Light-responsive self-expanding self-healing fluidified soil and preparation method thereof

Abstract

Specifically, this invention relates to a photoresponsive, self-expanding, self-healing fluidized solidified soil and its preparation method, comprising: a matrix of engineering waste soil and cementitious materials, and containing core-shell microcapsules: the core of the capsule is a photosensitive molecule-intercalated modified montmorillonite self-healing agent, the shell is a light-transmitting, alkali-resistant polymer, and a surface adsorbent dispersant; the capsules are uniformly dispersed in the matrix. The photosensitive molecules contain cationic functional groups (anchored between montmorillonite layers) and photoresponsive groups. The microcapsules and dispersant are added simultaneously during the final stage of low-speed stirring. The advantages of this invention are: by intercalating photosensitive molecules between montmorillonite layers and encapsulating them in light-transmitting, alkali-resistant microcapsules, the photosensitive molecules undergo molecular configuration changes under light irradiation, causing the interlayer spacing of the montmorillonite to increase, resulting in a layered expansion effect. Under the protection of the microcapsules, it resists the strong alkaline hydration environment and avoids damage from high-speed stirring, thereby triggering volume compensation and active repair of microcracks through light signal input in the later stage of hardening of the fluidized solidified soil.

Description

Technical Field

[0001] This invention relates to the fields of engineering materials for fluidized solidified soil and photoresponsive materials, specifically a photoresponsive self-expanding and self-healing fluidized solidified soil and its preparation method. Background Technology

[0002] Fluidized solidified soil, as a novel backfill material with good fluidity and self-compacting properties, has been widely used in recent years in projects such as foundation pit backfilling, underground pipeline backfilling, bridge backfilling, and integrated utility tunnel foundation backfilling. Existing technologies include extensive research on fluidized solidified soil formulations and construction methods, such as optimizing the cementitious material system and incorporating expanding agents, water-reducing agents, and other admixtures to improve fluidity, strength, and crack resistance.

[0003] To address the problem of cracking caused by shrinkage during the hardening process of fluidized solidified soil, some existing technologies have proposed shrinkage-resistant, crack-resistant, or self-curing fluidized solidified soil solutions. These solutions typically employ methods such as incorporating expansive agents to compensate for early shrinkage, adding fibers to enhance crack resistance, or introducing internal curing components to inhibit drying shrinkage. However, the expansion reaction relied upon by expansive agent-based solutions often occurs in the early stages of hydration, making the expansion process difficult to control precisely. Furthermore, once the early reaction is complete, new cracks caused by drying shrinkage, thermal shrinkage, or load effects in the later stages are difficult to compensate for with effective volume. In addition, existing compound systems are highly sensitive to mix proportions; insufficient compensation occurs when the dosage is too low, while excessive dosage may lead to excessive early expansion and loss of later compensation capacity.

[0004] In the field of self-healing, existing technologies have attempted to use microcapsules to encapsulate functional components to achieve self-healing of cracks in cement-based materials. However, most common microcapsule solutions rely on mechanical puncture of the capsule after crack propagation to release the repair agent, and their core material, wall material, and triggering mechanism are fundamentally different from those of photoresponsive systems. Existing solutions typically fail to simultaneously address the following issues: the stability of photosensitive components in the strongly alkaline hydration environment (pH 12–13) of cement-based materials, the integrity of the microcapsule wall layer under high-speed stirring conditions, the uniform dispersion of microcapsules in high-water-content slurries, and the problem of on-demand active triggering of volume compensation and microcrack repair in the later stages of hardening.

[0005] Therefore, there is an urgent need for a fluidized solidified soil technology that can stably store and uniformly disperse photoresponsive components under strong alkaline, high water content and stirring shear conditions, and achieve active compensation and repair through external signal input in the later stage of hardening. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a photoresponsive self-expanding self-healing fluidized solidified soil and its preparation method. This method involves intercalating photosensitive molecules between montmorillonite layers and encapsulating them in light-transmitting and alkali-resistant microcapsules. Under light irradiation, the photosensitive molecules undergo molecular configuration changes, causing the interlayer spacing of the montmorillonite to increase and produce a layered expansion effect. At the same time, the microcapsules protect the soil from strong alkaline hydration environment and prevent damage from high-speed stirring. Thus, in the later stage of hardening of the fluidized solidified soil, volume compensation and active repair of microcracks are triggered by light signal input.

[0007] To achieve the above objectives, a photoresponsive, self-expanding, self-healing fluidized solidified soil is designed. The matrix of the fluidized solidified soil is engineering waste soil and cementitious materials. The fluidized solidified soil comprises: a photosensitive molecule-intercalated modified montmorillonite composite self-healing agent as the encapsulated core material; a light-transmitting, alkali-resistant polymer microcapsule wall material as the outer shell wall material, forming a core-shell encapsulation structure; and a polymeric dispersant adsorbed on the surface of the microcapsules. The microcapsules are uniformly dispersed in the matrix. The photosensitive molecule is an organic molecule containing cationic functional groups and photoresponsive groups. The cationic functional groups are used for interaction with the montmorillonite layers. Exchangeable cations undergo exchange, forming the anchoring of the photosensitive molecules between montmorillonite layers; the light-transmitting and alkali-resistant polymer microcapsule wall material exhibits a light transmittance of ≥70% in the 350–500 nm wavelength band in alkaline hydration media and resists the effects of strong alkali at pH 12–13; in the fluidized solidified soil, the dosage of the microcapsules is 0.5%–2.0% of the mass of the cementitious material, and the dosage of the polymeric dispersant is 0.05%–0.30% of the mass of the cementitious material; the microcapsules and the polymeric dispersant are synchronously dispersed in the matrix during the final low-speed stirring stage at a stirring speed of 60–90 rpm and a stirring time of 60–90 s.

[0008] Preferably, the present invention further includes: the photosensitive molecule is any one of a quaternized azobenzene derivative, a quaternized spiropyran derivative, or a quaternized diarylethene derivative; the montmorillonite is sodium-based montmorillonite, and its cation exchange capacity is not less than 90 meq / 100g.

[0009] Preferably, the present invention further includes: the wall material of the light-transmitting and alkali-resistant polymer microcapsules is a polymethyl methacrylate-hydroxyethyl methacrylate copolymer wall material or a polyurea wall material; the particle size of the microcapsules ranges from 20 to 80 μm, and the wall thickness is from 1 to 3 μm.

[0010] Preferably, the present invention further includes: the polymeric dispersant is polyvinylpyrrolidone or hydroxypropyl methylcellulose; the mass ratio of the polymeric dispersant to the microcapsules is 1:10 to 1:6.67; and the polymeric dispersant is added simultaneously with the microcapsules.

[0011] Preferably, the present invention further includes: after the fluidized solidified soil hardens, volume compensation and microcrack filling are triggered by optical signal input, wherein the optical signal input method includes external irradiation, crack light transmission, light guiding through inspection holes, light guiding through grouting holes, light guiding through pre-embedded optical fibers or light guiding through pre-embedded light guiding components; the response wavelength of the optical signal is 365nm ultraviolet light or 450nm visible light.

[0012] This invention also provides a method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil, comprising the following steps: S1, dissolving photosensitive molecules containing cationic functional groups in an ethanol-water mixed solvent, dispersing sodium-based montmorillonite in water to form a suspension, adding the photosensitive molecule solution to the montmorillonite suspension, causing the cationic groups of the photosensitive molecules to undergo a cation exchange intercalation reaction with the exchangeable cations between the montmorillonite layers, and obtaining a photosensitive molecule intercalated modified montmorillonite composite self-healing agent after centrifugation, washing, drying, and sieving; S2, dispersing the composite self-healing agent obtained in step S1 in an oil phase containing wall material monomers and an initiator, adding the oil phase to an aqueous phase containing an emulsifier to form an oil-in-water emulsion, and heating under nitrogen protection to allow the wall material monomers to undergo a cation exchange intercalation reaction. A polymerization reaction occurs on the surface of the composite self-healing agent to form an encapsulation layer. After centrifugation, washing, freeze-drying, and grading, light-transmitting and alkali-resistant polymer microcapsules are obtained. In step S3, engineering slag, cementitious materials, water-reducing agents, and water are stirred at a stirring speed of not less than 200 rpm for 60-90 seconds to form a slurry. The stirring speed is then reduced to 60-90 rpm, and the microcapsules obtained in step S2 and the polymeric dispersant are added simultaneously under low-speed stirring at 60-90 rpm. After continuing low-speed stirring for 60-90 seconds, the material is discharged to obtain photoresponsive self-expanding and self-healing fluidized solidified soil. The dosage of the microcapsules is 0.5%-2.0% of the mass of the cementitious materials, and the dosage of the polymeric dispersant is 0.05%-0.30% of the mass of the cementitious materials.

[0013] Preferably, the present invention further includes: in step S1, the equivalent ratio of the photosensitive molecule to the montmorillonite cation exchange capacity is 1.0:1 to 1.5:1; the cation exchange intercalation reaction temperature is 50 to 70°C, the reaction time is 4 to 8 hours, the stirring speed is 500 rpm, and the reaction is carried out under light-protected conditions; the photosensitive molecule solution is added dropwise to the montmorillonite suspension at a rate of 2 mL / min using a peristaltic pump.

[0014] Preferably, the present invention further includes: in step S2, the wall material monomer is a mixture of methyl methacrylate and hydroxyethyl methacrylate in a mass ratio of 7:3, the initiator is azobisisobutyronitrile, the emulsifier is polyvinyl alcohol, and the mass ratio of the oil phase to the water phase is 1:3; the polymerization reaction temperature is 65-75°C, the reaction time is 4 hours, and the reaction is carried out under nitrogen protection.

[0015] Preferably, the present invention further includes: in step S2, the mass ratio of the microcapsule wall material monomer to the composite self-healing agent core material is 2:1 to 4:1; the grading step includes: first passing the freeze-dried microcapsule powder through a 100-mesh sieve to remove coarse particle agglomerates, and then collecting the fine powder portion that passes through a 200-mesh sieve to obtain microcapsules with a particle size range of 20 to 80 μm; the encapsulation rate of the microcapsules is 75% to 90%, and the encapsulation rate is determined by thermogravimetric analysis.

[0016] Preferably, the present invention further includes: in step S3, the stirring speed of the engineering waste soil, cementitious material, water-reducing agent and water is 200-300 rpm, and the stirring time is 60-90 s; the low-speed stirring speed is 60-90 rpm, and the stirring time is 60-90 s; the dosage of the microcapsules is 0.5%-2.0% of the mass of the cementitious material, and the dosage of the polymeric dispersant is 0.05%-0.30% of the mass of the cementitious material; the polymeric dispersant is polyvinylpyrrolidone.

[0017] Compared with the prior art, the advantages of this invention are: This invention endows solidified soil with photo-triggered self-expansion and microcrack self-healing functions without compromising its basic engineering properties. By intercalating photosensitive molecules between montmorillonite layers and encapsulating them in light-transmitting, alkali-resistant microcapsules, combined with a low-speed synchronous dispersion process at the end, premature deactivation of the photosensitive components in the strongly alkaline hydration environment of cement is effectively avoided. Simultaneously, capsule breakage and agglomeration during mixing are reduced, ensuring the photoresponsive components remain intact and uniformly distributed within the matrix. After hardening, when light signal input conditions are present inside or on the surface of the material, the photosensitive molecules undergo configurational changes, increasing the interlayer spacing of the montmorillonite, generating a local volume compensation effect, and promoting the closure of microcrack areas and interface filling. This self-healing effect does not rely on mechanical rupture to release the repair agent, but is actively triggered by the light signal, and can be initiated as needed in the later stages of hardening, overcoming the limitations of traditional expansion agents that complete early reactions and have insufficient later compensation capabilities.

[0018] Comparative experiments show that when photosensitive intercalation components are directly incorporated without microencapsulation, the phototriggered response capability is significantly weakened, and the crack repair effect is poor. If microcapsules are added during the high-speed stirring stage, the capsule breakage rate increases significantly, and the expansion and repair effects decrease dramatically. If the polymeric dispersant is omitted, the microcapsules are prone to aggregation, leading to reduced fluidity, strength loss, and uneven response distribution. This invention, through the synergistic effect of microencapsulation, low-speed addition at the end stage, and simultaneous dispersion, ensures the preservation of the activity and uniform dispersion of the photoresponsive components, thereby enabling the material to obtain stable and reliable phototriggered self-expansion and self-repair properties while maintaining good fluidity and mechanical strength.

[0019] This invention exhibits excellent compatibility with various photosensitive molecule types and microcapsule wall material systems. Photosensitive molecules responding to ultraviolet or visible light can be selected based on engineering light source conditions, and different light-transmitting and alkali-resistant polymer wall materials can also be used, all achieving effective volume compensation and crack repair. The resulting microcapsules are stored in solid powder form, maintaining good photoresponsive activity even after long-term storage, facilitating on-site measurement, transportation, and storage. The preparation process is mild, requiring no high-temperature or high-pressure equipment, and is compatible with existing fluidized bed mixing processes, eliminating the need for additional specialized equipment. In engineering applications, this invention is suitable for scenarios such as underground pipeline backfilling, bridge backfilling, foundation pit backfilling, and integrated utility tunnel foundation backfilling, especially suitable for locations with light input conditions such as external irradiation, crack light transmission, light guiding through inspection holes, light guiding through grouting holes, and pre-embedded optical fibers or light guiding components. In areas where microcracks have appeared, the cracks themselves can serve as light signal entry channels, allowing that area to respond preferentially and achieving precise local repair. This invention utilizes engineering waste soil as the main aggregate, which aligns with the direction of solid waste resource utilization. At the same time, by reducing later cracking and voids, it can lower maintenance and repair costs, demonstrating good comprehensive economic benefits and application prospects. Attached Figure Description

[0020] Fig. 1 This is a process flow diagram of the present invention; Fig. 2 This is a schematic diagram of the photosensitive molecule-montmorillonite intercalation structure and the photoinduced interlayer expansion mechanism; Fig. 3 This is a schematic diagram of the core-shell structure of microcapsules and the dual selective barrier mechanism; Fig. 4 This is a schematic diagram of the stirring principle of the final stage low-speed dispersion and incorporation process. Detailed Implementation

[0021] To make the purpose, principle and structure of the present invention clearer, the following description is provided in conjunction with the accompanying drawings and specific embodiments.

[0022] See Figs. 1 to 4 This invention provides a photoresponsive, self-expanding, self-healing fluidized solidified soil and its preparation method.

[0023] The photoresponsive, self-expanding, self-healing fluidized solidified soil of this invention comprises engineering waste soil and cementitious materials as its matrix, and includes a photosensitive molecule intercalation-modified montmorillonite composite self-healing agent and a light-transmitting, alkali-resistant polymer microcapsule wall material encapsulating the composite self-healing agent, as well as a polymeric dispersant. The photosensitive molecules are organic molecules containing cationic functional groups and photoresponsive groups. The cationic functional groups are used to exchange with exchangeable cations between montmorillonite layers, forming an anchorage of the photosensitive molecules between the montmorillonite layers. The light-transmitting, alkali-resistant polymer microcapsule wall material exhibits a transmittance of not less than 70% in the 350–500 nm wavelength band in alkaline hydration media and can resist the effects of strong alkalis at pH 12–13. In fluidized solidified soil, the dosage of microcapsules is 0.5% to 2.0% of the mass of cementitious materials, and the dosage of polymeric dispersant is 0.05% to 0.30% of the mass of cementitious materials. The microcapsules and polymeric dispersant are simultaneously dispersed in the matrix during the final low-speed stirring stage at a stirring speed of 60 to 90 rpm and a stirring time of 60 to 90 s.

[0024] The photosensitive molecule is preferably any one of quaternized azobenzene derivatives, quaternized spiropyran derivatives, or quaternized diarylethylene derivatives; the montmorillonite is preferably sodium-based montmorillonite, with a cation exchange capacity of not less than 90 meq / 100g. The wall material of the light-transmitting and alkali-resistant polymer microcapsules is preferably polymethyl methacrylate-hydroxyethyl methacrylate copolymer or polyurea; the particle size of the microcapsules ranges from 20 to 80 μm, and the wall thickness is 1 to 3 μm. The polymeric dispersant is preferably polyvinylpyrrolidone or hydroxypropyl methylcellulose; the mass ratio of the polymeric dispersant to the microcapsules is 1:10 to 1:6.67; the polymeric dispersant is added simultaneously with the microcapsules. After hardening, the fluidized solidified soil is triggered by optical signal input to achieve volume compensation and microcrack filling. The optical signal input methods include external irradiation, crack light transmission, light guiding through inspection holes, light guiding through grouting holes, light guiding through pre-embedded optical fibers, or light guiding through pre-embedded light guiding components; the response wavelength of the optical signal is 365nm ultraviolet light or 450nm visible light.

[0025] The preparation method of the photoresponsive self-expanding self-healing fluidized solidified soil described in this invention adopts a three-step process.

[0026] Step S1, cation exchange intercalation reaction. Quaternized azobenzene derivatives (in this specific embodiment, 4-(trimethylammonium)azobenzene chloride is a typical example) are dissolved in an ethanol-water mixture with a volume ratio of 1:3 to prepare a 2% (w / w) organic cation solution. Sodium-based montmorillonite is dispersed in deionized water with a solid content of 2 wt%, and stirred under high shear for 30 min to form a homogeneous suspension. The organic cation solution is slowly added dropwise to the montmorillonite suspension at a rate of 2 mL / min using a peristaltic pump. The equivalent ratio of the photosensitive molecule to the montmorillonite cation exchange capacity is 1.0:1 to 1.5:1; in this embodiment, it is 1.2:1. The reaction is carried out at 50–70°C, with mechanical stirring at 500 rpm, and in the dark for 4–8 h, allowing the quaternary ammonium cations in the quaternized photosensitive molecules to undergo a cation exchange intercalation reaction with the Na-montmorillonite interlayer, generating a composite self-healing agent (Na+) with photosensitive molecules stably anchored between the montmorillonite layers. - This refers to sodium-based montmorillonite, indicating that sodium ions (Na+) serve as exchangeable cations in the interlayer of the montmorillonite. Na+, or sodium ions, are the original positively charged exchangeable cations in the interlayer of montmorillonite, which are replaced by quaternary ammonium cations during the intercalation reaction. During the reaction, quaternary ammonium cations enter the interlayer of montmorillonite through ion exchange, replacing the original interlayer Na+. The photosensitive molecules are chemically anchored in the interlayer, avoiding the problems of easy desorption and uneven distribution of photosensitive molecules that occur in physical mixing. The reaction proceeds to the interlayer spacing d of the montmorillonite. 001 After increasing from approximately 1.2–1.5 nm to 1.8–2.2 nm, the sample was centrifuged (8000 rpm × 10 min) and washed with ethanol / water until Cl-free. - (Chloride ion) residue, vacuum drying at 50℃ for 24 h, and grinding through a 200-mesh sieve yielded a light yellow photosensitive molecule intercalated modified montmorillonite powder (M-MMT). The increased interlayer spacing of the montmorillonite after the intercalation reaction indicates that the photosensitive molecules have successfully entered the interlayer space, rather than merely adsorbing onto the surface of the montmorillonite particles. The light-protected conditions were implemented to prevent premature photoisomerization of the photosensitive molecules during the intercalation process, which would affect the subsequent intercalation effect and photoresponse performance.

[0027] Step S2: In-situ polymerization and microencapsulation. Using the M-MMT prepared in step S1 as the core material, core-shell structured microcapsules are formed through in-situ free radical polymerization. In this embodiment, the microcapsule wall material precursor is a comonomer of methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) in a mass ratio of 7:3, the initiator is azobisisobutyronitrile (AIBN), and the emulsion stabilizer is polyvinyl alcohol (PVA). This step is specifically divided into the following six sub-steps.

[0028] Sub-step S2.1: Oil phase dispersion of M-MMT powder. Take 30 wt% of the M-MMT powder prepared in step S1 and place it in a beaker. Separately, mix MMA and HEMA at a mass ratio of 7:3, add AIBN initiator (0.5 wt% of the total monomer mass), and stir until AIBN is completely dissolved to obtain a monomer oil phase solution. Add M-MMT powder in batches to the monomer oil phase and sonicate using an ultrasonic disperser (200W, 40kHz). Utilizing the hydrophobicity of the montmorillonite interlayer after cation exchange, M-MMT forms a stable dispersion in the oil phase. During sonication, the oil phase temperature must be maintained below 30℃ (using an ice bath for cooling) to prevent premature decomposition of AIBN. After quaternized photosensitive molecule intercalation, the montmorillonite interlayer changes from hydrophilic to hydrophobic, thus enabling good dispersion in the MMA / HEMA oil phase. This is a key prerequisite for the subsequent formation of uniform microcapsules.

[0029] Sub-step S2.2: Preparation of the aqueous emulsifier solution. Weigh PVA (88% degree of alcoholysis, 1750 degree of polymerization) and add it to deionized water to prepare a 1.5 wt% PVA aqueous solution. Heat and stir in an 85°C water bath for 60 min until the PVA is completely dissolved to form a transparent colloidal solution. Cool to room temperature (20–25°C) before use. PVA must be completely dissolved; otherwise, the emulsification effect will be poor. The aqueous solution must be cooled to room temperature before it can be used for emulsification; otherwise, high temperature will cause premature polymerization of AIBN in the oil phase.

[0030] Sub-step S2.3, preparation of the O / W microemulsion. The M-MMT oil phase dispersion prepared in sub-step S2.1 was slowly added dropwise to the PVA aqueous solution prepared in sub-step S2.2 at room temperature, with a dropwise acceleration rate of approximately 2 mL / min. Simultaneously, emulsification and dispersion were performed using a high-shear emulsifier at 6000 rpm. After the addition was complete, emulsification continued at 6000 rpm for 5 min to obtain a milky white, stable O / W microemulsion system. The oil phase dropwise acceleration rate should not be too fast, otherwise large oil droplets may form, leading to uneven microcapsule particle size. The emulsification speed must be strictly controlled within the range of 5500–6500 rpm; too low a speed will result in excessively large oil droplet size, while too high a speed may cause excessive shear force, potentially damaging the M-MMT structure. Under these rotational speed conditions, the oil phase is dispersed into micron-sized oil droplets. Each oil droplet contains M-MMT core material and dissolved MMA / HEMA monomers and AIBN initiator. The size of the oil droplet directly determines the final particle size of the microcapsules.

[0031] Sub-step S2.4: Deoxygenation treatment of the system. The O / W microemulsion prepared in sub-step S2.3 is transferred to a reaction vessel equipped with a nitrogen protection device, and a thermometer and nitrogen delivery tube are inserted. At room temperature (20–25°C), high-purity nitrogen (purity not less than 99.99%) is introduced at a flow rate controlled at 100–150 mL / min, while simultaneously mechanically stirring at a slow speed of 300 rpm for 30 min to remove dissolved oxygen from the system. Oxygen is an inhibitor of free radical polymerization; dissolved oxygen in the system consumes free radicals generated by the initiator, reducing the polymerization rate and monomer conversion rate. Therefore, thorough deoxygenation by nitrogen bubbling is essential.

[0032] Sub-step S2.5: In-situ free radical polymerization. After deoxygenation, maintain nitrogen protection and mechanical stirring at 300 rpm, and heat the reaction system to 65–75°C using a constant temperature water bath (heating rate approximately 5°C / min). Maintain the reaction temperature at 70±2°C for 4 hours, allowing the wall material monomers to undergo in-situ free radical polymerization coating on the surface of the oil droplets with the composite self-healing agent as the core. During the reaction, take approximately 0.5 mL of sample every 1 hour and monitor the polymerization progress using Fourier transform infrared spectroscopy: up to 1730 cm⁻¹. -1 The C=O peak appears completely at 1640 cm⁻¹ -1 After the C=C peak essentially disappears (residual peak intensity is less than 5%), heating is stopped, and the mixture is allowed to cool naturally to room temperature. The reaction temperature must be strictly controlled within the range of 68–72℃. Below 65℃, the initiation efficiency is low and the reaction rate is slow; above 75℃, explosive polymerization is likely to occur. Insufficient reaction time will lead to incomplete polymerization of the wall material and defects in the coating layer. Under these polymerization conditions, AIBN decomposes upon heating to generate free radicals, initiating a chain polymerization reaction of MMA and HEMA monomers inside the oil droplets and at the oil-water interface. The resulting PMMA-HEMA copolymer gradually deposits on the surface of the M-MMT core material, forming a continuous and dense polymer wall layer. This wall material is a light-transmitting polymer material with a transmittance of no less than 70% for trigger light in the 350–500 nm wavelength band. Simultaneously, it has a shielding effect on strongly alkaline hydration media with a pH of 12–13, achieving a dual selective barrier function of "light signals can pass through, but alkaline media are difficult to penetrate."

[0033] Sub-step S2.6: Separation, purification, and drying of microcapsules. After the reaction, the system was centrifuged (5000 rpm × 10 min) to separate the precipitate (crude microcapsules) and the supernatant (containing residual PVA, unreacted monomers, etc.). Deionized water was added to the precipitate, and the mixture was ultrasonically redispersed and centrifuged again. The washing process was repeated three times until PVA was undetectable in the supernatant. The washed wet microcapsules were dispersed in deionized water, transferred to a freeze-drying container, pre-frozen at -50°C for 12 h, and then freeze-dried at -50°C under a vacuum of less than 10 Pa for 48 h to obtain a white, loose microcapsule powder. Freeze-drying is superior to hot air drying or vacuum drying, as it avoids the deactivation of photosensitive molecules caused by high temperatures. The dried microcapsule powder was ground and graded using a standard sieve: first, it was passed through a 100-mesh sieve (150 μm) to remove coarse particle agglomerates, and then the fine powder fraction passing through a 200-mesh sieve (75 μm) was collected. Sieving and grading remove agglomerated particles, ensuring that the microcapsule particle size is compatible with the aggregate size of the fluidized solidified soil. The final product is white spherical M-MMT@PMMA-HEMA microcapsule powder with an encapsulation rate of 75%–90% (determined by thermogravimetric analysis), a particle size range of D50 = 20–80 μm, and a wall thickness of 1–3 μm. The core material retention rate was verified to be no less than 85% after 28 days of saturated Ca(OH)2 immersion. The preferred mass ratio of wall material monomer to M-MMT core material is 2:1–4:1, ensuring continuous sealing while reducing the wall layer thickness to 1–3 μm.

[0034] Step S3: Microcapsules and polymeric dispersants are simultaneously incorporated into the fluidized solidified soil during the final stage of low-speed mixing, ensuring they are stably dispersed in the fluidized solidified soil matrix in a complete and uniform state. Engineering waste soil, ordinary Portland cement (P.O42.5), polycarboxylate high-performance water-reducing agent, and an appropriate amount of mixing water are added to a forced mixer according to the designed mix ratio. The mixture is stirred at high speed (not less than 200 rpm, preferably 200–300 rpm) for 60–90 seconds to form a base slurry with a fluidity of not less than 200 mm. The speed is then reduced to low speed (60–90 rpm), and microcapsules (0.5%–2.0% of the cementitious material mass) and polymeric dispersants (polyvinylpyrrolidone PVP K30 or hydroxypropyl methylcellulose HPMC, 0.05%–0.30% of the cementitious material mass) are added simultaneously. Low-speed mixing continues for 60–90 seconds before the mixture is discharged and cast into shape. After pouring and natural curing, in the middle and late stages of hardening, trigger light signals are input through methods such as external UV 365nm lamp illumination, visible light seeping through cracks, or pre-embedded optical fiber guiding, to initiate the photosensitive self-expansion-self-healing process.

[0035] The adoption of the aforementioned low-speed synchronous addition method at the end is based on the following considerations: the microcapsule wall thickness is only 1-3 μm, and its shear tolerance is limited. If it is subjected to high-speed stirring (not less than 200 rpm) along with other raw materials, the capsule breakage rate may increase significantly, and the photosensitive component is more likely to be deactivated by premature contact with the strong alkaline hydration medium. At the same time, if the polymeric dispersant is added prematurely, it may be adsorbed or consumed by the hydration products of the gel phase, reducing its dispersing effect on the microcapsules. Therefore, this invention uses "synchronous addition of microcapsules and polymeric dispersant, final addition, and low-speed addition" as the preferred process conditions. Under low-speed stirring conditions, the shear stress on the microcapsules is significantly reduced, and the integrity of the wall layer is maintained; the polymeric dispersant is added simultaneously with the microcapsules, and can be immediately adsorbed on the surface of the microcapsules, preventing the aggregation between microcapsule particles through steric hindrance effect, so that they are uniformly dispersed in the slurry. The microcapsule dosage is 0.5%-2.0% and the dispersant dosage is 0.05%-0.30% according to the mass of the gelling material. When the microcapsule content is 0.5%, the material exhibits photoresponse compensation capability, but its expansion rate and healing rate are relatively low. When the microcapsule content is 1.0%–2.0%, better photo-triggered volume compensation and crack repair effects can be obtained. The preferred content is 1.0%–1.5%.

[0036] In the product obtained by this invention, the photosensitive molecules and montmorillonite, after being microencapsulated, can play a role in both photo-triggered expansion and shielding against strong alkaline environments, thereby improving the problem of poor late-stage expansion effect in existing expansion agent systems. Under specific wavelength illumination (UV 365nm or visible light 450nm), the photosensitive molecules undergo an isomerization transformation from a trans-state linear configuration to a cis-bent configuration. This configurational change leads to a shortening of molecular length and a change in dipole moment, generating an interlayer expansion effect within the nano-confined space of montmorillonite, increasing the interlayer spacing from approximately 1.5–1.8 nm to 2.0–2.4 nm. When multiple montmorillonite particles undergo photo-induced interlayer expansion simultaneously, measurable volume compensation can be formed on a macroscopic scale. This photo-triggered effect is predicated on the trigger light reaching the target region containing the photoresponsive microcapsules. The optical signal can enter the material interior through crack channels, external irradiation, inspection holes, grouting holes, pre-embedded optical fibers, or light guide components. In areas where microcracks or fissures have already appeared, light signals are more likely to propagate along the fissures and their adjacent areas, causing the photoresponsive microcapsules in that area to respond preferentially. This can generate local volume compensation and interface filling near the fissures, rather than requiring the entire backfill to expand synchronously.

[0037] The photo-triggered self-expansion and self-healing properties of this invention do not rely on mechanical rupture to release the repair agent, but are actively triggered by a light signal, and can be initiated on demand during the later stages of hardening. Microencapsulation physically isolates the photosensitive component from the strongly alkaline hydration medium, ensuring that it is not prematurely consumed or deactivated during the hardening process. The final low-speed synchronous dispersion process ensures the integrity and uniformity of the microcapsules within the matrix. The synergistic effect of these three elements enables the material to achieve stable and reliable photo-triggered self-expansion and self-healing properties while maintaining good flowability and mechanical strength.

[0038] This invention uses quaternized azobenzene as the photoresponsive component, Na-montmorillonite as the intercalation carrier, MMA-HEMA copolymer as the microcapsule wall material, and PVP as the dispersant. The preparation route includes three steps: cation exchange intercalation, in-situ polymerization microencapsulation, and final low-speed dispersion incorporation.

[0039] This experiment used P·O42.5 ordinary Portland cement. The excavated soil was taken from municipal foundation pits, with a natural moisture content of 28.5%. The water-reducing agent was polycarboxylate superplasticizer. The photosensitive molecule was 4-(trimethylammonium)azobenzene chloride. The montmorillonite was Na-montmorillonite with a CEC of 95 meq / 100g. The wall material monomers were MMA and HEMA in a mass ratio of 7:3. The initiator was AIBN. The emulsion stabilizer was PVA. The dispersant was PVPK30. Flowability was determined according to GB / T50080-2016. The 28-day compressive strength was determined according to GB / T50081-2019. The volumetric expansion rate was measured using a displacement sensor. The microcrack healing rate was determined using microscopic image analysis. All results are the average of three parallel experiments.

[0040] This invention employs a three-step process: First, quaternized azobenzene undergoes cation exchange with Na-montmorillonite to generate M-MMT; second, using M-MMT as the core material, it is polymerized in situ in an O / W emulsion system to form core-shell microcapsules; third, during the low-speed stage at the end of the fluidized bed mixing process, the microcapsules and a polymeric dispersant are simultaneously added. These three steps should not be interchanged because the photosensitive molecules need to be intercalated first, the wall material needs to be polymerized in the emulsion system, and the microcapsules need to be avoided during high-speed mixing.

[0041] The preferred conditions are as follows: The photosensitive molecule to montmorillonite CEC equivalent ratio is 1.0:1 to 1.5:1. The mass ratio of wall material monomer to M-MMT core material is 2:1 to 4:1. The microcapsule dosage is 0.5% to 2.0% of the cementitious material mass. The dispersant dosage is 0.05% to 0.30%. The first step uses a montmorillonite interlayer spacing d001 of 1.8 to 2.2 nm as the reaction endpoint. The second step uses FTIR at 1730 cm⁻¹... -1 The formation of the C=O peak marks the end of the reaction.

[0042] Example 1: Example 1 was prepared according to the following conditions: photosensitive molecule / MMT-CEC (Cation Exchange Capacity of Montmorillonite) equivalent ratio = 1.2, core-to-wall mass ratio = 1:3, microcapsule content in cementitious material = 1.0%, and PVP content in cementitious material = 0.10%.

[0043] Step 1: Cation exchange intercalation. Take 10.0 g of Na-montmorillonite (CEC = 95 meq / 100 g, corresponding exchangeable cation capacity = 10.0 × 0.95 = 9.5 mmol) and add it to 500 mL of deionized water. Stir at 6000 rpm for 30 min to form a homogeneous suspension. Separately, take 3.14 g of 4-(trimethylammonium)azobenzene chloride (11.4 mmol = 9.5 × 1.2, i.e., 1.2 times the CEC equivalent; calculated based on a molecular weight of 275.5 g / mol, the mass is 11.4 × 0.2755 = 3.14 g) and dissolve it in 160 mL of ethanol-water (volume ratio 1:3) mixed solvent (concentration approximately 2 wt% / v) to form a clear organic cation solution and store it in the dark. The photosensitive molecule solution was slowly added dropwise to the montmorillonite suspension at a rate of approximately 2 mL / min using a peristaltic pump under mechanical stirring at 500 rpm, 60°C, and in the dark. After the addition was complete, the reaction was maintained at this temperature for 6 hours. Samples were taken every 2 hours during the reaction, up to the montmorillonite interlayer spacing d. 001 The reaction stopped after expanding from an initial 1.24 nm to approximately 2.05 nm. The mixture was centrifuged (8000 rpm × 10 min) and washed three times with alternating ethanol / water until the supernatant showed no Cl- content upon AgNO3 detection. - The residue was dried under vacuum at 50℃ for 24 hours and ground through a 200-mesh sieve to obtain 10.3g of light yellow M-MMT powder (theoretical yield = 10.0 + 11.4 × 0.2755 − 11.4 × 0.023 = 13.1g, with about 0.67g of NaCl byproducts washed away; actual M-MMT yield 78.6%).

[0044] Step 2: In-situ polymerization and microencapsulation. 4.0 g of M-MMT was ultrasonically dispersed in an oil phase containing 8.4 g of MMA, 3.6 g of HEMA (total 12.0 g, mass ratio 7:3), and 0.06 g of AIBN (0.5 wt% of monomers) (total oil phase mass = 4.0 + 12.0 + 0.06 = 16.06 g, M-MMT accounts for 24.9 wt% of the oil phase, core-to-wall ratio = 4.0:12.0 = 1:3). The dispersion was ultrasonically dispersed for 30 min to form a stable oil phase dispersion (stable dispersion was achieved through the chemical basis of interlayer hydrophobicity following the first step of quaternization of M-MMT). This oil phase was then added to 48 g of a 1.5 wt% PVA aqueous solution (containing 0.72 g of PVA, oil:water = 16:48 = 1:3), and emulsified at 6000 rpm for 5 min to form a stable O / W microemulsion. Under slow stirring at 300 rpm, N2 was bubbled through for 30 minutes to remove dissolved oxygen. The temperature was then raised to 70°C and maintained for 4 hours to carry out the in-situ free radical polymerization coating reaction. During the reaction, samples were taken every 1 hour for FTIR (Fourier Transform Infrared Spectroscopy, an analytical technique that obtains information about functional groups in molecules by measuring the absorption of infrared light by a sample; in this invention, it is used to determine whether the polymerization reaction of the microcapsule wall material has been completed), up to 1730 cm⁻¹. -1 The C=O peak is fully formed at 1640 cm⁻¹. -1 The reaction was stopped after the C=C peak basically disappeared. The mixture was centrifuged (5000 rpm × 10 min), washed three times with deionized water to remove residual PVA, freeze-dried at -50℃ for 48 h, and sieved and classified to obtain 14.5 g of white spherical M-MMT@PMMA-HEMA microcapsule powder (12.0 g wall material monomer, 4.0 g core material, total 16.0 g; the actual product of 14.5 g corresponds to a total yield of 14.5 / 16.0 = 90.6%; TGA measured a mass loss of 75.2% in the thermal decomposition stage of the wall material and a residual mass of 24 g). The core material is 0.8%, corresponding to a drug loading rate of 24.8 wt% and an encapsulation rate of 14.5 × 24.8% / 4.0 = 89.9%. The "@" symbol indicates a core-shell encapsulation structure, read as "encapsulated" or "loaded on." The M-MMT (photosensitive molecular intercalation modified montmorillonite) before the "@" symbol is the encapsulated core (core material), and the PMMA-HEMA (methyl methacrylate-hydroxyethyl methacrylate copolymer) after the "@" symbol is the outer shell (wall material). This indicates that the microcapsule is a core-shell structure product formed by encapsulating the M-MMT core material with PMMA-HEMA copolymer as the wall material. SEM observation shows that the microcapsule morphology is a regular spherical shape. 50The diameter is approximately 42 μm, and the wall thickness is approximately 1.5 μm (the wall thickness is calculated based on the drug loading rate (the ratio of the core material mass to the total mass of the microcapsule), which can be used to estimate the relationship between the wall thickness and the particle size. The drug loading rate is the fraction of the core material volume to the total volume of the microcapsule, and its cube root corresponds to the ratio of the core material radius to the microcapsule radius. For example, when the drug loading rate is 75%, the core material radius is approximately 0.91 times the microcapsule radius, and the wall thickness accounts for approximately 9% of the radius. For microcapsules with a particle size of approximately 42 μm, the wall thickness is approximately 1.5 μm, consistent with SEM cross-sectional observations).

[0045] Step 3: Low-speed dispersion and incorporation of the fluidized solidified soil in the final stage. Prepare the foundation fluidized solidified soil according to the design mix proportions, per m³... 3 The feed composition is as follows: 1450 kg of construction waste soil (moisture content 28.5%, corresponding to dry soil = 1450 / (1+0.285) = 1128 kg), 120 kg of P·O42.5 cement, 1.2 kg of polycarboxylate superplasticizer, and 250 kg of mixing water, with a total mass of 1821 kg / m³. 3 The water-cement ratio (including mixing water and water carried over from the slag) = (250 + 1450 × 0.285 / 1.285) / 120 = (250 + 321) / 120 = 4.76. The base materials were added to a forced mixer and mixed at 250 rpm for 70 seconds to form a fluidized, solidified soil slurry. The flowability was tested and found to be 222 mm (meeting the ≥200 mm requirement). The mixing speed was then reduced to 80 rpm, and 1.20 kg / m³ of the M-MMT@PMMA-HEMA microcapsules obtained in the second step were added simultaneously. 3 (=120×1.0%=1.0wt% of cementitious material) and 0.12kg / m³ of PVPK30 dispersant 3 (=120×0.10%=0.10wt% of cementitious material, PVP K30's full English name is Polyvinylpyrrolidone K30, also known as polyvinylpyrrolidone K30), continue low-speed stirring for 80s, then discharge and cast into shape. The resulting fluidized solidified soil is poured into a mold and allowed to stand for molding, with slight venting if necessary, followed by natural curing under set conditions, marked as S-1. Strong vibrations or prolonged mechanical disturbances should be avoided during the molding process to reduce the risk of microcapsule breakage and uneven distribution.

[0046] Application example 1.

[0047] Tests were conducted on S-1: the flowability of the freshly mixed slurry was 222 mm, the microcapsule residue rate was 97.5%, and the 28-day compressive strength was 1.42 MPa, compared to 1.38 MPa in the blank control group. After 28 days of hardening, a 0.1 mm artificial crack was irradiated with UV 365 nm for 30 min; after 72 h, the volume expansion rate was 0.32%, and after another 24 h of irradiation, the crack healing area ratio was 72.5%. These results indicate that a 1.0% microcapsule dosage already exhibits photo-triggered compensation and crack repair effects.

[0048] The characterization results of S-1 are as follows: 1730 cm⁻¹ in FTIR -1 The presence of a C=O peak at this point indicates the formation of the PMMA-HEMA wall layer; 1030cm -1 The presence of Si-O signals indicates that the core material is still detectable. UV-Vis (Ultraviolet-Visible Spectroscopy) measurements showed that the transmittance of the wall layer in the 350–500 nm wavelength range was 73.2%; after 30 min of UV irradiation at 365 nm, the absorption peak of the core material at 358 nm decreased from 0.85 to 0.62. TGA measurements indicated that approximately 24.8 wt% of the core material remained; SEM showed that the microcapsules were spherical, with a particle size of 20–80 μm, a D50 of approximately 42 μm, and a wall thickness of 1–2 μm.

[0049] Example 2: Example 2 was prepared with a photosensitive molecule / MMT-CEC equivalent ratio of 1.2, a core-to-wall mass ratio of 1:3, a microcapsule dosage of 1.5%, and a PVP dosage of 0.15%. The preparation process (first and second steps) of the M-MMT composite self-healing agent and M-MMT@PMMA-HEMA microcapsules was exactly the same as in Example 1; in the third step, the microcapsule dosage was adjusted to 1.80 kg / m³. 3 (=120×1.5%), the PVPK30 dosage is adjusted to 0.18 kg / m³. 3 (=120×0.15%), the remaining basic fluidized solidified soil proportions are the same as in Example 1. The resulting fluidized solidified soil is labeled S-2. This example corresponds to the preferred formulation of the present invention.

[0050] Application Example 2.

[0051] Tests were conducted on S-2: the flowability was 218 mm, the microcapsule residue rate was 96.8%, and the 28-day compressive strength was 1.45 MPa. After 30 minutes of UV irradiation at 365 nm, the volume expansion rate was 0.42%, and the crack healing area ratio was 82.3%. These results are higher than those of S-1, indicating that increasing the microcapsule dosage to 1.5% further improves the photo-triggered compensation and crack repair effects.

[0052] Characterization results of product S-2: FTIR is basically the same as S-1. UV-Vis spectrum: wall layer transmittance is 73.2% (consistent with S-1, as the wall material is unchanged); after 30 min of illumination, the peak intensity at 358 nm decreased from 0.85 to 0.58 (a relative decrease of 31.8%, higher than S-1's 27.1%), indicating that under the same illumination conditions, the S-2 formulation has a higher degree of photosensitive molecule isomerism, which is consistent with the application results of this formulation having a larger number of microcapsules and the highest overall photoresponse efficiency.

[0053] Example 3: Example 3 was prepared with a photosensitive molecule / MMT-CEC equivalent ratio of 1.2, a core-to-wall ratio of 1:3, a microcapsule dosage of 0.5%, and a PVP dosage of 0.05%. The preparation process of M-MMT and microcapsules was the same as in Example 1; in the third step, the microcapsule dosage was adjusted to 0.60 kg / m³. 3 (=120×0.5%), PVPK30 adjusted to 0.06kg / m 3 (=120×0.05%), with the remaining proportions the same as in Example 1. The resulting fluidized solidified soil is labeled S-3. This example is used to verify the lowest effective response range of the present invention at lower dosages.

[0054] Application example 3.

[0055] Tests were conducted on S-3: the flowability was 225 mm, the microcapsule residue rate was 97.8%, and the 28-day compressive strength was 1.40 MPa. After 30 minutes of UV irradiation at 365 nm, the volume expansion rate was 0.18%, and the crack healing area ratio was 55.6%. These results are lower than those of S-1 and S-2, but higher than those of the unencapsulated control group, indicating that 0.5% doping is within the effective range for low doping. This group cannot be used to support the superior effects of "≥0.3% expansion rate" and "≥70% healing rate".

[0056] Example 4: (Alternative photosensitive molecule - visible light triggering scheme).

[0057] To illustrate the applicability of this invention to different families of photosensitive molecules, Example 4 uses a quaternized spiropyran derivative (specifically 1'-(3-(trimethylammonium)propyl)-3',3'-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-indoline]iodide, abbreviated as SP-Q⁺, with a molecular weight of approximately 478 g / mol) instead of the quaternized azobenzene in Example 2. In the first step, SP-Q is calculated based on 1.2 times the CEC equivalent. +The dosage is 9.5 × 1.2 × 0.478 = 5.45 g (corresponding to 10.0 g Na-MMT), and the remaining process conditions are the same as in Example 1; the second and third steps of the process and proportions are the same as in Example 2, and the resulting fluidized solidified soil is marked as S-4. The photoinduced ring-opening reaction response wavelength of the spiropyran derivative used in this example is 450 nm visible light, which can be passively triggered under natural light infiltration through cracks or visible light LED illumination, making it suitable for shallow burial conditions.

[0058] Application example 4.

[0059] The S-4 sample was tested and found to have a flowability of 219 mm and a 28-day compressive strength of 1.43 MPa. After irradiation with a 450 nm visible LED for 30 minutes, the volume expansion rate was 0.35%, and the crack healing area ratio was 75.8%. These results indicate that the photosensitive molecule can be replaced, and the trigger wavelength can also be adjusted.

[0060] Example 5: (Alternative wall material - interfacial polymerized polyurea solution).

[0061] To illustrate the applicability of this invention to different wall materials, in the second step of Example 5, interfacial polymerization was used to replace PMMA-HEMA in Example 2 with polyurea (PU) as the wall material. Specifically: 4.0 g of M-MMT was dispersed in 12 g of cyclohexane containing 3.5 g of toluene-2,4-diisocyanate (TDI) as the reaction oil phase; 1.45 g of triethylenetetramine (TETA) (molar ratio with TDI ≈ 1:2, reacting according to 4 NH and 2 NCO) was dissolved in 48 g of aqueous phase containing 1.5 wt% PVA as the reaction aqueous phase; O / W emulsification was carried out at an oil:water ratio ≈ 1:3 (6000 rpm × 5 min), and TDI and TETA underwent interfacial polymerization at the oil-water interface to form a polyurea wall layer, reacting at 65°C for 4 h; the remaining conditions were the same as in Example 2. The resulting microcapsules were labeled as M-MMT@PU microcapsules (wall thickness ≈ 2.0 μm, drug loading ≈ 26.5 wt%), and were incorporated into fluidized solidified soil at a low speed in the final stage of Example 2 to prepare S-5.

[0062] Application example 5.

[0063] Tests on S-5 showed the following: flowability of 216 mm, 28-day compressive strength of 1.41 MPa; after 30 minutes of UV 365 nm irradiation, volume expansion rate of 0.38%, and crack healing area ratio of 78.4%. These results indicate that polyurea wall materials can also be used in this invention.

[0064] Example 6: (Post-processing - preparation of solid products).

[0065] Example 6 used M-MMT@PMMA-HEMA microcapsule powder from S-2. The powder was sealed in a light-proof aluminum foil bag and stored under dry conditions at room temperature. After 6 months of storage, the phototriggered expansion rate decreased from 0.42% to 0.40%, and the crack healing rate decreased from 82.3% to 78.5%, indicating that the microcapsule powder has a certain degree of storage stability.

[0066] Comparative Example 1 (without microencapsulation—direct incorporation of M-MMT powder) The M-MMT composite self-healing agent powder obtained in the first step of Example 1 was directly added to the fluidized solidified soil in an equivalent core material amount without undergoing the second step of microencapsulation. Equivalent amount calculation: In Example 1, the microcapsule dosage was 1.0 wt% (percentage of cementitious material), with a drug loading rate of 24.8 wt%. The corresponding equivalent M-MMT dosage = 1.0% × 24.8% = 0.248 wt%. That is, the M-MMT powder dosage in Comparative Example 1 = 0.30 kg / m³. 3 (=120×0.25%), added to the fluidized solidified soil under the same high-speed mixing conditions as in Example 1. The resulting fluidized solidified soil is labeled C-1.

[0067] Compare with application example 1.

[0068] C-1 was tested and found to have a flowability of 210 mm and a 28-day compressive strength of 1.32 MPa. After 30 minutes of UV irradiation at 365 nm, the volume expansion rate was 0.08%, and the crack healing area ratio was 15.2%. Compared with S-1, the unencapsulated group showed a significantly lower response, indicating that microencapsulation helps protect the photosensitive components.

[0069] Comparative Example 2 (Violation of the low-speed addition process at the end - addition of microcapsules during the high-speed stirring stage).

[0070] Using the M-MMT@PMMA-HEMA microcapsules and PVPK30 dispersant obtained in Example 1, the principle of low-speed addition at the end was violated: the microcapsules and dispersant were added together to the base raw materials, and simultaneously stirred at high speed (250 rpm × 70 s) with the slag, cement, water-reducing agent, and water, without a low-speed synchronous addition process. The microcapsule dosage (1.0 wt%) and dispersant dosage (0.10 wt%) were the same as in Example 1. The resulting fluidized solidified soil was labeled C-2.

[0071] Compare with application example 2.

[0072] Tests on C-2 showed the following: flowability of 215 mm, microcapsule residue rate of 38.5%, and 28-day compressive strength of 1.36 MPa. After 30 minutes of UV irradiation at 365 nm, the volume expansion rate was 0.12%, and the crack healing area ratio was 28.3%. Compared with S-1, the addition at high speed resulted in more capsule rupture, indicating that low-speed addition at the end is a necessary process.

[0073] Comparative Example 3 (without polymeric dispersant).

[0074] The M-MMT@PMMA-HEMA microcapsules obtained in Example 1 were added using the same low-rate addition process at the end, but without any addition of the polymeric dispersant PVPK30. The microcapsule dosage was the same as in Example 1 (1.0 wt%). The resulting fluidized solidified soil was labeled C-3.

[0075] Compare with example 3.

[0076] Performance tests were conducted on the C-3 fluidized solidified soil obtained in Comparative Example 3: The freshly mixed slurry exhibited significant microcapsule aggregation (visible local white spots); the fluidity decreased from 222 mm in Example 1 to 196 mm (no longer meeting the ≥200 mm requirement, related to the sudden increase in local surface area and increased hydration water demand after microcapsule aggregation); the 28-day compressive strength was 1.18 MPa (retention rate was only 85.5%, accompanied by local "bulging" cracking). Phototriggered performance: After 30 minutes of UV 365nm irradiation, the average volume expansion rate was 0.21% (but the expansion difference between different areas of the specimen was >0.15%, with severely uneven distribution, reflecting inconsistent light signal penetration depth after aggregation); the crack healing area ratio was 32.8% (only 45.2% of Example 1). Compared with Example 1: The omission of the polymeric dispersant alone resulted in the fluidity falling below the design threshold, a 16.9% decrease in 28-day compressive strength, a 34.4% decrease in phototriggered expansion rate with severely uneven distribution, and a 54.8% decrease in healing rate. This confirms the necessity of simultaneously adding a polymeric dispersant in this invention.

[0077] Comparative Example 4 (using a non-photosensitive intercalation material—hexadecyltrimethylammonium bromide intercalated montmorillonite).

[0078] To demonstrate the necessity of the photosensitive molecule in this invention, a comparative example was set up in which a conventional quaternary ammonium salt surfactant (hexadecyltrimethylammonium bromide, CTAB) was used instead of the photosensitive molecule to intercalate montmorillonite. CTAB also has a quaternary ammonium cationic structure and can be intercalated between montmorillonite layers through cation exchange, but its molecular structure does not contain photoresponsive groups.

[0079] Step 1: Preparation of CTAB-intercalated montmorillonite. 10.0 g of Na-montmorillonite (CEC = 95 meq / 100 g) was added to 500 mL of deionized water and stirred at 6000 rpm for 30 min to form a homogeneous suspension. Separately, 4.16 g of hexadecyltrimethylammonium bromide (CTAB, molecular weight 364.45 g / mol) (11.4 mmol = 9.5 × 1.2, i.e., 1.2 times the CEC equivalent, maintaining the equivalence ratio of Example 1) was dissolved in 160 mL of hot water (60 °C). Under mechanical stirring at 500 rpm and 60 °C, the CTAB solution was slowly added dropwise to the montmorillonite suspension, and the reaction was allowed to proceed for 6 h. The mixture was centrifuged (8000 rpm × 10 min) and washed with deionized water until no Br was detected. - The residue was dried under vacuum at 50℃ for 24 hours and ground through a 200-mesh sieve to obtain 11.2 g of white CTAB-MMT powder. XRD analysis showed an interlayer spacing d. 001 =2.18nm (comparable to 2.05nm for M-MMT), confirming successful CTAB intercalation.

[0080] Steps 2 and 3: Microencapsulation and incorporation into fluidized bed soil. Using the same microencapsulation process (steps 2.1–2.6) and low-rate incorporation process as in Example 1, 14.3g of CTAB-MMT@PMMA-HEMA microcapsules (total yield 89.4%, drug loading 25.2wt%, encapsulation rate 90.1%) were prepared by using 4.0g of CTAB-MMT as the core material. These microcapsules were then added to the fluidized bed soil at a dosage of 1.0wt% to obtain the comparative fluidized bed soil C-4.

[0081] Compare with example 4.

[0082] Performance tests were conducted on the C-4 fluidized solidified soil obtained in Comparative Example 4: ① Flowability was 220 mm, microcapsule residue rate was 96.8%, and 28-day compressive strength was 1.41 MPa (retention rate 102.2%). These basic engineering performance indicators are basically equivalent to those of Example 1 (S-1); ② Phototriggered performance: After 30 min of UV 365 nm irradiation, the volume expansion rate was only 0.03% (0.32% in Example 1), and after 30 min of visible light 450 nm irradiation, the volume expansion rate was only 0.02%. After 24 h of continued UV 365 nm irradiation, the microcrack healing area ratio was only 8.5% (72.5% in Example 1). XRD monitoring showed that the interlayer spacing of CTAB-MMT remained unchanged at 2.18 nm before and after irradiation, confirming that the intercalated molecules did not undergo configurational changes. Compared with the slight expansion of 0.02–0.03% observed in Application Example 4, the controlled experiment verified that it mainly originated from the thermal expansion of the material caused by the local thermal effect of light (the blank control group also had a thermal expansion of 0.02% under the same light conditions), rather than being driven by photo-induced isomerization.

[0083] The results show that, while maintaining the intercalation equivalence ratio, microencapsulation process, and doping process as largely consistent, simply replacing the photosensitive molecule with a conventional quaternary ammonium salt (CTAB) without photoresponsive function reduced the phototriggered expansion rate of the material from 0.32% to 0.03%, and the microcrack healing rate from 72.5% to 8.5%. These results indicate that: ① The photoresponsive function of the photosensitive molecule is a crucial factor in achieving the phototriggered self-expansion-self-repair effect of this invention, and should not be replaced by conventional organic modifiers; ② The increased interlayer spacing resulting from intercalation modification is beneficial for microencapsulation, but without photoresponsive groups, it is difficult to achieve the phototriggered technology effect of this invention; ③ The technical contribution of this invention lies in combining photoresponsive function, interlayer intercalation structure, microencapsulation, and a low-speed doping process at the end, rather than simply using organically modified montmorillonite.

[0084] Comparative Example 5 (using gelatin-gum arabic composite cohesive wall material).

[0085] To demonstrate the superior encapsulation effect of the translucent, alkali-resistant polymer wall material (PMMA-HEMA copolymer) used in this invention, a comparative example using a traditional microcapsule wall material—gelatin-gum arabic coagulation system—was provided. The gelatin-gum arabic coagulation method is a classic microencapsulation technology widely used in the food, flavoring, and pharmaceutical industries, possessing advantages such as good biocompatibility, mature technology, and low cost. However, its application in cement-based strongly alkaline environments is rarely reported.

[0086] Step 1: Preparation of M-MMT composite self-healing agent. The same first step process as in Example 1 was used to prepare photosensitive molecular intercalation modified montmorillonite (M-MMT) powder for later use.

[0087] Step 2: Preparation of gelatin-gum arabic complex microcapsules. 6.0 g of type A gelatin (isoelectric point pI≈9.0) was weighed and added to 50 mL of deionized water. The mixture was heated in a 50°C water bath and stirred for 30 min until completely dissolved, yielding a 10 wt% gelatin solution. Separately, 6.0 g of gum arabic powder was weighed and added to 50 mL of deionized water. The mixture was stirred at room temperature for 60 min until completely dissolved, yielding a 10 wt% gum arabic solution. 4.0 g of M-MMT powder was ultrasonically dispersed in 12 mL of soybean oil (utilizing the hydrophobicity of M-MMT) and ultrasonically dispersed for 30 min to obtain an oil phase dispersion. The oil-phase dispersion was slowly added to a gelatin solution (50℃), and emulsified for 5 min at 50℃ and 6000 rpm to form an O / W primary emulsion. A gum arabic solution was added and stirred until homogeneous. Under slow stirring at 500 rpm, 10 wt% acetic acid solution was added dropwise to adjust the pH to 4.0 (the optimal pH range for gelatin and gum arabic coagulation). Stirring continued for 2 h to allow electrostatic coagulation to occur on the surface of the oil droplets, forming a coagulated layer. The system was cooled to 5℃ and held for 2 h. 2 mL of 25 wt% glutaraldehyde solution was added for crosslinking and curing (room temperature, 2 h). After crosslinking, the mixture was centrifuged (3000 rpm × 10 min), washed three times with deionized water, and freeze-dried (-50℃, 48 h) to obtain 13.8 g of pale yellow M-MMT@gelatin-gum arabic microcapsule powder (total yield 86.3%, drug loading 26.5 wt%, encapsulation rate 91.4%). SEM observation showed that the microcapsules were irregularly spherical with a slightly rough surface. 50 ≈55μm, wall thickness ≈3–5μm.

[0088] Step 3: Incorporation of fluidized solidified soil. Using the same mixing ratio and stirring process as in Example 1, M-MMT@gelatin-gum arabic microcapsules were added to the fluidized solidified soil at a low speed at the end of the process at a dosage of 1.0 wt% (as a percentage of the cementitious material) to prepare comparative fluidized solidified soil C-5.

[0089] Compare with example 5.

[0090] Performance tests were conducted on the C-5 fluidized solidified soil obtained in Comparative Example 5: ① Flowability was 218 mm, and the microcapsule retention rate was 94.5%, slightly lower than the 97.5% in Example 1; the 28-day compressive strength was 1.21 MPa, with a retention rate of 87.7%; ② Alkali resistance: After curing the C-5 slurry at room temperature, core samples were taken, and microcapsules were extracted by acetone dissolution and centrifugation. The core material retention rate was analyzed by TGA. The results showed that the core material retention rate was 62.3% after 24 hours of curing, and decreased to 38.5% after 7 days of curing. %, after 28 days of curing, it was 18.2%; ③ Phototriggering performance: after 28 days of curing, the volume expansion rate of the specimen after 30 minutes of UV 365nm irradiation was 0.06%, and after 24 hours of continued irradiation, the microcrack healing area ratio was 13.8%; ④ Light transmittance: the transmittance of the gelatin-gum arabic wall layer (thickness 3-5μm) in the 350-500nm wavelength band was tested using a UV-Vis spectrophotometer. The transmittance at 365nm was 48.3%, and the transmittance at 450nm was 65.8%.

[0091] The results showed that Comparative Example 5 and Example 1 were basically equivalent in terms of core material composition, microcapsule encapsulation rate, and incorporation process. However, after 28 days of curing, the core material retention rate decreased from ≥85% to 18.2%, the phototriggered expansion rate decreased from 0.32% to 0.06%, and the microcrack healing rate decreased from 72.5% to 13.8%. The reasons may be: ① The gelatin-gum arabic wall material has insufficient alkali resistance. The peptide bonds in the gelatin backbone and the glycosidic bonds in the gum arabic are easily hydrolyzed or degraded in the cement hydration environment at pH 12-13, leading to decreased stability of the wall structure and leakage of the core material; ② The gelatin-gum arabic wall material has insufficient light transmittance, with a transmittance of 48.3% at 365nm, lower than the 73.2% of the PMMA-HEMA wall material, thus reducing the light signal penetration efficiency. The comparison results show that the alkali resistance and light transmittance of the wall material have an important influence on the photo-triggering effect of the present invention; light-transmitting and alkali-resistant polymer wall materials such as PMMA-HEMA copolymer or polyurea are more suitable for photoresponsive microcapsules in cement-based strong alkaline environments.

[0092] As can be seen from the above embodiments, application examples and comparative application examples, the present invention, by encapsulating the photosensitive molecule-montmorillonite composite self-healing agent in a light-transmitting alkali-resistant microcapsule and then simultaneously adding it to the fluidized solidified soil matrix in a low-speed dispersion manner at the end, can obtain obvious light signal triggered self-expansion and active healing of microcracks at a low microcapsule dosage, while the basic engineering properties such as 28-day compressive strength and fluidity are not significantly reduced.

[0093] Regarding the phototriggered self-expansion effect, in Application Example 1 corresponding to Embodiment 1 of the present invention, S-1, with a microcapsule dosage of 1.0% and a dispersant dosage of 0.10%, achieved a volume expansion rate of 0.32% after 30 minutes of UV 365nm irradiation. However, under the same core material equivalent conditions (M-MMT equivalent dosage of 0.25%), the volume expansion rate of Comparative Application Example 1 (unencapsulated, directly incorporated M-MMT powder) was only 0.08%. Compared to Comparative Application Example 1, the phototriggered expansion rate of Application Example 1 increased from 0.08% to 0.32%, an increase of approximately 300%. This demonstrates that under the same core material equivalent conditions, the phototriggered expansion effect of the microencapsulated product of the present invention is significantly superior to the unencapsulated direct incorporation method.

[0094] In Application Example 2 corresponding to Example 2, S-2 achieved a volume expansion rate of 0.42% when the microcapsule dosage was 1.5% and the dispersant dosage was 0.15%. This result is not only higher than the 0.32% of Application Example 1, but also higher than the 0.12% of Comparative Application Example 2 (which violated the low-speed addition process at the end) and the 0.21% of Comparative Application Example 3 (without dispersant) (and the distribution was severely uneven). Combined with the low dosage results of Application Example 3, it can be seen that 0.5% to 2.0% is the effective dosage range, with 1.0% to 2.0% being the optimal response range. A 1.5% microcapsule dosage combined with 0.15% dispersant is the preferred formulation of this invention. Under the same microcapsule dosage of 1.0%, the expansion rate of Application Example 1 increased from 0.12% to 0.32% (an increase of 167%) compared to Comparative Application Example 2, and from 0.21% to 0.32% compared to Comparative Application Example 3 (and improved distribution uniformity).

[0095] In Application Example 3, corresponding to Example 3, when the microcapsule dosage was reduced to 0.5% and the dispersant dosage was reduced to 0.05%, the volume expansion rate was 0.18%, and the crack healing area ratio was 55.6%. This result is lower than Application Example 1 and Application Example 2, but still higher than the comparative Application Example 1, which was directly incorporated without microencapsulation. This demonstrates that the present invention still possesses identifiable light response compensation and microcrack repair capabilities at lower dosages. This example is more suitable as a low-dosage solution for cost-sensitive engineering projects, rather than a superior performance solution.

[0096] Regarding the microcrack repair effect, in Application Example 1, S-1 achieved a crack healing area ratio of 72.5% after 24 hours of UV 365nm irradiation, compared to only 15.2% in Comparative Application Example 1. In Application Example 2, the healing area ratio of S-2 further increased to 82.3%, higher than 28.3% in Comparative Application Example 2 and 32.8% in Comparative Application Example 3. In Application Example 3, S-3 achieved a healing area ratio of 55.6% at a lower doping concentration. These results indicate that microencapsulation, low-rate addition at the end of the process, and simultaneous addition of the dispersant all contribute to improving the photoresponsive microcrack repair effect. Among these, a microcapsule doping concentration of 1.0%–1.5% can achieve a higher healing area ratio; while a microcapsule doping concentration of 0.5% still has a repair effect, the degree of repair is relatively low.

[0097] From a mechanical property perspective, the 28-day compressive strength of this invention did not decrease significantly due to the introduction of functional microcapsule components. In Application Example 1, the 28-day compressive strength was 1.42 MPa, an increase of 0.04 MPa compared to the blank control group (1.38 MPa), with a strength retention rate of 102.9%. In Application Example 2, the 28-day compressive strength reached 1.45 MPa, an increase of 0.07 MPa compared to the blank control group, with a strength retention rate of 105.1%, the highest level among all examples. In Application Example 3, the 28-day compressive strength was 1.40 MPa, an increase of 0.02 MPa compared to the blank control group, with a strength retention rate of 101.4%. However, the compressive strength of the three comparative application examples was significantly lower than that of the blank control group: Comparative Application Example 1 was 1.32 MPa (retention rate 95.7%), Comparative Application Example 2 was 1.36 MPa (retention rate 98.6%), and Comparative Application Example 3 was 1.18 MPa (retention rate only 85.5%, accompanied by local "bulging" cracking). The above results demonstrate that the microencapsulation and low-speed synchronous dispersion process of the present invention not only did not damage the basic mechanical properties of the fluidized solidified soil, but also avoided the side effects of the unencapsulated components on hydration by isolating the photosensitive components from the hydration system, thus slightly improving the later strength.

[0098] In terms of fluidity, the fluidity of the freshly mixed slurry in Application Examples 1, 2, and 3 were 222, 218, and 225 mm, respectively, all within the design target range of 200–250 mm. However, the fluidity of Application Example 3 (without the addition of a polymeric dispersant) was only 196 mm, failing to meet the design requirement of ≥200 mm. This demonstrates that the simultaneous addition of a polymeric dispersant in this invention plays an indispensable role in maintaining the workability of the fluidized solidified soil.

[0099] The comparative results show that the advantages of this invention are mainly reflected in three aspects. First, the necessity of microencapsulation: taking Application Example 1 and Comparative Application Example 1 as examples, under the same core material equivalent conditions, the phototriggered expansion rate of the product of this invention increased from 0.08% to 0.32% (an increase of 300%), and the healing rate increased from 15.2% to 72.5% (an increase of 377%), confirming that microencapsulation is a key technical means to resist the damage of photosensitive components to the strong alkaline hydration environment of cement. Second, the necessity of the final low-speed addition process: taking Application Example 1 and Comparative Application Example 2 as examples, under the same microcapsule dosage conditions, the microcapsule residue rate of the process of this invention increased from 38.5% to 97.5% (an increase of 153%), and the corresponding expansion rate increased from... The increase from 0.12% to 0.32% (a 167% improvement) confirms the decisive role of stirring sequence in the integrity of the microcapsule wall layer. Thirdly, the necessity of simultaneously adding a polymeric dispersant is demonstrated: taking Application Example 1 and Comparative Application Example 3 as examples, under the same microcapsule dosage conditions, the flowability of the process of this invention increased from 196 mm to 222 mm (re-meeting design requirements), the 28-day compressive strength increased from 1.18 MPa to 1.42 MPa (a 20.3% improvement), the uniformity of expansion rate was significantly improved, and the healing rate increased from 32.8% to 72.5% (a 121% improvement), confirming the key role of the dispersant in the uniform dispersion of microcapsules in the slurry. These three key process points together constitute the core technical contribution of this invention, distinguishing it from existing expansion agent solutions.

[0100] Application Example 4 shows that, after replacing the photosensitive molecule from quaternized azobenzene to quaternized spiropyran SP-Q⁺, the product of this invention exhibits a volume expansion rate of 0.35%, a crack healing area ratio of 75.8%, and a 28-day compressive strength retention rate of 103.6% under visible light irradiation at 450 nm for 30 minutes. This result demonstrates that this invention can adapt to ultraviolet or visible light triggering conditions by selecting photosensitive molecules with different response wavelengths. For shallowly buried, cracked, or naturally light-accessible scenarios, a visible light response system can be preferentially adopted; for deep or enclosed backfilled areas, it is necessary to combine pre-embedded optical fibers, light guide components, inspection holes, or grouting holes to input the trigger light signal.

[0101] Application Example 5 shows that after replacing the microcapsule wall material system (from PMMA-HEMA copolymer to interfacial polymerized polyurea PU), the product of this invention still exhibits a volume expansion rate of 0.38% and a healing rate of 78.4% after 30 minutes of UV 365nm irradiation, and a 28-day compressive strength retention rate of 102.2%. This demonstrates the good flexibility of the wall material system in this invention—the polyurea wall material solution has certain advantages in long-term alkali resistance and stability, and can be used as an alternative in more demanding working conditions such as high cement usage and strong alkaline environments, further expanding the engineering application scope of this invention.

[0102] Example 6 shows that after the M-MMT@PMMA-HEMA microcapsules obtained in this invention are sealed in light-proof aluminum foil bags and stored at room temperature for 6 months in solid powder form, the phototriggered expansion rate still maintains 96.0% of the initial value and the healing rate still maintains 95.3% of the initial value. This indicates that the product of this invention has good storage stability, does not require on-site preparation of liquid form, facilitates on-site measurement, storage and long-distance transportation in engineering projects, and reduces the operational threshold and cost of practical engineering applications.

[0103] Furthermore, the preparation conditions of this invention are relatively mild. The first step, cation exchange intercalation, is completed at 50–70°C in a neutral medium; the second step, in-situ polymerization microencapsulation, is completed at 65–75°C under N2 protection, neither of which requires high-temperature and high-pressure equipment. The third step, low-speed dispersion incorporation, can be achieved simply by switching the speed setting on an existing forced mixer, without requiring additional investment in specialized equipment. The microcapsule product obtained by this invention can be used directly in solid powder form or is compatible with existing fluidized bed solidification processes and conventional admixtures such as polycarboxylate superplasticizers. For engineering scenarios requiring post-construction shrinkage compensation and active healing of microcracks in backfill, such as underground pipeline backfill, bridge backfill, deep foundation pit backfill, grouting in mined-out areas, integrated utility tunnel foundation backfill, and permeable backfill in sponge cities, this invention has outstanding engineering application value.

[0104] From an economic perspective, based on the formulation of the preferred embodiment 2 of this invention (microcapsule dosage of 1.5% of the cementitious material, corresponding to approximately 1.8 kg of microcapsules per m³ of fluidized solidified soil), the cost of the added functional components per m³ of fluidized solidified soil is estimated to be approximately 30-50 yuan, which is more economically affordable compared to traditional expansion agent solutions. At the same time, since this invention can delay the later cracking of the backfill, reduce the separation of the backfill from the existing structure, and reduce the later maintenance and repair costs, it has significant comprehensive economic benefits from the perspective of life cycle cost.

[0105] From the perspective of social and environmental benefits, this invention makes full use of bulk solid waste such as engineering waste soil as the main aggregate of fluidized solidified soil, which is in line with the "zero waste city" and "dual carbon" principles. By introducing an intelligent expansion-self-healing mechanism actively triggered by light signals, it significantly improves the durability and reliability of underground backfill, reduces secondary engineering problems such as municipal pipeline breakage, bridge approach slab settlement, and underground pipe gallery leakage caused by backfill cracking and settlement, and has positive significance for improving the safety level of urban infrastructure and reducing maintenance frequency and social operating costs.

[0106] In summary, the photoresponsive self-expanding self-healing fluidized solidified soil obtained by this invention exhibits certain photo-triggered volume compensation and microcrack repair capabilities within a microcapsule dosage range of 0.5% to 2.0%. A dosage of 0.5% is an effective solution for low-cost or low-response scenarios; dosages of 1.0% to 1.5% achieve more significant volume compensation and crack repair effects. Example 2, showing a preferred embodiment with 1.5% microcapsules and 0.15% dispersant, exhibits a volume expansion rate of 0.42% after 30 minutes of UV 365nm irradiation, a crack healing area ratio of 82.3% after 24 hours, a 28-day compressive strength of 1.45 MPa, and a flowability of 218 mm. These results demonstrate that this invention can achieve photo-triggered volume compensation and microcrack repair while maintaining basic engineering performance.

[0107] The above description is merely a specific embodiment of the invention, but the scope of protection of the invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the invention, based on the technical solution and concept of the invention, should be covered within the scope of protection of the invention.

Claims

1. A photoresponsive, self-expanding, self-healing, fluidized solidified soil, characterized in that, The matrix of the fluidized solidified soil is engineering slag and cementitious materials. The fluidized solidified soil includes: a photosensitive molecular intercalation modified montmorillonite composite self-healing agent as the core material to be coated, a light-transmitting and alkali-resistant polymer microcapsule wall material as the shell wall material to be coated on the outer layer, the core material and the shell wall material forming a core-shell coated structure of microcapsules, and also includes a polymer dispersant adsorbed on the surface of the microcapsules. The microcapsules are uniformly dispersed in the matrix. The photosensitive molecule is an organic molecule containing a cationic functional group and a photoresponsive group. The cationic functional group is used to exchange with exchangeable cations between montmorillonite layers to form an anchorage of the photosensitive molecule between montmorillonite layers. The transparent and alkali-resistant polymer microcapsule wall material has a light transmittance of ≥70% in the 350-500nm wavelength band in an alkaline hydration medium and resists the strong alkali effect of pH 12-13. In the fluidized solidified soil, the amount of microcapsules is 0.5% to 2.0% of the mass of the cementitious material, and the amount of polymeric dispersant is 0.05% to 0.30% of the mass of the cementitious material; the microcapsules and the polymeric dispersant are simultaneously dispersed in the matrix during the final low-speed stirring stage at a stirring speed of 60 to 90 rpm and a stirring time of 60 to 90 s.

2. The photoresponsive self-expanding self-healing fluidized solidified soil as described in claim 1, characterized in that, The photosensitive molecule is any one of a quaternized azobenzene derivative, a quaternized spiropyran derivative, or a quaternized diarylethene derivative; the montmorillonite is sodium-based montmorillonite with a cation exchange capacity of not less than 90 meq / 100g.

3. The photoresponsive self-expanding self-healing fluidized solidified soil as described in claim 1, characterized in that, The wall material of the light-transmitting and alkali-resistant polymer microcapsules is a polymethyl methacrylate-hydroxyethyl methacrylate copolymer wall material or a polyurea wall material; the particle size of the microcapsules ranges from 20 to 80 μm, and the wall thickness is from 1 to 3 μm.

4. The photoresponsive self-expanding self-healing fluidized solidified soil as described in claim 1, characterized in that, The polymeric dispersant is polyvinylpyrrolidone or hydroxypropyl methylcellulose; the mass ratio of the polymeric dispersant to the microcapsules is 1:10 to 1:6.67; the polymeric dispersant is added simultaneously with the microcapsules.

5. A photoresponsive, self-expanding, self-healing, fluidized solidified soil as described in any one of claims 1 to 4, characterized in that, After hardening, the fluidized solidified soil is triggered by optical signal input to achieve volume compensation and microcrack filling. The optical signal input methods include external irradiation, crack light transmission, light guiding through inspection holes, light guiding through grouting holes, light guiding through pre-embedded optical fibers, or light guiding through pre-embedded light guiding components. The response wavelength of the optical signal is 365nm ultraviolet light or 450nm visible light.

6. A method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil, characterized in that, Includes the following steps: S1, a photosensitive molecule containing a cationic functional group is dissolved in an ethanol-water mixed solvent, sodium-based montmorillonite is dispersed in water to form a suspension, the photosensitive molecule solution is added to the montmorillonite suspension, so that the cationic groups of the photosensitive molecule undergo a cation exchange intercalation reaction with the exchangeable cations between the montmorillonite layers, and after centrifugation, washing, drying and sieving, a photosensitive molecule intercalated modified montmorillonite composite self-healing agent is obtained; S2, the composite self-healing agent obtained in step S1 is dispersed in an oil phase containing wall material monomers and initiators. The oil phase is added to an aqueous phase containing emulsifiers to form an oil-in-water emulsion. Under nitrogen protection, the temperature is raised to cause the wall material monomers to polymerize on the surface of the composite self-healing agent to form an encapsulation layer. After centrifugation, washing, freeze drying and grading, light-transmitting and alkali-resistant polymer microcapsules are obtained. S3: Engineering waste soil, cementitious materials, water-reducing agent, and water are stirred at a stirring speed of not less than 200 rpm for 60-90 seconds to form a slurry. The stirring speed is then reduced to 60-90 rpm, and the microcapsules obtained in step S2 and the polymeric dispersant are added simultaneously under low-speed stirring conditions of 60-90 rpm. After continuing low-speed stirring for 60-90 seconds, the material is discharged to obtain photoresponsive self-expanding self-healing fluidized solidified soil. The dosage of the microcapsules is 0.5%-2.0% of the mass of the cementitious materials, and the dosage of the polymeric dispersant is 0.05%-0.30% of the mass of the cementitious materials.

7. The method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil as described in claim 6, characterized in that, In step S1, the equivalent ratio of the photosensitive molecule to the montmorillonite cation exchange capacity is 1.0:1 to 1.5:1; the cation exchange intercalation reaction temperature is 50 to 70°C, the reaction time is 4 to 8 hours, the stirring speed is 500 rpm, and the reaction is carried out under light-protected conditions; the photosensitive molecule solution is added dropwise to the montmorillonite suspension at a rate of 2 mL / min using a peristaltic pump.

8. The method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil as described in claim 6, characterized in that, In step S2, the wall material monomer is a mixture of methyl methacrylate and hydroxyethyl methacrylate in a mass ratio of 7:3, the initiator is azobisisobutyronitrile, the emulsifier is polyvinyl alcohol, and the mass ratio of the oil phase to the water phase is 1:3; the polymerization reaction temperature is 65-75℃, the reaction time is 4h, and it is carried out under nitrogen protection.

9. The method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil as described in claim 6, characterized in that, In step S2, the mass ratio of the microcapsule wall material monomer to the composite self-healing agent core material is 2:1 to 4:1; the grading step includes: first passing the freeze-dried microcapsule powder through a 100-mesh sieve to remove coarse particle agglomerates, and then collecting the fine powder portion that passes through a 200-mesh sieve to obtain microcapsules with a particle size range of 20 to 80 μm; the encapsulation rate of the microcapsules is 75% to 90%, and the encapsulation rate is determined by thermogravimetric analysis.

10. The method for preparing a photoresponsive, self-expanding, self-healing, fluidized solidified soil as described in claim 6, characterized in that, In step S3, the stirring speed of the engineering waste soil, cementitious material, water-reducing agent and water is 200-300 rpm, and the stirring time is 60-90 s; the low-speed stirring speed is 60-90 rpm, and the stirring time is 60-90 s; the dosage of the microcapsules is 0.5%-2.0% of the mass of the cementitious material, and the dosage of the polymeric dispersant is 0.05%-0.30% of the mass of the cementitious material; the polymeric dispersant is polyvinylpyrrolidone.

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