CN118108478A - Solid waste phosphogypsum roadbed improvement soil curing agent and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of soil curing agents, in particular to a solid waste phosphogypsum roadbed improvement soil curing agent and a preparation method thereof. The curing agent comprises the following raw materials in percentage by mass: the curing material is prepared by mixing a curing mixture and a stabilizer; the curing mixture comprises 7% of cement, 2% of lime, 10% of calcined phosphogypsum and 81% of phosphogypsum; the stabilizer comprises sodium silicate, sodium metaaluminate and calcium chloride; the proportion of the solidifying material to the soil is self-adaptive. Through the method, the early performance and the water stability of the solidified soil are better improved, so that the internal structure of the sample is more compact, and the strength is also greatly improved. The preparation method is used for preparing the solid waste phosphogypsum roadbed improving soil curing agent.

Description

Solid waste phosphogypsum roadbed improvement soil curing agent and preparation method thereof

Technical Field

The invention relates to the technical field of soil curing agents, in particular to a solid waste phosphogypsum roadbed improvement soil curing agent and a preparation method thereof.

Background

For the application of phosphogypsum in the aspect of road engineering base materials, for example, chinese patent publication No. CN114804675A provides a composite alkali-activated cementing material and a use method thereof, and the prepared composite alkali-activated cementing material has the advantages of low energy consumption, high strength, good durability and the like, can meet the same type of soil, and greatly improves the mechanical property of the soil. For example, the chinese patent of invention CN115893966a provides a cement stabilized phosphogypsum bottom ash stone for road base and a preparation method thereof, and the cement stabilized phosphogypsum bottom ash stone for road base can realize expansion of recycling utilization of bottom ash and phosphogypsum, full substitution of natural fine aggregate and reduction of cement production resource consumption, and save resources while protecting environment. For example, the Chinese patent publication No. CN115974515A provides a cohesive soil-based fluidized solidified soil and a preparation method thereof, and the invention realizes the preparation of the cohesive soil-based fluidized solidified soil and is an efficient, economical and stable cohesive soil fluidized solidified soil.

In view of the above, the feasibility of adding phosphogypsum for road bed construction has been confirmed, and it is one of the ways to solidify soil, but the amount of phosphogypsum is too small in the prior art due to the hydrophilicity of phosphogypsum, so that the purpose of consuming a large amount of phosphogypsum cannot be achieved. Or the types of the additives to be added are too many, so that the use process is complex and the cost is increased. It is therefore necessary to provide a cured material which can be used in a large amount to consume phosphogypsum and which also has a strength up to standard.

Disclosure of Invention

The invention aims at: in order to solve the problems, a solid waste phosphogypsum roadbed improving soil curing agent and a preparation method thereof are provided.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

The solid waste phosphogypsum roadbed improvement soil curing agent comprises the following raw materials in percentage by mass: the curing material is prepared by mixing a curing mixture and a stabilizer; the curing mixture comprises 7% of cement, 2% of lime, 10% of calcined phosphogypsum and 81% of phosphogypsum; the stabilizer comprises sodium silicate, sodium metaaluminate and calcium chloride; the proportion of the solidifying material to the soil is self-adaptive.

Preferably, the ratio of the curing mixture to the stabilizer is 98%:2%, the stabilizer comprises sodium silicate 100%; wherein, the proportion of the solidifying material and the soil is 20-30% and 70-80% of the solidifying material and the soil.

Preferably, the ratio of the curing material to the soil is 25%:75%.

Preferably, the ratio of the curing mixture to the stabilizer is 97.8%:2.2 percent of stabilizer comprising 90 percent of sodium silicate and 10 percent of sodium metaaluminate, wherein the mixture ratio of the curing material and the soil is 20 to 30 percent of the curing material and 70 to 80 percent of the soil.

Preferably, the ratio of the curing material to the soil is 25%:75%.

Preferably, the ratio of the curing mixture to the stabilizer is 97.5%:2.5 percent of stabilizer comprising 80 percent of sodium silicate and 20 percent of calcium chloride, wherein the mixture ratio of the curing material and the soil is 20 to 30 percent of the curing material and 70 to 80 percent of the soil.

Preferably, the ratio of the curing material to the soil is 25%:75%.

Preferably, the calcined phosphogypsum is prepared by calcining phosphogypsum in an oven at 150 ℃ for 2 hours so that the phosphogypsum is dehydrated.

A preparation method of a solid waste phosphogypsum roadbed improving soil curing agent, which is used for preparing the solid waste phosphogypsum roadbed improving soil curing agent, and comprises the following steps of,

S1, fully drying soil in an oven at 105 ℃ for more than 12 hours; grinding the dried soil sample, sieving with a 2mm sieve to obtain a powdery soil sample with uniform properties, and placing the powdery soil sample in a dry and sealed environment for later use;

s2, sequentially adding lime and phosphogypsum into the powdery soil sample in the S1 according to a proportion, and uniformly mixing;

S3, weighing a certain amount of water, adding a stabilizer into the water according to a proportion, and uniformly mixing to ensure that the stabilizer is completely dissolved in the water;

s4, uniformly stirring the stabilizer solution in the step S3 and the middle mixing soil in the step S2;

S5, sequentially adding cement and calcined phosphogypsum into the soil sample mixture in the S4 according to a proportion, and fully and uniformly mixing;

s6, static pressure is carried out on the soil sample mixture in the step S5 to form a cylindrical test piece with the diameter of 5cm and the height of 5 cm;

and S7, demolding the test piece in the step S6, and then placing the test piece in a sealing bag, and curing the test piece to a required age under standard curing conditions to obtain phosphogypsum composite material cured soil.

In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:

In the invention, calcined phosphogypsum is subjected to hydration reaction after meeting water, so as to generate phosphogypsum, gypsum grains are connected with each other to form a stable structure, and the internal cohesive force of the phosphogypsum is beneficial to maintaining the stability of the material and improving the strength. Phosphogypsum contains P ₂O₅ which is acidic, but has negative influence when the phosphogypsum composite material solidifies soil. Therefore, the addition of lime helps to inhibit leaching of water-soluble phosphorus and fluorine in phosphogypsum, neutralizes acidity of phosphogypsum, provides a favorable alkaline environment for hydration reaction to generate gel and ettringite, and improves early strength. Phosphogypsum reacts with cement hydration products to form ettringite, and pozzolanic reaction occurs between cement and lime, so that the process is durable and slow.

The introduction of sodium silicate promotes the hydration of cement, soil particles are gelled and wrapped by hydrated calcium silicate and fill pores to form a stable aggregate structure, a small amount of short columnar ettringite is locally generated, and the sodium silicate and cement hydration products are mutually overlapped and distributed in a net shape, so that the solidified soil particle structure is more compact. The early performance and the water stability of the solidified soil are better improved.

Sodium metaaluminate is easy to separate out aluminum hydroxide precipitate after being dissolved in water, and the solution is alkaline because the sodium metaaluminate does not react with alkali. Ettringite is a fine needle-like crystal that interpenetrates between hydrated calcium silicate and unhydrated phases, enhancing the connection force between particles and thus strength. The AL ³⁺,S0₄ ^2- in the solution is beneficial to the formation of ettringite and improves the strength, on one hand, the addition of sodium silicate and sodium metaaluminate can promote the generation of gel, and a large amount of hydrated calcium silicate can form an integral body after the soil particles are agglomerated, so that the strength is improved; on the other hand, sodium silicate reacts with sodium metaaluminate to generate aluminum hydroxide, and small gaps are filled, so that the internal structure of the sample is more compact, and the strength is greatly improved.

After the calcium chloride and the sodium silicate are doped together, the sodium silicate reacts with the calcium chloride to generate silica gel immediately, the reaction formula is ：Na₂O·nSiO₂+CaCl₂+mH₂O→nSiO₂·(m-1)H₂O+Ca(OH)₂+2NaCl., the gel material can wrap soil particles, the soil particles are glued between the soil particles, the pores are filled, and the strength is improved under standard curing conditions. Various crystals are formed by cross crystallization in the later stage of hydration, and are lapped tightly, but ettringite crystals exist in a gelatinous body generated by the reaction of calcium chloride and sodium silicate, so that the structural integrity is enhanced, and the strength is greatly improved.

Drawings

FIG. 1 is a schematic illustration of phosphogypsum sampling process;

FIG. 2 is a schematic diagram of the microscopic morphology of phosphogypsum;

FIG. 3 is a schematic XRD spectrum of phosphogypsum according to an embodiment of the present invention;

FIG. 4 is a schematic diagram showing a particle size distribution curve of phosphogypsum according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of an phosphogypsum compaction curve according to an embodiment of the present invention;

FIG. 6 is a schematic illustration of calcined phosphogypsum;

FIG. 7 is a schematic diagram of CPG microscopic morphology;

fig. 8 is a schematic view illustrating a particle size distribution curve of loess according to an embodiment of the present invention.

FIG. 9 is a schematic XRD spectrum of phosphogypsum composite solidified soil provided by the embodiment of the invention;

fig. 10 is a scanning image of an electron microscope of the phosphogypsum composite cured soil.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Referring to fig. 1-10, the present invention provides a technical solution:

The solid waste phosphogypsum roadbed improvement soil curing agent comprises the following raw materials in percentage by mass: the curing material is prepared by mixing a curing mixture and a stabilizer; the curing mixture comprises 7% of cement, 2% of lime, 10% of calcined phosphogypsum and 81% of phosphogypsum; the stabilizer comprises sodium silicate, sodium metaaluminate and calcium chloride; the proportion of the solidifying material to the soil is self-adaptive.

Example 1

The ratio of the curing mixture to the stabilizer is 98 percent: 2%, the stabilizer comprises sodium silicate 100%; wherein, the proportion of the solidifying material and the soil is 20 percent, and the soil is 80 percent.

Example 2

The ratio of the curing mixture to the stabilizer is 98 percent: 2%, the stabilizer comprises sodium silicate 100%; wherein, the proportion of the curing material to the soil is 25% of the curing material and 75% of the soil.

Example 3

The ratio of the curing mixture to the stabilizer is 98 percent: 2%, the stabilizer comprises sodium silicate 100%; wherein, the proportion of the solidifying material to the soil is 30 percent, and the soil is 70 percent.

Example 4

The ratio of the curing mixture to the stabilizer is 97.8 percent: 2.2 percent of stabilizer comprising 90 percent of sodium silicate and 10 percent of sodium metaaluminate, wherein the mixture ratio of the curing material and the soil is 20 percent of the curing material and 80 percent of the soil.

Example 5

The ratio of the curing mixture to the stabilizer is 97.8 percent: 2.2 percent of stabilizer comprising 90 percent of sodium silicate and 10 percent of sodium metaaluminate, wherein the curing material is 25 percent and the soil is 75 percent.

Example 6

The ratio of the curing mixture to the stabilizer is 97.8 percent: 2.2 percent of stabilizer comprises 90 percent of sodium silicate and 10 percent of sodium metaaluminate, wherein the curing material is 30 percent and the soil is 70 percent.

Example 7

The ratio of the curing mixture to the stabilizer is 97.5 percent: 2.5 percent of stabilizer comprises 80 percent of sodium silicate and 20 percent of calcium chloride, wherein the curing material is 20 percent and the soil is 80 percent.

Example 8

The ratio of the curing mixture to the stabilizer is 97.5 percent: 2.5 percent of stabilizer comprising 80 percent of sodium silicate and 20 percent of calcium chloride, wherein the curing material is 25 percent and the soil is 75 percent.

Example 9

The ratio of the curing mixture to the stabilizer is 97.5 percent: 2.5 percent of stabilizer comprises 80 percent of sodium silicate and 20 percent of calcium chloride, wherein the curing material is 30 percent and the soil is 70 percent.

Control group: soil 100%.

Wherein, calcined phosphogypsum is prepared by calcining phosphogypsum for 2 hours in an oven at 150 ℃ so that the phosphogypsum is dehydrated.

In the embodiment, the calcined phosphogypsum is subjected to hydration reaction after meeting water, so that phosphogypsum is generated, gypsum grains are connected with each other to form a stable structure, and the internal cohesive force of the phosphogypsum is beneficial to maintaining the stability of the material and improving the strength. Phosphogypsum contains P ₂O₅ which is acidic, but has negative influence when the phosphogypsum composite material solidifies soil. Therefore, the addition of lime helps to inhibit leaching of water-soluble phosphorus and fluorine in phosphogypsum, neutralizes acidity of phosphogypsum, provides a favorable alkaline environment for hydration reaction to generate gel and ettringite, and improves early strength. Phosphogypsum reacts with cement hydration products to form ettringite, and pozzolanic reaction occurs between cement and lime, so that the process is durable and slow.

The introduction of sodium silicate promotes the hydration of cement, soil particles are gelled and wrapped by hydrated calcium silicate and fill pores to form a stable aggregate structure, a small amount of short columnar ettringite is locally generated, and the sodium silicate and cement hydration products are mutually overlapped and distributed in a net shape, so that the solidified soil particle structure is more compact. The early performance and the water stability of the solidified soil are better improved.

Sodium metaaluminate is easy to separate out aluminum hydroxide precipitate after being dissolved in water, and the solution is alkaline because the sodium metaaluminate does not react with alkali. Ettringite is a fine needle-like crystal that interpenetrates between hydrated calcium silicate and unhydrated phases, enhancing the connection force between particles and thus strength. The AL ³⁺,S0₄ ^2- in the solution is beneficial to the formation of ettringite and improves the strength, on one hand, the addition of sodium silicate and sodium metaaluminate can promote the generation of gel, and a large amount of hydrated calcium silicate can form an integral body after the soil particles are agglomerated, so that the strength is improved; on the other hand, sodium silicate reacts with sodium metaaluminate to generate aluminum hydroxide, and small gaps are filled, so that the internal structure of the sample is more compact, and the strength is greatly improved.

After the calcium chloride and the sodium silicate are doped together, the sodium silicate reacts with the calcium chloride to generate silica gel immediately, the reaction formula is ：Na₂O·nSiO₂+CaCl₂+mH₂O→nSiO₂·(m-1)H₂O+Ca(OH)₂+2NaCl., the gel material can wrap soil particles, the soil particles are glued between the soil particles, the pores are filled, and the strength is improved under standard curing conditions. Various crystals are formed by cross crystallization in the later stage of hydration, and are lapped tightly, but ettringite crystals exist in a gelatinous body generated by the reaction of calcium chloride and sodium silicate, so that the structural integrity is enhanced, and the strength is greatly improved.

Further, phosphogypsum: in this embodiment, fig. 1 (a) is a view of phosphogypsum sampling. The color was dark gray before drying, mostly in powder form, with many lumps, pH 4.96, and water content up to 16.34%, as shown in FIG. 1 (b). Phosphogypsum is dried at 55 ℃, cooled and sieved by a 2mm sieve, as shown in fig. 1 (c). As shown in FIG. 2, the microscopic morphology of phosphogypsum is mainly in the form of plate crystals, and fine particles are attached to the surface. The chemical compositions of the phosphogypsum X-ray fluorescence spectrometer test materials are shown in table 1. According to the XRD spectrum of phosphogypsum of FIG. 3, the main component is calcium sulfate dihydrate (CaSO ₄·2H₂ O) and contains a small amount of P ₂O₂ and other impurities. The particle size distribution of the phosphogypsum after sieving is between 4m and 300m, and the particle size distribution curve of the phosphogypsum is shown in figure 4. The optimal water content is 12.1%, the maximum dry density is 1.575g/cm < 3 >, and the compaction curve is shown in figure 5;

TABLE 1 main chemical components of phosphogypsum (mass percent)

Calcining phosphogypsum: the Phosphogypsum (PG) is calcined for 2 hours in a baking oven at 150 ℃, so that the Phosphogypsum (PG) can instantly lose 1.5H2O due to rapid heat absorption, semi-hydrated gypsum (CaSO ₄·2H₂ O) is formed, the Calcined Phosphogypsum (CPG) for the test is obtained, the calcined phosphogypsum used in the test is processed by a chemical plant, the appearance of the calcined phosphogypsum is grey-white, and the powder is shown in figure 6. The chemical compositions of the calcined phosphogypsum X-ray fluorescence spectrometer test materials are shown in Table 2. The microscopic morphology is shown in FIG. 7. CPG presents smaller diamond-like platy particles, smoother surfaces, and more powdery material than phosphogypsum.

TABLE 1 main chemical components (mass percent) of calcined phosphogypsum

Cement lime: in this experiment, p.o42.5 portland cement, commercially available quicklime, was used, and the chemical composition of the test materials was measured by an X-ray fluorescence spectrometer as shown in table 3.

TABLE 2 Cement and lime Main chemical composition (mass percent)

Stabilizing agent: sodium silicate (Na ₂SiO₃·5H₂ O) produced by Tianjin far chemical agent Co., ltd, AR analytically pure, white granules or powder; sodium metaaluminate (NaAl O ₂), produced from the metallocene chemical reagent plant, tianjin, AR analytically pure, white powder; anhydrous calcium chloride (CaCl ₂), available from the company, inc. Of the chemical industry, AR, was analytically pure in spherical particulate form.

Loess: the test soil sampling site is a construction site in a certain university, and is directly used for sampling at a representative position, and the soil sample is directly characterized in that: the color is mainly yellow brown, and a small amount of gray brown soil is doped, wherein the soil contains less impurities such as stones or plants. The soil sample is put into a baking oven, the temperature is set to 105 ℃, the baking is carried out for 24 hours, and the dried soil is put into a ball mill for grinding after being cooled to room temperature. The laser particle sizer analyzes the particle size of the ball-milled loess, the particle size distribution of the ball-milled loess is between 1 μm and 70 μm, and the particle size distribution curve is shown in fig. 8. The main components of the soil are loess and fine sand, and the soil body is used for phosphogypsum composite solidification test in the scheme.

Proportioning: the main curing materials comprise 7% of cement, 2% of lime, 10% of calcined phosphogypsum and 81% of phosphogypsum. The stabilizer is one or more of sodium silicate, sodium metaaluminate and calcium chloride.

Further, three phosphogypsum composite material formulas are selected, and are mixed with test soil to prepare solid waste curing test soil (hereinafter referred to as curing soil), wherein the mixing amount of the phosphogypsum composite curing materials is 20%, 25% and 30%, and the mixing ratio scheme of the curing soil is shown in Table 4:

Table 4 paste composite cured clay test piece formulation

1. The unconfined compressive strength test gave the following data in table 5:

TABLE 5 unconfined compressive Strength results

Table 5 above shows the results of the 7d, 14d, 28d unconfined compressive strength test for the three-formulation solidified soil. As can be seen from the table, the unconfined compressive strength of the solidified soil increases with the curing age and the doping amount of the phosphogypsum composite material of each group. The addition of the stabilizer greatly improves the early strength, the main strength source is from the hydration reaction of phosphogypsum composite material, and more ettringite, hydrated calcium silicate, hydrated calcium aluminosilicate and other substances are generated in the solidified soil, so that the strength is provided for the solidified soil. On the other hand, after cement and soil are mixed, minerals on the surfaces of cement particles and water in the soil are subjected to hydration reaction, various hydrates are formed in the middle of the soil, and the hydrates are continuously hardened to form cement stone aggregate. Whereas calcium hydroxide in cement and lime hydration products can continue to react with CO ₂ in the air to form CaCO ₃, this process is slower and therefore still shows a tendency to increase in strength at age 28 d. The soil has larger porosity, a plurality of micro pores and cracks exist in the soil, and the addition of the dispersed phosphogypsum can increase the overall compactness and improve the binding force between matrixes.

Notably, the control group without added cured material was flushly dispersed, and the strength was that of the non-flushly. The strength of different ages is variable, which indicates that with the growth of the ages, the plain soil does not have the capability of strength growth and the strength of the plain soil is not high. The test piece added with the phosphogypsum composite material can still keep the integrity of the test piece after being immersed in water, because hydration products such as hydrated calcium silicate and the like are indissolvable mineral crystals, and the test piece is not dispersed when being in contact with water while cementing soil particles. The hydration product fills the pores of soil particles, and reduces the porosity and permeability of the solidified soil, thereby improving the water resistance and stability of the solidified soil. This is a result of the combined effect of the filling effect and the cementing effect, resulting in an improved water stability of the solidified soil.

2. The dry shrinkage crack resistance test shows that the quality loss rate and the dry shrinkage strain result data of the phosphogypsum composite material solidified soil are shown in the following table 6:

TABLE 6 quality loss rate and Dry shrinkage Strain results for phosphogypsum composite cured soil

Test number	Mass loss rate (%)	Strain in dry shrinkage (%)
			Example 1	9.91	0.77
Example 2	9.42	0.67
			Example 3	9.41	0.55
Example 4	10.02	0.81
			Example 5	9.75	0.59
Example 6	9.17	0.45
			Example 7	9.73	0.768
Example 8	9.18	0.55
			Example 9	8.97	0.53
Control group	13.42	1.05

The above table shows the quality loss rate and the shrinkage strain results of the phosphogypsum composite material solidified soil, and the quality loss rate and the shrinkage strain of the phosphogypsum composite material solidified soil are reduced along with the increase of the doping amount of the solidified material. On the one hand, the incorporation of the stabilizer creates a gelling substance and helps to fill the pores and increase the compactness of the material, which reduces the loss of water and thus the rate of water loss. On the other hand, the mixture is likely to undergo a chemical reaction when meeting water, and the generated expandable crystals such as ettringite are developed and expanded under the condition of water enrichment, but rich pores exist among soil particles, and most of the expansion of the crystals is represented as filling the pores among the soil particles, so that the strength of a solidified soil structure is improved, and the shrinkage strain of a sample is reduced. The solidified soil consumes a part of water when chemical reaction occurs, and the water is converted into crystal water in the generated compound, so that the water is not easy to lose, and the mass loss rate of the sample is reduced.

3. XRD spectrum analysis

As can be seen from the XRD spectra of 28d curing ages of example 3, example 6 and example 9 shown in fig. 10, a part of ettringite peak was detected, and the gel formed by hydration of cement was formed by binding phosphate of phosphogypsum in an alkaline environment. SO ₄ ^2- not only plays a role in promoting cement hydration, but also can excite phosphogypsum activity, and improves early strength and later strength; OH ^- will accelerate the dissolution of the active minerals and form calcium silicate hydrate and calcium aluminate hydrate; in addition, SO ₄ ^2- also reacts with aluminum in the soil to form ettringite, and crystals generated by the reactions increase the volume of the material, fill gaps among soil grains and connect the soil grains to form a net structure, SO that solidified soil becomes compact, and the strength and stability of the soil body are effectively enhanced. Meanwhile, the diffraction peak of the calcium sulfate dihydrate in the test piece still exists and is high, which indicates that much phosphogypsum is added and does not participate in the reaction. The hydration reaction is continuously carried out, so that a tighter structure is formed among different hydration products, and the compressive strength and durability of the solidified soil are further improved. Therefore, the sufficient curing time has important significance for improving the performance of the phosphogypsum composite solidified soil.

As can be seen from the scanning images of the phosphogypsum composite cured soil electron microscope of the three proportions of the example 3, the example 6 and the example 9 in FIG. 6, a large number of needle-shaped ettringite crystals exist in hydration products, and the higher the proportion strength is, the more ettringite crystals are in number. And flaky, flocculent or netlike hydrated calcium silicate products (C-S-H) can be observed, and the hydrated products are alternately doped among soil particles to form an integral framework and are connected with the soil particles, so that the phosphogypsum composite solidified soil has good mechanical strength. In addition to ettringite, a portion of unreacted phosphogypsum crystals in the form of flakes can be seen, as well as a small amount of gel, indicating that the cement hydration in the system is not complete; the group 3 of ettringite has more crystals, the crystal growth state is relatively stereo, the C-S-H gel wraps the ettringite and exists at the same time, and almost all ettringite which is seen in the group 9 is in staggered joint, and almost no C-S-H gel exists, so that the cement hydration is more thorough. The microscopic morphology comparison of the three proportions can well indicate that the strength of the phosphogypsum composite material solidified soil is mainly provided by ettringite which is a final product, and the alkaline environment has great promotion effect on the excitation of the activities of the cement and the minerals in the soil. It is noted that more of the figure is columnar ettringite, acicular ettringite metastable crystals, which will continue to react with calcium aluminohydrate in the presence of calcium aluminohydrate in the surrounding, resulting in columnar mono-sulfur calcium aluminohydrate (3cao.al2o3.caso4.12h2o) eventually reaching a steady state. The columnar ettringite has larger mutually-overlapped surfaces in the crystals in the growth process, and is mutually entangled, and when the columnar ettringite is stressed, the friction resistance between the crystals for resisting relative displacement is larger. The columnar crystals fill the structural space more fully, and the properties are more stable. Ettringite has high strength but contains a large amount of crystal water, and the solid phase volume can be increased by about 1.5 times under the condition of rich water, which is also the main reason why the sample swells to cause good drying shrinkage performance.

The invention also provides a technical scheme that:

The preparation method of the solid waste phosphogypsum roadbed improving soil curing agent is used for the solid waste phosphogypsum roadbed improving soil curing agent and comprises the following steps of,

S1, fully drying soil in an oven at 105 ℃ for more than 12 hours; grinding the dried soil sample, sieving with a 2mm sieve to obtain a powdery soil sample with uniform properties, and placing the powdery soil sample in a dry and sealed environment for later use;

s2, sequentially adding lime and phosphogypsum into the powdery soil sample in the S1 according to a proportion, and uniformly mixing;

S3, weighing a certain amount of water, adding a stabilizer into the water according to a proportion, and uniformly mixing to ensure that the stabilizer is completely dissolved in the water;

s4, uniformly stirring the stabilizer solution in the step S3 and the middle mixing soil in the step S2;

S5, sequentially adding cement and calcined phosphogypsum into the soil sample mixture in the S4 according to a proportion, and fully and uniformly mixing;

s6, static pressure is carried out on the soil sample mixture in the step S5 to form a cylindrical test piece with the diameter of 5cm and the height of 5 cm;

and S7, demolding the test piece in the step S6, and then placing the test piece in a sealing bag, and curing the test piece to a required age under standard curing conditions to obtain phosphogypsum composite material cured soil.

The previous description of the embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A solid waste phosphogypsum roadbed improvement soil curing agent is characterized in that: comprises the following raw materials in percentage by mass: the curing material is prepared by mixing a curing mixture and a stabilizer; the curing mixture comprises 7% of cement, 2% of lime, 10% of calcined phosphogypsum and 81% of phosphogypsum; the stabilizer comprises sodium silicate, sodium metaaluminate and calcium chloride; the proportion of the solidifying material to the soil is self-adaptive.

2. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 1, which is characterized in that: the ratio of the curing mixture to the stabilizer is 98 percent: 2%, the stabilizer comprises sodium silicate 100%; wherein, the proportion of the solidifying material and the soil is 20-30% and 70-80% of the solidifying material and the soil.

3. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 2, which is characterized in that: the proportion of the solidifying material to the soil is 25 percent: 75%.

4. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 1, which is characterized in that: the ratio of the curing mixture to the stabilizer is 97.8 percent: 2.2 percent of stabilizer comprising 90 percent of sodium silicate and 10 percent of sodium metaaluminate, wherein the mixture ratio of the curing material and the soil is 20 to 30 percent of the curing material and 70 to 80 percent of the soil.

5. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 2, which is characterized in that: the proportion of the solidifying material to the soil is 25 percent: 75%.

6. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 1, which is characterized in that: the ratio of the curing mixture to the stabilizer is 97.5 percent: 2.5 percent of stabilizer comprising 80 percent of sodium silicate and 20 percent of calcium chloride, wherein the mixture ratio of the curing material and the soil is 20 to 30 percent of the curing material and 70 to 80 percent of the soil.

7. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 6, which is characterized in that: the proportion of the solidifying material to the soil is 25 percent: 75%.

8. The solid waste phosphogypsum roadbed improving soil curing agent according to claim 1, which is characterized in that: the calcined phosphogypsum is prepared by calcining the phosphogypsum for 2 hours in an oven at 150 ℃ so that the phosphogypsum is dehydrated.

9. A method for preparing a solid waste phosphogypsum roadbed improving soil curing agent, which is used for preparing the solid waste phosphogypsum roadbed improving soil curing agent according to claim 1, and is characterized in that: the method comprises the steps of,

S1, fully drying soil in an oven at 105 ℃ for more than 12 hours; grinding the dried soil sample, sieving with a 2mm sieve to obtain a powdery soil sample with uniform properties, and placing the powdery soil sample in a dry and sealed environment for later use;

s2, sequentially adding lime and phosphogypsum into the powdery soil sample in the S1 according to a proportion, and uniformly mixing;

S3, weighing a certain amount of water, adding a stabilizer into the water according to a proportion, and uniformly mixing to ensure that the stabilizer is completely dissolved in the water;

s4, uniformly stirring the stabilizer solution in the step S3 and the middle mixing soil in the step S2;

S5, sequentially adding cement and calcined phosphogypsum into the soil sample mixture in the S4 according to a proportion, and fully and uniformly mixing;

s6, static pressure is carried out on the soil sample mixture in the step S5 to form a cylindrical test piece with the diameter of 5cm and the height of 5 cm;

and S7, demolding the test piece in the step S6, and then placing the test piece in a sealing bag, and curing the test piece to a required age under standard curing conditions to obtain phosphogypsum composite material cured soil.