A self-compacting ardealite road base material and a preparation method thereof

Abstract

The application provides a self-compacting phosphogypsum road base material and a preparation method thereof, and belongs to the technical field of building materials. The base material comprises phosphogypsum, cementitious material, aggregate, additive and water, and the components are in the following mass percentages: phosphogypsum 40-55%, cementitious material 4-13%, aggregate 35-50%, additive 0.2-0.7%, wherein the cementitious material comprises cement and slag powder, and the water-cement ratio is 4.5-7.5. The application fully utilizes the properties of phosphogypsum and cementitious material, and the self-compacting phosphogypsum road base material formed has a filling slump spread index reaching SF1 level (550-655 mm), an expansion time T 500 reaching VS1 level (≥2 s), a 28-day compressive strength ≥8 MPa, a water-soaking softening coefficient ≥85%, and a water absorption ≤10%. The phosphogypsum road base material of the application uses a lower amount of cement, effectively overcomes or avoids the occurrence of early diseases of the road base; meanwhile, a medium-high amount of phosphogypsum is used, which can quickly consume phosphogypsum, reduce inventory, and relieve the problem of stacking, and has significant environmental, economic and social benefits.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a self-compacting phosphogypsum road base material and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste generated during the wet process of industrially producing phosphoric acid and ammonium phosphate fertilizers from phosphate rock powder. Every ton of phosphoric acid produced generates approximately 4.5 to 5 tons of phosphogypsum. Because phosphogypsum contains impurities such as free carbon, hydrochloric acid, and sulfuric acid, it is difficult to fully utilize. Currently, phosphogypsum is primarily disposed of by accumulation, severely damaging the ecological environment, polluting groundwater resources, and wasting land resources. However, phosphogypsum exhibits a high hydration-hardening strength. Its use in road construction not only reduces the consumption of phosphogypsum but also significantly reduces road construction costs, offering significant social and economic benefits.

[0003] Traditional road base materials include cement-stabilized soil, lime-stabilized soil, and fly ash crushed stone. Cement in cement-stabilized soil, as a hydraulic material, forms colloids when it comes into contact with water. These colloids cannot form a unified whole in the soil and can disrupt the soil's structure and connections, creating numerous unstable spaces. These spaces become extremely fragile due to water intrusion and temperature fluctuations. As a result, road bases formed from cement-stabilized soil are highly susceptible to cracking and have poor crack resistance.

[0004] Chinese patent document CN114716223A, "A Gangue-Based Road Base Material and Preparation Method," discloses a road base material composed of a mixture of gangue A, gangue B, dihydrate phosphogypsum, carbide slag, and a water reducer. However, the phosphogypsum content is low, resulting in a low utilization rate, which is not conducive to rapid consumption of the phosphogypsum. Furthermore, the maximum 28-day compressive strength is 4.2 MPa. Chinese patent CN117361979A, "A Crack-Resistant and Water-Resistant Phosphogypsum Road Base Material and Preparation Method," discloses a road base material composed of a mixture of calcined phosphogypsum, natural coarse aggregate (i.e., limestone), natural fine aggregate, Portland cement, and additives. However, the phosphogypsum must be calcined before use, and the low content of calcined phosphogypsum and the high amount of natural coarse aggregate (limestone) create very favorable conditions for the formation of silica fume gypsum, which can easily cause cracking, arching, and other defects in the road base. Furthermore, the compressive strengths at 7 and 28 days differ significantly.

[0005] Therefore, the present invention relies on actual engineering and starts from the selection and construction of base materials to provide a self-compacting phosphogypsum road base material, which uses more phosphogypsum solid waste and less cement, plays a role in quickly consuming solid waste and reducing the occurrence of early road diseases; and delays the setting time of the base, facilitating construction and enhancing mechanical strength. Summary of the Invention

[0006] To address the deficiencies of the prior art, the first objective of the present invention is to provide a self-compacting phosphogypsum road base material. The phosphogypsum road base material of the present invention uses a relatively low cement content to effectively overcome or avoid the occurrence of early road base disease. Simultaneously, the use of medium to high amounts of phosphogypsum can rapidly consume phosphogypsum, reduce inventory, and alleviate stacking problems, thereby providing significant environmental, economic, and social benefits. The self-compacting phosphogypsum road base material of the present invention has good fluidity and high mechanical strength, and its filling slump expansion index reaches SF1 level (550-655mm). The expansion time T 500 The indicators reach VS1 level (≥2s), 28-day compressive strength ≥8MPa, water softening coefficient ≥85%, and water absorption rate ≤10%.

[0007] The second object of the present invention is to provide a method for preparing a self-compacting phosphogypsum road base material, which is simple and easy to implement.

[0008] To achieve the first purpose, the technical solution adopted by the present invention is:

[0009] A self-compacting phosphogypsum road base material comprises phosphogypsum, a cementitious material, an aggregate, an admixture, and the components are calculated in the following mass percentages: 40-55% of phosphogypsum, 4-13% of the cementitious material, 35-50% of the aggregate, and 0.2-0.7% of the admixture.

[0010] Preferably, the moisture content of the phosphogypsum is lower than 12%, and the particle size is 5-50 μm. The smaller the particle size, the more conducive it is to improving the uniformity and efficiency of the hydration reaction, and the more conducive it is to the hydration of ettringite.

[0011] Preferably, the cementitious material is S95 grade granulated blast furnace slag powder and 42.5 grade ordinary Portland cement;

[0012] The mass ratio of the 42.5 grade ordinary Portland cement is 1-4%, and its fineness, expressed as the residue on a 45μm square mesh sieve, is not less than 5%. The initial setting time is not less than 45 minutes, and the final setting time is not more than 600 minutes. The soundness is qualified by the boiling method. The chemical requirements (mass fraction) are: loss on ignition is not more than 5%, SO3 is not more than 3.5%, MgO is not more than 5%, and chloride ion is not more than 0.06%. The main chemical components are CaO (64-67%), SiO2 (20-23%), Al2O3 (4-8%), and Fe2O3 (3-6%).

[0013] The mass ratio of the S95 grade slag powder is 3-9%, and its density is not less than 2.8g / cm 3 , specific surface area not less than 400m 2 / kg, 28-day activity index not less than 95%, fluidity ratio not less than 95%, initial setting time ratio not greater than 200%, water content not greater than 1%, SO3 (mass fraction) not greater than 4%, loss on ignition not greater than 1%, insoluble matter (mass fraction) not greater than 3%; the main chemical components are CaO (34-36%), SiO2 (34-36%), Al2O3 (16-18%), and Fe2O3 (1~2%).

[0014] After cement is dissolved in water, it becomes alkaline due to the hydrolysis of CaO. When granulated blast furnace slag is mixed with water alone, the reaction is extremely slow and the short-term strength is extremely low. However, it can be hydrated quickly in calcium hydroxide solution, and the reaction is even faster in saturated calcium hydroxide solution, and a certain strength is generated. This is because it forms an alkaline solution with water, which can destroy the surface structure of the slag glass, making it easy for water to penetrate and undergo hydration reaction, causing the slag particles to disperse and disintegrate, and produce gelling calcium silicate hydrate and calcium aluminate hydrate. The main component of industrial waste slag phosphogypsum is CaSO4·2H2O, which hydrolyzes to generate excess free Ca 2 + With SO4 2- Adding a certain amount of calcium sulfate to an alkaline solution containing calcium hydroxide can fully unleash the hydration activity of the slag, resulting in significantly higher strength than adding an alkaline substance alone. It also generates hydrated calcium sulfoaluminate, further enhancing the strength. The self-compacting phosphogypsum base material of the present invention fully utilizes the hydration activity of S95-grade slag powder, the alkali-activated properties of 42.5-grade ordinary Portland cement, and the reactive nature of some phosphogypsum. By fully mixing and combining these three, a high-strength hydrated cementitious material is generated, thereby enhancing the strength of the base material.

[0015] The present invention strictly controls the amounts of phosphogypsum, cement and mineral powder (the mass ratio is 40-50:1-4:3-9), thereby ensuring the water stability and compressive strength of the obtained road base material, effectively coordinating the early strength and late strength of the road base, reducing the impact of impurities in the phosphogypsum on product performance, and simultaneously improving the water stability of the road base to prevent cracking.

[0016] Preferably, the mass ratio of the phosphogypsum to the cementitious material is 4-6:1, which controls the amount of ettringite formed, alleviates the self-shrinkage of the base material, and prevents cracking of the road.

[0017] Preferably, the aggregate is a mixture of sand and crushed stone, wherein the sand is machine-made fine sand with a particle size of less than 4.75 mm, and the crushed stone is continuously graded crushed stone, which is fine crushed stone with a particle size of 5-10 mm and coarse crushed stone with a particle size of 10-20 mm, with a mass ratio of 3:7;

[0018] The sand-gravel ratio is 0.2-0.3.

[0019] The mass ratio of the crushed stone is 30-41%, and the mass ratio of the machine-made fine sand is 8-10%.

[0020] Since phosphogypsum accounts for a relatively large proportion as fine aggregate, in order to make the self-compacting phosphogypsum base material have good fluidity, small-particle aggregate is used and the content of needle-shaped and flake-shaped aggregate is strictly controlled; the aggregate is designed according to the grading theory, and different aggregate particle sizes are matched and filled in the base material to form a tightly arranged multi-level spatial skeleton structure system with maximum friction, thereby improving the mechanical properties of the material.

[0021] Preferably, the admixtures include a slow-release agent and a water reducer, accounting for 0.3-0.4% of the total mass of the mixture.

[0022] The water reducer is a polycarboxylate water reducer, and the retarder is citric acid; the mass ratio is 1:0.1-0.3; the slow-release agent can stimulate the activity of slag powder and promote the formation of hydration products on the one hand, and control the hydration speed and prolong the setting time of cement on the other hand. The appropriate amount of citric acid can make the pores of the material smaller and more evenly distributed, which is conducive to improving the density and durability of the base material.

[0023] Preferably, the admixture further includes an anti-cracking agent, which is polypropylene fiber; it accounts for 0.01-0.03% of the mass of the admixture; the polypropylene fiber can effectively control the shrinkage of the material and microcracks caused by temperature changes, prevent the occurrence and development of cracks, and greatly improve the material's crack resistance, impermeability and impact resistance. Since polypropylene fiber has good ductility, after adding polypropylene fiber, the bridging effect of polypropylene fiber inhibits the expansion and formation speed of cracks, thereby improving the performance of the material and achieving the effect of preventing cracking.

[0024] The present invention prolongs the retarding time of the base material by adding a composite admixture, promotes the full hydration of slag powder, cement and phosphogypsum, enhances the strength of the base material and improves the durability of the material.

[0025] Preferably, the water reducer is an ester polycarboxylic acid water reducer.

[0026] The second object of the present invention is to provide a method for preparing a self-compacting phosphogypsum road base material, comprising the following steps:

[0027] S1. Weigh each raw material according to mass percentage and set aside;

[0028] S2 take 80-90% of the total amount of phosphogypsum and 60-70% of the total amount of water and mixed in a mixer, mixed uniformly to form a first mixture;

[0029] S3. The cementitious material, the remaining phosphogypsum, aggregate, admixture and the remaining water are mixed in a mixer and mixed to form a second mixture;

[0030] S4. The first mixture is added to the second mixture and mixed to form a third mixture;

[0031] S5. Fill the formed third mixture into a forming mold, and after standing and forming, a self-compacting phosphogypsum road base material is formed.

[0032] Preferably, in S2, the stirring speed of phosphogypsum and water is 100-200 r / min, and the time is 1-3 min.

[0033] Preferably, in S3, the stirring speed of each component is 100-200 r / min, and the time is 2-4 min.

[0034] Preferably, in S4, the stirring speed of each component is 100-200 r / min, and the time is 3-6 min.

[0035] The phosphogypsum road base material prepared by the above method has good strength, durability and fluidity; its filling slump expansion index reaches SF1 level (550-655mm), and its expansion time T500 index reaches VS1 level (≥2s).

[0036] The present invention also provides a self-compacting phosphogypsum base road, which is paved with the self-compacting phosphogypsum base material.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The self-compacting phosphogypsum road base material of the present invention has a filling slump expansion index reaching SF1 level (550-655mm) and an expansion time T 500 The indicators reach VS1 level (≥2s), 28-day compressive strength ≥8MPa, water softening coefficient ≥85%, and water absorption rate ≤10%.

[0039] 2. The present invention provides a method for preparing a self-compacting phosphogypsum road base material. The preparation method is simple and easy to implement. Through a large number of indoor tests, the mix ratio of the various components of the road base material that meets environmental protection requirements and road performance is quickly and accurately determined. The present invention uses a relatively low amount of cement to effectively overcome or avoid the occurrence of early diseases of the road base. At the same time, the use of medium to high amounts of phosphogypsum can not only quickly consume phosphogypsum, reduce inventory, and alleviate stacking problems, but also has significant environmental, economic and social benefits.

[0040] 3. The phosphogypsum road base material of the present invention adjusts the mix ratio of each component, fully utilizes the hydration properties of slag powder, the alkaline properties of cement, and a small amount of phosphogypsum to participate in the hydration reaction, and fully stirs and combines the three to generate a high-strength hydrated gelled material, thereby enhancing the mechanical properties of the phosphogypsum road base material.

[0041] 4. The present invention adopts a composite admixture containing a slow-release agent, a water-reducing agent and an anti-cracking agent to effectively improve the compressive strength, setting time and shrinkage crack working performance of the phosphogypsum road base material. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below with reference to the accompanying drawings and examples:

[0043] Figure 1 This is the XRD diagram of the self-compacting phosphogypsum base material sample of the test example of the present invention. DETAILED DESCRIPTION

[0044] In the self-compacting phosphogypsum road base material provided by the present invention, cement mainly provides a sufficient alkaline environment for the system to stimulate the activity of slag powder. However, if the cement content is too high, it will lead to the formation of excessive calcium hydroxide, destroying the cementitious material and affecting the structural strength of the product. The amount of slag powder added affects the amount of hydration products generated. As the slag powder content increases, more and more hydration cementation products are produced, which is conducive to improving the bonding strength of the product. However, when the ratio of slag powder to cement is too high, the activity of the active component cannot be fully stimulated, and the continuous increase in strength in the later stage is likely to cause local cracks. Therefore, under the condition of a certain amount of cement, the present invention strictly controls the amount of slag powder so that the activity stimulation of the slag powder and the degree of hydration reaction are optimally matched. In addition, with the increase of slag powder content, the shape of ettringite changes from coarse rods to thin rods; when the slag powder content reaches 3-9% of the mixture, finer needle-shaped ettringite structure appears in the product, and more thin-flaked C-S-H gel is formed. A large amount of needle-shaped ettringite and thin-flaked gel fills the gaps between the particles, forming a denser structure inside the sample, which is reflected in the improvement of the compressive strength of the sample on a macro scale.

[0045] The present invention uses phosphogypsum, slag powder, cement, and crushed stone as basic raw materials, designs different mix ratios, and prepares road base materials according to the mix ratio scheme. After uniformly stirring to form a mixture, the mechanical properties of the road base materials are tested. The mechanical properties of the road base materials under different mix ratios are compared and analyzed to determine the optimal mix ratio of slag powder and cement. The self-compacting properties and mechanical properties of the road base materials under different phosphogypsum dosages and the optimal mix ratio of slag powder and cement are compared and analyzed to determine the optimal mix ratio of each component.

[0046] The present invention can quickly and accurately obtain the mix ratio of each component of the base material through indoor experiments, and can be widely applied to base road filling, which is beneficial to solving the problems of large-scale stacking of phosphogypsum, occupation of land resources, and environmental pollution, saving a large amount of precious land resources, realizing the green recycling of industrial solid waste, reducing the cost of road engineering, and improving engineering quality. It has good economic, environmental, and social benefits and broad application prospects.

[0047] In the following examples and comparative examples, phosphogypsum aged for two years from Xinyangfeng, Yichang was used, and the agglomeration of the original aged phosphogypsum was treated by crushing and fine granulation, with a particle size of less than 5 mm. The phosphogypsum raw materials were fully turned and dried to below the plastic limit, and were dispersed in powder form with a free moisture content of less than 12%.

[0048] Refer to the "Ordinary Concrete Mix Design Code" (JGJ55-2011), and the preparation strength is determined by referring to the following formula:

[0049] f cu，0 ≥ f cu，k +1.645σ

[0050] f cu，0 ---Preparation strength (MPa);

[0051] f cu，k ---Design strength (MPa);

[0052] σ --- Strength standard deviation (MPa). According to the "Concrete Strength Test and Assessment Standard" GB / T50107-2010, the calculated laboratory test block strength standard deviation σ = 3.13MPa.

[0053] The original pavement base design indicators are that the unconfined compressive strength of the upper and lower bases should be no less than 4.0 MPa, and the unconfined compressive strength of the subbase should be no less than 3.0 MPa. The prepared strength is approximately: the upper and lower bases should be no less than 9.15 MPa, and the subbase should be no less than 8.15 MPa.

[0054] Performance testing:

[0055] The self-compacting properties of the self-compacting phosphogypsum base materials of the following examples and comparative examples were tested with reference to the test methods in JGJ / T283-2012 "Technical Specifications for the Application of Self-Compacting Concrete" and its Appendix A and the "Specifications for the Design of Ordinary Concrete Mix" (JGJ55-2011).

[0056] Example 1:

[0057] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 40% phosphogypsum, 41.5% crushed stone, 10% machine-made sand, 2% cement, 6.0% slag powder, and 0.5% admixture.

[0058] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0059] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0060] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0061] The sand-gravel ratio is 0.241; the water-cement ratio is 6.8;

[0062] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0063] This embodiment also provides a method for preparing a self-compacting phosphogypsum base material, comprising the following steps:

[0064] S1. Weigh each raw material according to mass percentage and set aside;

[0065] S2 was added to the mixer, 85% of the total amount of phosphogypsum and 65% of the total amount of water, stirred at a stirring speed of 150r / min for 2min to form a first mixture;

[0066] S3. To the mixer, the cementitious material, the remaining phosphogypsum, aggregate, admixture and the remaining water were added and stirred at a stirring speed of 150 r / min for 3 min to form a second mixture;

[0067] S4. The first mixture was added to the second mixture of S3 and stirred at 150r / min for 3min to form a third mixture;

[0068] S5. Fill the formed third mixture into a forming mold, and after standing and forming, a self-compacting phosphogypsum road base material is formed.

[0069] Example 2:

[0070] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 38.5% crushed stone, 9% machine-made sand, 2% cement, 5.0% slag powder, and 0.5% admixture.

[0071] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0072] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0073] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0074] The sand-gravel ratio is 0.234; the water-cement ratio is 6.125;

[0075] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0076] The preparation method is the same as that of Example 1.

[0077] Example 3:

[0078] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 55% phosphogypsum, 30.5% crushed stone, 7% machine-made sand, 2% cement, 5.0% slag powder, and 0.5% admixture.

[0079] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0080] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0081] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0082] The sand-gravel ratio is 0.230; the water-cement ratio is 7;

[0083] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0084] The preparation method is the same as that of Example 1.

[0085] Example 4:

[0086] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 40.6% crushed stone, 10% machine-made sand, 2% cement, 2.0% slag powder, and 0.4% admixture.

[0087] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0088] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0089] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0090] The sand-gravel ratio is 0.256; the water-cement ratio is 4.4;

[0091] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0092] The preparation method is the same as that of Example 1.

[0093] Example 5:

[0094] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 37.5% crushed stone, 9% machine-made sand, 2% cement, 6.0% slag powder, and 0.5% admixture.

[0095] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0096] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0097] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0098] The sand-gravel ratio is 0.240; the water-cement ratio is 6.8;

[0099] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0100] The preparation method is the same as that of Example 1.

[0101] Example 6:

[0102] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 35.1% crushed stone, 8.2% machine-made sand, 2% cement, 9.0% slag powder, and 0.7% admixture.

[0103] The moisture content of the phosphogypsum is less than 12%, and the particle size of the phosphogypsum is 5-50 μm;

[0104] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0105] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0106] The sand-gravel ratio is 0.234; the water-cement ratio is 9;

[0107] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0108] The preparation method is the same as that of Example 1.

[0109] Example 7:

[0110] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 37.7% crushed stone, 9% machine-made sand, 2% cement, 6.0% slag powder, and 0.3% admixture.

[0111] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0112] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0113] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0114] The sand-gravel ratio is 0.239; the water-cement ratio is 7.4;

[0115] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0116] The preparation method is the same as that of Example 1.

[0117] Example 8:

[0118] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components by mass percentage: 45% phosphogypsum, 37.5% crushed stone, 9.0% machine-made sand, 2.2% cement, 5.9% slag powder, and 0.4% admixture.

[0119] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0120] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0121] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0122] The sand-gravel ratio is 0.240; the water-cement ratio is 6.7;

[0123] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0124] The preparation method is the same as that of Example 1.

[0125] Example 9:

[0126] This embodiment provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, and an admixture, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone. The base material is made by mixing the following components in percentage by mass: 45% phosphogypsum, 37.5% crushed stone, 9.2% machine-made sand, 2.14% cement, 5.84% slag powder, and 0.31% admixture.

[0127] The preparation method of the phosphogypsum comprises crushing phosphogypsum aged for two years into fine particles to obtain phosphogypsum particles smaller than 5 mm in size, and then fully turning and drying the phosphogypsum until the particles are below the plastic limit and dispersed in a powdery state, with a free moisture content of less than 12%. The phosphogypsum is then placed in a ball mill for ball milling to obtain a phosphogypsum particle size of 5-50 μm.

[0128] The sand is machine-made fine sand with a particle size of less than 4.75 mm;

[0129] The crushed stone adopts continuous graded crushed stone, with particle size of 5-10mm, accounting for 30%; particle size of 10-20mm, accounting for 70%;

[0130] The admixtures are ester polycarboxylic acid water reducer, citric acid and polypropylene fiber, with a mass ratio of 1:0.3:0.02.

[0131] The sand-gravel ratio is 0.245; the water-cement ratio is 6.97;

[0132] The preparation method is the same as that of Example 1.

[0133] Comparative Example 1:

[0134] This comparative example provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone; the base material is prepared by mixing the following components by mass percentage: 60% phosphogypsum, 25.5% crushed stone, 6% machine-made sand, 2% cement, 6.0% slag powder, and 0.5% admixture;

[0135] The preparation method is the same as that of Example 1.

[0136] Comparative Example 2:

[0137] This comparative example provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone; the base material is prepared by mixing the following components by mass percentage: 85% phosphogypsum, 2% cement, 12.0% slag powder, and 1.0% admixture;

[0138] The preparation method is the same as that of Example 1.

[0139] Comparative Example 3:

[0140] This comparative example provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone; the base material is made by mixing the following components by mass percentage: 45% phosphogypsum, 32.3% crushed stone, 7.6% machine-made sand, 2% cement, 12.0% slag powder, and 1.1% admixture;

[0141] The preparation method is the same as Example 4.

[0142] Comparative Example 4:

[0143] This comparative example provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone; the base material is prepared by mixing the following components by mass percentage: 45% phosphogypsum, 29.6% crushed stone, 6.9% machine-made sand, 2% cement, 15.0% slag powder, and 1.5% admixture;

[0144] The preparation method is the same as Example 4.

[0145] Comparative Example 5:

[0146] This comparative example provides a self-compacting phosphogypsum base material, the base material comprising phosphogypsum, a cementitious material, an aggregate, an admixture, and water, wherein the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement, and the aggregate is a mixture of sand and crushed stone; the base material is prepared by mixing the following components by mass percentage: 45% phosphogypsum, 41.8% crushed stone, 6.0% machine-made sand, 2% cement, 5.0% slag powder, and 0.2% admixture;

[0147] The preparation method is the same as Example 4.

[0148] The self-compacting properties and mechanical properties of the phosphogypsum road base material samples of Examples 1-9 and Comparative Examples 1-5 were tested, and the results are shown in Table 1.

[0149] Table 1 Self-compacting properties and mechanical properties test results of different phosphogypsum road base materials

[0150]

[0151] Analysis of the data in Table 1, comparing Examples 1-3 with Comparative Examples 1-2, shows that the 85% high-content phosphogypsum self-compacting base material exhibits poor cohesion, rapid slump propagation, a long final setting time, surface shrinkage and cracking after test block formation, and low strength. The 60% phosphogypsum self-compacting base material exhibits a long final setting time and low strength. The 45% and 40% phosphogypsum gravel self-compacting base materials exhibit good cohesion, workability, and fluidity, and meet strength requirements. In other words, the compressive strength of the phosphogypsum self-compacting base material decreases with increasing phosphogypsum content, indicating that excessive phosphogypsum usage is not conducive to increasing compressive strength.

[0152] To avoid the occurrence of early pests and diseases, and because cement primarily stimulates the hydration activity of slag powder, the present invention selects a relatively low cement dosage to investigate the slag powder dosage. A comparison of Examples 4-9 and Comparative Examples 3-4 shows that, at a constant cement dosage, the 28-day strength gradually increases with increasing slag powder dosage. However, if the slag powder dosage is excessive, with a mass ratio of slag powder to cement exceeding 4.5, the 28-day strength increase is not significant. Furthermore, if the slag powder dosage is too high, the drying shrinkage is large, resulting in low early strength. The activity of the excess slag powder is not stimulated early, and the continued increase in strength later in life can easily lead to localized cracks.

[0153] In Examples 1-4, the 28-day unconfined compressive strength is low, and the difference in strength between 14 and 28 days is large, indicating that the cementitious material is not fully hydrated, which is not conducive to the stability of the base material. In Comparative Examples 1-5, the self-compactness and compressive strength of the materials do not meet the preparation requirements. In Examples 5-9, the 28-day unconfined compressive strength is greater than 9.45 MPa, meeting the strength requirements of the "Concrete Strength Test and Assessment Standard", and in Example 9, there is no significant difference in the strength between 14 and 28 days, indicating that ettringite does not continue to be generated with age, and the base structure is relatively stable as a whole.

[0154] In summary, the phosphogypsum road base material of the present invention, with a ratio of 45% phosphogypsum + 2.14% cement + 5.84% mineral powder and a water-cement ratio of 6.97, meets the preparation strength requirements, has low cost, and has stable strength for 14-28 days; and can be widely used in base road construction.

[0155] Test example

[0156] This experiment provides a self-compacting phosphogypsum road base, which is paved using the phosphogypsum base material of Example 9.

[0157] The test section is the motor vehicle lane of the Dianjun 1st Road (Juanqiaohe 2nd Road-Wulong 3rd Road) municipal engineering EPC project, i.e. K1+310~K1+490, a total of 170 meters. The phosphogypsum road base is used for engineering verification tests, and the following test methods are used to conduct performance testing and economic and social benefit evaluation on the road base of the engineering test.

[0158] With reference to JGJ / T283-2012 "Technical Specifications for Application of Self-compacting Concrete" and its Appendix A.1, the self-compacting performance of the engineering verification test core samples was tested.

[0159] With reference to GBT / 50784-2013 "Technical Standard for On-site Testing of Concrete Structures", the mechanical properties of on-site core samples and standard-cured test blocks were tested.

[0160] With reference to the water absorption grades and test methods of JGT / 266 "Foamed Concrete", water absorption tests were conducted on on-site core samples and standard-cured test blocks.

[0161] With reference to the “Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method”, pollutants in self-compacting phosphogypsum road base materials were tested.

[0162] 1. Performance testing

[0163] 1.1 Filling test

[0164] The filling performance needs to be tested for two indicators: slump expansion and expansion time. The test results are shown in Table 2.

[0165] Table 2 Slump expansion and expansion time of base material mixture

[0166]

[0167] As shown in Table 2, the slump expansion grade of the self-compacting phosphogypsum base material of the road base is SF1, and the expansion time (T 500 ) level is VS1, meeting the technical index requirements.

[0168] 1.2 Compressive strength

[0169] The compressive strength at 7 days, 14 days and 28 days was measured by coring the test section on site and standard curing test blocks in the laboratory. The test results are shown in Table 3.

[0170] Table 3 Compressive strength test of on-site core samples and standard curing test blocks

[0171]

[0172] As shown in Table 3, through the core sampling of the on-site test section and the standard curing test blocks in the laboratory, the 28-day compressive strength can reach above 5 MPa, meeting the technical index requirements.

[0173] 1.3 Softening coefficient

[0174] The 14-day-old field core samples and standard-cured test blocks were divided into two groups. One group was immersed in water for 14 to 28 days, and its strength was tested. The strength was compared with that of the core samples and standard-cured test blocks at normal 28 days of age to obtain the 28-day water softening coefficient. The results are shown in Table 4.

[0175] Table 4 Water softening resistance test of on-site core samples and standard curing test blocks

[0176]

[0177] As shown in Table 4, after testing, the softening coefficient after soaking in water far exceeds 85%, and the strength of the core sample soaked in water is better than the strength growth under natural conditions, meeting the technical index requirements.

[0178] 1.4 Water absorption

[0179] The water absorption rate of the 28-day-old field core samples and standard-cured test blocks was tested, and the data is shown in Table 7.

[0180] Table 5 Water absorption test of field core samples and standard curing test blocks

[0181]

[0182] As shown in Table 5, the water absorption rate of the 28-day-old field core samples and standard-cured test blocks was tested, and the average water absorption rates were 5.57% and 5.58% respectively, both meeting the technical index requirements.

[0183] 1.5 XRD

[0184] X-ray diffraction analysis was performed on samples of the self-compacting phosphogypsum base material mixture at 14 days and 28 days. The analysis results are shown in Figure 1 .

[0185] Comparing the XRD patterns of 14d and 28d samples of self-compacting phosphogypsum base materials, it can be seen that the ettringite content is low and there is no obvious difference between the two ages, indicating that ettringite does not continue to be generated with the increase of age, which is beneficial to the overall stability of the base structure.

[0186] 1.6 Environmental Assessment

[0187] The potential adverse environmental impacts of self-compacting phosphogypsum base materials stem primarily from the release of pollutants into the soil and surrounding environment after prolonged immersion or erosion by rainwater. Therefore, these materials were tested using a solid waste leaching toxicity test method, employing the horizontal oscillation method. Pollutant indicators in the leachate from 28-day-old core samples of the self-compacting phosphogypsum base materials were measured. The results are shown in Table 6.

[0188] Table 6 Test results of pollutant precipitation in the leaching solution of core samples at 28 days of age

[0189]

[0190] After the implementation of the test section, the leachate of the core sample of the self-compacting phosphogypsum base material in the test section at the age of 28 days was tested. The test results showed that after solidification and modification, the content of harmful substances in the leachate of the material was very low, which met the requirements of the emission standards and satisfied the environmental protection goals of the test section.

[0191] Based on the above test results, it can be seen that the self-compacting performance, mechanical properties and environmental impact of the road base paved with self-compacting phosphogypsum base material meet the technical standards.

[0192] 2. Economic and social benefits

[0193] 2.1 Economic Benefits

[0194] The economic comparison of self-compacting phosphogypsum base material and 5% cement stabilized crushed stone is shown in Table 7.

[0195] Table 7 Comparison of economic performance between self-compacting phosphogypsum base material and 5% cement stabilized crushed stone

[0196]

[0197] As shown in Table 7, the overall cost of a self-compacting phosphogypsum base material (45% phosphogypsum) for road base is roughly equivalent to that of a conventional 5% cement-stabilized gravel base. Considering the large-scale, integrated use of phosphogypsum in future projects, the cost of both the raw material and production costs of phosphogypsum will likely decrease significantly, indicating broad prospects for its widespread application and significant economic benefits.

[0198] 2.2 Social Benefits

[0199] Phosphogypsum, a solid waste, replaces a significant amount of aggregate in road bases. For urban trunk roads, with a 45% phosphogypsum content, the stabilized base of each highway is 35,000 tons, resulting in a consumption of approximately 15,800 tons of phosphogypsum slag per kilometer. This saves 15,800 tons of natural aggregate, effectively realizing the resource utilization and large-scale, efficient utilization of industrial waste, generating positive social benefits. This also significantly alleviates road construction challenges in areas with scarce mining stone resources, contributing to resource conservation, energy conservation, and sustainable urban development.

[0200] In summary, the present invention provides a self-compacting phosphogypsum base material and a preparation method thereof. The base material not only plays a role in quickly consuming phosphogypsum and reducing inventory stacking pressure, thereby achieving the effect of resource utilization and turning waste into treasure, but also has good fluidity and high mechanical strength. When used in base road construction, its filling performance, compressive strength, water absorption, softening coefficient, unstable substance crystal phase analysis, and pollutant indicators can all meet the road base performance requirements, construction work performance requirements, and pollutant emission requirements, and has significant economic and social benefits. It can be widely used in road bases in municipal and highway projects.

[0201] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A self-compacting phosphogypsum road base material, characterized by: The base material includes phosphogypsum, cementitious material, aggregate, admixture and water, and the solid components are calculated in the following mass percentages: phosphogypsum 40-55%, cementitious material 4-13%, aggregate 35-50%, admixture 0.2-0.7%, and water-cement ratio 4.5-7.5; the moisture content of the phosphogypsum is lower than 12%, and the particle size of the phosphogypsum is 5-45 μm; the cementitious material is S95-grade granulated blast furnace slag powder and 42.5-grade ordinary Portland cement; the mass ratio of the 42.5-grade ordinary Portland cement is 1-4%, and the mass ratio of the S95-grade slag powder is 3-9%.

2. The self-compacting phosphogypsum road base material according to claim 1, characterized in that: The aggregate is a mixture of sand and gravel, and the sand is machine-made fine sand with a particle size of less than 4.75 mm; The crushed stone is graded crushed stone, which is fine crushed stone with a particle size of 5-10 mm and coarse crushed stone with a particle size of 10-20 mm, with a mass ratio of 3:

7.

3. The self-compacting phosphogypsum road base material according to claim 1, characterized in that: The mass ratio of the cement to the slag powder is 1:1.5-4.

5.

4. The self-compacting phosphogypsum road base material according to claim 1, characterized in that: The admixtures include retarders and water reducers, accounting for 0.3-0.4% of the total mass of the mixture.

5. The self-compacting phosphogypsum road base material according to claim 4, characterized in that: The water reducer is a polycarboxylate water reducer, and the retarder is citric acid, with a mass ratio of 1:0.1-0.

3.

6. The self-compacting phosphogypsum road base material according to claim 1, characterized in that: The base material includes phosphogypsum, cementitious material, aggregate, admixture and water, and the components are calculated in the following mass percentages: phosphogypsum 40-50%, cementitious material 6-10%, aggregate 40-50%, admixture 0.3-0.4%, and water-cement ratio 6.5-7.

5.

7. The method for preparing the self-compacting phosphogypsum road base material according to claim 1, comprising the following steps: S1. Weigh each raw material according to mass percentage and set aside; S2. Take part of the phosphogypsum and an appropriate amount of water and mix in a mixer, mix well to form a first mixture; S3. The cementitious material, the remaining phosphogypsum, aggregate, admixture and the remaining water are mixed in a mixer and mixed to form a second mixture; S4. The first mixture is added to the second mixture and mixed to form a third mixture; S5. The third mixture is formed into a molding mold and allowed to stand to form a self-compacting phosphogypsum road base material; Among them, in S2, the amount of phosphogypsum is 80-90% of the total amount, and the amount of water is 60-70% of the total amount.

8. The method for preparing a self-compacting phosphogypsum road base material according to claim 7, characterized in that: In S2, the stirring speed of phosphogypsum and water is 100-200 r / min, and the time is 1-3 min; In S3, the stirring speed of each component is 100-200 r / min, and the time is 2-4 min; In S4, the stirring speed of each component is 100-200 r / min, and the time is 3-6 min.

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