Low-calcium high-aluminum coal gangue cement admixture and preparation process thereof

Abstract

The present application relates to solid waste utilization technical field, specifically to a kind of low calcium high alumina coal gangue cement admixture and its preparation process.The admixture can be prepared by calcium-increasing and calcining activation treatment to solid waste powder, and the mixture of solid waste powder and calcium hydroxide powder can realize calcium-increasing and activation under heating condition, promote a part of alumina component in solid waste powder and new ecological calcium oxide to form CaO·2Al2O3 and 12CaO·7Al2O3 type hydraulic mineral in calcining process.The remaining alumina component in the admixture can also be combined with cement reaction product to form 4CaO·Al2O3·13H2O type hydration product in subsequent hydration process, so that low calcium high alumina coal gangue cement has higher compressive strength.The present application is strong in pertinence, simple in operation, low in cost, high in efficiency, remarkable in strengthening effect, and has wide application prospect for comprehensive utilization of low calcium high alumina coal gangue.

Description

Technical Field

[0001] This invention relates to the field of solid waste utilization technology, specifically to a low-calcium, high-alumina coal gangue cement admixture and its preparation process. Background Technology

[0002] Coal gangue is a type of rock-like waste generated during coal mining. It occupies large areas of land, causes serious environmental pollution, and has become a heavy burden on the coal industry. The kaolinite component in coal gangue dehydrates and decomposes into amorphous metakaolinite during calcination. Metakaolinite has certain pozzolanic activity and can therefore be used as a cement admixture, reducing construction costs, making full use of solid waste, and benefiting environmental protection. The composition of coal gangue varies greatly among different coal-producing areas in my country. Based on alumina content and the alumina / silica molar ratio, coal gangue is classified into high-alumina coal gangue, claystone coal gangue, and sandstone coal gangue. In most coal-producing areas of my country, the alumina content in coal gangue ranges from 14.90 wt% to 34.30 wt%, the silica content ranges from 31.1 wt% to 66.4 wt%, and the calcium oxide content ranges from 0.21 wt% to 9.03 wt%. The alumina content in high-alumina coal gangue is significantly higher than that in ordinary silicate cement clinker, while the calcium oxide content is significantly lower. Therefore, if high-alumina coal gangue is calcined at 700℃ to prepare cement admixtures, the alumina in the coal gangue cannot be fully utilized, which will greatly affect the overall strength. If gypsum and fluorite are added to increase calcium content and calcined at temperatures above 1000℃, the preparation temperature is too high, consuming excessive energy.

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a low-calcium, high-alumina coal gangue cement admixture and its preparation process. Summary of the Invention

[0004] The purpose of this invention is to provide a low-calcium, high-alumina coal gangue cement admixture and its preparation process, so as to solve the problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A low-calcium, high-alumina coal gangue cement admixture includes low-calcium, high-alumina coal gangue powder and calcium hydroxide powder; the low-calcium, high-alumina coal gangue cement admixture contains 10-20 wt% calcium hydroxide powder and 40-90 wt% low-calcium, high-alumina coal gangue powder.

[0006] In a more optimized form, the content of each component in the low-calcium, high-alumina coal gangue powder is as follows: by mass fraction, 30%-38% alumina, 41%-47% silicon dioxide, 0.05%-0.15% calcium oxide, with the remainder being other impurities.

[0007] Ideally, the calcium hydroxide powder has a purity of ≥97% and a particle size of <25mm.

[0008] In a more optimized manner, the low-calcium high-alumina coal gangue cement admixture further includes fly ash powder, slag powder, and blast furnace slag powder; when the amount of low-calcium high-alumina coal gangue powder is 40-45 wt%, the mass ratio of low-calcium high-alumina coal gangue powder, blast furnace slag powder, slag powder, and fly ash powder is 5:2:2:0.5-1.

[0009] In a more optimized form, fly ash powder contains 52-62 wt% silica, 5-11 wt% alumina, and 4-6 wt% calcium oxide; slag powder contains 30-34 wt% silica, 20-25 wt% alumina, and 15-20 wt% calcium oxide; and blast furnace slag powder contains 30-50 wt% silica, 5-10 wt% alumina, and 20-30 wt% calcium oxide.

[0010] A preparation process for a low-calcium, high-alumina coal gangue cement admixture includes the following steps: mixing low-calcium, high-alumina coal gangue powder and calcium hydroxide powder evenly, and then calcining the mixture to obtain the low-calcium, high-alumina coal gangue cement admixture.

[0011] In a more optimized manner, the mixing time of low-calcium, high-alumina coal gangue powder and calcium hydroxide powder is 1.5-2.5 h; during calcination, the calcination temperature is 800-830℃ and the calcination time is 3-4 h.

[0012] An application of a cement admixture involves uniformly mixing low-calcium, high-alumina coal gangue cement admixture and cement clinker, wherein the amount of low-calcium, high-alumina coal gangue cement admixture is 20-30 wt%, and the amount of cement clinker is 70-80 wt%.

[0013] Ideally, the cement clinker is P.O42.5 ordinary Portland cement.

[0014] Ideally, the mixing time between low-calcium, high-alumina coal gangue cement admixture and cement clinker should be 25-35 minutes.

[0015] The beneficial effects of this invention are: This invention uses solid waste powder as the main material and adds calcium hydroxide to increase calcium content. Through calcination and activation at 800-830℃, calcium hydroxide undergoes dehydroxylation and reacts with carbon dioxide produced by the combustion of carbon in the solid waste powder to form calcium carbonate, as shown in reaction formulas (1) and (2).

[0016] Ca(OH)2=CaO+H2O (1) CaO + CO2 = CaCO3 (2) In 800-830 oDuring calcination of C, calcium carbonate undergoes complete decomposition, as shown in formula (3), forming active nascent calcium oxide, while coal gangue transforms into amorphous metakaolinite. Calcium oxide reacts with some of the silica and alumina in the metakaolinite, as shown in formulas (4), (5), and (6), forming hydraulic products of the types 2CaO•SiO2, CaO•2Al2O3, and 12CaO•7Al2O3. During the hydration process after mixing the prepared admixture with cement, the remaining alumina component in the metakaolinite can also react with cement to form the hydration product 4CaO•Al2O3•13H2O.

[0017] CaCO3 = CaO + CO2 (3) 2CaO + SiO2 = 2CaO•SiO2 (4) CaO+Al2O3=CaO·2Al2O3 (5) 12CaO+7Al2O3=12CaO·7Al2O3 (6) In summary, after calcination with calcium, solid waste powder forms CaO•2Al2O3 and 12CaO•7Al2O3, and during hydration, it forms 4CaO•Al2O3•13H2O. This invention mixes several solid waste powders and adds an appropriate amount of calcium hydroxide, then calcines the mixture at high temperature to increase calcium content. By mixing and calcining several industrial solid waste powders, the insufficient amount of alumina or calcium oxide components present in individual industrial solid waste powders is compensated for. This effectively utilizes the advantage of the mixed components having high contents of both alumina and calcium oxide components, and the addition of an appropriate amount of calcium hydroxide further promotes the formation of water hardening and hydration products, resulting in mortar samples prepared from low-calcium, high-alumina coal gangue admixture-cement exhibiting high strength. The preparation method of the low-calcium, high-alumina coal gangue admixture of this invention is simple, with low heating temperature and short holding time, thus resulting in high production efficiency. The raw materials used are few in number. Among them, the amount of calcium hydroxide used for calcium enrichment is small and the cost is low. In addition, the solid waste powder is almost free as a waste raw material, which has broad application prospects for the comprehensive utilization of low-calcium and high-alumina coal gangue. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is the XRD pattern of the low-calcium, high-aluminum coal gangue powder of the present invention; Figure 2 This is a scanning electron microscope image of the low-calcium, high-aluminum coal gangue powder of the present invention; Figure 3 This is the bulk density-particle size distribution of the low-calcium, high-alumina coal gangue powder of this invention. Figure 4 This is the XRD pattern of the low-calcium, high-alumina coal gangue admixture after calcium-enriched calcination at 830℃ in Example 4 of the present invention. Figure 5 This is a scanning electron microscope image of the low-calcium, high-alumina coal gangue admixture after calcium-enriched calcination at 830℃ in Example 4 of the present invention. Figure 6 yes Figure 5 The energy spectrum analysis diagram at position 122 in the photo; Figure 7 This is a photograph of the fracture surface of the 830℃ calcium-added calcined coal gangue-cement mortar sample from Example 4 of the present invention, taken during a flexural strength test. Figure 8 yes Figure 7 The energy spectrum analysis diagram marked position 19 in the photo; Detailed Implementation

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

[0020] Raw material source: Coal gangue, purchased from a coal mine in Datong City, Shanxi Province, has the chemical composition shown in Table 1. An XPC-100×150 jaw crusher was used to crush the gangue into particles smaller than 4 mm. Then, a GJ-1A sealed sample preparation pulverizer was used to further pulverize the gangue into powder with a particle size <127 mm. The particle size Dv(10) corresponding to a volume distribution of 10% was 2.13 mm, the particle size Dv(50) corresponding to a volume distribution of 50% was 14.9 mm, and the particle size Dv(90) corresponding to a volume distribution of 90% was 69.3 mm. The volume average particle size D(4,3) was 26.8 mm. Figure 1 This is the XRD pattern of the low-calcium, high-aluminum coal gangue powder of this invention. Figure 2 These are scanning electron microscope images of the low-calcium, high-aluminum coal gangue powder of this invention. Figure 3 This is the bulk density-particle size distribution of the low-calcium, high-aluminum coal gangue powder of this invention.

[0021] Calcium hydroxide, industrial grade, purity ≥97%, particle size <25mm.

[0022] The fly ash was purchased from a coal-fired power plant in Shijiazhuang City, Hebei Province. Its chemical composition is shown in Table 2, and the average particle size is 10-100 mm.

[0023] The slag powder was purchased from Shijiazhuang Metallurgical Plant in Hebei Province. Its chemical composition is shown in Table 3, and the average particle size is 10-50 mm.

[0024] The blast furnace slag powder was purchased from a steelmaking plant in Changsha, Hunan Province. Its chemical composition is shown in Table 4, and the average particle size is 10-30 mm.

[0025] Table 1 41.50 35.51 0.17 0.09 0.05 0.10 0.03 0.77 0.02 0.00 21.76 Table 2 62.02 11.32 5.19 6.07 1.54 1.64 0.13 1.00 1.04 — Table 3 34.32 20.31 4.88 20.02 4.52 — — — 3.85 — Table 4 37.54 9.03 3.48 29.03 5.57 — — — 2.31 — Example 1: Step 1: Mix 800g of low-calcium, high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 600℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0026] Example 2: Step 1: Mix 800g of low-calcium, high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 700℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0027] Example 3: Step 1: Mix 800g of low-calcium, high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 800℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0028] Example 4: Step 1: Mix 800g of low-calcium, high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0029] Example 5: Step 1: Mix 800g of low-calcium, high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 850℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0030] Example 6: Step 1: Mix 800g of low-calcium high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 900℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0031] Comparative Example 1: Mix 1350g of cement clinker, 4050g of standard sand and 675ml of water for 3 minutes, then pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. After compaction on a ZT-96 type vibrating table for 120s, the mold is formed. Demold the mold 22-24 hours after molding, place it in water at 20℃ for curing, and keep the water level 20mm above the surface of the sample to prepare the sample.

[0032] Testing and experimentation:

[0033] The flexural strength and compressive strength of Examples 1-6 and Comparative Example 1 were tested at 7d and 28d, respectively, and the results are shown in the table below; Comparative Example 1 5.80 35.73 7.48 43.24 Example 1 5.48 30.62 6.87 39.01 Example 2 5.69 34.85 7.19 42.96 Example 3 6.58 38.91 7.54 53.91 Example 4 6.88 42.36 7.88 59.75 Example 5 5.93 36.42 7.36 45.65 Example 6 3.55 25.34 6.53 43.38 Conclusion: In Examples 1-6, calcination temperatures were controlled at 600℃, 700℃, 800℃, 830℃, 850℃, and 900℃, respectively, with other conditions remaining unchanged. Six groups of samples and one control group were prepared. Analysis of the experimental results showed that as the temperature increased, the 7-day flexural strength, 7-day compressive strength, 28-day flexural strength, and 28-day compressive strength of Examples 1-6 all first increased and then decreased. Compared with the control group, the four strengths of Examples 1 and 2 were lower, while the four strengths of Examples 3-6 were higher than those of the control group.

[0034] in Figure 4 This is the XRD pattern of the low-calcium, high-alumina coal gangue cement admixture after calcination at 830℃ in Example 4. Figure 5 This is a scanning electron microscope image of the low-calcium, high-alumina coal gangue cement admixture after calcination at 830℃ in Example 4. Figure 6 yes Figure 5 The energy spectrum analysis diagram at position 122 in the photo; Figure 7 These are photographs of the fracture surfaces of coal gangue-cement mortar samples after calcination at 830℃, taken from a flexural strength test. Figure 8 yes Figure 7 The energy spectrum analysis diagram at position 19 in the photograph; Table 5 is... Figure 5 The chemical composition and corresponding products (wt%) at positions marked 121 and 122 are shown in Table 6. Figure 7 Chemical composition and corresponding products (wt) at positions marked 18 and 19.

[0035] Table 5 121 36.85 10.25 13.49 0.17 39.23 <![CDATA[C2S]]> 122 49.87 13.15 13.00 0.00 23.97 <![CDATA[C 12 A7]]> Table 6 18 63.77 5.25 7.52 0.20 23.24 <![CDATA[C4AH 13 ]]> 19 63.31 6.49 7.53 0.19 22.43 <![CDATA[C4AH 13 ]]> Example 7: Step 1: Mix 950g of low-calcium high-alumina coal gangue powder and 50g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0036] Example 8: Step 1: Mix 900g of low-calcium high-alumina coal gangue powder and 100g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0037] Example 9: Step 1: Mix 850g of low-calcium, high-alumina coal gangue powder and 150g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium, high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0038] Example 10: Step 1: Mix 800g of low-calcium high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0039] Example 11: Step 1: Mix 750g of low-calcium high-alumina coal gangue powder and 250g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0040] Testing and experimentation:

[0041] The flexural strength and compressive strength of Examples 7-11 were tested at 7d and 28d respectively, and the results are shown in the table below; Example 7 6.12 29.78 7.21 43.49 Example 8 6.17 36.17 7.52 50.61 Example 9 6.31 36.21 7.79 51.91 Example 10 6.88 42.36 7.88 59.75 Example 11 4.18 26.10 6.66 40.61 Conclusion: In Examples 7-11, five groups of samples were prepared by controlling the amount of calcium hydroxide added to coal gangue admixtures at 5%, 10%, 15%, 20%, and 25% by mass, respectively, while keeping other conditions unchanged. The experimental results show that as the amount of calcium hydroxide added increases, the 7-day flexural strength, 7-day compressive strength, 28-day flexural strength, and 28-day compressive strength of Examples 7-11 all first increase and then decrease.

[0042] Example 12: Step 1: Mix 2000g of low-calcium high-alumina coal gangue powder and 500g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Mix 135g of low-calcium, high-alumina coal gangue cement admixture and 1215g of cement clinker thoroughly for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0043] Example 13: Step 1: Mix 2000g of low-calcium high-alumina coal gangue powder and 500g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 270g of low-calcium, high-alumina coal gangue cement admixture and 1080g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0044] Example 14: Step 1: Mix 2000g of low-calcium high-alumina coal gangue powder and 500g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0045] Example 15: Step 1: Mix 2000g of low-calcium high-alumina coal gangue powder and 500g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Mix 540g of low-calcium, high-alumina coal gangue cement admixture and 810g of cement clinker thoroughly for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0046] Testing and experimentation:

[0047] The flexural strength and compressive strength of Examples 12-15 were tested at 7 days and 28 days, respectively, and the results are shown in the table below; Example 12 6.12 42.03 7.35 52.56 Example 13 6.07 40.83 7.43 55.31 Example 14 6.75 41.72 7.64 58.62 Example 15 4.98 33.66 5.70 41.12 Conclusion: In Examples 12-15, four groups of samples were prepared by controlling the amount of coal gangue admixture added to cement at 10%, 20%, 30%, and 40% respectively, while keeping other conditions unchanged. Analysis of the experimental results shows that as the amount of coal gangue admixture added increases, the 7-day flexural strength and 7-day compressive strength of Examples 12-15 first decrease, then increase, and then decrease again. The 28-day flexural strength and 28-day compressive strength of Examples 12-15 first increase and then decrease.

[0048] Example 16: Step 1: Mix 800g of low-calcium high-alumina coal gangue powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture; Step 2: Mix 446g of coal gangue admixture and 1041g of cement clinker thoroughly for 30 minutes, then add 2022g of standard sand, 624ml of water and 4505g of limestone pebbles and stir for 3 minutes. Then pour the mixture into a standard mortar plastic mold with dimensions of 150×150×150mm, compact it on a vibrating table, cover the surface with a film, let it stand for 24 hours, demold it, and cure it in a saturated calcium hydroxide solution for 28 days to prepare the sample.

[0049] Example 17: Step 1: 800g of low-calcium, high-alumina coal gangue powder was calcined at 830℃ for 3h to prepare calcined low-calcium, high-alumina coal gangue cement admixture; Step 2: Mix 446g of calcined coal gangue and 1041g of cement clinker thoroughly for 30 minutes, then add 2022g of standard sand, 624ml of water and 4505g of limestone pebbles and stir for 3 minutes. Then pour the mixture into a standard mortar plastic mold with dimensions of 150×150×150mm, compact it on a vibrating table, cover the surface with a film, let it stand for 24 hours, demold it, and cure it in a saturated calcium hydroxide solution for 28 days to prepare the sample.

[0050] Comparative Example 2: 1487g of cement clinker, 2022g of standard sand, 624ml of water and 4505g of limestone pebbles were mixed for 3 minutes, then poured into a standard mortar plastic mold with dimensions of 150×150×150mm, compacted on a vibrating table, then covered with a film, left to stand for 24 hours, demolded, and cured in a saturated calcium hydroxide solution for 28 days to prepare the sample.

[0051] Testing and experimentation:

[0052] The flexural strength of Examples 16-17 and Comparative Example 2 was tested for 28 days, and the results are shown in the table below; Example 16 52.38 Example 17 41.85 Comparative Example 2 49.28 Conclusion: Example 16 was prepared by controlling the amount of calcium hydroxide added to the coal gangue admixture to be 20% by mass; Example 17 was prepared by not adding calcium hydroxide, and a control group of samples were also prepared. The experimental results show that Example 16 had the highest 28-day flexural strength and the best mechanical properties.

[0053] Example 18: Step 1: Mix 400g of low-calcium high-alumina coal gangue powder, 160g of blast furnace slag powder, 160g of mineral slag powder, 80g of fly ash powder and 200g of calcium hydroxide powder thoroughly for 2 hours, and calcine at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0054] Comparative Example 3: The mass ratio of low-calcium high-alumina coal gangue powder, blast furnace slag powder, slag powder, and fly ash powder in step one was changed to 5:2:2:0.3. The remaining steps were the same as in Example 18. The specific steps are as follows: Step one: 430g of low-calcium high-alumina coal gangue powder, 172g of blast furnace slag powder, 172g of slag powder, 26g of fly ash powder, and 200g of calcium hydroxide powder were thoroughly mixed for 2 hours and calcined at 830℃ for 3 hours to prepare low-calcium high-alumina coal gangue cement admixture. Step 2: Thoroughly mix 405g of low-calcium, high-alumina coal gangue cement admixture and 945g of cement clinker for 30 minutes. Then add 4050g of standard sand and 675ml of water and stir for 3 minutes. Pour the mixture into a standard mortar plastic mold with dimensions of 40×40×160mm. Vibrate the mold on a ZT-96 type vibrating table for 120 seconds to form the sample. Demold the sample 22-24 hours after forming and place it in water at 20℃ for curing, keeping the water level 20mm above the sample surface. Prepare the sample.

[0055] Testing and experimentation:

[0056] The flexural strength and compressive strength of Example 18 and Comparative Example 3 were tested at 7d and 28d, respectively, and the results are shown in the table below; Example 18 7.13 47.25 8.29 65.42 Comparative Example 3 6.98 45.27 8.05 61.42 Conclusion: Example 18 was based on Example 4, where the low-calcium, high-alumina coal gangue powder was replaced with a mixture of several solid waste powders and calcium hydroxide powder for calcium enrichment and calcination, and then other components were added to prepare a sample. Analysis of the experimental results shows that, compared to Example 4, the product obtained by calcining after compounding several solid waste powders has higher compressive and flexural strengths, and the prepared admixture has superior strength properties. Comparative Example 3 involved changing the mass ratio of several solid waste powders to 5:2:2:0.3 for calcium enrichment and calcination, and then adding other components to prepare a sample. Analysis of the experimental results shows that, compared to Example 18, this compounding mass ratio is less than the compounding mass ratio specified in this invention. Within this range, the compressive and flexural strengths of the product prepared will decrease, and the strength properties of the admixture will decline.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process method article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process method article or apparatus.

[0058] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-calcium, high-alumina coal gangue cement admixture, characterized in that: Including low-calcium, high-alumina coal gangue powder and calcium hydroxide powder; low-calcium, high-alumina coal gangue cement admixture contains 10-20 wt% calcium hydroxide powder and 40-85 wt% low-calcium, high-alumina coal gangue powder. The composition of the low-calcium, high-alumina coal gangue powder is as follows (by mass fraction): 30%-38% alumina, 41%-47% silicon dioxide, 0.05%-0.15% calcium oxide, with the remainder being other impurities. The low-calcium, high-alumina coal gangue cement admixture also includes fly ash powder, slag powder, and blast furnace slag powder; when the amount of low-calcium, high-alumina coal gangue powder is 40-45 wt%, the mass ratio of low-calcium, high-alumina coal gangue powder, blast furnace slag powder, slag powder, and fly ash powder is 5:2:2:0.5-1.

2. The low-calcium, high-alumina coal gangue cement admixture according to claim 1, characterized in that: The purity of the calcium hydroxide powder is ≥97%, and the particle size is <25μm.

3. The low-calcium, high-alumina coal gangue cement admixture according to claim 1, characterized in that: Fly ash powder contains 52-62 wt% silica, 5-11 wt% alumina, and 4-6 wt% calcium oxide; slag powder contains 30-34 wt% silica, 20-25 wt% alumina, and 15-20 wt% calcium oxide; blast furnace slag powder contains 30-50 wt% silica, 5-10 wt% alumina, and 20-30 wt% calcium oxide.

4. A preparation process for a low-calcium, high-alumina coal gangue cement admixture according to any one of claims 1-3, characterized in that: Low-calcium, high-alumina coal gangue powder and calcium hydroxide powder are mixed evenly and then calcined to prepare low-calcium, high-alumina coal gangue cement admixture.

5. The preparation process of a low-calcium, high-alumina coal gangue cement admixture according to claim 4, characterized in that: The mixing time for low-calcium, high-alumina coal gangue powder and calcium hydroxide powder is 1.5-2.5 hours; during calcination, the calcination temperature is 800-830℃ and the calcination time is 3-4 hours.

6. An application of a cement admixture according to any one of claims 1-3, characterized in that: The low-calcium, high-alumina coal gangue cement admixture and cement clinker are mixed evenly, wherein the amount of low-calcium, high-alumina coal gangue cement admixture is 20-30 wt% and the amount of cement clinker is 70-80 wt%.

7. The application of a cement admixture according to claim 6, characterized in that: The cement clinker is P.O42.5 ordinary Portland cement.

8. The application of a cement admixture according to claim 6, characterized in that: The mixing time for low-calcium, high-alumina coal gangue cement admixture and cement clinker is 25-35 minutes.

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