A method for preparing active kaolinite clay through synergistic activation and its application as auxiliary cementitious material

Abstract

The present invention discloses a method for preparing active kaolinite clay by synergistic activation and its application as an auxiliary cementitious material, belonging to the technical field of auxiliary cementitious material production. The present invention combines thermal activation with mechanochemical activation to synergistically treat kaolinite clay, giving full play to the advantages of thermal activation and mechanochemical activation, maximizing the activity of clay minerals and non-clay minerals in kaolinite clay, realizing low-carbonization activation of kaolinite clay, and providing technical guarantee for the preparation of auxiliary cementitious materials (SCMs).

Description

Technical Field

[0001] The present invention belongs to the technical field of auxiliary gelling material production, and in particular relates to a method for preparing active kaolinite clay through synergistic activation and an application of the method as an auxiliary gelling material. Background Art

[0002] Kaolinite-based clays are a type of natural clay composed primarily of kaolinite, along with other clay and non-clay minerals. Kaolinite has a 1:1 (TO) structure consisting of a layer of silicon-oxygen tetrahedra sandwiched between a layer of aluminum-oxygen octahedra. Kaolinite-based clays, when incorporated into cement, generally serve as inert materials. To increase their activity, they require activation through effective methods, typically involving thermal and mechanochemical activation. Optimizing the activation process can yield highly active clay minerals. Compared to other clays, kaolinite-based clays have a wide distribution, a low thermal activation temperature, and their calcined products are excellent sources of activated alumina. Therefore, activated kaolinite-based clays have great potential for use as supplementary cementitious materials (SCMs) and exhibit excellent mechanical properties.

[0003] Kaolinite-based clays are typically thermally activated by high-temperature calcination. This dehydration, dehydroxylation, and amorphization of the primary clay mineral, kaolinite, results in a metakaolinite phase with highly variable structure and highly localized variations in the distribution of aluminum atoms, significantly enhancing volcanic ash activity. The dehydroxylation temperature for kaolinite is 400-600°C, lower than that of 2:1 clay minerals such as montmorillonite and illite, consisting of two layers of silicon-oxygen tetrahedra sandwiched between one layer of aluminum-oxygen octahedra. Currently, activated kaolinite-based clays are commonly prepared by calcining them at 700-800°C. Research has shown that mechanochemical activation can exploit the stress interactions of compression, shear (friction), impact, and collision during mechanical grinding to induce physical, crystalline, and chemical changes in the material. Mechanochemical activation significantly alters the crystal form and silicon-aluminum structure of clay minerals, effectively promoting delamination, dehydroxylation, and amorphization of clay minerals, leading to surface aluminum enrichment and significantly enhancing volcanic ash activity. Both activation methods have certain effects on improving the volcanic ash activity of kaolinite clay, but they also have certain drawbacks.

[0004] Calcination of kaolinite-based clays requires relatively high temperatures, which is inconsistent with the concepts of low carbon, environmental protection, and low energy consumption. Pure mechanochemical activation, typically performed using ball milling, planetary ball milling, and vibratory grinding, not only takes a long time and is inefficient to achieve optimal pozzolanic activity, but excessive grinding also reduces the pozzolanic activity of the clay minerals. Furthermore, the thermal activation temperatures of other clay minerals in kaolinite-based clays, such as montmorillonite and illite, are higher than those of kaolinite. The calcination temperature of kaolinite for optimal thermal activation is insufficient to dehydroxylate and amorphize the 2:1 clay minerals, such as montmorillonite and illite. If the calcination temperature is increased to ensure that the 2:1 clay minerals, such as montmorillonite and illite, reach the thermal activation temperature, kaolinite will recrystallize at this temperature, reducing its pozzolanic activity. Thermal activation cannot fully exploit the pozzolanic activity advantages of all clay minerals. Furthermore, non-clay mineral phases, such as feldspar and quartz, do not contribute to the clay's pozzolanic activity under thermal activation conditions. Therefore, thermal activation is no longer sufficient to maximize the pozzolanic activity of kaolinite-based clays. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a method for preparing active kaolinite clay by synergistic activation and its application as an auxiliary cementitious material. Based on thermal activation, the present invention combines mechanochemical activation to synergistically treat kaolinite clay, giving full play to the advantages of thermal activation and mechanochemical activation, maximizing the activity of clay minerals and non-clay minerals in kaolinite clay, realizing low-carbonization activation of kaolinite clay, and providing technical support for the preparation of supplementary cementitious materials (SCMs).

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing activated kaolinite clay by synergistic activation, comprising the following steps:

[0008] Performing a thermogravimetric analysis on the kaolinite clay, and performing a thermal activation treatment on the kaolinite clay using the peak temperature of the first-order thermogravimetric curve of the kaolinite clay as the thermal activation temperature point;

[0009] The kaolinite clay after the thermal activation treatment is subjected to a mechanochemical activation treatment to obtain the activated kaolinite clay.

[0010] Kaolinite-based clays are widely distributed, and their activated products are an excellent source of activated alumina, useful in the preparation of novel auxiliary cementitious materials. Current high-temperature calcination thermal activation systems struggle to effectively activate other clay and non-clay minerals in kaolinite-based clays, while mechanochemical activation systems suffer from long activation times and high energy consumption. The method of the present invention combines thermal activation with mechanochemical activation to synergistically treat kaolinite-based clays, achieving low-carbon activation while significantly enhancing volcanic ash activity, thereby producing high-quality, low-carbon auxiliary cementitious materials.

[0011] The kaolinite clay consists of 1:1 type kaolinite, other clay minerals and non-clay minerals.

[0012] Furthermore, the peak temperature of the first-order thermal gravimetric loss curve of the kaolinite clay is 525°C.

[0013] Furthermore, during the thermal activation treatment, the heating rate is 10°C / min and the holding time is 2h.

[0014] Furthermore, the mechanochemical activation treatment is a vibration mill.

[0015] Furthermore, the vibration mill adopts the following conditions: frequency of 50 Hz, power of 1.1 kW, and rotation speed of 1420 rpm.

[0016] Furthermore, the grinding time of the vibration mill is 20-100 min.

[0017] Preferably, the grinding time of the vibration mill is 20-40 min, more preferably the grinding time is 40 min.

[0018] The present invention also provides activated kaolinite clay prepared by the method.

[0019] The present invention also provides the use of the activated kaolinite clay as an auxiliary gelling material.

[0020] The present invention also provides a method for preparing cement mortar using the above-mentioned active kaolinite clay: PI cement, water, standard sand and the active kaolinite clay are uniformly mixed, the active kaolinite clay is used as an auxiliary cementitious material to replace 20% of the PI cement by mass, and the cement mortar is obtained after curing.

[0021] Exemplarily, the method for preparing cement mortar using the above-mentioned active kaolinite clay is as follows: 360 g of PI cement, 90 g of active kaolinite clay, 225 g of mixing water, and 1350 g of standard sand are weighed, and the above materials are added to a planetary cement mortar mixer, and stirred thoroughly and mixed evenly to obtain a mortar mortar;

[0022] The cement mortar is poured into a 40*40*1600mm mold, fully tamped, and vibrated on a vibration table for 60s. After the surface is smoothed, it is placed in a constant temperature and humidity curing box for curing to obtain the cement mortar.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] The present invention uses mechanochemical activation in conjunction with thermal activation to treat kaolinite clay, thereby crushing the particles and significantly increasing the specific surface area, while accelerating the transformation of the Al coordination form in kaolinite, that is, from hexacoordinate (Al(6)) to pentacoordinate (Al(5)) and tetracoordinate (Al(4)). Mechanochemical activation after thermal activation breaks the H bonds of adjacent kaolinite layers, increases the degree of structural disorder, and weakens the OH bond, thereby reducing the dehydroxylation temperature; porous aggregates are formed on the mineral surface after mechanical activation, which makes it easier to adsorb air water molecules, resulting in a significant increase in weight loss within the range of 50-200°C. Synergistic activation can significantly promote the complete delamination, dehydroxylation and amorphization of kaolinite, and can further enhance the volcanic ash activity of kaolinite clay compared to single thermal activation or mechanical activation.

[0025] The product prepared by mechanochemical activation and synergistic thermal activation (i.e., activated kaolinite clay) in the present invention is used as an auxiliary cementitious material to replace 20% of PI cement by mass. The 7-day (7d) and 28-day (28d) compressive strengths of the cement mortar test blocks were 43.8 MPa and 53.2 MPa, respectively, and the strength activity index (SAI) values ​​both reached over 100%. This is attributed to the fact that the auxiliary cementitious material formed by synergistic activation, the activated kaolinite clay, has stronger volcanic ash activity and consumes more portlandite. The hydration products formed contain more monosulfurized hydrated calcium sulfoaluminate (AFm phase), hydrated calcium aluminum feldspar, and hydrated calcium silicate (aluminum) gel (C-(A)-SH), thereby making the microstructure of the cementitious system more compact.

[0026] The present invention adopts a synergistic activation method to treat kaolinite clay, which is an effective method for activating clay minerals. It can improve the activation efficiency of clay minerals and non-clay minerals, realize low-carbon activation of clay resources, and alleviate the problems of traditional auxiliary cementitious materials such as insufficient supply and high cost. It is in line with the demand for environmentally friendly materials advocated by modern society and the goal of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 The thermogravimetric and first-order thermogravimetric analysis diagrams of kaolinite clay raw materials;

[0029] Figure 2 The particle size distribution diagram of the products of Comparative Examples 1-4 and Examples 1-5;

[0030] Figure 3 Microscopic morphology of the product of Comparative Example 1;

[0031] Figure 4 This is a microscopic morphology of the product of Comparative Example 2;

[0032] Figure 5 This is a microscopic morphology of the product of Comparative Example 3;

[0033] Figure 6 This is a microscopic morphology of the product of Example 1;

[0034] Figure 7 This is a microscopic morphology of the product of Example 2;

[0035] Figure 8 This is a microscopic morphology of the product of Example 3;

[0036] Figure 9 This is a microscopic morphology of the product of Example 4;

[0037] Figure 10 This is a microscopic morphology of the product of Example 5;

[0038] Figure 11 This is a microscopic morphology of the product of Comparative Example 4;

[0039] Figure 12 For the products of Comparative Examples 1-4 and Examples 1-5 27 Al solid-state NMR spectrum ( 27 Al SSNMR) images;

[0040] Figure 13 The X-ray diffraction (XRD) analysis spectra of the products of Comparative Examples 1-4 and Examples 1-5 are shown. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] An embodiment of the present invention provides a method for preparing activated kaolinite clay through synergistic activation, comprising the following steps:

[0047] The kaolinite clay was subjected to thermogravimetric analysis. The peak temperature (525°C) of the first-order thermogravimetric curve of the kaolinite clay was used as the thermal activation temperature. The kaolinite clay was thermally activated at a heating rate of 10°C / min and a holding time of 2h.

[0048] The thermally activated kaolinite clay was subjected to mechanochemical activation using a vibration mill to obtain activated kaolinite clay. The vibration mill was operated at a frequency of 50 Hz, a power of 1.1 kW, and a rotational speed of 1420 rpm. The grinding time was 20-100 minutes, preferably 20-40 minutes, and more preferably 40 minutes.

[0049] Kaolinite-based clays are widely distributed, and their activated products are an excellent source of activated alumina, useful in the preparation of novel auxiliary cementitious materials. Current high-temperature calcination thermal activation systems struggle to effectively activate other clay and non-clay minerals in kaolinite-based clays, while mechanochemical activation systems suffer from long activation times and high energy consumption. The method of the present invention combines thermal activation with mechanochemical activation to synergistically treat kaolinite-based clays, achieving low-carbon activation while significantly enhancing volcanic ash activity, thereby producing high-quality, low-carbon auxiliary cementitious materials.

[0050] During calcination, kaolinite undergoes dehydration, dehydroxylation, and recrystallization. The dehydration stage, which occurs at temperatures between 0 and 200°C, releases water molecules adsorbed in pores, structural channels, or bound to interlayer cations, without disrupting the crystal structures of the various mineral phases within the kaolinite. The dehydroxylation stage, which occurs at temperatures between 400 and 600°C, removes hydroxyl groups, disrupting the kaolinite's crystal structure. The silicon-oxygen tetrahedron and aluminum-oxygen octahedron structures shift, ultimately transforming into a volcanically active amorphous aluminosilicate phase called metakaolinite. The recrystallization phase transition occurs when the potentially active metakaolinite phase transforms to a stable, higher-temperature phase at thermal activation temperatures above 900°C. This phase represents a significant decrease in volcanic ash activity. At 925°C, metakaolinite transforms into aluminosilicate spinel (Al2O3·3SiO2) crystals and produces amorphous SiO2. At 1100°C, aluminosilicate spinel transforms into pseudomullite (Al2O3·SiO2). When the calcination temperature is increased to 1300°C, it transforms into mullite (3Al2O3·2SiO2) and cristobalite. The thermal activation temperature for kaolinite-based clays is generally selected to achieve complete dehydroxylation without reaching recrystallization, typically 600-800°C. This ensures a high degree of amorphization in the kaolinite-based clay, but this temperature is insufficient to enhance the activity of other 2:1 clay and non-clay minerals in the kaolinite-based clay. Furthermore, the high calcination temperature does not conform to low-carbon and environmentally friendly properties. Therefore, the present invention selects a lower thermal activation temperature point (the peak temperature point of kaolinite dehydroxylation), supplemented by mechanochemical activation, to activate the kaolinite clay by low carbonization while maximizing the volcanic ash activity of the kaolinite clay.

[0051] In the following examples and comparative examples of the present invention, kaolinite-based clays are composed of 1:1 kaolinite, other clay minerals, and non-clay minerals. 1:1 kaolinite refers to a layered silicate mineral whose structural unit layers are composed of silicon-oxygen tetrahedra (Si-O tetrahedra) and aluminum-oxygen octahedra (Al-(O,OH) octahedra).

[0052] The activated kaolinite-based clay provided in the embodiments of the present invention can be used as an auxiliary cementitious material to prepare cement mortar.

[0053] An embodiment of the present invention further provides a method for preparing cement mortar using the above-mentioned activated kaolinite clay: PI cement, water, standard sand and activated kaolinite clay are uniformly mixed, the activated kaolinite clay is used as an auxiliary cementitious material to replace 20% by mass of the PI cement, and cement mortar is obtained after curing.

[0054] Exemplarily, the method for preparing cement mortar using the above-mentioned active kaolinite clay is as follows: 360 g of PI cement, 90 g of active kaolinite clay, 225 g of mixing water, and 1350 g of standard sand are weighed, and the above materials are added to a planetary cement mortar mixer, and stirred thoroughly and mixed evenly to obtain a mortar mortar;

[0055] Pour the glue mortar into a 40*40*1600mm mold, tamp it thoroughly, vibrate it on a vibration table for 60s, smooth the surface, and place it in a constant temperature and humidity curing box for curing to obtain cement mortar.

[0056] In the following examples and comparative examples of the present invention, the flexural and compressive strengths of the mortar test blocks were measured according to GB / T 17671-2021 Test method for strength of cement mortar (ISO method), and the strength activity index was measured according to EN196-1:2016.

[0057] Kaolinite-based clays are widely distributed, and their activated products are an excellent source of activated alumina, useful in the preparation of novel auxiliary cementitious materials. Current high-temperature calcination thermal activation systems struggle to effectively activate other clay and non-clay minerals in kaolinite-based clays, while mechanochemical activation systems suffer from long activation times and high energy consumption. The method of the present invention combines thermal activation with mechanochemical activation to synergistically treat kaolinite-based clays, achieving low-carbon activation while significantly enhancing volcanic ash activity, thereby producing high-quality, low-carbon auxiliary cementitious materials.

[0058] In the following examples and comparative examples, the kaolinite-based clay consists of 1:1 kaolinite, other clay minerals, and non-clay minerals. The chemical compositions of the kaolinite-based clay and Portland cement with a strength grade of 42.5R (PI 42.5R) are shown in Table 1. The kaolinite-based clay contains 95.8% kaolinite, 1.0% illite, and 3.2% quartz.

[0059] Table 1 Chemical composition of raw materials (mass percentage)

[0060] Chemical composition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> <![CDATA[Na2O]]> Loss on ignition Kaolinite clay 36.59 29.82 0.94 0.02 0.05 0.15 0.31 13.99 PI 42.5R 20.16 4.68 3.51 62.49 4.04 2.30 0.71 0.046

[0061] Unless otherwise specified, the room temperature in the present invention is 25±2°C.

[0062] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention. For example, specific methods such as thermogravimetric analysis are all completed using conventional methods.

[0063] The technical solution of the present invention is further illustrated by the following examples.

[0064] Example 1

[0065] This embodiment provides a method for preparing activated kaolinite clay through synergistic activation, and the specific steps are as follows:

[0066] (1) After drying the kaolinite clay at 105°C, the thermogravimetric analysis was performed using a thermogravimetric analyzer ( Figure 1 ), selecting the peak temperature of the first-order thermal weight loss curve of 525°C as the thermal activation temperature point, and performing thermal activation treatment using a muffle furnace. During the thermal activation treatment, the kaolinite clay was placed in an alumina square box and calcined at 525°C for 2 hours at a heating rate of 10°C / min; after thermal activation, the alumina square box was removed from the muffle furnace, and the obtained product was spread on a steel plate and cooled under natural environmental conditions;

[0067] (2) A vibration mill with a frequency of 50 Hz, a power of 1.1 kW, and a rotation speed of 1420 rpm was further used for mechanochemical activation treatment. 50 g of sample was milled for 20 min each time. The ground powder was the activated kaolinite clay. The ground powder was immediately transferred to a sealed bag and stored at room temperature.

[0068] Example 2

[0069] Same as Example 1, except that the grinding time in step (2) is 40 min.

[0070] Example 3

[0071] Same as Example 1, except that the grinding time in step (2) is 60 min.

[0072] Example 4

[0073] Same as Example 1, except that the grinding time in step (2) is 80 min.

[0074] Example 5

[0075] Same as Example 1, except that the grinding time in step (2) is 100 min.

[0076] Comparative Example 1

[0077] Kaolinite clay samples were dried at 105°C.

[0078] Comparative Example 2

[0079] After the kaolinite clay was dried at 105°C, a thermogravimetric analysis was performed using a thermogravimetric analyzer. The peak temperature of the first-order thermogravimetric curve, 525°C, was selected as the thermal activation temperature point for thermal activation treatment. During the thermal activation treatment, the kaolinite clay was placed in an alumina square box and calcined at 525°C for 2 hours with a heating rate of 10°C / min. After thermal activation, the alumina square box was transferred out of the muffle furnace, and the obtained product was spread on a steel plate and cooled under natural environmental conditions to obtain activated kaolinite clay, which was then sealed and stored.

[0080] Comparative Example 3

[0081] After the kaolinite clay was dried at 105°C, a thermogravimetric analysis was performed using a thermogravimetric analyzer. The complete dehydroxylation temperature of 750°C was selected as the thermal activation temperature point for thermal activation treatment. During the thermal activation treatment, the kaolinite clay was placed in an alumina square box and calcined at 750°C for 2 hours with a heating rate of 10°C / min. After thermal activation, the alumina square box was transferred out of the muffle furnace, and the obtained product was spread on a steel plate and cooled under natural environmental conditions to obtain activated kaolinite clay, which was then sealed and stored.

[0082] Comparative Example 4

[0083] After drying the kaolinite clay at 105°C, a vibration mill with a frequency of 50 Hz, a power of 1.1 kW, and a rotation speed of 1420 rpm was used for mechanochemical activation. 50 g of sample was milled for 100 min each time. The ground powder sample was the activated kaolinite clay, which was immediately transferred to a sealed bag and stored at room temperature.

[0084] The activation systems of Examples 1-5 and Comparative Examples 1-4 are detailed in Table 2.

[0085] Table 2 Activation system

[0086] Group Revitalization system Activation temperature (℃) Activation time Example 1 Synergistic activation Heat activated 525 Calcination holding time 2h + mechanical grinding 20min Example 2 Synergistic activation Heat activated 525 Calcination holding time 2h + mechanical grinding 40min Example 3 Synergistic activation Heat activated 525 Calcination holding time 2h + mechanical grinding 60min Example 4 Synergistic activation Heat activated 525 Calcination holding time 2h + mechanical grinding 80min Example 5 Synergistic activation Heat activated 525 Calcination holding time 2h + mechanical grinding 100min Comparative Example 1 Not activated - - Comparative Example 2 Thermal activation 525 Calcination holding time 2h Comparative Example 3 Thermal activation 750 Calcination holding time 2h Comparative Example 4 Mechanochemical activation 25 Mechanical grinding 100min

[0087] The products of the above embodiments and comparative examples were subjected to laser particle size distribution measurement, microscopic morphology test, 27 Al solid NMR test ( 27 Al SSNMR), X-ray diffraction phase analysis (XRD) and volcanic ash activity test. The particle size distribution results of the products of each embodiment and comparative example are shown in Table 3.

[0088] Table 3 Particle size distribution of active kaolinite clays of Examples 1-5 and Comparative Examples 1-4

[0089] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 D10(μm) 0.99 1.04 1.00 0.96 0.85 0.92 1.03 1.67 0.89 D50(μm) 4.12 4.55 4.05 3.65 2.60 3.22 5.27 48.74 2.95 D90(μm) 40.26 42.98 39.47 36.09 28.99 98.22 106.21 127.26 30.59

[0090] According to the particle size distribution of kaolinite clay after synergistic activation treatment ( Figure 2 ) and micromorphological results ( Figure 3-Figure 11 ), it can be seen that the unactivated kaolinite has a hexagonal layered stacking structure, and the calcination at 525℃ and 750℃ has no obvious effect on the layered structure. Calcination at higher temperatures will lead to sintering and agglomerate formation, resulting in an increase in the average particle size. Further mechanochemical activation treatment leads to particle crushing and a significant increase in specific surface area, but grinding for a certain time will lead to the formation of porous aggregates.

[0091] The products of each embodiment and comparative example 27 Al SSNMR results are as follows Figure 12 As shown, it can be seen that comparative example 1 is mainly a 6-coordinate Al structure (Al(6)) with a chemical shift range of 0-20ppm; comparative example 2 shows that the Al structure is still Al(6), and the peak intensities of penta- and tetra-coordinate Al (Al(5) and Al(4)) are not obvious; comparative example 3 shows that the Al structure is Al(6), Al(5) and Al(4) structures with chemical shifts of 0-10, 10-40, and 30-60ppm, and the Al(5) peak intensity is the highest; in comparative example 4, the Al coordination structure includes Al(6), Al(5) and Al(4), among which the Al(6) peak intensity is the highest; for the embodiments, the Al(6) peak intensity in embodiment 1 is higher than that of Al(5) and Al(4), and with the increase of grinding time, the peak intensity of Al(6) with a chemical shift of 0-20ppm in embodiments 2-5 decreases, and the peak intensities of Al(5) and Al(4) with a chemical shift of 10-40 and 30-60ppm gradually increase. All the results showed that thermal activation and mechanochemical activation changed the Al coordination number. The aluminum structure of kaolinite was octahedral before activation, and the octahedron transitioned to pentahedron and tetrahedron after activation. The synergistic activation accelerated the transformation of the Al coordination form of kaolinite from Al(6) to Al(5) and Al(4), and the peak contents of Al(5) and Al(4) increased with the increase of grinding time.

[0092] The XRD test results of each embodiment and comparative example product are as follows Figure 13 As shown in the figure, under calcination at 525℃, the diffraction peak intensity of kaolinite (0,0,1) decreased significantly, indicating that calcination at 525℃ caused obvious interlayer damage to kaolinite; after calcination at 750℃, except for a small amount of diffraction peaks of quartz phase that did not disappear, the crystal structure of kaolinite turned into an amorphous phase; after calcination at 525℃ and then grinding for different times, it was shown that the kaolinite phase reached an amorphous state after grinding for 40 minutes, and extending the grinding time had no further effect on the amorphous state.

[0093] Volcanic ash activity test takes R 3 Combined with water test method, in which R 3The tested activated clay, calcium hydroxide, potassium sulfate, potassium hydroxide, and water were mixed in proportions of 6.25g, 18.75g, 0.815g, 0.07g, and 30g, respectively. After mixing, the mixture was cured in a 40°C water bath for 7 days, then dried at 110°C to constant weight. The mixture was then calcined in a muffle furnace to 350°C and held for 1 hour. The bound water content was then calculated after weighing. Table 4 lists the pozzolan activity test results for various examples and comparative examples. A higher bound water content indicates a higher pozzolan activity.

[0094] Table 4 Kaolinite clay R 3 Combined water content test results

[0095]

[0096] Compared to samples activated solely by heat, the synergistic effect of thermal and mechanochemical activation helped enhance pozzolanic reactivity. The samples with the highest bound water content were Examples 2 and 3, both of which had the same bound water content of 11.61%. Prolonged mechanical grinding reduced the bound water content, indicating that prolonged mechanochemical activation was not conducive to further enhancing pozzolanic activity. Based on the physicochemical characterization and pozzolanic activity results of all the aforementioned examples and comparative examples, Example 2, i.e., the kaolinitic clay calcined at 525°C and mechanically ground for 40 minutes, was selected as an auxiliary cementitious material to replace 20% PI cement.

[0097] Example 6

[0098] This embodiment provides an application of active kaolinite clay as an auxiliary cementitious material. The active kaolinite clay prepared in Example 2 is used as an auxiliary cementitious material to prepare cement mortar. The specific steps are as follows:

[0099] (1) Weigh 360 g of PI cement, 90 g of the activated kaolinite clay of Example 2, 225 g of mixing water, and 1350 g of standard sand, add the above materials into a planetary cement mortar mixer, and stir thoroughly to mix evenly;

[0100] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0101] Comparative Example 5

[0102] (1) Weigh 450 g of PI cement, 225 g of mixing water, and 1350 g of standard sand in parts by weight, add the above materials into a planetary cement mortar mixer, and stir thoroughly to mix them evenly.

[0103] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0104] Comparative Example 6

[0105] (1) Weigh 360 g of PI cement, 90 g of quartz sand, 225 g of mixing water, and 1350 g of standard sand in parts by weight. Add the above materials into a planetary cement mortar mixer and stir thoroughly to mix them evenly.

[0106] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0107] Comparative Example 7

[0108] (1) Weigh 360 g of PI cement, 90 g of kaolinite clay raw material (i.e., the kaolinite clay in Comparative Example 1), 225 g of mixing water, and 1350 g of standard sand in a planetary cement mortar mixer and stir thoroughly to mix evenly.

[0109] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0110] Comparative Example 8

[0111] (1) Weigh 360 g of PI cement, 90 g of the activated kaolinite clay of Comparative Example 2, 225 g of mixing water, and 1350 g of standard sand in parts by weight. Add the above materials into a planetary cement mortar mixer and stir thoroughly to mix evenly.

[0112] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0113] Comparative Example 9

[0114] (1) Weigh 360 g of PI cement, 90 g of the activated kaolinite clay of Comparative Example 3, 225 g of mixing water, and 1350 g of standard sand in parts by weight. Add the above materials into a planetary cement mortar mixer and stir thoroughly to mix evenly.

[0115] (2) Pour the mortar into a 40*40*1600mm mold, tamp it thoroughly, and vibrate it on a vibrating table for 60 seconds. After smoothing the surface, place it in a constant temperature and humidity curing box for 24 hours, then demold it and water-cure it to the ages of 3d, 7d, and 28d. The flexural strength, compressive strength, and strength activity index of the mortar specimens at each age were tested.

[0116] The test results of the flexural strength, compressive strength and strength activity index of the mortar test blocks of Example 6 and Comparative Examples 5-9 at various ages are shown in Table 5.

[0117] Table 5 Flexural strength, compressive strength and strength activity index of mortar specimens at different ages

[0118]

[0119] The above results show that the stronger the volcanic ash activity of the kaolinite clay sample, the greater the consumption of portlandite, and the higher the strength activity index (SAI). The compressive strength of the cement mortar test block of Example 6 exceeded that of PI cement at 7d and 28d, reaching 43.8MPa and 53.2MPa respectively, showing outstanding mechanical properties. The excellent mechanical properties show that mechanochemical synergistic thermal activation can effectively promote kaolinite clay to form an auxiliary cementitious material with high volcanic ash activity. This process consumes more portlandite and generates more hydration products, such as C-(A)-SH gel (calcium-(aluminum)-silicate hydrated gel), AFm phase (monosulfur type hydrated calcium sulfoaluminate) and hydrated calcium aluminum feldspar, thereby improving the macroscopic mechanical strength and making the microstructure more dense.

[0120] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing activated kaolinite clay by synergistic activation, characterized in that: The following steps are involved: Performing a thermogravimetric analysis on the kaolinite clay, and performing a thermal activation treatment on the kaolinite clay using the peak temperature of the first-order thermogravimetric curve of the kaolinite clay as the thermal activation temperature point; performing a mechanochemical activation treatment on the thermally activated kaolinite clay to obtain the activated kaolinite clay; The peak temperature of the first-order thermal weight loss curve of the kaolinite clay is 525°C; During the thermal activation treatment, the heating rate is 10°C / min and the holding time is 2h; The mechanochemical activation treatment is a vibration mill; The vibration mill was operated under the following conditions: frequency 50 Hz, power 1.1 kW, and rotation speed 1420 rpm; The grinding time of the vibration mill is 20-100 min.

2. The method for preparing activated kaolinite clay by synergistic activation according to claim 1, characterized in that: The grinding time of the vibration mill is 20-40 min.

3. An activated kaolinite clay, characterized in that: Prepared according to the method according to any one of claims 1-2.

4. Use of the activated kaolinite clay according to claim 3 as an auxiliary gelling material.

5. A method for preparing cement mortar using the activated kaolinite clay according to claim 3, characterized in that: PI cement, water, standard sand and the active kaolinite clay are uniformly mixed, the active kaolinite clay is used as an auxiliary cementitious material to replace 20% of the PI cement by mass, and the cement mortar is obtained after curing.

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