A roadbed filler with synergistic solidification of phosphogypsum and aeolian sand and a preparation method thereof

Abstract

The present invention relates to the technical field of road subgrade materials, and specifically discloses a road subgrade filler and a preparation method thereof that is synergistically solidified by phosphogypsum and aeolian sand. The subgrade filler is prepared from persulfated phosphogypsum slag cement, phosphogypsum, aeolian sand and water, wherein the total mass of phosphogypsum and aeolian sand accounts for not less than 80% of the mass fraction of the road subgrade filler, and the mass ratio of phosphogypsum and aeolian sand is (3:1) to (1:3). Replacing soil with phosphogypsum and aeolian sand improves water retention and cohesion relative to aeolian sand and is easier to compact, achieving high-volume comprehensive utilization of phosphogypsum and aeolian sand, the subgrade filler has an unconfined compressive strength of 0.450MPa to 0.760MPa at 14 days, and an unconfined compressive strength of 0.566MPa to 1.556MPa at 28 days, meeting the relevant requirements for subgrade construction strength and workability in JTG / T3610-2019 "Technical Specifications for Highway Subgrade Construction".

Description

Technical Field

[0001] The invention belongs to the technical field of road subgrade materials, and particularly relates to a road subgrade filler that is synergistically solidified with phosphogypsum and aeolian sand, and a preparation method thereof. Background Art

[0002] In recent years, numerous highways have been under construction along desert fringe and oasis areas. However, the unique characteristics of the desert environment, such as high temperatures, dryness, and frequent sandstorms, make conventional road construction materials inadequate. Furthermore, the long-distance transportation of high-quality gravel from distant regions undoubtedly increases construction costs and complexity. Therefore, converting the abundant local aeolian sand resources into roadbed fill material is a pressing technical challenge.

[0003] Persulfated phosphogypsum slag cement is a novel, unburned cementitious material primarily composed of a mixed powder of wet-ground modified phosphogypsum, granulated blast furnace slag, steel slag, and silicate clinker. Its preparation principle relies on the combined action of sulfate and an alkaline activator to activate the slag, initiating a reaction that produces a large amount of CSH gel and ettringite. These products tightly encapsulate and connect the phosphogypsum particles, forming a three-dimensional network structure. The development of this cement aims to address the problem of large-scale phosphogypsum accumulation and effectively utilize industrial waste residues, which aligns with the economic trend of energy conservation and emission reduction. Compared to traditional cements, persulfated phosphogypsum slag cement exhibits not only superior mechanical strength but also excellent sulfate corrosion resistance. Due to these significant advantages, persulfated phosphogypsum slag cement is widely used in various engineering projects in both freshwater and seawater environments and can be used as a solidifying agent for roadbed fill. However, research on cementitious materials for consolidating aeolian sand remains limited.

[0004] Chinese Patent Publication No. CN110204299B discloses a method for preparing a low-shrinkage, high-strength aeolian sand roadbed material. This method uses aeolian sand as the primary material, accounting for between 74% and 78% of the total mass; cement as a binder, accounting for between 6% and 8%; nanomaterials as reinforcing agents, added in amounts ranging from 1.5% to 2.5%; polyvinyl alcohol as a modifier, with a controlled content between 0.1% and 0.5%; a polymer emulsion as a stabilizer, accounting for 0.2% to 0.8%; and water glass as a curing agent, added in amounts between 0.5% and 1.2%. The remainder is water, used to adjust the overall material properties. It is worth noting that cement is used as the primary binder in this method, a choice that inevitably leads to increased greenhouse gas emissions. Furthermore, given the relatively high raw material costs involved in this method, the roadbed material prepared using this method does not offer significant economic advantages.

[0005] At present, there are few reports on the use of phosphogypsum and aeolian sand to synergistically solidify road subgrade fillers for desert highway construction. Summary of the Invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and provide a road subgrade filler that is synergistically solidified with phosphogypsum and aeolian sand, and a preparation method thereof. Phosphogypsum and aeolian sand are used to replace soil, thereby improving water retention and cohesion compared to aeolian sand and making it easier to compact. The properties of the mixed soil are between silt and silty clay, achieving high-dosage comprehensive utilization of phosphogypsum and aeolian sand, with the content of phosphogypsum and aeolian sand exceeding 80% of the total roadbed filler material.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A first aspect of the present invention is to provide a road subgrade filler in which phosphogypsum and aeolian sand are synergistically solidified. The road subgrade filler is prepared from persulfated phosphogypsum slag cement, a first modified phosphogypsum, aeolian sand and water, wherein the total mass of the first modified phosphogypsum and aeolian sand accounts for no less than 80% of the mass fraction of the road subgrade filler, the mass ratio of the first modified phosphogypsum to the aeolian sand is (3:1) to (1:3), and the persulfated phosphogypsum slag cement is prepared from a second modified phosphogypsum, slag powder and ordinary Portland cement.

[0009] Furthermore, the first modified phosphogypsum and the second modified phosphogypsum are both wet-ground modified phosphogypsum, and the preparation process is as follows: 92 to 95 parts by weight of original phosphogypsum, 4 to 6 parts of slag powder and 2 to 3 parts of general-purpose Portland cement are mixed and wet-ground at a water-cement ratio of 0.42 to 0.47, and the mixture is allowed to stand and age to obtain a modified phosphogypsum slurry, which is then dried.

[0010] Furthermore, the aeolian sand is aeolian sand from the Tengger Desert in Inner Mongolia Autonomous Region, with a particle size between 0.08 mm and 0.80 mm, and an effective particle size d 10 The average particle size d is 0.081 mm. 50 is 0.146 mm, controlling the particle size d 60 and d 30 They are 0.171mm and 0.115mm respectively.

[0011] Furthermore, in the persulfated phosphogypsum slag cement, the content of the second modified phosphogypsum is 40 to 50 parts by weight, the content of slag powder is 40 to 50 parts by weight, and the content of ordinary cement is 4 to 6 parts by weight.

[0012] Furthermore, the slag powder is S95 granulated blast furnace slag powder, the main components of which are SiO2, Al2O3 and MgO.

[0013] Furthermore, the density of the P.O42.5 ordinary Portland cement is 3.077 g / cm 3 , with a specific surface area of ​​358m 2 / kg, the main components are CaO, SiO2, Fe2O3 and Al2O3, and the main minerals are tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.

[0014] Furthermore, the persulfate gypsum slag cement is added by external mixing method, and the content thereof ranges from 6% to 15%.

[0015] Furthermore, the first modified phosphogypsum and aeolian sand are used as aggregates, and the proportion of aeolian sand in the aggregate is between 0.25 and 0.75.

[0016] The second aspect of the present invention is to provide a method for preparing the above-mentioned phosphogypsum aeolian sand co-solidified roadbed filler, comprising the following steps:

[0017] S1. Aggregate preparation: Crush larger lumps in the wet-ground modified phosphogypsum, dry them in an oven at 55°C to 60°C for 48 to 60 hours, and then pass them through a 0.6 mm pore size sieve to obtain the treated phosphogypsum;

[0018] Aeolian sand within different particle size ranges is screened, weighed according to a determined aeolian sand particle group gradation, and then evenly mixed with the graded particle group to obtain aeolian sand;

[0019] S2. Preparation of persulfated phosphogypsum slag cement: wet-ground modified phosphogypsum, granulated blast furnace slag powder, and ordinary Portland cement are mixed in a preset ratio, and then placed in a cement paste mixer and stirred at a total water-cement ratio of 0.42-0.47 to obtain persulfated phosphogypsum slag cement;

[0020] S3. Dry mixing: Mix the aggregate phosphogypsum and aeolian sand evenly according to a preset ratio, pour into a mortar mixer and stir for 3 to 7 minutes to obtain a first mixture.

[0021] S4. Wet mixing: Pour persulfate gypsum slag cement and water into a mixer according to a preset ratio, and stir at a speed of 500 r / min to 700 r / min for 5 to 10 minutes until uniform, to obtain a second mixture.

[0022] S5, shaping and curing: spreading and compacting the second mixture obtained in step S4, and curing the mixture by heat preservation and moisture retention to obtain the phosphogypsum and aeolian sand synergistically solidified roadbed filler.

[0023] Furthermore, in step S4, the water content of 15.064% to 16.274% and the maximum dry density of 1.717 g / cm 3 ~1.784g / cm 3 .

[0024] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0025] (1) The present invention provides a phosphogypsum and aeolian sand synergistically solidified road subgrade filler, which replaces soil with phosphogypsum and aeolian sand. Compared with aeolian sand, the mixed soil has improved water retention and cohesion and is easier to compact. The properties of the mixed soil are between silt and silty clay, achieving high-content comprehensive utilization of phosphogypsum and aeolian sand. The content of phosphogypsum and aeolian sand in the total roadbed filler material exceeds 80%.

[0026] (2) The different composition design ratios of the high-dosage phosphogypsum and aeolian sand synergistic solidifying materials provided by the present invention can meet the precise design of the composition of the new solidifying materials required in different application scenarios. The 14-day unconfined compressive strength of the roadbed filler cured at room temperature is 0.450MPa~0.760MPa, and the 28-day unconfined compressive strength is 0.566MPa~1.556MPa, which meets the relevant requirements for roadbed construction strength and working performance in JTG / T3610-2019 "Technical Specifications for Highway Roadbed Construction".

[0027] (3) The present invention uses persulfated phosphogypsum slag cement as a cementing material to solidify phosphogypsum aeolian sand mixture. The cement is a mixture of a large proportion of phosphogypsum (50%), slag powder (45%), and ordinary Portland cement (5%). This not only significantly reduces greenhouse gas emissions and achieves the goal of waste resource utilization (i.e., using waste to treat waste), but also fully taps the economic value of phosphogypsum.

[0028] (4) The roadbed filler solidified by the synergistic solidification of phosphogypsum and aeolian sand of the present invention is particularly suitable for application in desert environments. This technology makes full use of the aeolian sand resources along the roads in arid desert areas, and uses aeolian sand as an important component of aggregate to replace traditional roadbed fill materials, thereby significantly reducing the production cost and transportation cost of the materials. At the same time, by synergistically utilizing industrial waste such as phosphogypsum and slag powder, the effective recycling of resources is achieved and considerable economic benefits are created. This technology shows strong market promotion and application potential, indicating that it will play an important role in related fields.

[0029] (5) The preparation process provided by the present invention is extremely simple. It only requires wet grinding and modification of the original phosphogypsum, and then fully mixing the modified phosphogypsum with aeolian sand aggregate in a predetermined ratio. Then, a pre-set ratio of persulfated phosphogypsum slag cement and water is added, and the mixture is uniformly stirred again and shaped and cured. This produces a new type of solidified material that can meet the needs of various application scenarios. In this preparation process, the proportion of the externally added cementitious material can be flexibly adjusted within the range of 6% to 15%, with an adjustment gradient of 3%. At the same time, the proportion of aeolian sand in the aggregate can also be gradually increased within the range of 0 to 1, with an adjustment gradient of 0.2. By precisely controlling the ratio between the various components, the generation of its hydration products can be effectively regulated, and then, based on the hydration mechanism, a phosphogypsum aeolian sand co-solidified roadbed filler that meets the strength and performance requirements of various roads can be prepared. It is particularly worth mentioning that this preparation process does not require complex treatments such as calcination of the phosphogypsum, which greatly simplifies the construction process and improves construction efficiency.

[0030] (6) The present invention uses persulfated phosphogypsum slag cement to solidify phosphogypsum aeolian sand aggregate for roadbed filling. This solidification process does not rely solely on a single mechanism, but is the result of the synergistic and combined action of chemical mechanisms and physical effects. Specifically, the development of its mechanical strength involves multiple stages, including physical compaction, chemical excitation and ion exchange, gel and ettringite bonding, agglomeration effects, and physical filling processes, which together promote the strength development of the solidified body.

[0031] Physical compaction: After the phosphogypsum and aeolian sand are compacted and solidified into roadbed fillers, the internal structure of the solidified body shows the close interlocking and mutual extrusion between the gypsum crystal particles and the aeolian sand particles. The phosphogypsum crystals are mostly plate-like or columnar, but there are still some areas where tiny gaps are left between the gypsum crystal particles.

[0032] Chemical excitation and ion exchange: Under alkaline environmental conditions, the active components such as SiO2, Al2O3 and CaO in the raw materials undergo a chemical excitation process, accompanied by ion exchange reactions, thereby generating a honeycomb network of hydrated calcium silicate gel with cementing properties; at the same time, some gypsum crystals inside the phosphogypsum particles are converted into needle-shaped ettringite crystals under the action of sulfate excitation effect.

[0033] Bonding effect between gel and ettringite: Under the action of cementing force, the honeycomb-shaped three-dimensional network gel is interconnected and aggregated into a large number of compact flocculent gel aggregates. These aggregates are tightly adhered to the surfaces of gypsum crystal particles and aeolian sand particles. At the same time, the needle-shaped ettringite is also firmly adhered to the surface of these particles, together constructing a stable structural system.

[0034] Agglomeration: A large number of gel polymers gradually achieve comprehensive coverage and encapsulation of these particles by tightly adhering to the surfaces of phosphogypsum particles and aeolian sand particles. In this process, the phosphogypsum particles and aeolian sand particles wrapped by the gel are interconnected, forming a new layer of gel bonding. This bonding layer still has the function of connecting the phosphogypsum particles and aeolian sand particles. Through the continuous cycle of bonding, agglomerates with particle grading characteristics are gradually formed. The particles in these agglomerates are of different sizes and are embedded in each other, together constructing a stable spatial skeleton structure.

[0035] Physical filling: A large number of remaining phosphogypsum particles and aeolian sand particles are tightly embedded in each other, filling the gaps in the aggregate skeleton. At the same time, tiny needle-shaped ettringite crystals fill the gaps between the gypsum crystals, together constructing a dense skeleton space structure.

[0036] The core of the solidification mechanism of persulfated phosphogypsum slag cement on phosphogypsum and aeolian sand mixed soil lies in its gelation to tightly bond the phosphogypsum and aeolian sand particles, thereby forming a denser aggregate structure. In addition, the incompletely bonded phosphogypsum particles, aeolian sand particles and the generated ettringite act as filling materials to effectively fill the gaps in the structure, significantly improving the density of the mixed soil. The phosphogypsum particles not only support the skeleton structure of the solidified body, but also work together with aeolian sand particles and ettringite to play an important role in optimizing the skeleton void filling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the XRD pattern of the persulfate gypsum slag cement in the present invention;

[0038] Figure 2 The XRD pattern of the phosphogypsum aeolian sand synergistically solidified road subgrade filler of the present invention;

[0039] Figure 3 This is a 7d microscopic morphology of the persulfated gypsum slag cement of the present invention;

[0040] Figure 4 This is a 28d microscopic morphology of the persulfated gypsum slag cement of the present invention;

[0041] Figure 5 This is a 7d microscopic morphology of the phosphogypsum aeolian sand co-solidified roadbed filler of the present invention;

[0042] Figure 6 This is a 14d microscopic morphology of the phosphogypsum aeolian sand co-solidified roadbed filler of the present invention;

[0043] Figure 7 This is a 28d microscopic morphology of the phosphogypsum and aeolian sand co-solidified road subgrade filler of the present invention. DETAILED DESCRIPTION

[0044] To make the objects, technical solutions, and advantages of the present invention more apparent, the following describes the specific embodiments of the present invention in further detail with reference to the specific examples and accompanying drawings. Where specific test methods, instruments, or conditions are not specified in the examples, the methods or conditions described in the literature in the art or the product specifications were used. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0045] The aeolian sand selected for this invention is from the Inner Mongolia Autonomous Region. Its particle size is primarily concentrated between 0.5 and 0.075 mm, accounting for 90% to 95%. Its mechanical composition is relatively fine, with a large surface area and a coefficient of heterogeneity of Cu ≤ 5, classifying it as poorly graded fine sand. This type of aeolian sand contains little clay particles and exhibits excellent water permeability and water stability, but weak water retention. Its characteristics conform to those of typical sandy soils. The main components of aeolian sand are rock fragments, feldspar, and quartz, with the total content of these three types of particles exceeding 90%, with quartz particles being the most significant. Its surface is relatively smooth, and the aeolian sand exhibits a weakly alkaline nature. Furthermore, the internal friction angle of the aeolian sand is stable at approximately 39°, while its cohesion is almost negligible.

[0046] The present invention uses persulfated phosphogypsum slag cement to solidify the phosphogypsum aeolian sand mixed soil. The persulfated phosphogypsum slag cement is prepared from wet-ground modified phosphogypsum (PG), granulated blast furnace slag powder (S95) and P.O42.5 ordinary Portland cement. The composition of the phosphogypsum aeolian sand synergistically solidified road subgrade filler further integrates the above-mentioned persulfated phosphogypsum slag cement, phosphogypsum and aeolian sand to ensure the stability and durability of the road subgrade.

[0047] The wet-ground modified phosphogypsum prepared in the present invention comprises the following steps: mixing, by weight, 92 to 95 parts of original phosphogypsum, 4 to 6 parts of slag powder, and 2 to 3 parts of general-purpose Portland cement at a water-cement ratio of 0.42 to 0.47, wet-grinding the mixture, and allowing the mixture to stand for aging to obtain a modified phosphogypsum slurry, which is then dried.

[0048] The persulfated phosphogypsum slag cement used in the present invention has its constituent components precisely proportioned by weight as follows: wet-ground modified phosphogypsum accounts for 40% to 50% of the total weight, preferably 50%, granulated blast furnace slag powder accounts for 40% to 50%, preferably 45%, and ordinary Portland cement accounts for the remaining 4% to 6%, preferably 5%. After mixing the above ingredients, place them in a cement paste mixer and stir them at a total water-cement ratio of 0.42 to 0.47 to obtain the cement.

[0049] The phosphogypsum selected in this embodiment is wet-ground modified phosphogypsum. The original phosphogypsum, slag powder and general-purpose Portland cement are mixed in a ratio of 45:1:2 at a water-cement ratio of 0.43, wet-ground for 1 hour and allowed to stand for 24 hours to obtain a modified phosphogypsum slurry. After drying, the modified phosphogypsum powder is obtained, and its specific surface area is 170.4 m 2 / kg, in the form of gray granules, with a density of 2.35g / cm 3 The mass fraction of attached water is strictly controlled within the range of no more than 20%, while the mass fraction of CaSO4·2H2O is not less than 80%, the mass fraction of water-soluble P2O5 is limited to no more than 0.3%, and the mass fraction of water-soluble F - The mass fraction does not exceed 0.2%. X-ray fluorescence spectrometry (XRF) analysis determined that the main chemical components of the phosphogypsum are calcium oxide (CaO) and sulfur trioxide (SO3). X-ray diffraction analysis (XRD) technology further confirmed that its main mineral component is calcium sulfate dihydrate (CaSO4·2H2O). A laser particle size analyzer was used to accurately measure the particle size distribution of the phosphogypsum, and its particle size was mainly concentrated in the range of 10 to 110 μm.

[0050] The slag powder selected in this embodiment is S95 grade granulated blast furnace slag powder, and its specific surface area is measured to be 424m 2 / kg, and through X-ray fluorescence spectrometry (XRF) technology, it was determined that the main chemical components of the mineral powder are calcium oxide (CaO), aluminum oxide (Al2O3) and silicon dioxide (SiO2).

[0051] The density of P.O42.5 ordinary Portland cement selected in this embodiment is 3.077g / cm 3 , with a specific surface area of ​​358m 2 / kg, and its main chemical components were determined by X-ray fluorescence spectrometry (XRF) to be calcium oxide (CaO), silicon dioxide (SiO2), ferric oxide (Fe2O3) and aluminum oxide (Al2O3); further analysis showed that the main mineral components of the cement were tricalcium silicate (3CaO·SiO2), dicalcium silicate (2CaO·SiO2), tricalcium aluminate (3CaO·Al2O3) and tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3).

[0052] The aeolian sand selected in this example is the aeolian sand from the Tengger Desert in Inner Mongolia Autonomous Region. The particle size is between 0.08 mm and 0.80 mm. The effective particle size d 10 The average particle size d is 0.081 mm. 50 is 0.146 mm, controlling the particle size d 60 and d 30They are 0.171mm and 0.115mm respectively, the uniformity coefficient is 2.111, the curvature coefficient is 0.9555, and the gradation is poor.

[0053] The chemical compositions of the phosphogypsum, slag powder, and ordinary Portland cement used in this example are shown in Table 1.

[0054] Table 1

[0055]

[0056] The preparation of the roadbed filler of the present invention using phosphogypsum and aeolian sand as the co-solidification method specifically comprises the following steps:

[0057] Step S1, preparation of wet-ground modified phosphogypsum: mixing original phosphogypsum, slag powder and general Portland cement in a ratio of 45:1:2 at a water-cement ratio of 0.43, wet-grinding for 1 hour and aging for 24 hours to obtain modified phosphogypsum slurry, and drying to obtain modified phosphogypsum powder.

[0058] Step S2, treatment of phosphogypsum and aeolian sand: crushing the larger lumps in the wet-ground modified phosphogypsum, then drying the phosphogypsum in an oven at 55°C for 48 hours, and then passing it through a 0.6mm aperture sieve to obtain the treated phosphogypsum; spreading the yellow sand sample evenly for natural air drying, and after air drying, carefully screening the aeolian sand according to the preset particle size standard, that is, the particle size is between 0.08mm and 0.80mm, and then accurately weighing the aeolian sand according to the established aeolian sand particle group grading requirements, where the effective particle size d 10 Set to 0.081 mm, the average particle size d 50 0.146mm, and strictly control the particle size d 60 and d 30 They are 0.171mm and 0.115mm respectively. Finally, the weighed granulation groups of each level are fully mixed to ensure uniformity to prepare aeolian sand samples that meet the requirements.

[0059] Step S3, preparation of persulfated phosphogypsum slag cement: accurately weigh and thoroughly mix the wet-ground modified phosphogypsum, granulated blast furnace slag powder and ordinary Portland cement in a mass ratio of 50:45:5, and place the evenly mixed materials into a cement slurry mixer to ensure that the total water-cement ratio is 0.3 under stirring to prepare the required persulfated phosphogypsum slag cement.

[0060] Step S4, dry mixing: weighing phosphogypsum and aeolian sand aggregate according to a preset ratio, mixing them in a stirring pot, and stirring for 3 to 7 minutes until uniform, to obtain a first mixture.

[0061] Step S5, wet mixing: weigh the persulfate gypsum slag cement and water obtained in step S2 according to a preset ratio, pour them into a stirring pot, and stir for 3 to 10 minutes until uniform to obtain a second mixture.

[0062] Step S6, molding and curing: the second mixture obtained in step S5 is spread and compacted to form, and heat-insulating and moisture-retaining curing is performed to obtain the phosphogypsum aeolian sand synergistically solidified road subgrade filler.

[0063] Example 1

[0064] Weigh the raw materials according to the following mass: the mass ratio of phosphogypsum and aeolian sand to aggregate is 100% and 0 respectively, and the amount of supersulfurized phosphogypsum slag cement is 6%. Weigh the composite materials and determine the optimum moisture content of 16.341% and the maximum dry density of 1.708 g / cm according to the compaction test. 3 Weigh the water.

[0065] According to the specific steps of the production process, phosphogypsum aeolian sand synergistic solidification roadbed filler was prepared, and its relevant properties were tested using the following test methods:

[0066] Unconfined compressive strength: Based on the determination of the California Bearing Ratio (CBR) value of the phosphogypsum aeolian sand co-solidified road subgrade filler, the unconfined compressive strength is used as one of the core indicators for evaluating its strength performance; this indicator can quickly and accurately reflect the strength characteristics of the specimen. By adjusting the ratio range of the phosphogypsum aeolian sand co-solidified road subgrade filler and preparing relevant specimens with a compaction degree of 96%, the unconfined compressive strength of the specimens was measured using two curing methods: room temperature sealing and 55°C sealing. This process aims to comprehensively and systematically analyze the mechanical performance indicators of the filler.

[0067] Internal friction angle and cohesion: Set the vertical pressure as the horizontal axis and the shear strength as the vertical axis. Accurately mark the shear strength data points of each sample on the coordinate paper and connect these points with a straight line. The inclination angle of this line is the internal friction angle, and the intersection of the straight line and the vertical axis represents the cohesion.

[0068] Leachate pollutants: The release of harmful elements in the leachate of roadbed fillers has a significant impact on the surrounding environment, especially the quality of groundwater. The "Surface Water Environmental Quality Standard" (GB3838-2002) and the "Groundwater Quality Standard" (GB / T14848-2017) have strict standards for the content of phosphorus (P), fluorine (F), cadmium (Cd), arsenic (As), lead (Pb) and chromium in groundwater. The leachate of roadbed fillers should meet the groundwater standards; soak the standard specimen in water, take representative solution samples at the specified age for laboratory testing, and filter with a 0.45μm filter membrane before testing to obtain the leachate for test analysis.

[0069] The main performance indicators of the phosphogypsum aeolian sand co-solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 2:

[0070] Table 2.

[0071]

[0072] Example 2

[0073] Weigh the raw materials according to the following mass: the mass ratio of phosphogypsum and aeolian sand to aggregate is 100% and 0 respectively, and the amount of supersulfurized phosphogypsum slag cement is 15%. Weigh the composite materials and determine the optimum moisture content of 16.262% and the maximum dry density of 1.717g / cm according to the compaction test. 3 Weigh the water.

[0074] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 3:

[0075] Table 3.

[0076]

[0077] Example 3

[0078] Weigh the raw materials according to the following mass: phosphogypsum and aeolian sand account for 75% and 25% of the aggregate mass respectively, add 6% of sulphurized phosphogypsum slag cement, weigh the composite materials, and determine the optimum moisture content of 16.262% and the maximum dry density of 1.717g / cm according to the compaction test. 3 Weigh the water.

[0079] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 4:

[0080] Table 4.

[0081]

[0082] Example 4

[0083] Weigh the raw materials according to the following mass: the mass ratio of phosphogypsum and aeolian sand to aggregate is 75% and 25% respectively, the amount of extra-sulfurized phosphogypsum slag cement is 15%, weigh the composite materials, and determine the optimum moisture content of 16.274% and the maximum dry density of 1.781g / cm according to the compaction test. 3 Weigh the water.

[0084] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 5:

[0085] Table 5.

[0086]

[0087] Example 5

[0088] Weigh the raw materials according to the following mass: phosphogypsum and aeolian sand account for 50% and 50% of the aggregate mass respectively, add 6% of sulphurized phosphogypsum slag cement, weigh the composite materials, and determine the optimum moisture content of 16.274% and the maximum dry density of 1.781g / cm according to the compaction test. 3 Weigh the water.

[0089] The main performance indicators of the phosphogypsum aeolian sand co-cured roadbed filler prepared in this example were tested according to the above test method and are shown in Table 6:

[0090] Table 6.

[0091]

[0092] Example 6

[0093] Weigh the raw materials according to the following mass: phosphogypsum and aeolian sand account for 50% and 50% of the aggregate mass respectively, add 15% of sulphurized phosphogypsum slag cement, weigh the composite materials, and determine the optimum moisture content of 16.064% and the maximum dry density of 1.784g / cm according to the compaction test. 3 Weigh the water.

[0094] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 7:

[0095] Table 7.

[0096]

[0097] Example 7

[0098] Weigh the raw materials according to the following mass: phosphogypsum and aeolian sand account for 25% and 75% of the aggregate mass respectively, add 6% of sulphurized phosphogypsum slag cement, weigh the composite materials, and determine the optimum moisture content of 15.064% and the maximum dry density of 1.784g / cm according to the compaction test. 3 Weigh the water.

[0099] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 8:

[0100] Table 8.

[0101]

[0102] Example 8

[0103] Weigh the raw materials according to the following mass: phosphogypsum and aeolian sand account for 25% and 75% of the aggregate mass respectively, add 15% of sulphurized phosphogypsum slag cement, weigh the composite materials, and determine the optimum moisture content of 15.064% and the maximum dry density of 1.784g / cm according to the compaction test. 3 Weigh the water.

[0104] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 9:

[0105] Table 9.

[0106]

[0107] Example 9

[0108] Weigh the raw materials according to the following mass: the mass ratio of phosphogypsum and aeolian sand to aggregate is 0 and 25% respectively, and the amount of sulphurized phosphogypsum slag cement is 6%. Weigh the composite materials and determine the optimum moisture content of 16.432% and the maximum dry density of 1.818 g / cm according to the compaction test. 3 Weigh the water.

[0109] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 10:

[0110] Table 10.

[0111]

[0112] Example 10

[0113] Weigh the raw materials according to the following mass: the mass ratio of phosphogypsum and aeolian sand to aggregate is 0 and 25% respectively, and the amount of sulphurized phosphogypsum slag cement is 15%. Weigh the composite materials and determine the optimum moisture content of 15.910% and the maximum dry density of 1.823g / cm according to the compaction test. 3 Weigh the water.

[0114] The main performance indicators of the phosphogypsum aeolian sand synergistically solidified roadbed filler prepared in this example were tested according to the above test method and are shown in Table 11:

[0115] Table 11.

[0116]

[0117] It can be seen from Tables 2 to 11 that with the increase of the content of persulfated phosphogypsum slag cement and the content of phosphogypsum in the aggregate, the strength of the roadbed filler gradually increases; the early strength of the roadbed filler solidified by phosphogypsum aeolian sand at room temperature is low, and the later strength is high, up to 2217 kPa. The effective elements such as calcium and silicon in phosphogypsum and slag powder play a significant role in promoting the strength of the roadbed filler after the hydration reaction occurs, and make a great contribution to stabilizing the later strength; the cohesion and internal friction angle of the roadbed filler increase with the increase of the content of persulfated phosphogypsum slag cement, and increase with the increase of phosphogypsum in the aggregate when the content of cementitious material is the same, which is related to the change law of unconfined compressive strength; the cohesion and friction angle of Example 3 of the preferred ratio are 55 kPa and 19.19° respectively. According to the "Highway Roadbed Design Code" (JTG D30-2023) shows that the structural surface type of the sample is hard and has good shear strength. When the cementitious material content is fixed, the phosphorus content in the leachate increases with the phosphogypsum content in the aggregate. The phosphorus content in the leachate of Examples 6 to 10 all meets the Class V standard limit specified in the "Groundwater Environmental Quality Standard" (GB3832-2002). Phosphogypsum-aeolian sand co-solidified road subgrade filler is most suitable for environments with high temperatures and low rainfall.

[0118] In order to better illustrate the superior performance of the phosphogypsum aeolian sand synergistically solidified road subgrade filler of the present invention, the applicant conducted the following research:

[0119] like Figure 1 As shown in the figure, the X-ray diffraction (XRD) patterns of the persulfated phosphogypsum slag cement used in Examples 1 to 10 show that quartz is dominant in the mineral composition, followed by gypsum particles, while the content of ettringite is relatively low. Quartz, as an inherent mineral component in the raw material, is retained during the hydration reaction, while gypsum particles are one of the main minerals remaining after the hydration reaction. ettringite is a product jointly generated by phosphogypsum, blast furnace slag powder and ordinary Portland cement during the hydration reaction.

[0120] like Figure 2 As shown, the XRD superposition comparison diagram of the phosphogypsum aeolian sand co-solidified road subgrade filler and the phosphogypsum raw material prepared in Examples 1 to 6, it can be observed that the phosphogypsum aeolian sand co-solidified road subgrade filler also contains gypsum particles, quartz and ettringite, but the highest content is gypsum, followed by quartz, and the lowest peak is ettringite.

[0121] Depend on Figure 1 、 Figure 2It can be seen that the mineral phase that occupies a dominant position in the phosphogypsum aeolian sand co-solidified road subgrade filler has changed from quartz to gypsum compared with persulfated phosphogypsum slag cement. The phosphogypsum in the aggregate will also participate in the hydration reaction process, but its hydration degree is significantly lower than that of the phosphogypsum in persulfated phosphogypsum slag cement.

[0122] like Figure 3 and Figure 4 As shown in the figure, the microscopic morphologies of persulfated phosphogypsum slag cement at the ages of 7 days and 28 days respectively. It can be seen that part of the phosphogypsum participates in the hydration reaction, and the generated needle-shaped ettringite and hydrated calcium silicate gel and other products have played a positive role in promoting the strength growth of the material. Moreover, with the increase of age, the originally irregularly grown needle-shaped ettringite gradually aggregates and grows, and is interlocked, cemented and adhered to the phosphogypsum that does not participate in the hydration reaction, forming a more stable and dense structure.

[0123] like Figure 5 As shown in the figure, it is a microscopic morphology of the phosphogypsum aeolian sand co-solidified road subgrade filler of the present invention at the age of 7 days. It can be observed that the gypsum particles and quartz particles are tightly compacted, and the particles are irregularly filled with each other to form a dense structure. The phosphogypsum is mostly in the form of plates or columns, which further enhances the stability of the filler. Partially hydrated calcium silicate gel and ettringite are generated between the gaps of the particles and on the surface of the particles, which improves the overall strength and durability of the roadbed filler.

[0124] like Figure 6 As shown in the figure, it is a microscopic morphology of the phosphogypsum aeolian sand co-solidified road subgrade filler of the present invention at the age of 14 days. It can be seen that the active ingredients such as SiO2, Al2O3 and CaO in the raw materials successfully generate a honeycomb network hydrated silicate gel with significant cementing properties through the ion exchange mechanism under the conditions of an alkaline environment, and the gypsum crystals in some phosphogypsum particles form needle-shaped ettringite crystals under the stimulation of sulfate.

[0125] like Figure 7 As shown, this is a microscopic morphology of the phosphogypsum and aeolian sand co-cured roadbed filler of the present invention at the age of 28 days. It can be seen that individual spherical agglomerates are formed by gel-adhered phosphogypsum crystals and aeolian sand particles, and the hydrated calcium silicate gel bonds the individual agglomerates to form addition polymers.

[0126] Depend on Figure 6 and Figure 7It can be seen that a large number of gel aggregates gradually achieve comprehensive coverage and encapsulation of the particles by tightly adhering to the surfaces of phosphogypsum and aeolian sand particles. The phosphogypsum and aeolian sand particles encapsulated by the gel further form a new gel bonding layer through the gel's bonding action. This bonding layer also functions to connect the phosphogypsum and aeolian sand particles, thus promoting a cyclical process: the particles are continuously bonded by the gel, gradually forming agglomerates with particle gradation characteristics. The particles in these agglomerates vary in size, interlocking and compressing each other to form a spatial skeleton structure. At the same time, ettringite crystals, excess gypsum particles, and aeolian sand particles fill the gaps in this skeleton structure, ultimately forming a dense and stable overall structure.

[0127] In summary, by regulating the addition amount of persulfated phosphogypsum slag cement and the proportion of phosphogypsum in aggregate, the synergistic effect of phosphogypsum and aeolian sand can be promoted to form a more stable internal structure in the road subgrade filler. By effectively controlling the generation of hydration products, a phosphogypsum and aeolian sand synergistically solidified road subgrade filler that can meet the strength and other performance requirements of various types of roads can be fundamentally designed to meet the diverse road performance requirements and thus adapt to the actual application of different construction scenarios.

[0128] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A roadbed filler solidified by synergistic solidification of phosphogypsum and aeolian sand, characterized in that: The road subgrade filler is prepared from persulfated phosphogypsum slag cement, a first modified phosphogypsum, aeolian sand, and water, wherein the total mass of the first modified phosphogypsum and the aeolian sand accounts for no less than 80% of the mass fraction of the road subgrade filler, the mass ratio of the first modified phosphogypsum to the aeolian sand is (3:1) to (1:3), and the persulfated phosphogypsum slag cement is prepared from a second modified phosphogypsum, slag powder, and ordinary Portland cement; The first modified phosphogypsum and the second modified phosphogypsum are both wet-ground modified phosphogypsum. The preparation process is as follows: 92 to 95 parts by weight of original phosphogypsum, 4 to 6 parts of slag powder and 2 to 3 parts of general-purpose Portland cement are mixed and wet-ground at a water-cement ratio of 0.42 to 0.47, and the mixture is allowed to stand and age to obtain a modified phosphogypsum slurry, which is then dried.

2. The roadbed filler according to claim 1, characterized in that: The aeolian sand is aeolian sand from the Tengger Desert in Inner Mongolia Autonomous Region, with a particle size between 0.08 mm and 0.80 mm. 10 The average particle size d is 0.081 mm. 50 The particle size d is 0.146 mm. 60 and d 30 They are 0.171mm and 0.115mm respectively.

3. The road subgrade filler according to claim 1, characterized in that: In the persulfated phosphogypsum slag cement, the content of the second modified phosphogypsum is 40 to 50 parts by weight, the content of slag powder is 40 to 50 parts by weight, and the content of ordinary Portland cement is 4 to 6 parts by weight.

4. The road subgrade filler according to claim 3, characterized in that: The slag powder is S95 granulated blast furnace slag powder, the main components of which are SiO2, Al2O3 and MgO.

5. The road subgrade filler according to claim 4, characterized in that: The density of the ordinary Portland cement is 3.077 g / cm 3 , with a specific surface area of ​​358m 2 / kg, the main components are CaO, SiO2, Fe2O3 and Al2O3, and the main minerals are tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.

6. The road subgrade filler according to claim 5, characterized in that: Persulfate gypsum slag cement is added by external admixture method, and its content ranges from 6% to 15%.

7. The road subgrade filler according to claim 5, characterized in that: The first modified phosphogypsum and aeolian sand are used as aggregates, and the proportion of aeolian sand in the aggregate is between 0.25 and 0.

75.

8. The method for preparing a roadbed filler synergistically solidified by phosphogypsum and aeolian sand according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Aggregate preparation: Crush larger lumps in the wet-ground modified phosphogypsum, dry them in an oven at 55°C to 60°C for 48 to 60 hours, and then pass them through a 0.6 mm pore size sieve to obtain the treated phosphogypsum; Aeolian sand within different particle size ranges is screened, weighed according to a determined aeolian sand particle group gradation, and then evenly mixed with the graded particle group to obtain aeolian sand; S2. Preparation of persulfated phosphogypsum slag cement: wet-ground modified phosphogypsum, granulated blast furnace slag powder, and ordinary Portland cement are mixed according to a preset ratio, and then placed in a cement paste mixer and stirred at a total water-cement ratio of 0.42 to 0.47 to obtain persulfated phosphogypsum slag cement; S3, dry mixing: Mix the aggregate phosphogypsum and aeolian sand evenly according to a preset ratio, pour into a mortar mixer and stir for 3 to 7 minutes to obtain a first mixture; S4, wet mixing: pouring persulfate gypsum slag cement and water into a mixer according to a preset ratio, stirring at a speed of 500 rpm to 700 rpm for 5 min to 10 min until uniform, to obtain a second mixture; S5, shaping and curing: spreading and compacting the second mixture obtained in step S4, and curing the mixture by heat preservation and moisture retention to obtain the phosphogypsum and aeolian sand synergistically solidified roadbed filler.

9. The preparation method according to claim 8, wherein In step S4, the optimum moisture content of 15.064% to 16.274% and the maximum dry density of 1.717 g / cm 3 ~1.784g / cm 3 Weigh the water.

Images