Active coal gangue, preparation method and application thereof, cement-based composite material and preparation method thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to active coal gangue, a preparation method and application thereof, a cement-based composite material and a preparation method thereof. The invention provides a preparation method of activated coal gangue, which comprises the following steps: calcining coal gangue to obtain calcined coal gangue; and mixing the calcined coal gangue, fly ash and slag to obtain the activated coal gangue. The calcined coal gangue is modified by utilizing the fly ash and the slag, and the activity of the coal gangue can be further improved by utilizing the synergistic interaction effect of the fly ash, the slag and the coal gangue.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and specifically relates to an active coal gangue and a preparation method and application thereof, a cement-based composite material and a preparation method thereof. Background Art

[0002] Gangue is one of the main solid wastes in the coal industry. Due to the difficulty in utilizing gangue, it is still treated by traditional stacking. It is reported that the total amount of gangue currently piled up in my country is more than 6 billion tons, occupying about 13,000 hectares of land, posing a serious threat to the surrounding ecological environment. Improving the comprehensive utilization rate of gangue is of great significance to promoting the green development of the coal industry. Gangue is widely used in different scenarios according to its calorific value. Among them, low calorific value clay gangue is relatively widely distributed in my country and has a large stockpile. This type of gangue contains clay minerals such as kaolinite and illite, and after high-temperature calcination, it forms amorphous metakaolinite, etc., which makes it exhibit volcanic ash activity. Therefore, using calcined gangue as an auxiliary cementitious material is considered to be an effective way to improve the comprehensive utilization rate of low calorific value clay gangue, and has received widespread attention.

[0003] However, in addition to kaolinite, coal gangue usually contains inert minerals such as quartz and mica, which makes its volcanic ash activity worse than that of slag or metakaolinite. Further improving the volcanic ash activity of calcined coal gangue has become the key to increasing the amount of coal gangue used in cement. Summary of the invention

[0004] The purpose of the present invention is to provide an activated coal gangue and a preparation method and application thereof, a cement-based composite material and a preparation method thereof. The preparation method provided by the present invention can further improve the activity of calcined coal gangue.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing activated coal gangue, comprising the following steps: calcining the coal gangue to obtain calcined coal gangue; The calcined coal gangue, fly ash and slag are mixed to obtain the activated coal gangue.

[0006] Preferably, the coal gangue comprises the following components in percentage by mass: SiO2 62% to 63%, CaO 1% to 1.1%, Al2O3 22% to 23%, Fe2O3 4% to 5%, MgO 1% to 1.2%, TiO2 1% to 2%, SO3 0.5% to 0.7%, K2O 2.5% to 3% and Na2O 0.2% to 0.3%; The particle size of the coal gangue is 0.4-300 μm.

[0007] Preferably, the calcination temperature is 700-800° C., and the holding time is 1-1.5 h.

[0008] Preferably, the fly ash comprises the following components in percentage by mass: SiO2 51% to 52%, CaO 3.5% to 4%, Al2O3 33% to 34%, Fe2O3 6% to 6.5%, MgO 0.5% to 0.8%, TiO2 0.1% to 0.2%, SO3 1.3% to 1.6%, K2O 2% to 2.5% and Na2O 0.5% to 0.7%; The particle size of the fly ash is 0.5-200 μm; The slag comprises the following components in percentage by mass: SiO2 35% to 36%, CaO 36% to 36.5%, Al2O3 15% to 15.5%, Fe2O3 0.6% to 0.9%, MgO 9.5% to 9.7%, SO3 1% to 1.5%, K2O 0.3% to 0.5% and Na2O 0.10% to 0.2%; The particle size of the slag is 0.3-100 μm.

[0009] Preferably, the mass ratio of the calcined coal gangue, fly ash and slag is 2.9-3.1:4.8-5.1:1.9-2.1; The mixing method is grinding, the grinding speed is 30-300 rpm, and the grinding time is 20-30 min.

[0010] The present invention also provides activated coal gangue prepared by the preparation method described in the above technical solution.

[0011] The present invention also provides the use of the activated coal gangue described in the above technical solution as a cement auxiliary gelling material.

[0012] The present invention also provides a cement-based composite material, the preparation raw materials of which include cement, a cementitious material, sand and water, and the cementitious material is the activated coal gangue described in the above technical solution.

[0013] Preferably, the cement comprises PI 42.5 benchmark cement; The particle size of the sand is 0.4-100 μm; The mass of the cementitious material is 28% to 31% of the mass of the cement; The mass ratio of the total mass of the cement and the cementitious material to the mass of the sand is 0.9-1.1:2.9-3.1; The mass ratio of water to cement is 0.5-0.6:1.

[0014] The present invention also provides a method for preparing the cement-based composite material described in the above technical solution, comprising the following steps: The prepared raw materials are mixed to obtain the cement composite material.

[0015] The invention discloses a method for preparing activated coal gangue, comprising the following steps: calcining the coal gangue to obtain calcined coal gangue; and mixing the calcined coal gangue, fly ash and slag to obtain the activated coal gangue.

[0016] The present invention improves the activity of coal gangue by calcination activation. On the one hand, calcination can remove organic matter and moisture: under high temperature conditions, some organic matter and moisture in the coal gangue will be removed, which can improve its purity and thus enhance its reaction activity; at the same time, the calcination process can promote the transformation of clay minerals, quartz and other mineral phases in the coal gangue to form more active mineral phases (such as hydrated minerals and active oxides), thereby improving its reactivity; in addition, high-temperature calcination will cause changes in the pore structure inside the coal gangue to form more micropores and macropores, which helps to enhance its adsorption capacity and reaction activity; further, through calcination, the specific surface area of ​​the coal gangue will usually increase, which can provide more reaction sites, thereby enhancing its reactivity with other chemical substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD patterns of cement, fly ash, coal gangue and slag; Figure 2 The particle size distribution diagrams of cement, fly ash, coal gangue and slag; Figure 3 The XRD diagrams of the calcined coal gangue obtained in Examples 1-2 and Comparative Example 1; Figure 4 The flexural strength test results of the cement-based composite materials obtained in the examples and comparative examples are shown; Figure 5 The compressive strength test results of cement-based composite materials obtained in Examples and Comparative Examples are shown in FIG. Figure 6 The activity index test results of the cement-based composite materials obtained in the examples and comparative examples are shown; Figure 7 The fluidity test results of cement mortar obtained in the embodiments and comparative examples are as follows; Figure 8 The hydration heat release rate test results of the cement mortar obtained in the examples and comparative examples; Fig. 9 The hydration analysis test results of cement mortar obtained in the embodiments and comparative examples; Fig.10 This is the XRD diagram of the hydration product of the hardened paste after curing for 3 days in Test Example 5; Fig.11 This is the XRD diagram of the hydration product of the hardened paste after curing for 28 days in Test Example 5; Fig.12 It is the diffraction peak of calcium hydroxide of the hydration product of the hardened paste after curing for 28 days in Test Example 5. DETAILED DESCRIPTION

[0018] The present invention provides a method for preparing activated coal gangue, comprising the following steps: calcining the coal gangue to obtain calcined coal gangue; The calcined coal gangue, fly ash and slag are mixed to obtain the activated coal gangue.

[0019] The invention calcines the coal gangue to obtain calcined coal gangue.

[0020] In the present invention, the coal gangue preferably includes the following components in percentage by mass: SiO2 62%~63%, CaO 1%~1.1%, Al2O3 22%~23%, Fe2O3 4%~5%, MgO 1%~1.2%, TiO2 1%~2%, SO3 0.5%~0.7%, K2O 2.5%~3% and Na2O 0.2%~0.3%, and further preferably SiO2 62.85%, CaO 1.05%, Al2O3 22.46%, Fe2O3 4.63%, MgO 1.16%, TiO2 1.42%, SO3 0.58%, K2O 2.93% and Na2O 0.24%; the particle size of the coal gangue is preferably 0.4~300μm.

[0021] In the present invention, the calcination temperature is preferably 700-800° C., the heating rate is preferably 10° C. / min, and the holding time is preferably 1-1.5 h.

[0022] After obtaining the calcined coal gangue, the present invention mixes the calcined coal gangue, fly ash and slag to obtain the activated coal gangue.

[0023] In the present invention, the fly ash preferably includes the following components in percentage by mass: SiO2 51%~52%, CaO 3.5%~4%, Al2O3 33%~34%, Fe2O3 6%~6.5%, MgO 0.5%~0.8%, TiO2 0.1%~0.2%, SO3 1.3%~1.6%, K2O 2%~2.5% and Na2O 0.5%~0.7%, and further preferably SiO2 51.17%, CaO 3.65%, Al2O3 33.21%, Fe2O3 6.11%, MgO 0.71%, TiO2 0.12%, SO3 1.47%, K2O 2.27% and Na2O 0.65%; the particle size of the fly ash is preferably 0.5~200μm.

[0024] In the present invention, the slag preferably includes the following components in percentage by mass: SiO2 35%-36%, CaO 36%-36.5%, Al2O3 15%-15.5%, Fe2O3 0.6%-0.9%, MgO 9.5%-9.7%, SO3 1%-1.5%, K2O 0.3%-0.5% and Na2O 0.10%-0.2%, and further preferably includes SiO2 35.26%, CaO 36.03%, Al2O3 15.26%, Fe2O3 0.81%, MgO 9.52%, SO3 1.27%, K2O 0.43% and Na2O 0.10%; the particle size of the slag is preferably 0.3-100 μm.

[0025] In the present invention, the XRD patterns of cement, fly ash, coal gangue and slag are as follows: Figure 1 As shown in Figure 2, the particle size distribution of cement, fly ash, coal gangue and slag is shown in Figure 2. Figure 2 shown.

[0026] In the present invention, the mass ratio of the calcined gangue, fly ash and slag is preferably 2.9-3.1:4.8-5.1:1.9-2.1, and more preferably 3:5:2. In the present invention, the mixing method is preferably grinding, the grinding speed is preferably 30-300 rpm, and the grinding time is preferably 20-30 min.

[0027] The present invention also provides activated coal gangue prepared by the preparation method described in the above technical solution.

[0028] The present invention also provides the use of the activated coal gangue described in the above technical solution as a cement auxiliary gelling material.

[0029] The present invention also provides a cement-based composite material, the preparation raw materials of which include cement, a cementitious material, sand and water, and the cementitious material is the activated coal gangue described in the above technical solution.

[0030] In the present invention, the cement preferably includes PI 42.5 reference cement; the particle size of the sand is preferably 0.4-100 μm. In the present invention, the mass of the cementitious material is preferably 28%-31% of the mass of cement, and more preferably 30%; the mass ratio of the total mass of the cementitious material and cement to the mass ratio of sand (cement-sand ratio) is preferably 0.9-1.1:2.9-3.1, and more preferably 1:3; the mass ratio of water to cement (water-cement ratio) is preferably 0.5-0.6:1, and more preferably 0.5:1.

[0031] The present invention also provides a method for preparing the cement-based composite material described in the above technical solution, comprising the following steps: The prepared raw materials are mixed to obtain the cement composite material.

[0032] The present invention has no particular limitation on the mixing method, and the raw materials can be uniformly mixed in a manner well known to those skilled in the art. In the present invention, the cement-based composite material obtained after the mixing is cement mortar.

[0033] After the mixing, the present invention also preferably includes drying and curing the obtained mortar. The present invention has no special limitation on the curing process, and any method known to those skilled in the art can be adopted. In the present invention, after curing, the cement composite material is concrete.

[0034] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0035] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In the following examples, the compositions of cement, fly ash, coal gangue and slag are shown in Table 1. Figure 1 The XRD diagrams of cement, fly ash, coal gangue and slag are shown in Figure 2. Figure 2 The particle size distribution diagrams of cement, fly ash, coal gangue and slag; Table 1 Composition of cement, fly ash, coal gangue and slag

[0037] Example 1 The coal gangue is heated to 700°C at a heating rate of 10°C / min for calcination, and the temperature is kept for 1 hour to obtain calcined coal gangue; The calcined coal gangue, fly ash and slag were mixed in a ratio of 3:5:2, and ball-milled at a rotation speed of 100 rpm for 20 minutes to obtain activated coal gangue.

[0038] Example 2 Activated coal gangue was prepared in the same manner as in Example 1, except that the calcination temperature was adjusted to 800°C.

[0039] Example 3 Materials: PI 42.5 standard cement; sand with a particle size of 0.4~100μm; The activated coal gangue obtained in Example 1 is used as a cementitious material, mixed with cement, sand and water, wherein the mass of the activated coal gangue is 30% of the mass of the cement; the water-cement ratio is 0.5, and the mortar-sand ratio is 1:3, to obtain cement mortar; The slurry was placed in a mold and dried, and the obtained mortar test blocks were cured for 3 days and 28 days respectively to obtain a cement-based composite material. The size of the obtained cement-based composite material was 40 mm×40 mm×160 mm.

[0040] Example 4 The cement-based composite material was prepared in the manner of Example 3, except that the activated coal gangue was the activated coal gangue obtained in Example 2.

[0041] Comparative Example 1 Activated coal gangue was prepared in the same manner as in Example 1, except that the calcination temperature was adjusted to 900°C.

[0042] Comparative Example 2 A cement-based composite material was prepared in the manner of Example 3, except that the activated coal gangue was the activated coal gangue obtained in Comparative Example 1.

[0043] Comparative Example 3 Materials: PI 42.5 standard cement; sand with a particle size of 0.4~100μm; The calcined coal gangue and fly ash obtained in Example 1 are used as cementitious materials (wherein the mass ratio of calcined coal gangue to fly ash is 1:1), mixed with cement, sand and water, wherein the mass of the cementitious material is 30% of the mass of cement; the water-cement ratio is 0.5, and the cement-sand ratio is 1:3, to obtain cement mortar; The slurry was placed in a mold and dried, and the obtained mortar test blocks were cured for 3 days and 28 days respectively to obtain cement-based composite materials.

[0044] Comparative Example 4 A cement-based composite material was prepared in the manner of Comparative Example 3, wherein the calcined coal gangue was the calcined coal gangue obtained in Example 2.

[0045] Comparative Example 5 A cement-based composite material was prepared in the manner of Comparative Example 3, wherein the calcined coal gangue was the calcined coal gangue obtained in Comparative Example 1.

[0046] Performance Testing Test Example 1 Figure 3 The XRD diagrams of the calcined coal gangue obtained in Examples 1-2 and Comparative Example 1; Compared with untreated coal gangue ( Figure 1 ), the diffraction peak of kaolinite in the calcined gangue completely disappeared, and only the diffraction peaks of quartz, illite and hematite were observed. The dehydroxylation reaction of kaolinite to metakaolinite usually occurs above 450°C, as shown in formula (1).

[0047] Formula (1); At a calcination temperature of 700°C, it is speculated that the kaolinite in the coal gangue has been transformed into amorphous metakaolinite, so the diffraction peak of kaolinite disappears in the calcined coal gangue. The diffraction peak intensity of quartz gradually increases with the increase of calcination temperature, which means that the crystallinity of quartz increases significantly. This phenomenon reflects the decomposition of metakaolinite and the recrystallization of amorphous silica, as shown in formula (2) and formula (3).

[0048] Formula (2); Formula (3); Coal gangue is calcined between 700 and 900°C. Since illite usually undergoes dehydroxylation at 540 to 650°C, but its structure usually remains stable during the dehydroxylation process, and its crystal structure may not be destroyed until the temperature is above 900°C, the temperature of 700 to 900°C is sufficient to prompt illite to complete the dehydroxylation reaction, but may not destroy its mineral structure. Therefore, the diffraction peak intensity of illite does not change significantly with the increase of calcination temperature.

[0049] The diffraction peak of hematite was observed in the calcined coal gangue, which may be the result of the oxidation of iron-containing mineral components. It can be seen that the activity of coal gangue mainly comes from the metakaolinite formed after the dehydroxylation of kaolinite.

[0050] Test Example 2 The mechanical properties of the cement-based composite materials of Examples 3 to 4 and Comparative Examples 2 to 5 were tested, with cement alone as a blank control (i.e., OPC); The test standard for flexural strength and compressive strength is: GB / T17671-1999 Cement mortar strength test method, and the test results are shown in Table 2; Figure 4 is the flexural strength test result. Figure 5 The compressive strength test results are: Figure 6 is the activity index test result; Table 2 Performance test results of cement-based composite materials obtained in Examples and Comparative Examples

[0051] according to Figure 4 It can be seen that the strength of the composite material is affected by the curing age, the calcination temperature of the gangue and the slag content. After replacing 30% of the cement with cementitious materials, the 3d flexural strength of the mortar decreased significantly, with a decrease of 8% to 21%. Among them, the flexural strength of No. 3 (i.e., comparative example 5) was the lowest, at 5.18 MPa, and the flexural strength of No. 5 (i.e., Example 4) was the highest, reaching 5.94 MPa. After 28 days of curing, except for No. 3, the flexural strength of other samples increased significantly, and the difference with the control group was within 0.5 MPa, while the flexural strength of No. 3 was only 6.71 MPa.

[0052] according to Figure 5 It can be seen that the 3d compressive strength of the composite material using cementitious materials to replace 30% of cement is lower than that of the control group, with a decrease of 3% to 15%. The strength of No. 3 is the lowest, which is 21.43MPa, and the strength of No. 5 is the highest, reaching 24.54MPa. After 28 days, the compressive strength of all samples has increased significantly. The compressive strength of No. 4, 5, and 6 even exceeds that of the control group, reaching 48.96, 48.19, and 47.26MPa, respectively, while the compressive strength of the samples without slag addition did not reach the level of the control group, which were 45.14, 41.92, and 42.88MPa.

[0053] It can be seen that the use of cementitious materials to replace cement leads to a decrease in the early mechanical properties of cement composites. This may be because the hydration reaction of the auxiliary cementitious materials is slow, and the strength of the early mortar is mainly formed by the hydration products formed by cement hydration. The use of auxiliary cementitious materials leads to cement dilution, so the mechanical properties are significantly reduced. This is also reflected in the difference between the 3d flexural / compressive strength of the samples and the control group. The difference between the 3d flexural / compressive strength of No. 1, 2, and 3 and the control group is between 1.0~1.3MPa and 3.0~3.9MPa, respectively. After using slag to replace part of the coal gangue, the early mechanical properties of the samples are slightly improved. The difference between the 3d flexural / compressive strength of No. 4, 5, and 6 and the control group is between 0.5~1.22MPa and 0.7~2.9MPa, respectively. This may be because the volcanic ash activity of slag is high and it participates in the hydration reaction in advance; on the other hand, slag particles are finer than cement particles, have better nucleation and filling effects, and can improve the early performance of mortar. According to the mechanical properties test results of 3d and 28d, the activity of coal gangue tends to decrease with the increase of calcination temperature. This is directly reflected in the strength activity index of the composite powder at 28d, such as Figure 6 As shown in the figure, the activity index of the samples can be arranged from large to small as 4>5>6>1>3>2. It can be seen that the coal gangue calcined at 700℃ has the best activity.

[0054] Test Example 3 The fluidity of the cement mortar obtained in the examples and comparative examples was tested, with cement alone as a blank control (i.e., OPC); The test standard is: GB / T2419 cement mortar fluidity test method; The test results are shown in Table 3 and Figure 7 As shown; Table 3 Fluidity of cement mortar obtained in Example

[0055] Depend on Figure 7It can be seen that the addition of cementitious materials improves the fluidity of cement mortar. The fluidity of all samples is higher than that of the control group, which is increased by 3% to 13%. Among them, the one with the best fluidity is No. 4, which reaches 237 mm, which is about 13% higher than the pure cement control group. Fly ash has a positive effect on improving the fluidity of mortar. This is because fly ash is usually a regular spherical particle, which can reduce the friction between particles and play a good lubricating role. As the temperature of calcined coal gangue increases, the fluidity of mortar shows a decreasing trend, which indicates that the change of mineral composition in coal gangue caused by calcination may have a negative impact on the fluidity of mortar. After using slag to replace part of the coal gangue, the fluidity of mortar is further improved, indicating that the addition of slag is also conducive to improving the fluidity of mortar. This is because slag particles are finer than other materials and can also play a certain lubricating role. In addition, since these auxiliary cementitious materials have a low degree of reaction in the early stage of hydration and can be regarded as inert materials, they can release more free water for lubrication, thereby improving the fluidity of mortar.

[0056] Test Example 4 Analysis of the hydrothermal and hydration kinetics of the cement mortars of Examples 3 to 4 and Comparative Examples 2 to 5; (1) Test the heat release rate of hydration heat of cement mortar. Observe the heat release peak of cement mortar and compare it with the benchmark cement. The test results are as follows: Figure 8 As shown; The heat release rate of hydration heat of cement mortar was analyzed. Cement mortar showed two obvious exothermic peaks, similar to the benchmark cement. The first exothermic peak was caused by the wetting and dissolution of cement and auxiliary cementitious material particles, which occurred approximately in the first hour. The second exothermic peak occurred around 4-18h, indicating the formation of hydration products. The use of auxiliary cementitious materials to replace part of the cement usually leads to a decrease in the peak value of the second peak. Since the peak value of the second peak is mainly related to cement hydration, it is speculated that high-temperature calcined coal gangue has a better nucleation effect and can promote cement hydration. In addition, the calcination temperature and slag content of coal gangue have little effect on the end of the induction period and the time to reach the peak value of the second peak, which means that these factors will not delay cement hydration.

[0057] (2) The hydration process was further analyzed using the Krstulovic-Dabic hydration kinetic model and hydration heat data. In this model, the hydration process is divided into three stages: nucleation and crystal growth (NG), phase interface (I), and diffusion (D), and each stage is considered to be independent of each other. The calculation process is as follows: NG: Formula (4); I: Formula (5); D: Formula (6); Differentiation process: NG: Formula (7); I: Formula (8); D: Formula (9); Where n, KNG, KI, and KD are hydration kinetic parameters obtained by curve fitting of equations (4) to (6); α represents the degree of hydration, which is calculated using the following formula: Formula (10) Formula (11) In the formula, QMax is the theoretical cumulative heat release, calculated using the following formula: Formula (12) Where Q(t) is the heat released by the slurry from the hydration acceleration period to time t; 50 It is the time when the cumulative heat release reaches half of the theoretical cumulative heat release; t0 is the time when the induction period ends or the acceleration period begins.

[0058] The hydration process was further analyzed using the Krstulovic-Dabic hydration kinetic model and hydration heat data, and the hydration analysis was performed using the hydration rate curve of cement mortar and the calculated simulation curve. The test results obtained are as follows Fig. 9 As shown; The hydration rate curve of cement mortar and the calculated simulation curve were analyzed. The model can accurately simulate the NG and D processes of composite cement paste, but the simulation effect of the process is slightly poor because the hydration exothermicity of auxiliary cementitious materials and the phase change exothermicity of calcium sulfonate are both in the I process. Through the analysis of the hydration kinetic parameters of cement mortar, n reflects the crystallization nucleation and crystal growth of hydration products, and fluctuates within a certain range with the increase of the temperature and slag content of calcined coal gangue, indicating that the calcination temperature and slag content of coal gangue have little effect on the geometric production process of hydration products. The value of composite cement KNG' is about 5 times that of KI' and about 30 times that of KD', indicating that the hydration reaction of cement mortar is mainly controlled by the NG process. This is because the NG process is mainly controlled by the autocatalytic reaction of cement, and the hydration products grow rapidly in this process. At the same time, the calcination temperature and slag content have little effect on the value of KNG'. The auxiliary cementitious materials hardly participate in the reaction in the early stage of hydration and can be regarded as inert materials. The calcination temperature of coal gangue has little effect on the reaction rate of process I, but the addition of slag reduces the reaction rate of process I. As the hydration time increases, the reaction enters process D, at which time the calcination temperature and slag content have little effect on the reaction rate of process D, indicating that the calcination temperature and slag content have little effect on ion diffusion.

[0059] Test Example 5 Analyze the hydration products; Preparation of test samples: refer to the preparation method of cement mortar in Examples 3 to 4 and Comparative Examples 2 to 5, except that: the sand in each example or comparative example is removed, the water-cement ratio is adjusted to 0.35, and a cement paste is obtained, which is formed and cured in a 10 mL centrifuge tube (serial numbers 1 to 6 still correspond to the test samples obtained in the above-mentioned examples and comparative examples, that is, 1 is comparative example 3, 2 is comparative example 4, 3 is comparative example 5, 4 is example 3, 5 is example 4, and 6 is comparative example 2), and cured for 3 d and 28 d respectively; after curing to the target age, the cement is crushed into powder, soaked in isopropanol for 1 h to terminate hydration, baked in an oven at 40° C. for 12 h, and then sealed and stored for hydration product analysis; blank cement is used as a control; in, Fig.10 This is the XRD diagram of the hydration product of the hardened paste after 3 days of curing. Fig.11 This is the XRD diagram of the hydration product of the hardened paste after 28 days of curing. Fig.12 It is the diffraction peak of calcium hydroxide which is the hydration product of the hardened paste after curing for 28 days; By analyzing the XRD pattern, the main hydration products in the hardened paste are calcium hydroxide, calcium sulfonate, monosulfate, hemicarbonate and monocarbonate. A "hump" can be observed at 2θ of 20-40°, indicating an amorphous phase, including unreacted auxiliary cementitious materials and CSH gel.

[0060] After 3 days of curing, the hydration products in the control group were mainly calcium hydroxide and calcium sulfonate, while in the composite cement (i.e., the present invention), in addition to the above two hydration products, monosulfate also existed. The diffraction peak intensity of calcium hydroxide in the composite cement was lower than that of the pure cement control group, which was the result of the dilution effect and the pozzolanic reaction of the auxiliary cementitious material. The formation of monosulfate observed in the composite cement means that there is an excess of aluminate and insufficient sulfate in the composite cement system. Since the alumina content in fly ash, coal gangue and slag is higher than that in cement, and the content of sulfur trioxide is lower than that in cement. When the above materials are used to replace cement, the content of active aluminate in the system will increase while the content of sulfur trioxide will decrease, so that the composite system presents a phenomenon of excessive aluminate and insufficient sulfate, thereby inducing the phase transition of calcium sulfonate to monosulfate. The exothermic process of calcium sulfonate to monosulfate usually occurs after about 16 hours, and usually forms a small exothermic peak.

[0061] When the curing time was extended to 28 days, the type of hydration products in the hardened paste changed again. Compared with 3 days, the diffraction peaks of hemicarbonate and monocarbonate were observed in the control group, while the diffraction peak of calcium sulfonate in the composite cement completely disappeared, and only the diffraction peak of monosulfate was observed. This shows that with the increase of curing time, the control group is greatly affected by carbonation, and calcium sulfonate contacts with carbon dioxide in the air to form monocarbonate and hemicarbonate, which is consistent with the existing research conclusions. In the composite cement, after the auxiliary cementitious materials gradually participate in the hydration reaction, calcium sulfonate further combines with the aluminate in the auxiliary cementitious materials and is converted into monosulfate. This may be due to the relatively poor activity of aluminate in the auxiliary cementitious materials, and a longer hydration time is required to completely convert the calcium sulfonate in the hardened paste. At the same time, this also confirms that the composite cement belongs to a system with excessive aluminate and insufficient sulfate.

[0062] In order to further evaluate the volcanic ash activity of the auxiliary cementitious material, the diffraction peak of calcium hydroxide after curing the hardened paste for 28 days was amplified. The diffraction peak intensity of calcium hydroxide of the sample in Example 1 is the lowest, indicating that the activity of the coal gangue calcined at 700°C is the best, which is consistent with the previous conclusion. After replacing part of the coal gangue with slag, the diffraction peak intensity of calcium hydroxide increased slightly, because the hydration reaction of slag consumes relatively little calcium hydroxide. At the same time, after using slag to replace coal gangue, the activity difference of calcined coal gangue is further amplified, indicating that there is a synergistic effect between slag and coal gangue, which can stimulate the volcanic ash reaction of highly active coal gangue.

[0063] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing activated coal gangue, characterized in that: The following steps are involved: calcining the coal gangue to obtain calcined coal gangue; The calcined coal gangue, fly ash and slag are mixed to obtain the activated coal gangue.

2. The preparation method according to claim 1, characterized in that: The coal gangue comprises the following components in percentage by mass: SiO2 62%-63%, CaO 1%-1.1%, Al2O3 22%-23%, Fe2O3 4%-5%, MgO 1%-1.2%, TiO2 1%-2%, SO3 0.5%-0.7%, K2O 2.5%-3% and Na2O 0.2%-0.3%; The particle size of the coal gangue is 0.4-300 μm.

3. The preparation method according to claim 1, characterized in that: The calcination temperature is 700-800° C., and the heat preservation time is 1-1.5 hours.

4. The preparation method according to claim 1, characterized in that: The fly ash comprises the following components in percentage by mass: SiO2 51%-52%, CaO 3.5%-4%, Al2O3 33%-34%, Fe2O3 6%-6.5%, MgO 0.5%-0.8%, TiO2 0.1%-0.2%, SO3 1.3%-1.6%, K2O 2%-2.5% and Na2O 0.5%-0.7%; The particle size of the fly ash is 0.5-200 μm; The slag comprises the following components in percentage by mass: SiO2 35%-36%, CaO 36%-36.5%, Al2O3 15%-15.5%, Fe2O3 0.6%-0.9%, MgO 9.5%-9.7%, SO3 1%-1.5%, K2O 0.3%-0.5% and Na2O 0.10%-0.2%; The particle size of the slag is 0.3-100 μm.

5. The preparation method according to claim 1, 2 or 4, characterized in that: The mass ratio of the calcined coal gangue, fly ash and slag is 2.9-3.1:4.8-5.1:1.9-2.1; The mixing method is grinding, the grinding speed is 30-300 rpm, and the grinding time is 20-30 min.

6. The activated coal gangue prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the activated coal gangue according to claim 6 as a cement auxiliary cementitious material.

8. A cement-based composite material, characterized in that: The preparation raw materials include cement, cementitious material, sand and water, and the cementitious material is the activated coal gangue as described in claim 6.

9. The cement-based composite material according to claim 8, characterized in that: The cement comprises PI 42.5 benchmark cement; The particle size of the sand is 0.4-100 μm; The mass of the cementitious material is 28% to 31% of the mass of the cement; The mass ratio of the total mass of the cement and the cementitious material to the mass of the sand is 0.9-1.1:2.9-3.1; The mass ratio of water to cement is 0.5-0.6:

1.

10. The method for preparing the cement-based composite material according to claim 8 or 9, characterized in that: The following steps are involved: The prepared raw materials are mixed to obtain the cement composite material.

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