Self-compacting solidified soil for pipeline backfilling and preparation method of self-compacting solidified soil

Abstract

The invention discloses self-compacting solidified soil for pipeline backfill and a preparation method thereof. The self-compacting solidified soil for pipeline backfill is prepared from the following raw materials in parts by weight: 50-60 parts of plain soil, 8-15 parts of cement, 20-30 parts of slag powder, 5-10 parts of silica fume, 2-3 parts of an AlF3-CaF2 / PAM nano-composite, 18-22 parts of water, 0.8-1.2 parts of a polycarboxylate superplasticizer, 3-5 parts of a magnesium oxide expanding agent and 0.3-0.5 part of polypropylene fiber. The self-compacting solidified soil for pipeline backfill has the beneficial effects that the self-compacting solidified soil for pipeline backfill provided by the invention has good mechanical properties, the compressive strength of the soil for 7 days reaches 1.48-2.14 MPa, the compressive strength of the soil for 28 days reaches 2.62-4.25 MPa, the risk of early structural damage can be reduced, and pipeline deformation or fracture caused by settlement is avoided; the elasticity modulus reaches 4.8-7.4%, and the moderate elasticity modulus can better adapt to dynamic loads.

Description

Technical Field

[0001] This invention relates to the field of space backfilling technology, and more specifically, to a self-compacting solidified soil for pipeline backfilling and its preparation method. Background Technology

[0002] With the continuous expansion of urban land and the rapid development of urban infrastructure, various engineering projects are increasing, such as foundation pit excavation, underground pipeline laying, and road construction, generating a large demand for backfilling. Traditional backfilling materials and methods are gradually revealing many problems, making it difficult to meet the requirements of modern engineering construction in terms of backfilling quality, efficiency, and environmental protection. There is an urgent need for more advanced and reliable backfilling materials and technologies. Developing self-compacting solidified soil can also effectively utilize engineering waste, construction debris, and other waste materials, achieving resource recycling and complying with environmental protection policies and sustainable development requirements.

[0003] In the prior art, such as the Chinese invention patent with application number 202111201686.7, a self-compacting solidified soil is proposed. Although this patent achieves the characteristics of self-leveling, self-compacting, and self-filling through reasonable proportioning of various raw materials, and can achieve high density without vibration or rolling, solving the problem of backfill compaction in narrow spaces and complex working conditions, it still has deficiencies in mechanical properties and durability. After 28 days of curing, the compressive strength of the molded specimen is 0.73 MPa, and the shrinkage settlement of the backfill section after hardening is 1.4 mm / 3 m. It has certain limitations in harsh scenarios such as bearing high loads, low temperature and high temperature dry environment.

[0004] In summary, the existing self-compacting solidified soil for pipeline backfill has the following technical problems: insufficient mechanical properties such as compressive strength and elastic modulus, as well as insufficient durability. Therefore, there is a need for a self-compacting solidified soil for pipeline backfill that can solve the above problems and its preparation method. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a self-compacting solidified soil for pipeline backfilling and its preparation method, thereby overcoming the aforementioned technical problems existing in the existing related technologies.

[0006] The technical solution of this invention is implemented as follows:

[0007] According to one aspect of the present invention, a self-compacting solidified soil for pipeline backfilling and a method for preparing the same are provided.

[0008] The pipeline backfill is made of self-compacting soil composed of the following raw materials in parts by weight:

[0009] 50-60 parts of plain soil, 8-15 parts of cement, 20-30 parts of slag powder, 5-10 parts of silica fume, 2-3 parts of AlF3-CaF2 / PAM nanocomposite, 18-22 parts of water, 0.8-1.2 parts of polycarboxylate superplasticizer, 3-5 parts of magnesium oxide expansion agent, and 0.3-0.5 parts of polypropylene fiber.

[0010] Furthermore, the subgrade soil is the original soil at the construction site, which can be one or a combination of clay, silt, or sand; the cement is silicate cement, preferably one or a combination of P.O42.5 and P.O52.5; the slag powder is S95 grade slag powder with a density of 2.8-2.9 g / cm³; the silica fume has a density of 2.2-2.3 g / cm³; the polycarboxylate superplasticizer is a powder type polycarboxylate superplasticizer with a water reduction rate of 20%-30% and a bulk density of 500-600 kg / m³; the magnesium oxide expanding agent has a magnesium oxide content ≥82%; and the polypropylene fiber has a diameter of 18-48 μm and a density of 0.90-0.92 g / cm³.

[0011] Furthermore, the AlF3-CaF2 / PAM nanocomposite comprises AlF3-CaF2 nanoparticles prepared from AlCl3, CaCl2, and ammonium fluoride, and the AlF3-CaF2 nanoparticles are compounded with polyacrylamide colloid to obtain the AlF3-CaF2 / PAM nanocomposite.

[0012] Furthermore, the molar ratio of AlCl3 to CaCl2 is 1-3:1; the mass ratio of AlF3-CaF2 nanoparticles to polyacrylamide colloid is 1-4:9.

[0013] According to another aspect of the present invention, a method for preparing self-compacting solidified soil for pipeline backfill is provided.

[0014] The method for preparing self-compacting and solidifying soil for pipeline backfill includes the following steps:

[0015] Material preparation: Weigh each component material according to the above proportions and stack them in categories;

[0016] Preparation of AlF3-CaF2 nanoparticles: Weigh out pre-weighed AlCl3 and CaCl2 and dissolve them in deionized water to prepare a 0.1-0.5 mol / L mixed salt solution. The molar ratio of AlCl3 to CaCl2 is 1-3:1. After stirring evenly, add ammonium fluoride solution dropwise while stirring at 150-200 rpm. The molar ratio of ammonium fluoride solution to the mixed salt solution is 5-6:1. After addition, continue stirring for 30-60 min to form a white flocculent precipitate. Then, age the precipitate in a water bath at 60-80℃ for 2-4 h. After aging, centrifuge at 8000-9000 rpm for 10-15 min. Discard the supernatant after centrifugation and vacuum dry the precipitate at 60-70℃ for 12-14 h to obtain AlF3-CaF2 nanoparticles.

[0017] Preparation of AlF3-CaF2 / PAM nanocomposite: Take a pre-weighed amount of polyacrylamide and dissolve it in deionized water. Stir at 100-150 rpm for 2-3 hours. After dissolution, let it stand for 12-14 hours to obtain polyacrylamide colloid with a mass percentage concentration of 1%-3%. Then, add AlF3-CaF2 nanoparticles and silane coupling agent to the polyacrylamide colloid at 25-35℃ and stir for 10-15 minutes at a stirring rate of 300-500 rpm. Then, sonicate for 30-60 minutes at an ultrasonic frequency of 30-50 kHz to form an AlF3-CaF2 / PAM nanocomposite solution.

[0018] Preparation of self-compacting soil: Take pre-weighed cement, slag powder, silica fume, and magnesium oxide expanding agent and stir evenly for 3-5 minutes at a stirring speed of 50-80 rpm. Then add polycarboxylate superplasticizer and continue stirring for 2-4 minutes to obtain dry material. Add the AlF3-CaF2 / PAM nanocomposite solution to the dry material and stir at high speed until there are no dry powder particles. Then sprinkle in polypropylene fiber and stir at low speed until the fiber is evenly dispersed to obtain self-compacting soil.

[0019] Furthermore, in the AlF3-CaF2 nanoparticle preparation steps, the aging temperature of the aging treatment is 60-80℃, and the aging time is 2-4h; the centrifugation speed is 8000-9000rpm, and the time is 10-15min; the vacuum drying temperature is 60-70℃, and the time is 12-14h.

[0020] Furthermore, in the preparation step of the AlF3-CaF2 / PAM nanocomposite, the silane coupling agent is KH550 silane coupling agent; the polyacrylamide is anionic polyacrylamide with a degree of hydrolysis of 10%-30% and a solid content of ≥92%; the ultrasonic treatment time is 30-60 min, and the ultrasonic frequency is 30-50 kHz.

[0021] Furthermore, the mass ratio of the AlF3-CaF2 nanoparticles, the silane coupling agent, and the polyacrylamide colloid is 1-4:0.02-0.08:9.

[0022] Furthermore, in the self-compacting solidified soil preparation step, the high-speed stirring speed is 180-200 rpm and the stirring time is 5-9 min; the low-speed stirring speed is 50-60 rpm and the stirring time is 3-5 min.

[0023] The beneficial effects of this invention are as follows:

[0024] The self-compacting and solidified soil for pipeline backfilling provided by this invention has good mechanical properties, with a 7-day compressive strength of 1.48-2.14 MPa and a 28-day compressive strength of 2.62-4.25 MPa, which can reduce the risk of early structural damage and avoid pipeline deformation or breakage due to settlement; the elastic modulus reaches 4.8-7.4%, and the moderate elastic modulus can better adapt to dynamic loads.

[0025] The self-compacting and solidified soil for pipeline backfilling provided by this invention has good durability, with an impermeability grade of P6-P8. It can effectively prevent soil softening and strength reduction caused by groundwater or rainwater infiltration, thus extending the service life of the backfill structure. It can withstand 96-124 freeze-thaw cycles, making it well-suited to cold environments and reducing periodic maintenance costs. It is resistant to sulfate erosion with a strength loss rate of 6.2-18.1%, effectively preventing sudden strength drop and cracking caused by erosion.

[0026] The self-compacting solidified soil for pipeline backfilling provided by this invention has good self-compacting performance, with a flow spread of 239-266 mm and a V-shaped funnel time of 15.4-18.6 s. The suitable flow spread and V-shaped funnel time indicate that the solidified soil of this invention has both fluidity and anti-segregation ability, meeting the requirements for self-compacting construction. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart illustrating the steps of a pipeline backfill self-compacting solidified soil and its preparation method according to an embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] To better understand the above technical solutions of the present invention, the following detailed description of the solutions of the present invention is provided through specific examples.

[0031] According to an embodiment of the present invention, a self-compacting solidified soil for pipeline backfilling and its preparation method are provided.

[0032] Example 1

[0033] A self-compacting and solidifying soil for pipeline backfilling is made from the following raw materials in parts by weight:

[0034] 50 parts plain soil, 8 parts cement, 30 parts slag powder, 5 parts silica fume, 3 parts AlF3-CaF2 / PAM nanocomposite, 22 parts water, 0.8 parts polycarboxylate superplasticizer, 5 parts magnesium oxide expansion agent, and 0.5 parts polypropylene fiber.

[0035] The method for preparing self-compacting solidified soil by backfilling pipelines includes the following steps:

[0036] Material preparation: Weigh each component material according to the above proportions and stack them in categories;

[0037] Preparation of AlF3-CaF2 nanoparticles: Pre-weighed AlCl3 and CaCl2 were dissolved in deionized water to prepare a 0.1 mol / L mixed salt solution with a molar ratio of AlCl3 to CaCl2 of 1:1. After stirring thoroughly, ammonium fluoride solution was added dropwise while stirring at 200 rpm. The molar ratio of ammonium fluoride solution to the mixed salt solution was 5:1. After the addition was complete, stirring continued for 30 min, forming a white flocculent precipitate. This precipitate was then aged in a 60℃ water bath for 2 h. After aging, it was centrifuged at 8000 rpm for 10 min. The supernatant was discarded after centrifugation, and the precipitate was vacuum dried at 60℃ for 12 h to obtain AlF3-CaF2 nanoparticles.

[0038] Preparation of AlF3-CaF2 / PAM nanocomposite: Pre-weighed polyacrylamide was dissolved in deionized water and stirred at 100 rpm for 2 hours. After dissolution, the solution was allowed to stand for 12 hours to obtain a polyacrylamide colloid with a mass percentage concentration of 1%. AlF3-CaF2 nanoparticles and a silane coupling agent were added to the polyacrylamide colloid at 25°C and stirred for 10 minutes at a stirring speed of 300 rpm. The mixture was then sonicated for 30 minutes at a sonic frequency of 30 kHz to form an AlF3-CaF2 / PAM nanocomposite solution. The mass ratio of AlF3-CaF2 nanoparticles, silane coupling agent, and polyacrylamide colloid was 1:0.02:9. The silane coupling agent was KH550, and the polyacrylamide was anionic with a degree of hydrolysis of 10%-30% and a solid content ≥92%.

[0039] Preparation of self-compacting soil: Take pre-weighed cement, slag powder, silica fume, and magnesium oxide expansion agent and stir evenly for 3 minutes at a stirring speed of 50 rpm. Then add polycarboxylate superplasticizer and continue stirring for 2 minutes to obtain dry material. Then add AlF3-CaF2 / PAM nanocomposite solution to the dry material and stir at high speed until there are no dry powder particles. Then sprinkle in polypropylene fiber and stir at low speed until the fiber is evenly dispersed to obtain self-compacting soil.

[0040] The high-speed stirring was performed at a stirring rate of 180 rpm for 5 minutes, while the low-speed stirring was performed at a stirring rate of 50 rpm for 3 minutes.

[0041] Example 2

[0042] A self-compacting and solidifying soil for pipeline backfilling is made from the following raw materials in parts by weight:

[0043] 55 parts of plain soil, 12 parts of cement, 25 parts of slag powder, 8 parts of silica fume, 2.5 parts of AlF3-CaF2 / PAM nanocomposite, 20 parts of water, 1 part of polycarboxylate superplasticizer, 4 parts of magnesium oxide expansion agent, and 0.4 parts of polypropylene fiber.

[0044] The method for preparing self-compacting solidified soil by backfilling pipelines includes the following steps:

[0045] Material preparation: Weigh each component material according to the above proportions and stack them in categories;

[0046] Preparation of AlF3-CaF2 nanoparticles: Pre-weighed AlCl3 and CaCl2 were dissolved in deionized water to prepare a 0.3 mol / L mixed salt solution with a molar ratio of AlCl3 to CaCl2 of 2:1. After thorough stirring, ammonium fluoride solution was added dropwise while stirring at 180 rpm. The molar ratio of ammonium fluoride solution to the mixed salt solution was 5.5:1. After the addition was complete, stirring continued for 45 min, resulting in a white flocculent precipitate. This precipitate was then aged in a 70℃ water bath for 3 h. After aging, it was centrifuged at 8500 rpm for 13 min. The supernatant was discarded after centrifugation, and the precipitate was vacuum dried at 65℃ for 12 h to obtain AlF3-CaF2 nanoparticles.

[0047] Preparation of AlF3-CaF2 / PAM nanocomposite: Pre-weighed polyacrylamide was dissolved in deionized water and stirred at 125 rpm for 2.5 h. After dissolution, the solution was allowed to stand for 13 h to obtain a polyacrylamide colloid with a mass percentage concentration of 2%. AlF3-CaF2 nanoparticles and a silane coupling agent were added to the polyacrylamide colloid at 30 °C and stirred for 13 min at a stirring rate of 400 rpm. The mixture was then sonicated for 45 min at a sonic frequency of 40 kHz to form an AlF3-CaF2 / PAM nanocomposite solution. The mass ratio of AlF3-CaF2 nanoparticles, silane coupling agent, and polyacrylamide colloid was 2.5:0.025:9. The silane coupling agent was KH550, and the polyacrylamide was anionic with a degree of hydrolysis of 10%-30% and a solid content ≥92%.

[0048] Preparation of self-compacting soil: Take pre-weighed cement, slag powder, silica fume, and magnesium oxide expansion agent and stir evenly for 4 minutes at a stirring speed of 65 rpm. Then add polycarboxylate superplasticizer and continue stirring for 3 minutes to obtain dry material. Then add AlF3-CaF2 / PAM nanocomposite solution to the dry material and stir at high speed until there are no dry powder particles. Then sprinkle in polypropylene fiber and stir at low speed until the fiber is evenly dispersed to obtain self-compacting soil.

[0049] The high-speed stirring was performed at a stirring rate of 190 rpm for 7 minutes, while the low-speed stirring was performed at a stirring rate of 55 rpm for 4 minutes.

[0050] Example 3

[0051] A self-compacting and solidifying soil for pipeline backfilling is made from the following raw materials in parts by weight:

[0052] The ingredients are: 60 parts plain soil, 15 parts cement, 20 parts slag powder, 10 parts silica fume, 2 parts AlF3-CaF2 / PAM nanocomposite, 18 parts water, 1.2 parts polycarboxylate superplasticizer, 3 parts magnesium oxide expansion agent, and 0.3 parts polypropylene fiber.

[0053] The method for preparing self-compacting solidified soil by backfilling pipelines includes the following steps:

[0054] Material preparation: Weigh each component material according to the above proportions and stack them in categories;

[0055] Preparation of AlF3-CaF2 nanoparticles: Pre-weighed AlCl3 and CaCl2 were dissolved in deionized water to prepare a 0.5 mol / L mixed salt solution with a molar ratio of AlCl3 to CaCl2 of 3:1. After stirring evenly, ammonium fluoride solution was added dropwise while stirring at 200 rpm. The molar ratio of ammonium fluoride solution to mixed salt solution was 6:1. After the addition was complete, stirring was continued for 60 min to form a white flocculent precipitate. The precipitate was then aged in an 80℃ water bath for 4 h. After aging, centrifugation was performed at 9000 rpm for 15 min. The supernatant was discarded after centrifugation, and the precipitate was vacuum dried at 70℃ for 14 h to obtain AlF3-CaF2 nanoparticles.

[0056] Preparation of AlF3-CaF2 / PAM nanocomposite: Pre-weighed polyacrylamide was dissolved in deionized water and stirred at 150 rpm for 3 hours. After dissolution, the solution was allowed to stand for 14 hours to obtain a polyacrylamide colloid with a mass percentage concentration of 3%. AlF3-CaF2 nanoparticles and a silane coupling agent were added to the polyacrylamide colloid at 35°C and stirred for 15 minutes at a stirring rate of 500 rpm. The mixture was then sonicated for 60 minutes at a sonic frequency of 50 kHz to form an AlF3-CaF2 / PAM nanocomposite solution. The mass ratio of AlF3-CaF2 nanoparticles, silane coupling agent, and polyacrylamide colloid was 4:0.08:9. The silane coupling agent was KH550, and the polyacrylamide was anionic with a degree of hydrolysis of 10%-30% and a solid content ≥92%.

[0057] Preparation of self-compacting soil: Take pre-weighed cement, slag powder, silica fume, and magnesium oxide expansion agent and stir evenly for 5 minutes at a stirring speed of 80 rpm. Then add polycarboxylate superplasticizer and continue stirring for 4 minutes to obtain dry material. Then add AlF3-CaF2 / PAM nanocomposite solution to the dry material and stir at high speed until there are no dry powder particles. Then sprinkle in polypropylene fiber and stir at low speed until the fiber is evenly dispersed to obtain self-compacting soil.

[0058] The high-speed stirring was performed at a stirring rate of 200 rpm for 9 minutes, while the low-speed stirring was performed at a stirring rate of 60 rpm for 5 minutes.

[0059] Example 4

[0060] A self-compacting and solidifying soil for pipeline backfilling is made from the following raw materials in parts by weight:

[0061] 55 parts plain soil, 12 parts cement, 25 parts slag powder, 8 parts silica fume, 2.5 parts polyacrylamide, 20 parts water, 1 part polycarboxylate superplasticizer, 4 parts magnesium oxide expansion agent, and 0.4 parts polypropylene fiber.

[0062] The method for preparing self-compacting solidified soil by backfilling pipelines includes the following steps:

[0063] Cement, slag powder, silica fume, and magnesium oxide expanding agent were stirred for 4 minutes at a speed of 65 rpm. Polycarboxylate superplasticizer was added, and stirring was continued for 3 minutes to obtain a dry material. Then, AlF3-CaF2 / PAM nanocomposite solution was added to the dry material, and the mixture was stirred at high speed until no dry powder particles remained. Polypropylene fibers were then sprinkled in and stirred at low speed until the fibers were evenly dispersed to obtain self-compacting solidified soil.

[0064] The high-speed stirring was performed at a stirring rate of 190 rpm for 7 minutes, while the low-speed stirring was performed at a stirring rate of 55 rpm for 4 minutes.

[0065] In addition, mechanical properties of the solidified soils in Examples 1-4 were tested, and Example 4 was selected as a control example. The specific test results are shown in Table 1.

[0066] Table 1 shows the test results of the mechanical properties of solidified soil:

[0067] Test Standards Example 1 Example 2 Example 3 Example 4 (Comparative Example) 7-day compressive strength (MPa) GB / T50123-2019 1.48 1.43 2.14 0.71 28-day compressive strength (MPa) GB / T50123-2019 2.62 3.84 4.25 1.44 Elastic modulus (GPa) Unconfined compression test 3.9 5.2 7.1 2.7

[0068] As shown in Table 1, Examples 1-3 exhibit good mechanical properties, with 7-day compressive strength reaching 1.48-2.14 MPa, 28-day compressive strength reaching 2.62-4.25 MPa, and elastic modulus reaching 4.8-7.4%. The high 7-day compressive strength indicates high early-stage strength, stronger resistance to short-term mechanical stress, and reduced risk of early structural failure. The high 28-day compressive strength demonstrates strong long-term bearing capacity of the solidified soil, ensuring the stability of the soil surrounding the pipeline and preventing pipeline deformation or breakage due to settlement. The moderate elastic modulus matches the deformation compatibility of the pipeline material, making it more adaptable to dynamic loads.

[0069] (ii) Durability tests were conducted on the solidified soils of Examples 1-4. The specific test results are shown in Table 2.

[0070] Table 2 shows the results of the durability test of the solidified soil.

[0071] Test Standards Example 1 Example 2 Example 3 Example 4 (Comparative Example) Permeability rating (MPa) GB / T50108-2008 P6 P7 P8 P4 Number of freeze-thaw cycles (times) GB / T50082-2009 96 109 124 48 Sulfate erosion resistance strength loss rate (%, 90 days) GB / T50082-2009 18.1 12.7 6.2 25.8

[0072] As shown in Table 2, Examples 1-3 exhibit good durability, with impermeability grades reaching P6-P8, freeze-thaw cycle resistance reaching 96-124 cycles, and sulfate erosion strength loss rate reaching 6.2%-18.1%. Higher impermeability grades indicate higher soil density, preventing groundwater or rainwater infiltration that could lead to soil softening and strength reduction, thus extending the service life of the backfill structure. Higher freeze-thaw cycle resistance indicates that the solidified soil can adapt to cold environments, resisting soil expansion, cracking, and strength degradation caused by freeze-thaw cycles. Low sulfate erosion strength loss rate indicates strong chemical stability of the solidified soil in sulfate environments, protecting the integrity of the soil structure and preventing sudden strength drops and cracking due to erosion.

[0073] (III) The self-compacting performance of the solidified soil in Examples 1-3 and the comparative examples was tested. The specific test results are shown in Table 3.

[0074] Table 3 shows the test results of the self-compacting performance of solidified soil.

[0075] Test Standards Example 1 Example 2 Example 3 Example 4 (Comparative Example) Flow spread (mm) GB / T2419-2015 266 253 239 207 V-shaped funnel time (s) T / CECS1175-2022 16.3 15.4 18.6 18.9

[0076] As shown in Table 3, Examples 1-3 exhibit good self-compacting properties, with a flow spread of 239-266 mm and a V-funnel time of 15.4-18.6 s. The suitable flow spread ensures self-compacting without vibration, avoiding mechanical damage to the pipeline caused by manual compaction. The moderate V-funnel time indicates that the solidified soil possesses both fluidity and anti-segregation capabilities, meeting the requirements for self-compacting construction.

[0077] In summary, the test analysis of mechanical properties, durability and self-compacting properties shows that the self-compacting solidified soil for pipeline backfilling of the present invention has good mechanical properties, durability and self-compacting properties, and meets the multiple requirements of pipeline backfilling for mechanical strength, durability and construction convenience.

[0078] To facilitate understanding of the above technical solutions of the present invention, the flow of the above solutions of the present invention will be described in detail below with reference to the accompanying drawings, as follows:

[0079] According to an embodiment of the present invention, a method for preparing self-compacting solidified soil for pipeline backfill is also provided.

[0080] like Figure 1 As shown, the method for preparing self-compacting and solidifying soil for pipeline backfill in actual production includes the following steps:

[0081] Step S101, material preparation: Weigh each component material according to the above proportions and stack them in categories;

[0082] Step S103: Take pre-weighed AlCl3 and CaCl2 and dissolve them in deionized water to prepare a 0.1-0.5 mol / L mixed salt solution, with a molar ratio of AlCl3 to CaCl2 of 1-3:1; after stirring evenly, add ammonium fluoride solution dropwise while stirring at 150-200 rpm, with a molar ratio of ammonium fluoride solution to mixed salt solution of 5-6:1. After adding the solution, continue stirring for 30-60 min to form a white flocculent precipitate. Then, age the precipitate in a water bath at 60-80℃ for 2-4 h. After aging, centrifuge at 8000-9000 rpm for 10-15 min. After centrifugation, discard the supernatant and vacuum dry the precipitate at 60-70℃ for 12-14 h to obtain AlF3-CaF2 nanoparticles.

[0083] Step S105: Take a pre-weighed amount of polyacrylamide and dissolve it in deionized water. Stir at 100-150 rpm for 2-3 hours. After dissolution, let it stand for 12-14 hours to obtain polyacrylamide colloid with a mass percentage concentration of 1%-3%. Then, add AlF3-CaF2 nanoparticles and silane coupling agent to the polyacrylamide colloid at 25-35℃ and stir for 10-15 minutes at a stirring rate of 300-500 rpm. Then, sonicate for 30-60 minutes at an ultrasonic frequency of 30-50 kHz to form an AlF3-CaF2 / PAM nanocomposite solution.

[0084] Step S107: Take the pre-weighed cement, slag powder, silica fume, and magnesium oxide expansion agent and stir them evenly for 3-5 minutes at a stirring speed of 50-80 rpm. Then add polycarboxylate superplasticizer and continue stirring for 2-4 minutes to obtain dry material. Add the AlF3-CaF2 / PAM nanocomposite solution to the dry material and stir at high speed until there are no dry powder particles. Then sprinkle in polypropylene fiber and stir at low speed until the fiber is evenly dispersed to obtain self-compacting solidified soil.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A self-compacting and solidifying soil for pipeline backfilling, characterized in that, It consists of the following raw materials in parts by weight: 50-60 parts of plain soil, 8-15 parts of cement, 20-30 parts of slag powder, 5-10 parts of silica fume, 2-3 parts of AlF3-CaF2 / PAM nanocomposite, 18-22 parts of water, 0.8-1.2 parts of polycarboxylate superplasticizer, 3-5 parts of magnesium oxide expansion agent, and 0.3-0.5 parts of polypropylene fiber.

2. The self-compacting and solidifying soil for pipeline backfilling according to claim 1, characterized in that, The AlF3-CaF2 / PAM nanocomposite comprises AlF3-CaF2 nanoparticles prepared from AlCl3, CaCl2 and ammonium fluoride, and the AlF3-CaF2 nanoparticles are compounded with polyacrylamide colloid to obtain the AlF3-CaF2 / PAM nanocomposite.

3. The pipeline backfill self-compacting solidified soil according to claim 2, characterized in that, The molar ratio of AlCl3 to CaCl2 is 1-3:1; the mass ratio of AlF3-CaF2 nanoparticles to polyacrylamide colloid is 1-4:

9.

4. The self-compacting and solidifying soil for pipeline backfilling according to claim 3, characterized in that, The polycarboxylate superplasticizer is a powder type, with a water reduction rate of 20%-30% and a bulk density of 500-600 kg / m³; the magnesium oxide expanding agent has a magnesium oxide content of ≥82%; the polypropylene fiber has a diameter of 18-48 μm and a density of 0.90-0.92 g / cm³.

5. A method for preparing self-compacting and solidified soil for pipeline backfilling, characterized in that, The self-compacting and solidifying soil for pipeline backfilling as described in claim 4 includes the following steps: Material preparation: Weigh each component material according to the above proportions and stack them in categories; Preparation of AlF3-CaF2 nanoparticles: Take pre-weighed AlCl3 and CaCl2 and dissolve them in deionized water. After stirring evenly, add ammonium fluoride solution dropwise. After adding the solution, continue stirring for 30-60 minutes to form a precipitate. Then, after aging, centrifugation, and vacuum drying, AlF3-CaF2 nanoparticles are obtained. Preparation of AlF3-CaF2 / PAM nanocomposite: Take a pre-weighed amount of polyacrylamide and dissolve it in deionized water. After stirring and dissolving, allow it to stand to obtain polyacrylamide colloid. Then, add the AlF3-CaF2 nanoparticles and silane coupling agent to the polyacrylamide colloid. After uniform stirring and mixing, sonicate to form AlF3-CaF2 / PAM nanocomposite solution. Preparation of self-compacting soil: Take pre-weighed cement, slag powder, silica fume, and magnesium oxide expansion agent, stir them evenly, and add polycarboxylate superplasticizer. After stirring, dry material is obtained. Add the AlF3-CaF2 / PAM nanocomposite solution to the dry material, stir at high speed until there are no dry powder particles, sprinkle in polypropylene fiber, and then stir at low speed until the fiber is evenly dispersed to obtain self-compacting soil.

6. The method for preparing self-compacting and solidified soil for pipeline backfill according to claim 5, characterized in that, In the AlF3-CaF2 nanoparticle preparation steps, the aging temperature of the aging treatment is 60-80℃, and the aging time is 2-4h; the centrifugation speed is 8000-9000rpm, and the time is 10-15min; the vacuum drying temperature is 60-70℃, and the time is 12-14h.

7. The method for preparing self-compacting and solidified soil for pipeline backfill according to claim 6, characterized in that, In the preparation steps of the AlF3-CaF2 / PAM nanocomposite, the silane coupling agent is KH550 silane coupling agent; the polyacrylamide is anionic polyacrylamide with a degree of hydrolysis of 10%-30% and a solid content of ≥92%; the ultrasonic treatment time is 30-60 min and the ultrasonic frequency is 30-50 kHz.

8. The method for preparing self-compacting and solidified soil for pipeline backfill according to claim 7, characterized in that, The mass ratio of the AlF3-CaF2 nanoparticles, the silane coupling agent, and the polyacrylamide colloid is 1-4:0.02-0.08:

9.

9. The method for preparing self-compacting and solidified soil for pipeline backfill according to claim 8, characterized in that, In the self-compacting solidified soil preparation step, the high-speed stirring speed is 180-200 rpm and the stirring time is 5-9 min; the low-speed stirring speed is 50-60 rpm and the stirring time is 3-5 min.

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