Method for preparing red mud-phosphogypsum roadbed material through hydration-carbonization synergistic maintenance

Abstract

This invention discloses a method for preparing red mud-phosphogypsum roadbed material through hydration-carbonation synergistic curing, belonging to the field of resource utilization of bulk industrial solid waste and road engineering technology. The invention involves drying, grinding, and sieving red mud and phosphogypsum to obtain red mud powder and phosphogypsum powder, respectively. The red mud powder, phosphogypsum powder, blast furnace slag powder, and cement are then thoroughly mixed in a certain proportion, water is added, and the mixture is pressed into shape and then subjected to hydration-carbonation synergistic curing to obtain the red mud-phosphogypsum roadbed material. This invention can transform red mud, phosphogypsum, and blast furnace slag into materials with good water resistance and mechanical strength that meet the requirements of roadbed construction projects. It enables the resource utilization, harmlessness, and reduction of industrial solid waste such as red mud and phosphogypsum, while simultaneously achieving carbon dioxide fixation through the carbonization process, thus achieving the goal of synergistic efficiency improvement in pollution reduction and carbon reduction, generating significant economic, social, and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of bulk industrial solid waste and road engineering technology, specifically involving a method for preparing red mud-phosphogypsum roadbed material by hydration-carbonation synergistic preparation. Background Technology

[0002] Roadbeds are the foundation of highways, and their construction requires substantial amounts of soil and stone resources. In some regions, due to numerous construction projects and high material demands, over-exploitation has led to a severe shortage of roadbed filling materials. Red mud is a major solid waste product of the alumina industry, while phosphogypsum is a byproduct of the phosphate fertilizer industry. Currently, the comprehensive utilization rate of red mud and phosphogypsum in my country remains low, resulting in the long-term accumulation of large amounts of solid waste, severely encroaching on land resources and hindering the sustainable development of related industries.

[0003] However, directly using red mud and phosphogypsum to prepare roadbed materials suffers from engineering defects such as low early mechanical strength and extremely poor water resistance, failing to meet the standards and requirements of roadbed construction. Therefore, this invention proposes a method for the synergistic preparation of red mud-phosphogypsum roadbed materials through hydration-carbonation. This invention uses blast furnace slag powder and cement as auxiliary cementing materials, mixed with red mud and phosphogypsum. First, an initial strength framework is constructed through hydration reaction. Then, an innovative accelerated carbonation curing process is introduced, utilizing carbon dioxide to react with hydration products and unreacted components, depositing calcium carbonate at the material pores and interfaces, thereby achieving microstructural densification. This method not only effectively overcomes the limitations of single hydration curing but also fundamentally avoids the fatal flaw of the conventional "carbonation first, hydration later" process—that is, early carbonation rapidly forms a calcium carbonate shell on the surface of unreacted particles, creating a "coating effect" that blocks subsequent water penetration, leading to hindered internal hydration and the inability to establish an effective strength framework. The invention's strictly defined sequence of "hydration followed by moderate carbonization" truly achieves a synergistic effect mechanism of "hydration to create a framework + carbonization to fill pores". Summary of the Invention

[0004] To address the shortcomings of existing red mud and phosphogypsum-based roadbed materials, which suffer from low early-stage mechanical strength and poor water resistance, this invention proposes a method for the synergistic preparation of red mud-phosphogypsum roadbed materials through hydration and carbonization. This method optimizes the microstructure of multi-source solid waste materials using a synergistic curing system of "hydration framework + moderate carbonization densification," providing a new approach for the large-scale resource utilization of red mud and phosphogypsum. This method achieves the resource utilization of carbon dioxide while meeting the mechanical strength and durability requirements for roadbed construction.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing red mud-phosphogypsum roadbed material by hydration-carbonation synergistic process, comprising the following steps:

[0006] (1) Red mud, phosphogypsum and blast furnace slag are dried, ground and sieved to obtain red mud powder, phosphogypsum powder and blast furnace slag powder respectively;

[0007] (2) The red mud powder, phosphogypsum powder, blast furnace slag powder and cement are mixed thoroughly in proportion to obtain a solid mixture;

[0008] (3) Add water to the solid mixture and stir thoroughly to form a homogeneous slurry. After molding, perform hydration-carbonation co-curing to obtain red mud-phosphogypsum roadbed material.

[0009] In a preferred embodiment of the present invention, the cement is ordinary Portland cement.

[0010] As a preferred embodiment of the present invention, in step (1), the drying temperature is 80-105°C and the time is 12-24h; the grinding and sieving specifically involves passing through a 60-100 mesh sieve.

[0011] In a preferred embodiment of the present invention, in step (2), the mass ratio of the red mud powder and the phosphogypsum powder is 1:1; based on the total mass of the solid mixture, the mass percentage of the blast furnace slag powder is 5%, and the mass percentage of the cement is 6%.

[0012] As a preferred embodiment of the present invention, in step (3), the liquid-solid mass ratio of the added water to the solid mixture is 0.6; an automatic stirring is performed using a planetary mixer; the molding process specifically involves injecting the slurry into a mold and vibrating it for 2 minutes to remove air bubbles, followed by smoothing the surface.

[0013] As a preferred embodiment of the present invention, in step (3), the hydration-carbonation synergistic curing is specifically as follows: first, the initial curing is carried out under standard conditions of temperature 20±2℃ and relative humidity ≥95% for 24±2h; after demolding, hydration curing is continued under standard conditions, and then at the end of the curing cycle, the environment is switched to an environment with carbon dioxide volume concentration of 10%~20% and relative humidity of 60% for accelerated carbonation curing.

[0014] As a preferred embodiment of the present invention, the total age of the hydration-carbonation synergistic curing is fixed at 168h, wherein the accelerated carbonization curing time is 3 to 28h, corresponding to the standard hydration curing time after demolding as (144h - accelerated carbonization curing time); preferably, the accelerated carbonization curing time is 7h.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) An efficient hydration-carbonation synergistic system was constructed. Blast furnace slag with high specific surface area and fine pore size can promote the nucleation and formation of early hydration products; cement provides a key Ca source to jointly drive early hydration; red mud and phosphogypsum mainly provide Al / Si and SO4. 2- This process promotes the formation of a dense hydration framework (such as ettringite, CSH gel, etc.) in the early stages of the system. The subsequent introduction of moderately accelerated carbonization curing further promotes the deposition and filling of CaCO3 at pores and interfaces, thereby accelerating the densification of the microstructure. This method effectively overcomes the limitations of single hydration curing or single carbonization curing, forming a synergistic mechanism of "hydration framework + moderate carbonization densification".

[0017] (2) Significantly improved mechanical properties and water resistance of the material. Under a specific cross-curing process of hydration followed by carbonization, red mud, phosphogypsum, blast furnace slag and cement not only meet but also far exceed the engineering requirements of traditional roadbed materials. Its 7-day unconfined compressive strength can reach more than 5.0 MPa; and the filling effect of calcium carbonate greatly reduces the pore channels for water intrusion, exhibiting excellent water resistance, with a softening coefficient of up to 0.93.

[0018] (3) Outstanding environmental and economic benefits. This invention uses a hydration-carbonation synergistic process to prepare roadbed materials, which can not only dispose of red mud and phosphogypsum, two major industrial solid wastes, on a large scale and reduce land encroachment, but also achieve permanent physical sequestration of the greenhouse gas carbon dioxide through mineralization reaction. Compared with traditional roadbed filling materials, this invention greatly reduces the dependence on natural stone and soil, and the production process is clear and controllable, with significant social and economic benefits. Attached Figure Description

[0019] Figure 1 A process flow diagram for the synergistic preparation of red mud-phosphogypsum roadbed material by hydration-carbonation;

[0020] Figure 2 This is a comparison chart of the unconfined compressive strength and splitting tensile strength test results of the subgrade materials prepared in Examples 1-5 and Comparative Examples 1-3 at a total age of 7 days;

[0021] Figure 3 The graph shows a comparison of the softening coefficient evaluation results of the subgrade materials prepared in Examples 1-5 and Comparative Examples 1-3 at a total age of 7 days. Detailed Implementation

[0022] To better illustrate the purpose, technical solution, and significant progress of this invention, the invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0023] The auxiliary cementing material used in the embodiments and comparative examples of this invention is ordinary Portland cement (P·O 42.5 grade); the red mud comes from industrial solid waste discharged from the Bayer process of bauxite leaching; and the phosphogypsum comes from industrial solid waste discharged from the wet process of phosphoric acid.

[0024] Example 1

[0025] like Figure 1 As shown, a method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation includes the following steps:

[0026] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0027] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0028] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0029] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0030] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0031] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0032] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0033] (8) After demolding, the test block continued to undergo hydration curing under standard conditions for 137 hours, and then immediately transferred to a carbonization curing chamber with a carbon dioxide volume concentration of 10% and a relative humidity of 60% for 7 hours of accelerated carbonization curing. The total curing age of the test block was 168 hours, and the hydration-carbonation synergistic modified roadbed material was finally obtained.

[0034] Example 2

[0035] like Figure 1As shown, a method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation includes the following steps:

[0036] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0037] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0038] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0039] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0040] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0041] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0042] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 h of initial molded hydration curing, and then demold.

[0043] (8) After demolding, the test block continued to undergo hydration curing under standard conditions for 137 hours, and then was immediately transferred to a carbonization curing chamber with a carbon dioxide volume concentration of 15% and a relative humidity of 60% for 7 hours of accelerated carbonization curing. The total curing age of the test block was 168 hours, and the hydration-carbonation synergistic modified roadbed material was finally obtained.

[0044] Example 3

[0045] like Figure 1 As shown, a method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation includes the following steps:

[0046] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0047] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0048] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0049] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0050] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0051] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0052] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0053] (8) After demolding, the test block continued to undergo hydration curing under standard conditions for 137 hours, and then was immediately transferred to a carbonization curing chamber with a carbon dioxide volume concentration of 20% and a relative humidity of 60% for 7 hours of accelerated carbonization curing. The total curing age of the test block was 168 hours, and the hydration-carbonation synergistic modified roadbed material was finally obtained.

[0054] Example 4

[0055] like Figure 1 As shown, a method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation includes the following steps:

[0056] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0057] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0058] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0059] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0060] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0061] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0062] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0063] (8) After demolding, the test block continued to be hydrated and cured under standard conditions for 141 hours. Then it was immediately transferred to a carbonization curing chamber with a carbon dioxide volume concentration of 20% and a relative humidity of 60% for 3 hours of accelerated carbonization curing. The total curing age was 168 hours, and the hydration-carbonization synergistic modified roadbed material was finally obtained.

[0064] Example 5

[0065] like Figure 1 As shown, a method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation includes the following steps:

[0066] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0067] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0068] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0069] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0070] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0071] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0072] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0073] (8) After demolding, the test block continued to be hydrated and cured under standard conditions for 130 hours. Then it was immediately transferred to a carbonization curing chamber with a carbon dioxide volume concentration of 20% and a relative humidity of 60% for 14 hours of accelerated carbonization curing. The total curing age was 168 hours, and the hydrated-carbonized synergistic modified roadbed material was finally obtained.

[0074] Comparative Example 1

[0075] The raw material ratios in this comparative example are exactly the same as in Example 1, except that an accelerated carbonization process is not introduced. The specific steps are as follows:

[0076] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0077] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0078] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0079] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0080] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0081] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0082] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0083] (8) After demolding, the test block continues to be hydrated and cured for 144 hours under the standard conditions of temperature 20±2℃ and relative humidity ≥95% until the total curing age reaches 168 hours. That is, the test block only undergoes a single hydration curing process throughout its entire life cycle, resulting in a single hydration roadbed material.

[0084] Comparative Example 2

[0085] The raw material ratio of this comparative example is exactly the same as that of Example 1, except that the accelerated carbonization time is significantly extended. The specific steps are as follows:

[0086] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0087] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0088] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0089] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0090] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0091] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0092] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0093] (8) After demolding, the test block continued to be hydrated and cured under standard conditions for 116 hours, and then transferred to a carbonization box with a carbon dioxide volume concentration of 20% and a relative humidity of 60% for accelerated carbonization and curing for up to 28 hours. The total curing period was 168 hours.

[0094] Comparative Example 3

[0095] The raw material ratios in this comparative example are exactly the same as in Example 1, except that the order of intervention of the hydration and carbonization processes is reversed. The specific steps are as follows:

[0096] (1) The red mud was placed in an electric heating constant temperature drying oven and dried at 105℃ for 24 hours. After being crushed by grinding equipment, it was passed through an 80-mesh sieve to obtain red mud powder for later use.

[0097] (2) Place the phosphogypsum in an electric heating constant temperature drying oven and dry it at 80°C for 24 hours. After grinding, it is pulverized by a grinding equipment and passed through an 80-mesh sieve to obtain phosphogypsum powder for later use.

[0098] (3) Place the blast furnace slag in an electric heating constant temperature drying oven and dry it at 105℃ for 24 hours. After grinding, it is crushed by grinding equipment and passed through an 80-mesh sieve to obtain blast furnace slag powder for later use.

[0099] (4) The red mud powder, phosphogypsum powder, blast furnace slag powder and ordinary silicate cement prepared above are precisely proportioned and fully mixed according to the mass percentage of 44.5%:44.5%:5%:6% to obtain a solid mixture;

[0100] (5) Add mixing water to the above solid mixture at a liquid-to-solid ratio of 0.6, place it in a planetary mixer and stir automatically at a uniform speed to obtain a homogeneous modified red mud-phosphogypsum slurry.

[0101] (6) The slurry is injected in layers into a cylindrical standard mold of Φ50×50mm, and continuously vibrated on a vibrating table for 2 minutes to fully remove the micro air bubbles trapped inside the slurry, and then the surface is scraped smooth.

[0102] (7) Place the molded specimen under standard curing conditions of 20±2℃ and relative humidity ≥95% for 24 hours of initial molded hydration curing, and then demold.

[0103] (8) After demolding, the test block was first transferred to a carbonization box with a carbon dioxide volume concentration of 20% and a relative humidity of 60% for 7 hours of early accelerated carbonization curing, and then transferred to standard conditions for 137 hours of subsequent hydration curing, with a total curing age of 168 hours.

[0104] The hydration-carbonation synergistic roadbed materials prepared in Examples 1-5 and Comparative Examples 1-3 mainly existed in the form of slurry. The slurry was poured into a Φ50×50mm mold, allowed to stand at room temperature for 24 hours, and then demolded to obtain cylindrical test blocks. Subsequently, the blocks underwent a hydration-carbonation synergistic curing process according to the predetermined paths for each group. At the end of the 7-day total curing period, the unconfined compressive strength and splitting tensile strength of the test blocks were measured. Simultaneously, the test blocks were immersed to saturation and their residual strength was measured to calculate the softening coefficient, which reflects the material's water resistance. The relevant test data are shown in Table 1.

[0105] Table 1

[0106] Unconfined compressive strength Splitting strength Softening coefficient Example 1 4.3 1.12 0.88 Example 2 4.6 1.23 0.84 Example 3 5.3 1.3 0.93 Example 4 5.1 1.2 0.9 Example 5 4.8 1.25 0.87 Comparative Example 1 2.7 0.25 0.45 Comparative Example 2 2.8 0.3 0.67 Comparative Example 3 1.4 0.33 0.75

[0107] From Table 1, Figure 2 and Figure 3 It is evident that the subgrade material prepared using the hydration-carbonation synergistic curing method described in this invention possesses excellent mechanical strength and water resistance. It not only meets the engineering strength requirements for road base construction but also enables large-scale disposal of industrial solid wastes such as red mud and phosphogypsum. Comparison shows that the unconfined compressive strength, splitting tensile strength, and softening coefficient of the subgrade material prepared using the hydration-carbonation synergistic method are significantly affected by the curing regime and carbonation time. Specifically, standard hydration curing followed by 7 hours of moderately accelerated carbonation curing results in the most significant strength improvement and excellent water resistance. Adding appropriate amounts of blast furnace slag powder and cement as auxiliary materials effectively reduces the total cement usage, and both the unconfined compressive strength and splitting tensile strength meet construction standards.

[0108] Furthermore, data from Examples 1 (10% CO2 concentration), 2 (15% CO2 concentration), and 3 (20% CO2 concentration) show that composite roadbed materials exhibit good mechanical strength and water resistance within a carbon dioxide concentration range of 10%–20%. With an appropriate increase in carbon dioxide concentration, the carbonization and densification effect is further enhanced, and the unconfined compressive strength steadily increases from 4.3 MPa to 5.3 MPa. Various mechanical and durability indicators show a gradual optimization trend, with the synergistic maintenance effect at a 20% CO2 concentration being the best.

[0109] In particular, a direct comparison between Example 3 and Comparative Example 3 clearly shows that, under the premise of completely identical raw material ratios, if the curing sequence is reversed to "early carbonization for 7 hours followed by hydration for 137 hours" (Comparative Example 3), the 7-day unconfined compressive strength of the test block is only 1.4 MPa, and the softening coefficient drops sharply to 0.75; while the compressive strength of Example 3 of this invention is as high as 5.3 MPa, and the softening coefficient reaches 0.93. This directly confirms with detailed data that if carbonization is performed first, the resulting products will severely hinder the construction of the early hydration skeleton, leading to a sharp deterioration in mechanical properties. This further confirms the non-obvious but significant progress of the synergistic curing system of "hydration first, followed by moderate carbonization" of this invention in effectively optimizing the microstructure of materials and improving mechanical properties and durability.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing red mud-phosphogypsum roadbed material through hydration-carbonation synergistic curing, characterized in that, Includes the following steps: (1) Red mud, phosphogypsum and blast furnace slag are dried, ground and sieved to obtain red mud powder, phosphogypsum powder and blast furnace slag powder respectively; (2) The obtained red mud powder, phosphogypsum powder, and blast furnace slag powder are mixed with cement to obtain a solid mixture; (3) Add water to the solid mixture and stir thoroughly. After molding, perform hydration-carbonation co-curing to obtain red mud-phosphogypsum roadbed material.

2. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The cement is ordinary Portland cement.

3. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The drying temperature in step (1) is 80-105℃ and the drying time is 12-24h.

4. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The grinding and sieving in step (1) specifically refers to grinding with grinding equipment and then passing through a 60-100 mesh sieve.

5. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The hydration-carbonization co-curing process in step (3) specifically involves first curing the material in the mold for 24±2 hours under standard conditions of 20±2℃ and relative humidity ≥95%, and then demolding it for hydration curing. Subsequently, the material is transferred to an environment with a carbon dioxide concentration of 10%~20% and a relative humidity of 60% for accelerated carbonization curing.

6. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The mass ratio of red mud powder to phosphogypsum powder is 1:1, and the blast furnace slag powder and cement account for 5% and 6% of the total mass of the solid mixture, respectively.

7. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The liquid-solid mass ratio of the water and solid mixture added in step (3) is 0.6; the thorough stirring is carried out by automatic stirring with a planetary mixer; the molding process involves injecting the slurry into the mold and vibrating it for 2 minutes to remove air bubbles, and then scraping the surface smooth.

8. The method for preparing red mud-phosphogypsum roadbed material by synergistic hydration-carbonation according to claim 1, characterized in that, The total time for the hydration-carbonization co-curing process in step (3) is 7 days, of which the accelerated carbonization curing time is 3 to 28 hours.

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