Cement-free geopolymer excited by nanometer silicon mortar and preparation method of cement-free geopolymer

Abstract

The invention belongs to the technical field of building materials, and particularly relates to a cement-free geopolymer excited by nanometer silicon mortar and a preparation method of the cement-free geopolymer. The cement-free geopolymer excited by the nano silica mortar is prepared from the following components in parts by weight: 400 to 600 parts of slag, 200 to 350 parts of coal ash, 80 to 120 parts of alkali activator, 30 to 60 parts of nano silica mortar, 500 to 800 parts of quartz sand, 120 to 160 parts of water and 5 to 10 parts of water reducing agent. The technical scheme disclosed by the invention aims to fundamentally solve a pair of common core contradictions of slow early strength development and overlarge later shrinkage of the existing alkali-activated slag-fly ash-based geopolymer, and the comprehensive performance, environmental protection benefit and engineering applicability of the material are remarkably improved while complete non-cementation is realized.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and in particular relates to a cementless geopolymer excited by nano-silica slurry and its preparation method. Background Technology

[0002] Geopolymers are a new type of environmentally friendly cementitious material, whose main raw materials come from industrial solid waste, such as slag and fly ash. Through an alkali-activated reaction, these wastes can form a hardened body with good cementitious properties. The entire process does not require the participation of cement clinker, thus significantly reducing carbon dioxide emissions and aligning with the industry trend of green building and sustainable development. In recent years, with the increasing demand for low-carbon materials in the construction industry, geopolymers have been increasingly widely used in structural engineering, road base courses, repair and reinforcement, and other fields. However, key performance bottlenecks still restrict their large-scale engineering promotion.

[0003] Currently, alkali-activated slag-fly ash geopolymers, which are widely studied, generally have two major defects in terms of mechanical and deformation properties: First, the early strength development is slow, with the 7-day compressive strength mostly below 20 MPa, which cannot meet the requirements of rapid construction and early load-bearing capacity; second, the later shrinkage is significant, with the 28-day drying shrinkage rate often exceeding 500 με. Excessive autogenous shrinkage and drying shrinkage can easily lead to component cracking, seriously affecting the long-term durability and safety of the structure.

[0004] In-depth analysis of existing technical solutions reveals that the root cause of the aforementioned problems lies primarily in the insufficient optimization of the activation system design, failing to effectively control the reaction products and microstructure. Currently disclosed alkali-activated geopolymers mostly use water glass as a single activator. Such systems primarily generate a single CASH gel, whose three-dimensional network structure has limited density, leading to a bottleneck in early strength improvement. Some existing technologies have attempted to use a composite activation of sodium hydroxide and sodium sulfate, but due to the lack of a secondary activation component with structural control functions, the generation ratio and growth sequence of different gel phases cannot be coordinated, thus the later shrinkage problem remains unresolved. Alternatively, attempts have been made to improve performance using nanomaterials; however, the developed nanoparticles have poor dispersibility, making it difficult to form a uniform and stable dual-network gel structure. Some technical solutions even fail to completely eliminate dependence on cement, failing to achieve a truly all-waste cementitious system. For example, the existing technology CN104098282A discloses a geopolymer material that, although it achieves a suitable setting time and early strength by combining a silicon-containing powder material with an alkaline activator of a specific composition, requires a CaO content of not less than 4% in its raw materials and is mainly composed of fly ash. The system design still focuses on the formation of a single gel structure, and is obviously insufficient in controlling the volume stability and microstructure diversification in the later stage.

[0005] Furthermore, current technologies for utilizing nanomaterials are mostly limited to physical filling and nucleation effects, failing to delve into their synergistic effects as secondary activators or structure-directing agents in regulating polymerization processes and optimizing gel phase composition. This limitation means that early strength development and later shrinkage deformation often move in opposite directions, making simultaneous optimization difficult. Consequently, the application of geopolymers in key engineering scenarios requiring high performance and high durability is restricted.

[0006] Therefore, developing an alkali-activated geopolymer preparation technology that can simultaneously improve early strength and effectively suppress later shrinkage has become the key to promoting the wider application of this type of environmentally friendly material.

[0007] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] This invention belongs to the field of building materials technology, and in particular relates to a cementless geopolymer excited by nano-silica slurry and its preparation method.

[0009] To address the aforementioned technical problems, one objective of this invention is to provide a cementless geopolymer activated by nano-silica slurry, comprising the following components by weight: 400-600 parts slag, 200-350 parts fly ash, 80-120 parts alkali activator, 30-60 parts nano-silica slurry, 500-800 parts quartz sand, 120-160 parts water, and 5-10 parts water-reducing agent.

[0010] According to a preferred embodiment, the cementless geopolymer excited by nano-silica slurry further comprises 10-20 parts of an optional expanding agent. Preferably, the optional expanding agent is an ettringite-type expanding agent.

[0011] According to a preferred embodiment, the molar ratio of Al2O3 / SiO2 in the nano-silica slurry is 0.18-0.22.

[0012] According to a preferred embodiment, the fineness modulus of the quartz sand is 2.6-3.0.

[0013] According to a preferred embodiment, the mass fraction of calcium oxide in the slag is not less than 40%.

[0014] According to a preferred embodiment, the mass fraction of SiO2 and Al2O3 in fly ash is not less than 70%.

[0015] According to a preferred embodiment, the alkali activator is a mixture of sodium hydroxide and water glass, with a mass ratio of sodium hydroxide to water glass of 1:3-5. Preferably, the mass ratio of sodium hydroxide to water glass is 1:3. Alternatively, the mass ratio is 1:4. Or, the mass ratio is 1:5.

[0016] According to a preferred embodiment, the water glass modulus, i.e., SiO2 / Na2O, is 1.5-2.0.

[0017] One of the objectives of this invention is to provide a method for preparing a cementless geopolymer excited by nano-silica slurry, comprising the following steps, in parts by weight: Mix 400-600 parts slag, 200-350 parts fly ash, and 500-800 parts quartz sand until homogeneous to obtain dry material; Mix 80-120 parts of alkali activator with 120-160 parts of water, and then add 5-10 parts of water-reducing agent to form a mixed solution; The mixed solution and dry materials are stirred evenly to form an initial slurry; Add 30-60 parts of nano silica slurry to the initial slurry and stir until the slurry is uniform and fine, without sedimentation or stratification.

[0018] One of the objectives of this invention is to provide the application of cement-free geopolymers excited by nano-silica slurry in road base courses and tailings solid waste disposal projects.

[0019] The beneficial effects of this technical solution are: This invention provides a cementless dual-network gel geopolymer and its preparation method, aiming to fundamentally solve the core contradiction of slow early strength development and excessive late shrinkage in existing alkali-activated slag-fly ash geopolymers. While achieving complete cementlessness, it significantly improves the material's comprehensive performance, environmental benefits, and engineering applicability.

[0020] The beneficial effects of this invention stem from its unique reaction mechanism and meticulous component design. Its core lies in introducing nano-silica slurry with precisely controlled components and proportions as a secondary activator, guiding the system to react stepwise and in an orderly manner, ultimately forming a synergistically enhanced dual-network gel structure. Specifically: First, the alkaline activator preferentially reacts with the active components in slag-fly ash, causing the calcium and silicon in the slag and the silicon and aluminum in the fly ash to dissolve rapidly, quickly generating an early-strength framework mainly composed of ettringite and initial CASH gel. Second, the pre-prepared nano-silica slurry then plays a crucial role in secondary activation and structural regulation, its rich high-activity silicon and aluminum components interacting with the remaining active ions in the system (such as Ca). 2+ [Al(OH)4] -Further reactions (such as...) generate a large amount of NASH gel with a denser structure and better stability. This gel does not simply coexist with the previously formed CASH gel, but rather they are intertwined, permeated and constrained at the microscopic level, jointly constructing an interlocking "CASH / NASH" dual network structure.

[0021] Based on the above mechanism, the present invention has achieved the following significant advancements in several aspects: Significantly enhanced early strength: The secondary activation effect of nano-silica mortar greatly accelerates the formation rate and total amount of cementitious phase, especially the rapid formation and strengthening of the early strength skeleton, so that the compressive strength of the material can stably reach 25-30 MPa at 7 days and not less than 40 MPa at 28 days, effectively meeting the engineering requirements of rapid construction turnover and early load-bearing.

[0022] Excellent volume stability in the later stage: The two gels, CASH and NASH, restrain each other during formation and development. This dual-network structure can effectively suppress macroscopic volume deformation caused by continuous shrinkage or moisture loss of a single gel phase, and stably control the 28-day drying shrinkage rate below 300 με, fundamentally reducing the risk of structural cracking and greatly improving the long-term durability of the component.

[0023] Achieving complete cement-free production with outstanding environmental advantages: The system completely eliminates cement clinker, using industrial solid waste (slag, fly ash) as the main raw material, supplemented by low-dosage nano-silica slurry, significantly reducing carbon emissions from the source. Compared with ordinary silicate cement concrete, its carbon emissions throughout the entire life cycle are expected to be reduced by more than 60%, with extremely significant environmental benefits.

[0024] Stable and controllable performance with good reproducibility: By precisely designing and controlling the key Al2O3 / SiO2 molar ratio in nano silica slurry, the directionality of the secondary excitation reaction and the stability of the double network gel structure are ensured, so that the fluctuation range of the final product in mechanical properties and volume stability is less than 5%, with high reliability and consistency.

[0025] It has good economic viability and promotion potential: the main raw materials used are bulk industrial waste and common building materials. Nano silica slurry is used as a key additive. Its dosage is low and its efficiency is high. The overall material cost is basically the same as that of conventional geopolymers. It can achieve high performance without significantly increasing costs, and has economic feasibility for large-scale production and widespread application.

[0026] In summary, this invention, through mechanistic innovation, successfully achieves synergistic optimization of early strength and long-term stability of geopolymer materials, providing a practical solution for promoting the engineering application of high-performance, high-durability, pure waste-based green cementitious materials. Detailed Implementation

[0027] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0028] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0029] The parameters and functions of each component in the following examples are described below.

[0030] Slag: Specific surface area ≥ 400 m² 2 / kg, CaO content ≥40% (mass fraction), providing the calcium source required for geopolymer reaction and ensuring CASH gel formation.

[0031] Fly ash: Class F fly ash, loss on ignition ≤5%, SiO2+Al2O3 content ≥70%, as a silica-alumina raw material, participates in the construction of gel network.

[0032] Alkali activator: It is composed of sodium hydroxide and water glass. The concentration of sodium hydroxide is 8-12 mol / L, the modulus of water glass (SiO2 / Na2O) is 1.5-2.0, and the mass ratio of the mixture is 1:3-5. It is responsible for initially activating the hydration reaction of slag-fly ash.

[0033] Nano-silica slurry: Al2O3 / SiO2 molar ratio of 0.18-0.22, particle size ≤50 nm, solid content of 30-40%, as a secondary activator to regulate the composition of the gel phase and promote NASH gel formation.

[0034] Quartz sand: fineness modulus of 2.6-3.0, maximum particle size ≤8 mm, mud content <1%, used as aggregate to improve the density of materials.

[0035] Water-reducing agent: Polycarboxylate-based high-efficiency water-reducing agent (powder), with a water reduction rate of ≥30%, reduces the water-cement ratio and optimizes the microstructure.

[0036] Expanding agent: Erythrite-type expanding agent (UEA) limits later shrinkage and further improves volume stability.

[0037] Example 1 This embodiment relates to a cementless geopolymer excited by nano-silica slurry and its preparation method.

[0038] The components, by weight, are: 450 parts slag, 250 parts fly ash, 90 parts alkali activator (8 mol / L sodium hydroxide + water glass modulus 2.0, compounded by mass ratio 1:4), 40 parts nano silica slurry (Al2O3 / SiO2 molar ratio 0.18), 600 parts quartz sand (fineness modulus 3.0), 130 parts water, and 6 parts water-reducing agent.

[0039] The preparation method includes the following steps: Mix slag, fly ash, and quartz sand in the above proportions, and dry mix for 2 minutes until uniform; Mix the alkali activator with water and stir, then add the water-reducing agent to dissolve it, thus obtaining a mixed solution; Pour the mixed solution into the dry material and stir for 3 minutes to form the initial slurry; Add nano silica fume slurry and stir continuously for 5 minutes until the slurry is uniform and smooth, without sedimentation or stratification; Pour the slurry into the mold and vibrate it to form the shape (vibration frequency 50 Hz, time 30 s), then cure it according to standard until the specified age.

[0040] Example 2 This embodiment relates to a cementless geopolymer excited by nano-silica slurry and its preparation method.

[0041] The components, by weight, are: 500 parts slag, 300 parts fly ash, 100 parts alkali activator (sodium hydroxide 10 mol / L + water glass modulus 1.8, compounded by mass ratio 1:5), 50 parts nano silica slurry (Al2O3 / SiO2 molar ratio 0.20), 700 parts quartz sand (fineness modulus 2.8), 140 parts water, 8 parts water-reducing agent, and 15 parts expansion agent.

[0042] Preparation steps: Same as in Example 1, except that an expanding agent is added when mixing the dry materials.

[0043] Example 3 Components by weight: 550 parts slag, 320 parts fly ash, 110 parts alkali activator (sodium hydroxide 12 mol / L + water glass modulus 1.5, compounded by mass ratio 1:3), 55 parts nano silica slurry (Al2O3 / SiO2 molar ratio 0.22), 750 parts quartz sand (fineness modulus 2.6), 150 parts water, and 9 parts water-reducing agent.

[0044] Preparation steps: Same as in Example 1.

[0045] Compare with Example 1 A cementless geopolymer excited by nano-silica slurry and its preparation method include the following steps: Difference from Example 1: No nano silica slurry is included, and the amount of alkali activator is increased to 130 parts (single alkali activation system).

[0046] Compare with Example 2 A cementless geopolymer excited by nano-silica slurry and its preparation method include the following steps: The difference from Example 2 is that the Al2O3 / SiO2 molar ratio of the nano silica slurry is 0.15 (outside the scope of this invention).

[0047] Compare with Example 3 A cementless geopolymer excited by nano-silica slurry and its preparation method include the following steps: The difference from Example 3 is that it contains 100 parts cement, replacing slag, and the amount of nano-silica slurry is reduced to 20 parts.

[0048] Compare with Example 4 The component ratio of the comparative example is consistent with that of Example 1. The difference lies in that the preparation method of the nano-silica slurry-inspired cementless geopolymer proposed in the comparative example includes the following steps: Mix all components directly and stir until the slurry is uniform and smooth, without sedimentation or stratification. Pour the slurry into the mold and vibrate it to form the shape (vibration frequency 50 Hz, time 30 s), then cure it according to standard until the specified age.

[0049] Compare with Example 5 The component ratio of the comparative example is consistent with that of Example 1. The difference lies in that the preparation method of the nano-silica slurry-inspired cementless geopolymer proposed in the comparative example includes the following steps: Mix slag, fly ash, and quartz sand in the specified proportions, and dry mix for 2 minutes until uniform. Mix the alkali activator with water and stir, then add the water-reducing agent to dissolve it, thus obtaining a mixed solution; The mixed solution is added to nano-silica slurry and stirred evenly to form the initial slurry; Pour the dry material into the initial slurry and stir continuously for 5 minutes until the slurry is uniform and smooth, without sedimentation or stratification. Pour the slurry into the mold and vibrate it to form the shape (vibration frequency 50 Hz, time 30 s), then cure it according to standard until the specified age.

[0050] Compare with Example 6 The component ratio of the comparative example is consistent with that of Example 1. The difference lies in that the comparative example, which proposes a nano-silica slurry-inspired cementless geopolymer and its preparation method, includes the following steps: Mix slag, fly ash, quartz sand and nano silica fume slurry in proportion, and dry mix for 2 minutes until uniform to obtain dry material; Mix the alkali activator with water and stir, then add the water-reducing agent to dissolve it, thus obtaining a mixed solution; Add the dry material to the mixed solution and stir until the slurry is uniform and smooth, without any sedimentation or stratification. Pour the slurry into the mold and vibrate it to form the shape (vibration frequency 50 Hz, time 30 s), then cure it according to standard until the specified age.

[0051] The performance of the examples and control examples was tested, and the results are shown in Table 1 below.

[0052] Table 1

[0053] As shown in Table 1, Examples 1-3 all exhibited high early strength and low shrinkage, demonstrating the effectiveness of the dual-network gel system.

[0054] Comparative Example 1, lacking nano-silica slurry, only formed a single CASH gel, resulting in insufficient early strength and severe shrinkage. As shown in Comparative Example 2, when the molar ratio of nano-silica slurry exceeded the specified range, the product could not effectively form a double-network gel, leading to a significant decrease in performance. In Comparative Example 3, although the strength slightly improved after adding cement, the shrinkage rate remained high, and the environmental advantage of being cement-free was lost. In Comparative Example 4, because all components were directly mixed and stirred without following the step-by-step process of "dry material premixing → mixed solution preparation → dry material and solution mixing → subsequent addition of nano-silica slurry," the reaction sequence was disordered, the nano-silica slurry was unevenly dispersed, and the double-network gel structure could not be formed in an orderly manner, resulting in significantly lower early strength and greater later shrinkage.

[0055] Comparative Example 5 reversed the order of adding the nano silica slurry by first mixing the mixed solution with the nano silica slurry and then adding the dry material and stirring. This disrupted the reaction conditions for secondary activation, resulting in a poorer interlocking effect of the double network gel. Consequently, the mechanical properties and volume stability of the material were significantly inferior to those of the Example.

[0056] Comparative Example 6 showed that the nano-silica slurry was dry-mixed with slag, fly ash, and quartz sand, which caused the nano-silica slurry to agglomerate in the dry material. This prevented it from playing an effective role in secondary activation and structural regulation, resulting in insufficient formation of the double-network gel. Ultimately, this manifested as insufficient early strength and high shrinkage rate in the later stage.

[0057] It should be noted that the above specific embodiments are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions are all within the scope of the disclosure of this invention and fall within the protection scope of this invention.

Claims

1. A cementless geopolymer excited by nano-silica slurry, characterized in that, By weight, it comprises the following components: 400-600 parts slag, 200-350 parts fly ash, 80-120 parts alkali activator, 30-60 parts nano silica slurry, 500-800 parts quartz sand, 120-160 parts water and 5-10 parts water-reducing agent.

2. The cementless geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The cementless geopolymer excited by the nano-silica slurry also contains 10-20 parts of an optional expansion agent.

3. The cement-free geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The molar ratio of Al2O3 / SiO2 in the nano-silica slurry is 0.18-0.

22.

4. The cementless geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The fineness modulus of the quartz sand is 2.6-3.

0.

5. The cementless geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The mass fraction of calcium oxide in the slag is not less than 40%.

6. The cementless geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The mass fraction of SiO2 and Al2O3 in the fly ash shall not be less than 70%.

7. The cementless geopolymer excited by nano-silica slurry according to claim 1, characterized in that, The alkali activator is a compound of sodium hydroxide and water glass, with a mass ratio of sodium hydroxide to water glass of 1:3-5.

8. The cementless geopolymer excited by nano-silica slurry according to claim 7, characterized in that, The modulus of the water glass, i.e., SiO2 / Na2O, is 1.5-2.

0.

9. A method for preparing a cementless geopolymer excited by nano-silica slurry, characterized in that, Includes the following steps, in parts by weight: Mix 400-600 parts slag, 200-350 parts fly ash, and 500-800 parts quartz sand until homogeneous to obtain dry material; Mix 80-120 parts of alkali activator with 120-160 parts of water, and then add 5-10 parts of water-reducing agent to form a mixed solution; The mixed solution and dry materials are stirred evenly to form an initial slurry; Add 30-60 parts of nano silica slurry to the initial slurry and stir until the slurry is uniform and fine, without sedimentation or stratification.

10. Application of cement-free geopolymers excited by nano silica slurry in road base courses and tailings solid waste disposal projects.

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