Large-dosage undisturbed phosphogypsum curing material for roadbed

Abstract

The invention relates to the technical field of civil engineering materials, and particularly discloses a large-dosage undisturbed phosphogypsum curing material for a roadbed and a preparation method of the large-dosage undisturbed phosphogypsum curing material. The curing material is prepared from the following components in percentage by mass: 40-60% of undisturbed phosphogypsum, 10-50% of slag, 10-30% of ordinary Portland cement and optional nano micro powder which accounts for 0-5% of the total mass of the three materials. Through scientific proportion design, a large amount of industrial byproduct ardealite is successfully recycled, and the defects that the ardealite is poor in water stability and easy to swell are overcome. After being mixed with soil, the material can generate a series of physical and chemical reactions to generate a gelling body with strength and effectively control volume change, so that the mechanical property and long-term stability of subgrade soil are remarkably improved. The invention not only provides a new way for the bulk consumption of phosphogypsum, but also reduces the dependence of roadbed engineering on traditional cement and lime, and has remarkable economic benefit and environmental protection value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste resource utilization and civil engineering materials, in particular to a large-mixing-amount raw phosphogypsum solidified material for roadbed. BACKGROUND

[0002] The large-scale construction of current highway infrastructure consumes a large amount of traditional road-building materials such as natural stone, lime and cement. With the increasing attention of the state to mineral resource exploitation and environmental protection, the cost of obtaining these traditional materials is rising and is not sustainable. At the same time, the chemical industry in China produces a large amount of industrial by-product phosphogypsum every year, which not only occupies a large amount of land, but also contains soluble phosphorus, fluorine and other impurities that pose a potential pollution risk to the surrounding water and soil, and a large-scale, high-value resource utilization approach is urgently needed.

[0003] Using phosphogypsum for roadbed engineering is one of the ideal directions for large-scale disposal. Domestic and foreign researchers have made many attempts, such as compounding phosphogypsum with cement, lime or other industrial waste residues for soil stabilization. However, the residual acidic impurities in phosphogypsum and its swelling properties after water contact have always been a technical bottleneck. When the mixing amount is high, it often leads to insufficient late strength growth, deterioration of water stability and uncontrolled volume expansion of the solidified body, making it difficult to meet the specification requirements of highway base materials and limiting its large-scale engineering application.

[0004] Therefore, developing a roadbed solidified material that can overcome the above technical obstacles and achieve high-mixing-amount, high-performance utilization of phosphogypsum is of great significance to promote the development of circular economy and reduce the cost of engineering construction. SUMMARY

[0005] The purpose of the present application is to provide a large-mixing-amount raw phosphogypsum solidified material for roadbed to solve the technical problems raised in the background.

[0006] To achieve the above purpose, the present application provides the following technical solutions: A large-mixing-amount raw phosphogypsum solidified material for roadbed, characterized by being composed of the following raw materials in mass percentage: (1) phosphogypsum mass percentage 40-60%; (2) slag mass percentage 10-50%; (3) Portland cement mass percentage 10-30%; and, optionally, nano-micropowder: 0-5% of the total mass of the raw phosphogypsum, slag and Portland cement.

[0007]

[0008] The application also provides a preparation method of the solidified material, namely: according to a designed mass ratio, raw phosphogypsum, slag, Portland cement and optional nano micro-powder are put into a mixing device, and mechanical stirring is performed until the mixture is uniform, so that the solidified material for roadbed is obtained.

[0009] Compared with the prior art, the application has the following beneficial effects: 1. The application has high resource utilization rate and remarkable environmental protection benefits: the application uses industrial solid waste phosphogypsum and slag as main raw materials, and the content can be up to 90% or more, which greatly promotes the recycling of industrial by-products and reduces environmental pressure.

[0010] 2. The application has excellent performance: Good strength development: through the synergistic effect of the ternary composite system of phosphogypsum, slag and cement, the alkaline environment provided by slag and cement in the hydration process stimulates the activity of phosphogypsum, and the hydration products mainly composed of ettringite are generated together to build a solid skeleton structure, so that the material has high early and later compressive strength (see example data); Controllable volume stability: after the solidified material is mixed with soil, a chemical reaction occurs, and part of the reaction products can produce micro-expansion to compensate for the shrinkage of the solidified soil. The micro-expansion effect of the system reaction can effectively offset the drying shrinkage of the solidified soil body, avoid performance degradation caused by shrinkage cracking, achieve controllable expansion, and ensure the long-term stability of the volume of the roadbed; Improving poor soil: especially suitable for saline soil, silt soil and other poor roadbed soil. The components in the material can react with the salt and clay minerals in the soil, and the phosphogypsum can react with silicates and other substances in the saline silt soil to generate new cementitious materials, fill the pores, provide support for the strength and water resistance of the solidified soil, and at the same time reduce the salt content of the silt soil, improve the engineering performance and physicochemical properties of the silt soil, and reduce the salt content and plasticity of the soil, and comprehensively improve the engineering properties of the soil. DETAILED DESCRIPTION

[0011] In the description of the application, unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail" and the like is only for the convenience of describing the application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second", "third" and the like are only for description purposes and cannot be understood as indicating or implying relative importance.

[0012] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0013] The present application provides a technical solution: A large amount of raw phosphogypsum solidification material for subgrade, characterized by being composed of raw materials in the following mass percentages: (1) The mass percentage of phosphogypsum is 40-60%; (2) The mass percentage of slag is 10-50%; (3) The mass percentage of Portland cement is 10-30%; and, optionally, nano-micropowder: 0-5% of the total mass of the raw phosphogypsum, slag and Portland cement.

[0014] Raw materials: The chemical composition of the raw phosphogypsum, granulated blast furnace slag and ordinary Portland cement (P.O 42.5) used in the present application is shown in the following table:

[0015] The subgrade soil used is placed in a 80°C blast drying oven for 24h to ensure that all the moisture in the soil is evaporated, with a moisture content of 0%; Sample preparation and testing method: 1. Soil sample pretreatment: Take the subgrade soil from the construction site, dry it in an 80°C blast drying oven to constant weight (about 24h), crush and sieve it for use; 2. Preparation of curing agent: according to the ratio (mass percentage) of the examples, weigh each dry powder component (phosphogypsum, slag, cement) and place it in a blender for dry mixing for at least 5 minutes until it is evenly mixed; 3. Compaction sample preparation: mix the mixed solidification material with the pretreated soil in a certain proportion (such as 20% curing agent + 80% dry soil), add water with the best water content, stir evenly and pour into a mold, and compact it into a Φ50 mm x 50 mm cylindrical test piece under standard compaction work; 4. Curing and testing: after the test piece is demolded, it is placed in standard curing conditions (temperature 20±2°C, humidity ≥90%) for curing to the specified age (3d, 28d, 60d), and then the unconfined compressive strength (UCS) is tested using a universal testing machine. Example 1

[0016] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 40%, slag 30%, cement 30%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added, and stirring is continued for 3 minutes (slow stirring for 2 minutes, fast stirring for 1 minute). Discharge, place the mixed solidified material into a hollow cylindrical steel mold with an inner diameter of φ50mmx50mm, and press into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2℃ and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 2

[0017] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 40%, slag 40%, cement 20%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added, and stirring is continued for 3 minutes (slow stirring for 2 minutes, fast stirring for 1 minute). Discharge, place the mixed solidified material into a hollow cylindrical steel mold with an inner diameter of φ50mmx50mm, and press into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2℃ and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 3

[0018] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 40%, slag 50%, cement 10%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added, and stirring is continued for 3 minutes (slow stirring for 2 minutes, fast stirring for 1 minute). Discharge, place the mixed solidified material into a hollow cylindrical steel mold with an inner diameter of φ50mmx50mm, and press into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2℃ and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 4

[0019] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 50%, slag 20%, cement 30%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added, and stirring is continued for 3 minutes (slow stirring for 2 minutes, fast stirring for 1 minute). Discharge, place the mixed solidified material into a hollow cylindrical steel mold with an inner diameter of φ50mmx50mm, and press into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2℃ and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 5

[0020] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 50%, slag 30%, cement 20%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added and stirred for 3 minutes (slow stirring for 2 minutes and fast stirring for 1 minute). The mixed solidified material is discharged and placed in a φ50mm x 50mm hollow cylindrical steel mold. The sample is pressed into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2°C and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 6

[0021] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 50%, slag 40%, cement 10%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added and stirred for 3 minutes (slow stirring for 2 minutes and fast stirring for 1 minute). The mixed solidified material is discharged and placed in a φ50mm x 50mm hollow cylindrical steel mold. The sample is pressed into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2°C and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 7

[0022] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 60%, slag 10%, cement 30%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added and stirred for 3 minutes (slow stirring for 2 minutes and fast stirring for 1 minute). The mixed solidified material is discharged and placed in a φ50mm x 50mm hollow cylindrical steel mold. The sample is pressed into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2°C and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 8

[0023] The mixing ratio of the phosphogypsum solidified material in this embodiment is: phosphogypsum 60%, slag 20%, cement 20%, and the three materials are mixed uniformly for standby. The subgrade soil and the solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and the solidified agent are stirred uniformly, the weighed water is slowly added and stirred for 3 minutes (slow stirring for 2 minutes and fast stirring for 1 minute). The mixed solidified material is discharged and placed in a φ50mm x 50mm hollow cylindrical steel mold. The sample is pressed into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2°C and a humidity of 90% for curing. The engineering performance test results are shown in Table 1. Example 9

[0024] The mixing ratio of the phosphogypsum solidified material in this example is: phosphogypsum 60%, slag 30%, cement 10%, and the three materials are mixed uniformly for standby. The subgrade soil and solidified agent are placed in a stirring pot and stirred for 30 seconds. After the soil and solidified agent are uniformly stirred, the weighed water is slowly added and continues to be stirred for 3 minutes (slow stirring for 2 minutes and fast stirring for 1 minute). The mixed solidified material is discharged and placed in a φ50mm x 50mm hollow cylindrical steel mold, and is pressed into shape using a testing machine. After demolding, the sample is placed in a constant temperature and humidity standard curing box with a temperature of 20+2℃ and a humidity of 90% for curing. The engineering performance test results are shown in Table 1.

[0025]

[0026] As can be seen from the data in Table 1, in all examples, the 28-day compressive strength of the material is above 15 MPa, and the highest can reach 32 MPa (Example 1).

[0027] The 60-day strength of most of the mixtures remains stable or slightly increases, showing good long-term stability. In particular, the mixture with a phosphogypsum content of 40%-50% and a total slag and cement content of 50%-60% (such as Example 1: phosphogypsum 40% + slag 30% + cement 30%) exhibits the best strength development rule and comprehensive performance, fully meeting or even exceeding the requirements of general subgrade materials for strength.

[0028] The 28-day strength of the high-dosage phosphogypsum solidified material is in the range of 15-32 MPa; this strength value is much higher than the requirements for base layer (3.0-7.0 MPa) and subbase layer (≥2.0-3.0 MPa) in the specification.

[0029] This shows that by optimizing the mixture ratio, the material fully meets or even far exceeds the requirements of high-grade highways in terms of strength performance, successfully realizing the unification of high dosage and high performance of phosphogypsum.

[0030] It can be understood that the above implementation is only an exemplary implementation adopted for the purpose of illustrating the principles of the present application, but the present application is not limited thereto. Those skilled in the art can make various modifications and improvements without departing from the spirit and essence of the present application, and these modifications and improvements are also considered within the protection scope of the present application.

Claims

1. A large amount of raw state phosphogypsum solidification material for subgrade, characterized by, consists of the following raw materials in the following mass percentages: (1) phosphogypsum mass percentage of 40-60%; (2) slag mass percentage of 10-50%; (3) Portland cement mass percentage of 10-30%; and, optionally, nano-micropowder: 0-5% of the total mass of the raw phosphogypsum, slag and Portland cement.

2. The large-amount-of-addition raw phosphogypsum solidified material for roadbed according to claim 1, characterized in that:

3. The large-amount-of-addition raw phosphogypsum solidified material for roadbed according to claim 1, characterized in that:

4. The large-amount-of-addition raw phosphogypsum solidified material for roadbed according to claim 1, characterized in that: the following step: according to the designed mass ratio, raw phosphogypsum, slag, Portland cement and optional nano-micropowder are put into a mixing device, and are fully mechanically stirred until mixed uniformly, to obtain the solidified material for roadbed.

5. A method of making a large volume raw phosphogypsum based solidified material according to any one of claims 1 to 4, characterized in that: ​

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