Modified ardealite-based artificial aggregate and application thereof in road base

Abstract

The invention discloses a modified ardealite-based artificial aggregate and application thereof in a road base, and a preparation method of the artificial aggregate comprises the following steps: crushing and screening ardealite, mixing and stirring with composite modified slurry, and forming and curing to obtain the modified ardealite-based artificial aggregate. According to the preparation method, the phosphogypsum is subjected to enhancement and hydrophobic modification through the composite modified slurry, the prepared artificial aggregate has excellent mechanical properties and water stability, the 24-hour water absorption rate is lower than 5%, the surface hydrophobic angle is larger than 150 degrees, the dissolution rate of soluble phosphorus and soluble fluorine is reduced by 85% or above compared with that of unmodified homologous phosphogypsum, and the prepared artificial aggregate has a good application prospect. The artificial aggregate is used as a main aggregate for a road base material, and the unconfined compressive strength and the strength retention rate after water immersion of the artificial aggregate are subjected to formula adjustment according to a road grade or a structural layer position and are not lower than those of existing cement concrete; bulk and high-value utilization of the ardealite is realized, and the method has remarkable environmental protection and economic benefits.

Description

A modified phosphogypsum-based artificial aggregate and its application in road base courses Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and building materials technology, specifically relating to a modified phosphogypsum-based artificial aggregate and its application in road base courses. Background Technology

[0002] Phosphogypsum is a major industrial byproduct of wet-process phosphoric acid production, primarily composed of calcium sulfate dihydrate (CaSO4·2H2O). my country has a large stockpile of phosphogypsum with low comprehensive utilization rates. This stockpiling not only occupies land but also poses potential environmental risks due to impurities such as soluble phosphorus and fluorine. Currently, the application of phosphogypsum in the building materials sector is mainly limited to the production of low-value-added products such as gypsum board and cement retarders, or its use after calcination, resulting in high energy consumption. Directly utilizing undisturbed phosphogypsum as a road base material or concrete admixture suffers from inherent defects such as low strength, poor water resistance (softening and disintegration upon contact with water), poor volume stability, and environmental pollution from leaching of soluble substances, severely limiting its large-scale, high-value engineering applications.

[0003] Although existing technologies (such as the CJJ / T286-2018 standard) propose methods for stabilizing soils (including gypsum-containing soils) using traditional cementitious materials such as cement and lime, their effectiveness is limited, particularly regarding phosphogypsum's water resistance and long-term stability. There are no reports of integrating performance enhancement and surface hydrophobic modification of phosphogypsum to prepare an artificial aggregate that can directly replace natural aggregates in high-performance concrete. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified phosphogypsum-based artificial aggregate and its preparation method that can improve the mechanical properties and water resistance of phosphogypsum and inhibit the leaching of harmful substances. This invention also provides the application of the modified phosphogypsum-based artificial aggregate in road base courses to absorb large quantities of phosphogypsum.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing modified phosphogypsum-based artificial aggregate, comprising the following steps: S1. Raw material pretreatment: Selecting wet phosphogypsum material, or phosphogypsum powder with a particle size ≤1.5mm after crushing and sieving; crushing and sieving the phosphogypsum, and crushing it by ball milling to reduce the particle size and adjust the particle size distribution, so that the crushed phosphogypsum powder has a particle size ≤1.5mm, which is more uniformly distributed, increases the bulk density, and increases the uniformity of mixing with the composite modified slurry, reactivity and molding performance in subsequent processes. Meanwhile, the increased surface area of ​​the crushed particles facilitates more uniform mixing with quicklime in the auxiliary cementitious material, thereby adjusting the pH value, reducing the risk of corrosion to the equipment, improving strength, and shortening the setting time; S2. Preparation of composite modified slurry: Mix nano-active silicon superhydrophobic material with 30 times the amount of water and stir evenly to form a composite modified slurry; the nano-active silicon superhydrophobic material includes tetraethoxysilane, octyltriethoxysilane and nano-active silicon mixed in a mass ratio of 30:30:40, containing a small amount of ethanol and hydrochloric acid as solvent and catalyst, wherein the particle size distribution D50 of the nano-active silicon is 12~20nm.

[0006] S3. Modification treatment: 83% of the phosphogypsum powder obtained in step S1 is mixed and stirred with the composite modified slurry from step S2 and auxiliary cementitious materials such as quicklime and stone powder, so that the slurry evenly coats or penetrates the surface and internal pores of the phosphogypsum particles; the amount of the composite modified slurry is based on the weight of the phosphogypsum powder plus the auxiliary cementitious materials, and its addition ratio is 0.5% to 2% of the total weight, depending on the different requirements of the product.

[0007] S4. Molding and curing: After the modified phosphogypsum mixture is piled up and moderately compacted, it is then cured at room temperature or under standard curing conditions (temperature 20±2℃, humidity ≥90%) for 7~28 days to obtain the modified phosphogypsum-based artificial aggregate.

[0008] Further, in step S3 of the present invention, the amount of the auxiliary cementing material is 15-20% of the dry basis weight of the phosphogypsum powder; the auxiliary cementing material is selected from one or more of quicklime, stone powder, slag powder, and fly ash, preferably, the ratio of modified phosphogypsum to cementing material (slag powder + quicklime) is 100: (8-10).

[0009] Furthermore, in step S4 of the present invention, the molding is compression molding or stacking and compaction; the curing conditions are standard curing with a temperature of 20±2℃ and a relative humidity of not less than 90%.

[0010] Secondly, the present invention provides a modified phosphogypsum-based artificial aggregate prepared by the above-described preparation method. This aggregate possesses a micro-nano rough surface structure and low surface energy characteristics, with a 24-hour water absorption rate of less than 5%, and its surface exhibits superhydrophobicity, a static water contact angle greater than 150°, and its crushing value meets the relevant specifications for road aggregates.

[0011] Furthermore, the hydrophobicity of the artificial aggregate described in this invention can ensure the reduction of the adverse effects of rainwater or groundwater on the soluble phosphorus and soluble fluoride of phosphogypsum on road engineering. The aggregate was tested in a 24-hour water immersion test, and the results showed that it reduced the phosphorus and fluoride content by more than 85% compared to the unmodified homologous phosphogypsum.

[0012] Thirdly, the present invention provides the application of the above-mentioned modified phosphogypsum-based artificial aggregate in road engineering, wherein the modified phosphogypsum-based artificial aggregate is used as aggregate and mixed with cementitious materials for paving the base or subbase of roads.

[0013] Furthermore, the modified phosphogypsum-based artificial aggregate of the present invention is applied to the base or subbase of paved roads, comprising: 20-30% of natural crushed stone with a diameter of 5-31.5mm as cementing material, 5-10% of PO42.5 cement, 65-75% of modified phosphogypsum-based artificial aggregate, and 5-7% of the total weight of the above materials as water.

[0014] Furthermore, the cementitious material is PO42.5 cement, 70% of modified phosphogypsum-based artificial aggregate of various gradations, 30% of natural crushed stone, and composite modified slurry (containing nano-active silicon superhydrophobic material accounting for 0.2% of the weight of water) and water.

[0015] The modified phosphogypsum-based artificial aggregate of the present invention is used as a main aggregate or to partially replace natural aggregate, and is mixed with cementitious materials and water for use in the subbase, base course or pavement functional layer of roads.

[0016] This invention has the following beneficial effects: 1. This invention mixes nano-active silicon superhydrophobic material with 30 times its volume of water and stirs it evenly to form a hydrophobic composite modified slurry; the composite modified slurry is then mixed and stirred with crushed and sieved phosphogypsum particles. During the stirring process, the organosilicon resin in the composite modified slurry provides a silicon-oxygen-silicon (Si-O-Si) inorganic network (siloxane network) structure, giving the phosphogypsum hardness, adhesion, weather resistance, and chemical stability, forming a three-dimensional network structure on the substrate surface; long-chain alkyl silanes are key hydrophobic components. One end (alkoxy group) of these silanes chemically bonds with the active silicon network, while the long-chain alkyl group at the other end is arranged on the phosphogypsum surface like a brush, greatly reducing the surface energy to achieve superhydrophobic properties; hydrophobic nano-silica is included to construct a micro-nano rough structure, forming a micron-nano level rough structure on the surface and inside of the material during the curing process. When low surface energy chemicals cover this rough structure, they can trap air to the maximum extent to form an air cushion, preventing water from wetting, thus achieving the "lotus effect". Meanwhile, impurities in phosphogypsum are encapsulated within the phosphogypsum particles by the composite modified slurry, reducing the leaching of harmful ions. By integrating the modification of phosphogypsum into artificial aggregates that improve strength, water resistance, and environmental friendliness, it directly replaces natural aggregates, solving the problems of phosphogypsum softening upon contact with water and the leaching of harmful ions.

[0017] 2. The artificial aggregate preparation process of the present invention is simple, does not require high-temperature calcination, has low energy consumption, and the resulting artificial aggregate has stable performance. It can be applied to road base engineering with high requirements for strength, water resistance and environmental protection, breaking through the limitations of traditional phosphogypsum applications. Solid waste can be industrialized and disposed of in batches, realizing the maximum resource utilization of phosphogypsum.

[0018] 3. The application method of the modified phosphogypsum-based artificial aggregate of the present invention in roads is similar to that of conventional aggregates, without changing the existing main construction process, and is easy to promote. Attached Figure Description

[0019] Figure 1 is a diagram of a superhydrophobic stone block made from the modified phosphogypsum-based artificial aggregate prepared in Example 1 of the present invention; Figure 2 is a diagram of a superhydrophobic surface similar to a lotus leaf formed by applying the modified phosphogypsum-based artificial aggregate prepared in Example 1 of the present invention to the surface of a roadbed; Figure 3 is a diagram of the modified phosphogypsum-based artificial aggregate prepared in Example 1 of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to embodiments and comparative examples. However, the scope of protection of the present invention is not limited thereto.

[0021] The following examples use phosphogypsum with a CaSO4·0.5H2O content > 62%, a 2-hour flexural strength ≥ 3.1 MPa, and a 2-hour compressive strength ≥ 6 MPa.

[0022] The following Examples 1-2 and Comparative Examples 1-3 use nano-active silicon superhydrophobic materials, including tetraethoxysilane, octyltriethoxysilane and nano-active silicon mixed in a mass ratio of 30:30:40, containing a small amount of ethanol and hydrochloric acid as solvent and catalyst, wherein the particle size distribution D50 of the nano-active silicon is 12-20 nm; or nano-active silicon superhydrophobic materials purchased directly from Yufa Technology Co., Ltd. are used.

[0023] The following examples illustrate the preparation of the composite modified slurry: Nano-active silicon superhydrophobic material was mixed with 30 times its volume of water and stirred until homogeneous to form the composite modified slurry. Example 1

[0024] Wet phosphogypsum was mixed with a composite modified slurry at 0.5% of its content. This slurry was then thoroughly mixed with 83% phosphogypsum, 7% quicklime, and 10% fly ash, as shown in Figure 3. Hydrophobic nano-silica constructed a micro-nano rough structure. During curing, this formed a micron-nano level rough structure on the material's surface and inside. When low surface energy chemicals covered this rough structure, they could trap air to the maximum extent, forming an air cushion that prevented water from wetting, achieving a "lotus effect." Simultaneously, impurities in the phosphogypsum were encapsulated within the phosphogypsum particles by the composite modified slurry, reducing the leaching of harmful ions. The mixture was poured into a mold and pressed at 10 MPa for 30 seconds to form a stone specimen as shown in Figure 1. After demolding, the specimen was placed in a standard curing room (20℃, 95%RH) for 28 days to obtain modified phosphogypsum artificial aggregate specimen A.

[0025] Comparative Example 1: Except for the absence of composite modified slurry, the same as in Example 1 was used to prepare test block B.

[0026] Comparative Example 2: Only 2% of nano-active silicon superhydrophobic material was added, without quicklime and fly ash, and the rest was the same as in Example 1, to obtain test block C.

[0027] Comparative Example 3: Only quicklime and fly ash were added, without the addition of nano-active silicon superhydrophobic material, and the rest was the same as in Example 1, to obtain test block D.

[0028] The testing methods used in Examples 1-2 and Comparative Examples 1-3 are as follows: 1. The 7-day unconfined compressive strength of the material is tested in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTGE51-2009).

[0029] 2. Specimens were molded according to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009). The specimens were cured for 28 days, then immersed in water for 24 hours, and then dried in a 40℃ oven for 24 hours. This process constitutes one wet-dry cycle. The cycle was repeated four times. The unconfined compressive strength and specimen mass were tested, and the strength loss and mass loss rate were calculated. Strength loss rate = (P - P) / P; where P is the strength before the wet-dry cycle, and P is the strength after four wet-dry cycles. Mass loss rate = (M - M / M); where M is the strength before the wet-dry cycle, and M is the strength after four wet-dry cycles.

[0030] 3. Using samples with tested 28 mm unconfined compressive strength, leachate was prepared using the "Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method" (H 557-2010). Total phosphorus and fluoride in the leachate were tested to meet the requirements of the "Surface Water Environmental Quality Standard" (GB3838-2002).

[0031] The unconfined compressive strength (UCS), strength retention after 24 hours of immersion in water, water absorption rate after 24 hours, contact angle, water-soluble fluoride ion concentration, and water-soluble phosphorus pentoxide content of test blocks A, B, C, and D were tested. The results are shown in Table 1.

[0032] Table 1. Performance test results of specimens made from the artificial aggregate of the present invention and the aggregate of the comparative example.

[0033] The results show that the artificial aggregate prepared by the modified composite slurry of the present invention has significantly improved strength (especially late-stage strength) and water resistance. Its strength retention rate and low water absorption after immersion demonstrate its excellent long-term strength and water resistance stability. Example 2

[0034] By mass, 70 parts of modified phosphogypsum artificial aggregate with a particle size of 5-31.5 mm prepared in Example 1, 30 parts of natural crushed stone (5-31.5 mm), 8 parts of PO42.5 cement, and nano-active silicon superhydrophobic material (0.2% of water mass) were mixed evenly to obtain a road base mixture. Specimens were prepared and cured according to the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009). The unconfined compressive strength after 7 days was measured to be 4.8 MPa, and the strength after 24 hours of immersion in water was 5.9 MPa, as shown in Figure 2. The surface of the roadbed formed a superhydrophobic surface pattern similar to a lotus leaf, exhibiting excellent water stability and meeting the strength requirements of heavy traffic road base.

[0035] This invention creatively proposes a comprehensive solution for transforming industrial solid waste phosphogypsum into high-performance building materials. By deeply processing phosphogypsum through composite modified slurry, it is prepared into artificial aggregates that can be directly used in harsh engineering environments, providing a new way for the high-value and large-scale utilization of phosphogypsum, a major solid waste.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing modified phosphogypsum-based artificial aggregate, characterized in that, Includes the following steps: S1. Raw material pretreatment: Select wet phosphogypsum or phosphogypsum powder with a particle size ≤1.5mm after crushing and sieving; S2. Preparation of composite modified slurry: Mix nano-active silicon superhydrophobic material with 30 times the amount of water and stir evenly to form a composite modified slurry; S3. Modification treatment: Mix 83% of the phosphogypsum powder from step S1 with the composite modified slurry and auxiliary cementitious material from step S2; The amount of nano-active silicon superhydrophobic material is 0.5~2% of the total weight of phosphogypsum powder and auxiliary cementitious material; S4. Molding and curing: Cure the modified phosphogypsum from step S3 for 7~28 days to obtain modified phosphogypsum-based artificial aggregate.

2. The preparation method according to claim 1, characterized in that, In step S3, the amount of the auxiliary cementing material is 15-20% of the dry basis weight of the phosphogypsum powder; the auxiliary cementing material is selected from one or more of quicklime, stone powder, slag powder, and fly ash.

3. The preparation method according to claim 1, characterized in that, In step S4, the molding is either compression molding or stacking and compaction; the curing conditions are standard curing with a temperature of 20±2℃ and a relative humidity of not less than 90%.

4. A modified phosphogypsum-based artificial aggregate prepared by the preparation method according to any one of claims 1 to 3, characterized in that, The artificial aggregate has a 24-hour water absorption rate of less than 5% and its surface has a superhydrophobic coating with a static water contact angle greater than 150°.

5. The modified phosphogypsum-based artificial aggregate according to claim 4, characterized in that, The crushing value of the artificial aggregate is no more than 30%, and the leaching concentration of soluble phosphorus and soluble fluoride ions is reduced by more than 85% compared with that of unmodified homologous phosphogypsum.

6. The application of the modified phosphogypsum-based artificial aggregate according to claim 4 or 5 in road engineering, characterized in that, The modified phosphogypsum-based artificial aggregate is used as an aggregate and mixed with cementitious materials for use in the base or subbase of roads.

7. The application according to claim 6, characterized in that, It is used for the base or subbase of road paving, including: 20-30% natural crushed stone with a diameter of 5-31.5mm, 5-10% PO42.5 cement, 65-75% modified phosphogypsum-based artificial aggregate, and water of 5-7% of the total weight of the above materials.

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