Environment-friendly deep foundation pit trench backfill material and preparation method thereof

Abstract

The application relates to an environment-friendly deep foundation pit fertilizer groove backfill material and a preparation method thereof, which comprises the following components in mass fractions: cement 70-90 parts, recycled fine powder 300-450 parts, recycled fine aggregate 600-800 parts, recycled coarse aggregate 1000-1200 parts, rheological modifier 2-4 parts, composite self-repairing system 15-40 parts, water reducing agent 4-8 parts, and water 140-180 parts; the composite self-repairing system comprises temperature change adjusting microcapsules, polysulfide prepolymer microcapsules and a supported vulcanization trigger agent. The application has the effects of improving the crack resistance, self-repairing property and impermeability and durability of the deep foundation pit fertilizer groove backfill material.

Description

Technical Field

[0001] This application relates to the field of backfill materials, and in particular to an environmentally friendly deep foundation pit backfill material and its preparation method. Background Technology

[0002] Deep foundation pit trenches are narrow, elongated spaces left between the basement exterior walls and the foundation pit support structure. Taking the soft soil areas of the Yangtze River Delta as an example, the width of these trenches is typically 0.5–1.5 meters, while their depth often exceeds 10 meters, forming a typical deep and narrow confined space. Large compaction machinery cannot be used in this space; workers must enter the trench to spread the material in layers and compact it manually. Manual compaction involves low energy and extremely uneven energy distribution, resulting in significant dispersion in the density of the backfill layer. This makes it highly susceptible to uneven settlement later on, seriously threatening the safety of surrounding roads and pipelines. Furthermore, manual work in these deep and narrow spaces also faces significant safety risks such as collapse and oxygen deficiency.

[0003] To control settlement, traditional backfill materials have strict requirements for particle size distribution. However, when manually spread in narrow trenches, the material is prone to segregation, making it difficult to stabilize the gradation within the design range and exacerbating uneven compaction. Furthermore, the demolition of the foundation pit support structure generates a large amount of waste concrete, resulting in high costs for off-site disposal, which is a serious departure from green building principles. Although there are precedents for crushing waste concrete into recycled aggregate for backfilling, the resulting dry-hard mixture is difficult to spread and compact in deep, narrow trenches, and the quality of the project cannot be guaranteed. Summary of the Invention

[0004] To mitigate the risk of early thermal cracking in deep foundation pit backfill materials, this application provides an environmentally friendly deep foundation pit backfill material and its preparation method.

[0005] Firstly, this application provides an environmentally friendly deep foundation pit backfill material, which adopts the following technical solution: An environmentally friendly deep foundation pit backfill material comprises the following components in parts by weight: 70-90 parts cement, 300-450 parts recycled fine powder, 600-800 parts recycled fine aggregate, 1000-1200 parts recycled coarse aggregate, 2-4 parts rheology modifier, 15-40 parts composite self-healing system, 4-8 parts water-reducing agent, and 140-180 parts water. The composite self-healing system includes temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and a supported vulcanization trigger.

[0006] By adopting the above technical solution, cement and recycled fine powder together form a cementitious filling system. Recycled fine aggregate and recycled coarse aggregate provide a particle skeleton. Water-reducing agent and rheology modifier jointly improve the fluidity and anti-segregation properties of the paste. At the same time, a composite self-healing system is also added to the system, which is a combination of temperature-regulating microcapsules, polysulfide prepolymer microcapsules and a loaded vulcanization trigger. The temperature-regulating microcapsules absorb heat during the early stage of cement hydration and reduce the internal temperature rise and temperature gradient of the backfill, thereby reducing early thermal cracks and shrinkage microcracks from the source. When the cracks expand during service life, the polysulfide prepolymer microcapsules are stressed and rupture to release the polysulfide prepolymer. The loaded vulcanization trigger is dispersed on the recycled fine powder carrier. When the polysulfide prepolymer flows along the crack interface, it can contact the trigger and solidify to form an elastic seal.

[0007] Preferably, the mass ratio of the temperature-regulating microcapsules, the polysulfide prepolymer microcapsules, and the supported vulcanization trigger is 5:(1.5-3.5):1.

[0008] By adopting the above technical solution, the mass ratio between the temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and the supported vulcanization trigger is preferably within the above range. This ensures sufficient prepolymer release when cracks occur, without affecting the matrix gel strength and flow stability due to excessive organic components. The supported vulcanization trigger serves as the interface triggering site for the curing reaction, and the polysulfide prepolymer is fully cured. By limiting the mass ratio of the three components to the above range, temperature control, crack prevention, crack release, and interface curing can be matched.

[0009] Preferably, the temperature-regulating microcapsules are prepared by the following method: Phase change core material is mixed with porous inorganic adsorbent to obtain supported phase change core material; the supported phase change core material is dispersed in shell forming liquid containing silicon source and aluminum source, and then silane sealing agent is added for sealing treatment to obtain temperature-regulating microcapsules.

[0010] By adopting the above technical solutions, porous inorganic adsorbents can adsorb and fix phase change core materials, reduce leakage of phase change core materials during mixing and hardening, further improve the compatibility of silicon-aluminum composite shells with cement-based materials, enhance the stability of microcapsules in strong alkali cement slurry, and further reduce the risk of core material migration in shell pores and improve the interfacial bonding between microcapsules and cement matrix.

[0011] Preferably, the mass ratio of the phase change core material, the porous inorganic adsorbent, and the raw materials forming the silicon-aluminum composite shell is 4:(1.6-2.2):1.

[0012] By adopting the above technical solution, and optimizing the mass ratio between the phase change core material, the porous inorganic adsorbent, and the silicon-aluminum composite shell material within the above range, sufficient confinement space for the core material can be provided, and an alkali-resistant and mixing-shear-resistant shell structure can be formed. This is beneficial for forming a shell structure that combines the stability of silicon and the interfacial activity of aluminum, enabling the microcapsules to have good stability and interfacial compatibility in a cement-based strong alkaline environment, thereby improving the long-term effectiveness of the phase change temperature regulation function.

[0013] Preferably, the polysulfide prepolymer microcapsules are prepared by the following method: The thiol-terminated liquid polysulfide rubber was mixed with an interfacial adhesion modifier to obtain a core phase; the core phase was emulsified and dispersed in an aqueous phase containing an emulsifier to obtain a core emulsion; a wall material forming component was added to the core emulsion to obtain polysulfide prepolymer microcapsules.

[0014] By adopting the above technical solution, using terminal mercapto liquid polysulfide rubber and interfacial adhesion modifier as the core phase, and allowing the wall material forming component to polymerize in situ on the surface of the core droplet, stress-triggered microcapsules with the core material encapsulated by the wall material can be obtained. This isolates the polysulfide prepolymer during mixing, pumping, and early hardening stages, preventing it from contacting the loaded vulcanization trigger prematurely and causing an increase in system viscosity.

[0015] Preferably, the mass ratio of the terminal mercapto liquid polysulfide rubber to the interfacial adhesion modifier is (40-60):1.

[0016] By adopting the above technical solution, the mass ratio between the terminal mercapto liquid polysulfide rubber and the interface adhesion modifier is preferably within the above range. While improving the sufficient release and fluidity of the polysulfide prepolymer, it further promotes the interfacial adhesion between the cured sealant and the inorganic matrix, so that the repaired crack has better impermeability and durability.

[0017] Preferably, the interfacial adhesion modifier is one or more of mercaptosilane coupling agents, epoxysilane coupling agents, and aminosilane coupling agents.

[0018] By adopting the above technical solutions, one end of the silane coupling agent can interact with the hydroxyl groups on the surface of inorganic cement-based materials, recycled aggregates, or recycled fine powders, while the other end can form an organic phase compatible or reactive bond with polysulfide prepolymers or their curing systems, thereby improving the bonding strength between the polysulfide cured product and the crack wall. The mercaptosilane coupling agent has good compatibility with end-mercaptopolysulfide prepolymers, and the epoxy-based silane coupling agent can react with components containing active hydrogen or alkaline interfaces. The aminosilane coupling agent helps to improve the affinity of inorganic powder surfaces.

[0019] Preferably, the supported vulcanization initiator is prepared by the following method: The regenerated fine powder was dispersed in a solution containing a surface modifier for surface modification to obtain modified regenerated fine powder; the vulcanization trigger dispersion was mixed with the modified regenerated fine powder, and the solid-liquid separation was performed to obtain a supported vulcanization trigger.

[0020] By adopting the above technical solution, the surface of the recycled fine powder is first modified, and then the vulcanization trigger is loaded onto the surface and pores of the modified recycled fine powder. When the polysulfide prepolymer microcapsules rupture and release the core material when the cracks expand, the polysulfide prepolymer flows along the cracks and contacts the loaded vulcanization trigger, thereby causing a curing reaction at the cracks.

[0021] Preferably, the mass ratio of the vulcanization trigger to the modified recycled fine powder is (0.25-0.35):1.

[0022] By adopting the above technical solution, the mass ratio between the sulfidation trigger and the modified recycled fine powder is preferably within the above range, so that a sufficient number of sulfidation trigger sites are formed on the recycled fine powder carrier, while maintaining the dispersibility of the carrier particles in the cement-based slurry.

[0023] Secondly, this application provides a method for preparing an environmentally friendly deep foundation pit backfill material, which adopts the following technical solution: A method for preparing an environmentally friendly deep foundation pit backfill material includes the following steps: Cement, recycled fine powder, recycled fine aggregate, and recycled coarse aggregate are mixed to obtain a mixture. Water-reducing agent and rheology modifier are mixed with water and then added to the mixture. The mixture is stirred to obtain a matrix slurry. Finally, a composite self-healing system is added to the matrix slurry and stirred to obtain an environmentally friendly deep foundation pit backfill material.

[0024] In summary, this application includes at least one of the following beneficial technical effects: Solid waste is recycled through a three-stage waste concrete recycling system consisting of recycled fine powder, recycled fine aggregate, and recycled coarse aggregate. A composite self-healing system is also introduced, comprising temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and a loaded vulcanization trigger. The temperature-regulating microcapsules absorb heat during the exothermic hydration stage of cement, reducing the internal temperature rise and temperature gradient of the backfill, thus minimizing early-stage heat-induced cracks and shrinkage microcracks. The temperature-regulating microcapsules employ a porous inorganic adsorbent pre-loaded with a phase change core material, followed by encapsulation with a silicon-aluminum composite shell and silane sealing. The porous adsorbent provides a confined space for the phase change core material, reducing leakage during mixing and hardening. The silicon-aluminum composite shell exhibits excellent compatibility with cement-based materials, maintaining structural integrity even in strongly alkaline environments. The silane sealing treatment further reduces the risk of core material migration within the shell pores, while simultaneously improving the interfacial bonding between the microcapsules and the cement matrix. In the composite self-healing system, the polysulfide prepolymer microcapsules use terminal thiol liquid polysulfide rubber and interfacial adhesion modifier as core materials and are completely encapsulated by the wall material. During the mixing, pumping and early hardening stages, they are physically isolated from the loaded vulcanization trigger to avoid premature contact curing and increase the viscosity of the slurry. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the embodiments: Raw material description: All raw materials in the examples are commercially available; the cement is P.O42.5 silicate cement; the recycled fine powder, recycled fine aggregate, and recycled coarse aggregate are obtained from waste concrete through crushing, screening, and impurity removal; the recycled fine powder is powder with a particle size less than 0.075 mm, the recycled fine aggregate is aggregate with a particle size of 0.075-4.75 mm, and the recycled coarse aggregate is aggregate with a particle size of 4.75-16 mm; the water-reducing agent is polycarboxylate water-reducing agent; the rheology modifier is a compound of hydroxypropyl methylcellulose ether, bentonite, and xanthan gum in a mass ratio of 1:3:0.2; the phase change core material is a composite of paraffin wax and polyethylene glycol in a mass ratio of 1:1; porous non-porous... Expanded perlite is used as the adsorbent; tetraethyl orthosilicate is used as the silicon source, aluminum isopropoxide is used as the aluminum source, methyltriethoxysilane (CAS No.: 2031-67-6) is used as the silane sealing agent, and liquid polysulfide rubber with a number average molecular weight of approximately 1000-4000 can be selected; γ-mercaptopropyltrimethoxysilane (CAS No.: 4420-74-0) is used as the interfacial adhesion modifier; sodium dodecylbenzenesulfonate (CAS No.: 25155-30-0) and polyvinyl alcohol (CAS No.: 9002-89-5) are used as the emulsifier; the wall material forming component is a compound system of urea, formaldehyde and resorcinol (CAS No.: 108-46-3). The vulcanization trigger is a compound of manganese dioxide and zinc oxide in a mass ratio of 3:1; γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) is used as the surface modifier. Example 1

[0026] Preparation of temperature-regulating capsules: 4g of composite phase change core material was mixed with 1.6g of expanded perlite and stirred at 300rpm for 1h at 60℃ to obtain a supported phase change core material. 1g of silicon-aluminum composite shell-forming material was added to a mixture of ethanol and water, and the pH of the system was adjusted to 9 to obtain a shell-forming solution. The silicon source was tetraethyl orthosilicate, and the aluminum source was aluminum isopropoxide, with a mass ratio of silicon source to aluminum source of 3:1. The supported phase change core material was added to the shell-forming solution and stirred at 45℃ for 3h. Then, 0.8g of methyltriethoxysilane was added and stirring was continued for 1h. The mixture was then filtered, washed with deionized water, and dried at 50℃ for 12h to obtain temperature-regulating microcapsules.

[0027] Preparation of polysulfide prepolymer microcapsules: 40g of mercapto-terminated liquid polysulfide rubber was mixed with 1g of γ-mercaptopropyltrimethoxysilane and stirred at 25°C for 30min to obtain the core phase. 2g of sodium dodecylbenzenesulfonate and 1g of polyvinyl alcohol were added to 300g of deionized water and stirred at 40°C to obtain an aqueous phase containing an emulsifier. The core material was added to the aqueous phase containing the emulsifier and emulsified at 1200rpm for 20min to obtain a core emulsion. 6g of urea, 12g of formaldehyde aqueous solution, and 0.5g of resorcinol were added to the core emulsion to adjust the pH to 3. The mixture was reacted at 55°C for 3h, then cooled, filtered, washed, and dried at 40°C for 12h to obtain polysulfide prepolymer microcapsules.

[0028] Preparation of supported vulcanization triggers: 10g of regenerated fine powder was mixed with 1.5g of γ-aminopropyltriethoxysilane, 100g of deionized water and 20g of ethanol, stirred at 50℃ for 2h, filtered and dried at 80℃ to obtain modified regenerated fine powder. 2.5g of vulcanization trigger was added to 150g of ethanol and ultrasonically dispersed for 20min to obtain vulcanization trigger dispersion. The modified regenerated fine powder was added to the vulcanization trigger dispersion and stirred at 40℃ for 2h. After filtration and drying at 60℃, the supported vulcanization trigger was obtained.

[0029] Preparation of a composite self-healing system: A composite self-healing system was obtained by mixing thermochromic microcapsules, polysulfide prepolymer microcapsules, and a supported vulcanization trigger in a mass ratio of 5:1.5:1.

[0030] Preparation of environmentally friendly deep foundation pit backfill material: Mix 70g cement, 300g recycled fine powder, 600g recycled fine aggregate, and 1000g recycled coarse aggregate for 3 minutes to obtain a mixture. Mix 4g polycarboxylate superplasticizer, 2g rheology modifier, and 140g water, and then add the mixture to the mixture. Stir at 500 rpm for 3 minutes to obtain a matrix slurry. Finally, add 15g of composite self-healing system to the matrix slurry and stir at 200 rpm for 20 minutes to obtain an environmentally friendly deep foundation pit backfill material. Example 2

[0031] Preparation of temperature-regulating capsules: 4g of composite phase change core material was mixed with 2.2g of expanded perlite and stirred at 300rpm for 1h at 60℃ to obtain a supported phase change core material. 1g of silicon-aluminum composite shell-forming material was added to a mixture of ethanol and water, and the pH of the system was adjusted to 9 to obtain a shell-forming solution. The silicon source was tetraethyl orthosilicate, and the aluminum source was aluminum isopropoxide, with a mass ratio of silicon source to aluminum source of 3:1. The supported phase change core material was added to the shell-forming solution and stirred at 45℃ for 3h. Then, 0.8g of methyltriethoxysilane was added and stirring was continued for 1h. The mixture was then filtered, washed with deionized water, and dried at 50℃ for 12h to obtain temperature-regulating microcapsules.

[0032] Preparation of polysulfide prepolymer microcapsules: 60g of mercapto-terminated liquid polysulfide rubber was mixed with 1g of γ-mercaptopropyltrimethoxysilane and stirred at 25°C for 30min to obtain the core phase. 2g of sodium dodecylbenzenesulfonate and 1g of polyvinyl alcohol were added to 300g of deionized water and stirred at 40°C to obtain an aqueous phase containing an emulsifier. The core material was added to the aqueous phase containing the emulsifier and emulsified at 1200rpm for 20min to obtain a core emulsion. 6g of urea, 12g of formaldehyde aqueous solution, and 0.5g of resorcinol were added to the core emulsion to adjust the pH to 3. The mixture was reacted at 55°C for 3h, then cooled, filtered, washed, and dried at 40°C for 12h to obtain polysulfide prepolymer microcapsules.

[0033] Preparation of supported vulcanization triggers: 10g of regenerated fine powder was mixed with 1.5g of γ-aminopropyltriethoxysilane, 100g of deionized water and 20g of ethanol, stirred at 50℃ for 2h, filtered and dried at 80℃ to obtain modified regenerated fine powder. 3.5g of vulcanization trigger was added to 150g of ethanol and ultrasonically dispersed for 20min to obtain vulcanization trigger dispersion. The modified regenerated fine powder was added to the vulcanization trigger dispersion and stirred at 40℃ for 2h. After filtration and drying at 60℃, the supported vulcanization trigger was obtained.

[0034] Preparation of a composite self-healing system: A composite self-healing system was obtained by mixing thermochromic microcapsules, polysulfide prepolymer microcapsules, and a supported vulcanization trigger in a mass ratio of 5:3.5:1.

[0035] Preparation of environmentally friendly deep foundation pit backfill material: Mix 90g of cement, 450g of recycled fine powder, 800g of recycled fine aggregate, and 1200g of recycled coarse aggregate for 3 minutes to obtain a mixture. Mix 8g of polycarboxylate superplasticizer, 4g of rheology modifier, and 180g of water, and then add the mixture to the mixture. Stir at 500 rpm for 3 minutes to obtain a matrix slurry. Finally, add 40g of composite self-healing system to the matrix slurry and stir at 200 rpm for 20 minutes to obtain an environmentally friendly deep foundation pit backfill material. Example 3

[0036] Preparation of temperature-regulating capsules: 4g of composite phase change core material was mixed with 1.9g of expanded perlite and stirred at 300rpm for 1h at 60℃ to obtain a supported phase change core material. 1g of silicon-aluminum composite shell-forming material was added to a mixture of ethanol and water, and the pH of the system was adjusted to 9 to obtain a shell-forming solution. The silicon source was tetraethyl orthosilicate, and the aluminum source was aluminum isopropoxide, with a mass ratio of silicon source to aluminum source of 3:1. The supported phase change core material was added to the shell-forming solution and stirred at 45℃ for 3h. Then, 0.8g of methyltriethoxysilane was added and stirring was continued for 1h. The mixture was then filtered, washed with deionized water, and dried at 50℃ for 12h to obtain temperature-regulating microcapsules.

[0037] Preparation of polysulfide prepolymer microcapsules: 50g of mercapto-terminated liquid polysulfide rubber was mixed with 1g of γ-mercaptopropyltrimethoxysilane and stirred at 25°C for 30min to obtain the core phase. 2g of sodium dodecylbenzenesulfonate and 1g of polyvinyl alcohol were added to 300g of deionized water and stirred at 40°C to obtain an aqueous phase containing an emulsifier. The core material was added to the aqueous phase containing the emulsifier and emulsified at 1200rpm for 20min to obtain a core emulsion. 6g of urea, 12g of formaldehyde aqueous solution, and 0.5g of resorcinol were added to the core emulsion to adjust the pH to 3. The mixture was reacted at 55°C for 3h, then cooled, filtered, washed, and dried at 40°C for 12h to obtain polysulfide prepolymer microcapsules.

[0038] Preparation of supported vulcanization triggers: 10g of regenerated fine powder was mixed with 1.5g of γ-aminopropyltriethoxysilane, 100g of deionized water and 20g of ethanol, stirred at 50℃ for 2h, filtered and dried at 80℃ to obtain modified regenerated fine powder. 3.0g of vulcanization trigger was added to 150g of ethanol and ultrasonically dispersed for 20min to obtain vulcanization trigger dispersion. The modified regenerated fine powder was added to the vulcanization trigger dispersion and stirred at 40℃ for 2h. After filtration and drying at 60℃, the supported vulcanization trigger was obtained.

[0039] Preparation of a composite self-healing system: A composite self-healing system was obtained by mixing thermochromic microcapsules, polysulfide prepolymer microcapsules, and a supported vulcanization trigger in a mass ratio of 5:2.5:1.

[0040] Preparation of environmentally friendly deep foundation pit backfill material: Mix 80g of cement, 380g of recycled fine powder, 700g of recycled fine aggregate, and 1100g of recycled coarse aggregate for 3 minutes to obtain a mixture. Mix 6g of polycarboxylate superplasticizer, 3g of rheology modifier, and 160g of water, and then add the mixture to the mixture. Stir at 500 rpm for 3 minutes to obtain a matrix slurry. Finally, add 28g of composite self-healing system to the matrix slurry and stir at 200 rpm for 20 minutes to obtain an environmentally friendly deep foundation pit backfill material. Example 4

[0041] Example 4 is based on Example 3. The difference between Example 4 and Example 3 is that in Example 4, when preparing temperature-regulating microcapsules, the amount of expanded perlite is 2.2g, and the mass ratio of the phase change core material, porous inorganic adsorbent and silicon-aluminum composite shell forming raw materials is 4:2.2:1. Example 5

[0042] Example 5 is based on Example 3. The difference between Example 5 and Example 3 is that in Example 5, when preparing temperature-regulating microcapsules, the amount of expanded perlite is 1.6g, and the mass ratio of the phase change core material, porous inorganic adsorbent and silicon-aluminum composite shell forming raw materials is 4:1.6:1. Example 6

[0043] Example 6 is based on Example 3. The difference between Example 6 and Example 3 is that in Example 6, the amount of thiol-terminated liquid polysulfide rubber used in preparing sulfur prepolymer microcapsules is 60g. Example 7

[0044] Example 7 is based on Example 3. The difference between Example 7 and Example 3 is that in Example 7, the amount of thiol-terminated liquid polysulfide rubber used in preparing sulfur prepolymer microcapsules is 40g. Example 8

[0045] Example 8 is based on Example 3. The difference between Example 8 and Example 3 is that in Example 8, the amount of vulcanizing initiator used in preparing the supported vulcanizing initiator is 3.5g. Example 9

[0046] Example 9 is based on Example 3. The difference between Example 9 and Example 3 is that in Example 9, the amount of vulcanizing initiator used in preparing the supported vulcanizing initiator is 2.5g. Example 10

[0047] Example 10 is based on Example 3. The difference between Example 10 and Example 3 is that in Example 10, the mass ratio between the temperature-regulating microcapsules, the polysulfide prepolymer microcapsules and the supported vulcanization trigger is 5:3.5:1 when preparing the composite self-healing system. Example 11

[0048] Example 11 is based on Example 3. The difference between Example 11 and Example 3 is that in Example 11, the mass ratio between the temperature-regulating microcapsules, the polysulfide prepolymer microcapsules and the supported vulcanization trigger is 5:1.5:1 when preparing the composite self-healing system. Example 12

[0049] Example 12 is based on Example 3. The difference between Example 12 and Example 3 is that in Example 12, when preparing temperature-modulated microcapsules, the composite phase change core material is replaced with an equal amount of polyethylene glycol (molecular weight 4000). Example 13

[0050] Example 13 is based on Example 3. The difference between Example 13 and Example 3 is that in Example 13, when preparing the composite self-healing system, the polysulfide prepolymer microcapsules are replaced with an equal mass of end-thiol liquid polysulfide rubber, and no microcapsule encapsulation is performed. Example 14

[0051] Example 14 is based on Example 3. The difference between Example 14 and Example 3 is that when the supported vulcanization trigger was prepared in Example 14, the regenerated fine powder was not modified with a silane coupling agent. Example 15

[0052] Example 15 is based on Example 3. The difference between Example 15 and Example 3 is that when preparing temperature-regulating microcapsules in Example 15, expanded perlite is not used, and the composite phase change core material is directly added to the shell forming liquid for encapsulation. Example 16

[0053] Example 16 is based on Example 3. The difference between Example 16 and Example 3 is that no interfacial bonding modifier is added to the core material phase when preparing polysulfide prepolymer microcapsules in Example 16. Example 17

[0054] Example 17 is based on Example 3. The difference between Example 17 and Example 3 is that when preparing temperature-regulating microcapsules in Example 17, the silicon-aluminum shell formation liquid coating step is not performed. After the expanded perlite adsorbs the phase change core material, the pores are directly sealed with methyltriethoxysilane.

[0055] Comparative Example 1 Comparative Example 1 is based on Example 3, but without the addition of temperature-regulating microcapsules; instead, an equal amount of regenerated fine powder is used to make up for the difference.

[0056] Comparative Example 2 Comparative Example 2 is based on Example 3, but without the addition of polysulfide prepolymer microcapsules; instead, an equal amount of recycled fine powder was used to make up the difference.

[0057] Comparative Example 3 Comparative Example 3 is based on Example 3, but no supported vulcanization trigger was added in Comparative Example 3, and an equal amount of modified recycled fine powder was used to make up for it.

[0058] Comparative Example 4 Comparative Example 4 is based on Example 3, except that the supported vulcanization trigger is replaced with an equal mass of free vulcanization trigger powder, and no regenerated fine powder loading treatment is performed.

[0059] Performance testing The following performance tests were performed on the samples of Examples 1-17 and Comparative Examples 1-4: (1) Early crack resistance Using GB / T 50082-2024 as the testing reference, the early crack resistance of the samples was tested. Each sample was tested 3 times, and the average value was taken. The test results were filled in Table 1. (2) 28d cube compressive strength Using GB / T 50081-2019 as the testing reference, the compressive strength of the samples was tested. Each sample was tested 3 times, and the average value was taken. The test results were recorded in Table 1. (3) Self-healing performance test After 28 days of curing, a crack of about 0.30 mm was pre-formed on the specimen and placed in an environment of 20±2℃ and relative humidity ≥95% for 7 days. Then, the impermeability pressure of the repaired specimen was tested. Each specimen was tested 3 times and the average value was taken. The test results were recorded in Table 1.

[0060] (4) Semi-adiabatic temperature rise test The freshly mixed backfill material was placed into an insulated test mold with a built-in thermocouple. The temperature of the specimen center and the ambient temperature were recorded every 10 minutes for 72 hours. The maximum difference between the specimen center temperature and the initial temperature was taken as the peak temperature rise over 72 hours. Each sample was tested 3 times, and the average value was taken. The test results were recorded in Table 1.

[0061] Table 1 Performance test results of Examples 1-17 and Comparative Examples 1-4

[0062] As shown in Table 1, the crack area after 24 hours in Examples 1-3 is all below 70 mm² / m², the compressive strength after 28 days is all above 28 MPa, and the compressive strength after self-healing is all above 25 MPa. This indicates that the backfill material prepared in this application has good crack resistance and self-healing properties.

[0063] In Examples 4 and 5, the mass ratios of the phase change core material, porous inorganic adsorbent, and silicon-aluminum composite shell forming raw materials are not within the range specified in this application. When the expanded perlite content is too high, the effective content of the phase change core material in the microcapsule decreases, and the heat absorption capacity decreases. When the expanded perlite content is insufficient, the effective content of the phase change core material is high, but the core material migrates during the mixing and hardening stages, and the phase change temperature regulation performance decreases.

[0064] In Examples 6 and 7, the mass ratio of end-thiol liquid polysulfide rubber to interfacial adhesive modifier is not within the range specified in this application. When the end-thiol liquid polysulfide rubber is in excess, although it can provide more sufficient crack filler, the excessive organic core material will have an adverse effect on the strength of the hardened matrix. When the end-thiol liquid polysulfide rubber is insufficient, the continuity of the elastic seal formed in the crack decreases, affecting the strength of the system.

[0065] In Examples 8 and 9, the mass ratio of vulcanization trigger to modified recycled fine powder is not within the range specified in this application. When the vulcanization trigger is excessive, the number of triggering sites increases and the polysulfide prepolymer solidifies. However, the polysulfide prepolymer at the release site of the broken microcapsules undergoes localized solidification and thickening. When the vulcanization trigger is insufficient, the number of solidification triggering sites that can be released at the crack interface decreases.

[0066] In Examples 10 and 11, the mass ratios of the temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and supported vulcanization triggers are not within the ranges specified in this application. When the proportion of polysulfide prepolymer microcapsules is increased, more repair agent can be released at the crack, but the stability decreases. When there are insufficient polysulfide prepolymer microcapsules, the amount of crack repair agent released is insufficient, making it difficult to form a continuous seal.

[0067] In Example 12, replacing the composite phase change core material with PEG4000 weakened the early hydration heat absorption and temperature gradient control of the system.

[0068] Example 13 did not microencapsulate the polysulfide prepolymer, resulting in premature thickening or localized solidification of the system, which reduced both the system strength and repair performance.

[0069] In Example 14, the regenerated fine powder was not modified with silane, resulting in decreased loading stability and dispersion uniformity of the trigger on the surface of the regenerated fine powder, and reduced self-healing performance.

[0070] Example 15 directly coated the phase change core material without using expanded perlite. The phase change core material leaked and migrated during the mixing and hardening stages, affecting the performance of the system.

[0071] In Example 16, without the addition of an interfacial bonding modifier, the lack of a silane-based interfacial bonding modifier resulted in insufficient adhesion between the polysulfide cured material and the cement matrix, recycled aggregate, or recycled fine powder crack walls, thus affecting both strength and repair performance.

[0072] Example 17: No silicon-aluminum shell layer is formed; only silane is used for pore sealing after adsorption. The structural integrity of the microcapsules decreases in the strong alkaline environment of cement.

[0073] In Comparative Example 1, without the addition of temperature-regulating microcapsules, early thermal cracks and shrinkage microcracks were significantly increased.

[0074] Comparative Example 2, without the addition of polysulfide prepolymer microcapsules, lacked key self-healing components. Even with an increase in matrix density, its subsequent repair performance and stability both declined.

[0075] Comparative Example 3 replaced the loaded vulcanization trigger with modified recycled fine powder. Lacking curing trigger sites at the crack interface, the released material could not be quickly and fully cured into a stable seal, resulting in decreased repair performance.

[0076] Comparative Example 4 did not undergo regenerated fine powder loading treatment, resulting in unstable dispersion of the free vulcanization trigger powder, which was prone to localized breakage and decreased stability.

[0077] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. An environmentally friendly deep foundation pit backfill material, characterized in that: The components include the following parts by mass: 70-90 parts cement, 300-450 parts recycled fine powder, 600-800 parts recycled fine aggregate, 1000-1200 parts recycled coarse aggregate, 2-4 parts rheology modifier, 15-40 parts composite self-healing system, 4-8 parts water-reducing agent, and 140-180 parts water. The composite self-healing system includes temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and a supported vulcanization trigger.

2. The environmentally friendly deep foundation trench backfill material according to claim 1, characterized in that: The mass ratio of the temperature-regulating microcapsules, polysulfide prepolymer microcapsules, and supported vulcanization trigger is 5:(1.5-3.5):

1.

3. The environmentally friendly deep foundation pit backfill material according to claim 1, characterized in that: The temperature-regulating microcapsules were prepared using the following method: Phase change core material is mixed with porous inorganic adsorbent to obtain supported phase change core material; the supported phase change core material is dispersed in shell forming liquid containing silicon source and aluminum source, and then silane sealing agent is added for sealing treatment to obtain temperature-regulating microcapsules.

4. The environmentally friendly deep foundation pit backfill material according to claim 3, characterized in that: The mass ratio of the phase change core material, the porous inorganic adsorbent, and the silicon-aluminum composite shell forming raw materials is 4:(1.6-2.2):

1.

5. The environmentally friendly deep foundation pit backfill material according to claim 1, characterized in that: The polysulfide prepolymer microcapsules were prepared using the following method: The thiol-terminated liquid polysulfide rubber was mixed with an interfacial adhesion modifier to obtain a core phase; the core phase was emulsified and dispersed in an aqueous phase containing an emulsifier to obtain a core emulsion; a wall material forming component was added to the core emulsion to obtain polysulfide prepolymer microcapsules.

6. The environmentally friendly deep foundation pit backfill material according to claim 5, characterized in that: The mass ratio between the terminal mercapto liquid polysulfide rubber and the interfacial adhesion modifier is (40-60):

1.

7. The environmentally friendly deep foundation pit backfill material according to claim 5, characterized in that: The interfacial adhesion modifier is one or more of the following: mercaptosilane coupling agent, epoxysilane coupling agent, and aminosilane coupling agent.

8. The environmentally friendly deep foundation pit backfill material according to claim 1, characterized in that: The supported vulcanization trigger is prepared by the following method: The regenerated fine powder was dispersed in a solution containing a surface modifier for surface modification to obtain modified regenerated fine powder; the vulcanization trigger dispersion was mixed with the modified regenerated fine powder, and the solid-liquid separation was performed to obtain a supported vulcanization trigger.

9. The environmentally friendly deep foundation pit backfill material according to claim 8, characterized in that: The mass ratio of the vulcanization trigger to the modified recycled fine powder is (0.25-0.35):

1.

10. A method for preparing the environmentally friendly deep foundation pit backfill material according to any one of claims 1-9, characterized in that: Includes the following steps: Cement, recycled fine powder, recycled fine aggregate, and recycled coarse aggregate are mixed to obtain a mixture. Water-reducing agent and rheology modifier are mixed with water and then added to the mixture. The mixture is stirred to obtain a matrix slurry. Finally, a composite self-healing system is added to the matrix slurry and stirred to obtain an environmentally friendly deep foundation pit backfill material.

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