Geopolymer with self-enhancing function, preparation method and application

Abstract

The invention relates to the technical field of building materials, in particular to a geopolymer with a self-enhancement function, a preparation method and application. The geopolymer is prepared by the preparation method. The preparation method comprises the following steps: feeding and uniformly mixing metakaolin and slag according to a mass ratio of 4: 6 to obtain a precursor; uniformly mixing an alkali activator, water and the precursor according to a mass ratio of 4: 35: 100 to obtain a reaction system; and injecting the reaction system into a mold, carrying out first maintenance, demolding, and then carrying out second maintenance to obtain the geopolymer with the self-enhancement function. The application comprises application of the geopolymer in a dry-wet alternating environment and application of the geopolymer in a chemical medium erosion environment. According to the invention, the geopolymer which has high initial strength and shows a reactive self-enhancement function in harsh environments such as dry-wet alternation, chemical medium (such as sulfate) erosion and the like can be prepared at low cost, so that the durability of the geopolymer is improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a geopolymer with self-reinforcing properties, its preparation method, and its application. Background Technology

[0002] Geopolymers, as a novel green cementitious material, have attracted widespread attention due to their high early strength, excellent corrosion resistance, and low carbon emissions, and are considered a potential alternative to traditional silicate cement. Currently, research on geopolymers mainly focuses on improving their initial mechanical properties (such as compressive and flexural strength) and the density of their microstructure through formulation optimization. This is because it is generally believed in the industry that to achieve better durability, geopolymers often need to possess higher initial strength and a denser microstructure.

[0003] However, in practical engineering applications, geopolymer materials are exposed to harsh environments for extended periods, such as repeated wet-dry cycles and chemical corrosion (e.g., sulfates). These environments typically lead to varying degrees of strength loss, cracking, or spalling in geopolymer materials, limiting their application in high-performance and long-life structures. While research has focused on improving the long-term durability of geopolymers, the underlying approach remains focused on passively resisting the effects of harsh environments by forming a denser initial structure, rather than actively reinforcing geopolymer materials during service. This approach inevitably leads to increased material costs.

[0004] Therefore, it is necessary to provide a self-reinforcing geopolymer, its preparation method, and its application to solve the problem at low cost that geopolymer materials in the prior art are exposed to harsh environments such as repeated wet-dry cycles and chemical media (such as sulfates) for a long time, resulting in varying degrees of strength loss, cracking, or peeling. Summary of the Invention

[0005] The purpose of this invention is to provide a geopolymer with self-reinforcing properties, its preparation method, and its applications. The specific technical solution is as follows: In a first aspect, the present invention provides a method for preparing a geopolymer with self-reinforcing properties, comprising: Metakaolin and slag were mixed at a mass ratio of 4:6 to obtain a precursor; an alkali activator, water and the precursor were mixed at a mass ratio of 4:35:100 to obtain a reaction system; the reaction system was injected into a mold, and after a first curing, it was demolded, and then after a second curing, a geopolymer with self-reinforcing function was obtained.

[0006] Optionally, the alkali activator comprises water glass with a modulus of 1.5.

[0007] Optionally, the first curing is room temperature curing, and the curing conditions include a curing temperature of 20±5℃, a relative humidity of ≥95%, and a curing time of 1~3 days.

[0008] Optionally, the first curing is heating curing, which uses curing conditions including steam curing or oven curing, with a curing temperature of 40~80℃ and a curing time of 6~24h.

[0009] Optionally, the second maintenance is natural maintenance at room temperature, which takes 25 to 27 days.

[0010] Optionally, the second maintenance is natural maintenance at room temperature, which takes 27 to 27.75 days.

[0011] In a second aspect, the present invention provides a geopolymer with self-reinforcing properties, which is prepared by the method for preparing the geopolymer with self-reinforcing properties described above.

[0012] Optionally, the 28-day compressive strength of the geopolymer is not less than 30 MPa.

[0013] In a third aspect, the present invention provides the application of the self-reinforcing geopolymer in alternating wet and dry environments, wherein the compressive strength of the geopolymer increases by at least 40% after 12 cycles of alternating wet and dry environments. The dry-wet alternating environment uses a dry environment temperature of 60±2℃, a relative humidity of ≤ 50%, and a single dry environment application time of 12h. The wet and dry alternating environment uses a wet environment temperature of 20±2℃, a relative humidity of ≥95%, and a single wet environment application time of 12h.

[0014] In a fourth aspect, the present invention provides the application of the self-reinforcing geopolymer in a chemically corrosive environment, wherein the compressive strength of the geopolymer increases by at least 20% after 14 days of application in the chemically corrosive environment; The chemical erosion environment used in the chemical medium erosion environment has a chemical medium erosion temperature of 20±2℃; The chemical medium includes a 5% sodium sulfate solution by mass.

[0015] The application of the technical solution of the present invention has at least the following beneficial effects: This invention provides a method for preparing a geopolymer with self-reinforcing properties. This method enables the preparation of geopolymers with high initial strength and reactive self-reinforcing properties under harsh environments such as alternating wet and dry conditions and chemical media (such as sulfate) erosion at low cost. This improves the durability of geopolymers and solves the problem in the prior art where geopolymer materials are exposed to repeated wet and dry conditions and chemical media (such as sulfate) erosion for a long time, resulting in varying degrees of strength loss, cracking, or peeling.

[0016] In principle: Firstly, regarding the initial strength of the geopolymer, the alkali activator used in the reaction system of this invention can induce the breakage of the alumina tetrahedral and silicon tetrahedral chemical bonds in metakaolin, releasing aluminate and silicate ions. Furthermore, the aluminate and silicate ions undergo a condensation reaction to form a three-dimensional network of amorphous hydrated sodium aluminosilicate gel. This gel forms the main framework of the geopolymer, providing the material with toughness and long-term chemical stability. Simultaneously, the alkali activator can induce the disintegration of the glassy network on the slag surface, releasing a large number of calcium ions. These calcium ions react with... The silicate ions released by metakaolin react to rapidly generate amorphous or low-crystallinity hydrated calcium aluminosilicate gel. This gel grows rapidly and mainly contributes to the early strength and density of the geopolymer material. Since the metakaolin and slag in the reaction system are uniformly distributed, they interweave and permeate each other at the microscale of forming sodium aluminosilicate gel and calcium aluminosilicate gel, jointly filling the gaps between precursor particles and cementing the unreacted precursor skeleton particles together. As a result, the reaction system gradually hardens under the first and second curing conditions and reaches the predetermined mechanical strength.

[0017] Secondly, regarding the reactive self-reinforcing function of geopolymers under harsh environments such as alternating wet and dry conditions and chemical media (e.g., sulfate erosion), this invention uses a low dosage of alkali activator in the reaction system, which not only reduces raw material costs but also facilitates the retention of some unreacted precursors, thus forming a "potential reaction reservoir." Under alternating wet and dry conditions, external moisture easily penetrates into the pores and microcracks of the geopolymer, dissolving the residual, unlocked alkali activator in these pores and microcracks, forming a localized alkaline microenvironment. This, in turn, promotes the hydrolysis and activation of the surface of unreacted slag particles surrounding this alkaline microenvironment, releasing calcium ions, which then react with silicate ions in the pore fluid, resulting in the in-situ growth of dense hydrated calcium aluminosilicate gel. This secondary-generated hydrated calcium aluminosilicate gel exhibits significant spatial orientation, growing and filling along moisture transport channels (cracks and capillaries), leading to pore size refinement and a significant increase in matrix density. This, in turn, macroscopically demonstrates a reactive self-reinforcing function, enhancing the durability of the geopolymer. In the corrosive environment of chemical media (such as sulfate), in addition to moisture penetration, sulfate ions that penetrate into the pores and microcracks of the geopolymer also participate in the reaction, generating trace amounts of ettringite or gypsum crystal micro-expansion products. Within the confined space of the geopolymer pores and microcracks, these micro-expansion products play a positive role in compaction, thus further exhibiting a reactive self-reinforcing function on a macroscopic level, enhancing the durability of the geopolymer. Therefore, unlike the depolymerization-condensation reaction induced by the alkali activator in the first and second curing stages, the reactive self-reinforcing process follows a two-stage reaction mechanism of "environmental activation - surface dissolution - in-situ filling".

[0018] Furthermore, the modulus of the alkali activator used in this invention should not be too large or too small. A modulus that is too large (e.g., >1.6) is because: an excessively high modulus means that the silicate content in the alkali activator is too high and the alkalinity is relatively low. This will lead to excessive viscosity of the reaction system, which is not conducive to construction; at the same time, the low alkalinity is insufficient to effectively etch and destroy the glassy structure on the slag surface, making it difficult to activate its "potential hydraulic properties" in the later stages, resulting in weakened self-reinforcing ability (as shown in Comparative Example 4). A modulus that is too small (e.g., <1.4) is because: an excessively low modulus means that the alkali activator is too alkaline but lacks soluble silica. This will lead to explosive coagulation (flash coagulation) in the early stages of the reaction, hindering the orderly growth of the gel network and resulting in low initial strength (as shown in Comparative Example 3); and excessive alkalinity may excessively consume the slag in the "potential reaction reservoir" in the early stages, resulting in a lack of sufficient unreacted slag particles to cope with alternating wet and dry conditions and the corrosive environment of chemical media, weakening or even losing the reactive self-reinforcing function. This invention selects a modulus of 1.5 for the alkali activator as the balance point, which takes into account both suitable alkalinity etching capability and sufficient silicon source, so as to reserve a "potential reaction reservoir" and retain the reactive self-enhancing function for geopolymers to cope with alternating wet and dry conditions and chemical media erosion environments.

[0019] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 The XRD results of the reaction system prepared in Example 1 were obtained by sampling and injecting it into the mold at different curing periods of 3 days, 7 days and 28 days.

[0022] Figure 2 SEM image of the geopolymer prepared in Example 1 before 12 wet-dry cycles.

[0023] Figure 3 SEM image of the geopolymer prepared in Example 1 after 12 wet-dry cycles. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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.

[0025] Example 1: A method for preparing a geopolymer with self-reinforcing properties, comprising: Metakaolin and slag were mixed at a mass ratio of 4:6 to obtain a precursor; an alkali activator, water and the precursor were mixed at a mass ratio of 4:35:100 to obtain a reaction system; the reaction system was injected into a mold, and after a first curing, it was demolded, and then after a second curing, a geopolymer with self-reinforcing function was obtained.

[0026] The alkaline activator is water glass with a modulus of 1.5.

[0027] The first curing process is room temperature curing, with the following conditions: curing temperature of 20±2℃, relative humidity of ≥95% (or film covering for moisture retention), and curing time of 24 hours (1 day). Demolding is then performed, followed by a second curing process. The second curing process is natural curing at room temperature, with the following conditions: curing temperature of 20±2℃, relative humidity of ≥95%, and curing time of 27 days (thus achieving the total curing age of the 28-day testing standard).

[0028] Comparative Example 1: Unlike Example 1, metakaolin and slag were mixed at a mass ratio of 7:3 to obtain a precursor; alkali activator, water and the precursor were mixed at a mass ratio of 10:35:100 to obtain a reaction system.

[0029] Comparative Example 2: Unlike Example 1, metakaolin and slag were mixed at a mass ratio of 1:9 to obtain a precursor; alkali activator, water and the precursor were mixed at a mass ratio of 7:35:100 to obtain a reaction system.

[0030] Comparative Example 3: Unlike Example 1, the alkaline activator, water and the precursor were mixed in a mass ratio of 7:35:100 to obtain the reaction system; the modulus of the water glass was 1.2.

[0031] Comparative Example 4: Unlike Example 1, the alkaline activator, water and the precursor were mixed in a mass ratio of 10:35:100 to obtain the reaction system; the modulus of the water glass was 1.8.

[0032] The geopolymers prepared in Example 1 and Comparative Examples 1-4 were sampled and tested for compressive strength after 28 days. The geopolymers prepared in Example 1 and Comparative Examples 1-4 were also sampled and tested in alternating wet and dry environments and in environments eroded by chemical media. The compressive strength data after application were recorded, and the rate of change in compressive strength was calculated. The test results are shown in Table 1 (in Table 1, "+" indicates an increase; "-" indicates a decrease).

[0033] In the alternating dry and wet environment test, the geopolymer was placed in an alternating dry and wet environment for 12 cycles. The dry environment temperature was 60±2℃, the relative humidity was ≤50%, and the application time of each dry environment cycle was 12 hours. The wet environment temperature was 20±2℃, the relative humidity was ≥95%, and the application time of each wet environment cycle was 12 hours. The chemical medium used in the test was a 5% sodium sulfate solution. The geopolymer was placed in the sodium sulfate solution for 14 days at a temperature of 20±2℃. The compressive strength test was conducted according to the standard GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)".

[0034] Table 1 Test Results

[0035] From the data in Table 1, we know that: Although the 28-day compressive strength of the geopolymer prepared in Example 1 was lower than that of Comparative Examples 1-4, it still met the requirements of the C30 strength grade in the application standard JC / T 899-2016 "Concrete Curbstones". Furthermore, the geopolymer prepared in Example 1 showed a 42.5% increase in compressive strength change rate after 12 cycles of wet-dry alternation, and a 23.8% increase after 14 days of chemical erosion, significantly better than Comparative Examples 1-4. This indicates that the geopolymer prepared in Example 1 exhibits reactive self-reinforcing capabilities in harsh environments such as wet-dry alternation and chemical erosion (e.g., sulfate), overturning the traditional understanding that the mechanical properties of geopolymer materials inevitably deteriorate under harsh conditions, and fully demonstrating that the geopolymer prepared in Example 1 possesses reactive self-reinforcing capabilities.

[0036] In Comparative Examples 1 and 2, altering the mass ratio of metakaolin and slag in the precursors and increasing the amount of alkali activator resulted in geopolymers with higher 28-day compressive strength, but they lost the reactive self-reinforcing function exhibited by geopolymers under harsh environments such as alternating wet and dry conditions and chemical media (e.g., sulfate erosion). This indicates that using a higher dosage of alkali activator can promote the complete reaction and depletion of the precursors to form geopolymers with high compressive strength. Such geopolymers contain little or no unreacted precursors, thus losing their reactive self-reinforcing function under harsh environments such as alternating wet and dry conditions and chemical media (e.g., sulfate erosion). This also demonstrates that only by using a reaction system with appropriate mass ratios can geopolymers with suitable 28-day compressive strength and reactive self-reinforcing function be prepared.

[0037] In Comparative Example 3, simply increasing the amount of alkali activator and decreasing its modulus resulted in a geopolymer with higher 28-day compressive strength, but it lost the reactive self-reinforcing function exhibited by geopolymers under harsh environments such as alternating wet and dry conditions and chemical media (e.g., sulfate erosion). This indicates that using a higher dosage of alkali activator can promote the complete reaction and depletion of precursors to form a geopolymer with high compressive strength. This results in geopolymers containing little or no unreacted precursors, thus causing them to lose their reactive self-reinforcing function under harsh environments such as alternating wet and dry conditions and chemical media (e.g., sulfate erosion). This also demonstrates that only by using a reaction system with appropriate mass ratios can geopolymers with suitable 28-day compressive strength and reactive self-reinforcing function be prepared.

[0038] In Comparative Example 4, excessively increasing the dosage and modulus of the alkali activator resulted in a geopolymer exhibiting higher 28-day compressive strength and a 5.1% increase in the rate of change of compressive strength after 14 days of chemical erosion. However, it lost the reactive self-reinforcing function exhibited by geopolymers in alternating wet and dry environments. This indicates that using excessively high dosages and moduli of the alkali activator can promote the complete reaction and depletion of precursors to form geopolymers with high compressive strength and high density. This results in the absence of unreacted precursors in such geopolymers, thus causing them to lose their reactive self-reinforcing function in alternating wet and dry environments. The compressive strength change rate of the geopolymer prepared in Comparative Example 4 increased by 5.1% after 14 days of chemical erosion. This is because, under the sodium sulfate erosion environment, in addition to water penetration, sulfate ions that penetrate into the pores and microcracks of this high-density geopolymer also participate in the reaction, generating trace amounts of ettringite or gypsum crystal micro-expansion products. In the confined space within the pores and microcracks of the geopolymer, these micro-expansion products play a positive role in densification, thereby increasing the compressive strength change rate of this high-density geopolymer.

[0039] After sampling and injecting the reaction system prepared in Example 1 into molds, samples were taken at different curing periods (3 days, 7 days, and 28 days, according to the first and second curing conditions in Example 1) for XRD testing. The test results are shown below. Figure 1 .

[0040] Depend on Figure 1 It is known that all samples of different ages exhibited significant diffuse scattering peaks within the 2θ range of 20°–35°, proving the formation of an amorphous gel phase. Meanwhile, in Figure 1 The clearly visible sharp characteristic peaks of SiO2 (derived from metakaolinite) and TiO2 (derived from metakaolinite) indicate that the reaction system retains an incompletely reacted metakaolinite framework, constituting a "potential reaction reservoir." Furthermore, the presence of a CaCO3 (derived from slag) characteristic peak at 28 days of curing confirms the retention of an incompletely reacted slag framework within the system. Additionally, the enhanced CaCO3 peak in the 28-day spectrum indicates a benign mineralization reaction occurred in the matrix during the later stages of curing, with the generated calcium carbonate microcrystals further filling the micropores and promoting matrix densification.

[0041] Before and after the 12 wet-dry alternation tests mentioned in Table 1, the geopolymer prepared in Example 1 was sampled and its morphology was compared using scanning electron microscopy. The comparison results are shown in [reference]. Figure 2 and Figure 3 .

[0042] exist Figure 2 In the study, it can be observed that the geopolymer prepared in Example 1 encapsulates a large number of unreacted slag and metakaolin particles with smooth surfaces and clear edges before 12 wet-dry alternation tests; in addition, there are certain native micropores in the geopolymer structure.

[0043] exist Figure 3 In the experiment, it was observed that after 12 cycles of wet-dry alternation, the geopolymer prepared in Example 1 exhibited numerous nanoscale dissolution pits on the surface of the previously unreacted slag and metakaolin particles, indicating that they dissolved and reacted under the stimulation of moisture in the wet-dry alternation environment. At the same time, newly formed dense flocculent gels were observed around the slag and metakaolin particles and in the original pores. This in-situ filling effect directly led to the improvement of the macroscopic strength of the geopolymer, which confirms the data in Table 1 that the compressive strength of the geopolymer prepared in Example 1 increased by 42.5% after 12 cycles of wet-dry alternation.

[0044] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A method for preparing a geopolymer with self-reinforcing properties, characterized in that, include: The precursor was obtained by mixing metakaolin and slag at a mass ratio of 4:

6. The alkali activator, water and the precursor were mixed at a mass ratio of 4:35:100 to obtain a reaction system; the reaction system was injected into a mold, and after a first curing, it was demolded, and then after a second curing, a geopolymer with self-reinforcing function was obtained. The alkaline activator includes water glass with a modulus of 1.5; The first type of curing is room temperature curing or heated curing; the second type of curing is natural curing at room temperature.

2. The method for preparing the self-reinforcing geopolymer as described in claim 1, characterized in that, When the first type of curing is room temperature curing, the curing conditions include a curing temperature of 20±5℃, a relative humidity of ≥95%, and a curing time of 1~3 days.

3. The method for preparing the geopolymer with self-reinforcing function as described in claim 1, characterized in that, When the first curing is heat curing, the curing conditions used include steam curing or oven curing, with a curing temperature of 40~80℃ and a curing time of 6~24h.

4. The method for preparing the geopolymer with self-reinforcing function as described in claim 2, characterized in that, The second maintenance procedure takes 25 to 27 days.

5. The method for preparing the geopolymer with self-reinforcing function as described in claim 3, characterized in that, The second maintenance period is 27 to 27.75 days.

6. A geopolymer with self-reinforcing properties, characterized in that, It is prepared using the method for preparing a self-reinforcing geopolymer as described in claim 4 or 5.

7. The geopolymer with self-reinforcing function as described in claim 6, characterized in that, The compressive strength after 28 days is not less than 30 MPa.

8. The application of the self-reinforcing geopolymer as described in claim 7 in alternating wet and dry environments, characterized in that, The compressive strength of the geopolymer increases by at least 40% after 12 cycles of wet-dry cycles. The dry-wet alternating environment uses a dry environment temperature of 60±2℃, a relative humidity of ≤ 50%, and a single dry environment application time of 12h. The wet and dry alternating environment uses a wet environment temperature of 20±2℃, a relative humidity of ≥95%, and a single wet environment application time of 12h.

9. The application of the self-reinforcing geopolymer as described in claim 7 in a chemically corrosive environment, characterized in that, The compressive strength of the geopolymer increases by at least 20% after 14 days of application in a chemically corrosive environment. The chemical erosion environment used in the chemical medium erosion environment has a chemical medium erosion temperature of 20±2℃; The chemical medium includes a 5% sodium sulfate solution by mass.

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