Over-wet soil precipitation curing agent, preparation method thereof and over-wet soil precipitation method

Abstract

The invention discloses an over-wet soil precipitation curing agent, a preparation method thereof and an over-wet soil precipitation method, and relates to the technical field of road engineering. The over-wet soil precipitation curing agent comprises the following raw materials in percentage by mass: 10%-20% of cement, 20%-30% of carbide slag, 50%-69% of mineral powder and 0.1%-1% of amino modified polyacrylonitrile fiber. The amino-modified polyacrylonitrile fibers are polyacrylonitrile fibers with amino groups introduced on the surfaces. The over-wet soil precipitation curing agent provided by the invention can quickly reduce the water content of over-wet soil and improve the strength of a soil body, and is environment-friendly and low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, and in particular to an over-wet soil dewatering solidifying agent and a preparation method thereof, and an over-wet soil dewatering method. Background Art

[0002] Earth-filled roadbed is a common foundation type in domestic road construction. It is located under the pavement structure and directly bears the load of the pavement and the influence of the natural environment. Earth-filled roadbed mainly uses mechanical compaction to make the soil denser and reduce the porosity, thereby improving the overall stability and bearing capacity of the roadbed. In addition, the friction and inter-biting between coarse-grained soil and the enhancement of molecular attraction between fine-grained soil further improve the strength and stability of the soil. The construction process of earth-filled roadbed is relatively simple and does not require complex equipment and technology, so the construction cost is low. At the same time, earthwork materials are widely available and easy to obtain, which makes earth-filled roadbed more economically advantageous.

[0003] The raw soil required for earthwork filling roadbed is generally taken from the in-situ soil around the project. These soils usually have a high water content due to groundwater immersion or rainfall, and are over-wet soil. Over-wet soil cannot be directly used for roadbed filling, mainly because the high water content will cause the soil particles to be wrapped in a thick water film. During mechanical compaction, this water film will hinder the discharge of air, making it impossible for soil particles to gather effectively, resulting in a decrease in the density of the soil layer. In addition, water is incompressible, and an overly thick water film will further affect the compaction effect of the soil, thereby weakening the overall performance of the roadbed. Therefore, before the construction of earthwork filling roadbed, the over-wet soil must be treated with precipitation to ensure that it meets the construction requirements.

[0004] In order to effectively reduce the moisture content of over-wet soil, traditional methods usually use natural drying or adding materials such as lime. However, natural drying is limited by weather conditions, has low efficiency and a long cycle; and although the addition of lime can accelerate precipitation, it may cause cracks in the earthwork roadbed due to its volume expansion after absorbing water, and increase the cost of the project. Therefore, it is particularly important to develop an efficient, environmentally friendly and economical over-wet soil precipitation material. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an over-wet soil dehydration and solidification agent, which can quickly reduce the water content of over-wet soil, improve the strength of the soil, and is environmentally friendly and low-cost.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides an over-wet soil precipitation solidifying agent, comprising the following raw materials in percentage by mass: 10% to 20% cement, 20% to 30% carbide slag, 50% to 69% mineral powder and 0.1% to 1% amino-modified polyacrylonitrile fiber;

[0007] The amino-modified polyacrylonitrile fiber is a polyacrylonitrile fiber with amino groups introduced into the surface.

[0008] As an improvement of the above technical solution, the specific surface area of ​​the mineral powder is 450m 2 / kg~550m 2 / kg.

[0009] As an improvement of the above technical solution, the specific surface area of ​​the cement is 400m 2 / kg~500m 2 / kg.

[0010] As an improvement of the above technical solution, the fiber length of the amino-modified polyacrylonitrile fiber is 10 mm to 30 mm.

[0011] As an improvement of the above technical solution, the content of calcium hydroxide in the carbide slag is ≥85% calculated by mass percentage;

[0012] The cement is silicate cement.

[0013] As an improvement of the above technical solution, calculated by mass percentage, the raw materials of the amino-modified polyacrylonitrile fiber include 15% to 30% polyacrylonitrile fiber, 10% to 20% ethylenediamine and 60% to 75% water.

[0014] As an improvement of the above technical solution, the amino-modified polyacrylonitrile fiber is prepared by the following method:

[0015] Mixing water and ethylenediamine to prepare an ethylenediamine solution;

[0016] The polyacrylonitrile fiber is immersed in an ethylenediamine solution to obtain a mixture;

[0017] Heat the mixture to 60°C to 80°C and maintain the temperature under reflux for 10 to 14 hours, take out the fiber and rinse it with clean water;

[0018] The washed fibers are dried to obtain amino-modified polyacrylonitrile fibers.

[0019] Accordingly, the second aspect of the present invention provides a method for preparing an over-wet soil precipitation solidifying agent, which is used to prepare the above-mentioned wet soil precipitation solidifying agent, comprising the following steps:

[0020] (1) drying cement, carbide slag and mineral powder respectively, and ball-milling the dried cement and mineral powder respectively;

[0021] (2) According to the proportion, the cement, carbide slag and mineral powder treated in step (1) are mixed evenly, and then amino-modified polyacrylonitrile fiber is added and mixed evenly to obtain an over-wet soil dewatering solidifying agent.

[0022] As an improvement of the above technical solution, in step (1), the conditions for ball milling the dried cement are as follows: the ball milling time is 40 min to 80 min, the rotation speed is 400 r / min to 600 r / min, and the ball-to-cement ratio is 3:1 to 5:1;

[0023] The conditions for ball milling the dried mineral powder are as follows: ball milling time is 90 to 150 min, rotation speed is 400 r / min to 600 r / min, and ball-to-material ratio is 3:1 to 5:1.

[0024] As an improvement of the above technical solution, before step (2), a preparation step of amino-modified polyacrylonitrile fiber is further included. The preparation method of amino-modified polyacrylonitrile fiber includes the following steps:

[0025] Mixing water and ethylenediamine under ice bath conditions to prepare an ethylenediamine solution;

[0026] The polyacrylonitrile fiber is completely immersed in the ethylenediamine solution to obtain a mixture;

[0027] The mixture is heated to 60°C to 80°C and maintained at reflux temperature for 10 to 14 hours, then cooled to room temperature, the fiber is taken out and rinsed with clean water;

[0028] The washed fiber is dried at 40° C. to 60° C. for 10 to 16 hours to obtain amino-modified polyacrylonitrile fiber.

[0029] Correspondingly, the third aspect of the present invention provides a method for dewatering an over-wet soil, comprising the following steps: adding an over-wet soil dewatering and solidifying agent to the over-wet soil and stirring evenly, waiting for the moisture content of the over-wet soil to decrease, and when the moisture content of the over-wet soil decreases to a preset moisture content, the dewatering treatment of the over-wet soil can be completed, and the roadbed filler can be collected; the over-wet soil dewatering and solidifying agent is the above-mentioned over-wet soil dewatering and solidifying agent.

[0030] The implementation of the present invention has the following beneficial effects: the raw materials of the over-wet soil precipitation curing agent of this embodiment include 10% to 20% cement, 20% to 30% calcium carbide slag, 50% to 69% mineral powder and 0.1% to 1% amino-modified polyacrylonitrile fiber. The over-wet soil precipitation curing agent using this formula can achieve the dual precipitation effect of physical adsorption and chemical reaction, can quickly reduce the water content of over-wet soil, and improve the strength of the soil. The amino-modified polyacrylonitrile fiber is introduced into the formula, and the conversion between kinetic energy and thermal energy is achieved through the interaction between water molecules in the over-wet soil and the hydrophilic group (amino group) in the fiber, so that the fiber releases heat, thereby improving the precipitation rate of the over-wet soil. In addition, the introduction of amino-modified polyacrylonitrile fiber can also effectively improve the durability of over-wet soil. In the over-wet soil dehydration and solidification agent, cement and mineral powder are used as cementitious materials. Through the hydration reaction of cement and mineral powder and its exothermic effect, the dehydration rate of over-wet soil is significantly improved. In addition, cement and mineral powder can produce a synergistic effect with amino-modified polyacrylonitrile fiber, using the fiber to absorb the water vapor generated by the reaction of cement and mineral powder, thereby achieving the effect of liquefaction and exothermic, making the heating process of the entire system more durable. Carbide slag in the over-wet soil dehydration and solidification agent is used as an activator to improve the hydration efficiency of mineral powder. In addition, carbide slag is low in cost and belongs to the recycling of industrial solid waste, which is environmentally friendly. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0032] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. Raw materials used without specifying the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] This embodiment discloses an over-wet soil precipitation solidifying agent, comprising the following raw materials in percentage by mass: 10% to 20% cement, 20% to 30% carbide slag, 50% to 69% mineral powder and 0.1% to 1% amino-modified polyacrylonitrile fiber;

[0034] The amino-modified polyacrylonitrile fiber is a polyacrylonitrile fiber with amino groups introduced into the surface.

[0035] The over-wet soil precipitation solidifying agent of the present embodiment can quickly absorb moisture in the soil through physical and chemical effects, reduce the water content of the soil, and improve the strength and stability of the soil. At the same time, the over-wet soil precipitation solidifying agent of the present embodiment has low preparation cost and is environmentally friendly, is easy to mass produce, and can meet the actual needs of engineering projects.

[0036] It is worth noting that over-wet soil refers to soil with a high water content, such as soil with a water content of 20% to 45%. Since these soils are in a water-saturated state for a long time, if they are directly used for construction, the so-called "spring soil" phenomenon is very likely to occur, resulting in ineffective compaction. After completion, under the influence of vehicle loads, the roadbed and road surface are very likely to suffer from settlement, deformation, and loss of stability. In order to overcome these difficulties, this embodiment proposes an over-wet soil precipitation and curing agent, which is used to precipitate and solidify the over-wet soil. Under the combined action of the two precipitation mechanisms of hydration reaction and fiber heat release, the rapid precipitation of the over-wet soil can be achieved, and the treated over-wet soil is used as a roadbed filler. After compaction, the remaining active ingredients in the over-wet soil precipitation and curing agent can form a gel-like network structure under the excitation of hydroxide ions to fill the pores of the soil, thereby enhancing the bearing capacity and stability of the soil. Therefore, the over-wet soil treated with the over-wet soil precipitation solidification agent of this embodiment can not only meet the construction requirements, but also has good stability and durability during long-term use, effectively avoiding the problem of roadbed and pavement damage caused by excessively high soil moisture content.

[0037] To further explain, when cement comes into contact with over-wet soil, due to the influence of electrostatic force, cement particles will firmly adhere to the surface of the over-wet soil, competing with soil particles for water while preventing the agglomeration of soil particles, increasing the surface area of ​​the over-wet soil, and thus improving the efficiency of precipitation. After the cement hardens, some soil particles are converted into cement soil, which has a certain hardness and can be used as aggregate, thereby enhancing the strength and stability of the roadbed.

[0038] Mineral powder is an industrial solid waste generated during the blast furnace metal smelting process. Its main component is calcium aluminosilicate, which exists in the form of glass. Since the activity of mineral powder is lower than that of cement, during the initial mixing process, the mineral powder is mainly adsorbed on the surface of the over-wet soil, causing large pieces of soil to decompose into small particles, thereby increasing the surface area of ​​the soil. After the over-wet soil is compacted as a roadbed filler, it is - Under the action of ions, the glassy substances in the mineral powder gradually dissolve, releasing elements such as silicon, calcium and aluminum. These elements recombine in the form of ions to form CSH gels, which together with the hydration products of cement that has not completely reacted during the precipitation stage form a network skeleton, providing strength support for solidifying over-wet soil, filling the gaps in the soil, and further improving the mechanical properties and durability of the soil.

[0039] Calcium carbide slag is a byproduct of industrial production, mainly from the waste residue left after calcium carbide produces acetylene gas, which is rich in calcium hydroxide. When calcium carbide slag comes into contact with over-wet soil, it will dissolve in the moisture in the soil and release a large amount of OH -Ions. These ions act as stimulants to activate the activity of mineral powder, thereby avoiding the inability to provide a sufficient alkaline environment for mineral powder reaction due to excessive cement consumption in the precipitation stage. In addition, the rich calcium ions in carbide slag help promote the formation of a cementitious network in the system, thereby enhancing the early mechanical properties of over-wet soil.

[0040] The amino-modified polyacrylonitrile fiber used in this embodiment refers to a polyacrylonitrile fiber that has been hydrophilically improved and a large number of hydrophilic groups, amino groups, are introduced on the surface, thereby significantly improving the hydrophilic performance. By introducing strongly hydrophilic amino groups on the surface of the polyacrylonitrile fiber, the ability of the polyacrylonitrile fiber to compete with soil particles for water is improved, so that the polyacrylonitrile fiber can more easily absorb water from the soil particles, contact the water film that wraps the soil particles, and increase the speed of water volatilization in the over-wet soil. After the amino-modified polyacrylonitrile fiber absorbs water, the hydrophilic groups on the fiber combine with water molecules, and the water molecules change from a state of irregular motion to a state of rest. According to the law of conservation of energy, the kinetic energy of the water molecules is converted into heat energy at this time, which is manifested as the amino-modified polyacrylonitrile fiber releasing heat, accelerating the volatilization of water in the over-wet soil. In addition, the hydration reaction caused by cement and mineral powder will generate heat, causing part of the water in the over-wet soil to volatilize in the form of water vapor, and part of the volatilized water vapor will be adsorbed on the amino-modified polyacrylonitrile fiber, changing from a gaseous state to a liquid state, and the liquefaction process will also generate heat, which can make the heat release process in the entire system more durable, further accelerating the precipitation efficiency of the over-wet soil. Therefore, by introducing amino-modified polyacrylonitrile fiber into the over-wet soil precipitation solidifier, the heating efficiency and duration of the whole system can be improved, so that most of the water in the over-wet soil evaporates in the form of water vapor, and a small part is transferred to the fiber. The water transferred to the fiber will not affect the mutual aggregation of soil particles during the compaction process; on the contrary, after the soil is compacted, the water remaining on the fiber will gradually evaporate over time, effectively improving the shrinkage caused by water loss in the soil and the cessation of hydration reaction, thereby improving the density of the soil, reducing shrinkage, and improving durability.

[0041] In one embodiment, the specific surface area of ​​the mineral powder is 450m 2 / kg~550m 2 / kg. Within this specific surface area range, the water demand of the mineral powder can reach the maximum value, which is beneficial to reduce the moisture content of the soil and improve the precipitation efficiency. If the specific surface area of ​​the mineral powder is too large or too small, its water demand will be reduced, thereby affecting the precipitation efficiency.

[0042] Specifically, the specific surface area of ​​the mineral powder is 450 m 2 / kg, 460m 2 / kg, 470m 2 / kg, 480m 2 / kg, 490m 2 / kg、500m 2 / kg, 510m 2 / kg, 520m 2 / kg, 530m 2 / kg, 540m 2 / kg, 550m 2 / kg, but not limited to.

[0043] In one embodiment, the specific surface area of ​​the cement is 400 m 2 / kg~500m 2 / kg, the specific surface area of ​​cement is controlled within this range, which can further improve the hydration rate of cement and further enhance the water precipitation efficiency of cement. And when the specific surface area of ​​cement is maintained at 400m 2 / kg~500m 2 / kg, higher precipitation efficiency and economic benefits can be achieved.

[0044] Specifically, the specific surface area of ​​cement is exemplarily 400 m 2 / kg, 410m 2 / kg, 420m 2 / kg, 430m 2 / kg, 440m 2 / kg, 450m 2 / kg, 460m 2 / kg, 470m 2 / kg, 480m 2 / kg, 490m 2 / kg、500m 2 / kg, but not limited to.

[0045] In one embodiment, the amino-modified polyacrylonitrile fiber has a fiber length of 10 mm to 30 mm. The use of amino-modified polyacrylonitrile fiber with a fiber length of 10 mm to 30 mm can not only further improve the ability of the fiber to compete with soil particles for water, thereby further increasing the rate of water volatilization in over-wet soil, but also better reduce the shrinkage of the soil body and further improve the durability of the soil body.

[0046] Specifically, the fiber length of the amino-modified polyacrylonitrile fiber is exemplarily 10 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, and 30 mm, but is not limited thereto.

[0047] Preferably, the mineral powder is S95 grade, which has higher activity.

[0048] In one embodiment, the calcium hydroxide content in the carbide slag is ≥85% calculated by mass percentage, which can more effectively activate the activity of the mineral powder and enhance the early mechanical properties of the over-wet soil.

[0049] In one embodiment, the cement is silicate cement. The main components of silicate cement are silicate cement clinker, admixtures and gypsum. When the components such as tricalcium silicate and dicalcium silicate in the silicate cement clinker come into contact with water, a hydration reaction will occur rapidly, consuming the water in the wet soil and releasing heat energy, further accelerating the evaporation of water, thereby achieving a more efficient precipitation effect.

[0050] In an optional embodiment of the present invention, PO425 type silicate cement can be used.

[0051] In one embodiment, calculated by mass percentage, the raw materials of the amino-modified polyacrylonitrile fiber include 15% to 30% polyacrylonitrile fiber, 10% to 20% ethylenediamine and 60% to 75% water.

[0052] In one embodiment, the amino-modified polyacrylonitrile fiber is prepared by the following method:

[0053] a. Mixing water and ethylenediamine to prepare an ethylenediamine solution;

[0054] b. immersing the polyacrylonitrile fiber in an ethylenediamine solution to obtain a mixture;

[0055] c. Heat the mixture to 60°C to 80°C and maintain the temperature under reflux for 10 to 14 hours, take out the fiber and rinse it with clean water;

[0056] d. Drying the rinsed fibers to obtain amino-modified polyacrylonitrile fibers.

[0057] By hydrophilically modifying polyacrylonitrile fiber, the amino-modified polyacrylonitrile fiber can compete for moisture in the soil more effectively, reduce the soil's binding effect on water, and thus increase the precipitation rate of over-wet soil.

[0058] More preferably, in the above step a, water and ethylenediamine are mixed under ice bath conditions to prepare an ethylenediamine solution.

[0059] More preferably, in the above step b, the polyacrylonitrile fiber needs to be completely immersed in the ethylenediamine solution.

[0060] More preferably, in the above step c, after the reflux is completed, the mixture is cooled to room temperature, and then the fibers are taken out and rinsed with clean water.

[0061] More preferably, in the above step d, the washed fiber is dried at 40° C. to 60° C. for 10 to 16 hours to obtain amino-modified polyacrylonitrile fiber.

[0062] Accordingly, a method for preparing an over-wet soil precipitation solidifying agent is also disclosed, which is used to prepare the above-mentioned wet soil precipitation solidifying agent, comprising the following steps:

[0063] (1) drying cement, carbide slag and mineral powder respectively, and ball-milling the dried cement and mineral powder respectively;

[0064] (2) According to the proportion, the cement, carbide slag and mineral powder treated in step (1) are mixed evenly, and then amino-modified polyacrylonitrile fiber is added and mixed evenly to obtain an over-wet soil dewatering solidifying agent.

[0065] More preferably, in step (1), cement, carbide slag and mineral powder are placed in an oven at 100°C to 110°C for drying for ≥8 hours until the materials are completely dried. Subsequently, the dried carbide slag is stored in a sealed container for later use, and the dried cement and mineral powder are ball-milled respectively, and the processed materials are stored in a sealed container for later use.

[0066] In one embodiment, in step (1), the dried cement is subjected to ball milling treatment under the following conditions: ball milling time is 40 min to 80 min, rotation speed is 400 r / min to 600 r / min, and ball to material ratio is 3:1 to 5:1. The use of this ball milling process to treat cement can ensure that the cement is fully ground, thereby effectively increasing the specific surface area of ​​the cement, so that the specific surface area of ​​the cement is controlled within 400 m 2 / kg~500m 2 / kg, thereby promoting the hydration rate of cement and enhancing its precipitation efficiency.

[0067] In one embodiment, the conditions for ball milling the dried mineral powder are as follows: ball milling time is 90 to 150 minutes, rotation speed is 400 r / min to 600 r / min, and ball to material ratio is 3:1 to 5:1. The ball milling process can ensure that the mineral powder is fully ground and the specific surface area of ​​the mineral powder is controlled within 450 m 2 / kg~550m 2 / kg, which can effectively increase the reaction area and reaction rate of the mineral powder, further improve the water absorption rate of the over-wet soil precipitation solidifier and enhance the strength of the over-wet soil after solidification.

[0068] Accordingly, this embodiment also provides a method for dewatering over-wet soil, comprising the following steps: adding an over-wet soil dewatering and curing agent to the over-wet soil and stirring evenly, waiting for the moisture content of the over-wet soil to decrease, and when the moisture content of the over-wet soil decreases to a preset moisture content, the dewatering treatment of the over-wet soil is completed, and the roadbed filler is collected; the over-wet soil dewatering and curing agent is the above-mentioned over-wet soil dewatering and curing agent. Among them, the preset moisture content is preferably a moisture content corresponding to a better compaction effect of the soil body, thereby ensuring the stability and bearing capacity of the roadbed after compaction; more preferably, the preset moisture content can be selected from the optimal moisture content of the over-wet soil, and the optimal moisture content can be obtained through a compaction test.

[0069] The over-wet soil precipitation method of this embodiment can achieve precipitation and solidification effects on over-wet soil by combining ball-milled cement and mineral powder with calcium carbide slag and amino-modified polyacrylonitrile fiber. In practical applications, the over-wet soil precipitation solidifying agent is stirred and mixed with the over-wet soil in a certain proportion. As the stirring process continues, the originally large pieces of over-wet soil are gradually decomposed into smaller particles. Under the combined action of the two precipitation mechanisms of hydration reaction and fiber heat release, the rapid precipitation of over-wet soil is successfully achieved. After the moisture content drops to the preset moisture content range, the roadbed filler can be collected. In subsequent use, the roadbed filler is compacted, and the remaining active ingredients in the over-wet soil precipitation solidifying agent form a gel-like network structure under the stimulation of hydroxide ions, filling the pores of the soil, thereby enhancing the bearing capacity and stability of the soil.

[0070] More preferably, after breaking large pieces of over-wet soil into small pieces, an over-wet soil dewatering and solidifying agent is added to the over-wet soil to further increase the contact area between the over-wet soil and the over-wet soil dewatering and solidifying agent, thereby further improving the dewatering efficiency.

[0071] In one embodiment, the moisture content of the over-wet soil is 20% to 45%. Calculated by mass percentage, when the over-wet soil is subjected to precipitation treatment, the added amount of the over-wet soil precipitation solidifying agent is 5% to 12% of the total mass of the over-wet soil. Within this range, a better precipitation effect can be achieved, and the time required to reach the preset moisture content is shorter.

[0072] The technical solution of the present invention is further described below through examples and comparative examples.

[0073] Example 1

[0074] The over-wet soil precipitation solidifying agent of this embodiment comprises the following raw materials in percentage by weight: 15.0% cement, 20.0% carbide slag, 64.0% mineral powder and 1.0% amino-modified polyacrylonitrile fiber;

[0075] Among them, the specific surface area of ​​the mineral powder is 490m 2 / kg, the specific surface area of ​​cement is 450m 2 / kg, the fiber length of the amino-modified polyacrylonitrile fiber is 20mm, the content of calcium hydroxide in the carbide slag is 86%, and the cement is silicate cement.

[0076] The preparation method of the over-wet soil precipitation curing agent in this embodiment comprises the following steps:

[0077] (1) Cement, carbide slag and mineral powder are placed in an oven at 105°C for drying, and the heating and drying are continued for 8 hours. The dried cement and mineral powder are respectively subjected to ball milling treatment; wherein the conditions for ball milling the dried cement are as follows: ball milling time is 60 minutes, rotation speed is 500 r / min, and ball-to-material ratio is 3:1; the conditions for ball milling the dried mineral powder are as follows: ball milling time is 110 minutes, rotation speed is 400 r / min, and ball-to-material ratio is 4:1;

[0078] (2) Calculated by mass percentage, 62% of water and 15% of ethylenediamine are slowly mixed in an ice bath to prepare an ethylenediamine solution; 23% of polyacrylonitrile fibers are completely immersed in the ethylenediamine solution to obtain a mixture; the mixture is heated to 70° C. and maintained at reflux temperature for 12 hours, then cooled to room temperature, the fibers are taken out and rinsed with clean water; the rinsed fibers are dried at 50° C. for 12 hours to obtain amino-modified polyacrylonitrile fibers.

[0079] (3) According to the proportion, the cement, carbide slag and mineral powder treated in step (1) are put into a dry mixer for mixing. After the mixture is evenly mixed, amino-modified polyacrylonitrile fiber is added and the mixture is fully stirred again to obtain an over-wet soil precipitation solidifying agent.

[0080] Example 2

[0081] The over-wet soil precipitation solidifying agent of this embodiment comprises the following raw materials in percentage by weight: 15.0% cement, 25.0% carbide slag, 59.6% mineral powder and 0.4% amino-modified polyacrylonitrile fiber, wherein the cement, carbide slag, mineral powder and amino-modified polyacrylonitrile fiber used in this embodiment are the same as those in Example 1; the preparation method of the over-wet soil precipitation solidifying agent of this embodiment is the same as that in Example 1.

[0082] Example 3

[0083] The over-wet soil precipitation solidifying agent of this embodiment comprises the following raw materials in percentage by weight: 14.0% cement, 23.0% carbide slag, 62.5% mineral powder and 0.5% amino-modified polyacrylonitrile fiber, wherein the cement, carbide slag, mineral powder and amino-modified polyacrylonitrile fiber used in this embodiment are the same as those in Example 1; the preparation method of the over-wet soil precipitation solidifying agent of this embodiment is the same as that in Example 1.

[0084] Example 4

[0085] The over-wet soil precipitation solidifying agent of this embodiment comprises the following raw materials in percentage by weight: 20.0% cement, 27.0% carbide slag, 52.4% mineral powder and 0.6% amino-modified polyacrylonitrile fiber, wherein the cement, carbide slag, mineral powder and amino-modified polyacrylonitrile fiber used in this embodiment are the same as those in Example 1; the preparation method of the over-wet soil precipitation solidifying agent of this embodiment is the same as that in Example 1.

[0086] Example 5

[0087] The over-wet soil precipitation solidifying agent of this embodiment comprises the following raw materials in percentage by weight: 17.0% cement, 26.0% carbide slag, 56.7% mineral powder and 0.3% amino-modified polyacrylonitrile fiber, wherein the cement, carbide slag, mineral powder and amino-modified polyacrylonitrile fiber used in this embodiment are the same as those in Example 1; the preparation method of the over-wet soil precipitation solidifying agent of this embodiment is the same as that in Example 1.

[0088] Comparative Example 1

[0089] The over-wet soil precipitation solidifying agent of this comparative example comprises the following raw materials in percentage by weight: 15.0% cement, 20.0% carbide slag and 65.0% mineral powder. The cement, carbide slag and mineral powder used in this comparative example are the same as those in Example 1.

[0090] The preparation method of the over-wet soil precipitation solidifying agent of this comparative example comprises the following steps:

[0091] (1) Cement, carbide slag and mineral powder are placed in an oven at 105°C for drying, and the heating and drying are continued for 8 hours. The dried cement and mineral powder are respectively subjected to ball milling treatment; wherein the conditions for ball milling the dried cement are as follows: ball milling time is 60 minutes, rotation speed is 500 r / min, and ball-to-material ratio is 3:1; the conditions for ball milling the dried mineral powder are as follows: ball milling time is 110 minutes, rotation speed is 400 r / min, and ball-to-material ratio is 4:1;

[0092] (2) according to the proportion, the cement, carbide slag and mineral powder treated in step (1) are put into a dry mixer for mixing, and after mixing evenly, an over-wet soil precipitation solidifying agent is obtained.

[0093] Performance Testing

[0094] The moisture content of the over-wet soil was 30% after testing. The best moisture content of the over-wet soil was 17% and the maximum dry density was 1.80 g / cm 3 .

[0095] Take 7 equal portions of the above-mentioned over-wet soil samples, of which 5 portions are used as experimental groups, respectively labeled A1, A2, A3, A4 and A5, and 2 portions are used as control groups, respectively labeled B1 and B2. The over-wet soil precipitation curing agent of Examples 1 to 5 is added to the experimental groups and stirred evenly, and the addition amount of the over-wet soil precipitation curing agent is 8% (calculated by the mass of the over-wet soil); in the control group, B1 is added with the over-wet soil precipitation curing agent of Comparative Example 1 and stirred evenly, and the addition amount of the over-wet soil precipitation curing agent of Comparative Example 1 is 8% (calculated by the mass of the over-wet soil), and in the control group, B2 is not added with any over-wet soil precipitation curing agent.

[0096] The above A1, A2, A3, A4, A5, B1 and B2 were respectively loaded into different open containers and placed in a constant temperature and humidity chamber (temperature: 20°C, humidity: 60%). The temperature sensor was used to record the change of soil temperature over time, and the maximum temperature and heating duration of the soil were recorded. At the same time, the moisture content of the soil was measured and the time required to reach the optimal moisture content was recorded. The results are shown in Table 1 below.

[0097] After the moisture content of the soils of A1, A2, A3, A4, A5, B1 and B2 is reduced to the optimum moisture content, the amount required for forming a single specimen is calculated according to the maximum dry density, and the required amount of the above-mentioned improved over-wet soil is weighed respectively, and the above-mentioned improved over-wet soil is statically pressed into cylindrical specimens with a diameter of 100 mm and a height of 100 mm using a hydraulic press, and the obtained specimens are sealed in bags and placed under standard curing conditions for curing until the required age is reached, and finally the over-wet soil solidified specimens are obtained. According to JTGE51-2009 "Test Procedures for Inorganic Binders", the over-wet soil solidified specimens obtained from A1, A2, A3, A4, A5, B1 and B2 were tested for unconfined compressive strength, and the test results are shown in Table 2 below.

[0098] Table 1 Table of relevant parameters of soil during precipitation process

[0099] Maximum temperature / ℃ Fever duration / h Time required to reach the optimum moisture content / h A1 29 9 38 A2 29 8 41 A3 28 7 43 A4 31 11 31 A5 30 10 35 B1 25 4 63 B2 20 0 210

[0100] It can be seen from the experimental data in Table 1 above that in the absence of external conditions (B2), the precipitation efficiency of the over-wet soil itself is extremely slow, and it takes 210 hours to reach the optimal moisture content. However, once the over-wet soil precipitation solidifier is added, the precipitation efficiency of the over-wet soil can be significantly improved. This is because pure over-wet soil can only rely on volatilization to slowly release its own water into the surrounding environment, resulting in its slow precipitation efficiency. After the over-wet soil precipitation solidifier is added, the cementitious material components (cement, mineral powder) in the over-wet soil precipitation solidifier react with water to not only solidify the free water in the over-wet soil into bound water, but also release heat to promote the volatilization of water in the over-wet soil, greatly improving the precipitation efficiency of the over-wet soil.

[0101] From the experimental data of A1 to A5 in Table 1, it can also be found that when amino-modified polyacrylonitrile fiber is introduced into the precipitation curing agent of over-wet soil, the maximum temperature that the whole system can reach and the duration of heating are improved compared with before the introduction (i.e. B1), and the time required for the over-wet soil to reach the optimal moisture content is greatly shortened. This is because after the introduction of amino-modified polyacrylonitrile fiber, the free water in the over-wet soil combines with the hydrophilic groups on the fiber, and the water molecules change from a state of irregular motion to a state of rest. According to the law of conservation of energy, the kinetic energy of the water molecules is converted into heat energy at this time, which is manifested as the release of heat by the amino-modified polyacrylonitrile fiber, further increasing the overall temperature of the system. In addition, the volatile water vapor is partially adsorbed on the amino-modified polyacrylonitrile fiber, and changes from gas to liquid to release heat. Under the above two mechanisms of action, the maximum temperature and duration of heating of the whole system increase, which greatly promotes the precipitation efficiency of over-wet soil.

[0102] Table 2 Unconfined compressive strength test results

[0103] 7d unconfined compressive strength / MPa 28d unconfined compressive strength / MPa A1 1.7 2.9 A2 1.7 3.0 A3 1.6 2.8 A4 1.9 3.5 A5 1.8 3.3 B1 1.6 2.3 B2 0.3 0.4

[0104] From the data in Table 2, it can be seen that the over-wet soil (i.e. B2) without any precipitation curing agent is supported only by the friction between soil particles after compaction. This force is weak, resulting in low unconfined compressive strength and no obvious development of strength over time. When the precipitation curing agent is introduced, the self-hydration reaction of the residual cement after precipitation and the hydration reaction of the mineral powder under the stimulation of carbide slag produce a gel network in the system, filling the gaps between soil particles and forming a strong skeleton to support the soil. Therefore, the unconfined compressive strength of B1 and A1~A5 is higher than that of the pure over-wet soil specimen (i.e. B2). When amino-modified polyacrylonitrile fiber is introduced (i.e. A1~A5), since the fiber has a certain moisture absorption and water retention, it will slowly release water over time, which is conducive to prolonging the hydration reaction time and avoiding the cessation of the reaction of the mineral powder due to lack of water in the later stage. Therefore, the introduction of amino-modified polyacrylonitrile fiber can make the hydration reaction of mineral powder more thorough and improve the density of soil in the later stage. Specifically, after the introduction of amino-modified polyacrylonitrile fiber, the unconfined compressive strength of the specimen in the later stage is higher than that of the fiber-free group (i.e. B1).

[0105] The above disclosure is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A precipitation solidifying agent for over-wet soil, characterized in that: The raw materials include the following percentages by weight: 10% to 20% cement, 20% to 30% carbide slag, 50% to 69% mineral powder and 0.1% to 1% amino-modified polyacrylonitrile fiber; The amino-modified polyacrylonitrile fiber is a polyacrylonitrile fiber with amino groups introduced into the surface.

2. The over-wet soil precipitation solidifying agent according to claim 1, characterized in that: The specific surface area of ​​the mineral powder is 450m 2 / kg~550m 2 / kg; the specific surface area of ​​the cement is 400m 2 / kg~500m 2 / kg.

3. The over-wet soil precipitation solidifying agent according to claim 1, characterized in that: Calculated by mass percentage, the content of calcium hydroxide in the carbide slag is ≥85%; The cement is silicate cement.

4. The over-wet soil precipitation solidifying agent according to claim 1, characterized in that: The amino-modified polyacrylonitrile fiber has a fiber length of 10 mm to 30 mm.

5. The over-wet soil precipitation solidifying agent according to claim 1 or 4, characterized in that: Calculated by mass percentage, the raw materials of the amino-modified polyacrylonitrile fiber include 15% to 30% of polyacrylonitrile fiber, 10% to 20% of ethylenediamine and 60% to 75% of water.

6. The over-wet soil precipitation solidifying agent according to claim 5, characterized in that: The amino-modified polyacrylonitrile fiber is prepared by the following method: Mixing water and ethylenediamine to prepare an ethylenediamine solution; The polyacrylonitrile fiber is immersed in an ethylenediamine solution to obtain a mixture; Heat the mixture to 60°C to 80°C and maintain the temperature under reflux for 10 to 14 hours, take out the fiber and rinse it with clean water; The washed fibers are dried to obtain amino-modified polyacrylonitrile fibers.

7. A method for preparing an over-wet soil precipitation solidifying agent, characterized in that: The method for preparing the wet soil precipitation solidifying agent according to any one of claims 1 to 6 comprises the following steps: (1) drying cement, carbide slag and mineral powder respectively, and ball-milling the dried cement and mineral powder respectively; (2) According to the proportion, the cement, carbide slag and mineral powder treated in step (1) are mixed evenly, and then amino-modified polyacrylonitrile fiber is added and mixed evenly to obtain an over-wet soil dewatering solidifying agent.

8. The method for preparing the over-wet soil precipitation solidifying agent according to claim 7, characterized in that: In step (1), the dried cement is subjected to ball milling treatment under the following conditions: ball milling time is 40 min to 80 min, rotation speed is 400 r / min to 600 r / min, and ball to material ratio is 3:1 to 5:1; The conditions for ball milling the dried mineral powder are as follows: ball milling time is 90 to 150 min, rotation speed is 400 r / min to 600 r / min, and ball-to-material ratio is 3:1 to 5:

1.

9. The method for preparing the over-wet soil precipitation solidifying agent according to claim 1, characterized in that: Before step (2), the method further includes a step of preparing amino-modified polyacrylonitrile fiber, wherein the method for preparing amino-modified polyacrylonitrile fiber includes the following steps: Mixing water and ethylenediamine to prepare an ethylenediamine solution; The polyacrylonitrile fiber is immersed in an ethylenediamine solution to obtain a mixture; Heat the mixture to 60°C to 80°C and maintain the temperature under reflux for 10 to 14 hours, take out the fiber and rinse it with clean water; The washed fibers are dried to obtain amino-modified polyacrylonitrile fibers.

10. A method for dewatering over-wet soil, characterized in that: The method comprises the following steps: adding an over-wet soil precipitation solidifying agent into the over-wet soil and stirring evenly, waiting for the moisture content of the over-wet soil to decrease, and when the moisture content of the over-wet soil decreases to a preset moisture content, the precipitation treatment of the over-wet soil can be completed, and the roadbed filler can be collected; the over-wet soil precipitation solidifying agent is the over-wet soil precipitation solidifying agent described in any one of claims 1 to 6.