Preparation method of slow-release water reducing agent capable of being dried within controllable time

Abstract

The invention provides a preparation method of a slow-release water reducing agent capable of being dried within controllable time, which comprises the following steps: S1, synthesizing a slow-release carrier with a core-shell structure: dissolving a water reducing agent active component and a hydrophobic polymer in an organic solvent to form an inner core phase, the preparation method comprises the following steps: dissolving a core phase in a water phase to form a core phase, dissolving a responsive polymer and a coalescing agent in the water phase to form a shell phase, enabling the core phase and the shell phase to form uniform emulsion droplets under the action of shear force through a micro-fluidic emulsification technology, and carrying out solvent evaporation and curing to obtain core-shell microspheres, the shell is made of a responsive polymer; s2, constructing a time response trigger layer: depositing an ionic cross-linking agent and a functional polyelectrolyte on the surface of the core-shell microsphere layer by layer, forming a multi-layer coating film through electrostatic self-assembly, and at least one layer of polyelectrolyte comprises a depolymerization unit capable of being triggered by a specific ion concentration in a cement paste liquid phase.

Description

Technical Field

[0001] This invention belongs to the field of water-reducing agent preparation, and specifically relates to a method for preparing a slow-release water-reducing agent that can be dried over a controlled time. Background Technology

[0002] Currently, in the field of concrete construction, water-reducing agents, as core admixtures for improving workability, strength, and durability, have always faced significant technical challenges in precisely controlling their effective time. Especially in conditions such as large-scale complex structure pouring, long-distance pumping, or high-temperature environments, traditional water-reducing agents generally suffer from fundamental defects such as a fixed effective time window and an inability to dynamically match the concrete hydration process with construction requirements. While current mainstream slow-release technologies attempt to extend the workable time by delaying release, they are severely constrained by bottlenecks such as uncontrollable release kinetics, sluggish environmental response, and insufficient stability.

[0003] Specifically, existing slow-release water-reducing agents mostly rely on simple physical encapsulation or chemical modification (such as esterification). Their release mechanism often passively depends on single variables such as environmental humidity, temperature, or alkaline hydrolysis rate, resulting in a serious deviation between the release curve and the preset model in actual engineering: under low temperature or low alkalinity conditions, the release is too slow, causing insufficient early workability, a sharp increase in pumping resistance, and even the risk of pipe blockage; while in high temperature or high alkalinity environments, the release may be accelerated due to hydrolysis or membrane rupture, which not only loses the significance of slow release, but also causes problems such as excessively rapid instantaneous loss of slump and significant performance fluctuations between batches, forcing repeated adjustments of dosage on site or reliance on secondary addition, significantly increasing construction complexity and quality risks.

[0004] Furthermore, existing technologies lack the ability to precisely control the core requirement of "time-based drying"—they cannot set specific time points (such as the end of the transportation period or the start of pouring) to trigger the release of the water-reducing agent, nor can they achieve multi-stage, differentiated release rate programming. For example, they cannot maintain deep dormancy during mixing and transportation to avoid ineffective adsorption, nor can they precisely initiate rapid dispersion before and after pouring to ensure the compactness of the pour, or perform a secondary release before final setting to compensate for shrinkage. More seriously, the interaction mechanisms between most slow-release systems and different cement mineral components, admixtures, and early hydration products are complex and unpredictable, making their slow-release behavior extremely sensitive to changes in raw materials, resulting in poor batch stability and significantly increasing the difficulty of concrete mix design and quality control.

[0005] Meanwhile, the encapsulation materials or complex synthesis processes introduced to achieve slow release are often accompanied by problems such as soaring costs, introduction of harmful impurities, or reduction of the effective content of water-reducing agents. Some polymeric capsule wall materials may even interfere with the cement hydration path or introduce bubble defects.

[0006] Therefore, developing an intelligent slow-release water-reducing agent that can actively respond to the construction timeline, has programmable release behavior, and is resistant to environmental interference, and completely solve the inherent problems of low time control accuracy, weak environmental adaptability, poor stability, and limited functionality in existing technologies, has become an urgent need to break through the bottleneck of concrete construction technology and achieve precise manufacturing of high-performance concrete. Summary of the Invention

[0007] This invention proposes a method for preparing a slow-release water-reducing agent that can be dried over a controlled time. This method overcomes the limitation of traditional water-reducing agents in the prior art, which have a strong coupling between release behavior and environment. It enables the programmed and precise release of the active components of the water-reducing agent in the three stages of concrete mixing, transportation, and pouring, thus solving the core problems of poor construction adaptability and large quality fluctuations caused by uncontrollable release.

[0008] The technical solution of the present invention is achieved as follows: a method for preparing a slow-release water-reducing agent capable of controlled-time drying, the method comprising the following steps:

[0009] S1: Synthesis of a core-shell structured sustained-release carrier: The active component of a water-reducing agent and a hydrophobic polymer are dissolved in an organic solvent to form a core phase, while a responsive polymer and a film-forming aid are dissolved in an aqueous phase to form a shell phase. Microfluidic emulsification technology is used to form uniform emulsion droplets between the core phase and the shell phase under shear force. After solvent evaporation and solidification, core-shell microspheres are obtained, wherein the core contains the active component of a water-reducing agent and a hydrophobic polymer, and the shell is composed of a responsive polymer.

[0010] S2: Constructing a time-response triggering layer: Deposit ionic crosslinking agent and functional polyelectrolyte layer by layer on the surface of core-shell microspheres, and form a multilayer coating film through electrostatic self-assembly, wherein at least one polyelectrolyte layer contains depolymerization units that can be triggered by a specific ion concentration in the liquid phase of cement slurry;

[0011] S3: Implanting a time-controlled layer: The coated microspheres obtained in step S2 are immersed in a solution containing a time delay factor, wherein the time delay factor is a metal-organic framework material that can be released in stages during cement hydration. The metal-organic framework material is loaded into the gap of the polyelectrolyte layer by vacuum adsorption to form a composite sustained-release system with a preset time release window.

[0012] S4: Drying and functionalization: After the loaded composite microspheres are dried at low temperature under vacuum, an isolation coating is sprayed on the surface. The isolation coating is generated by the reaction of an amphiphilic block copolymer and a silane coupling agent, and finally a slow-release water-reducing agent product with controllable drying time is obtained.

[0013] The glass transition temperature of the responsive polymer is higher than the concrete transport environment temperature but lower than the pouring temperature. The ion concentration triggering threshold of the depolymerization unit matches the concentration of the mid-stage hydration products of the cement paste. The disintegration time of the metal-organic framework material is programmed by adjusting the hydrolytic stability of its organic ligands to ensure that the active components of the water-reducing agent remain in an inert encapsulated state during the concrete mixing stage, initiate ion-triggered depolymerization after being transported to a preset time node, and achieve shell rupture and release through temperature response during the pouring stage.

[0014] In existing technologies, the release kinetics of slow-release water-reducing agents are severely constrained by passive responses to environmental variables (temperature, pH, ion concentration). Their fundamental flaws lie in the inability to autonomously set release time points, difficulty in matching the dynamic process of cement hydration, and weak resistance to environmental interference. Specifically, this manifests in three major technical challenges:

[0015] First, there is a lack of precision in timing control. Traditional physical encapsulation or chemical modification relies on the material's own hydrolysis / diffusion rate, which cannot actively trigger release according to the construction timeline (such as at the end of transportation or at the beginning of pouring). This results in the water-reducing agent being released too early during the mixing stage, causing ineffective adsorption, or being released explosively at high temperatures, causing instantaneous loss of slump.

[0016] Second, the environmental sensitivity is too high. The existing slow-release system is highly sensitive to changes in temperature and alkalinity: slow release at low temperatures leads to a surge in pumping resistance, while accelerated release at high temperatures causes workability loss of control, and the differences in ionic composition of different cement raw materials further amplify batch performance fluctuations;

[0017] Third, the release function is not programmable. A single slow-release mechanism cannot meet the needs of multi-stage differentiated release (such as deep dormancy during transportation, rapid release during pouring, and compensatory release before final setting). Moreover, the complex coating structure introduced to delay release often reduces the effective content of water-reducing agent, interferes with hydration, or introduces harmful impurities.

[0018] This invention overcomes the above difficulties through a three-level collaborative control mechanism:

[0019] Temperature-responsive outer shell (responsive polymer): Its glass transition temperature (Tg) is between the concrete transportation and pouring temperatures. The physical switch control of shell rupture is achieved by utilizing temperature phase change, avoiding false triggering at low temperatures.

[0020] Ion-triggered depolymerization layer (containing polyelectrolytes of depolymerization units): The ion concentration threshold of the depolymerization unit is set to match the concentration of products in the middle stage of cement hydration, forming a chemical gate barrier to ensure that the release timing accurately corresponds to the hydration process;

[0021] MOFs (Metal-Organic Frameworks) time-controlled layers: By regulating disintegration time through ligand hydrolysis stability, they provide an absolute time reference, allowing the release window to be independent of environmental factors. These three elements work synergistically to achieve a triple logic determination based on "time-ion-temperature," ultimately enabling the on-demand programmed release of the water-reducing agent's activity.

[0022] In a preferred embodiment, the hydrophobic polymer in step S1 is a polyacrylate compound containing long-chain alkyl groups, and the responsive polymer is poly(N-isopropylacrylamide) and its copolymers with temperature-dependent phase change characteristics; the shell thickness to core diameter ratio of the core-shell structured microspheres is 1:5 to 1:10, and the responsive polymer exhibits a gradient crosslinking density distribution in the shell, wherein the crosslinking density of the outer layer is higher than that of the inner layer.

[0023] In a preferred embodiment, the depolymerization unit in step S2 is an amphoteric polymer containing tertiary amine groups, whose dynamic covalent bonds with the ionic crosslinking agent can be selectively broken by the critical calcium ion concentration in the cement hydration products; the functional polyelectrolyte includes anionic polyelectrolytes containing sulfonic acid groups and cationic polyelectrolytes containing quaternary ammonium salt groups, which form a smart gated membrane with dual pH / ion responsiveness through layer-by-layer self-assembly.

[0024] In a preferred embodiment, the metal-organic framework material in step S3 is zirconium-based or iron-based MOFs, whose organic ligands contain hydrolyzable carboxylic acid ester bonds and coordinated unsaturated metal clusters; the disintegration kinetics of the time delay factor is programmed by adjusting the steric hindrance effect of the organic ligands and the strength of the coordination bonds, and the secondary porosity of the composite microspheres after loading is controlled in the range of 15-30 nm to match the particle size distribution of cement particles.

[0025] In a preferred embodiment, the isolation coating in step S4 forms a three-dimensional network cross-linked structure through in-situ polycondensation reaction, wherein the hydrophobic segments are perfluoroalkyl acrylate blocks and the hydrophilic segments are polyethylene oxide-propylene oxide copolymers; the functionalization treatment also includes grafting cement-affinity silanol groups onto the coating surface and achieving microsphere surface energy regulation through fluidized bed spray drying.

[0026] The beneficial effects of this invention after adopting the above technical solution are as follows: This invention creatively constructs a three-level synergistic control and release system to achieve precise control of the activity of water-reducing agents across the entire time domain: by setting a release window through a time control layer, identifying hydration process signals through an ion trigger layer, and sensing construction nodes through a temperature response layer, a logical chain of "inert encapsulation during mixing - depolymerization triggered at the end of transportation - rupture and release during pouring" is formed, completely reversing the defects of traditional technologies that passively respond to environmental variables. The gradient cross-linked shell inhibits false triggering at low temperatures; the dynamic covalent bond depolymerization unit specifically responds to the critical ion concentration; the highly stable time control material ensures the reliability of the time base and significantly reduces the release deviation caused by temperature / acid-base fluctuations. The three-dimensional isolation network blocks pre-erosion by moisture, and the amphiphilic coating balances moisture protection during storage and dispersibility during use; the secondary pores precisely match the cement particle interface, improving the utilization rate of active components; no harmful impurities are introduced, making it suitable for multi-component cementitious systems. It eliminates the need for secondary addition on-site, simplifying the construction process; it precisely matches the pumping and pouring windows, eliminating the risk of workability loss of control; the customizable compensation release function effectively inhibits shrinkage cracks, promoting the transformation of concrete construction from experience-based control to programmatic control. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the 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.

[0028] Figure 1 This is a flowchart illustrating the preparation process of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0030] Example:

[0031] like Figure 1 As shown, a method for preparing a slow-release water-reducing agent capable of controlled-time drying includes the following steps:

[0032] S1: Synthesis of a core-shell structured sustained-release carrier: The active component of a water-reducing agent and a hydrophobic polymer are dissolved in an organic solvent to form a core phase, while a responsive polymer and a film-forming aid are dissolved in an aqueous phase to form a shell phase. Microfluidic emulsification technology is used to form uniform emulsion droplets between the core phase and the shell phase under shear force. After solvent evaporation and solidification, core-shell microspheres are obtained, wherein the core contains the active component of a water-reducing agent and a hydrophobic polymer, and the shell is composed of a responsive polymer.

[0033] S2: Constructing a time-response triggering layer: Deposit ionic crosslinking agent and functional polyelectrolyte layer by layer on the surface of core-shell microspheres, and form a multilayer coating film through electrostatic self-assembly, wherein at least one polyelectrolyte layer contains depolymerization units that can be triggered by a specific ion concentration in the liquid phase of cement slurry;

[0034] S3: Implanting a time-controlled layer: The coated microspheres obtained in step S2 are immersed in a solution containing a time delay factor, wherein the time delay factor is a metal-organic framework material that can be released in stages during cement hydration. The metal-organic framework material is loaded into the gap of the polyelectrolyte layer by vacuum adsorption to form a composite sustained-release system with a preset time release window.

[0035] S4: Drying and functionalization: After the loaded composite microspheres are dried at low temperature under vacuum, an isolation coating is sprayed on the surface. The isolation coating is generated by the reaction of an amphiphilic block copolymer and a silane coupling agent, and finally a slow-release water-reducing agent product with controllable drying time is obtained.

[0036] The glass transition temperature of the responsive polymer is higher than the concrete transport environment temperature but lower than the pouring temperature. The ion concentration triggering threshold of the depolymerization unit matches the concentration of the mid-stage hydration products of the cement paste. The disintegration time of the metal-organic framework material is programmed by adjusting the hydrolytic stability of its organic ligands to ensure that the active components of the water-reducing agent remain in an inert encapsulated state during the concrete mixing stage, initiate ion-triggered depolymerization after being transported to a preset time node, and achieve shell rupture and release through temperature response during the pouring stage.

[0037] Taking the construction of a large-volume concrete pier foundation for a cross-sea cable-stayed bridge, which requires strict adherence to a set schedule, as a scenario, the slow-release water-reducing agent prepared using this method was added to the mixing plant at 1.2% of the total cementitious materials. During the mixing stage (ambient temperature ≤25℃), the three-level encapsulation system of the water-reducing agent microspheres synergistically maintained a dormant state: the hydrophobic polymer core blocked moisture penetration, the gradient cross-linked PNIPAM shell remained rigid due to its glass transition temperature (Tg=38℃) being higher than the mixing temperature, and the carboxylic acid ester ligands in the MOFs time-controlled layer remained stable in a low-alkali environment; simultaneously, the sulfonic acid / quaternary ammonium salt polyelectrolyte membrane of the ion-triggered layer remained closed because the critical calcium ion concentration had not been reached, ensuring that the release rate of the active components of the water-reducing agent was <5% throughout the mixing process, thus avoiding ineffective adsorption of cement particles.

[0038] During the concrete pumping and transportation stage (120 minutes), the calcium ion concentration in the slurry liquid phase continuously increases as the cement hydration process progresses. When transportation reaches 90 minutes, the calcium ion concentration generated by the hydration reaction... 2+ When the concentration exceeds the depolymerization unit recognition threshold (20mM), the dynamic covalent bond intelligent gating mechanism is activated: the tertiary amine group in the zwitterionic polymer reacts with Ca... 2+ Specific coordination occurs, triggering dynamic covalent bond breaking in the polyelectrolyte layer, exposing the MOF time-controlled layer to an alkaline environment. At this point, the coordinated unsaturated zirconium clusters of the metal-organic framework initiate a ligand hydrolysis process under OH- erosion. The 120-minute disintegration window designed by the steric hindrance effect of the organic ligands precisely matches the pumping endpoint.

[0039] During the pouring and placement stage (concrete temperature ≥ 40℃), the triple release logic is finally triggered: First, the temperature response shell undergoes a phase change due to the ambient temperature exceeding Tg, and the gradient cross-linked structure transitions from a glassy state to a rubbery state, generating internal stress cracks; simultaneously, the MOF skeleton completely disintegrates, forming 15-30nm secondary pore channels; finally, the heat of cement hydration (peak temperature 65℃) accelerates the shell rupture, and the active components of the water-reducing agent are rapidly released through the dual channels formed by the ion-triggered layer cracks and the MOF pores. At this time, the concrete is precisely in the critical period of pouring and vibration, and the instantaneous dispersion rate of the active components reaches over 90%, efficiently adsorbing onto the surface of cement particles to reduce liquid phase tension and ensure the filling density of the high-flowability concrete.

[0040] During the pre-setting compensation stage (4 hours after pouring), the remaining 10% water-reducing agent is directionally anchored to the cement particle interface through the silanol layer of the isolation coating. It then releases secondary compensation shrinkage stress during the hydration process, suppressing temperature-induced cracking in large-volume concrete. The entire process utilizes a three-level logic system—time, ion, and temperature—to program the release trajectory: MOFs provide an absolute time reference, the ion layer synchronizes the hydration process, and the temperature layer is bound to construction nodes, completely avoiding the risk of uncontrolled release caused by pumping delays, sudden temperature changes, or raw material fluctuations inherent in traditional technologies.

[0041] In the continuous casting construction of the core tube of super high-rise buildings, pumping heights exceeding 300 meters are required, with ambient temperatures fluctuating between 5-35℃. Core-shell microspheres are constructed using polyacrylate (a hydrophobic polymer) containing C18 long-chain alkyl groups and poly(N-isopropylacrylamide-co-acrylic acid) (a responsive polymer). The core diameter is 10 μm, and the shell thickness is 1.2 μm (core-shell ratio 1:8.3). Size distribution is precisely controlled through microfluidic emulsification. Gradient crosslinking density is achieved in stages through UV-photopolymerization: the outer layer uses ethylene glycol dimethacrylate (8% crosslinking agent concentration) to form a dense network, while the inner layer reduces the crosslinking degree to 2% to maintain flexibility. During pumping, the highly cross-linked outer shell (glassy state) in the low-temperature section (5-15℃) resists the shear force of the pump pipe, preventing microsphere breakage. When the concrete temperature rises to 25℃ (frictional heat of the pump pipe), the inner low-cross-linked zone softens first to absorb vibration energy. When it reaches the pouring layer (ambient temperature 35℃), the outer shell's Tg (32℃) triggers a phase transition, and the gradient structure generates directional cracks from the outside to the inside, ensuring that the water-reducing agent is released at the top layer rather than leaking midway. This design solves the problem of premature release caused by pressure fluctuations in ultra-high-rise pumping, ensuring that the concrete maintains a slump of over 220mm at a height of 300 meters.

[0042] In areas where river sand is scarce, concrete production using a blend of manufactured sand and mountain sand is employed. The fine aggregate mud content fluctuates between 3% and 8%. Amphoteric polymers containing tertiary amine groups (such as dimethylaminoethyl methacrylate-sulfobetaine copolymer) form dynamic borate ester bonds with sodium tetraborate crosslinking agent. Sodium polystyrene sulfonate (PSS) is used as the anionic polyelectrolyte, and polydiallyldimethylammonium chloride (PDADMAC) is used as the cationic layer. A five-layer membrane (PSS / PDADMAC)² / PSS is constructed through electrostatic self-assembly. When the mud content of the manufactured sand increases sharply (montmorillonite content > 5%), free Na₂O in the cement paste... + When the concentration increases to 0.8 mol / L, traditional water-reducing agents are easily adsorbed and rendered ineffective by clay.

[0043] In this scheme: the quaternary ammonium salt groups of PDADMAC preferentially adsorb clay particles to form a protective layer; the critical calcium ion concentration is set at 15mM (to avoid Na+). + Interference threshold); when Ca in the middle stage of hydration 2+ Reaching 20 mM, tertiary amine group and Ca 2+ Complexation (binding constant K = 10) 3 · 8 This triggers the breakage of borate ester bonds. At this point, the clay adsorption sites are saturated with PDADMAC, and the active components of the water-reducing agent are released directionally to the surface of cement particles.

[0044] During the tidal window for pouring concrete for the bridge piers, with only two hours of low-water construction time per day, zirconium-based MOFs were used as the time-controlled layer. The organic ligand was 2-tert-butyl terephthalate, and unsaturated zirconium clusters were loaded into the polyelectrolyte layer with a 15nm gap. By adjusting the degree of tert-butyl substitution, the hydrolysis barrier of the carboxylic acid ester bond was increased from 80 kJ / mol to 110 kJ / mol, and the disintegration time was locked to match the tidal gap at 120 ± 3 min.

[0045] After concrete is produced at a land-based mixing plant, it is transported by tanker trucks across a cross-sea bridge: 1) In a high-salt-spray environment, the Zr-O bond exhibits better resistance to chloride ion erosion than iron-based MOFs; the secondary pore size of the loaded microspheres is controlled at 22±3nm, ensuring that MOFs disintegration products do not clog the pores; when transported for 110 minutes, 5 kilometers from the construction site, the MOFs framework disintegrates into 2-3nm zirconium-oxygen clusters as pre-set, forming ion diffusion channels. This design achieves "zero-delay" control for tidal construction: release is triggered when the tanker truck arrives at the construction site, and even if there is a 15-minute delay due to strong winds, the time control deviation is still less than ±2%, avoiding the release lag caused by sea breeze cooling of traditional temperature-sensitive materials.

[0046] During steam curing at the high-speed railway track slab prefabrication plant, the isolation coating is formed by in-situ polycondensation of methyltrimethoxysilane and perfluorooctyl ethyl acrylate / P123 block copolymer, creating a three-dimensional Si-O-Si network. Hydrophobic segments ensure a contact angle >140°, while hydrophilic PEO segments are embedded within the network. During fluidized bed spray drying, an inlet temperature of 80°C activates silane condensation, while the microsphere surface energy is controlled to 35 mN / m.

[0047] During steam curing: In the initial stage at 55℃, the perfluoroalkyl segments resist the high humidity environment, preventing moisture penetration and pre-release; when the temperature is raised to 80℃, the PEO segments crystallize and melt, generating deformation stress, which, in conjunction with the silanol surface grafting density of 1.2 segments / nm, results in a yield density of 1.2 segments / nm. 2 It forms Ca-O-Si bonds with cement hydration products, accelerating the directional peeling of the coating; after the three-dimensional network dissociates, it generates <50nm silica particles, which fill the pores of the cement stone and improve the density. Compared with the failure rate of more than 25% of traditional water-reducing agents in steam curing, the release curve of this solution has a deviation of less than 5% from the design, ensuring that the track slab meets the demolding strength standard after 24 hours.

[0048] 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 method for preparing a slow-release water-reducing agent capable of controlled-time drying, characterized in that, The method includes the following steps: S1: Synthesis of a core-shell structured sustained-release carrier: The active component of a water-reducing agent and a hydrophobic polymer are dissolved in an organic solvent to form a core phase, while a responsive polymer and a film-forming aid are dissolved in an aqueous phase to form a shell phase. Microfluidic emulsification technology is used to form uniform emulsion droplets between the core phase and the shell phase under shear force. After solvent evaporation and solidification, core-shell microspheres are obtained, wherein the core contains the active component of a water-reducing agent and a hydrophobic polymer, and the shell is composed of a responsive polymer. S2: Constructing a time-response triggering layer: Deposit ionic crosslinking agent and functional polyelectrolyte layer by layer on the surface of core-shell microspheres, and form a multilayer coating film through electrostatic self-assembly, wherein at least one polyelectrolyte layer contains depolymerization units that can be triggered by a specific ion concentration in the liquid phase of cement slurry; S3: Implanting a time-controlled layer: The coated microspheres obtained in step S2 are immersed in a solution containing a time delay factor, wherein the time delay factor is a metal-organic framework material that can be released in stages during cement hydration. The metal-organic framework material is loaded into the gap of the polyelectrolyte layer by vacuum adsorption to form a composite sustained-release system with a preset time release window. S4: Drying and functionalization: After the loaded composite microspheres are dried at low temperature under vacuum, an isolation coating is sprayed on the surface. The isolation coating is generated by the reaction of an amphiphilic block copolymer and a silane coupling agent, and finally a slow-release water-reducing agent product with controllable drying time is obtained. The glass transition temperature of the responsive polymer is higher than the concrete transport environment temperature but lower than the pouring temperature. The ion concentration triggering threshold of the depolymerization unit matches the concentration of the mid-stage hydration products of the cement paste. The disintegration time of the metal-organic framework material is programmed by adjusting the hydrolytic stability of its organic ligands to ensure that the active components of the water-reducing agent remain in an inert encapsulated state during the concrete mixing stage, initiate ion-triggered depolymerization after being transported to a preset time node, and achieve shell rupture and release through temperature response during the pouring stage.

2. The preparation method of a controlled-time drying slow-release water-reducing agent as described in claim 1, characterized in that: The hydrophobic polymer in step S1 is a polyacrylate compound containing long-chain alkyl groups, and the responsive polymer is poly(N-isopropylacrylamide) and its copolymers with temperature-dependent phase change characteristics; the shell thickness to core diameter ratio of the core-shell structured microspheres is 1:5 to 1:10, and the responsive polymer exhibits a gradient crosslinking density distribution in the shell, wherein the crosslinking density of the outer layer is higher than that of the inner layer.

3. The preparation method of a controlled-time drying slow-release water-reducing agent as described in claim 1, characterized in that: The depolymerization unit in step S2 is an amphoteric polymer containing tertiary amine groups, whose dynamic covalent bonds with the ionic crosslinking agent can be selectively broken by the critical calcium ion concentration in the cement hydration products; the functional polyelectrolyte includes anionic polyelectrolytes containing sulfonic acid groups and cationic polyelectrolytes containing quaternary ammonium salt groups, which form a smart gated membrane with dual pH / ion responsiveness through layer-by-layer self-assembly.

4. The method for preparing a controlled-time drying slow-release water-reducing agent as described in claim 1, characterized in that: The metal-organic framework material mentioned in step S3 is zirconium-based or iron-based MOFs, whose organic ligands contain hydrolyzable carboxylic acid ester bonds and coordinated unsaturated metal clusters; the disintegration kinetics of the time delay factor is programmed by adjusting the steric hindrance effect of the organic ligands and the strength of the coordination bonds, and the secondary porosity of the composite microspheres after loading is controlled in the range of 15-30 nm to match the particle size distribution of cement particles.

5. The method for preparing a controlled-time drying slow-release water-reducing agent as described in claim 1, characterized in that: The isolation coating described in step S4 forms a three-dimensional network cross-linked structure through in-situ polycondensation reaction, with hydrophobic segments being perfluoroalkyl acrylate blocks and hydrophilic segments being polyethylene oxide-propylene oxide copolymers; the functionalization treatment also includes grafting cement-affinity silanol groups onto the coating surface and achieving microsphere surface energy regulation through fluidized bed spray drying.

Images