Phosphogypsum road base water stable material and construction method thereof

Abstract

The application discloses a kind of phosphogypsum road base water stable material and its construction method, by weight fraction, including calcined phosphogypsum 300~2000 parts, cement clinker 300~2000 parts, limestone 50~500 parts, toughening agent 1~10 parts, high-strength water-resistant agent 10~200 parts, sodium bentonite 50~100 parts, glass fiber 1~10 parts;The high-strength water-resistant agent is magnesium chloride, magnesium oxide, dimethyl chlorosilane is added with 1:1:0.05~0.5, the toughening agent is polyvinyl alcohol and EVA is mixed with 1:0.5~1 to form.The water stable material produced by using industrial by-product phosphogypsum calcined building gypsum as raw material has strong water resistance, high compressive strength and surface hardness, and is resistant to cracking caused by expansion;After premixing at construction site, road construction is carried out, the setting time meets the construction requirements, the water-soluble fluorine ion concentration of road surface is less than 3.50mg / L, water-soluble phosphorus pentoxide is not detected, the liquid leached under rainwater washing has no environmental pollution, the water stable material of the application enables the engineering of solid waste to be batched, and realizes the maximum resource utilization of phosphogypsum.

Description

A phosphogypsum road base water-stabilized material and its construction method Technical Field

[0001] This invention relates to the field of phosphogypsum resource utilization technology, specifically to a phosphogypsum road base water-stabilized material and its construction method. Background Technology

[0002] The large-scale accumulation of phosphogypsum not only occupies land resources but also severely pollutes the environment and groundwater due to its high content of harmful impurities. Unlike desulfurization gypsum, phosphogypsum consists of 5-50 micrometer grayish-black particles with a crystal water content of 20-25%. Its main components are calcium sulfate dihydrate, residual phosphoric acid, fluorides, acid-insoluble substances, and organic matter, making it extremely unstable and resulting in low utilization. Expanding the utilization pathways of phosphogypsum and continuing to promote its use in cement production and new building materials is crucial. Improving the purification and treatment levels of complex and difficult-to-use bulk solid wastes like phosphogypsum will create conditions for its comprehensive utilization.

[0003] Currently, the utilization of phosphogypsum waste typically includes: 1. Adding 1-10% to building gypsum to produce wall materials, such as partition wall materials. However, the dosage is relatively small, and its use in producing wall decoration materials is limited due to its gray-black color, which makes it unsuitable for decoration; 2. Using it as backfill material in mining operations. However, due to the complex and diverse geographical conditions of mines, and the fact that backfill materials are ductile failure materials, it may lead to unstable ground pressure, deep-well rock bursts, surface subsidence, and easy collapse of mined-out areas, which poses a significant risk to mining safety. Therefore, its application is not yet well-established; 3. Using phosphogypsum as a substitute for cement-stabilized crushed stone base courses in road concrete pavement. This could increase the utilization of phosphogypsum, expand its application scope, and reduce the mining of non-renewable resources such as sand and stone, as illustrated in publication number CN117361979A. The patent, titled "A Crack-Resistant and Water-Resistant Phosphogypsum Road Base Material and Its Preparation Method," uses 15-25% calcined phosphogypsum and 43-47% natural coarse aggregate. It consumes a large amount of natural coarse aggregate, which is difficult to regenerate in the short term. While adding EVA and PU emulsions reduces cracking in the road base material, PU emulsion is prone to aging and has poor durability. Its density, hydraulic properties, and other mechanical properties are not high. Over long-term use, the road surface's load-bearing capacity, compressive strength, water resistance, and crack resistance decrease, leading to road surface fragility or cracking. Furthermore, the utilization rate of phosphogypsum is limited. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a phosphogypsum road base water-stabilized material and its construction method that can absorb large amounts of phosphogypsum, has excellent compressive strength, water resistance and crack resistance, and is easy to construct.

[0005] The technical solution of the present invention is as follows:

[0006] A phosphogypsum road base water-stabilized material, by weight, comprises 300-2000 parts calcined phosphogypsum, 300-2000 parts cement clinker, 50-500 parts limestone, 1-10 parts toughening agent, 10-200 parts high-strength water-resistant agent, 50-100 parts sodium bentonite, and 1-10 parts glass fiber; wherein the high-strength water-resistant agent is magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.05-0.5, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:0.5-1.

[0007] A phosphogypsum road base water-stabilized material, by weight, comprises 1800 parts calcined phosphogypsum, 2000 parts cement clinker, 100 parts limestone, 10 parts toughening agent, 150 parts high-strength water-resistant agent, 50 parts sodium bentonite, and 5 parts glass fiber; wherein the high-strength water-resistant agent is magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.5, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:1.

[0008] Furthermore, the calcined phosphogypsum described in this invention is calcined building gypsum with a CaSO4·0.5H2O content >60%, a 2h flexural strength ≥3MPa, and a 2h compressive strength ≥6MPa.

[0009] The water-soluble fluoride ion concentration of the phosphogypsum road base water-stabilized material described in this invention is less than 3.50 mg / L, and water-soluble phosphorus pentoxide was not detected.

[0010] This invention provides a method for preparing phosphogypsum road base water-stabilized material, the method steps of which are as follows:

[0011] S1. Weigh the raw materials according to the proportion of the phosphogypsum road base water-stabilized material;

[0012] S2. Mix calcined phosphogypsum, cement clinker, limestone, magnesium chloride, magnesium oxide, sodium bentonite, and glass fiber evenly to prepare a base material;

[0013] S3. Dissolve polyvinyl alcohol and mix it with EVA solution in a certain proportion to prepare toughening agent solution;

[0014] S4. Add water to the base material described in step S2, with the water amounting to 50-70% of the total base material. Stir until homogeneous, then add toughening agent and diluted dimethylchlorosilane in sequence and continue stirring to produce a phosphogypsum road base water-stabilized material with an initial setting time greater than 4 hours and a final setting time of not less than 6 hours.

[0015] This invention provides a construction method for phosphogypsum road base water-stabilized material. The roadbed is poured using a layered paving method. From the bottom layer to the top layer of the road base, a 15-20cm layer of crushed stone subbase with a particle size of 5-60mm and a compaction coefficient >0.80 is laid, followed by a 35-45cm layer of phosphogypsum road base water-stabilized material, an ES-2 slurry seal coat, a 6-10cm layer of AC-25 coarse asphalt concrete, a 4-8cm layer of AC-20 medium-grained asphalt concrete, and a 2-5cm layer of AC-13 fine-grained modified asphalt concrete. After construction, the material is covered with a film for curing for 8 days.

[0016] Furthermore, during the layered paving process, mechanical compaction is used to compact the material twice, resulting in a compaction coefficient of 0.98.

[0017] Furthermore, the two compaction processes are as follows: the initial compaction is performed by a vibratory roller at a speed of 1.5~1.7 km / h, with static compaction once; the secondary compaction is performed by a vibratory roller at a speed of 1.8~2.2 km / h, with light vibration twice; the secondary compaction is performed by a vibratory roller at a speed of 1.8~2.2 km / h, with heavy vibration twice; and the final compaction is performed by a pneumatic tire roller at a speed of 1.5~1.7 km / h, with compaction once or twice.

[0018] Furthermore, the compaction process involves sequentially applying pressure, light vibration, heavy vibration, and then applying pressure to finish the surface until the surface is essentially free of wheel tracks. During compaction, the wheel tracks overlap by at least 1 / 3 of the wheel width. After compaction, the degree of compaction is tested using the sand-filling method. The degree of compaction should be greater than 98%, and the unconfined compressive strength after 7 days should be greater than 4.0 MPa.

[0019] The present invention has the following beneficial effects:

[0020] 1. This invention incorporates limestone, magnesium chloride, and magnesium oxide into calcined phosphogypsum. The soluble phosphorus and fluorine in the phosphogypsum form calcium phosphate and calcium fluoride, resulting in a water-soluble fluoride ion concentration in the water-stabilized material of less than 3.50 mg / L. Water-soluble phosphorus pentoxide is undetectable, and the leached liquid under rainwater runoff does not pollute the environment, meeting environmental protection requirements. Simultaneously, magnesium chloride and magnesium oxide activate the phosphogypsum, improving the hydraulic properties of the water-stabilized material, thereby increasing its compressive strength and surface hardness, and effectively increasing the amount of phosphogypsum added. Dimethylchlorosilane disperses in the pores and surface of the water-stabilized material, forming a hydrophobic film that blocks the pores and prevents water molecules from entering the interior of the water-stabilized material, further improving the water resistance and rainwater runoff resistance of the water-stabilized material.

[0021] 2. The sodium-based bentonite added in this invention fills the pores formed after the activation of phosphogypsum, magnesium chloride, and magnesium oxide, increasing the density of the water-stabilized material. At the same time, it causes the water-stabilized material to expand to a certain extent, reducing the shrinkage rate and thus reducing cracking caused by expansion, improving the durability of the water-stabilized material, extending the service life of the road, increasing the amount of phosphogypsum added, and increasing the utilization of phosphogypsum.

[0022] 3. This invention utilizes calcined building gypsum, a byproduct of industrial phosphogypsum, as raw material. The preparation method is simple, the reaction conditions are mild, and the prepared water-stabilized material has an initial setting time of more than 4 hours and a final setting time of not less than 6 hours. It can be pre-mixed on the construction site for road construction, enabling the industrial-scale disposal of solid waste and maximizing the resource utilization of phosphogypsum. Attached Figure Description

[0023] Figure 1 is a schematic diagram of the road base paving structure using the water-stabilized material of Example 3;

[0024] Figure 2 shows the on-site compaction diagram of the water-stabilized material used in Example 3;

[0025] Figure 3 shows the paving and compaction process of the water-stabilized material used in Example 3 at the construction site.

[0026] Figure 4 shows the road covering and curing treatment using the water-stabilized material of Example 3;

[0027] Figures 5 and 6 show the road surface rebound deflection test results using the water-stabilized material of Example 3;

[0028] Figures 7 and 8 are on-site core sampling test diagrams of the road surface using the water-stabilized material of Example 3; Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments.

[0030] The following examples use calcined phosphogypsum from Yunnan Xiangfeng Environmental Protection Technology Co., Ltd. The phosphogypsum contains >60% CaSO4·0.5H2O, has a 2-hour flexural strength ≥3MPa, and a 2-hour compressive strength ≥6MPa. Example 1

[0031] A phosphogypsum-based road base water-stabilized material, by weight, comprises 1800 parts calcined phosphogypsum, 2000 parts cement clinker, 100 parts limestone, 10 parts toughening agent, 150 parts high-strength water-resistant agent, 50 parts sodium-based bentonite, and 5 parts glass fiber; the high-strength water-resistant agent is composed of magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.5, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:1. Example 2

[0032] A phosphogypsum-based road base water-stabilized material, by weight, comprises 2000 parts calcined phosphogypsum, 2000 parts cement clinker, 500 parts limestone, 8 parts toughening agent, 200 parts high-strength water-resistant agent, 100 parts sodium bentonite, and 10 parts glass fiber; the high-strength water-resistant agent is composed of magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.1, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:0.5. Example 3

[0033] A phosphogypsum-based road base water-stabilized material, by weight, comprises 1500 parts calcined phosphogypsum, 700 parts cement clinker, 50 parts limestone, 5 parts toughening agent, 100 parts high-strength water-resistant agent, 60 parts sodium bentonite, and 3 parts glass fiber; the high-strength water-resistant agent is composed of magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.05, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:0.5. Example 4

[0034] A phosphogypsum road base water-stabilized material, by weight, comprises 1500 parts calcined phosphogypsum, 900 parts cement clinker, 90 parts limestone, 8 parts toughening agent, 150 parts high-strength water-resistant agent, 80 parts sodium bentonite, and 5 parts glass fiber; wherein the high-strength water-resistant agent is composed of magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.3, and the toughening agent is composed of polyvinyl alcohol and EVA mixed in a ratio of 1:0.6.

[0035] The proportions of Examples 1-4 above are prepared according to the preparation method of the phosphogypsum road base water-stabilized material provided by the present invention, and the method steps are as follows:

[0036] S1. Weigh the raw materials according to the proportion of the phosphogypsum road base water-stabilized material;

[0037] S2. Mix calcined phosphogypsum, cement clinker, limestone, magnesium chloride, magnesium oxide, sodium bentonite, and glass fiber evenly to prepare a base material;

[0038] S3. Dissolve polyvinyl alcohol and mix it with EVA solution in a certain proportion to prepare toughening agent solution;

[0039] S4. Add water to the base material described in step S2 to make up 50-70% of the total base material and stir evenly. Then add toughening agent and diluted dimethylchlorosilane in sequence and continue stirring to make a phosphogypsum road base water-stabilized material with an initial setting time of more than 4 hours and a final setting time of not less than 6 hours.

[0040] As shown in Figure 1, the roadbed is poured using a layered paving method. From the bottom to the top of the road base, a 20cm layer of crushed stone subbase with a particle size of 5-60mm and a compaction coefficient of 0.97 is laid, followed by a 40cm layer of phosphogypsum road base water-stabilized material, an ES-2 emulsified asphalt slurry seal coat, an 8cm layer of AC-25 coarse asphalt concrete, a 6cm layer of AC-20 medium-grained asphalt concrete, and a 4cm layer of AC-13 fine-grained modified asphalt concrete. After construction, the roadbed is covered with a film for 8 days for curing.

[0041] As shown in Figures 2-4, the layered paving process employs a two-stage mechanical compaction method with a compaction coefficient of 0.98. The specific two compaction stages are as follows: the initial compaction is performed by a vibratory roller at a speed of 1.5-1.7 km / h, with one pass of static compaction; the secondary compaction is performed by a vibratory roller at a speed of 1.8-2.2 km / h, with two passes of light, high-frequency vibration; the final compaction is performed by a pneumatic tire roller at a speed of 1.5-1.7 km / h, with one to two passes of compaction.

[0042] The compaction process involves sequential steps of stabilizing, light vibration, heavy vibration, and final stabilizing until the surface is essentially free of wheel tracks. During compaction, wheel tracks should overlap by at least 1 / 3 of the wheel width. After compaction, the degree of compaction is tested using the sand cone method. The degree of compaction should be greater than 98%, as shown in Figures 5-8. The construction pavement of this embodiment is then tested.

[0043] The detection methods used in Examples 1-4 are as follows:

[0044] 1. The CBR value and CBR water swelling amount of water-stabilized materials shall be tested in accordance with the "Specifications for Testing Geotechnical Materials for Highways" (JTG3430-2020).

[0045] 2. The 7-day unconfined compressive strength of the stabilized material shall be tested in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009).

[0046] 3. 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 = (P0 - P1) / P0; where: P is the strength before the wet-dry cycle, and P0 is the strength after four wet-dry cycles; Mass loss rate = (M0 - M0) / M0; where: M0 is the strength before the wet-dry cycle, and M0 is the strength after four wet-dry cycles.

[0047] 4. 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). The concentrations of total phosphorus, fluoride, and various heavy metals in the leachate were tested and met the requirements of the "Surface Water Environmental Quality Standard" (GB3838-2002).

[0048] The performance test results of the water-stabilized materials in Examples 1-4 are shown in Table 1:

[0049] Table 1. Performance test results of water-stabilized materials in Examples 1-4

[0050]

[0051] The calcined phosphogypsum raw material used in this invention is widely available. In actual use, the proportions of the formula can be adjusted within the range of the formula to meet the different requirements of the project for strength or water resistance, thus satisfying the requirements of different regional climates. The water-stabilized material of this invention meets environmental protection standards, has excellent mechanical properties and durability, and can provide better road infrastructure protection when applied to rural road construction and municipal engineering. It also broadens the utilization of phosphogypsum and can dispose of a large amount of solid waste phosphogypsum.

[0052] 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 phosphogypsum road base water-stabilized material, characterized in that, By weight, it comprises 300-2000 parts calcined phosphogypsum, 300-2000 parts cement clinker, 50-500 parts limestone, 1-10 parts toughening agent, 10-200 parts high-strength water-resistant agent, 50-100 parts sodium bentonite, and 1-10 parts glass fiber; the high-strength water-resistant agent is magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.05-0.5, and the toughening agent is a mixture of polyvinyl alcohol and EVA in a ratio of 1:0.5-1.

2. The phosphogypsum road base water-stabilized material according to claim 1, characterized in that, By weight, the composition includes 1800 parts calcined phosphogypsum, 2000 parts cement clinker, 100 parts limestone, 10 parts toughening agent, 150 parts high-strength water-resistant agent, 50 parts sodium bentonite, and 5 parts glass fiber; the high-strength water-resistant agent is composed of magnesium chloride, magnesium oxide, and dimethylchlorosilane added in a ratio of 1:1:0.5, and the toughening agent is composed of polyvinyl alcohol and EVA mixed in a ratio of 1:

1.

3. A phosphogypsum road base water-stabilized material according to claim 1 or 2, characterized in that, The calcined phosphogypsum is calcined building gypsum with a CaSO4·0.5H2O content >60%, a 2h flexural strength ≥3MPa, and a 2h compressive strength ≥6MPa.

4. A phosphogypsum road base water-stabilized material according to claim 1 or 2, characterized in that, The water-soluble fluoride ion concentration of the phosphogypsum road base water-stabilized material is less than 3.50 mg / L, and water-soluble phosphorus pentoxide was not detected.

5. A method for preparing a phosphogypsum road base water-stabilized material as described in claim 1 or 2, characterized in that, The method steps are as follows: S1. Weigh the raw materials according to the proportion of the phosphogypsum road base water-stabilized material; S2. Mix calcined phosphogypsum, cement clinker, limestone, magnesium chloride, magnesium oxide, sodium bentonite, and glass fiber evenly to prepare a base material; S3. Dissolve polyvinyl alcohol and mix it with EVA solution in proportion to prepare a toughening agent solution; S4. Add water to the base material in step S2 and stir evenly, then add the toughening agent and diluted dimethylchlorosilane in sequence and continue stirring to prepare a phosphogypsum road base water-stabilized material with an initial setting time of more than 4 hours and a final setting time of not less than 6 hours.

6. A construction method for a phosphogypsum road base water-stabilized material as described in claim 1 or 2, characterized in that, The roadbed is poured using a layered paving method. From the bottom to the top of the road base, a 15-20cm layer of crushed stone subbase with a particle size of 5-60mm is laid, with a compaction coefficient >0.

80. Then, a 35-45cm layer of phosphogypsum road base water-stabilized material is laid, followed by an ES-2 slurry seal, a 6-10cm layer of AC-25 coarse-grained asphalt concrete, a 4-8cm layer of AC-20 medium-grained asphalt concrete, and a 2-5cm layer of AC-13 fine-grained modified asphalt concrete. After construction, the roadbed is covered with a film for 8 days for curing.

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