Method for preparing road base using solid waste phosphogypsum and oyster shell in cooperation

Abstract

This invention relates to the field of solid waste resource utilization and road base material preparation technology, and discloses a method for preparing road base materials by synergistic modification of solid waste phosphogypsum and oyster shells. The method includes: detecting the raw material state of the phosphogypsum to be utilized, generating a characterization of the acidic impurity load of the phosphogypsum; pretreating the oyster shells to obtain oyster shell powder, detecting the calcium source state of the oyster shell powder, obtaining oyster shell powder state data, and generating a characterization of calcium source adjustment for the oyster shell powder; matching the acidic impurity load characterization of the phosphogypsum with the calcium source adjustment characterization of the oyster shell powder to determine the target feed combination for the road base mixture; performing segmented mixing, aging stabilization, and moisture content correction according to the target feed combination, and outputting a synergistically modified mixture for road base materials. This invention can improve the batch adaptability, compaction stability, and applicability of different batches of phosphogypsum and oyster shell powder synergistically modified road base materials.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and road base material preparation technology, specifically a method for the synergistic modification of solid waste phosphogypsum and oyster shells for use as road base material preparation. Background Technology

[0002] Phosphogypsum is a major industrial byproduct of wet-process phosphoric acid or phosphate fertilizer production, typically containing free acid, soluble phosphorus, soluble fluoride, and a certain amount of free water. Due to differences in the source, storage time, and pretreatment degree of phosphogypsum, different batches exhibit significant variations in pH value, moisture content, soluble phosphorus content, and soluble fluoride content. Direct application of phosphogypsum to road base materials can easily lead to problems such as acidic components affecting the gelation reaction, soluble impurities affecting stability, and moisture content deviating from the optimal compaction state. Oyster shells are shellfish solid waste generated during seafood processing and kitchen waste recycling, with calcium carbonate as their main component. After washing, drying, crushing, and screening, oyster shell powder can be used for acid neutralization, calcium supplementation, and granular filling; however, different batches of oyster shell powder also vary in effective calcium carbonate content, particle size distribution, moisture content, and organic residue levels.

[0003] Current processing methods often use oyster shell powder as a common filler added in a fixed proportion, without matching it to the acid impurity load of phosphogypsum and the calcium source adjustment capacity of oyster shell powder. Therefore, existing methods for preparing phosphogypsum road base materials still have problems such as poor adaptability of fixed proportions, unstable acid neutralization, deviation of moisture content from molding requirements after aging, and large fluctuations in the performance of base materials made from different batches of solid waste raw materials.

[0004] To address the aforementioned issues, there is an urgent need for innovative designs based on existing methods for preparing road base layers using solid waste phosphogypsum and oyster shells. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the synergistic modification of solid waste phosphogypsum and oyster shells for use in the preparation of road base materials, in order to solve the problem mentioned in the background art that when the properties of different batches of phosphogypsum and oyster shell powder fluctuate, it is difficult to stably control the acid neutralization state, gelation stability state and molding moisture content of the road base mixture with a fixed ratio.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for synergistic modification of solid waste phosphogypsum and oyster shells for use in the preparation of road base layers, the method comprising: S1. Perform raw material state testing on the phosphogypsum to be used to obtain phosphogypsum state data, and generate a characterization of the acidic impurity load of phosphogypsum based on the phosphogypsum state data. S2. Pre-treat oyster shells to obtain oyster shell powder, perform calcium source state detection on the oyster shell powder to obtain oyster shell powder state data, and generate oyster shell powder calcium source regulation characterization based on the oyster shell powder state data. S3. Match the acidic impurity load characterization of the phosphogypsum with the calcium source regulation characterization of the oyster shell powder to generate a dual solid waste synergistic modification state, and determine the target feeding combination of the road base mixture based on the dual solid waste synergistic modification state. S4. According to the target feeding combination, phosphogypsum, oyster shell powder, auxiliary cementitious materials, graded aggregates and mixing water are mixed in stages to obtain the initial mixture; S5. The initial mixture is aged and stabilized to obtain an aged mixture. The target feed combination is modified according to the release state and molding moisture content of the aged mixture, and a synergistic modified mixture for road base is output.

[0007] Furthermore, the raw material state of the phosphogypsum to be utilized is tested to obtain phosphogypsum state data, including: Obtain batch information of the phosphogypsum to be used; The phosphogypsum to be used is broken up and sieved to obtain the phosphogypsum to be tested; The moisture content, pH value, soluble phosphorus content, and soluble fluorine content of the phosphogypsum to be tested were determined. The state data of the phosphogypsum is composed of the moisture content, pH value, soluble phosphorus content, and soluble fluorine content.

[0008] Further, based on the phosphogypsum state data, a characterization of the acidic impurity load of phosphogypsum is generated, including: The acidity of phosphogypsum is determined based on the pH value. The degree of soluble impurities in phosphogypsum is determined based on the soluble phosphorus content and soluble fluorine content. The degree of moisture shift in phosphogypsum is determined based on the stated moisture content. The acidity level of phosphogypsum, the degree of soluble impurities in phosphogypsum, and the degree of moisture shift in phosphogypsum are combined to generate a characterization of the acid impurity load of phosphogypsum.

[0009] Furthermore, the oyster shells are pretreated to obtain oyster shell powder, and the calcium source state of the oyster shell powder is detected to obtain oyster shell powder state data, including: The oyster shells are washed, dried, crushed and sieved in sequence to obtain oyster shell powder with different particle size ranges; The effective calcium carbonate content, particle size distribution, moisture content, and organic residue level of the oyster shell powder were tested. The oyster shell powder state data is composed of the effective calcium carbonate content, particle size distribution, moisture content, and degree of organic residue.

[0010] Furthermore, based on the oyster shell powder state data, a characterization of oyster shell powder calcium source regulation is generated, including: The acid neutralization capacity of oyster shell powder is determined based on the effective calcium carbonate content. The pore-filling capacity of the oyster shell powder is determined based on the particle size distribution. The mixing and compatibility of oyster shell powder is determined based on the moisture content and degree of organic residue. The acid neutralization ability, pore filling ability and mixing and adaptability are combined to generate the calcium source regulation characterization of the oyster shell powder.

[0011] Furthermore, the acidic impurity load characterization of the phosphogypsum is matched with the calcium source regulation characterization of the oyster shell powder to generate a dual solid waste synergistic modification state, including: The neutralization requirement, moisture balance requirement, and gel stability requirement of phosphogypsum are determined based on the acid impurity load characterization of the phosphogypsum. The calcium source supply capacity, particle filling capacity, and mixing and water absorption capacity of oyster shell powder were determined based on the calcium source regulation characterization of oyster shell powder. By matching the neutralization requirement with the calcium source supply capacity, the moisture balance requirement with the mixing and water absorption capacity, and the gelation stabilization requirement with the particle filling capacity, the dual solid waste synergistic modification state is generated.

[0012] Further, the target feed combination for the road base mixture is determined based on the aforementioned dual solid waste synergistic modification state, including: Based on the matching results between the neutralization demand and the calcium source supply capacity, the target amount of oyster shell powder to be added is determined; Based on the matching results between the gel stability requirements and the particle filling capacity, the target addition amounts of auxiliary cementitious materials and graded aggregates are determined. Based on the matching results between the moisture balance requirements and the mixing water absorption capacity, determine the target amount of mixing water and the amount of reclaimed dry material. The target feeding combination is composed of the target amount of oyster shell powder, the target amount of auxiliary cementitious material and graded aggregate, the target amount of mixing water, and the reserved amount of reclaimed material.

[0013] Further, according to the target feed combination, phosphogypsum, oyster shell powder, auxiliary cementitious materials, graded aggregates, and mixing water are mixed in stages to obtain an initial mixture, including: Phosphogypsum was premixed with fine-particle oyster shell powder for acid neutralization to obtain a pre-neutralized material; The pre-neutralized material is dry-mixed with oyster shell powder for gradation supplementation, auxiliary cementitious materials and graded aggregates to obtain dry-mixed material; Add mixing water to the dry mixture for wet mixing, so that the oyster shell powder is distributed in the gaps between the phosphogypsum particles, to obtain the initial mixture.

[0014] Further, the initial mixture is aged and stabilized to obtain an aged mixture, and the target feed combination is modified according to the release state and molding moisture content of the aged mixture, including: The initial mixture is covered and piled up for aging to obtain an aged mixture; The pH value, moisture content, soluble phosphorus content, and soluble fluoride content of the aged mixture were tested. The release status is determined based on the pH value, soluble phosphorus content, and soluble fluorine content of the aged mixture. The molding moisture content is determined based on the comparison between the moisture content of the aged mixture and the target molding moisture content range; Based on the release status and the moisture content of the molding, adjust the amount of oyster shell powder, auxiliary gelling material, mixing water, and re-drying material added.

[0015] Furthermore, after the output is used for the co-modified mixture of road base course, it also includes: The unconfined compressive strength, compaction degree, water stability coefficient and leaching index of the synergistically modified mixture were tested. The road base course suitability evaluation results are generated based on the unconfined compressive strength, compaction degree, water stability coefficient, and leaching index. The road base suitability evaluation results are fed back to the dual solid waste synergistic modification status to update the target feed combination for subsequent batches.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: The method for co-modifying solid waste phosphogypsum with oyster shells for use as a road base material involves performing state testing on the phosphogypsum and oyster shell powder, and matching the acid impurity load characterization of phosphogypsum with the calcium source adjustment characterization of oyster shell powder. This allows the feeding combination of the road base mixture to be determined based on the acidity, impurity state, moisture state, and calcium source adjustment capacity of different batches of solid waste raw materials, thereby improving the adaptability and preparation stability of the phosphogypsum and oyster shell powder co-modification method when used as a road base material. Specifically: 1. This invention detects the moisture content, pH value, soluble phosphorus content, and soluble fluorine content of the phosphogypsum to be used, and generates a characterization of the acid impurity load of phosphogypsum. It can transform the acidity, soluble impurity, and moisture deviation of different batches of phosphogypsum into the basis for determining the subsequent target feeding combination, reducing the problems of insufficient neutralization, insufficient gelation stability, or deviation of the molding moisture content caused by batch fluctuations of phosphogypsum under a fixed ratio. 2. This invention involves cleaning, drying, crushing, and sieving oyster shells, and then testing the effective calcium carbonate content, particle size distribution, moisture content, and organic residue level of the oyster shell powder. This process generates a calcium source regulation characterization of the oyster shell powder, enabling the oyster shell powder to participate in the formulation based on its acid neutralization capacity, pore filling capacity, and mixing adaptability, rather than simply being added as a common filler. This improves the synergistic utilization effect of oyster shell powder in acid neutralization, particle filling, and moisture regulation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the preparation method of the present invention; Figure 2 This is a schematic diagram illustrating the generation of raw material state characterization in this invention; Figure 3 This is a schematic diagram illustrating the collaborative matching and target material combination generation of the present invention; Figure 4 This is a schematic diagram of the segmented mixing and aging correction process of the present invention; Figure 5 This is a schematic diagram comparing the unconfined compressive strength of the present invention; Figure 6 This is a schematic diagram comparing the evaluation results of the applicability of the road base course according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: The present invention provides a technical solution: a method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells. The specific details are as follows: S1. Perform raw material state testing on the phosphogypsum to be utilized to obtain phosphogypsum state data, and generate a characterization of the acidic impurity load of phosphogypsum based on the phosphogypsum state data. Specifically, the phosphogypsum to be utilized is a solid byproduct generated and stored during the production of wet-process phosphoric acid or phosphate fertilizer. Before entering the co-modification treatment, the batch information of the phosphogypsum to be utilized is obtained. The batch information includes the source of raw materials, storage area, arrival time, sampling location and sampling number. The batch information is used to establish a correlation between the phosphogypsum state data obtained from subsequent testing and the corresponding raw material batch, so as to avoid the mixed use of phosphogypsum in different storage states.

[0020] After obtaining batch information, the phosphogypsum to be used is dispersed and sieved. Dispersion is used to break up clumps formed during the stockpiling process, and sieving is used to remove large-diameter hard lumps, impurities, and agglomerated particles that are not suitable for mixing, to obtain the phosphogypsum to be tested. The phosphogypsum to be tested refers to the phosphogypsum sample that, after being dispersed and sieved, can represent the state of the current batch of raw materials and can be used for testing. The moisture content, pH value, soluble phosphorus content, and soluble fluorine content of the phosphogypsum to be tested are respectively measured. Among them, the moisture content is used to characterize the effect of free water and adsorbed water in phosphogypsum on the amount of water added for subsequent mixing and the water content of the molding. The pH value is used to characterize the effect of free acidic components in phosphogypsum on the neutralization requirements of oyster shell powder. The soluble phosphorus content and soluble fluorine content are used to characterize the effect of migratable impurities in phosphogypsum on the stability of the gelation reaction and the applicability of the road base layer. In this embodiment, the moisture content can be detected by drying and weighing. The initial mass of the phosphogypsum sample to be tested is weighed, and after drying to constant weight, the dry mass is weighed. The moisture content is determined based on the difference between the initial mass and the dry mass. The pH value can be detected by measuring the pH value of the extract after water extraction. The soluble phosphorus content and soluble fluoride content can be detected by measuring the phosphorus ion and fluoride ion content in the extract after extraction.

[0021] The state data of phosphogypsum is composed of moisture content, pH value, soluble phosphorus content, and soluble fluorine content. In this embodiment, three batches of phosphogypsum to be used were selected for raw material state testing. All three batches of phosphogypsum were sampled and tested after being dispersed and sieved. The test results are shown in Table 1 below: Batch A 21.8 2.6 68 42 High rise Slightly damp High load characterization Batch B 16.2 3.4 45 28 Moderate Controllable adaptation Stable load characterization Batch C 10.5 4.2 22 15 Low Controllable Dry Low acidity and dryness characterization Table 1. Phospholipid state data and acidic impurity load characterization As shown in Table 1, batch A of phosphogypsum exhibits a low pH value, high soluble phosphorus content, high soluble fluoride content, and high moisture content, thus it is characterized as a high-load batch, corresponding to the subsequent high requirements for neutralization, gel stabilization, and re-drying adjustment. Batch B of phosphogypsum has relatively stable pH value, soluble phosphorus content, soluble fluoride content, and moisture content, thus it is characterized as a stable-load batch, corresponding to the subsequent requirements for conventional synergistic modification. Batch C of phosphogypsum has a relatively high pH value and controllable levels of soluble impurities, but its moisture content is below the suitable range for mixing; therefore, it is characterized as a low-acid, slightly dry batch, corresponding to the subsequent requirements for water replenishment adjustment.

[0022] In this embodiment, the preset pH boundary range, preset phosphorus content threshold, preset fluorine content threshold, and preset mixing and suitable moisture content range can be determined according to the design requirements of road base materials and local testing standards. As an optional embodiment, when the pH value is less than 3.0, it is determined to be highly acidic; when the pH value is greater than or equal to 3.0 and less than or equal to 4.0, it is determined to be moderately acidic; when the pH value is greater than 4.0, it is determined to be less acidic. When the soluble phosphorus content is greater than 50 mg·L⁻¹ or the soluble fluorine content is greater than 35 mg·L⁻¹, it is determined to be an increased level of soluble impurities. When the moisture content is greater than 18%, it is determined to be a slightly wet state; when the moisture content is greater than or equal to 12% and less than or equal to 18%, it is determined to be a suitable state; when the moisture content is less than 12%, it is determined to be a slightly dry state.

[0023] The state data of phosphogypsum is not a single test result, but a combination of data used to collectively describe the moisture state, acidity state, and soluble impurity state of the current batch of phosphogypsum. The specific judgment is as follows: The acidity of phosphogypsum is determined by comparing the pH value with a preset pH range. When the pH value is lower than the preset lower pH limit, the acidity of the batch of phosphogypsum is determined to be too high. When the pH value is within the preset pH range, the acidity of the batch of phosphogypsum is determined to be moderate. When the pH value is higher than the preset upper pH limit, the acidity of the batch of phosphogypsum is determined to be too low. The degree of soluble impurities in phosphogypsum is determined based on the soluble phosphorus content and soluble fluorine content. Specifically, the soluble phosphorus content is compared with a preset phosphorus content threshold, and the soluble fluorine content is compared with a preset fluorine content threshold. When at least one of them exceeds the corresponding threshold, the degree of soluble impurities in the batch of phosphogypsum is determined to be increased. When neither of them exceeds the corresponding threshold, the degree of soluble impurities in the batch of phosphogypsum is determined to be under control. The degree of moisture deviation of phosphogypsum is determined based on the moisture content. Specifically, the moisture content is compared with the preset mixing and suitable moisture content range. When the moisture content is higher than the upper limit of the preset mixing and suitable moisture content range, the batch of phosphogypsum is determined to be in a slightly wet state. When the moisture content is lower than the lower limit of the preset mixing and suitable moisture content range, the batch of phosphogypsum is determined to be in a slightly dry state. When the moisture content is within the preset mixing and suitable moisture content range, the moisture state of the batch of phosphogypsum is determined to be suitable for subsequent mixing. The acidity level of phosphogypsum, the degree of soluble impurities in phosphogypsum, and the degree of moisture shift in phosphogypsum are combined to generate a characterization of the acidity impurity load of phosphogypsum. The characterization of the acidity impurity load of phosphogypsum is used to represent the comprehensive requirements of the current batch of phosphogypsum for the acidity neutralization ability of oyster shell powder, the stabilization ability of auxiliary cementitious materials, and the subsequent mixing moisture content adjustment ability.

[0024] In one specific implementation method, when the acidity of phosphogypsum is high, the degree of soluble impurities is increased, and the moisture state is too wet, the corresponding acid impurity load characterization of phosphogypsum is determined as a high load characterization. This characterization indicates that it is necessary to increase the participation ratio of fine-particle-size components in oyster shell powder and reserve more space for adjustment of dry material in the target feed combination.

[0025] In another specific implementation method, when the acidity of phosphogypsum is moderate, the degree of soluble impurities is under control, and the moisture content is within the preset mixing and suitable water content range, the corresponding acid impurity load characterization of phosphogypsum is determined as the stable load characterization. This characterization indicates that the subsequent characterization can be adjusted by matching the calcium source of oyster shell powder according to the conventional synergistic modification ratio.

[0026] In another specific implementation method, when the acidity of phosphogypsum is low, the level of soluble impurities is under control, but the moisture content is relatively dry, the corresponding acid impurity load characterization of phosphogypsum is determined as low acidity and relatively dry. This characterization indicates that there is no need to increase the amount of oyster shell powder used for neutralization, but the water absorption requirement of this batch of phosphogypsum needs to be compensated when determining the amount of mixing water added.

[0027] Through the above treatment, the acid impurity load characterization of phosphogypsum formed in S1 can transform the batch fluctuations of the phosphogypsum to be utilized into a basis for the subsequent matching and callable raw material state. This makes the generation of the dual solid waste synergistic modification state in S3 no longer dependent on fixed empirical ratios, but can determine the configuration direction of oyster shell powder, auxiliary cementitious materials, mixing water and return dry material based on the actual acid impurity load and moisture shift of the phosphogypsum.

[0028] S2. Oyster shells are pretreated to obtain oyster shell powder. The calcium source status of the oyster shell powder is detected to obtain oyster shell powder status data. Based on the oyster shell powder status data, a calcium source regulation characterization of oyster shell powder is generated. Specifically, oyster shells are shellfish solid waste generated during seafood processing or kitchen waste collection. Before being used for co-modification, the oyster shells are first collected according to their source batches, and the source, collection time, cleaning status and temporary storage conditions of the oyster shells are recorded so that the oyster shell powder status data obtained later can be associated with the corresponding oyster shell batches.

[0029] The collected oyster shells are cleaned to remove mud, sand, salt, and attached organic residues from the surface. After cleaning, the oyster shells are dried to reduce surface and internal moisture, ensuring stable feeding for subsequent crushing and screening processes. The dried oyster shells are then crushed, and the crushed shell particles are screened to form oyster shell powder with different particle size ranges. The finer particle size range of oyster shell powder is mainly used to increase the contact area with the acidic components of phosphogypsum, while the medium particle size range of oyster shell powder is mainly used to supplement the particle size distribution and fill pores in the road base mixture. Different particle size ranges refer to dividing oyster shell powder into powder ranges that can participate in acid neutralization, pore filling, and gradation supplementation according to the sieve aperture size of the screening equipment. It is not limited to a fixed mesh size. Those skilled in the art can determine the specific screening boundaries according to the gradation requirements of road base mixtures and the compatibility of mixing equipment. The calcium source status of the sieved oyster shell powder is tested. The test items include effective calcium carbonate content, particle size distribution, moisture content, and organic residue level. The effective calcium carbonate content is used to characterize the ability of oyster shell powder to participate in acid neutralization and calcium source supplementation. The particle size distribution is used to characterize its filling ability after entering the gaps between phosphogypsum particles. The moisture content is used to characterize its impact on mixing water demand and water absorption balance. The organic residue level is used to characterize its impact on subsequent gelation stability and road base durability.

[0030] The effective calcium carbonate content can be obtained through acid dissolution reaction or calcium carbonate content detection method; the particle size distribution can be obtained through sieving or particle size analysis method; the moisture content can be obtained through drying and weighing method; and the degree of organic residue can be obtained through loss on ignition, volatile residue detection, or preset organic matter detection method. The effective calcium carbonate content, particle size distribution, moisture content, and degree of organic residue together constitute the state data of oyster shell powder. In this embodiment, three batches of oyster shells were washed, dried, crushed, and sieved to obtain the corresponding oyster shell powder. The calcium source state of each batch of oyster shell powder was detected, and the detection results are shown in Table 2 below. Batch A 92.4 48 37 1.9 1.2 Strong Strong Meets requirements Characterization of high calcium source regulation Batch B 85.6 32 45 2.5 1.8 Moderate Strong Meets requirements Graded supplementary characterization Batch C 82.1 24 51 2.2 1.5 Moderate Strong Meets requirements Graded supplementary characterization Table 2. State data and calcium source regulation characteristics of oyster shell powder As shown in Table 2, batch a of oyster shell powder has a higher effective calcium carbonate content and a higher proportion of fine-particle-size powder, thus exhibiting stronger acid neutralization and pore-filling capabilities, making it suitable for matching with phosphogypsum characterized by high load. Batches b and c of oyster shell powder have a higher proportion of medium-particle-size powder, enabling them to better participate in the particle size distribution supplementation of road base course mixtures; therefore, they can be used as gradation supplementation components in subsequent matching.

[0031] The oyster shell powder state data is used to describe the overall material state of the current batch of oyster shell powder in terms of acid neutralization, pore filling, and mixing adaptation. In this embodiment, fine-particle-size powder refers to oyster shell powder used to improve the acid neutralization contact area and micropore filling effect, while medium-particle-size powder refers to oyster shell powder used to supplement the particle size distribution and skeleton filling of road base mixtures. As an optional embodiment, fine-particle-size powder can be powder that passes through a 0.075mm sieve, and medium-particle-size powder can be powder with a particle size greater than 0.075mm and not greater than 2mm. When the effective calcium carbonate content is not less than 90%, the acid neutralizing ability of oyster shell powder is determined to be strong; when the effective calcium carbonate content is greater than or equal to 80% and less than 90%, the acid neutralizing ability of oyster shell powder is determined to be moderate; when the effective calcium carbonate content is less than 80%, the acid neutralizing ability of oyster shell powder is determined to be weak; when the moisture content is not greater than 3% and the organic residue is not greater than 2%, its mixing suitability is determined to meet the requirements; the acid neutralizing ability of oyster shell powder is determined based on the effective calcium carbonate content, specifically by... The effective calcium content was compared with the preset calcium source evaluation range. When the effective calcium carbonate content was in the higher range, the batch of oyster shell powder was judged to have a strong acid-neutralizing ability; when the effective calcium carbonate content was in the middle range, the batch of oyster shell powder was judged to have a moderate acid-neutralizing ability; and when the effective calcium carbonate content was below the lower limit of the preset calcium source evaluation range, the batch of oyster shell powder was judged to have a weak acid-neutralizing ability. The pore-filling capacity of the oyster shell powder was determined based on the particle size distribution, specifically by statistically analyzing the fine and medium particle size ranges in oyster shell powder. The proportion of oyster shell powder in the total amount is determined as follows: when the proportion of fine particles is higher than the preset fine particle size threshold, it is determined that its filling effect on the micropores between phosphogypsum particles is strong; when the proportion of medium particles is higher than the preset medium particle size threshold, it is determined that its supplementary effect on the particle size distribution of road base mixture is strong; when the proportion of coarse particles is higher than the preset coarse particle size threshold, it is determined that its pore filling capacity is insufficient and it needs to be re-screened or the proportion of fine particles needs to be increased. The mixing adaptability of oyster shell powder is determined according to the moisture content and the degree of organic residue. Specifically, the moisture content is compared with the preset powder mixing moisture content range, and the degree of organic residue is compared with the preset organic residue limit. When the moisture content is within the preset powder mixing moisture content range and the degree of organic residue is not higher than the preset organic residue limit, the mixing adaptability of this batch of oyster shell powder is determined to meet the requirements. When the moisture content is too high, it is determined that it is easy to affect the amount of mixing water added in the target feed combination. When the degree of organic residue is too high, it is determined that it needs to extend the washing or drying process before entering the subsequent matching process.

[0032] By combining acid neutralization capacity, pore filling capacity, and mixing adaptability, a calcium source regulation characterization of oyster shell powder is generated. This characterization is used to represent the neutralization and support capacity of the current batch of oyster shell powder for the acidic impurities in phosphogypsum, its filling and support capacity for the particle skeleton of the mixture, and its moisture adaptability during the segmented mixing process.

[0033] In one specific implementation method, when the effective calcium carbonate content of oyster shell powder is high, the proportion of fine particle size range is high, the moisture content is within the preset powder mixing moisture range and the degree of organic residue is not higher than the preset organic residue limit, the corresponding oyster shell powder calcium source regulation characterization is determined as high calcium source regulation characterization. This characterization indicates that this batch of oyster shell powder can be preferentially used to undertake the role of acid neutralization and micropore filling in the future.

[0034] In another specific implementation method, when the effective calcium carbonate content of oyster shell powder is moderate, the particle size distribution is mainly in the medium particle size range, and the moisture content is within the preset powder mixing moisture range, the corresponding oyster shell powder calcium source adjustment characterization is determined as a gradation supplement type characterization. This characterization indicates that the batch of oyster shell powder can be mainly used for particle gradation supplementation and skeleton filling of road base mixture.

[0035] In another specific implementation method, when the effective calcium carbonate content of oyster shell powder is too low, the proportion of coarse particles is too high, the moisture content is too high, or the degree of organic residue is too high, the corresponding calcium source adjustment characterization of oyster shell powder is determined to be a low fit characterization. This characterization indicates that the batch of oyster shell powder needs to be re-sieved, supplemented with fine particle size powder, dried again, or washed again before being matched with the acidic impurity load characterization of phosphogypsum.

[0036] Through the above treatment, the calcium source regulation characterization of oyster shell powder formed in S2 can transform the batch differences of oyster shell powder into a basis for subsequent matching of material capabilities. This enables the generation of the dual solid waste synergistic modification state in S3 to simultaneously consider the neutralization requirements, moisture balance requirements, and gelation stability requirements of phosphogypsum, and avoids adding oyster shell powder as just an ordinary inert filler to the road base mixture.

[0037] S3. Match the acid impurity load characterization of phosphogypsum with the calcium source regulation characterization of oyster shell powder to generate a dual solid waste synergistic modification state, and determine the target feeding combination of road base mixture based on the dual solid waste synergistic modification state. Specifically, the acid impurity load characterization of phosphogypsum comes from the acidity of phosphogypsum, the degree of soluble impurities in phosphogypsum, and the degree of moisture shift in phosphogypsum formed in S1. The calcium source regulation characterization of oyster shell powder comes from the acid neutralization capacity, pore filling capacity, and mixing and adaptability formed in S2. In S3, these two types of characterization are no longer used as isolated test results, but are converted into supply and demand matching basis for determining the material ratio.

[0038] The neutralization requirement, moisture balance requirement, and gel stability requirement of phosphogypsum were determined based on the characterization of acidic impurity load. The neutralization requirement indicates the degree to which acidic components in phosphogypsum need to be buffered by oyster shell powder calcium. The moisture balance requirement indicates the impact of the current batch of phosphogypsum on the reduction of mixing water, replenishment water, or the reservation of re-drying material. The gel stability requirement indicates the impact of soluble phosphorus and soluble fluorine on the reaction stability of auxiliary gelling materials. When the acidity of phosphogypsum is high, the neutralization requirement is increased to a higher level. When the soluble impurity level of phosphogypsum increases, the gel stability requirement is increased to a higher level. When the moisture shift of phosphogypsum is in a wet state, the moisture balance requirement is determined to be a re-drying adjustment type. When the moisture shift of phosphogypsum is in a dry state, the moisture balance requirement is determined to be a replenishment adjustment type.

[0039] Based on the characterization of calcium source regulation in oyster shell powder, the calcium source supply capacity, particle filling capacity, and mixing water absorption capacity of oyster shell powder were determined. Among them, the calcium source supply capacity corresponds to the neutralizing and supporting effect of the effective calcium carbonate content in oyster shell powder on the acidic components of phosphogypsum; the particle filling capacity corresponds to the filling effect of oyster shell powder of different particle size ranges on the interparticle gaps of phosphogypsum and the particle skeleton of road base; and the mixing water absorption capacity corresponds to the influence of the moisture content and powder state of oyster shell powder on the redistribution of water during wet mixing. When the acid neutralization capacity of oyster shell powder is strong, the calcium source supply capacity is determined to be in a high supply state; when the pore filling capacity is strong, the particle filling capacity is determined to be in a high filling state; when the mixing adaptability meets the preset requirements, the mixing water absorption capacity is determined to be in a stable water absorption state; and when the mixing adaptability is insufficient, the mixing water absorption capacity is determined to be in a state requiring pretreatment adjustment.

[0040] Matching neutralization demand with calcium source supply capacity: When neutralization demand exceeds calcium source supply capacity, increase the proportion of fine-particle oyster shell powder in the total amount of oyster shell powder added; when neutralization demand matches calcium source supply capacity, maintain the basic addition proportion of oyster shell powder; when neutralization demand is lower than calcium source supply capacity, reduce the addition proportion of fine-particle oyster shell powder and increase the proportion of medium-particle oyster shell powder used for gradation supplementation. Matching moisture balance demand with mixing and water absorption capacity: When moisture balance demand is of the re-drying adjustment type and mixing and water absorption capacity is in a stable water absorption state, reserve dry oyster shell powder and dry graded aggregate as re-drying material; when moisture balance demand is of the water replenishment adjustment type... To increase the target amount of mixing water, when the mixing water absorption capacity is in a state requiring pretreatment adjustment, the corresponding oyster shell powder should be dried or sieved again before being included in the target feeding combination; the gel stability requirement should be matched with the particle filling capacity. When the gel stability requirement is high and the particle filling capacity is weak, the amount of auxiliary cementitious material added should be increased and the proportion of fine aggregate in the graded aggregate should be increased. When the gel stability requirement is high and the particle filling capacity is strong, the basic amount of auxiliary cementitious material added should be maintained and the particle filling effect of oyster shell powder should be used to reduce the interconnected pores between phosphogypsum particles. When the gel stability requirement is low, the amount of auxiliary cementitious material added should be determined according to the design strength requirements of the road base.

[0041] The dual solid waste synergistic modification state is generated by the matching results of neutralization demand and calcium source supply capacity, moisture balance demand and mixing water absorption capacity, and gelation stability demand and particle filling capacity. The dual solid waste synergistic modification state represents the compatibility relationship between the current batch of phosphogypsum and the current batch of oyster shell powder in three aspects: acid neutralization, moisture regulation, and skeleton stabilization. Based on the matching results of neutralization demand and calcium source supply capacity, the target addition amount of oyster shell powder is determined. The target addition amount of fine-particle-size oyster shell powder is primarily determined by neutralization demand, while the target addition amount of medium-particle-size oyster shell powder is primarily determined by particle filling capacity and gradation supplementation demand, so that oyster shell powder can participate in acid neutralization and base skeleton filling at the same time. Based on the matching results of cementitious stability requirements and particle filling capacity, the target addition amounts of auxiliary cementitious materials and graded aggregates are determined. The auxiliary cementitious materials are used to ensure the early strength and water stability of the synergistic system of phosphogypsum and oyster shell powder, while the graded aggregates are used to supplement the load-bearing skeleton of the road base mixture and reduce the risk of compaction dispersion caused by excessive powder materials. Based on the matching results of moisture balance requirements and mixing water absorption capacity, the target addition amount of mixing water and the reserved amount of re-dried material are determined. The target addition amount of mixing water is used to make the subsequent wet mixture reach a mixable state, while the reserved amount of re-dried material is used to adjust the moisture content of the aged mixture when the moisture content is too high after aging.

[0042] The target feeding combination consists of the target amount of oyster shell powder, the target amount of auxiliary cementitious materials and graded aggregates, the target amount of mixing water, and the reserved amount of re-dried material. In this embodiment, the acidic impurity load characterization of phosphogypsum and the calcium source adjustment characterization of oyster shell powder were used to generate a synergistic modification state of the two solid wastes according to the relationship shown in Table 3A, as shown in the table below: High load characterization Characterization of high calcium source regulation High load matchable status Increase the amount of fine-grained oyster shell powder added and increase the amount of re-dried material reserved. High load characterization Graded supplementary characterization High-load reinforcement status Increase the amount of auxiliary cementitious materials added and increase the proportion of fine-particle oyster shell powder sieved. High load characterization Low-fit characterization High load and weak matching state Oyster shell powder is used after being re-sieved or dried, and the amount of auxiliary gelling materials added is increased. Stable load characterization Characterization of high calcium source regulation Stable neutral state Maintain the basic fine-particle size oyster shell powder addition amount Stable load characterization Graded supplementary characterization Stable cooperative state Fine-grained oyster shell powder and medium-grained oyster shell powder are added together in a basic ratio. Low acidity and dryness characterization Graded supplementary characterization Low acid grade replenishment status Reduce the amount of fine-particle oyster shell powder added, and increase the amount of medium-particle oyster shell powder and mixing water added. Table 3A: State Matching Relationship for Synergistic Modification of Two Solid Wastes Table 3A establishes a correspondence between the neutralization requirements, moisture balance requirements, and gelation stabilization requirements of phosphogypsum and the calcium source supply capacity, particle filling capacity, and mixing and water absorption capacity of oyster shell powder, thus providing a clear basis for the generation of the target feed combination.

[0043] In this embodiment, batch A of phosphogypsum is matched with batch a of oyster shell powder, batch B of phosphogypsum is matched with batch b of oyster shell powder, and batch C of phosphogypsum is matched with batch c of oyster shell powder. The target feed combination is determined based on the matching results. The target feed combination is calculated based on 100 parts of the total dry material mass, as shown in Table 3 below. Combination 1 Batch A Batch A High load matchable status 52 8.5 3.5 6 4 26 12.8 4.0 Combination 2 Batch B Batch B Stable cooperative state 55 5.5 4.5 5 4 26 13.5 2.5 Combination 3 Batch C Batch C Low acid grade replenishment status 58 3.0 7.0 5 3 24 14.6 1.5 Table 3. Synergistic modification status of two solid wastes and target feed combinations In combination 1, batch A of phosphogypsum corresponds to high-load characterization, and batch a of oyster shell powder corresponds to high-calcium source adjustment characterization. Therefore, the amount of fine-particle-size oyster shell powder added is increased, and a higher allowance for re-drying material is set, so that the fine-particle-size oyster shell powder can simultaneously undertake the functions of acid neutralization and moisture content adjustment. In combination 2, batch B of phosphogypsum corresponds to stable-load characterization, and batch b of oyster shell powder corresponds to gradation supplementation characterization. Therefore, a medium proportion of fine-particle-size and medium-particle-size oyster shell powder is used, so that it can have both acid neutralization and gradation supplementation functions. In combination 3, batch C of phosphogypsum corresponds to low-acid and slightly dry characterization, and batch c of oyster shell powder corresponds to gradation supplementation characterization. Therefore, the amount of fine-particle-size oyster shell powder added is reduced, while the amount of medium-particle-size oyster shell powder added and the proportion of mixing water to dry material mass are increased.

[0044] The target feed combination is not a fixed empirical formula, but a dynamic feed result formed based on the supply and demand matching of the current batch of phosphogypsum and the current batch of oyster shell powder.

[0045] In one specific implementation method, when phosphogypsum exhibits a high acid impurity load and oyster shell powder exhibits a high calcium source regulation characteristic, the dual solid waste synergistic modification state is determined to be a high load matching state. In the target feeding combination, the target addition amount of fine-particle-size oyster shell powder is increased while the target addition amount of auxiliary cementitious materials is kept within the basic range.

[0046] In another specific implementation method, when phosphogypsum exhibits a high acid impurity load and oyster shell powder exhibits a low fit, the dual solid waste synergistic modification state is determined to be a high load and weak matching state. The target addition amount of auxiliary cementitious material is increased in the target feed combination, and the oyster shell powder is required to be screened or dried again before participating in the segmented mixing.

[0047] In another specific implementation method, when phosphogypsum exhibits a low-acid, dry character and oyster shell powder exhibits a gradation-supplementing character, the dual solid waste synergistic modification state is determined to be a low-acid gradation-supplementing state. The target addition amount of fine-particle-size oyster shell powder is reduced in the target feeding combination, the target addition amount of mixing water is increased, and medium-particle-size oyster shell powder is used for gradation supplementation.

[0048] Through the above treatment, S3 transforms the acidic impurity load on the phosphogypsum side and the calcium source regulation capacity on the oyster shell powder side into a dual solid waste synergistic modification state, and further forms a target feeding combination, so that the subsequent segmented mixing in S4 can be carried out simultaneously around acid neutralization, skeleton filling and moisture regulation, thereby avoiding insufficient neutralization, compaction moisture imbalance and base layer strength fluctuation caused by simply mixing phosphogypsum and oyster shell powder in a fixed ratio.

[0049] S4. According to the target feeding combination, the phosphogypsum, oyster shell powder, auxiliary cementitious materials, graded aggregates and mixing water are mixed in stages to obtain the initial mixture; Specifically, the target feed combination originates from the dual solid waste synergistic modification state formed by S3. The target feed combination includes at least the target addition amount of phosphogypsum, the target addition amount of oyster shell powder, the target addition amount of auxiliary cementitious materials, the target addition amount of graded aggregate, and the target addition amount of mixing water. The target addition amount of oyster shell powder is further divided into the addition amount of fine-particle oyster shell powder used for acid neutralization and the addition amount of oyster shell powder used for gradation supplementation.

[0050] Segmented mixing refers to dividing the mixing process into three consecutive stages: premixing, secondary dry mixing, and wet mixing, according to the sequence of the materials' roles in acid neutralization, particle filling, and gel stabilization. This allows oyster shell powder to first fully contact the acidic components in phosphogypsum, and then form the particle skeleton of the road base mixture with auxiliary cementitious materials and graded aggregates. First, phosphogypsum and fine-grained oyster shell powder for acid neutralization are weighed according to the target feeding combination and put into a dry mixing device for premixing. This allows the fine-grained oyster shell powder to adhere to and distribute on the surface of the phosphogypsum particles, resulting in a pre-neutralized material. The pre-neutralized material refers to the powder mixture formed after the phosphogypsum and fine-grained oyster shell powder have undergone preliminary uniform contact. During the premixing process, the fine-grained oyster shell powder preferentially fills the depressions on the surface of the phosphogypsum particles and the tiny gaps between the particles, and forms a contact interface with the free acidic components in the phosphogypsum, thus providing a uniform contact basis for the acid neutralization reaction after subsequent wet mixing and water addition. When the neutralization requirement determined in S3 is high, the premixing stage increases the proportion of fine-particle oyster shell powder in the total amount of oyster shell powder added and extends the premixing time so that the fine-particle oyster shell powder preferentially covers the surface of phosphogypsum particles with high acid impurity load. When the neutralization requirement determined in S3 is low but the particle filling requirement is high, the premixing stage maintains the basic addition amount of fine-particle oyster shell powder, and more oyster shell powder is reserved for subsequent secondary dry mixing stage to participate in gradation supplementation. After premixing, the pre-neutralized material is dry-mixed a second time with oyster shell powder for gradation supplementation, auxiliary cementitious materials, and graded aggregates to obtain a dry mix. The oyster shell powder for gradation supplementation includes medium-sized oyster shell powder. The auxiliary cementitious materials are used to improve the early strength and water stability of the mixture, and the graded aggregates are used to form the load-bearing skeleton of the road base. During the second dry mixing, the pre-neutralized material is first mixed with the oyster shell powder for gradation supplementation, and then the auxiliary cementitious materials and graded aggregates are added. This allows the fine-sized powder, medium-sized powder, and aggregate particles to form a continuous gradation in the dry state, avoiding direct local contact between the auxiliary cementitious materials and the high-acid phosphogypsum, which could cause uneven cementitious reaction. During the second dry mixing process, if the cementitious stability requirement determined in S3 is high, the dispersion uniformity of the auxiliary cementitious materials in the dry mix is ​​improved, and the auxiliary cementitious materials are preferentially distributed in the interface area between the pre-neutralized material and the graded aggregates to enhance the bonding effect between the powder and the aggregates after subsequent wet mixing. If the particle filling capacity determined in S3 is insufficient, the proportion of medium-sized oyster shell powder and fine-sized aggregate in the graded aggregate is increased during the secondary dry mixing stage to fill the gaps between phosphogypsum particles and graded aggregate, reducing the risk of local loosening of the initial mixture before compaction. After the secondary dry mixing is completed, mixing water is added to the dry mixture for wet mixing. The amount of mixing water added is in accordance with the target amount of mixing water determined in S3, and is added in stages according to the degree of moisture shift of phosphogypsum and the water absorption capacity of oyster shell powder, so that the powder material is gradually wetted rather than forming local agglomeration at one time.

[0051] During wet mixing, the mixing water promotes full contact between the fine-particle oyster shell powder and the acidic components in phosphogypsum, while simultaneously allowing the auxiliary cementitious materials to begin forming an initial cementing environment and distributing the oyster shell powder in the gaps between phosphogypsum particles and the pores between graded aggregates. When local clumping occurs in the dry mix, the amount of water added at one time is reduced and the wet mixing time is extended, allowing the water to gradually diffuse in the powder material. When the dry mix is ​​loose and difficult to form agglomerates, the subsequent water addition is increased within the target amount range to bring the wet mix to a mixable state. A mixable state means that the wet-mixed material can be continuously turned over in the mixing equipment without obvious dry powder clumps or mud clumps, and there is no obvious stratification of phosphogypsum, oyster shell powder, auxiliary cementitious materials, and graded aggregates when sampled and observed. After wet mixing, an initial mixture is obtained. In this embodiment, combinations 1 to 3 are all mixed in stages according to the sequence of premixing, secondary dry mixing, and wet mixing. The control results of each stage are shown in Table 4 below. Combination 1 phosphogypsum and fine-particle oyster shell powder 5 Pre-mixed material, medium-sized oyster shell powder, cement, fly ash, graded aggregate 4 Add water in two batches. 5 No obvious dry powder lumps or mud lumps Combination 2 phosphogypsum and fine-particle oyster shell powder 4 Pre-mixed material, medium-sized oyster shell powder, cement, fly ash, graded aggregate 4 Add water in two batches. 4 Mixed evenly with no obvious layering Combination 3 phosphogypsum and fine-particle oyster shell powder 3 Pre-mixed material, medium-sized oyster shell powder, cement, fly ash, graded aggregate 5 Add water three times 5 It can be flipped continuously without obvious layering. Table 4 Results of Segmented Mixing Control As shown in Table 4, combination 1 corresponds to a high-load matching state, so the premixing time is relatively longer, allowing fine-particle oyster shell powder to preferentially cover the surface of phosphogypsum particles and form a pre-neutralized material. Combination 3 corresponds to a low-acid gradation supplementation state and has a low moisture content of phosphogypsum, so water is added in three stages during wet mixing, allowing the mixing water to gradually disperse among the phosphogypsum, oyster shell powder, auxiliary cementitious materials, and graded aggregates.

[0052] In the initial mixture, fine-particle-size oyster shell powder is distributed on the surface of phosphogypsum particles and in the micropores between particles. Medium-particle-size oyster shell powder and graded aggregates work together to supplement the skeleton. Auxiliary cementitious materials are distributed in the contact area between phosphogypsum, oyster shell powder and graded aggregates.

[0053] In one specific implementation method, when the target feed combination corresponds to a high load matching state, S4 prioritizes the pre-mixing of phosphogypsum and fine-particle oyster shell powder, and then performs secondary dry mixing of pre-neutralized material, auxiliary cementitious material and graded aggregate, so that the phosphogypsum with high acid impurity load is covered with fine-particle oyster shell powder before entering the wet mixing.

[0054] In another specific implementation method, when the target feed combination corresponds to the low acid gradation supplementation state, S4 shortens the premixing time and improves the mixing uniformity of medium-sized oyster shell powder and graded aggregate in the secondary dry mixing stage, so that the oyster shell powder mainly undertakes the functions of pore filling and gradation supplementation.

[0055] Through the above processing, S4 transforms the target feed combination obtained in S3 into an initial mixture with the characteristics of first neutralization, then skeleton formation, and finally wet mixing activation. This allows phosphogypsum, oyster shell powder, auxiliary cementitious materials, and graded aggregates to no longer be simply mixed in a one-time feeding manner, but to participate in synergistic modification in sequence according to the acid neutralization requirements, particle filling requirements, and mixing moisture requirements.

[0056] S5. The initial mixture is aged and stabilized to obtain an aged mixture. The target feed combination is modified according to the release state and molding moisture content of the aged mixture, and a synergistic modified mixture for road base is output.

[0057] Specifically, the initial mixture obtained in S4 is transferred to the aging area for covered stacking and aging. Covering and stacking are used to reduce the rapid loss of surface moisture of the initial mixture and promote the redistribution of internal moisture in the initial mixture, so that the fine-particle oyster shell powder, phosphogypsum acidic components and auxiliary cementing materials can continue to be in contact in a relatively stable water-containing environment.

[0058] Aging stabilization refers to a short-term static treatment of the initial mixture before paving and compaction, allowing the acidic components in the phosphogypsum to continue contacting the calcium carbonate components in the oyster shell powder, and enabling the auxiliary cementing material to form an initial cementing environment between the powder particles. This reduces the risk of insufficient local neutralization and uneven moisture content caused by direct discharge. During aging, fine-particle-size oyster shell powder in the initial mixture continues to be distributed on the surface of the phosphogypsum particles and in the micropores between the particles, while medium-particle-size oyster shell powder and graded aggregate maintain the particle skeleton. The auxiliary cementing material is distributed at the interface between phosphogypsum, oyster shell powder, and graded aggregate, so that the aged mixture simultaneously possesses neutralization stability, particle filling, and an initial cementing foundation. After aging, the aged mixture is sampled and tested. In this embodiment, the initial mixtures of combinations 1 to 3 are all covered and stacked for aging for 12 hours. The release status and molding moisture content test results after aging are shown in Table 5 below. Combination 1 5.8 7.1 15.2 13.5-15.5 12 8 Release status Adaptation status Direct output Combination 2 6.1 6.8 14.4 13.5-15.5 15 10 Release status Adaptation status Direct output Combination 3 6.6 7.3 12.9 13.5-15.5 18 12 Release status Dry state Add water and mix again. Table 5. Aging Test Results and Correction Methods As shown in Table 5, after aging, the pH value of combination 1 increased from 5.8 to 7.1, and the soluble phosphorus and soluble fluoride contents decreased to below the release limit. This indicates that fine-particle oyster shell powder has an acid neutralization and soluble impurity stabilizing effect on phosphogypsum under high load. The release state of combination 3 after aging meets the requirements, but the moisture content is lower than the lower limit of the target molding moisture content range. Therefore, only mixing water is added and secondary mixing is carried out. No more oyster shell powder and auxiliary cementing materials are added to avoid destroying the already formed acid-base matching relationship and particle size distribution relationship. The testing items include pH value, moisture content, soluble phosphorus content, and soluble fluoride content. The pH value is used to determine whether the acidity neutralization meets the requirements for the release of road base mixtures, the moisture content is used to determine whether it is suitable for compaction, and the soluble phosphorus content and soluble fluoride content are used to determine whether migratable impurities are under control.

[0059] The release status is determined based on the pH value, soluble phosphorus content, and soluble fluoride content of the aged mixture. In this embodiment, the preset pH release range is 6.5-8.5, the release limit for soluble phosphorus content is 20 mg·L⁻¹, and the release limit for soluble fluoride content is 15 mg·L⁻¹. The release status refers to whether the aged mixture meets the conditions for entering the molding moisture content adjustment and road base application in terms of acid buffering and soluble impurity control. When the pH value of the aged mixture is within the preset pH release range, and the soluble phosphorus content and soluble fluoride content are not higher than the corresponding release limits, the release status is determined to be a releaseable status, indicating that the current aged mixture has completed the necessary acid buffering. The release status is determined as follows: when the pH value of the aging mixture is lower than the lower limit of the preset pH release range, and the soluble phosphorus content or soluble fluoride content is higher than the corresponding release limit, the release status is determined as the neutralization and adjustment state, indicating that the current aging mixture still has a problem of high acid impurity load, and fine-grained oyster shell powder needs to be added and wet-mixed for aging again; when the pH value of the aging mixture is within the preset pH release range, but the soluble phosphorus content or soluble fluoride content is higher than the corresponding release limit, the release status is determined as the gelation stabilization and adjustment state, indicating that the acidity of the current aging mixture has been buffered but the control of migratable impurities is insufficient, and auxiliary gelling materials need to be added and wet-mixed for aging again. The moisture content of the aged mixture is determined by comparing it with the target moisture content range. The target moisture content range refers to the allowable moisture content range corresponding to the road base mixture reaching the design compaction degree, which can be determined based on compaction tests, field compaction tests, or road base construction control requirements. When the moisture content of the aged mixture is lower than the lower limit of the target moisture content range, the moisture content is determined to be slightly dry, and mixing water is added for secondary mixing to redistribute the added water among phosphogypsum, oyster shell powder, auxiliary cementitious materials, and graded aggregates. When the moisture content of the aged mixture is higher than the upper limit of the target moisture content range, the moisture content is determined to be slightly wet, and a re-drying material is added for secondary mixing. The re-drying material is a mixture of at least two of the following: dry oyster shell powder, dry graded aggregates, and dry auxiliary cementitious materials. When the moisture content of the aged mixture is within the target molding moisture content range, the molding moisture content is determined as the suitable state, and the current discharge conditions are kept unchanged, so that the aged mixture can be directly output as a co-modified mixture for road base.

[0060] In this embodiment, modifying the target feed combination does not alter the initial feeding process that has already been weighed and mixed. Instead, based on the actual test results of the aging mixture, it determines the amount of oyster shell powder, auxiliary cementitious material, mixing water, or re-dried material that needs to be added to the current aging mixture. This addition correction result serves as the basis for updating the target feed combination for subsequent batches of the same type. The addition correction method for the aging mixture is determined based on the release status and the moisture content of the formed product. The amount of oyster shell powder added to the current aging mixture is primarily determined based on the state requiring neutralization and re-adjustment; the amount of auxiliary cementitious material added is primarily determined based on the state requiring cementitious stabilization and re-adjustment; and the amount of mixing water and re-dried material added is primarily determined based on the moisture content of the formed product. When the release status requires neutralization and adjustment, fine-grained oyster shell powder is added and the mixture is wet-mixed and aged again to ensure continued contact between the fine-grained oyster shell powder and the acidic components in the phosphogypsum. When the release status requires gelation stabilization and adjustment, auxiliary gelling materials are added and the mixture is wet-mixed and aged again to further stabilize soluble phosphorus and soluble fluorine in the gelation system. When the molding moisture content is relatively dry, mixing water is added and the mixture is mixed a second time. When the molding moisture content is relatively wet, dehydrated material is added and the mixture is mixed a second time. The corrected addition amount is used for the current aging mixture, and the corresponding correction results are fed back into the determination process of the target feed combination for subsequent batches.

[0061] In one specific implementation method, when the release status is a state requiring neutralization and adjustment and the forming moisture content is a slightly wet state, fine-particle-size dry oyster shell powder is preferentially added as part of the drying material, so that it can simultaneously undertake the functions of acid neutralization and moisture content adjustment.

[0062] In another specific implementation method, when the release state is a state requiring gelation stabilization and the molding moisture content is a suitable state, auxiliary gelling material is added and then a short-term secondary wet mixing is performed, while maintaining the amount of mixing water added unchanged, so that the correction focuses on improving the stabilization effect of soluble impurities.

[0063] In another specific implementation method, when the release status is releaseable and the molding moisture content is relatively dry, only mixing water is added and a second mixing is performed. No more oyster shell powder and auxiliary cementitious materials are added to avoid changing the already formed acid-base matching relationship and particle size distribution relationship.

[0064] The aged mixture, after correction for its release state and moisture content during molding, is output as a co-modified mixture for road base courses. This co-modified mixture contains uniformly dispersed phosphogypsum particles, oyster shell powder filling structures, auxiliary cementitious material interface distribution, and a moisture content suitable for compaction. The output co-modified mixture can be used for road base paving and compaction. After molding, its unconfined compressive strength, compaction degree, water stability coefficient, leachate soluble phosphorus content, and leachate soluble fluoride content are tested. The unconfined compressive strength is used to evaluate the load-bearing capacity of the base material, the compaction degree to evaluate the on-site compaction density, and the water stability coefficient to evaluate the strength retention after immersion in water. The leaching capacity, including the soluble phosphorus content and soluble fluoride content of the leachate, is used to evaluate the control effect of migratable impurities. The road base course suitability evaluation results are generated based on unconfined compressive strength, compaction degree, water stability coefficient, and leaching indicators. In this embodiment, the synergistically modified mixtures output from combinations 1 to 3 are molded and cured, and their unconfined compressive strength, compaction degree, water stability coefficient, and leaching indicators are tested. A fixed-ratio control group is set up as a comparison. The fixed-ratio control group does not distinguish between the acidic impurity load characterization of phosphogypsum and the calcium source adjustment characterization of oyster shell powder, and no correction is made based on the molding moisture content after aging. The test results are shown in Table 6 below. Combination 1 3.0 4.5 97.5 0.86 12 8 Combination 2 2.8 4.2 97.2 0.84 15 10 Combination 3 2.6 4.0 96.8 0.82 18 12 Fixed ratio control group 2.1 3.2 95.1 0.74 28 18 Table 6. Results of Road Base Course Suitability Test As shown in Table 6, the 7-day unconfined compressive strength, 28-day unconfined compressive strength, compaction degree, and water stability coefficient of combinations 1 to 3 are all higher than those of the fixed-ratio control group, while the soluble phosphorus content and soluble fluoride content of the leachate are lower than those of the fixed-ratio control group. The above results indicate that the present invention, by matching the acid impurity load characterization of phosphogypsum with the calcium source adjustment characterization of oyster shell powder, and by supplementing and correcting according to the release state and molding moisture content of the aged mixture, and by feeding the supplementary correction results back to the target feed combination of subsequent batches, can improve the strength stability, compaction stability, water stability, and leaching control effect of road base mixtures under different batches of solid waste raw materials.

[0065] The results of the road base course suitability evaluation are used to determine whether the current batch of co-modified mixtures meets the requirements for road base course use, and to identify the material items that need to be optimized in the target feed combination.

[0066] When the road base course suitability evaluation results show insufficient unconfined compressive strength, the evaluation results will be fed back to the cementitious stability requirement matching relationship in the dual-solid-waste synergistic modification state, and the target addition amount of auxiliary cementitious materials or the target addition amount of optimized graded aggregates will be increased in subsequent batches. When the road base course suitability evaluation results show insufficient compaction or low water stability coefficient, the evaluation results will be fed back to the particle filling capacity and moisture balance requirement matching relationship in the dual-solid-waste synergistic modification state, and the target addition amounts of medium-sized oyster shell powder, graded aggregates, mixing water, and re-dried material will be adjusted in subsequent batches. When the road base course suitability evaluation results show that the leaching index does not meet the requirements, the evaluation results will be fed back to the neutralization requirement and cementitious stability requirement matching relationship in the dual-solid-waste synergistic modification state, and the target addition amount of fine-sized oyster shell powder or auxiliary cementitious materials will be increased in subsequent batches.

[0067] Through the above processing, S5 connects aging stabilization, release judgment, molding moisture content correction and finished product evaluation feedback into a closed loop, enabling the synergistic modified mixture to complete acid impurity stabilization and moisture content correction before output, and enabling the target feed combination of subsequent batches to be continuously corrected based on the road base suitability evaluation results.

[0068] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells, characterized in that, The method includes: S1. Perform raw material state testing on the phosphogypsum to be used to obtain phosphogypsum state data, and generate a characterization of the acidic impurity load of phosphogypsum based on the phosphogypsum state data. S2. Pre-treat oyster shells to obtain oyster shell powder, perform calcium source state detection on the oyster shell powder to obtain oyster shell powder state data, and generate oyster shell powder calcium source regulation characterization based on the oyster shell powder state data. S3. Match the acidic impurity load characterization of the phosphogypsum with the calcium source regulation characterization of the oyster shell powder to generate a dual solid waste synergistic modification state, and determine the target feeding combination of the road base mixture based on the dual solid waste synergistic modification state. S4. According to the target feeding combination, phosphogypsum, oyster shell powder, auxiliary cementitious materials, graded aggregates and mixing water are mixed in stages to obtain the initial mixture; S5. The initial mixture is aged and stabilized to obtain an aged mixture. The target feed combination is modified according to the release state and molding moisture content of the aged mixture, and a synergistic modified mixture for road base is output.

2. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 1, characterized in that, The raw material condition of phosphogypsum was tested to obtain phosphogypsum condition data, including: Obtain batch information of the phosphogypsum to be used; The phosphogypsum to be used is broken down and sieved to obtain the phosphogypsum to be tested; The moisture content, pH value, soluble phosphorus content, and soluble fluorine content of the phosphogypsum to be tested were determined. The state data of the phosphogypsum is composed of the moisture content, pH value, soluble phosphorus content, and soluble fluorine content.

3. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 2, characterized in that, Based on the aforementioned phosphogypsum state data, a characterization of the acidic impurity load of phosphogypsum is generated, including: The acidity of phosphogypsum is determined based on the pH value. The degree of soluble impurities in phosphogypsum is determined based on the soluble phosphorus content and soluble fluorine content. The degree of moisture shift in phosphogypsum is determined based on the stated moisture content. The acidity level of phosphogypsum, the degree of soluble impurities in phosphogypsum, and the degree of moisture shift in phosphogypsum are combined to generate a characterization of the acid impurity load of phosphogypsum.

4. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 1, characterized in that, Oyster shells are pretreated to obtain oyster shell powder. The calcium source state of the oyster shell powder is then detected to obtain oyster shell powder state data, including: The oyster shells are washed, dried, crushed and sieved in sequence to obtain oyster shell powder with different particle size ranges; The effective calcium carbonate content, particle size distribution, moisture content, and organic residue level of the oyster shell powder were tested. The oyster shell powder state data is composed of the effective calcium carbonate content, particle size distribution, moisture content, and degree of organic residue.

5. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 4, characterized in that, Based on the oyster shell powder state data, a characterization of oyster shell powder calcium source regulation is generated, including: The acid neutralization capacity of oyster shell powder is determined based on the effective calcium carbonate content. The pore-filling capacity of the oyster shell powder is determined based on the particle size distribution. The mixing and compatibility of oyster shell powder is determined based on the moisture content and degree of organic residue. The acid neutralization ability, pore filling ability and mixing and adaptability are combined to generate the calcium source regulation characterization of the oyster shell powder.

6. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 1, characterized in that, The acidic impurity load characterization of the phosphogypsum was matched with the calcium source regulation characterization of the oyster shell powder to generate a dual solid waste synergistic modification state, including: The neutralization requirement, moisture balance requirement, and gel stability requirement of phosphogypsum are determined based on the acid impurity load characterization of the phosphogypsum. The calcium source supply capacity, particle filling capacity, and mixing and water absorption capacity of oyster shell powder were determined based on the calcium source regulation characterization of oyster shell powder. By matching the neutralization requirement with the calcium source supply capacity, the moisture balance requirement with the mixing and water absorption capacity, and the gelation stabilization requirement with the particle filling capacity, the dual solid waste synergistic modification state is generated.

7. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 6, characterized in that, The target feed combination for road base course mixture is determined based on the aforementioned dual solid waste synergistic modification state, including: Based on the matching results between the neutralization demand and the calcium source supply capacity, the target amount of oyster shell powder to be added is determined; Based on the matching results between the gel stability requirements and the particle filling capacity, the target addition amounts of auxiliary cementitious materials and graded aggregates are determined. Based on the matching results between the moisture balance requirements and the mixing water absorption capacity, determine the target amount of mixing water and the amount of reclaimed dry material. The target feeding combination is composed of the target amount of oyster shell powder, the target amount of auxiliary cementitious material and graded aggregate, the target amount of mixing water, and the reserved amount of reclaimed material.

8. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 1, characterized in that, According to the target feed combination, phosphogypsum, oyster shell powder, auxiliary cementitious materials, graded aggregates, and mixing water are mixed in stages to obtain an initial mixture, including: Phosphogypsum was premixed with fine-particle oyster shell powder for acid neutralization to obtain a pre-neutralized material; The pre-neutralized material is dry-mixed with oyster shell powder for gradation supplementation, auxiliary cementitious materials and graded aggregates to obtain dry-mixed material; Add mixing water to the dry mixture for wet mixing, so that the oyster shell powder is distributed in the gaps between the phosphogypsum particles, to obtain the initial mixture.

9. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 1, characterized in that, The initial mixture is aged and stabilized to obtain an aged mixture. The target feed combination is then modified based on the release state and molding moisture content of the aged mixture, including: The initial mixture is covered and piled up for aging to obtain an aged mixture; The pH value, moisture content, soluble phosphorus content, and soluble fluoride content of the aged mixture were tested. The release status is determined based on the pH value, soluble phosphorus content, and soluble fluorine content of the aged mixture. The molding moisture content is determined based on the comparison between the moisture content of the aged mixture and the target molding moisture content range; Based on the release status and the moisture content of the molding, adjust the amount of oyster shell powder, auxiliary gelling material, mixing water, and re-drying material added.

10. The method for preparing road base course by synergistic modification of solid waste phosphogypsum and oyster shells according to claim 9, characterized in that, The output, after being used for the co-modified mixture of road base course, also includes: The unconfined compressive strength, compaction degree, water stability coefficient and leaching index of the synergistically modified mixture were tested. The road base course suitability evaluation results are generated based on the unconfined compressive strength, compaction degree, water stability coefficient, and leaching index. The road base suitability evaluation results are fed back to the dual solid waste synergistic modification status to update the target feed combination for subsequent batches.

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