A u-phase nucleus inducing expansion agent, a preparation method and use thereof

Abstract

This application discloses a U-phase nucleation-induced expansion agent, its preparation method, and its uses. The U-phase nucleation-induced expansion agent, by weight, comprises the following components: 20-50 parts aluminum-containing raw material; 5-40 parts calcium-containing raw material; 5-25 parts sulfate; 80-120 parts pH adjuster; and 0.5-2 parts auxiliary regulator. The aluminum-containing raw material, calcium-containing raw material, and sulfate are the raw materials for forming the U-phase structure. The pH adjuster provides a strongly alkaline environment to promote the dissolution of the raw materials into active substances. The auxiliary regulator enables the active substances to complete nucleation, growth, and stacking, thereby achieving the controllable generation of the U-phase structure. This application utilizes the in-situ generation of more U-phase crystal products based on induction, thereby reducing the proportion of gel phase products in geopolymers to decrease shrinkage, while simultaneously utilizing the water-absorbing and swelling properties of the U-phase to further inhibit shrinkage.

Description

Technical Field

[0001] This application relates to the field of building material preparation technology, and in particular to a U-phase nucleation-induced expansion agent, its preparation method and application. Background Technology

[0002] Compared to traditional silicate cement, geopolymers exhibit greater volume shrinkage during the hardening process, severely impacting the volume stability of geopolymer concrete products. This has become a major technical challenge limiting the large-scale application of such materials. Existing crystallization expansion agents suitable for cement-based materials, such as CaO, MgO, and ettringite, all utilize the crystallization expansion characteristics of their hydration products (Ca(OH)2, Mg(OH)2, and ettringite) to induce expansion. However, these crystallization products exhibit poor stability in the highly alkaline environment and complex pore solution ionic environment of geopolymers, making it difficult to achieve safe and efficient expansion and shrinkage inhibition effects. Summary of the Invention

[0003] In view of this, this application provides a U-phase nucleus-induced expansion agent, a preparation method and its use, which generates more U-phase crystal products in situ based on the induction effect, thereby reducing the proportion of gel phase products in geopolymers to reduce shrinkage, while utilizing the water absorption and expansion characteristics of the U-phase to further inhibit shrinkage.

[0004] This application provides a U-phase crystal nucleation-induced expansion agent, which, by weight, comprises the following components: 20-50 parts aluminum-containing raw material; 5-40 parts calcium-containing raw material; 5-25 parts sulfate; 80-120 parts pH adjuster; and 0.5-2 parts auxiliary regulator. The aluminum-containing raw material, the calcium-containing raw material, and the sulfate are raw materials for forming the U-phase structure; the pH adjuster is used to provide a strongly alkaline environment to promote the dissolution of the raw materials into active substances; the auxiliary regulator is used to enable the active substances to complete nucleation, growth, and stacking, so as to achieve the controllable generation of the U-phase structure.

[0005] In some embodiments, the pH range of the strongly alkaline environment is 9 to 14; the pH adjuster is selected from at least one of sodium hydroxide and potassium hydroxide.

[0006] In some embodiments, the auxiliary regulating agent comprises inorganic microparticles and hexagonal liquid crystal; the mass ratio of the inorganic microparticles to the hexagonal liquid crystal is 1:1 to 2.5; wherein the microstructure of the inorganic microparticles is hexagonal plate-like or hexagonal short columnar; the average particle size D of the inorganic microparticles is... 50The particle size is 0.5~5 μm; the inorganic micro powder is selected from at least one of nepheline, hematite, and tourmaline; the hexagonal liquid crystal is formed by the self-assembly of an amphiphilic substance in a solvent, and the amphiphilic substance is selected from at least one of polyethylene oxide-polypropylene oxide block copolymer, alkyl trimethylammonium salt, and polyoxyethylene alkyl ether.

[0007] In some embodiments, the aluminum-containing raw material includes at least one of alumina, aluminum hydroxide, sodium aluminate, and aluminum powder.

[0008] In some embodiments, the sulfate-containing raw material includes at least one of sodium sulfate, potassium sulfate, and lithium sulfate.

[0009] In some embodiments, the calcium-containing raw material includes at least one of calcium hydroxide, calcium oxide, calcium carbonate, and their hydrates.

[0010] In some embodiments, the auxiliary regulator further includes a dispersant, wherein the mass ratio of the dispersant to the inorganic micro powder is 1 to 2.5:1; the dispersant is selected from at least one of polycarboxylate, polyacrylate, and lignin sulfonate.

[0011] In some embodiments, this application also provides a method for preparing a U-phase nucleation-induced expansion agent, comprising: Take the corresponding weight parts of aluminum-containing raw materials and pH adjuster, mix, stir, and heat to obtain the first reaction medium, which contains aluminate under alkaline conditions; Add the corresponding mass fraction of sulfate to the first reaction medium, mix, and allow the sulfate ions provided by the sulfate to coordinate with the aluminate ions to construct an anionic framework with a layered structure. Continue adding calcium-containing raw materials to the first reaction medium to allow calcium ions to insert into the anion framework to form an intercalated structure. Then, continue stirring to stabilize and aggregate the intercalated structure to obtain the second reaction medium. Add the corresponding mass fraction of auxiliary regulator to the second reaction medium, and stir to obtain the precursor; The precursor was transferred to a closed environment and subjected to hydrothermal reaction, cooling, washing, and drying to obtain a U-phase nucleation-induced expansion agent.

[0012] In some embodiments, the temperature of the hydrothermal reaction is 60~150°C; the time of the hydrothermal reaction is 24~168h.

[0013] In some embodiments, this application also provides the use of the U-phase nucleus-induced expansion agent in geopolymers as a concrete admixture, wherein the dosage of the U-phase nucleus-induced expansion agent in the geopolymer is 2-5 wt%.

[0014] The beneficial effects of this application are as follows: The U-phase nucleation-induced expansion agent provided in this application promotes the in-situ generation of the U-phase in geopolymer by utilizing the nucleation-induced effect of the U-phase, thereby achieving the effects of expansion and inhibition of shrinkage; the U-phase nucleation-induced expansion agent prepared in this application can exist stably in the highly alkaline environment of the geopolymer, while utilizing the alkaline activator in the geopolymer and the Na dissolved from the slag + Ca 2+ Al(OH)4 - and SO4 2- Further crystallization and growth induce the in-situ generation of more U-phase crystal products, thereby reducing the proportion of CASH gel phase products in the geopolymer and minimizing shrinkage. Simultaneously, the water-absorbing and swelling properties of the U-phase further inhibit shrinkage. This dual-pronged shrinkage-swelling mechanism can more effectively solve the shrinkage and cracking problem of geopolymers.

[0015] The preparation method of this application is easy to operate and the raw materials are readily available. The crystal nucleation expander can be prepared by simple hydrothermal synthesis. The hydration synthesis temperature is only 150℃ at most. The preparation process can be completed by making full use of clean energy. It is a low-carbon and environmentally friendly synthesis preparation method. Attached Figure Description

[0016] Figure 1 This is a finished product diagram of the U-phase nucleation-induced expansion agent provided in the embodiments of this application; Figure 2 The XRD pattern is that of the geopolymer obtained by adding the expanding agent in Example 1; Figure 3 The microstructure of the cross section of the geopolymer hardened body obtained using the expanding agent of Example 1; Figure 4 The microstructure of the cross section of the geopolymer hardened body obtained using the expanding agent of Comparative Example 3 is shown. Detailed Implementation

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and conciseness and should not be construed as a hard limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within that range. For example, it should be assumed that the description of a range from 1 to 6 specifically discloses subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0018] Geopolymers are a new type of low-carbon cementitious material prepared by mixing silica-alumina-rich solid waste (fly ash and granulated blast furnace slag, etc.) with alkaline activators (sodium hydroxide, water glass, sodium carbonate, and sodium sulfate, etc.) through an alkaline-activated reaction. They possess characteristics such as high early strength, dense and impermeable structure, and excellent resistance to chemical erosion, making them promising for applications in underground engineering, concrete structure repair, and solid waste resource utilization.

[0019] However, compared to traditional silicate cement, geopolymers exhibit greater volume shrinkage during the hardening process, severely impacting the volume stability of geopolymer concrete products. This has become a major technical challenge limiting the large-scale application of this type of material. Related research indicates that the main hydration products in geopolymers are sodium aluminosilicate (NASH) and calcium aluminosilicate (CASH) gel phases. Due to the lack of limiting effect from crystalline phase products, the gel phase continuously induces shrinkage stress within the geopolymer during drying and dehydration, thereby accelerating the volume shrinkage of the hardened body and potentially leading to crack propagation. More importantly, existing crystallization expansion agents suitable for cement-based materials, such as CaO, MgO, and ettringite, all utilize the crystallization expansion characteristics of hydration products (Ca(OH)2, Mg(OH)2, and ettringite) to induce expansion. However, these crystalline products exhibit poor stability in the highly alkaline environment and complex pore solution ionic environment of geopolymers, making it difficult to achieve safe and efficient expansion and shrinkage inhibition effects. Therefore, adjusting the composition and specific gravity of the crystalline and gel phases within geopolymers has become one of the main technical approaches for controlling their volume shrinkage and stability.

[0020] To address the aforementioned issues, this application provides a U-phase nucleation-induced expansion agent, comprising the following components by weight: 20-50 parts aluminum-containing raw material; 5-40 parts calcium-containing raw material; 5-25 parts sulfate; 80-120 parts pH adjuster; and 0.5-2 parts auxiliary regulator. The aluminum-containing raw material, calcium-containing raw material, and sulfate are the raw materials for forming the U-phase structure. The pH adjuster provides a strongly alkaline environment to promote the dissolution of the raw material into an active substance. The auxiliary regulator enables the active substance to complete nucleation, lamellar growth, and orderly stacking in a controlled manner, thereby achieving the controllable generation of the U-phase structure.

[0021] In some embodiments, the term "U-phase structure" refers to a typical crystalline phase with an intercalated structure, which can be represented by the general formula 3CaO·Al₂O₃·CaSO₄·12H₂O. The U-phase structure consists of aluminum-containing octahedral sheets and calcium coordination layers, with the interlayer spaces occupied by sulfate ions and water of crystallization, maintaining the stability of the layered structure through hydrogen bonding or electrostatic interactions. Scanning electron microscopy reveals that the U-phase typically exhibits a hexahedral or plate-like structure with orderly stacking of sheets, exhibiting typical layered hydrate morphology. Regarding formation conditions, the U-phase often forms in a highly alkaline liquid phase with both calcium and sulfate sources, and its formation process is controlled by multiple factors such as pH, ionic strength, sulfate concentration, and temperature. The U-phase often serves as an intermediate or secondary product in sulfate etching or specific aluminate hydration processes. Since the U phase can exist stably in a highly alkaline environment, and its controllable layered structure and composition give it a certain degree of structural designability, this application synthesizes the U phase to prepare it as a nucleation-induced expansion agent and incorporates it into the geopolymer. The proportion of the gel phase product is reduced by the nucleation and growth of the U phase, while the micro-expansion effect of the U phase is used to inhibit the volume shrinkage of the geopolymer and improve its volume stability.

[0022] In some embodiments, the above-mentioned U-phase nucleus-induced expansion preparation system is a crystal growth system under hydrothermal conditions composed of aluminum-containing raw materials, calcium-containing raw materials, sulfate-containing raw materials, pH adjusting agents, and auxiliary regulators. The aluminum-containing, calcium-containing, and sulfate-containing raw materials synergistically provide the key ionic components required for the formation of the U-phase main layer structure and interlayer structure; the pH adjusting agent provides a strongly alkaline environment to promote raw material dissolution, structural rearrangement, and the formation of active ligands; and the auxiliary regulators, without affecting the main reaction, enable active species to complete nucleation, lamellar growth, and orderly stacking in a controlled manner during the hydrothermal process, thereby achieving the controllable generation of the U-phase lamellar structure.

[0023] In some embodiments, the pH range of the strongly alkaline environment regulated by the pH adjuster is 9 to 14; for example, the pH can be any one of 9, 10, 11, 12, 13, and 14, or a range between any two values. The pH adjuster is selected from at least one of sodium hydroxide and potassium hydroxide.

[0024] It should be noted that the pH adjuster is prepared by water and an alkaline component, which includes any one or more of sodium hydroxide and potassium hydroxide. The mass ratio of the alkaline component to water in the pH adjuster is 15:85, and the resulting solution maintains the system in a strongly alkaline environment. The pH adjuster promotes the dissolution and activation of aluminum-containing and calcium-containing raw materials in the reaction system and provides the high pH conditions required for the formation of layered hydrate crystals. More importantly, a strongly alkaline environment is crucial for the stable existence of the U phase. By adjusting the ratio and concentration of the alkaline component, the overall dissolution equilibrium, ionic composition, and reaction rate of the system can be affected, thereby regulating the nucleation behavior, lamellar construction process, and crystal structure stability of the U phase, and promoting the uniform and orderly formation of layered hydrate crystals under hydrothermal conditions.

[0025] In some embodiments, the auxiliary control agent includes inorganic micropowder and hexagonal liquid crystal. The mass ratio of the inorganic micropowder to the hexagonal liquid crystal is 1:1 to 2.5; for example, the mass ratio can be any one or any two of the following ratios: 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5. Within the aforementioned mass ratio range, the aspect ratio and thermodynamic stability of the U-phase crystal can be controlled.

[0026] Inorganic micropowders refer to aggregates of solid particles in the micrometer or submicrometer scale, composed of inorganic substances (such as metals, oxides, ceramics, and minerals) that do not contain carbon-hydrogen bonds (CH bonds). They typically refer to particles with a diameter between 0.1 micrometers and 100 micrometers. Hexagonal liquid crystals are a typical phase in lyotropic liquid crystals, formed by the self-assembly of amphiphilic molecules (such as lipids and surfactants) in a solvent. In this phase, molecules aggregate to form infinitely long cylindrical micelles. These cylinders are arranged in parallel in space according to a two-dimensional hexagonal lattice, exhibiting long-range orientational order.

[0027] In some embodiments, the inorganic micropowder exhibits a hexagonal plate-like or hexagonal short columnar morphology; the inorganic micropowder is selected from at least one of nepheline, hematite, and tourmaline. It is understood that the microscopic geometric characteristics of the inorganic micropowder have a very high geometric similarity to the layered hexagonal structure of the target product U phase. In the initial stage of the reaction, these inorganic micropowders act as "heterogeneous nucleation sites," significantly reducing the nucleation barrier of the U phase through lattice matching at the interface; simultaneously, the lattice parameters on the micropowder surface induce the U phase to preferentially adhere to its specific crystal faces for epitaxial growth, thereby stabilizing the initial nuclei of the U phase and guiding it to eventually develop into a regular, dense layered structure.

[0028] In some embodiments, the average particle size D of the inorganic micropowder 50 The average particle size is 0.5–5 μm; for example, the average particle size of inorganic micropowders can be any one or any two values ​​from 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm. 50 "" refers to the particle size value that corresponds to the cumulative particle weight (or volume, number) distribution percentage reaching 50% in a particle group.

[0029] In some embodiments, hexagonal liquid crystals are formed by the self-assembly of amphiphilic substances in a solvent. The amphiphilic substances are selected from at least one of polyethylene oxide-polypropylene oxide block copolymers, alkyl trimethylammonium salts, and polyoxyethylene alkyl ethers. In a hydrothermal reaction system, the hexagonal liquid crystals self-assemble to form hexagonally arranged cylindrical micelles with a long-range ordered structure. These micelles automatically arrange themselves into numerous honeycomb-like nanoscale cylindrical channels in the reaction solution, encapsulating the inorganic powder and the nascent U-phase crystal nuclei. This unique channel structure acts as a spatial confinement mechanism, forcing the crystals to grow orderly only along the internal space of the channels, preventing them from growing large or disorderly. It also acts as a protective film on the crystal surface, effectively preventing particles from colliding, adhering, or merging, thus ensuring that the final U-phase product has a regular shape, uniform size, and does not agglomerate.

[0030] It should be noted that polyethylene oxide-polypropylene oxide block copolymers (PEO-PPO block copolymers) are nonionic polymeric surfactants composed of hydrophilic polyethylene oxide (PEO) segments and oleophobic / hydrophobic polypropylene oxide (PPO) segments linked by covalent bonds. The ratio of PEO to PPO segments is adjustable. Alkyl trimethylammonium salts are typical cationic surfactants, belonging to the quaternary ammonium salt class of compounds. Their structural characteristic is a central nitrogen atom connected to three methyl groups and a long-chain alkyl hydrophobic group, carrying a positive charge and bonded to an anion (usually a chloride or bromide ion). Typical substances include hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and dodecyltrimethylammonium chloride (DTAC). Polyoxyethylene alkyl ethers are nonionic surfactants, often simply referred to as "alcohol ethers" or the Brij series. They are prepared by the addition reaction of fatty alcohols with ethylene oxide (EO) under the action of a catalyst. Typical substances include Brij 35 (polyoxyethylene (23) lauryl ether), Brij 58 (polyoxyethylene (20) cetyl ether), AEO-7 / AEO-9 (fatty alcohol polyoxyethylene ether), etc.

[0031] In some embodiments, the auxiliary modifier is an "organic-inorganic composite dual-template system" composed of inorganic micropowder and hexagonal liquid crystal. The inorganic micropowder serves as a hard template, and the hexagonal liquid crystal serves as a soft template.

[0032] In some embodiments, the aluminum-containing raw material is selected from at least one of alumina, aluminum hydroxide, sodium aluminate, and aluminum powder. Under alkaline and hydrothermal conditions, the aforementioned aluminum-containing raw materials can provide aluminate species that can participate in the construction of layered structures, serving as the main aluminum source for forming the U-phase layered main structure. By selecting aluminum-containing raw materials of different forms or combinations thereof, the dissolution mode, reactivity, and supply rate of aluminate in the system can be adjusted, thereby having an overall impact on the nucleation behavior of the U-phase, the lamellar formation process, and the stability of the crystal structure, promoting the orderly formation of layered hydrate crystals during the hydrothermal reaction.

[0033] In some embodiments, the sulfate-containing raw material is selected from at least one of sodium sulfate, potassium sulfate, and lithium sulfate. The above-mentioned sulfate-containing raw material can stably release sulfate ions (SO42-) in the hydrothermal reaction system. 2- This ion, as an important component of the U phase of layered hydrate crystals, can participate in the construction of interlayer structures and the regulation of charge balance during crystal formation. By adjusting the type and amount of sulfate-containing raw materials, the supply mode, dissolution behavior, and ionic composition of sulfate ions in the system can be effectively affected, thereby exerting an overall regulatory effect on the nucleation rate, lamellar stacking regularity, and crystal integrity of the U phase, promoting the formation of layered hydrate crystal materials with stable structural characteristics.

[0034] In some embodiments, the calcium-containing raw material is selected from at least one of calcium hydroxide, calcium oxide, calcium carbonate, and their hydrates. These calcium-containing raw materials, in alkaline or hydrothermal environments, can provide the system with calcium ions required for the formation of layered structures, serving as a key cation source in constructing the U-phase main framework. By adjusting the type and amount of different forms of calcium-containing raw materials, the dissolution rate, effective concentration, and distribution characteristics of calcium ions in the reaction system can be affected, thereby exerting an overall regulatory effect on the lamellar construction of the U-phase, the interlayer charge balance, and the integrity of the crystal structure, promoting the stable formation of layered hydrate crystals during the hydrothermal reaction.

[0035] In some embodiments, the auxiliary control agent further includes a dispersant, wherein the mass ratio of the dispersant to the inorganic micro powder is 1 to 2.5:1. For example, the mass ratio of the dispersant to the inorganic micro powder can be any one or any two of the following ratios: 2.5:1, 2.4:1, 2.3:1, 2.2:1, 2.1:1, 2:1, 1.9:1, 1.8:1, 1.7:1, 1.6:1, 1.5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1, 1:1.

[0036] In some embodiments, the mass ratio of dispersant, inorganic micro powder and hexagonal liquid crystal is 1~2.5:1:1~2.5.

[0037] In some embodiments, the dispersant is selected from at least one of polycarboxylate, polyacrylate, and lignin sulfonate. The dispersant is a dispersion system capable of providing electrostatic or steric stabilization. The dispersant primarily improves the dispersion state of the solid-liquid interface in the reaction system by providing electrostatic repulsion or steric hindrance effects, inhibiting non-selective aggregation between particles, thereby maintaining a uniform distribution of active species and nascent crystal nuclei in the solution. The dispersant mainly acts on the overall dispersion and stabilization of the system, playing a continuous dispersing and stabilizing role throughout the crystal nucleation and growth process. By adjusting the type and amount of dispersant, the degree of particle dispersion, lamellar stacking state, and microstructural uniformity during crystal growth can be comprehensively affected, thereby helping to obtain U-phase layered hydrate crystal materials with regular structure, uniform lamellar structure, and high crystallinity.

[0038] In some embodiments, polycarboxylates are a class of high-molecular-weight electrolytes containing multiple carboxyl groups (-COOM, where M is a metal ion or ammonium group) in their main molecular chain. Their molecular structure exhibits a typical "comb-like" characteristic: the main chain consists of an active monomer containing carboxyl groups, with relatively long polyether side chains (such as polyethylene glycol side chains). Polyacrylates are homopolymers or copolymers formed by free radical polymerization of acrylic acid or its salts as the main monomers. They belong to linear high-molecular-weight electrolytes, and their applications vary significantly depending on their molecular weight: low molecular weight polyacrylates are often used as dispersants and scale inhibitors; high molecular weight polyacrylates are used as thickeners or superabsorbent resins. Lignosulfonates are byproducts of the sulfonation reaction of lignin during the sulfite papermaking process and are a type of natural high-molecular-weight surfactant. Their structure is extremely complex and is generally considered to be a polycyclic aromatic amorphous polymer with sulfonic acid groups, hydroxyl groups, and methoxy groups.

[0039] In some embodiments, a method for preparing a U-phase nucleation-induced expansion agent is provided, comprising: mixing, stirring, and heating aluminum-containing raw materials and pH adjusters in corresponding weight parts to obtain a first reaction medium, wherein the first reaction medium contains aluminate under alkaline conditions; adding sulfate in corresponding weight parts to the first reaction medium, and after mixing, coordinating the sulfate ions provided by the sulfate with the aluminate ions to construct an anionic framework with a layered structure; continuing to add calcium-containing raw materials to the first reaction medium, allowing calcium ions to insert into the anionic framework to form an intercalated structure, and then continuously stirring to allow the intercalated structure to stably aggregate, thereby obtaining a second reaction medium; adding auxiliary regulators in corresponding weight parts to the second reaction medium, and stirring to obtain a precursor; transferring the precursor to a closed environment, and subjecting it to hydrothermal reaction, cooling, washing, and drying to obtain the U-phase nucleation-induced expansion agent.

[0040] It is understandable that this embodiment employs a stepwise reaction route in the preparation of U-phase layered hydrate crystals, namely, sequentially undergoing three stages: the formation of the aluminate precursor, the intercalation regulation of sulfate ions, and the structural fixation of calcium ions. This reaction sequence is not a simple process choice, but rather a key technical condition established based on the differences in reactivity and interaction patterns of the reactants in a strongly alkaline hydrothermal system. First, the preferential formation of a stable aluminate precursor under a strongly alkaline environment is beneficial for constructing a well-defined layered framework. Subsequently, sulfate ions are introduced, enabling ordered intercalation within the existing layered structure, thus preventing direct reaction between sulfate and calcium ions in the early stages to generate irrelevant phases such as gypsum. Finally, calcium ions are introduced to fix and stabilize the layered structure, effectively suppressing the formation of amorphous gels or non-target hydration products. If the above stepwise sequence is not adopted, and the components are added simultaneously or in reverse order, non-selective reactions easily occur in the system, generating impurities such as gypsum, hydrogarnet, or amorphous alumina-calcium gel, making it difficult to obtain U-phase crystals with a regular structure and high purity. Therefore, this stepwise reaction sequence plays an irreplaceable role in suppressing the formation of impurity phases, improving the selectivity of the target phase, and stabilizing the formation of the U phase.

[0041] In some embodiments, the above-mentioned material system undergoes a hydrothermal reaction. Hydrothermal temperature and reaction time are key parameters for the formation of stable U-phase crystals, directly affecting the nucleation rate, lamellar growth kinetics, and structural regularity. Excessively high hydrothermal temperatures lead to rapid reactions between aluminate and calcium ions, causing rapid deposition of lamellar structures and reducing interlayer order. Conversely, excessively low temperatures result in insufficient nucleation and growth rates, leading to a loose crystal structure and low crystallinity. By controlling the hydrothermal curing conditions, a dynamic equilibrium can be achieved between ion dissolution rate, coordination rearrangement, and lamellar stacking, thereby obtaining a structurally stable, uniformly spaced, and well-ordered U-phase layered hydrate crystal.

[0042] In some embodiments, the specific steps of the above preparation method include: First, take 20-50 parts of aluminum-containing raw material and add it to 80-120 parts of pre-prepared pH adjuster. Under stirring, gradually heat the mixture to 40-70°C to dissolve the aluminate ions from the aluminum raw material under alkaline conditions. Continue stirring for 10-30 minutes and then adjust the pH of the system to 11-14 to form a reactive aluminate solution. The second step involves adding 5-25 parts of sulfate-containing raw material to the above transparent or semi-transparent reaction solution and mixing it at a stirring speed of 80-150 r / min to allow the sulfate ions provided by the sulfate-containing raw material to undergo preliminary coordination with the aluminate ions, thereby constructing an anionic framework with a layered structure. The third step involves slowly adding 5-40 parts of calcium-containing raw material while continuously stirring, allowing divalent metal cations to insert into the intercalation structure formed by the anionic framework, which is the main structure of the crystallization expansion agent; through stirring for 20-60 minutes, the primary main intercalation structure is stably aggregated. Fourth step: Add 0.5-2 parts of auxiliary regulator and stir rapidly for 5-15 minutes to allow it to adsorb onto the surface of the crystal precursor, thereby achieving interface regulation, lattice directionality induction and aggregate stabilization, providing the necessary reaction environment for subsequent structural rearrangement, lattice stacking and hydration crystallization of the main intercalation structure. The fifth step involves transferring the above-mentioned mixed system, which serves as the precursor for preparing the nucleus-induced expansion agent, into a closed reactor and allowing it to undergo a hydrothermal reaction at 60-150°C for 24-168 hours. This allows the precursor to undergo structural rearrangement, lamellar stacking, and hydration crystallization under a high-temperature alkaline environment, ultimately yielding a nucleus-induced expansion agent with a master-guest intercalation structure. Step 6: After hydrothermal synthesis, the product is naturally cooled to room temperature. It is then washed 2-5 times with deionized water to remove residual ions, followed by drying at 40-80℃ for 3-10 hours to obtain the product as shown below. Figure 1 The image shows a finished product of a white powdery nucleation-induced expansion agent.

[0043] In some embodiments, the hydrothermal reaction temperature is 60~150°C; the hydrothermal reaction time is 24~168h.

[0044] In some embodiments, this application also discloses the use of a U-phase nucleation-induced expansion agent in geopolymers as a concrete admixture.

[0045] It should be noted that concrete admixtures are substances added during the concrete mixing process to improve the performance of concrete. In some embodiments, the U-phase nucleus-induced expansion agent of this embodiment is incorporated into the geopolymer system at 2-5% of the mass of the geopolymer to regulate the phase composition and structural evolution of the material.

[0046] The present disclosure will be described in detail below with reference to specific embodiments. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments of the present disclosure are provided so that this specification will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0047] Experimental methods not specifying specific conditions in the embodiments of this disclosure are generally performed under conventional conditions or as recommended by the raw material or product manufacturer. Reagents not specifying their source are commercially available, conventional reagents.

[0048] The known starting materials disclosed herein can be synthesized using or in accordance with methods known in the art, or can be purchased from companies such as Adamas and Aladdin.

[0049] In the examples, room temperature refers to the range of 25±5℃.

[0050] Example 1 First, take 30 parts of aluminum hydroxide and add them to 100 parts of a pre-prepared pH adjuster made of sodium hydroxide (the mass ratio of sodium hydroxide to water is 15:85). Under stirring, gradually heat the mixture to 50°C and continue stirring for 20 minutes to adjust the pH of the system to 12. The second step is to add 15 parts of sodium sulfate to the above transparent or semi-transparent reaction solution and mix at a stirring speed of 100 r / min. Third, slowly add 15 parts of calcium hydroxide while stirring continuously, and stir for 40 minutes. Fourth, add 1 part of auxiliary regulator, specifically including 0.3 parts of nepheline and 0.7 parts of polyethylene oxide-polypropylene oxide block copolymer (specifically Pluronic P123, with an average molecular weight of approximately 5800 and the general structural formula EO). 20 -PO 70 -EO 20 Stir rapidly for 10 minutes to obtain the precursor; The fifth step involves transferring the precursor to a sealed reactor and allowing it to undergo hydrothermal reaction at 80°C for 120 hours. After hydrothermal synthesis, the product is naturally cooled to room temperature. The product is then washed three times with deionized water to remove residual ions and subsequently dried at 60°C for 5 hours to obtain the U-phase nucleus-induced expansion agent.

[0051] Example 2 First, take 20 parts of sodium aluminate and add it to 80 parts of pre-prepared pH adjuster made of potassium hydroxide (where the mass ratio of potassium hydroxide component to water is 15:85). Under stirring conditions, gradually raise the temperature to 50°C, continue stirring for 20 min, and then adjust the pH of the system to 13. The second step is to add 5 parts of potassium sulfate to the above transparent or semi-transparent reaction solution and mix at a stirring speed of 100 r / min. The third step is to slowly add 5 parts of calcium oxide while stirring continuously, and stir for 40 minutes. Fourth step, add 0.5 parts of auxiliary regulator, specifically including 0.15 parts of hematite and 0.35 parts of alkyltrimethylammonium salt (specifically hexadecyltrimethylammonium bromide, abbreviated as CTAB, with a molecular weight of approximately 364.5), stir rapidly for 10 minutes to obtain the precursor; The fifth step involves transferring the precursor to a sealed reactor and allowing it to undergo hydrothermal reaction at 100°C for 100 hours. After hydrothermal synthesis, the product is naturally cooled to room temperature. The product is then washed three times with deionized water to remove residual ions and subsequently dried at 40°C for 10 hours to obtain the U-phase nucleation-induced expansion agent.

[0052] Example 3 First, take 50 parts of alumina and add it to 120 parts of a pre-prepared pH adjuster made of potassium hydroxide (where the mass ratio of potassium hydroxide component to water is 15:85). Under stirring conditions, gradually raise the temperature to 50°C, continue stirring for 20 minutes, and then adjust the pH of the system to 14. The second step is to add 25 parts of lithium sulfate to the above transparent or semi-transparent reaction solution and mix at a stirring speed of 100 r / min. The third step is to slowly add 40 parts of calcium carbonate while stirring continuously, and stir for 40 minutes. Fourth step, add 2 parts of auxiliary regulator, specifically including 0.6 parts of tourmaline and 1.4 parts of polyoxyethylene alkyl ether (specifically Brij 35, i.e. polyoxyethylene (23) lauryl ether, with an average molecular weight of about 1198), stir rapidly for 10 min to obtain the precursor; The fifth step involves transferring the precursor to a sealed reactor and allowing it to undergo hydrothermal reaction at 150°C for 30 hours. After hydrothermal synthesis, the product is naturally cooled to room temperature. The product is then washed three times with deionized water to remove residual ions and subsequently dried at 80°C for 5 hours to obtain the U-phase nucleus-induced expansion agent.

[0053] Example 4 The specific preparation process is the same as in Example 1, except that: In the fourth step, 1.5 parts of auxiliary regulators are added, specifically including 0.5 parts of polyacrylic acid (average molecular weight approximately 5000), 0.3 parts of nepheline, and 0.7 parts of polyethylene oxide-polypropylene oxide block copolymer (specifically Pluronic P123, average molecular weight approximately 5800, general structural formula EO). 20 -PO 70 -EO 20 ).

[0054] Example 5 The specific preparation process is the same as in Example 2, except that: In the fourth step, 1.5 parts of auxiliary regulators are added, specifically including 0.5 parts of polymethacrylic acid (average molecular weight of about 5000), 0.3 parts of hematite and 0.7 parts of alkyltrimethylammonium salt (specifically hexadecyltrimethylammonium bromide, abbreviated as CTAB, with a molecular weight of about 364.5).

[0055] Example 6 The specific preparation process is the same as in Example 3, except that: In the fourth step, 1.5 parts of auxiliary regulators are added, specifically including 0.5 parts of lignin sulfonate (specifically sodium lignin sulfonate with an average molecular weight of about 10,000), 0.3 parts of tourmaline and 0.7 parts of polyoxyethylene alkyl ether (specifically Brij 58, i.e. polyoxyethylene (20) cetyl ether with an average molecular weight of about 1,124).

[0056] Comparative Example 1 The expanding agent used is a commercially available calcium sulfoaluminate expanding agent, specifically a commercially available HCSA type high-performance calcium sulfoaluminate expanding agent, whose main active mineral components are anhydrous calcium sulfoaluminate and anhydrite.

[0057] Comparative Example 2 An expansion agent is provided, and the specific preparation process is the same as in Example 1, except that the product of the third step is directly subjected to a hydrothermal reaction without the addition of any auxiliary regulators.

[0058] Comparative Example 3 An expanding agent is provided, and the specific preparation process is the same as in Example 1, except that the auxiliary regulating agent added in the fourth step is only a single hexagonal phase liquid crystal, specifically, 1 part of a polyethylene oxide-polypropylene oxide block copolymer (specifically Pluronic P123, with an average molecular weight of approximately 5800 and a general structural formula of EO). 20 -PO 70 -EO 20 ).

[0059] Comparative Example 4 An expansion agent is provided, and the specific preparation process is the same as in Example 1, except that the auxiliary regulator added in the fourth step is a single inorganic micro powder, specifically 1 part of nepheline.

[0060] The products of Examples 1-6 and Comparative Examples 1-4 were added to the geopolymer as admixtures. The geopolymer comprised 100 parts of a precursor composed of slag and fly ash, wherein the slag was S95 grade slag, accounting for 50% of the precursor mass, and the fly ash was grade II fly ash, accounting for 50% of the precursor mass; 20 parts of a solid activator composed of calcium hydroxide, gypsum, sodium hydroxide, and sodium silicate; and 50 parts of mixing water. The admixture dosage was 2% of the total mass of the geopolymer.

[0061] The XRD pattern of the geopolymer obtained by adding the expanding agent of Example 1 is shown below. Figure 2 As shown, by Figure 2As can be seen, strong and sharp U-phase characteristic diffraction peaks appeared in the spectrum, especially the main diffraction peaks around 9° and 18°, which were extremely significant. This indicates that U-phase crystals with extremely high crystallinity and regular layered structure were successfully generated in Example 1. Meanwhile, only extremely weak gypsum and anhydrous sodium sulfate diffraction peaks were observed in the spectrum. This fully confirms that under the synergistic regulation of the "inorganic micropowder-hexagonal liquid crystal" composite dual template designed in this application, the occurrence of side reactions can be effectively suppressed, and high-purity U-phase materials can be synthesized with high selectivity. When incorporated into the geopolymer system, this highly crystalline dominant phase can exist stably and provide sufficient micro-expansion sources as ideal crystal nuclei, thereby effectively compensating for the volume shrinkage of the geopolymer.

[0062] See Figure 3 and Figure 4 , Figure 3 The microstructure of the cross-section of the geopolymer hardened body obtained using the expanding agent of Example 1; Figure 4 The microstructure of the geopolymer hardened body obtained using the expanding agent in Comparative Example 3 is shown. As seen in Example 1, under the combined regulation of inorganic micropowder and hexagonal liquid crystal, the generated U-phase crystals have regular morphology and good dispersibility, and can exist stably in the geopolymer, exhibiting good expansion performance. However, in Comparative Example 3, due to the lack of heterogeneous nucleation sites and lattice matching stabilization provided by the inorganic micropowder, the thermodynamic stability of the U-phase crystals is extremely poor. After incorporation into the geopolymer, under the erosion of a sodium-ion-rich, strongly alkaline porous solution, the U-phase crystal structure gradually disintegrates, with most or even all transforming into an amorphous gel or the more stable ettringite phase, leading to the failure of the expansion function.

[0063] The chemical shrinkage of the geopolymers obtained in Examples 1-6 and Comparative Examples 1-4 was measured to investigate the shrinkage-reducing effect of the nucleation-induced expansion agent. The results are shown in Table 1, in mL / 100g. The geopolymer samples were tested using the absolute volume method, referring to ASTM C1608-17 standard. A graduated pipette with a 2ml range and a minimum graduation of 0.02ml was used. The glass measuring tube was inserted into a rubber stopper with a 6.67mm hole in the center. The well-stirred slurry was poured into a flat-bottomed wide-mouth glass bottle with a diameter of 25mm and a height of 55mm, maintaining the slurry height between 5-8mm. Deionized water was slowly added to the glass bottle containing the slurry, and the rubber stopper was inserted. A 4-8mm thick layer of oil was poured above the water surface in the measuring tube to prevent evaporation of water from the bottle. The prepared chemical shrinkage specimens were placed in a water bath at 20 ± 0.2℃ and cured until the test age was reached. The chemical shrinkage data were measured and calculated using the following formula: ; in, Chemical volume shrinkage rate, unit: mL / 100 g; Initial liquid level height, unit: mL; The liquid level is measured at a fixed age. The weight of the slurry added to the glass bottle, in grams; The weight of the glass bottle is in grams.

[0064] Table 1. Chemical volume shrinkage rate of geopolymers

[0065] As shown in Table 1, the chemical shrinkage values ​​of all samples increased rapidly with hydration in the initial stage of the reaction, and then gradually stabilized. Compared with Comparative Examples 1-4, the final chemical shrinkage values ​​of Examples 1-6 were significantly reduced, verifying that the U-phase crystal under the "organic-inorganic dual template" regulation can effectively compensate for shrinkage. Among them, Example 5 performed the best, with a final chemical shrinkage of only 3.2 mL / 100g, the lowest among all groups. This is attributed to the excellent lattice matching stability provided by hematite, combined with the confinement of hexagonal liquid crystal, resulting in highly dense and stable U-phase crystals, thereby maximally suppressing the volume shrinkage of the geopolymer. Conversely, the deterioration of Comparative Examples 1-4 is attributed to the inability of a single or mismatched regulation strategy to simultaneously optimize the morphology and thermodynamic stability of the U-phase crystal. Specifically, the traditional ettringite-based expanding agent in Comparative Example 1 was not effective in geopolymers, mainly due to its lack of thermodynamic stability. Traditional expansion agents rely on the formation and growth of ettringite crystals to generate expansion pressure. However, in the uniquely alkaline and complex ionic porous environment of geopolymers, ettringite crystals are difficult to maintain stability and are prone to decomposition or transformation into non-expanding phases. This results in a lack of sustained and effective expansion driving force to offset the significant volume shrinkage during geopolymer hardening, leading to the failure of shrinkage reduction and crack resistance. Comparative Example 2, lacking an auxiliary regulator, produced a sparse and disordered agglomeration of the U-phase, failing to generate sufficient crystal growth pressure to offset the self-drying shrinkage of the matrix. Comparative Example 3 exhibited a more severe late-stage shrinkage rebound phenomenon. This was due to the lack of sufficient inorganic micropowder to provide heterogeneous nucleation and lattice pinning effects. The U-phase induced solely by organic liquid crystals had extremely poor thermodynamic stability in the strongly alkaline geopolymer porous solution, gradually disintegrating or transforming into a non-expanding phase with increasing age. This not only resulted in the loss of expansion compensation ability but also exacerbated volume shrinkage during decomposition, leading to a final effect even worse than Comparative Example 2. While Comparative Example 4 showed acceptable stability, the U phase tended to develop into coarse, thick plate-like crystals due to the lack of spatial confinement effect of the hexagonal liquid crystal. Because of its small specific surface area and uneven distribution, its pore filling efficiency and micro-expansion performance were far lower than the fine, high aspect ratio crystals generated by the "dual-template synergy" strategy of this invention.

[0066] The drying shrinkage strain of the U-phase nucleation-induced expansion agents suitable for geopolymers prepared in Examples 1-6 and Comparative Examples 1-4 was measured respectively, as shown in Table 2, with units of μm / m. Dry shrinkage specimens were prepared by mixing solid activators according to the mixing ratio. First, the cementitious material, activator, and water were poured into a mixer and stirred for 30 s. Then, starting from the second 30 s, sand was uniformly added to the slurry pot, followed by high-speed stirring for 30 s, a 90 s pause, and then high-speed stirring for another 60 s. The resulting slurry was poured into a prismatic sample mold to form shrinkage specimens. After the mold was sealed with plastic wrap and nail heads on both sides, it was cured in a standard curing box for 24 hours before demolding. The initial length of the sample was measured using a standard length comparator. The sample was then moved to a drying oven at 20°C with a relative humidity maintained at 60 ± 5% potassium bromide (KBr) saturated solution for further curing. The length of the specimen at different times was measured using a length comparator. The drying linear shrinkage rate of the specimen was calculated using the following formula: A = (BC) / D, where A is the drying shrinkage rate, μm / m; B is the initial length of the specimen, mm; C is the length of the specimen measured at a fixed age, mm; and D is the gauge length of the specimen, i.e., the length of the cuboid specimen minus the embedment depth of the nail heads on both sides.

[0067] Table 2. Drying shrinkage rate of geopolymers

[0068] As shown in Table 2, the drying shrinkage values ​​of Examples 1-6 remained at a low level throughout the entire age, significantly lower than the comparative examples. Among them, Example 5 performed best, with a final shrinkage value of only 405 μm / m. This is attributed to the extremely strong thermodynamic stability provided by hematite through lattice matching, preventing the decomposition of the U phase under strongly alkaline conditions. At the same time, the alkyl trimethylammonium salt (such as hexadecyltrimethylammonium bromide) allowed the crystals to grow densely and finely through spatial confinement. This highly stable and highly dispersed U phase crystal generated continuous and uniform micro-expansion stress during the geopolymer hardening process, most effectively offsetting the drying shrinkage of the matrix. In contrast, the shrinkage effects of Comparative Examples 1-4 were all unsatisfactory, with different failure mechanisms: Comparative Example 1 had a certain compensatory effect in the early stage of the reaction, but due to the thermodynamic instability of the ettringite phase in the highly alkaline environment of the geopolymer, it underwent a large amount of decomposition and dissolution as the age increased, resulting in the loss of the expansion prestress established in the early stage. Moreover, the crystal water discharged by decomposition exacerbated the capillary tension, causing its shrinkage value to rebound sharply in the later stage. Comparative Example 2 performed the worst, with a final shrinkage value as high as 1200 μm / m, confirming that the U phase crystal structure, which completely lacked template-induced shrinkage, was loose and extremely unstable, and rapidly disintegrated under alkaline erosion. This structural collapse not only failed to provide expansion energy, but the ions released by decomposition also destroyed the integrity of the cementitious structure, causing severe volume shrinkage. Although Comparative Examples 3 and 4 were better than Comparative Example 2, due to the lack of synergistic anchoring and spatial confinement effect of "organic-inorganic dual templates", the crystal development was incomplete or the morphology was uneven, and the expansion driving force generated was insufficient to effectively offset the huge shrinkage stress of the geopolymer.

[0069] In summary, only by employing specific dual-template and dispersion control processes can this application synthesize a U-phase nucleation expander that exhibits long-term stability and efficient "shrinkage-expansion" dual effects under high-alkali conditions.

[0070] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0071] The products and preparation methods provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A U-phase nucleation-induced expansion agent, characterized in that, By weight, it includes the following components: 20-50 parts aluminum-containing raw material; 5-40 parts calcium-containing raw material; 5-25 parts sulfate; 80-120 parts pH adjuster; 0.5-2 parts auxiliary regulator; The aluminum-containing raw material, the calcium-containing raw material, and the sulfate are raw materials for forming the U-phase structure; the pH adjuster is used to provide a strongly alkaline environment to promote the dissolution of the raw materials into active substances; the auxiliary regulator is used to enable the active substances to complete nucleation, growth, and stacking, so as to achieve the controllable generation of the U-phase structure.

2. The U-phase nucleation-induced expansion agent according to claim 1, characterized in that, The pH range of the strongly alkaline environment is 9-14; The pH adjuster is selected from at least one of sodium hydroxide and potassium hydroxide.

3. The U-phase nucleation-induced expansion agent according to claim 1, characterized in that, The auxiliary regulating agent comprises inorganic micro powder and hexagonal liquid crystal; the mass ratio of the inorganic micro powder to the hexagonal liquid crystal is 1:1~2.5; The inorganic micropowder exhibits a hexagonal plate-like or hexagonal short columnar morphology; the average particle size D of the inorganic micropowder is... 50 The particle size is 0.5~5 μm; the inorganic micro powder is selected from at least one of nepheline, hematite, and tourmaline; The hexagonal liquid crystal is formed by the self-assembly of an amphiphilic substance in a solvent, wherein the amphiphilic substance is selected from at least one of polyethylene oxide-polypropylene oxide block copolymer, alkyl trimethylammonium salt, and polyoxyethylene alkyl ether.

4. The U-phase nucleation-induced expansion agent according to claim 1, characterized in that, The aluminum-containing raw material is selected from at least one of alumina, aluminum hydroxide, sodium aluminate, and aluminum powder.

5. The U-phase nucleation-induced expansion agent according to claim 1, characterized in that, The sulfate raw material is selected from at least one of sodium sulfate, potassium sulfate, and lithium sulfate.

6. The U-phase nucleation-induced expansion agent according to claim 1, characterized in that, The calcium-containing raw material is selected from at least one of calcium hydroxide, calcium oxide, calcium carbonate and their hydrates.

7. The U-phase nucleation-induced expansion agent according to claim 3, characterized in that, The auxiliary regulator also includes a dispersant, wherein the mass ratio of the dispersant to the inorganic micro powder is 1~2.5:1; the dispersant is selected from at least one of polycarboxylate, polyacrylate, and lignin sulfonate.

8. A method for preparing a U-phase nucleation-induced expansion agent according to any one of claims 1-7, characterized in that, include: Take the corresponding weight parts of aluminum-containing raw materials and pH adjuster, mix, stir, and heat to obtain the first reaction medium, which contains aluminate under alkaline conditions; Add the corresponding mass fraction of sulfate to the first reaction medium, mix, and allow the sulfate ions provided by the sulfate to coordinate with the aluminate ions to construct an anionic framework with a layered structure. Continue adding calcium-containing raw materials to the first reaction medium to allow calcium ions to insert into the anion framework to form an intercalated structure. Then, continue stirring to stabilize and aggregate the intercalated structure to obtain the second reaction medium. Add the corresponding mass fraction of auxiliary regulator to the second reaction medium, and stir to obtain the precursor; The precursor was transferred to a closed environment and subjected to hydrothermal reaction, cooling, washing, and drying to obtain a U-phase nucleation-induced expansion agent.

9. The method for preparing a U-phase nucleation-induced expansion agent according to claim 8, characterized in that, The hydrothermal reaction temperature is 60~150℃; the hydrothermal reaction time is 24~168 h.

10. The use of the U-phase nucleation-induced expansion agent according to any one of claims 1-7 in geopolymers as a concrete admixture, characterized in that, The U-phase nucleus-induced expansion agent is added to the geopolymer at a dosage of 2-5 wt%.

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