A three-layer structure alkali-inhibiting and early-strength dual-function microcapsule and a preparation method thereof

Abstract

The application specifically relates to a three-layer structure alkali-inhibiting and early-strength dual-function microcapsule and a preparation method thereof. The preparation method of the dual-function microcapsule comprises the following steps: preparing an alkali-inhibiting inner core by adopting a spray drying method with metakaolin and nano Ca-Al LDH, coating a C-S-H-PCE@nano SiO2 early-strength layer on the surface of the alkali-inhibiting inner core by adopting a static electron assembly and in-situ deposition method, and realizing precise coating of an outer shell PLA-POEGMA-PLA by adopting a starvation dropping, nano precipitation and solvent evaporation method. The intelligent response shell is temperature-sensitive and shrinks when cement hydration heat (45-60 DEG C) is generated, triggers the time sequence release of early-strength components, and realizes the synergistic function of 'first alkali inhibition and durability preservation and then early-strength promotion and development'. The microcapsule can be widely applied to cement-based concrete, geopolymer, gypsum-based materials and 3D printing, sprayed concrete and other special building materials, and the dosage is 1.0-3.5%, thereby effectively solving the contradiction between early strength and long-term durability.

Description

Technical Field

[0001] This invention relates to the field of building technology, specifically to a three-layer structured dual-function microcapsule for inhibiting alkali and early strength, and its preparation method. Background Technology

[0002] Efflorescence in cement-based materials is a common durability problem in construction engineering. It manifests primarily as a white, salt-like efflorescence appearing on the surface of cement mortar, concrete, or putty, severely impacting the aesthetics of the finish, coating adhesion, and structural durability. The mechanism of efflorescence originates from the formation of a large amount of soluble calcium during cement hydration. 2+ Na + K + Ions migrate to the material surface with capillary water, and after the water evaporates, they form crystalline deposits such as carbonates and sulfates.

[0003] Existing alkali suppression technologies are mainly divided into three categories: First, chemical neutralization, which uses acidic substances to consume Ca(OH)2 and lower the pH of the system. However, excessive alkali reduction can damage the stability of hydration products such as CSH, leading to a reduction in strength. Second, physical blocking, which uses hydrophobic agents such as silanes and stearates to reduce water absorption. However, traditional hydrophobic agents have poor dispersibility, are prone to migration and failure, and are insufficient in controlling alkali return in the later stages. Third, ion exchange, which uses zeolites, layered double hydroxides, etc. to adsorb alkali metal ions. However, conventional materials have low selectivity and are difficult to guarantee long-term effectiveness.

[0004] In recent years, microencapsulation controlled-release technology has attracted attention in the building materials field. However, existing alkali-inhibiting microcapsules have significant drawbacks: most are simple time-controlled or humidity-controlled releases, and the response signal is disconnected from the efflorescence mechanism; the core component has a single function, and encapsulating acidic salts, ion traps, and hydrophobic precursors in the same core causes the components to react with each other, resulting in failure during the storage period; the shell degradation in the strongly alkaline environment of cement is uncontrollable. For example, the polylactic acid (PLA) shell is completely hydrolyzed in cement pore solutions with pH>12 within 2-3 days, failing to achieve the claimed "7-day start-up and 28-day peak release" sustained-release effect. In addition, existing technologies have not solved the "targeting" problem. Efflorescence preferentially occurs in the interfacial transition zone (ITZ) and capillary-rich areas, but traditional alkali inhibitors are indiscriminately distributed in the slurry, resulting in low effective concentrations and potentially interfering with early cement hydration.

[0005] It is noteworthy that CSH (calcium silicate hydrate), as a core hydration product comprising 50%-70% of the cement paste volume, is the fundamental source of cement hardening and strength. Its nucleation process directly determines the critical starting point for the transition of the paste from a liquid to a solid state. Early strength technology inducing heterogeneous CSH nucleation is relatively mature, but existing alkali suppression schemes completely fail to consider synergy with cement hydration kinetics during design, sometimes even sacrificing early strength for alkali suppression. Therefore, developing an intelligent alkali suppression microcapsule with a response signal matching the efflorescence mechanism, synergistic function of core components, controllable shell degradation, and targeted enrichment capability in the interface transition zone, would effectively suppress efflorescence while promoting early structural strength through regulating CSH nucleation. This would have significant engineering value for improving the durability and mechanical properties of cement-based materials. Summary of the Invention

[0006] To address existing problems, this invention proposes a three-layer structured dual-functional microcapsule for alkali inhibition and early strength, along with its preparation method. This microcapsule, used in cement construction, resolves the conflict between early strength and long-term durability, achieving temperature-responsive release and adapting to the cement hydration process.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A three-layer structured dual-function microcapsule for alkali inhibition and early strength, wherein the microcapsule has a three-layer core-shell structure, consisting of an alkali-inhibiting core, an early strength layer, and a sustained-release shell from the inside out. The alkali-suppressing core comprises metakaolin and calcium-aluminum layered double hydroxide (Ca-Al LDH), forming a particle size of 100-200 nm. The early strength layer is a uniformly coated layer on the surface of the core, comprising CSH-PCE / nano SiO2, with a thickness of 40-80 nm; The slow-release shell is wrapped around the surface of the early strength layer and is a PLA shell with a thickness of 50-100 nm. The total particle size of the microcapsules is 1-5 μm.

[0008] Furthermore, the mass ratio of the metakaolinite to nano-Ca-Al LDH is 1.2-1.6:1.

[0009] Furthermore, the preparation method of the aforementioned three-layer structure alkali-inhibiting and early-strength dual-functional microcapsules includes the following steps: (1) Weigh metakaolin (MK) and nano-Ca-Al LDH, add deionized water, add 0.5% PVP-K30 solution, and magnetically stir to form a uniform suspension; adjust the pH to 5.5-60 with dilute nitric acid to ensure that the LDH structure is intact, the dispersion is uniform, and the PVP is stable and effective; make the particle surface positively charged, ultrasonically disperse, and spray dry at 120-150℃ to obtain alkali-suppressing core MK / Ca-AlLDH with a particle size of 100-200nm; (2) Under N2 protection, the prepared Ca(NO3)2 solution and Na2SiO3 solution were added dropwise to the PCE (polycarboxylate superplasticizer) solution, and nano SiO2 dispersion was added dropwise at the same time; the pH value was adjusted to 10.8-11.2 with nitric acid or sodium hydroxide, and the reaction was stirred at room temperature for 20-24 h to obtain CSH-PCE / SiO2 nano dispersion; (3) Disperse the alkali-suppressing core in deionized water and ultrasonically disperse it. Adjust the pH to 8.5-9.0. The isoelectric point (IEP) of LDH (layered double hydroxide) is usually around pH 10-12. Under near-neutral or weakly acidic conditions, the positive charge density on the LDH surface is significantly lower than that at pH 8.5-9.0. Maximize the surface positive charge density and enhance the electrostatic coating driving force; obtain the alkali-suppressing core suspension; under room temperature stirring conditions, add the CSH-PCE / SiO2 nano-dispersion from step (2) dropwise to the alkali-suppressing core suspension. After the dropwise addition is completed, continue stirring for 2-4 hours, then let it stand for 10-14 hours. After centrifugation and washing, vacuum dry to obtain alkali-suppressing core@CSH-PCE / SiO2 bilayer particles with a particle size of 300-500 nm; (4a) Oligopolyethylene glycol methyl ether methacrylate POEGMA (6-8 ethylene glycol units (OEG), LCST 50-70℃) and ethylene glycol were added to anhydrous toluene at a molar ratio of 8-10:1 and mixed evenly. Then, stannous octoate Sn(Oct)4 catalyst was added and reacted at 110-130℃ for 11-14 h under nitrogen protection. After cooling to room temperature, the macromolecular glycol HO-POEGMA-OH was obtained. (4b) The macromolecular diol obtained in step (4a) and D,L-lactide (D,L-LA) were dissolved in anhydrous toluene at a molar ratio of 1:7-20. The catalyst Sn(Oct)4 octanoate was added, and the reaction was carried out at 110-130℃ for 11-14h under nitrogen protection. After cooling to room temperature, the PLA-POEGMA-PLA triblock copolymer was obtained. (5) Dissolve the PLA-POEGMA-PLA triblock copolymer from step (4b) in acetone at 0-40℃ at a concentration of 0.5-2wt%; disperse the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles from step (3) in deionized water at a concentration of 0.1-0.5wt%, and ultrasonically disperse to obtain a suspension; Under room temperature stirring conditions, the acetone solution of the triblock copolymer was added dropwise at a starvation gradient of 0.05-0.2 mL / min to the suspension of alkali-suppressing core @CSH-PCE / SiO2 bilayer particles. The starvation dropwise addition was carried out in stages to control nucleation and growth, avoiding the formation of a large number of free micelles of polymer, which would result in low coating efficiency. The total dropwise addition time was 3-6 h. After the addition was completed, the acetone was slowly evaporated under negative pressure. The mixture was dialyzed with deionized water in a dialysis bag for 24 h to remove unreacted polymer and acetone. The precipitate was collected by centrifugation, washed, and freeze-dried under vacuum to obtain trilayer microcapsules with a total particle size of 1-5 μm.

[0010] Preferably, under room temperature (25℃) and stirring conditions at 300 rpm, the triblock copolymer acetone solution is added dropwise to the bilayer particle suspension at a gradient increasing rate of 0.05, 0.1, and 0.2 mL / min. The dropwise addition method, which is slow at first and then fast, allows the polymer to be anchored preferentially on the surface of the bilayer particles and then thickened. The total dropwise addition time is controlled at 3-6 h to achieve nano-self-assembly coating. Furthermore, in step (1), the mass ratio of metakaolin and calcium-aluminum bimetallic layered double hydroxide is 3-5:1.

[0011] Furthermore, in step (1), the zeta potential of the alkali-suppressing core surface is (+25)~(+35) mV.

[0012] Further, in step (2), the molar ratio of Ca(NO3)2 to Na2SiO3 is 1.2-1.6:1; the concentration of Na2SiO3 in the mixed solution is 0.9-1.1 mmol / mL; the initial concentration of PCE in the mixed solution is 0.9-1.1 g / mL; the mass fraction of nano-SiO2 in the mixed solution is 1-3%; and the particle size of nano-silica is 10-30 nm.

[0013] Further, in step (3), the mass fraction of the alkali-suppressing core suspension is 1 wt%, the mass ratio of CSH-PCE / SiO2 to the alkali-suppressing core is 2-4:1, and the dropping rate of the CSH-PCE / SiO2 nano-dispersion is 2-8 mL / min.

[0014] Further, in step (4a), the amount of catalyst added is 0.03-0.08% of the total molar amount of the reactants; the purification steps in steps (4a) and (4b) include adding cold methanol to the product after the reaction to precipitate the precipitate, collecting the precipitate, washing with cold diethyl ether, and vacuum drying.

[0015] Furthermore, in step (4b), the amount of catalyst added is 0.10-0.20% of the total molar amount of the reactants.

[0016] Further, in step (5), the stirring speed is 600-1000 r / min; the concentration of the acetone solution of PLA-POEGMA-PLA triblock copolymer is 25-40 mg / mL; the volume ratio of acetone / water is 1:5~1:7; the conditions for slow evaporation of acetone under negative pressure are: rotary evaporation, 35-40℃, vacuum degree -0.08 MPa, 30-60 min, followed by heating to 45-50℃ and maintaining for 2 h to promote densification of the coating layer, promote PLA rearrangement, and enhance the stability of the coating layer; the temperature of vacuum freeze drying is (-60)-(-40)℃, and the time is 24 h.

[0017] The beneficial effects of this invention are: 1. This invention is the first to construct a three-layer microcapsule consisting of an "alkali-suppressing core, an early-strength intermediate layer, and an intelligent outer shell," resolving the functional conflict between alkali suppression and early strength, and achieving time-sequential release. The alkali-suppressing core (MK / LDH) provides long-lasting alkali suppression, while the CSH crystal nucleation effect in the intermediate layer accelerates cement hydration. The nano-SiO2 filling effect optimizes the interface; and the PLA-POEGMA-PLA triblock copolymer shrinks during the exothermic hydration of cement, triggering the release of early-strength components. This resolves the contradiction between early strength and long-term durability.

[0018] 2. The three-layer microcapsule of "alkali-suppressing core-early strength intermediate layer-intelligent shell" described in this invention uses simple and readily available raw materials that are environmentally friendly. PLA is derived from renewable resources (lactic acid) and can be hydrolyzed and degraded in an alkaline environment. POEGMA has good biocompatibility and is non-toxic. The preparation conditions are mild, and both electrostatic self-assembly and nanoprecipitation methods are suitable for industrial production with low energy consumption. Spray drying and solvent evaporation are mature processes that meet the standards of green building materials.

[0019] 3. In the three-layer structure of this invention, the alkali-suppressing core contains nano-SiO2. The filling effect and the synergistic effect of the pozzolanic reaction optimize the interfacial transition zone (ITZ), reduce the porosity, optimize the pore structure, and reduce the chloride ion diffusion coefficient by 60-76%. The CSH crystal nuclei induce ordered growth, resulting in a denser structure, which can further improve the impermeability level.

[0020] 4. The three-layer structured microcapsules of this invention are used in high-strength / ultra-high-strength concrete to resolve the contradiction between early strength and long-term durability; they are suitable for large-volume concrete and can reduce the risk of alkali-aggregate reaction caused by early hydration heat; they can shorten the steam curing time for precast components and improve production efficiency; they can achieve rapid setting and dimensional stability, and their resistance to chloride ion penetration and early strength development work synergistically, making them suitable for a variety of application scenarios. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The graph shows the initial setting time and final setting time for application examples and comparative application examples. Figure 2 This is a graph showing the change in compressive strength over time. Figure 3 The change of pore fluid pH over time in application examples and comparative application examples; Figure 4 The chloride ion diffusion coefficients (×10) at 28 days and 90 days are shown in the application examples and comparative application examples. -12 m 2 / s). Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0024] This embodiment prepares a three-layer structured dual-functional microcapsule for inhibiting alkali and early strength, and the steps are as follows: (1) Weigh metakaolin and nano-Ca-Al LDH at a mass ratio of 4:1, add deionized water, add 0.5% PVP-K30 solution, and magnetically stir to form a uniform suspension; adjust the pH to 5.5-60 with dilute nitric acid to make the particle surface positively charged, disperse by ultrasonication, and spray dry at 135℃ to obtain alkali-suppressing core MK / Ca-Al LDH with a particle size of 150nm; the zeta potential of the alkali-suppressing core surface is +30mV; (2) Under N2 protection, the prepared Ca(NO3)2 solution and Na2SiO3 solution were added dropwise to the PCE solution, and nano-SiO2 dispersion was added dropwise at the same time; the pH value was adjusted to 11.0 with nitric acid or sodium hydroxide, and the reaction was stirred at room temperature for 22 h to obtain CSH-PCE / SiO2 nano dispersion; the molar ratio of Ca(NO3)2 to Na2SiO3 was 1.4:1; the initial concentration of Na2SiO3 in the mixed solution was 1.0 mmol / mL; the initial concentration of PCE in the mixed solution was 1.0 g / mL; the mass fraction of nano-SiO2 in the mixed solution was 2%; and the particle size of nano-silica was 20 nm.

[0025] (3) Disperse the alkali-suppressing kernel in deionized water and ultrasonically disperse it, adjust the pH to 8.5-9.0 to obtain an alkali-suppressing kernel suspension; Under room temperature stirring conditions, the CSH-PCE / SiO2 nano-dispersion from step (2) was added dropwise to the alkali-suppressing core suspension at a rate of 5 mL / min. The mass ratio of CSH-PCE / SiO2 to the alkali-suppressing core was 3:1. After the addition was completed, stirring was continued for 3 h, and then the mixture was allowed to stand for 12 h. After centrifugation and washing, the alkali-suppressing core@CSH-PCE / SiO2 bilayer particles were obtained by vacuum drying, with a particle size of 300-500 nm. (4a) Oligoethylene glycol methyl ether methacrylate (POEGMEMA, with 7 units of ethylene glycol) and ethylene glycol were added to anhydrous toluene at a molar ratio of 9:1 and mixed evenly. Then, 0.05% of the total monomer molar amount of catalyst Sn(Oct)4 was added and reacted at 120°C for 12.5 h under nitrogen protection. The purification steps were as follows: cooled to room temperature, cold methanol was added to the product after reaction to precipitate the precipitate, the precipitate was collected, washed with cold diethyl ether, and dried under vacuum to obtain macromolecular glycol HO-POEGMA-OH; (4b) The macromolecular diol obtained in step (4a) and D,L-lactide (D,L-LA) were dissolved in anhydrous toluene at a molar ratio of 1:13.5. 0.15% of the total monomer molar amount of catalyst Sn(Oct)4 was added. The reaction was carried out at 120°C for 12.5 h under nitrogen protection. After cooling to room temperature, the PLA-POEGMA-PLA triblock copolymer was obtained by purification. (5) Dissolve the PLA-POEGMA-PLA triblock copolymer from step (4b) in acetone at 0-40℃ at a concentration of 1.25wt%; disperse the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles from step (3) in deionized water at 0.1-0.5wt% and ultrasonically disperse to obtain a suspension; At room temperature (25℃) and under stirring at 300 rpm, the triblock copolymer acetone solution was added dropwise to the bilayer particle suspension at progressively increasing rates of 0.05, 0.1, and 0.2 mL / min, with a total addition time controlled at 4.5 h. The coating was achieved via nano-self-assembly. After the addition was complete, acetone was slowly evaporated under negative pressure. The conditions for this slow evaporation were: rotary evaporation, 37.5℃, vacuum degree -0.08 MPa, 30-60 min, followed by heating to 47.5℃ and maintaining the temperature for 2 h. This promoted PLA rearrangement and enhanced the stability of the coating layer. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 3.5 kDa and dialyzed with deionized water for 24 h (with 3 liquid changes) to remove unreacted polymer and acetone. The precipitate was collected by centrifugation at 9000 rpm for 10 min, washed three times with deionized water, and then freeze-dried under vacuum at -50 ℃ for 24 h to obtain alkali-inhibiting and early-strength bifunctional microcapsules with a total particle size of 2.5 μm and a shell thickness of 85 nm. Example 2

[0026] This embodiment provides a method for preparing a dual-functional microcapsule for inhibiting alkali and promoting early strength, comprising the following steps: (1) Weigh metakaolin and nano-Ca-Al LDH at a mass ratio of 3:1, add deionized water, add 0.5% PVP-K30 solution, and magnetically stir to form a uniform suspension; adjust the pH to 5.5-60 with dilute nitric acid to make the particle surface positively charged, disperse by ultrasonication, and spray dry at 120℃ to obtain alkali-suppressing core MK / Ca-Al LDH with a particle size of 100nm; the zeta potential of the alkali-suppressing core surface is (+35)mV; (2) Under N2 protection, the prepared Ca(NO3)2 solution and Na2SiO3 solution were added dropwise to the PCE solution, with a molar ratio of Ca(NO3)2 to Na2SiO3 of 1.6:1; at the same time, nano-SiO2 dispersion was added dropwise; the pH value was adjusted to 11.2 with nitric acid or sodium hydroxide, and the reaction was stirred at room temperature for 22 h to obtain CSH-PCE / SiO2 nano-dispersion; the initial concentration of Na2SiO3 in the mixed solution was 1.1 mmol / mL; the initial concentration of PCE in the mixed solution was 1.1 g / mL; the mass fraction of nano-SiO2 in the mixed solution was 3%; and the particle size of nano-silica was 10 nm.

[0027] (3) Disperse the alkali-suppressing kernel in deionized water and ultrasonically disperse it, adjust the pH to 8.5-9.0 to obtain an alkali-suppressing kernel suspension; Under room temperature stirring conditions, the CSH-PCE / SiO2 nano-dispersion from step (2) was added dropwise to the alkali-suppressing core suspension at a rate of 2 mL / min. The mass ratio of CSH-PCE / SiO2 to the alkali-suppressing core was 4:1. After the addition was completed, stirring was continued for 4 h, and then the mixture was allowed to stand for 10 h. After centrifugation and washing, the alkali-suppressing core@CSH-PCE / SiO2 bilayer particles were obtained by vacuum drying, with a particle size of 300-500 nm. (4a) POEGMEMA (6 units of ethylene glycol) and ethylene glycol were added to anhydrous toluene at a molar ratio of 8-10:1 and mixed evenly. Then, 0.08% of the total monomer molar amount of the catalyst Sn(Oct)4 was added. The reaction was carried out at 130°C for 11 h under nitrogen protection. The purification steps were as follows: cooled to room temperature, cold methanol was added to the product after the reaction to precipitate the precipitate, the precipitate was collected, washed with cold diethyl ether, and dried under vacuum to obtain the macromolecular glycol HO-POEGMA-OH. (4b) The macromolecular diol obtained in step (4a) and D,L-lactide (D,L-LA) were dissolved in anhydrous toluene at a molar ratio of 1:7. 0.10% of the total monomer molar amount of catalyst Sn(Oct)4 was added. The reaction was carried out at 130°C for 11 h under nitrogen protection. After cooling to room temperature, the PLA-POEGMA-PLA triblock copolymer was obtained by purification. (5) Dissolve the PLA-POEGMA-PLA triblock copolymer from step (4b) in acetone at 0-40℃ at a concentration of 0.5wt%; disperse the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles from step (3) in deionized water at a concentration of 0.5wt%, and then ultrasonically disperse to obtain a suspension. At room temperature (25℃) and under stirring at 300 rpm, the triblock copolymer acetone solution was added dropwise to the bilayer particle suspension at progressively increasing rates of 0.05, 0.1, and 0.2 mL / min, with a total addition time controlled at 3 h. The coating was achieved via nano-self-assembly. After the addition was complete, acetone was slowly evaporated under negative pressure. The conditions for this slow evaporation were: rotary evaporation, 35℃, vacuum degree -0.08 MPa, 60 min, followed by heating to 45℃ and maintaining the temperature for 2 h. This promoted PLA rearrangement and enhanced the stability of the coating layer. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 3.5 kDa and dialyzed with deionized water for 24 h (with 3 liquid changes) to remove unreacted polymer and acetone. The precipitate was collected by centrifugation at 8000 rpm for 10 min, washed three times with deionized water, and then freeze-dried under vacuum at -60 ℃ for 24 h to obtain alkali-inhibiting and early-strength bifunctional microcapsules with a total particle size of 1.8 μm and a shell thickness of 45 nm. Example 3

[0028] This embodiment provides a method for preparing a dual-functional microcapsule for inhibiting alkali and promoting early strength, comprising the following steps: (1) Weigh metakaolin and nano-Ca-Al LDH at a mass ratio of 5:1, add deionized water, add 0.5% PVP-K30 solution, and magnetically stir to form a uniform suspension; adjust the pH to 5.5-60 with dilute nitric acid to make the particle surface positively charged, disperse by ultrasonication, and spray dry at 150℃ to obtain alkali-suppressing core MK / Ca-Al LDH with a particle size of 200nm; the zeta potential of the alkali-suppressing core surface is (+25)mV; (2) Under N2 protection, the prepared Ca(NO3)2 solution and Na2SiO3 solution were added dropwise to the PCE solution, with a molar ratio of Ca(NO3)2 to Na2SiO3 of 1.2:1; at the same time, nano-SiO2 dispersion was added dropwise; the pH value was adjusted to 10.8 with nitric acid or sodium hydroxide, and the reaction was stirred at room temperature for 20 h to obtain CSH-PCE / SiO2 nano-dispersion; the initial concentration of Na2SiO3 in the mixed solution was 0.9 mmol / mL; the initial concentration of PCE in the mixed solution was 0.9 g / mL; the mass fraction of nano-SiO2 in the mixed solution was 1-3%; and the particle size of nano-silica was 30 nm.

[0029] (3) Disperse the alkali-suppressing kernel in deionized water and ultrasonically disperse it, adjust the pH to 8.5-9.0 to obtain an alkali-suppressing kernel suspension; Under room temperature stirring conditions, the CSH-PCE / SiO2 nano-dispersion from step (2) was added dropwise to the alkali-suppressing core suspension at a rate of 8 mL / min. The mass ratio of CSH-PCE / SiO2 to the alkali-suppressing core was 2:1. After the addition was completed, stirring was continued for 2 h, and then the mixture was allowed to stand for 14 h. After centrifugation and washing, the alkali-suppressing core@CSH-PCE / SiO2 bilayer particles were obtained by vacuum drying, with a particle size of 300-500 nm. (4a) Oligoethylene glycol methyl ether methacrylate (POEGMEMA, with 8 units of ethylene glycol) and ethylene glycol were added to anhydrous toluene at a molar ratio of 8:1 and mixed evenly. Then, 0.03% of the total monomer molar amount of catalyst Sn(Oct)4 was added and reacted at 110°C for 14 h under nitrogen protection. The purification steps were as follows: cooled to room temperature, cold methanol was added to the product after reaction to precipitate the precipitate, the precipitate was collected, washed with cold diethyl ether, and dried under vacuum to obtain macromolecular glycol HO-POEGMA-OH. (4b) The macromolecular diol obtained in step (4a) and D,L-lactide (D,L-LA) were dissolved in anhydrous toluene at a molar ratio of 1:20. 0.10% of the total monomer molar amount of catalyst Sn(Oct)4 was added. The reaction was carried out at 110°C for 14 h under nitrogen protection. After cooling to room temperature, the PLA-POEGMA-PLA triblock copolymer was obtained by purification. (5) Dissolve the PLA-POEGMA-PLA triblock copolymer from step (4b) in acetone at 0-40℃ at a concentration of 2wt%; disperse the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles from step (3) in deionized water at 0.1wt% and ultrasonically disperse to obtain a suspension; At room temperature (25℃) and under stirring at 300 rpm, the triblock copolymer acetone solution was added dropwise to the bilayer particle suspension at progressively increasing rates of 0.05, 0.1, and 0.2 mL / min, with a total addition time controlled at 3 h. The coating was achieved via nano-self-assembly. After the addition was complete, acetone was slowly evaporated under negative pressure. The conditions for this slow evaporation were: rotary evaporation, 40℃, vacuum degree -0.08 MPa, 30 min, followed by heating to 50℃ and maintaining the temperature for 2 h. This promoted PLA rearrangement and enhanced the stability of the coating layer. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 3.5 kDa and dialyzed with deionized water for 24 h (with 3 liquid changes) to remove unreacted polymers and acetone. The precipitate was collected by centrifugation at 10,000 rpm for 10 min, washed three times with deionized water, and then freeze-dried under vacuum at -40 ℃ for 24 h to obtain alkali-inhibiting and early-strength bifunctional microcapsules with a total particle size of 4.2 μm and a shell thickness of 125 nm. Comparative Example 1

[0030] This comparative example provides an alkali inhibitor, which is the same as step (1) of Example 1, except that only the alkali inhibitor core (MK / Ca-AlLDH) is prepared, without the intermediate layer and the outer shell being coated. Comparative Example 2

[0031] This comparative example provides a microcapsule that is identical to steps (1)-(3) of Example 1, except that only the alkali-inhibiting core @CSH-PCE / SiO2 bilayer particles are prepared, without any outer shell coating. Comparative Example 3

[0032] This comparative example provides a three-layer structured microcapsule. The preparation and coating of the alkali-suppressing core and the intermediate layer are the same as steps (1)-(3) of Example 1. The difference is that the coating layer outside the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles is a pure PLA homopolymer. The preparation method is that PLA is dissolved in acetone and directly coated. Comparative Example 4

[0033] This comparative example provides a three-layer structured microcapsule. The preparation and coating of the alkali-suppressing core and the intermediate layer are the same as steps (1)-(3) of Example 1. The alkali-suppressing core and the outer shell are the same as in Example 1. No nano SiO2 is added when preparing the intermediate layer. The CSH-PCE dispersion directly coats the core. Comparative Example 5

[0034] This comparative example provides a three-layer microcapsule with an alkali-suppressing core consisting solely of metakaolin (MK) and free of Ca-AlLDH. The preparation steps for the middle layer and the outer shell are the same as in Example 1. Application Examples 1-3

[0035] The three-layer microcapsules prepared in Examples 1-3 were applied to high-strength concrete at dosages of 2.0 wt%, 3.0 wt%, and 2.5 wt%, respectively, corresponding to Application Examples 1-3. The dosage was 2.0%. The high-strength concrete formula was: 48 kg of P·Ⅱ52.5 cement, 8 kg of fly ash, 4 kg of silica fume, 72 kg of river sand, 108 kg of crushed stone (5-25 mm), 0.76 kg of polycarboxylate superplasticizer, and 15.2 kg of water, with a water-cement ratio of 0.25. The mixing process is as follows: Weigh cement, fly ash, silica fume, and microcapsules; mix at low speed for 30 seconds; add 2 / 3 of the water; mix at medium speed for 60 seconds; add river sand and crushed stone; mix at medium speed for 60 seconds; dissolve the water-reducing agent in the remaining 1 / 3 of the water; add slowly; mix at high speed for 90 seconds; let stand; mix slowly for 30 seconds before unloading. Pour into molds for shaping; cure at 20±2℃, RH>95%, standard conditions. Compare and contrast examples 1-5

[0036] The samples prepared in Comparative Examples 1-5 were added to concrete at 2.0 wt%. The composition of the concrete was the same as in Application Example 1, except for the microcapsules. The mixing process and curing method were also the same as in Application Example 1. Comparative Application Examples 1-5 were obtained respectively. Comparative Application Example 6

[0037] A concrete is provided that does not contain any form of alkali inhibitor. The composition of the concrete is the same as in Application Example 1, except that the microcapsules are used. The mixing process and curing method are also the same as in Application Example 1.

[0038] Performance testing The initial setting time and final setting time (min) refer to GB / T 1346; The test methods for compressive strength (MPa) and elastic modulus (GPa) are as follows: GB / T 50081. Pore ​​fluid pH: Pressure filtration; Chloride ion diffusion coefficient (×10) -12 m 2 / s), electromigration method. Implementation Results Example

[0039] The initial setting time and final setting time of application examples and comparative application examples are as follows: Figure 1 As shown, the compressive strength changes with time as follows: Figure 2 As shown in the diagram, the relationship between Examples 1-3 of this invention indicates that Example 2 features a short PLA chain (1:7), a thin outer shell (0.5%), 6 OEG units, a phase transition temperature of approximately 60°C, and a low trigger temperature; it exhibits rapid release within 2-3 days (3-day release rate of 58.5%), and compared to the blank control example 6, the 1-day intensity is increased by 90.3%. Example 3 has a long PLA chain (1:20), a thick shell (2.0%), 8 OEG units, a phase transition temperature of about 80°C, a high trigger temperature, and a release delayed to 5-7 days (7-day release rate of 58.2%). Compared with the blank control example 6, the 1-day strength is only increased by 23.2%, but the 28-day strength is the highest, at 82.3 MPa.

[0040] Compared with the control example, although the pH of the pore liquid in control example 1 decreased to 12.55 after 28 days (showing some alkali suppression effect), the strength at 1 day was only 17.2 MPa, far lower than the 28.5 MPa of control example 1, and the strength at 28 days was only 58.6 MPa, significantly lower than the strength of 78.5 MPa of control example 1. This proves that a single-layer structure cannot achieve early strength and its long-term strength development is limited.

[0041] Compared to Application Example 1, Application Example 2 showed an abnormally high 1-day strength (24.3 MPa) due to the premature release of the early-strength component (65.5% release rate at 1 day), a shortened initial setting time to 95 minutes, loss of workability, and a pore liquid pH of 12.22 at 28 days (e.g., ...). Figure 3 As shown, the alkali suppression is insufficient, with the alkali-aggregate reaction expansion rate reaching 0.065% at 56 days (vs. 0.062%, close to the critical value). This demonstrates that without the outer shell, there is a conflict between the alkali suppression and early strength functions. CSH is consumed prematurely for early strength and cannot continuously suppress alkalinity; at the same time, the early strength component competes with cement hydration, leading to long-term structural deterioration.

[0042] Compared to Application Example 3, which lacks a temperature-sensitive shrinkage mechanism, the outer shell degradation relies solely on hydrolysis (15-20 days), resulting in a 1-day early strength component release rate of only 12.5%, close to the 8.5% of Application Example 1. However, the 3-day early strength component release rate of 28.5% is significantly lower than the 42.5% of Application Example 1. The 3-day strength is 34.2 MPa, lower than the 42.6 MPa of Application Example 1, and the 7-day strength is 50.1 MPa, lower than the 58.3 MPa of Application Example 1. This demonstrates the crucial role of the POEGMA temperature-sensitive block in triggering the "exothermic reaction of cement hydration." Ordinary PLA cannot respond to temperature signals, resulting in delayed early strength release and missing the optimal hydration window. Therefore, the three-layer structure is indispensable. A single layer only inhibits alkali; a double layer has conflicting functions (early release of early strength destroys alkali inhibition); and without a temperature-sensitive outer shell, there can be no temporal synergy.

[0043] Compared to Application Example 4, Application Example 1 lacks nano-SiO2 in its core, resulting in lower strength at both 1 day and 28 days compared to Application Example 1. This demonstrates that the absence of SiO2 filling effect leads to weak early-stage interfaces and insufficient long-term density. Figure 4 As shown, the chloride ion diffusion coefficient of Application Example 4 after 28 days was significantly higher than that of Application Example 1, which also confirms that nano-silica has a filling effect, and its absence will lead to an increase in porosity. The "filling effect" of nano-SiO2 not only physically fills the pores, but also consumes Ca(OH)2 through the volcanic ash reaction to generate additional CSH, optimizing the Ca / Si ratio and density of the interfacial transition zone (ITZ). In Application Example 4, after the absence of SiO2, the thickness of the interfacial transition zone increased, becoming a rapid channel for chloride ion penetration.

[0044] Compared to Application Example 1 and Comparative Application Example 5, the layered double hydroxide structure of Ca-Al LDH provides dual functions: (1) Anion exchange to capture OH- - (1) Long-lasting alkali suppression; (2) Interlayer adsorption and fixation of Cl - This improves impermeability. Comparative Example 6 relies solely on the volcanic ash effect of MK, exhibiting limited alkali suppression capabilities; after 90 days, the pH remained at 12.15. Figure 3 The value was significantly higher than 11.92 in Application Example 1, and the layered structure lacked the anchoring effect of corrosive ions.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-layer structure alkaline-inhibiting and early-strength dual functional microcapsule, characterized in that, The microcapsule has a three-layer core-shell structure, consisting of an alkali-inhibiting core, an early-strength layer, and a sustained-release shell from the inside out. The alkali-suppressing core comprises metakaolin and Ca-Al LDH, forming a particle size of 100-200 nm. The early strength layer is a uniformly coated layer on the surface of the core, comprising CSH-PCE / nano SiO2, with a thickness of 40-80 nm; The sustained-release shell is wrapped around the surface of the early strength layer and is a PLA-POEGMA-PLA shell with a thickness of 50-100 nm. The total particle size of the microcapsules is 1-5 μm.

2. The tri-layer structure alkaline-inhibiting and early-strength dual functional microcapsule according to claim 1, characterized in that, The mass ratio of metakaolin to Ca-Al LDH is 1.2-1.6:

1.

3. The process for the preparation of the tri-layer structure alkaline-early strength dual functional microcapsule according to claim 1, characterized in that, Includes the following steps: (1) Weigh metakaolin and nano-Ca-Al LDH, add deionized water, add 0.5% PVP-K30 solution, and magnetically stir to form a uniform suspension; adjust the pH to 5.5-60 with dilute nitric acid to make the particle surface positively charged, disperse by ultrasonication, and spray dry at 120-150℃ to obtain alkali-suppressing core MK / Ca-Al LDH with a particle size of 100-200nm; (2) Under N2 protection, the prepared Ca(NO3)2 solution and Na2SiO3 solution were added dropwise to the PCE solution, and nano SiO2 dispersion was added dropwise at the same time; the pH value was adjusted to 10.8-11.2 with nitric acid or sodium hydroxide, and the reaction was stirred at room temperature for 20-24 h to obtain CSH-PCE / SiO2 nano dispersion; (3) Disperse the alkali-suppressing core in deionized water and ultrasonically disperse it. Adjust the pH to 8.5-9.0 to obtain an alkali-suppressing core suspension. Under stirring conditions at room temperature, add the CSH-PCE / SiO2 nano-dispersion from step (2) dropwise to the alkali-suppressing core suspension. After the addition is complete, continue stirring for 2-4 hours. Then let it stand for 10-14 hours. After centrifugation and washing, vacuum dry to obtain alkali-suppressing core@CSH-PCE / SiO2 bilayer particles with a particle size of 300-500 nm. (4a) POEGMA and ethylene glycol are added to anhydrous toluene at a molar ratio of 8-10:1 and mixed evenly. Then, stannous octoate catalyst is added and reacted at 110-130℃ for 11-14h under nitrogen protection. After cooling to room temperature, the macromolecular glycol HO-POEGMA-OH is obtained. (4b) The macromolecular diol HO-POEGMA-OH and D,L-lactide obtained in step (4a) were dissolved in anhydrous toluene at a molar ratio of 1:7-20. Stannous octoate catalyst was added, and the reaction was carried out at 110-130℃ for 11-14h under nitrogen protection. After cooling to room temperature, the PLA-POEGMA-PLA triblock copolymer was obtained. (5) Dissolve the PLA-POEGMA-PLA triblock copolymer from step (4b) in acetone at 0-40℃ at a concentration of 0.5-2wt%; disperse the alkali-suppressing core @CSH-PCE / SiO2 bilayer particles from step (3) in deionized water at a concentration of 0.1-0.5wt%, and ultrasonically disperse to obtain a suspension; Under room temperature stirring conditions, the acetone solution of the triblock copolymer was added dropwise at a starvation gradient of 0.05-0.2 mL / min to the suspension of alkali-inhibiting core @CSH-PCE / SiO2 bilayer particles for a total addition time of 3-6 h. After the addition was completed, the acetone was slowly evaporated under negative pressure. The mixture was dialyzed with deionized water in a dialysis bag for 24 h to remove unreacted polymer and acetone. The precipitate was collected by centrifugation, washed, and freeze-dried under vacuum to obtain a trilayer structure alkali-inhibiting and early-strength bifunctional microcapsule with a total particle size of 1-5 μm.

4. The process for the preparation of tri-layer structured alkalinity-early strength dual functional microcapsules according to claim 3, characterized in that, In step (1), the mass ratio of metakaolin to Ca-Al LDH is 3-5:

1.

5. The preparation method of the three-layer structure alkali-inhibiting and early-strength dual-functional microcapsules according to claim 3, characterized in that, In step (1), the zeta potential of the alkali-suppressing core surface is (+25)~(+35) mV.

6. The preparation method of the three-layer structure alkali-inhibiting and early-strength dual-functional microcapsules according to claim 3, characterized in that, In step (2), the molar ratio of Ca(NO3)2 to Na2SiO3 is 1.2-1.6:1; the concentration of Na2SiO3 in the mixed solution is 0.9-1.1 mmol / mL; the initial concentration of PCE in the mixed solution is 0.9-1.1 g / mL; the mass fraction of nano-SiO2 in the mixed solution is 1-3%; and the particle size of nano-silica is 10-30 nm.

7. The preparation method of the three-layer structure alkali-inhibiting and early-strength dual-functional microcapsules according to claim 3, characterized in that, In step (3), the mass fraction of the alkali-suppressing core suspension is 1 wt%, the mass ratio of CSH-PCE / SiO2 to the alkali-suppressing core is 2-4:1, and the dropping rate of the CSH-PCE / SiO2 nano-dispersion is 2-8 mL / min.

8. The method for preparing the three-layer structure alkali-suppressing and early-strength dual functional microcapsules according to claim 3, characterized in that, In step (4a), the number of ethylene glycol units in the oligoethylene glycol methyl ether methacrylate is 6-8, and the LCST is 50-70℃; the amount of catalyst added is 0.03-0.08% of the total molar amount of the reactants; the purification steps in steps (4a) and (4b) include adding cold methanol to the product after the reaction to precipitate the precipitate, collecting the precipitate, washing with cold diethyl ether, and vacuum drying.

9. The method for preparing the three-layer structure alkali-suppressing and early-strength dual functional microcapsule according to claim 3, characterized in that, In step (4b), the amount of catalyst added is 0.10-0.20% of the total molar amount of the reactants.

10. The process for the preparation of tri-layer structured alkalinity-early strength dual functional microcapsules according to claim 3, characterized in that, In step (5), the stirring speed is 300-800 r / min; the conditions for slow evaporation of acetone under negative pressure are: rotary evaporation, 35-40℃, vacuum degree -0.08 MPa, 30-60 min, followed by heating to 45-50℃ and maintaining for 2 h; the temperature for vacuum freeze drying is (-60)-(-40)℃, and the time is 24 h.

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