the reinforcing and modifying agent (sodium hexametaphosphate) in a portion of the added water (60-80%), then add magnesium sulfate solid and stir to dissolve, thus preparing a magnesium sulfate modified solution; S2. Material pretreatment and forced dry mixing of multiphase components: Determine the initial moisture content of the soil at the construction site; screen the soil to ensure that the particle size is controlled below 10mm; feed the soil, waste residue of water purification agent, aluminate cement, water-resistant modifier (nano silica) and active magnesium oxide into the mixer in proportion, and dry mix for no less than 90s using mechanical force to ensure uniform powder dispersion. S3. High-shear wet mixing: Add magnesium sulfate modified liquid to the dry mixture, stir evenly, then add the remaining external water, and perform high-shear mixing at a speed of not less than 150 r / min to form a homogeneous slurry. The mixing time shall not be less than 120 s. S4. Pumping and self-leveling backfilling: After determining that the initial fluidity of the slurry is within the range of 160mm to 260mm, start the pumping equipment to press it into the bridge abutment backfilling space. The pumping pressure is 0.5-3.0MPa, and the drop height of the slurry is controlled within 3m. The slurry's own weight is used to achieve self-leveling filling of narrow and irregular areas. S5. In-situ curing and quality monitoring: After pouring, cover and moisturize the cement. Utilize the synergistic effect of aluminate cement hydration products and water purification agent waste to promote the preferential fixation of chloride ions in the interlayer structure of hydrotalcite-like materials (LDHs). At the same time, induce the formation of a high-density magnesium-aluminum-calcium-based composite crystalline network to counteract drying shrinkage and form a solidified body with low sedimentation.

[0017] The fluidized solidified soil of this invention employs a forced mixing process: in the dry mixing stage, the distribution of soil materials, waste residue from water purification agents, aluminate cement, water-resistant modifiers, magnesium oxide, and other powders is ensured to be uniform, with a mixing time of no less than 90 seconds; in the wet mixing stage, a high-shear mixing process (speed not less than 150 r / min) is used to achieve a microscopic homogeneous state in the slurry, with a preferred wet mixing time of 180-300 seconds. The initial fluidity of the resulting fluidized solidified soil is stably controlled between 160-260 mm, ensuring self-leveling filling in complex bridge abutment areas.

[0018] Under the above formula and process, the 28-day unconfined compressive strength of the fluidized solidified soil is precisely controllable within the range of 1.5-5.0 MPa. This invention limits the strength to this range based on in-depth logical optimization for specific bridge abutment backfill conditions. According to the "Highway Subgrade Design Code," the strength of bridge abutment backfill materials should not be too high. Excessive strength often leads to a significant increase in structural brittleness and causes severe abrupt changes in stiffness between the backfill and adjacent subgrade, resulting in pavement cracking. This invention utilizes the synergistic chemical action of aluminate cement, waste water treatment agent, and magnesium oxysulfate cement to lock the strength within a "performance window" of 1.5-5.0 MPa. While ensuring that the bearing capacity is far higher than the specification requirements (>1.2 MPa), it maximizes the preservation of the material's deformation compatibility.

[0019] Experiments show that this design effectively solves the problems of brittle cracking caused by excessive strength development of conventional fluid fillers and poor volume stability caused by large amounts of solid waste. It achieves a smooth transition of stiffness between the backfill area and the roadbed, fundamentally eliminating the technical problem of bridge approach slab settlement. It has significant technological progress and engineering application value.

[0020] Beneficial effects: This invention utilizes the synergistic effect of water purification agent waste residue, aluminate cement, and magnesium sulfate-magnesium oxysulfate cement to effectively fix harmful chloride ions. In this ternary synergistic system, the effective calcium source and aluminum component provided by aluminate cement, together with the excess active aluminum and free chloride ions in the water purification agent waste residue and the magnesium ions in the magnesium sulfate-magnesium oxysulfate cement system, interact to generate stable layered double hydroxide (LDHs) crystalline phases through an in-situ induced large-scale co-precipitation process. Simultaneously, the high-alumina environment provided by aluminate cement promotes the fixation of chloride ions. - Preferential embedding and stable fixation within the interlayer structure of hydrotalcite-like materials (LDHs) reduces their migration and dissolution risks in a sulfate ion environment. This mechanism not only utilizes the unique interlayer ion exchange capacity of LDHs to effectively capture and lock chloride ions, inhibiting the disintegration of the crystal framework caused by chloride ion dissolution, but also promotes the interpenetration of the 5·1·7 crystalline phase of magnesium sulfate-oxygenated cement with the newly formed LDH phase, constructing a regular and dense magnesium-aluminum-calcium-based three-dimensional cross-linked crystalline network. This synergistically constructed crystalline network repairs the interfacial defects between waste particles and the matrix at the microscopic level, solving the problem of strength attenuation and performance degradation that easily occurs in high-volume solid waste systems under groundwater seepage environments.

[0021] Addressing the technical challenge of significant drying shrinkage and subsequent detachment from the abutment backfill caused by the discharge of free water in conventional fluid materials, this invention utilizes the volume self-compensation characteristics of a magnesium-aluminum-calcium-based composite crystalline network during its growth process to compensate for drying shrinkage. The microcrystalline pressure generated by this composite crystalline phase precisely counteracts the capillary shrinkage stress generated during the hardening and dehydration process of the fluid soil. This dynamic balance between chemical micro-expansion and physical shrinkage, combined with the filling of micropores by nano-silica, constructs a stable three-dimensional support framework between particles. Experimental data show that the long-term volume deformation rate of each embodiment of this invention is low (e.g., only -0.04% in Example 2), ensuring a tight bond between the backfill and the abutment backfill, eliminating seepage cavities, and fundamentally preventing the occurrence of differential settlement—the core cause of bridge approach slab settlement.

[0022] To address the limited space requirements of narrow and irregularly shaped bridge abutment backfill areas, this invention employs gradation control of waste residue particle size and a high-shear homogenization process to enable the waste residue particles to possess both "micro-aggregate filling" and "lubricating rolling" effects. Combined with the dynamic compensation process for the oxygen-sulfur ratio (5.5-7.8) and water-sulfur ratio (18.0-29.5) described in this invention, the slurry is ensured to possess a high initial fluidity of over 180mm while exhibiting extremely low fluidity loss over time (e.g., only 4.1% in Example 7) and extremely strong anti-segregation ability. This guarantees the material's excellent self-leveling filling capability, enabling long-distance pumping and achieving seamless filling of compacted dead corners in the backfill area, resulting in a high-performance backfill structure that combines high fluidity, ultra-low settlement, and long-term erosion resistance. Detailed Implementation

[0023] The following detailed description, with reference to specific embodiments, illustrates the ternary synergistic fluidized solidified soil composed of water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement, and its preparation method thereof. The embodiments shown are merely illustrative of the technical solution of this invention and are not intended to limit the scope of protection of this invention. Those skilled in the art can make equivalent substitutions or optimizations to the proportions, process parameters, material sources, etc., without departing from the principles and spirit of this invention, and all such substitutions should fall within the scope of protection of this invention.

[0024] The soil particle size is less than 10mm, the plasticity index is 7-18, and the dry density is not less than 1.5g / cm³.

[0025] The aluminate cement is CA-50 type aluminate cement, in which the alumina (Al2O3) content is 50%-60% and the specific surface area is 300-500m² / kg.

[0026] The activity of activated magnesium oxide is 85%, and the specific surface area is 300-500 m² / kg.

[0027] The water-resistant modifier is nano-silica with an average particle size of 20-50 nm.

[0028] The reinforcing modifier is sodium hexametaphosphate, with an effective ingredient content of ≥95.0%.

[0029] Waste residue from water purification agents: This waste residue is aluminum-containing industrial waste residue generated during the production of polyaluminum chloride by water purification agent manufacturers. After mechanical dehydration, the raw waste residue is placed in an electrically heated forced-air drying oven and continuously dried at 105±5℃ for at least 12 hours until the mass change rate of the sample is less than 0.1% within 1 hour (i.e., reaching constant weight), ensuring that its residual moisture content is below 0.5%. The dried material is then mechanically ground to a median particle size D. 50 After sieving to a thickness of approximately 0.075 mm, dried water purification agent waste powder was obtained and set aside for later use. The dried base material was a pale yellow powder with a neutral pH. XRF analysis (Table 1) showed that the dry basis chemical composition of the water purification agent waste powder contained 27.80% Al2O3 and 3.42% Fe2O3 by mass. Phase composition analysis revealed the presence of SiO2, CaCO3, CaTiO3, and Al2O3 in the waste powder. Microscopic morphology observation showed that the sample was irregularly shaped thin flakes with a certain degree of agglomeration. Particle size distribution testing indicated that the sample particle size was predominantly tens of micrometers, with a D... 50 ≈0.075mm, D 90 ≈0.15mm.

[0030] Table 1. Main chemical components of water purification agent waste residue (mass percentage %) Example 1 A fluidized solidified soil for bridge abutment backfill comprises, by weight, 101 parts low liquid limit clay (100 parts dry soil, containing 1 part water), 85 parts waste residue from a water purification agent, 10 parts aluminate cement, 45 parts activated magnesium oxide, 35 parts magnesium sulfate heptahydrate (containing 17.91 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 51 parts added water. Calculations show that in this embodiment, the molar ratio (oxygen-sulfur ratio) of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate is 6.68:1, and the molar ratio (water-sulfur ratio) of total water (69.91 parts) to sulfur in the magnesium sulfate heptahydrate is 27.32:1.

[0031] A method for preparing fluidized solidified soil for bridge abutment backfill includes the following steps: S1. Take 39 parts of external water (approximately 76.5% of the total external water), dissolve 2 parts of sodium hexametaphosphate in it, then add 35 parts of magnesium sulfate heptahydrate, stir until the solid is fully dissolved, and prepare a magnesium sulfate modified solution. S2. Dry mix 101 parts of low liquid limit clay, 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 3 parts of nano silica and 45 parts of active magnesium oxide for 100 seconds to ensure uniform powder dispersion. S3. Add the magnesium sulfate modified liquid prepared in step S1 to the dry mixture in step S2, stir evenly, then add the remaining external water (12 parts), and then stir at a high shear speed of 200 r / min for 240 s to form a uniform slurry, which is the fluidized solidified soil.

[0032] Example 2 A fluidized solidified soil for bridge abutment backfilling is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 100 parts waste residue from a water purification agent, 15 parts aluminate cement, 55 parts activated magnesium oxide, 50 parts magnesium sulfate heptahydrate (containing 25.58 parts water of crystallization), 5 parts nano-silica, 3 parts sodium hexametaphosphate, and 65 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.72:1, and the molar ratio of total water (91.58 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 25.05:1.

[0033] Example 3 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 70 parts waste water treatment agent residue, 5 parts aluminate cement, 30 parts activated magnesium oxide, 25 parts magnesium sulfate heptahydrate (containing 12.79 parts water of crystallization), 1 part nano-silica, 1 part sodium hexametaphosphate, and 40 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 6.24:1, and the molar ratio of total water (53.79 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 29.43:1.

[0034] Example 4 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 80 parts waste water treatment agent residue, 8 parts aluminate cement, 45 parts activated magnesium oxide, 40 parts magnesium sulfate heptahydrate (containing 20.46 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 50 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.85:1, and the molar ratio of total water (71.46 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 24.44:1.

[0035] Example 5 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, containing 1 part water), 80 parts waste water treatment agent residue, 12 parts aluminate cement, 45 parts activated magnesium oxide, 30 parts magnesium sulfate heptahydrate (containing 15.35 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 48 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 7.80:1, and the molar ratio of total water (64.35 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 29.35:1.

[0036] Example 6 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 90 parts waste water treatment agent residue, 10 parts aluminate cement, 45 parts activated magnesium oxide, 40 parts magnesium sulfate heptahydrate (containing 20.46 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 42 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.85:1, and the molar ratio of total water (63.46 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 21.71:1.

[0037] Example 7 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 90 parts waste water treatment agent residue, 10 parts aluminate cement, 45 parts activated magnesium oxide, 40 parts magnesium sulfate heptahydrate (containing 20.46 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 48 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.85:1, and the molar ratio of total water (69.46 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 23.76:1.

[0038] Example 8 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 85 parts waste water treatment agent residue, 10 parts aluminate cement, 40 parts activated magnesium oxide, 35 parts magnesium sulfate heptahydrate (containing 17.91 parts water of crystallization), 5 parts nano-silica, 1 part sodium hexametaphosphate, and 50 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.94:1, and the molar ratio of total water (68.91 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 26.94:1.

[0039] Example 9 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 85 parts waste water treatment agent residue, 10 parts aluminate cement, 40 parts activated magnesium oxide, 35 parts magnesium sulfate heptahydrate (containing 17.91 parts water of crystallization), 1 part nano-silica, 3 parts sodium hexametaphosphate, and 50 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.94:1, and the molar ratio of total water (68.91 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 26.94:1.

[0040] Example 10 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 101 parts low liquid limit clay (100 parts dry soil, 1 part water), 100 parts waste water treatment agent residue, 5 parts aluminate cement, 45 parts activated magnesium oxide, 35 parts magnesium sulfate heptahydrate (containing 17.91 parts water of crystallization), 3 parts nano-silica, 2 parts sodium hexametaphosphate, and 55 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 6.68:1, and the molar ratio of total water (73.91 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 28.89:1.

[0041] Example 11 A synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum ternary components, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 120 parts of undisturbed silty soil from the construction site (100 parts dry soil, 20 parts water content), 80 parts of waste water treatment agent residue, 10 parts of aluminate cement, 40 parts of activated magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano-silica, 2 parts of sodium hexametaphosphate, and 35 parts of added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.94:1, and the molar ratio of total water (72.91 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 28.50:1.

[0042] Example 12 A ternary synergistic fluidized bed solidified soil, consisting of waste water treatment agent residue and magnesium-aluminum alloy, for bridge abutment backfilling, is prepared using the same method as in Example 1. The components, by weight, include: 105 parts construction waste soil (100 parts dry soil, containing 5 parts water), 90 parts waste water treatment agent residue, 12 parts aluminate cement, 45 parts activated magnesium oxide, 40 parts magnesium sulfate heptahydrate (containing 20.46 parts water of crystallization), 4 parts nano-silica, 2.5 parts sodium hexametaphosphate, and 58 parts added water. Calculations show that the molar ratio of oxygen in the activated magnesium oxide to sulfur in the magnesium sulfate heptahydrate (oxygen-sulfur ratio) in this example is 5.85:1, and the molar ratio of total water (83.46 parts) to sulfur in the magnesium sulfate heptahydrate (water-sulfur ratio) is 28.54:1.

[0043] Control group 1 A comparative method for preparing traditional backfill soil includes the following steps (by weight): add water to 101 parts of low liquid limit clay (100 parts of dry soil and 1 part of water) according to 60 parts of total water, and stir to obtain the final product.

[0044] Control group 2 A comparative preparation method for solidified soil lacking aluminate cement is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0045] Control group 3 A comparative preparation method for solidified soil using magnesium chloride oxychloride cement instead of magnesium sulfur oxychloride cement is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 29 parts of magnesium chloride hexahydrate (MgCl2·6H2O), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0046] Control group 4 A comparative preparation method for solidified soil lacking functional modifier is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), and 51 parts of added water.

[0047] Control group 5 A comparative preparation method for solidified soil using ordinary silicate cement is described. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, 1 part of water), 85 parts of waste residue from water purification agent, 90 parts of ordinary silicate cement (PO 42.5) (used to replace the active magnesium oxide, magnesium sulfate heptahydrate and aluminate cement in Example 1), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0048] Control group 6 A comparative preparation method for solidified soil with an oxygen-sulfur ratio exceeding the upper limit is disclosed. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts dry soil, containing 1 part water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 70 parts of activated magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano-silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water. Calculations show that the oxygen-sulfur ratio in this control group is 10.39:1, exceeding the upper limit of the oxygen-sulfur ratio limit.

[0049] Control group 7 A comparative preparation method for solidified soil with a water-to-sulfur ratio exceeding the upper limit is disclosed. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of activated magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano-silica, 2 parts of sodium hexametaphosphate, and 90 parts of added water. Calculations show that due to the extremely large amount of added water, the water-to-sulfur ratio reaches 42.56:1, exceeding the acceptable range.

[0050] control group 8 A comparative preparation method for solidified soil with an imbalanced aluminum slag ratio is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 2.5 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0051] Control group 9 A comparative preparation method for solidified soil with a low amount of nano-silica is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 0.2 parts of nano-silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0052] control group 10 A comparative preparation method for solidified soil with a relatively high amount of nano-silica is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 10 parts of nano-silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0053] Control group 11 A comparative preparation method for solidified soil with a low sodium hexametaphosphate content is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 0.3 parts of sodium hexametaphosphate, and 51 parts of added water.

[0054] control group 12 A comparative preparation method for solidified soil with a relatively high sodium hexametaphosphate content is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 7 parts of sodium hexametaphosphate, and 51 parts of added water.

[0055] Control group 13 A comparative preparation method for solidified soil using sulfoaluminate cement instead of aluminate cement is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of sulfoaluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0056] Control group 14 A comparative preparation method for solidified soil that replaces the water-resistant modifier is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of calcium stearate, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0057] control group 15 A comparative preparation method for solidified soil with a replacement reinforcing modifier is provided. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of waste residue from water purification agent, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 2 parts of citric acid, and 51 parts of added water.

[0058] control group 16 A comparative preparation method for solidified soil using an equal amount of inert powder to replace waste residue is described. The preparation method is the same as in Example 1. The components, by weight, include: 101 parts of low liquid limit clay (100 parts of dry soil, containing 1 part of water), 85 parts of fly ash, 10 parts of aluminate cement, 45 parts of active magnesium oxide, 35 parts of magnesium sulfate heptahydrate (containing 17.91 parts of water of crystallization), 3 parts of nano silica, 2 parts of sodium hexametaphosphate, and 51 parts of added water.

[0059] Performance testing 1. 28-day compressive strength test According to the test method specified in JGJ / T 233-2011 "Specification for Cement-Soil Mix Design", the slurry of Examples 1-12 and Control Groups 1-16 was injected into molds and cured for 28 days at a temperature of 20±2℃ and a humidity of 95%. The 28-day unconfined compressive strength was measured. The specific results are shown in Tables 2 and 3.

[0060] Table 2. Compressive strength test results of solidified soil in the examples (Note: Total water volume = added water + inherent moisture content of soil + water of crystallization in magnesium sulfate heptahydrate) Table 3. Compressive strength test results of the control group solidified soil As shown in Table 2, the synergistic mechanism of water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement described in this invention exhibits a significant ability to regulate the 28-day compressive strength of the consolidated body within a defined proportion range. The strength range covers 1.86 MPa to 4.92 MPa, accurately covering the technical requirements of different engineering levels. Using Example 1 as a typical benchmark mix, its 28-day compressive strength reached 3.72 MPa, confirming that under the synergistic activation of the three components, the system can construct a dense composite crystalline network with excellent mechanical properties. Under the dominance of this synergistic mechanism, each example exhibits extremely high performance stability and range adaptability: Examples 6 and 3 respectively demonstrate the upper limit of the strength development of this synergistic system (4.92 MPa) and the lower limit of meeting basic engineering requirements (1.86 MPa), with both data jointly defining the effective performance boundary of the technical solution of this invention in practical applications. Furthermore, the results of Example 2 confirm that by adjusting the component proportions in the synergistic system of water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement, directional strengthening of strength can be achieved. Examples 8 and 9 maintained the same key components except for the functional modifier, with only minor adjustments to the amounts of nano-silica and sodium hexametaphosphate. Their 28-day compressive strengths were 3.65 MPa and 4.31 MPa, respectively. This result demonstrates that, within the ternary synergistic system of this invention, changes in the proportion of the functional modifier significantly affect crystal development and strength formation, allowing for precise control of material properties. Data from Example 10 further confirms that even under extreme conditions with 100 parts of waste water treatment agent and a reduced aluminate cement ratio, the system maintains a stable strength of 2.65 MPa through the synergistic mechanism of the three components in reconstructing the chemical activity of industrial solid waste. This fully demonstrates the reliability and technical versatility of this invention for utilizing high proportions of solid waste.

[0061] Data from Examples 4 and 5 jointly confirm the performance stability and proportioning flexibility of the system of the present invention under the synergistic mechanism of water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement. Specifically, although the water-sulfur ratio in Example 5 (29.35:1) is higher than that in Example 4 (24.44:1), the compressive strength in Example 5 still reaches 4.25 MPa due to the precise control of the oxygen-sulfur ratio (7.80:1). This result proves that in the synergistic system, precise control of the oxygen-sulfur ratio plays a decisive supporting role in improving the quality of crystalline phase development and mechanical properties, and its positive contribution ensures that the system can maintain a dense structure even within a wide range of water-sulfur ratio fluctuations. Furthermore, data from Examples 6 and 7 show that, relying on the above-mentioned synergistic mechanism, the compressive strength can be effectively controlled by dynamically adjusting the water-sulfur ratio to meet the requirements of different working conditions. Meanwhile, Examples 11 and 12, based on the strength performance of high-moisture-content silty soil and construction waste soil at the construction site (2.28 MPa and 3.05 MPa, respectively), further verified that the synergistic mechanism of the three has excellent chemical compatibility and solidification effect on complex soils, demonstrating the strong engineering applicability of the technical solution of the present invention.

[0062] The control group data in Table 3 further confirms the nonlinear synergistic enhancement effect among the components of this invention: compared with the data of control group 1 (0.12 MPa), it can be seen that the uncured soil has no bearing capacity at all, while the strength of each embodiment of this invention has achieved an order of magnitude improvement; firstly, the data demonstrates the irreplaceability of the synergistic system of water purification agent waste residue-aluminate cement-sulfooxymagnesium cement. The strength of control group 2 without aluminate cement is only 2.15 MPa, which is significantly lower than the 3.72 MPa of the baseline embodiment 1, proving that aluminate cement is crucial for the formation of a dense composite crystalline network; secondly, the data demonstrates the unique synergistic gain effect of aluminate cement and the sulfooxymagnesium system. Compared with control group 3, it can be seen that even with the addition of aluminate cement in the magnesium oxychloride system, its strength (1.86 MPa) is still much lower than that of Example 1, and even lower than that of the magnesium oxysulfate system without aluminate (control group 2). This proves that aluminate cement must be coupled with the magnesium oxysulfate system of the present invention to activate synergistic strengthening potential, thereby achieving optimal ion curing and strength performance. Third, the data demonstrates the role of the modifier. The strength of control group 4 without the modifier is only 1.62 MPa, which is significantly lower than that of the baseline Example 1. Fourth, the control experiment confirms the strictness of the component ratio. The strength of control groups 6 and 7 dropped significantly due to the excessive oxygen-sulfur ratio (leading to poor structural integrity) and the excessive water-sulfur ratio (leading to loose structure), respectively, proving the scientific nature of the formulation range.

[0063] Finally, the data from controls 9-12 revealed the criticality of the added modifier content: insufficient nano-silica or sodium hexametaphosphate (controls 9 and 11) led to the failure of the nucleation and dispersion effects, resulting in a significant decrease in strength compared to Example 1; while excessive addition (controls 10 and 12) also caused a significant decrease in strength due to nano-agglomeration or severe retardation interfering with crystal growth. In particular, the high dose of sodium hexametaphosphate in control 12 caused the strength to drop to 1.42 MPa, with a significant retardation side effect. In addition, the strength of control 13 after replacing aluminate cement with sulfoaluminate cement (2.55 MPa) was significantly lower than that of Example 1. This is because the ettringite crystals produced by the hydration of sulfoaluminate cement have poor compatibility with the magnesium-aluminum ternary system, and their inherent sulfate ions interfere with the preset oxygen-sulfur molar ratio balance of sulfoaluminate cement, resulting in insufficient structural density. Conversely, the aluminum-rich environment produced by the hydration of aluminate cement can couple in situ with magnesium components to form a hydrotalcite-like (LDHs) reinforcing phase, thereby achieving molecular-level interweaving with the sulfoaluminate magnesium crystal network. Control groups 14 and 15, which underwent functional substitution with calcium stearate and citric acid respectively, showed actual strengths (1.38 MPa and 1.52 MPa) far lower than Example 1, demonstrating the high compatibility of nano-silica and sodium hexametaphosphate with the synergistic system of water treatment agent waste residue and magnesium-aluminum ternary system in the original formulation. Control group 16, after replacing the waste residue with fly ash, had a strength of only 2.05 MPa, further confirming the significant chemical activity contribution of the water treatment agent waste residue in this system. Furthermore, control group 5 demonstrated that ordinary silicate cement has a strength of only 1.78 MPa under the same weight and extremely poor fluidity, which cannot meet the construction requirements of fluid soil.

[0064] Of particular note is the comparison of data from control groups 2 and 8. It is evident that, with an extremely low aluminate cement content (2.5 parts), the compressive strength of control group 8 (1.12 MPa) was significantly lower than that of control group 2 (2.15 MPa) without aluminate cement. This phenomenon indicates that the introduction of aluminate cement does not simply linearly enhance the system's performance. When the aluminum salt content is insufficient to form an effective ternary synergistic network of water treatment agent waste residue and magnesium-aluminum, the introduced aluminum / calcium ions may compete with the original hydration reaction of the magnesium cementitious system, interfering with the continuous growth and interlocking of the magnesium oxysulfate crystalline phase (such as the 5.1.7 phase), thus leading to defects in the internal structure of the hardened body. Only when the aluminate cement content increases to the range defined in this invention can the aluminum component generate a positive ternary synergistic effect with the active magnesium oxide and water treatment agent waste residue, constructing in situ a stable composite crystalline framework composed of magnesium oxysulfate crystals, a hydrotalcite-like phase, and aluminosilicate gel, effectively improving the overall mechanical properties of the material.

[0065] The above experimental data fully demonstrate that the present invention, through the directional synergistic effect of aluminate cement on the active aluminum in the waste residue of water purification agent, constructs an in-situ reinforced magnesium-aluminum-calcium-based composite crystalline framework in the specific microenvironment provided by the magnesium cementing system. This performance leap achieved based on the precise matching of chemical components enables the material to achieve excellent strength and durability while maintaining high fluidity, thus solving the technical difficulties of low solid waste utilization and poor environmental adaptability in the field of bridge abutment backfilling.

[0066] 2. Initial flowability, 30-minute flowability loss rate, and 28-day long-term volume shrinkage rate tests This study tested the initial flowability, 30-minute flowability loss rate, and 28-day long-term volume shrinkage rate of the fluidized solidified soil of this invention. The flowability test was performed in accordance with CJJ / T 177-2012 "Technical Specification for Filling Engineering of Bubble-Mixed Lightweight Soil", and the volume deformation rate test was performed in accordance with GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". These indicators evaluated the self-leveling filling ability, rheological stability over time, and volume stability after hardening of the material, respectively. The results are shown in Table 4.

[0067] Table 4. Test results of flow properties and volume shrinkage rate of materials in each group. As shown in Table 4, the embodiments of the three-component synergistic mechanism of water purification agent waste residue-aluminate cement-magnesium oxysulfate cement described in this invention maintain high fluidity of 185-260mm while the fluidity loss rate of 30min remains at a low level of 4.1-18.2%, demonstrating excellent construction stability.

[0068] Using Example 1 as a typical baseline ratio, its initial fluidity and volume stability are both at the preferred level of the technical solution of this invention, confirming the core contribution of the synergistic activation mechanism of the three components to the rheology of the slurry and the density of the hardened body structure. Relying on the volume compensation effect generated by the magnesium-aluminum-calcium-based composite crystalline network synergistically constructed by the magnesium-aluminum-based cementitious components and the waste residue active components, the long-term volume shrinkage rate of each example was significantly reduced to the range of -0.035% to -0.098%. Specifically, Example 2, at a high dosage ratio, maintained a high initial fluidity of 237 mm and an extremely low shrinkage rate of -0.040%; Example 3, with the components set at the lower limit, still maintained an initial fluidity of 185 mm and a shrinkage rate controlled at -0.098%.

[0069] Furthermore, the data from Examples 6 and 7 further confirm that, under the synergistic mechanism of the water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement, precise control of construction performance can be achieved by fine-tuning the water-sulfur ratio (e.g., increasing the initial fluidity to 260 mm in Example 7). This demonstrates that the system maintains volume stability while possessing excellent construction adjustment flexibility. In contrast, the control groups that did not form a synergistic system showed significant deterioration in fluidity maintenance and shrinkage control, highlighting the significant technical advantages of the embodiments of the present invention in solving the problems of self-leveling filling and settlement control in bridge abutment backfill.

[0070] Data from Examples 11 and 12 show that the synergistic mechanism of the water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement described in this invention has extremely strong engineering adaptability. When treating sludge with high water content and construction waste, the shrinkage rate can still be stably controlled within -0.1% (-0.078% and -0.083% respectively), and good initial fluidity of 208mm and 218mm can be maintained, which fully demonstrates the excellent engineering deformation coordination under this synergistic mechanism.

[0071] Analysis of Examples 4 and 5 reveals that, under the synergistic mechanism of the water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement, optimizing the coupling relationship between the oxygen-sulfur ratio and the water-sulfur ratio ensures excellent rheological stability of the slurry under different moisture conditions. For example, in Example 5, under a higher water-sulfur ratio, the 30-minute fluidity loss rate (7.2%) and shrinkage rate (-0.070%) remained at excellent levels, confirming the profound influence of component ratio on improving the compactness of the hardened body's microstructure. Meanwhile, data from Examples 8 and 9 (fluidity of 200 mm and 190 mm, respectively, with shrinkage rates both within -0.072%) demonstrate that fine-tuning the modifier ratio can achieve precise control of the microstructure within the synergistic system. Furthermore, Example 10 further confirms that even when the amount of waste residue from the water purification agent is significantly increased to 100 parts, the initial fluidity (188 mm) and volume stability (-0.093%) of the system remain stable due to the chemical activity reconstruction through the synergistic mechanism of the three components, which strongly supports the technical advantages of this invention in the utilization of large-volume industrial solid waste.

[0072] In contrast, the initial fluidity of control group 2 (lacking aluminate cement) was only 124 mm, and the fluidity loss rate was as high as 46.2% after 30 min, with a long-term volume shrinkage rate of -0.152%, indicating that the lack of aluminate cement synergy leads to the slurry losing its self-leveling ability and having extremely poor stability.

[0073] In particular, the data from control groups 6 and 7 further validated the scientific validity of the formulation design of this invention: Control group 6 had a long-term volume deformation rate of +0.155% due to an excessively high proportion of active magnesium oxide (exceeding the oxygen-sulfur ratio limit). This uncontrolled late-stage expansion leads to outward tensile stress in the solidified body, causing macroscopically visible structural cracking.

[0074] Although the initial fluidity of control group 7 reached 270 mm, the excessively high water-to-sulfur ratio (too much water) led to severe bleeding of the slurry. Its long-term volume shrinkage rate was as high as -0.210%, and the large number of interconnected pores left after the excessive water evaporated resulted in a loose structure that could not meet the requirements for bridge abutment backfilling.

[0075] Further analysis of control group 3 (magnesium oxychloride cement replacing magnesium oxysulfate system) revealed that although the initial fluidity (168 mm) was acceptable, its 30-minute fluidity loss rate was as high as 28.7%, significantly higher than that of Example 1 (8.3%), and its shrinkage rate (-0.121%) was much greater than that of Example 1. This strongly demonstrates that in environments containing aluminum and chlorine waste residue, the traditional magnesium oxychloride system, due to ion interference, cannot construct a stable composite salt network like the magnesium oxysulfate system of this invention. Meanwhile, data from control group 1 showed that the fluidity of the uncured soil was less than 50 mm and deformation data could not be measured, completely lacking construction and load-bearing capacity.

[0076] Meanwhile, the data from control groups 4, 5, and 8 reveal the uniqueness and superiority of the system of this invention from different dimensions: Control group 4 lacked nano-silica and sodium hexametaphosphate, resulting in severe slurry flocculation and a significant increase in shrinkage rate to -0.187%. Control group 5 used 90 parts of ordinary cement as a substitute, with an initial fluidity of only 125 mm and a shrinkage rate as high as -0.254%, which is more than 3.3 times that of Example 1, highlighting the technological leap of this invention in terms of volume stability. In control group 8, the amount of aluminate cement was insufficient, and the fluidity loss rate surged to 33.2%, while the shrinkage rate also deteriorated to -0.178%, proving the necessity of aluminate cement in structural support and deformation control.

[0077] Furthermore, the data from control groups 13-16 further confirmed the importance of component compatibility: although control group 13, which used sulfoaluminate cement to replace aluminate cement, performed reasonably well, its volume stability (-0.095%) was still inferior to that of Example 1; control groups 14 and 15, which used calcium stearate and citric acid for functional substitution respectively, showed a significant decline in initial flowability (172 mm, 175 mm) and volume stability (-0.187%, -0.162%) compared to Example 1, confirming the uniqueness of the original formula modifier; and control group 16, which used fly ash to replace waste residue, showed a significant increase in shrinkage (-0.115%), corroborating that the waste residue of the water purification agent is not only a filler in this system, but also an active contributing component.

[0078] Finally, as can be seen from the control groups 9-12, an imbalance in the proportion of additives can severely disrupt the slurry balance: excessive nano-silica (control group 10) leads to impaired flowability and a surge in the loss rate to 32.8%; excessive sodium hexametaphosphate (control group 12), although initially having high flowability (245 mm), leads to a deterioration in the shrinkage rate to -0.120%.

[0079] In summary, the fluidized solidified soil prepared by this invention exhibits significant technical advantages in terms of fluidity, rheological stability, and volume stability. Through the synergistic chemical effect of each component, it effectively solves the core technical requirements of high self-compacting filling and low differential settlement in bridge abutment backfilling projects.

[0080] 3. Changes in strength and mass under wet-dry cycles and freeze-thaw cycles This study recorded the performance evolution of each group of fluidized solidified soil under wet-dry cycles and freeze-thaw cycles, and the results are shown in Tables 5 and 6. Cylindrical specimens with dimensions ϕ50mm × H50mm were used in the experiments. Durability evaluation was conducted after standard curing to 28 days. The wet-dry cycle test was performed in 24-hour intervals (12 hours immersed in a 20℃ constant-temperature water bath, followed by 12 hours of drying at 50℃). The freeze-thaw cycle test was also performed in 24-hour intervals (12 hours frozen at -16℃, followed by 12 hours thawed at ℃). The unconfined compressive strength and specimen mass were measured after 0 (baseline), 5, 10, and 15 cycles. Strength retention rate and mass loss rate were calculated to systematically evaluate the mechanical stability and structural integrity of the fluidized solidified soil under alternating wet-dry and cold climatic conditions.

[0081] Table 5 Summary of Strength and Mass Changes of Samples under Wet-Dry Cycling Table 6 Summary of Strength and Mass Changes of Samples under Freeze-Thaw Cycles As can be seen from the experimental data in Table 5, the embodiments of the present invention exhibit excellent volume stability and strength retention under alternating wet and dry conditions. Taking Example 1 as an example, the strength retention rate after 15 cycles is as high as 87.63%, with a mass loss of only 2.36%. Other embodiments also show significant advantages. For example, Example 2, due to sufficient active components, achieves a retention rate of 88.67% after 15 cycles; although the component in Example 3 is at the lower limit, the retention rate can still be maintained at 91.94%, demonstrating extremely strong chemical stability.

[0082] A comprehensive comparison with the control groups revealed that control group 1 (pure soil) disintegrated within 5 cycles, control group 2 (lacking aluminate cement) also disintegrated after 15 cycles, while control group 5 (using ordinary silicate cement) had a retention rate of only 46.63%, and control group 13 (using sulfoaluminate cement) had a retention rate of only 33.33%. In particular, control group 3 (using magnesium oxychloride cement instead of sulfoaluminate cement) had a retention rate of only 27.42% after 15 cycles. This confirms that only through the "ternary synergistic effect" of the aluminate cement, magnesium salts, and waste water treatment agent described in this invention can a unique "magnesium-aluminum-waste residue composite synergistic network" be formed. In this network, aluminate cement induces the active components in the waste water treatment agent to deeply participate in the hydration reaction, forming a denser skeletal structure than traditional cementitious systems, thus exhibiting excellent structural stability under repeated water erosion.

[0083] Regarding the proportioning parameters and material composition, the retention rates of control groups 6 (oxygen-sulfur ratio exceeding the limit), 7 (water-sulfur ratio exceeding the limit), and 8 (aluminum slag ratio imbalance) were 40.00%, 20.00%, and 42.86%, respectively, significantly lower than those of the embodiments. This empirically demonstrates the scientific validity of the core proportioning range defined in this invention; deviation from this range will lead to system imbalance. Furthermore, after replacing the waste residue with an equal amount of inert materials such as fly ash (control group 16), the retention rate dropped to 30.24%, proving that the waste residue of the water purification agent is not only a filler but also a source of activity.

[0084] Precise control of additives is equally essential. The retention rate of control group 4 (without modifier) ​​was only 41.36%, while excessive or insufficient dosage of nano-silica (control groups 9 and 10) or sodium hexametaphosphate (control groups 11 and 12) led to a further significant decrease in retention rate or even disintegration (e.g., control group 11 disintegrated after 15 cycles, and control group 12 had a retention rate of only 12.68%). This indicates that additives are highly sensitive to the control of crystal morphology. If calcium stearate (control group 14) or citric acid (control group 15) were used instead, the specimens also showed interface softening or a sharp reduction in performance (control group 14 disintegrated in the later stages of wet and dry cycling, and control group 15 had a retention rate of only 25.00%), highlighting the irreplaceable nature of the modifiers selected in this invention.

[0085] Table 6, with its freeze-thaw cycle data, further verifies the adaptability of this invention under extreme climate conditions. Example 1 showed a retention rate of 80.11%. The freeze-thaw retention rates of Examples 2 to 9 ranged from 80.19% to 88.24%, with Example 5 reaching a high of 88.24%, demonstrating the extremely high structural strength of this system in frigid environments. Example 12 (using construction waste soil), despite its complex soil source, still maintained a retention rate of 81.31% after 15 cycles. Example 11, using silty soil from the construction site, still achieved a retention rate of 81.58% after 15 freeze-thaw cycles. This significant advantage proves that this invention can utilize the aluminum / iron components in the waste residue to form a stronger bond with the soil particle interface, greatly improving the service reliability of bridge abutment backfill projects in cold regions and demonstrating the universality of the technology.

[0086] In contrast, control groups 1 (pure clay) and 2 (aluminate-free cement) disintegrated within 5 to 10 cycles. Control group 12 (high sodium hexametaphosphate content) also disintegrated after 10 cycles, indicating a lack of a dense framework formed by the synergistic effect of active components and precision additives, rendering the material unable to withstand the expansion pressure of ice crystals. Under freeze-thaw conditions, the deterioration due to deviations in the proportions was even more extreme: the retention rate of control group 7 (excessive water-sulfur ratio) was only 10.67%; the retention rates of control group 6 (excessive oxygen-sulfur ratio) and control group 8 (imbalanced aluminum slag ratio) were also as low as 32.14% and 28.57%, respectively, further demonstrating the crucial role of precise proportions in maintaining the stability of the microstructure at low temperatures.

[0087] Furthermore, the freeze-thaw retention rate of control group 11 was only 5.77%, close to collapse. Compared with control group 4 (without modifier, 25.93%), it was found that improper component ratios could even produce negative synergistic effects. Inappropriate nano-silica doping (control groups 9 and 10) also led to performance decline, with retention rates of only 16.28% and 21.49%, respectively. Specimens using calcium stearate (control group 14) and citric acid (control group 15) disintegrated successively within 10-15 cycles, clearly indicating that other additives could not meet the freeze-thaw resistance requirements of this system. Meanwhile, control group 3, which was replaced by the magnesium oxychloride system, had a freeze-thaw retention rate of only 18.28%, and after replacing the waste residue with fly ash (control group 16), the retention rate was 17.95%, confirming the key contribution of the active components of the waste residue in enhancing interfacial bonding and resisting freeze-thaw erosion.

[0088] In contrast, the retention rates of conventional cement systems (control group 5) and sulfoaluminate salt systems (control group 13) under the same environment were only 29.21% and 12.55%, respectively. Even in Example 10, which had relatively lower performance in the examples, its durability index (72.65%) still far exceeded that of all control groups, further confirming the overall advantages of this technical system.

[0089] 4. Softening coefficient and bleeding rate This study systematically tested the softening coefficient and bleeding rate of the fluidized solidified soil of this invention, and the relevant results are shown in Table 7. The softening coefficient test was strictly performed in accordance with GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" and JGJ / T 233-2011 "Specification for Mix Proportioning Design of Cement-Soil". The results were compared with the 28-day standard curing strength f. std The saturated compressive strength f after immersion in water for 48 hours sat According to the formula K=f std / f sat The calculations were used to evaluate the material's resistance to water erosion; the bleeding rate test was conducted in accordance with GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The slurry was placed in a 1000mL graduated cylinder and allowed to stand for 24 hours before the proportion of surface water was measured to evaluate the homogeneity and anti-segregation performance of the slurry.

[0090] Table 7. Test results of softening coefficient and bleeding rate of materials in each group. Based on the data listed in Table 7, this invention systematically analyzed the softening coefficient and bleeding rate of 12 embodiments and 16 control groups. Overall, the fluidized solidified soil described in this invention exhibits excellent resistance to water erosion and slurry stability.

[0091] Using Example 1 as a typical benchmark, its softening coefficient and bleeding rate both exhibited excellent parameter levels, fully confirming that under the synergistic mechanism of water purification agent waste residue, aluminate cement, and magnesium oxysulfate cement, the system can construct an extremely dense composite crystalline network. Under the guarantee of this synergistic mechanism, the softening coefficients of Examples 1 to 12 remained consistently in the high range of 0.87 to 0.94 (such as Examples 2, 3, 5, and 7, which all reached 0.92-0.94). This strongly demonstrates that the synergistic effect of the three components described in this invention can effectively lock the structural framework and block water penetration, giving the material excellent water resistance.

[0092] Meanwhile, under the water-retention system synergistically constructed by the three components, the bleeding rate of each embodiment was well controlled, remaining stable between 0.1% and 0.6%. Specifically, the bleeding rate of Example 2 was 0.1%, while Examples 4, 5, 7, and 9 were all stable at 0.2%. These data further confirm that within the proportioning range defined by this invention, the slurry possesses extremely strong water retention capacity and anti-segregation performance, ensuring high homogeneity during construction. In contrast, the control groups that did not form the synergistic system showed a significant decline in water resistance and slurry stability, highlighting the significant technical advantages of the embodiments of this invention in ensuring the long-term service performance and construction quality of the backfill.

[0093] By comparing Example 1 with Control Groups 1 to 3 and Control Group 8, the drastic impact of component deficiency on material properties can be clearly observed. The uncured Control Group 1 (plain soil) had a softening coefficient of only 0.15 and a bleeding rate as high as 15.2%, making it completely unsuitable for engineering applications. When aluminate cement was missing (Control Group 2), the softening coefficient plummeted to 0.52, and the bleeding rate increased to 2.2%. When the aluminate cement content was insufficient (Control Group 8), the softening coefficient further deteriorated to 0.48, and the bleeding rate increased to 2.4%. This reflects that insufficient aluminum not only fails to form a reinforcing network but may also interfere with the crystallization development of the original magnesium cementitious system. Furthermore, Control Group 3, which used a traditional magnesium oxychloride system as a substitute, had a softening coefficient of only 0.55 and a bleeding rate of 1.8%, confirming that the magnesium oxychloride synergistic system described in this invention has a significant advantage in chemical stability in the chloride-rich waste residue microenvironment.

[0094] Further analysis of the performance degradation caused by imbalanced proportioning parameters provided strong evidence from control groups 6 and 7. When the oxygen-sulfur ratio exceeded the limit (control group 6), although the early strength was acceptable, the softening coefficient was only 0.58. This was because the uncontrolled expansion caused by excessive active magnesium oxide weakened the density of the structure. When the water-sulfur ratio exceeded the limit (control group 7), the excessive water caused severe segregation and bleeding of the slurry, with a bleeding rate as high as 10.5%. The softening coefficient also dropped to 0.32, indicating that the interconnected pores formed after the excess water evaporated severely damaged the water resistance of the material. Meanwhile, in control group 4, which lacked the modifier, the bleeding rate increased significantly to 3.5%, and the softening coefficient was only 0.61, demonstrating the key role of the modifier in optimizing the interface and slurry structure.

[0095] Finally, a comprehensive review of the functional components and alternative materials (control groups 9-16) further confirmed the precision and uniqueness of the technical solution of this invention. In the experiment on the deviation of modifier dosage, the imbalance of the ratio of either nano-silica (control groups 9 and 10) or sodium hexametaphosphate (control groups 11 and 12) led to a decrease in the softening coefficient to the range of 0.42-0.68, while the water bleeding rate fluctuated and increased. In particular, the excessive sodium hexametaphosphate in control group 12 caused the water bleeding rate to surge to 4.2%. If calcium stearate (control group 14) or citric acid (control group 15) were used as functional substitutes, the softening coefficients were only 0.45 and 0.51, respectively, which could not achieve the high adaptability effect of this invention. Furthermore, by comparing the data of ordinary silicate cement (control group 5, softening coefficient 0.63), sulfoaluminate cement (control group 13, softening coefficient 0.65), and the use of inert fly ash to replace waste residue (control group 16, softening coefficient 0.58), it can be clearly concluded that only under the specific ternary synergistic system described in this invention, by utilizing the active components of the water purification agent waste residue to react directionally with magnesium aluminum salts, can ultra-high water resistance performance at extremely low bleeding rate be achieved, thereby meeting the stringent requirements of bridge abutment backfilling projects.

[0096] This invention achieves a fundamental improvement in the performance of fluidized solidified soil at the microscopic level by constructing a synergistic activation mechanism among waste water treatment agent residue, aluminate cement, and magnesium sulfate-oxygenated cement. Utilizing the chemical synergy between aluminate cement and waste water treatment agent residue in a magnesium sulfate-oxygenated environment, a magnesium-aluminum-calcium-based composite crystalline network is induced in situ. This network interpenetrates and encapsulates the interfacial transition zone between the waste residue microparticles and the matrix, effectively repairing the crystal defects of traditional magnesium cement. Through the capture and solidification of free chloride ions by this composite crystalline network, the water resistance and chemical stability of the material are significantly enhanced, improving its strength retention rate under long-term immersion conditions and ensuring excellent long-term durability of the backfill when bearing road loads.

[0097] Meanwhile, this invention utilizes the micro-aggregate filling effect and chemical activity reconstruction of waste particles from water purification agents to significantly improve the homogeneity and self-leveling performance of the slurry while achieving resource utilization of large-volume industrial solid waste. Based on the volume self-compensation characteristics generated during the growth of the composite crystalline network, this invention precisely counteracts the physical shrinkage of the fluidized soil during hardening and water loss, achieving self-compacting filling and settlement control of the backfill area. This invention effectively solves the technical challenge of conventional fluidized fillers in simultaneously achieving high solid waste utilization, volume stability, and water and erosion resistance, providing a high-flowability, ultra-low-settlement, and long-term stable high-performance backfill material for solving the problem of bridge approach slab settlement.

Claims

1. A fluidized solidified soil with ternary synergistic composition of water purification agent waste residue, aluminate cement, and magnesium sulfate-oxygen cement for bridge abutment backfilling, characterized in that, The components, by weight, include: soil (100 parts by dry soil weight), 70-100 parts by waste residue of water purification agent, 5-15 parts by aluminate cement, 30-55 parts by activated magnesium oxide, 25-50 parts by magnesium sulfate heptahydrate, 1-5 parts by water-resistant modifier, 1-3 parts by reinforcing modifier, and added water; the molar ratio of total water to sulfur in magnesium sulfate heptahydrate is (18.0-29.5):1, and the total water includes added water, moisture carried in the soil, and crystal water in magnesium sulfate heptahydrate.

2. The fluidized solidified soil according to claim 1, characterized in that, The particle size of the soil material is controlled to be below 10 mm.

3. The fluidized solidified soil according to claim 1, characterized in that, The waste residue from the water purification agent is an aluminum-containing industrial waste residue generated during the preparation of polyaluminum chloride water purification agent, which is dried and ground for later use; the pH value is 6-8, and the D... 50 The median particle size is 0.045-0.09 mm, and the residue on a 0.075 mm standard sieve is less than 15%.

4. The fluidized solidified soil according to claim 1, characterized in that, The aluminate cement is CA-50 type aluminate cement, wherein the alumina (Al2O3) content is 50%-60% and the specific surface area is 300-500 m² / kg; the active magnesium oxide has an activity of over 60% and a specific surface area of ​​300-500 m² / kg; the water-resistant modifier is nano-silica with an average particle size of 20-50 nm; and the reinforcing modifier is sodium hexametaphosphate with an effective component content ≥95.0%.

5. The fluidized solidified soil according to claim 1, characterized in that, The molar ratio of oxygen in activated magnesium oxide to sulfur in magnesium sulfate heptahydrate is (5.5-7.8):1; the molar ratio of total water in the mixture to sulfur in magnesium sulfate heptahydrate is (21.5-29.5):

1.

6. A method for preparing fluidized solidified soil as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Dissolve the reinforcing modifier in part of the added water, then add magnesium sulfate heptahydrate, and stir until the magnesium sulfate solid is fully dissolved to prepare a magnesium sulfate modified solution. S2. Dry mix the soil, waste residue from water purification agent, aluminate cement, water-resistant modifier, and active magnesium oxide to ensure uniform powder dispersion; S3. Add the magnesium sulfate modified solution prepared in step S1 to the dry mixture in step S2, stir evenly, then add the remaining external water and perform high-shear stirring to form a uniform slurry.

7. The preparation method according to claim 6, characterized in that, In step S3, the high-shear stirring time shall not be less than 120s and the rotation speed shall not be less than 150r / min.

8. The preparation method according to claim 7, characterized in that, In step S3, the high-shear stirring time is 180-300s.

9. The preparation method according to claim 6, characterized in that, The fluidity of the prepared slurry is 160-260 mm.

10. The preparation method according to claim 6, characterized in that, After preparation, the slurry is pumped to the backfill area for self-leveling filling and curing; the pumping pressure is 0.5-3.0MPa, and the drop height of the slurry is controlled within 3m.

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