Fireproof composite geopolymer and preparation method thereof

Abstract

This invention belongs to the field of functional building material preparation technology, specifically relating to a fire-resistant composite geopolymer and its preparation method. The raw materials of the fire-resistant composite geopolymer, by mass percentage, include the following components: (35%~65%): (20%~40%): (20%~35%): (1.5%~3.5%) fly ash, sand, alkali activator solution, and polyethyleneimine-modified halloysite nanotubes. This invention effectively controls the fire resistance and mechanical hardness of the material by regulating the surface properties of halloysite nanotubes and uniformly dispersing them in the geopolymer matrix. Furthermore, through static pressing and heating, the shape and thickness of the bricks can be precisely controlled, resulting in products with good structural shape stability.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of inorganic non-metallic materials and building fire protection technology, specifically relating to a composite geopolymer material with excellent fire resistance and its preparation method. This material is suitable for building structures and protective engineering projects with high requirements for fire resistance, high-temperature stability, and mechanical properties. Through compositional design and process optimization within a geopolymer matrix, it can enhance structural integrity and fire resistance at high temperatures. Background Technology

[0002] Geopolymers, as a new generation of inorganic cementitious materials, demonstrate strategic value in sustainable construction and special engineering fields due to their unique properties and environmental friendliness. Their core advantages can be systematically summarized into the following four points: high temperature resistance, capable of withstanding temperatures above 1000°C for extended periods. o Geopolymers exhibit a high degree of environmental friendliness; excellent corrosion resistance, effectively resisting the erosion of acids, salts, and various chemical media; low carbon and environmental friendliness, with its main raw materials being industrial solid wastes such as fly ash and metakaolin, resulting in carbon emissions 60-80% lower than traditional cement; and controllable mechanical properties, achieving precise solidification control from minutes to hours through technologies such as nano-clay coating. These characteristics make them irreplaceable in special engineering fields such as high-temperature industries, harsh corrosive environments, and rapid repairs, and they have been successfully applied in several key scenarios, including oil drilling cementing, metallurgical furnace linings, chemical corrosion protection, marine engineering, and emergency repairs. From a materials science perspective, the performance of geopolymers stems from their aluminosilicate raw material system. Fly ash, metakaolin, and rice husk ash are the core raw materials, with the main chemical components being active SiO2 and Al2O3, supplemented by small amounts of calcium, magnesium, potassium, and sodium oxides. This compositional characteristic gives it a dual role in the field of building materials: First, as mineral admixtures, they can be directly used in cement and concrete, partially replacing cement, significantly improving the workability of the mixture, enhancing structural durability, and reducing the heat of hydration. More importantly, these raw materials play the role of a reactive framework in geopolymer systems. Taking fly ash as an example, under the action of strong alkaline activators, its glassy structure undergoes a chain reaction of "dissolution-gelation-polymerization," ultimately forming a stable three-dimensional network structure composed of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. It is this microstructure that gives geopolymer products their superior high-temperature resistance, corrosion resistance, and overall mechanical properties compared to traditional cement-based materials.

[0003] However, traditional geopolymers generally suffer from slow solidification rates and insufficient early strength development at room temperature, directly leading to prolonged demolding and curing cycles and low molding efficiency, making it difficult to meet the rapid construction requirements of modern building engineering. Furthermore, the slow curing process may also affect the uniformity and density of its microstructure, thus limiting the mechanical properties and durability of the final product. Therefore, under the premise of ensuring long-term material performance stability, introducing novel nano- or micro-scale functional additives and optimizing compatible molding and curing processes to significantly accelerate the early curing of geopolymers and improve their initial mechanical strength has become a key technological breakthrough for promoting the large-scale, high-efficiency engineering applications of such materials. Summary of the Invention

[0004] Based on the shortcomings of existing technologies in terms of fire resistance, preparation process, and stability of geopolymers, this invention aims to provide a fire-resistant composite geopolymer and its preparation method to improve the structural stability and durability of traditional geopolymer materials at high temperatures, optimize its preparation process, and enhance the overall performance of the material.

[0005] Therefore, this invention provides a fire-resistant composite geopolymer, the raw materials of which, by mass percentage, comprise the following components (35%~65%): (20%~40%): (20%~35%): (1.5%~3.5%): fly ash, sand, alkali activator solution, and polyethyleneimine-modified halloysite nanotubes. It should be noted that, compared to other porous natural mineral materials such as kaolin nanoparticles, montmorillonite, and silica nanoparticles, the use of halloysite nanotubes in this invention significantly improves strength and fire resistance.

[0006] Preferably, the sand is quartz.

[0007] Preferably, the alkaline activator solution is composed of sodium silicate and a high-concentration alkaline solution, wherein the high-concentration alkaline solution is a 10 M to 16 M sodium hydroxide or potassium hydroxide solution. The weight ratio of sodium silicate to the hydroxide solution is controlled between 0.5:1 and 4:1 to provide suitable alkalinity and silicon source, promoting the formation of the three-dimensional network structure of the geopolymer.

[0008] This invention provides a method for preparing a fire-retardant composite geopolymer, comprising the following steps: Fly ash, sand, alkali activator solution, and polyethyleneimine-modified halloysite nanotubes were weighed out and mixed evenly to form a slurry mixture. The mixture was then transferred to a mold and extruded and shaped using a static press to obtain a preliminary shaped body. After that, it was placed on a heating platform for heat treatment to accelerate the curing and shaping process of the geopolymer, and finally a dense and stable geopolymer material was obtained.

[0009] Preferably, the mixing method includes, but is not limited to, stirring and ultrasonication.

[0010] Preferably, the static pressure of the press is 100 to 150 tons.

[0011] Preferably, the pressure application time is 0.1 to 1 min.

[0012] Preferably, the heating temperature is 150°C. o C~200 o C.

[0013] Preferably, the heating time is 2 to 24 hours.

[0014] Preferably, the polyethyleneimine-modified halloysite nanotubes are obtained through the following steps: weighing polyethyleneimine and halloysite nanotubes in a mass ratio of 1:0.01 to 1:0.8, mixing and adsorbing them in an aqueous solution, centrifuging and washing to remove unadsorbed polyethyleneimine, and drying for later use. Preferably, the mixing method includes, but is not limited to, stirring and ultrasonication. Preferably, the adsorption time is 15 min to 1 h.

[0015] The beneficial effects of this invention are as follows: 1. The fire-retardant composite geopolymer provided by this invention uses aluminosilicate raw materials, sand, and modified nanoparticles as raw materials. In the gelation step, aluminate and silicate species, together with silicates from the activator solution, condense to form a complex gel-like mixture. The polymerization step includes increasing gel connectivity through large-scale crosslinking and rearrangement, as well as the accompanying continuous condensation, resulting in the formation of a three-dimensional network called a geopolymer, thereby increasing its stability.

[0016] 2. The modified nanoparticles added in this invention can be adsorbed by aluminosilicate raw materials and, after gelation, can be uniformly dispersed into the gel network of the geopolymer. This uniform dispersion of nanoparticles effectively improves the mechanical properties of the geopolymer. As nanoscale reinforcements, they dissipate fracture energy through mechanisms such as crack deflection and bridging, thereby increasing the compressive strength and significantly improving the toughness of the material. Simultaneously, the nanoparticles can promote ceramization transformation at high temperatures, forming a more stable refractory barrier layer, thus increasing the fire resistance limit of the modified geopolymer.

[0017] 3. This invention employs a synergistic process of static pressing and thermal activation to achieve rapid and efficient shaping of geopolymers. Specifically, a static press applies directional pressure to the pre-mixed slurry or pre-formulated material, achieving initial optimization of particle density, moisture rearrangement, and pore structure within the mold, forming a dense and precisely shaped preform. Subsequent heat treatment, a temperature-controlled process, significantly accelerates the alkali-activated reaction, promoting rapid cross-linking and solidification of the gel network, thus completing the structural transformation from a plastic to a solid state in a short time. This composite process not only significantly shortens the molding cycle but also effectively improves the early strength, dimensional stability, and final mechanical properties of the product, making it suitable for large-scale production of high-precision geopolymer components. Attached Figure Description

[0018] Figure 1 Here is a scanning electron microscope image of halloysite nanotubes from Example 1; Figure 2 The diagram shows the Zeta potential before and after surface modification of halloysite nanotubes in Example 1. Figure 3 The images show the scanning electron microscope (SEM) image and zeta potential diagram of fly ash from Example 1. Figure 4 Scanning electron microscope image of the adsorption behavior of coal dust on halloysite nanotubes modified in Example 1; Figure 5 Photograph of the composite geopolymer prepared in Example 1; Figure 6 This is the hardness test report for the composite geopolymer prepared in Example 1; Figure 7 Photographs of the fire resistance test of the composite geopolymer prepared in Example 1; Figure 8 For Comparative Example 1, a scanning electron microscope image of the adsorption behavior of fly ash on halloysite before modification. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments represent only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment further provides a method for preparing a fire-retardant composite geopolymer, comprising the following steps: 1) Surface modification of halloysite nanotubes (1) Weigh a certain mass of polyethyleneimine (PEI), dissolve it in deionized water, and prepare a 0.05 g / mL PEI aqueous solution; (2) Weigh 10 parts by mass of halloysite nanotubes and measure a certain mass of PEI solution (the amount of PEI is 1 / 10 of the amount of halloysite nanotubes). Add both to an appropriate amount of deionized water and mix well. Then place the mixture in a constant temperature shaker and shake continuously at room temperature for 30 min to allow PEI to be fully adsorbed onto the surface of the halloysite nanotubes. After the reaction is complete, centrifuge the resulting suspension using a high-speed centrifuge and discard the supernatant to completely remove unbonded free PEI. Finally, place the washed solid product in a vacuum drying oven to dry, grind it, and obtain PEI-modified halloysite nanotubes, which are then sealed and stored for later use.

[0021] Figure 1 The scanning electron microscope image of the halloysite nanotubes used in this embodiment shows that halloysite exhibits a hollow tubular structure with a smooth surface, a diameter of about tens of nanometers, and a length of up to micrometers.

[0022] Figure 2 In this embodiment, halloysite nanotubes modified with polyethyleneimine (PEI) exhibit a significant reversal of their surface charge properties: unmodified halloysite, due to the negative charge of its surface silanol groups (Zeta potential approximately -15 to -30 mV), readily aggregates in water; while PEI, through protonated amino groups, adsorbs onto the halloysite surface, transforming its Zeta potential to a positive value (approximately +40 to +60 mV). This charge reversal effectively enhances the electrostatic repulsion between nanotubes, inhibits aggregation, and improves its dispersibility and interfacial compatibility in alkaline geopolymer slurries, providing a crucial surface chemical basis for enhancing the functionality of the composite material.

[0023] 2). Geopolymer Preparation This embodiment provides a fire-resistant composite geopolymer material, the raw materials of which include fly ash, quartz sand, sodium hydroxide / water glass alkali activator solution (wherein the weight ratio of sodium hydroxide to water glass is controlled at 3:1) and modified halloysite nanotubes in a mass ratio of 41%:26%:30%:2.5% to provide suitable alkalinity and silicon source to promote the three-dimensional network structure of the geopolymer.

[0024] The preparation method of the above-mentioned geopolymer includes the following steps: (1) Weigh out specific amounts of coal ash, quartz sand, sodium hydroxide / water glass alkali activator solution and modified halloysite nanotubes respectively, and mix them thoroughly in a mass ratio of 41%:26%:30%:2.5% to form a slurry mixture.

[0025] (2) The mixture is then transferred to a pre-prepared mold and shaped by extrusion using a static press to obtain a preliminary molded body.

[0026] (3) Then place it on the heating platform, 90 o C-heat treatment is used to accelerate the curing and shaping process of the geopolymer, ultimately resulting in a dense and stable geopolymer material.

[0027] Figure 3 The image shown is a scanning electron microscope image of the coal dust used in this embodiment. It can be seen that the coal dust has a rough surface and is spherical or irregular in shape, with a particle size in the range of 1~10 µm and a negative charge.

[0028] Figure 4 The images shown are scanning electron microscope (SEM) images of the mixture of fly ash and modified halloysite nanotubes in this embodiment. The images reveal that the fly ash particles carry a significant negative charge (Zeta potential of approximately -13 mV), while the halloysite nanotubes modified with polyethyleneimine (PEI) have a positive charge. SEM observation after mixing the two particles shows that the positively charged modified halloysite nanotubes can be uniformly and densely attached to the negatively charged fly ash particles through electrostatic adsorption, forming a distinct core-shell structure or surface modification layer. These results confirm that electrostatic self-assembly based on charge complementarity is an effective way to achieve uniform modification of nanoparticles on the surface of micron-sized powders, which helps improve the dispersibility and interfacial bonding strength of the composite powder in subsequent geopolymer matrices.

[0029] Figure 5 The coal ash / haloysite composite geopolymer entity obtained in this embodiment after being pressed by a static press and heat-treated exhibits a typical densified structure and a stable overall morphology.

[0030] Strength testing: The dimensions of the submitted test sample (c) were 20 cm × 10 cm × 6 cm (length × width × height). Strength testing was conducted according to JC / T 239-2014 "Autoclaved Fly Ash Bricks". Refractoriness testing: The test sample was burned using an oxidizing flame (oxygen to propane volume ratio of 5:1). The nozzle was 15 cm from the sample surface, and a fixed-point spray method was used for continuous combustion for 30 minutes. Under these conditions, the flame temperature was approximately 2520 °C. o C. Test results as follows Figure 6 As shown, the test results indicate that the strength values ​​of the 10 geopolymer material samples of the present invention range from 19.05 MPa to 22.45 MPa, with an average value of 21.0 MPa and a minimum value of 19.0 MPa. This meets the requirements of the standard that the average value is ≥20.0 MPa and the minimum value is ≥16.0 MPa, and the strength grade reaches MU20, which is a high-quality product.

[0031] Figure 7The fire resistance test of the composite geopolymer in this embodiment shows that under continuous open flame from a blowtorch (temperature approximately 2520°C)... o Under direct impact (C, duration 30 min), although the sample surface rapidly heated to a red-hot state, the overall structure remained intact, without cracking, collapse, or significant deformation, and there was no heat penetration on the unexposed side. This further confirms that the material has excellent thermal shock resistance, high-temperature structural stability, and effective thermal insulation capabilities under real fire conditions.

[0032] Comparative Example 1 This embodiment provides a fire-resistant composite geopolymer material, the raw materials of which include fly ash, quartz sand, sodium hydroxide / water glass alkali activator solution and unmodified halloysite nanoparticles in a mass ratio of 41%:26%:30%:2.5%. The weight ratio of sodium silicate to the hydroxide solution in the alkali activator solution is controlled at 3:1 to provide suitable alkalinity and silicon source, thereby promoting the three-dimensional network structure of the geopolymer.

[0033] The preparation method of the above-mentioned geopolymer includes the following steps: (1) Weigh out specific amounts of coal ash, quartz sand, sodium hydroxide alkali activator solution and unmodified halloysite nanoparticles, and mix them thoroughly in a mass ratio of 41%:26%:30%:2.5% to form a slurry mixture.

[0034] (2) The mixture is then transferred to a pre-prepared mold and shaped by extrusion using a static press to obtain a preliminary molded body.

[0035] (3) Then place it on a heating platform and heat it to accelerate the solidification and shaping process of the geopolymer, and finally obtain a geopolymer material with a dense structure and stable performance.

[0036] Figure 8 The images shown are scanning electron microscope (SEM) images of the mixture of fly ash and unmodified halloysite in this comparative example. The SEM images clearly demonstrate the electrostatic repulsion between the fly ash particles and the unmodified halloysite. The fly ash particles carry a significant negative surface charge (Zeta potential approximately -13 mV), while the unmodified halloysite nanotubes also exhibit negative charge (Zeta potential approximately -15 mV). Due to the repulsion of like charges on the surfaces, the two particles failed to form effective adsorption and tight bonding in the mixture.

Claims

1. A fire-resistant composite geopolymer, the raw materials comprising the following components by mass percentage (35%~65%): (20%~40%): (20%~35%): (1.5%~3.5%) fly ash, sand, alkali activator solution, and polyethyleneimine-modified halloysite nanotubes.

2. The fire-resistant composite geopolymer according to claim 1, wherein the sand is quartz stone.

3. The fire-retardant composite geopolymer according to claim 1, wherein the alkali activator solution is composed of sodium silicate and a high-concentration alkali solution, wherein, The high-concentration alkaline solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 10 M to 16 M; the weight ratio of sodium silicate to the hydroxide solution is controlled between 0.5:1 and 4:

1.

4. A method for preparing the fire-retardant composite geopolymer according to any one of claims 1-3, comprising the following steps: Fly ash, sand, alkali activator solution, and polyethyleneimine-modified halloysite nanotubes were weighed out and mixed evenly to form a slurry mixture. The mixture was then transferred to a mold and extruded and shaped using a static press to obtain a preliminary shaped body. After that, it was placed on a heating platform for heat treatment to accelerate the curing and shaping process of the geopolymer, and finally a dense and stable geopolymer material was obtained.

5. The preparation method according to claim 4, wherein the mixing method is stirring and / or ultrasound.

6. The preparation method according to claim 4, wherein the static pressure of the press is 100-150 tons.

7. The preparation method according to claim 4, wherein the pressure application time is 0.1~1 min.

8. The preparation method according to claim 4, wherein the heating temperature is 150°C. o C~200 o C.

9. The preparation method according to claim 4, wherein the heating time is 2-24 h.

10. The preparation method according to claim 4, wherein the polyethyleneimine-modified halloysite nanotubes are obtained by the following steps: weighing polyethyleneimine and halloysite nanotubes in a mass ratio of 1:0.01 to 1:0.8, mixing and adsorbing them in an aqueous solution, centrifuging and washing to remove unadsorbed polyethyleneimine, and drying for later use; preferably, the mixing method includes, but is not limited to, stirring and sonication; preferably, the adsorption time is 15 min to 1 h.

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