A composition for geopolymer, geopolymer and application thereof

Abstract

This invention relates to the field of building materials technology, and discloses a geopolymer composition, a geopolymer, and its applications. The composition comprises: a precursor, standard sand, an alkali activator, a shrinkage-reducing agent, and water; the standard sand content is 200-300 parts by weight relative to 100 parts by weight of the precursor; the alkali activator content is 10-16 parts by weight; the shrinkage-reducing agent content is 6-12 parts by weight; and the water content is 32-37 parts by weight; the shrinkage-reducing agent is a magnesium silicate mineral and / or a magnesium carbonate mineral; the median particle size of the shrinkage-reducing agent is 6-20 μm; and the modulus of the alkali activator is 0.4-0.8. The geopolymer prepared based on this composition has the characteristics of good shrinkage reduction effect, high strength, and good durability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a geopolymer composition, geopolymer, and its applications. Background Technology

[0002] Geopolymers are a novel type of green cementitious material, considered one of the most promising candidates to replace traditional silicate cement. The main raw materials used in their preparation are typically solid powders rich in silica (SiO2) and alumina (Al2O3), such as fly ash, slag, metakaolin, coal gangue, and other industrial solid wastes. Under the action of alkaline activators (such as sodium hydroxide, potassium hydroxide, and water glass), these silica-alumina materials undergo desilication, dealumination reactions, and subsequent polycondensation reactions to generate a three-dimensional network gel structure dominated by NASH or CASH, thereby endowing geopolymers with excellent mechanical properties and durability. Compared with traditional silicate cement, geopolymers can reduce carbon dioxide emissions by 20-50% and implicit energy consumption by more than 40% during production, thus showing broad application prospects in the context of carbon neutrality and sustainable development.

[0003] However, the practical application of geopolymers as building materials still faces significant challenges, with shrinkage being a particularly prominent issue. Studies have shown that their autogenous shrinkage and drying shrinkage rates are often 5-7 times that of silicate cement. Excessive shrinkage deformation can easily lead to cracks in concrete structures, thereby weakening the structural load-bearing capacity, posing potential durability hazards and safety risks, and in severe cases, even causing structural failure.

[0004] To address the above issues, common measures for inhibiting systolic contraction mainly include the following categories:

[0005] 1. Adding shrinkage-reducing agents or expanding agents: Shrinkage-reducing agents can reduce capillary tension to some extent, but may interfere with the formation of gel structures, such as altering the polymerization state of chain silicates. Simultaneously, the inherently high alkalinity (high pH) of geopolymer systems may cause some shrinkage-reducing agents to become ineffective or less effective, and their long-term stability remains questionable. Expanding agents (such as activated MgO, gypsum, etc.) counteract shrinkage strain by generating expansive hydration products (such as hydrotalcite, ettringite, Aft). However, the effectiveness of this method is significantly limited: on the one hand, the expansion effect is highly dependent on the dosage, activity, and reaction timing of the additive; on the other hand, if the dosage is too high, it may lead to excessive expansion in the later stages, thereby triggering new cracking risks.

[0006] 2. Regulating the internal humidity environment: The introduction of internal curing agents can alleviate self-shrinkage to some extent, but it is almost ineffective against drying shrinkage. In an open system, once the humidity of the slurry reaches equilibrium with the external environment, the formation mechanism of capillary stress is not eliminated by internal water storage. In addition, the introduction of internal curing agents may have a negative impact on mechanical properties such as compressive strength.

[0007] 3. External curing condition control: Steam curing is a common measure for controlling external humidity and temperature, which can significantly improve drying shrinkage. However, it has high energy consumption and complex process, making it difficult to promote and apply in large-scale projects.

[0008] In summary, existing shrinkage control methods all have certain shortcomings: they either have limited effectiveness, insufficient stability, or are difficult to apply on a large scale in engineering practice. Therefore, there is an urgent need to propose a more efficient and operable shrinkage control approach to solve the engineering challenges posed by the high shrinkage of geopolymer systems. Summary of the Invention

[0009] The purpose of this invention is to provide a geopolymer with good shrinkage effect, high strength, and good durability.

[0010] Specifically, in order to achieve the above objectives, a first aspect of the present invention provides a composition for geopolymers, the composition comprising: a precursor, standard sand, an alkali activator, a shrinkage reducing agent, and water;

[0011] The content of the standard sand is 200-300 parts by weight relative to 100 parts by weight of the precursor; the content of the alkali activator is 10-16 parts by weight; the content of the shrinkage reducer is 6-12 parts by weight; and the content of water is 32-37 parts by weight.

[0012] The shrinkage reducing agent is a magnesium silicate mineral and / or a magnesium carbonate mineral;

[0013] The median particle size of the shrinkage-reducing agent is 6-20 μm;

[0014] The modulus of the alkali activator is 0.4-0.8.

[0015] A second aspect of the present invention provides a geopolymer obtained by mixing the components of the composition described in the first aspect.

[0016] A third aspect of the invention provides a geopolymer composition as described in the first aspect and the application of the geopolymer as described in the second aspect in building materials.

[0017] Compared with the prior art, the present invention has at least the following advantages:

[0018] (1) The shrinkage-reducing agent provided by the present invention can be used as an active magnesium component to participate in the geopolymer reaction process, promote the generation of expansive products such as hydrotalcite, alkali silicate gel and hydrated magnesium silicate gel, and chemically counteract the shrinkage driving force.

[0019] (2) The shrinkage reducing agent provided by the present invention has a significant crystal structure and a stable phase generated by its reaction (including partially hydrated magnesium silicate gel, unreacted mineral particles, etc.), which can be uniformly dispersed in the geopolymer as a micro-rigid filling phase. By filling the pores, the pore size is refined and the capillary pore negative pressure is reduced; local rigid nodes or reinforcing networks are formed, which hinder the shrinkage and deformation of the matrix gel phase at the microscale. Attached Figure Description

[0020] Figure 1 This is a SEM image of the geopolymer prepared in Example 1 of the present invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] In this invention, the particle size refers to the diameter of the particle;

[0023] The magnesium silicate minerals refer to minerals that mainly contain magnesium silicates, and the magnesium carbonate minerals refer to minerals that mainly contain magnesium carbonates.

[0024] The median particle size (D50) refers to the particle diameter that corresponds to a cumulative distribution percentage of 50% in the particle group.

[0025] The modulus of the alkali activator refers to the molar ratio of silicon dioxide (SiO2) to sodium oxide (Na2O) in the alkali activator.

[0026] As previously described, a first aspect of the present invention provides a composition for geopolymers, the composition comprising: a precursor, standard sand, an alkali activator, a shrinkage reducing agent, and water;

[0027] The content of the standard sand is 200-300 parts by weight relative to 100 parts by weight of the precursor; the content of the alkali activator is 10-16 parts by weight; the content of the shrinkage reducer is 6-12 parts by weight; and the content of water is 32-37 parts by weight.

[0028] The shrinkage reducing agent is a magnesium silicate mineral and / or a magnesium carbonate mineral;

[0029] The median particle size of the shrinkage-reducing agent is 6-20 μm;

[0030] The modulus of the alkali activator is 0.4-0.8.

[0031] The inventors of this invention discovered in their research that geopolymers prepared using magnesium silicate minerals and / or magnesium carbonate minerals as shrinkage reducing agents, compared to those prepared using pure substances (magnesium silicate, magnesium carbonate compounds, etc.) as shrinkage reducing agents, can exert the synergistic effect of multiple active components in the minerals. In geopolymers, nucleation densification and moderate expansion compensation effects are provided simultaneously, thereby more effectively suppressing shrinkage, reducing the risk of cracking, and improving service performance.

[0032] This invention specifically limits the median particle size of the shrinkage-reducing agent to the aforementioned range, which can effectively fill the micropores in the geopolymer matrix, reduce the generation of capillary stress, and at the same time ensure the reactivity of the shrinkage-reducing agent in an alkaline environment. Thus, while inhibiting shrinkage, it promotes the densification of the matrix structure. Furthermore, the alkaline activator with a specific modulus can ensure that the precursor silicon-aluminum components are fully dissolved and hydrated, so that the resulting geopolymer has sufficient early and late strength. The aforementioned technical features, combined with the magnesium silicate mineral and / or magnesium carbonate mineral shrinkage-reducing agent specifically used in this invention, can promote the synergistic formation of MSH gel, hydrotalcite or highly hygroscopic amorphous silica and alkali silicate (ASR) gel at the microscopic level, significantly reduce self-shrinkage and drying shrinkage at the macroscopic level, and improve the volume stability, mechanical properties and durability of the material, thereby producing geopolymer materials with controllable shrinkage, excellent strength and excellent long-term service performance.

[0033] In a preferred embodiment, the shrinkage reducing agent is a combination of magnesium silicate minerals and magnesium carbonate minerals.

[0034] Preferably, the mass ratio of the magnesium silicate mineral to the magnesium carbonate mineral is 1.5-4.0:1.

[0035] In a preferred embodiment, the content of magnesium silicate and / or magnesium carbonate in the shrinkage-reducing agent is >85%. The inventors discovered that under these preferred conditions, magnesium ions are readily dissolved, reacting with magnesium silicate or magnesium carbonate components in an alkaline environment to generate MSH gel and hydrotalcite, achieving pore filling and moderate expansion compensation, significantly improving the volume stability of the system. Compared to using pure magnesium oxide as a shrinkage-reducing agent, the magnesium silicate and / or magnesium carbonate minerals used in this invention can achieve a more balanced and controllable shrinkage inhibition effect at lower dosages, avoiding the risk of excessive expansion and cracking in the later stages due to excessive dosage, and ensuring that the system maintains good mechanical properties and durability while improving volume stability.

[0036] According to a preferred embodiment, the shrinkage reducing agent is selected from at least one of serpentine, dolomite, magnesite, forsterite, and talc.

[0037] Preferably, the shrinkage-reducing agent is a combination of serpentine, magnesite, and talc. Under these preferred conditions, the inventors discovered that the shrinkage-reducing agent can induce the formation of MSH gel and hydrotalcite phase in an alkaline environment, accompanied by the formation of a certain amount of highly absorbent alkali silicate (ASR) gel. The incompletely reacted mineral particles can also fill the pores, thereby making the system structure more compact and possessing a good shrinkage compensation effect.

[0038] Preferably, the mass ratio of the serpentine, the magnesite, and the talc is 1:0.5-1.2:0.3-1.0.

[0039] More preferably, the mass ratio of the serpentine, the magnesite, and the talc is 1:0.8-1.2:0.5-1.0.

[0040] In a preferred embodiment, the shrinkage-reducing agent is prepared by an operation comprising the following steps: grinding the magnesium silicate mineral and / or the magnesium carbonate mineral to obtain the shrinkage-reducing agent.

[0041] This invention does not impose any particular limitation on the specific grinding method, as long as the median particle size of the shrinkage-reducing agent is 6-20 μm. Those skilled in the art can select the appropriate method based on known techniques. This invention will not be described in detail here, and those skilled in the art should not construe this as a limitation of the invention.

[0042] In a preferred embodiment, the precursor is selected from at least one of mineral powder, fly ash, metakaolin, silica fume, and metallurgical slag powder.

[0043] Preferably, the mineral powder is selected from at least one of S75 grade mineral powder, S95 grade mineral powder, and S105 grade mineral powder. The grading of the mineral powder shall comply with the Chinese national standard GB / T 18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete".

[0044] Preferably, the fly ash is Grade I fly ash and / or Grade II fly ash. The classification of the fly ash conforms to the Chinese national standard GB / T 1596-2017 "Fly Ash for Cement and Concrete".

[0045] The present invention does not have any special requirements on the source of the metakaolin; it can be commercially available or self-made. Furthermore, there are no special requirements on the self-made method; it can be prepared using methods known in the art.

[0046] Preferably, the SiO2 content of the silica fume is ≥90wt%.

[0047] Preferably, the metallurgical slag powder is nickel-iron slag powder.

[0048] In a preferred embodiment, the standard sand has a particle size range of 0.08-2 mm, a silica content of >96 wt%, and a loss on ignition of ≤0.4 wt%.

[0049] In this invention, the particle size range of the standard sand refers to a minimum particle size ≥ 0.08 mm and a maximum particle size ≤ 2 mm.

[0050] In a preferred embodiment, the alkaline activator is a combination of sodium hydroxide and sodium silicate.

[0051] Preferably, the solid content of the sodium silicate is 32-38 wt%.

[0052] A second aspect of the invention provides a geopolymer obtained by mixing the components of the composition described in the first aspect.

[0053] Preferably, the method for preparing the geopolymer utilizes the components of the composition described in the first aspect, and the method includes:

[0054] (1) The precursor is first mixed with standard sand to obtain mixture I; and the alkali activator is second mixed with mixture I to obtain mixture II;

[0055] (2) Mix the mixture II with water for a third time to obtain mixture III;

[0056] (3) Mix the mixture III with the shrinkage reducer in a fourth mixing to obtain the geopolymer.

[0057] In this invention, the first mixing, the second mixing, the third mixing, and the fourth mixing are each carried out independently under stirring conditions.

[0058] According to a preferred embodiment, the conditions for the first mixing and the second mixing each independently include: a rotation speed of 130-150 rpm, a time of 2-6 min, and a temperature of 20-35°C.

[0059] According to another preferred embodiment, the conditions for the third mixing and the fourth mixing each independently include: a rotation speed of 250-350 rpm, a time of 4-8 min, and a temperature of 20-35℃.

[0060] The third aspect of the invention provides a geopolymer composition as described in the first aspect and the application of the geopolymer as described in the second aspect in building materials.

[0061] The present invention will be described in detail below through examples. Unless otherwise specified, specific experimental steps or conditions in the following examples can be performed according to known experimental steps or conditions described in the literature in this field. Unless otherwise specified, the raw materials or instruments used are commercially available. Unless otherwise specified, the reaction temperature in the following examples is at room temperature, which refers to 25±2℃.

[0062] In the examples below, each part by weight represents 4.5g.

[0063] Shrinkage reducer:

[0064] Shrinkage reducer M1: It is obtained by mixing serpentine powder, magnesite powder and talc powder in a mass ratio of 1:0.8:0.5; the median particle size is 11µm.

[0065] Shrinkage reducer M2: Serpentine powder with a median particle size of 7µm was obtained by ball milling and screening serpentine (a magnesium silicate mineral).

[0066] Shrinkage reducer M3: Magnesite powder with a median particle size of 20µm was obtained by ball milling and screening magnesite (a magnesium carbonate mineral).

[0067] Shrinkage reducer M4: Talc powder with a median particle size of 15µm was obtained by ball milling and screening talc (a magnesium silicate mineral).

[0068] Shrinkage reducer M5: It is obtained by mixing serpentine powder and magnesite powder in a mass ratio of 1:1; the median particle size is 13.5µm.

[0069] Shrinkage reducer DM1: A shrinkage reducer with a median particle size of 30µm is obtained by ball milling serpentine, magnesite and talc in a mass ratio of 1:0.8:0.5.

[0070] Shrinkage reducer DM2: It is obtained by ball milling serpentine, magnesite and talc in a mass ratio of 1:0.8:0.5 and then screening to obtain a median particle size of 2µm.

[0071] Shrinkage reducer DM3: Magnesium oxide with a median particle size of 2.5µm.

[0072] Shrinkage reducer DM4: calcium oxide with a median particle size of 5µm.

[0073] Shrinkage reducer DM5: Magnesium silicate with a median particle size of 7µm.

[0074] Precursor:

[0075] Mineral powder: S95 grade mineral powder, purchased from Hunan Sanhong Building Materials Co., Ltd.

[0076] Metakaolin: Purchased from Inner Mongolia Chaopai New Materials Co., Ltd.

[0077] Fly ash: Grade II fly ash, purchased from China Resources Power Co., Ltd.

[0078] Standard sand:

[0079] Chinese ISO standard sand was purchased from Xiamen Aisiou Standard Sand Co., Ltd.

[0080] Alkali activator:

[0081] Alkali activator I: a combination of sodium hydroxide and sodium silicate, with the sodium silicate having a solid content of 35.8 wt% and a modulus of 0.5.

[0082] Alkali activator II: a combination of sodium hydroxide and sodium silicate, with the sodium silicate having a solid content of 35.8 wt% and a modulus of 1.0.

[0083] Alkali activator III: a combination of sodium hydroxide and sodium silicate, with the sodium silicate having a solid content of 35.8 wt% and a modulus of 0.6.

[0084] Example 1

[0085] (1) The mineral powder and standard sand are first mixed to obtain mixture I; and the alkali activator I is second mixed with mixture I to obtain mixture II;

[0086] (2) Mixture II is mixed with water for the third time to obtain mixture III;

[0087] (3) Mixture III and shrinkage-reducing agent M1 are mixed for the fourth time to obtain geopolymer;

[0088] Of which, relative to 100 parts by weight of mineral powder, the content of standard sand is 300 parts by weight; the content of alkali activator I is 12 parts by weight; the content of shrinkage reducer M1 is 10 parts by weight; and the content of water is 36 parts by weight.

[0089] The conditions for the first mixing are: 140 rpm, 4 min, and 25°C.

[0090] The conditions for the second mixing are: 140 rpm, 4 min, and 25°C.

[0091] The conditions for the third mixing process include: a rotation speed of 285 rpm, a time of 6 min, and a temperature of 25°C.

[0092] The conditions for the fourth mixing were: 285 rpm, 4 min, and 25°C.

[0093] Example 2

[0094] (1) The mineral powder and standard sand are first mixed to obtain mixture I; and the alkali activator III is second mixed with mixture I to obtain mixture II;

[0095] (2) Mixture II is mixed with water for the third time to obtain mixture III;

[0096] (3) Mixture III and shrinkage-reducing agent M1 are mixed for the fourth time to obtain geopolymer;

[0097] Of which, relative to 100 parts by weight of mineral powder, the content of standard sand is 300 parts by weight; the content of alkali activator III is 10 parts by weight; the content of shrinkage reducer M1 is 12 parts by weight; and the content of water is 32 parts by weight.

[0098] The conditions for the first mixing are: 150 rpm, 6 min, and 20°C.

[0099] The conditions for the second mixing are: a rotation speed of 130 rpm, a time of 2 min, and a temperature of 25°C.

[0100] The conditions for the third mixing process include: a rotation speed of 300 rpm, a time of 6 min, and a temperature of 35°C.

[0101] The conditions for the fourth mixing process include: a rotation speed of 300 rpm, a time of 6 min, and a temperature of 35°C.

[0102] Example 3

[0103] (1) Fly ash and standard sand are first mixed to obtain mixture I; and alkali activator I is second mixed with mixture I to obtain mixture II;

[0104] (2) Mixture II is mixed with water for the third time to obtain mixture III;

[0105] (3) Mixture III and shrinkage-reducing agent M1 are mixed for the fourth time to obtain geopolymer;

[0106] Of which, relative to 100 parts by weight of fly ash, the content of standard sand is 200 parts by weight; the content of alkali activator I is 16 parts by weight; the content of shrinkage reducer M1 is 6 parts by weight; and the content of water is 32 parts by weight.

[0107] The conditions for the first mixing are: 130 rpm, 2 min, and 35°C.

[0108] The conditions for the second mixing are: 150 rpm, 6 min, and 20°C.

[0109] The conditions for the third mixing process include: a rotation speed of 350 rpm, a time of 4 min, and a temperature of 30°C.

[0110] The conditions for the fourth mixing process include: a rotation speed of 350 rpm, a time of 6 min, and a temperature of 35°C.

[0111] Example 4

[0112] The same method as in Example 1 was used, except that shrinkage agent M1 in step (3) was replaced with an equal mass of shrinkage agent M2 to obtain the geopolymer.

[0113] Example 5

[0114] The same method as in Example 1 was used, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent M3 to obtain the geopolymer.

[0115] Example 6

[0116] The same method as in Example 1 was used, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent M4 to obtain the geopolymer.

[0117] Example 7

[0118] The same method as in Example 1 was used, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent M5 to obtain the geopolymer.

[0119] Comparative Example 1

[0120] (1) The mineral powder and standard sand are first mixed to obtain mixture I; and the alkali activator II is second mixed with mixture I to obtain mixture II;

[0121] (2) Mixture II is mixed with water for the third time to obtain mixture III;

[0122] (3) Mixture III and shrinkage-reducing agent M1 are mixed for the fourth time to obtain geopolymer;

[0123] Of which, relative to 100 parts by weight of mineral powder, the content of standard sand is 300 parts by weight; the content of alkali activator II is 18 parts by weight; the content of shrinkage reducer M1 is 10 parts by weight; and the content of water is 30 parts by weight.

[0124] The conditions for the first mixing are: 140 rpm, 4 min, and 25°C.

[0125] The conditions for the second mixing are: 140 rpm, 4 min, and 25°C.

[0126] The conditions for the third mixing process include: a rotation speed of 285 rpm, a time of 6 min, and a temperature of 25°C.

[0127] The conditions for the fourth mixing were: 285 rpm, 4 min, and 25°C.

[0128] Comparative Example 2

[0129] The same method as Comparative Example 1 was used, except that shrinkage reducing agent M1 in step (3) was replaced with an equal mass of shrinkage reducing agent M2 to obtain geopolymer.

[0130] Comparative Example 3

[0131] The same method as Comparative Example 1 was used, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent M3 to obtain geopolymer.

[0132] Comparative Example 4

[0133] The same method as Comparative Example 1 was used, except that shrinkage reducing agent M1 in step (3) was replaced with an equal mass of shrinkage reducing agent M4 to obtain geopolymer.

[0134] Comparative Example 5

[0135] The process was carried out in a similar manner to Comparative Example 1, except that no shrinkage-reducing agent was added. Specifically, (1) mineral powder and standard sand were first mixed to obtain mixture I; and alkali activator II was second mixed with mixture I to obtain mixture II.

[0136] (2) Mixture II is mixed with water for a third time to obtain the geopolymer;

[0137] The types and amounts of the remaining components remained unchanged.

[0138] Comparative Example 6

[0139] The same method as Comparative Example 1 was used, except that shrinkage reducing agent M1 in step (3) was replaced with an equal mass of shrinkage reducing agent DM1 to obtain geopolymer.

[0140] Comparative Example 7

[0141] The same method as Comparative Example 1 was used, except that shrinkage reducing agent M1 in step (3) was replaced with an equal mass of shrinkage reducing agent DM2 to obtain geopolymer.

[0142] Comparative Example 8

[0143] The process was carried out in a similar manner to that in Example 1, except that no shrinkage-reducing agent was added. Specifically, (1) mineral powder and standard sand were first mixed to obtain mixture I; and alkali activator I was second mixed with mixture I to obtain mixture II.

[0144] (2) Mixture II is mixed with water for a third time to obtain the geopolymer;

[0145] The types and amounts of the remaining components remained unchanged.

[0146] Comparative Example 9

[0147] The process was carried out using a method similar to that in Example 1, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent DM1 to obtain the geopolymer.

[0148] Comparative Example 10

[0149] The same method as in Example 1 was used, except that shrinkage agent M1 in step (3) was replaced with an equal mass of shrinkage agent DM2 to obtain the geopolymer.

[0150] Comparative Example 11

[0151] The same method as in Example 1 was used, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent DM3 to obtain the geopolymer.

[0152] Comparative Example 12

[0153] The same method as in Example 1 was used, except that shrinkage agent M1 in step (3) was replaced with an equal mass of shrinkage agent DM4 to obtain the geopolymer.

[0154] Comparative Example 13

[0155] The process was carried out using a method similar to that in Example 1, except that shrinkage-reducing agent M1 in step (3) was replaced with an equal mass of shrinkage-reducing agent DM5 to obtain the geopolymer.

[0156] Comparative Example 14

[0157] The method was similar to that in Example 1, except that the mineral powder in step (1) was replaced with an equal mass of metakaolin, and the shrinkage reducer M1 in step (3) was replaced with an equal mass of shrinkage reducer DM1 to obtain the geopolymer.

[0158] The present invention provides, by way of example, SEM images of the geopolymer prepared in Example 1, as follows: Figure 1As shown in the figure, layered and flocculent CASH gels are uniformly distributed in each product and form the main hydration products, thus providing a good structural framework for the material. Simultaneously, a large amount of MSH gel and hydrotalcite crystals are generated. These products are tightly bonded together and effectively fill the pores, significantly densifying the system structure and providing a micro-expansion effect to some extent. The geopolymer obtained in this invention not only has a richer variety of microstructure product phases but also a more uniform distribution. The formation of MSH and hydrotalcite not only improves the volume stability and crack resistance of the gel structure but also endows the material with excellent durability. Therefore, the geopolymer of this invention exhibits significant advantages in shrinkage control and service performance.

[0159] Test Example 1

[0160] The geopolymers prepared in the examples and comparative examples were tested according to the following methods:

[0161] (1) The self-shrinkage strain of the geopolymer was determined by using the non-contact bellows shrinkage and expansion method, referring to the American standard ASTM C1698-2009.

[0162] (2) The drying shrinkage strain of the geopolymer was determined with reference to GB / T 29417-2012 Test Method for Drying Shrinkage Cracking Performance of Cement Mortar and Concrete.

[0163] (3) The 28-day strength of the geopolymer was measured with reference to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0164] The test results are shown in Table 1.

[0165] Table 1

[0166]

[0167] As can be seen from the results in Table 1, the geopolymer prepared by the geopolymer composition provided by the present invention has low self-shrinkage and drying shrinkage properties, demonstrating good shrinkage reduction effect and high volume stability, while also having high strength and good durability.

[0168] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for geopolymer, characterized by, The composition comprises: a precursor, standard sand, an alkali activator, a shrinkage reducing agent, and water; The content of the standard sand is 200-300 parts by weight, the content of the alkali activator is 10-16 parts by weight, the content of the shrinkage reducing agent is 6-12 parts by weight, and the content of the water is 32-37 parts by weight, relative to 100 parts by weight of the precursor; The shrinkage reducing agent is a magnesium-containing silicate mineral and / or a magnesium-containing carbonate mineral; The median particle size of the shrinkage reducing agent is 6-20 μm; The modulus of the alkali activator is 0.4-0.8; The precursor is selected from at least one of mineral powder, fly ash, metakaolin, silica fume, and metallurgical slag powder.

2. The composition of claim 1, wherein, The shrinkage reducing agent is a combination of a magnesium-containing silicate mineral and a magnesium-containing carbonate mineral. The mass ratio of the magnesium-containing silicate mineral to the magnesium-containing carbonate mineral is 1.5-4.0:

1.

3. The composition according to claim 1 or 2, characterized in that, The shrinkage reducing agent is selected from at least one of serpentine, dolomite, magnesite, forsterite, and talc.

4. The composition of claim 3, wherein, The shrinkage reducing agent is a combination of serpentine, magnesite, and talc.

5. The composition of claim 4, wherein, The mass ratio of the serpentine, the magnesite, and the talc is 1:0.5-1.2:0.3-1.

0.

6. The composition according to claim 1 or 2, characterized in that, The particle size of the standard sand is in the range of 0.08-2 mm, the content of silicon dioxide is >96 wt%, and the loss on ignition is ≤0.4 wt%.

7. The composition according to claim 1 or 2, characterized in that, The alkali activator is a combination of sodium hydroxide and sodium water glass.

8. A geopolymer, characterized in that, The geopolymer is obtained by mixing the components in the composition of any one of claims 1-7.

9. Use of the geopolymer of any one of claims 1-7 or the geopolymer of claim 8 in building materials.

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