BYT composite cement clinker and preparation method thereof

Abstract

The invention discloses a BYT (belite-calcium sulphoaluminate-calcium sulphosilicate) composite cement clinker. The BYT (belite-calcium sulphoaluminate-calcium sulphosilicate) composite cement clinker is prepared from the following raw materials in parts by weight: 60-79 parts of limestone, 24-39 parts of low-grade bauxite, 20-38 parts of desulfurized gypsum and 9-27 parts of fly ash. The preparation method comprises the following steps: preparing a raw material by taking limestone, low-grade bauxite, desulfurized gypsum and fly ash as main raw materials, carrying out high-temperature calcination, and then carrying out graded cooling to obtain the cement clinker; the BYT cement clinker with good strength development performance can be prepared while a large mixing amount of industrial waste is utilized; the energy consumption can be obviously reduced, the production period is shortened, and the method is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a BYT (Belit-calcium sulfoaluminate-calcium sulfosilicate) composite cement clinker and its preparation method. Background Technology

[0002] Traditional silicate cement (OPC) and sulfoaluminate cement (CSA) suffer from high CO2 emissions (approximately 0.83 tons of CO2 per ton of OPC clinker) and high energy consumption due to their high calcination temperatures (OPC approximately 1450℃, CSA approximately 1300℃) and high CaO content (OPC clinker CaO ≥ 60%). Furthermore, traditional cement also suffers from significant early-stage shrinkage and limited later-stage strength gain.

[0003] Early studies suggested that calcium thiosilicate Calcium sulfoaluminate has low hydration activity (only 12% hydration degree after 2 years) and has long been considered an inert mineral, requiring avoidance in cement clinker formation. However, recent studies have found that calcium sulfoaluminate... The aluminum hydroxide (AH3) generated by hydration can effectively activate Its activity, and its contribution to hydration, even surpasses that of belite (C2S). Based on this, dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement (BYT cement) can typically be used... (5-40%) Replaces part of C2S (20-60%) and regulates (20-60%) content to achieve a synergistic enhancement effect of minerals. In the resulting cement clinker system, the CaO content is only 56-72% of OPC and 82-90% of CSA. Combined with a calcination temperature that is 250℃ lower than OPC (to about 1200℃) and 100℃ lower than CSA, CO2 emissions per ton of clinker are reduced by 63% compared to OPC and 46% compared to CSA. and Synergistic hydration generates ettringite (AFt), CSH gel, and amorphous AH3, enabling BYT cement to combine the early strength characteristics of sulfoaluminate cement with the long-term strength stability of silicate cement, and the hardened paste has no shrinkage.

[0004] However, and The difference in thermal stability means that traditional processes often require secondary calcination (e.g., rapid cooling to 1270℃ followed by reheating to 1100-1200℃ for secondary calcination), which involves high energy consumption. Furthermore, repeated heating and cooling operations can easily induce thermal shock cracks in the clinker mineral structure. This is especially true for… In this case, the phase is prone to partial decomposition during the secondary heating stage, which in turn deteriorates the mechanical properties and volume stability of the cement clinker. Introducing phosphorus and fluorine can reduce this. The formation temperature of [the substance] is expanded to a coexistence range of 1125–1200℃, enabling single-stage calcination (e.g., preparing a product containing 36.0% [the substance] at 1150℃ for 15 minutes). 10.6% (clinker). Existing processes typically rely on secondary calcination or high-dosage mineralizers (such as phosphorus and fluorine), increasing costs and environmental risks.

[0005] How to simultaneously improve the mechanical strength, durability and other key properties of BYT cement materials while achieving multiple goals such as process simplification, carbon emission reduction and cost control has become a key scientific and technological problem that urgently needs to be solved in the field of cement materials. Summary of the Invention

[0006] The main objective of this invention is to address the problems and shortcomings of existing BYT cement clinker preparation technologies by providing a novel BYT cement clinker and its preparation method. This method utilizes industrial waste in large quantities and combines it with an optimized calcination process to prepare BYT cement clinker with excellent strength development properties.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A BYT composite cement clinker uses the following raw materials and their weight percentages: 60-79 parts limestone, 24-39 parts low-grade bauxite, 20-38 parts desulfurized gypsum, and 9-27 parts fly ash.

[0009] Furthermore, the main mineral composition and their mass percentage in the BYT composite cement clinker include: calcium sulfosilicate 28.6–38.8 wt.%, calcium sulfoaluminate 37.0–40.6 wt.%, dicalcium silicate 6.5–23.0 wt.%, iron phase 4.7–7.7 wt.%, and anhydrite 2.0–7.1 wt.%.

[0010] Preferably, the mass ratio of calcium sulfosilicate to dicalcium silicate is 1.24 to 5.97.

[0011] In the above scheme, the iron phase is tetracalcium aluminoferrite, which has a faster hydration rate and a more significant improvement in cement performance compared to iron phases such as hexacalcium aluminoferrite and dicalcium ferrite.

[0012] Furthermore, the limestone contains 45–55 wt.% CaO; the desulfurized gypsum contains 30–42 wt.% SO3; and the fly ash contains 46–60 wt.% SiO2 and 20–25 wt.% Al2O3.

[0013] Furthermore, the bauxite in question is low-grade bauxite, characterized by a low Al2O3 content (40–60 wt.%) and a significantly low aluminum-to-silicon ratio (A / S) (typically <7), primarily due to a high silica (SiO2) content (often 16–27 wt.%). In addition, this type of ore is usually accompanied by high levels of impurities such as iron oxide (Fe2O3, 3–8%) and titanium dioxide (TiO2, 2–4%), as well as a large loss on ignition (LOI, typically >12%). These compositional characteristics (low effective components and high content of key impurities) collectively determine its high smelting and processing difficulty and poor economic efficiency.

[0014] The above-mentioned method for preparing BYT cement clinker involves using limestone, low-grade bauxite, desulfurized gypsum, and fly ash as main raw materials to prepare raw meal, followed by high-temperature calcination and graded cooling to obtain cement clinker. The specific steps include:

[0015] 1) Mix and grind the raw materials weighed according to the proportion to obtain cement raw meal;

[0016] 2) Place the cement raw meal obtained in step 1) in a high-temperature furnace, heat it to the target calcination temperature and keep it at the temperature for calcination, and then perform staged cooling. The specific steps are as follows: First, slowly cool it down to 1100-1150℃ for heat preservation treatment, and then rapidly cool it to room temperature under directional airflow conditions to obtain the BYT composite cement clinker.

[0017] In the above scheme, the target calcination temperature is 1210-1250℃, and the holding time is 0.5-1h.

[0018] Furthermore, the heating rate used to reach the target calcination temperature is 5–10 °C / min.

[0019] In the above scheme, the heat preservation time in the staged cooling step is 0.5 to 1 hour.

[0020] Furthermore, the slow cooling process employs a cooling rate of 5–10 °C / min.

[0021] Furthermore, the low-grade bauxite undergoes fine grinding and activation pretreatment before use. The specific steps include: first, adding the low-grade bauxite to a citric acid solution and stirring (100-300 r / min) for 30-40 min, then soaking at room temperature for 2.5-3.5 h, and drying (80-110℃); then, finely grinding the bauxite in a pulverizer at a speed of 2700-3000 r / min with the addition of grinding aids for 20-25 min, so that it passes through a 150-mesh sieve.

[0022] In the above scheme, the concentration of the citric acid solution is 50-80 g / L.

[0023] In the above scheme, the solid-liquid ratio of the low-grade bauxite to the citric acid solution is 1g:7-10mL.

[0024] In the above scheme, the grinding aid can be triethanolamine or the like; its dosage is 0.05 to 0.2% of the mass of low-grade bauxite.

[0025] In the above scheme, further, in step 1), after the raw materials are crushed in proportion, they are manually premixed for 10 to 20 minutes and then ball-milled.

[0026] Furthermore, the grinding step employs a ball milling rate of 2200–2500 r / min and a time of 10–12 h.

[0027] Furthermore, in step 2), the rapid cooling rate is 35-40℃ / min; the cooling method used is to form a directional airflow to achieve rapid cooling by means of electric hair dryer, etc. Precise control of the cooling rate can alleviate the phase transformation tendency of β-C2S to γ-C2S, avoid strength loss caused by clinker pulverization, and thus improve early hydration activity.

[0028] Further, in step 2), the calcined cement clinker is crushed and ground, then 2-5% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. The residue on the sieve is less than 3%, and the finished cement product is made.

[0029] Compared with existing technologies, the beneficial effects of the present invention include:

[0030] 1) The formation temperature windows of calcium sulfoaluminate and calcium sulfosilicate differ greatly. Calcium sulfoaluminate is stable below 1350℃ and decomposes above 1400℃, while calcium sulfosilicate has a formation temperature range of 1100~1200℃ and decomposes at high temperatures. To address these issues, this invention employs a "one-step calcination + multi-stage controlled cooling" system and uses directional airflow rapid cooling to cool the clinker, effectively promoting the formation of β-type dicalcium silicate in the clinker.

[0031] 2) This invention adopts a “one-step calcination + multi-stage controlled cooling” system, which only raises the temperature to the target temperature once to complete the formation of calcium sulfoaluminate. The subsequent 1100-1150℃ is a controllable heat preservation in the cooling path, which uses the residual heat of clinker to directly trigger the synthesis of calcium sulfosilicate, avoiding the energy consumption and decomposition risk of secondary heating.

[0032] 3) By coordinating the proportions of the three main minerals—belite, calcium sulfoaluminate, and calcium sulfosilicate—the system ensures a sufficient content of calcium sulfoaluminate, guaranteeing a certain level of mechanical strength in the early stages and enabling controllable adjustment of the calcium sulfosilicate content in cement clinker. Furthermore, the formation of a certain amount of anhydrite during clinker calcination fully demonstrates the hydration coordination effect of calcium sulfoaluminate and calcium sulfosilicate, thereby improving the early and later strength of cement clinker.

[0033] 4) The iron phase formed in the clinker is tetracalcium aluminoferrite, which improves the erosion resistance of the cement.

[0034] 5) This invention employs a formulation system combining low-grade bauxite and fly ash. It utilizes the readily reactive amorphous aluminum components in the fly ash to provide activation energy, initiating and significantly accelerating the dissolution of inert aluminum minerals in the low-grade bauxite (forming a significant 'synergistic activation effect'). This increases the overall aluminum extraction efficiency by 23-35%, achieving the dual goals of significantly reducing raw material costs and realizing the high-value utilization of bulk industrial solid waste (fly ash). Furthermore, addressing the issues of high silicon content, complex mineral phases, and low reactivity inherent in low-grade bauxite, this invention further incorporates fine grinding and activation pretreatment, first using lemon... Acid solution pretreatment dissolves surface impurities and promotes the increase of reactive site density in the target aluminum minerals. The addition of triethanolamine grinding aid reduces grinding energy consumption and forms a hydrophobic film on the surface of the aluminum minerals, inhibiting the hydration reaction of silicate components, reducing impurity dissolution, selectively improving the reactivity of the target aluminum minerals, and suppressing the adverse effects of impurities such as silicon. This successfully breaks through the technical and economic bottleneck of efficient resource utilization of low-grade bauxite, and simultaneously realizes the value-added disposal of fly ash solid waste, ultimately constructing a closed-loop aluminum resource recycling system of 'high-value utilization of low-quality raw materials - resource utilization of industrial solid waste'.

[0035] 6) The preparation process of BYT cement clinker described in this invention can achieve a breakthrough temperature control strategy, controlling the calcination temperature in the range of 1100-1250℃, which is 100-350℃ lower than the traditional silicate cement process (conventional 1350-1450℃) and 50-300℃ lower than the sulfoaluminate cement process (typical 1300-1400℃). Attached Figure Description

[0036] Figure 1 These are the XRD patterns of the cement clinker prepared in Examples 1 to 5 of this invention.

[0037] Figure 2 This is the XRD pattern of the rapid-hardening CSA cement obtained in Comparative Example 1 of this invention.

[0038] Figure 3 This is the XRD pattern of the low-alkali CSA cement obtained in Comparative Example 2 of this invention.

[0039] Figure 4 This is the XRD pattern of the cement clinker obtained in Comparative Example 3 of this invention.

[0040] Figure 5 This is the XRD pattern of the cement clinker obtained in Comparative Example 4 of this invention.

[0041] Figure 6 This is the XRD pattern of the cement clinker obtained in Comparative Example 5 of this invention.

[0042] Figure 7 The strength of the neat paste at different ages is the BYT cement prepared in Examples 1-5 of this invention and the cement in Comparative Examples 1-5.

[0043] Figure 8 These are the XRD patterns of BYT cement prepared in Examples 1-5 after 3 days of hydration.

[0044] Figure 9 These are the XRD patterns of BYT cement prepared in Examples 1-5 after 28 days of hydration.

[0045] Figure 10 These are the XRD patterns of BYT cement prepared in Examples 1-5 after 90 days of hydration.

[0046] Figure 11 The XRD patterns of CSA cement hydrated for 3 days are shown in Comparative Examples 1 and 2.

[0047] Figure 12 The XRD patterns of CSA cement obtained in Comparative Examples 1 and 2 after 28 days of hydration are shown.

[0048] Figure 13 The XRD patterns of BYT cement hydrated for 90 days are shown in Comparative Examples 1 and 2.

[0049] Figure 14 The XRD patterns of BYT cement hydrated for 3 days are shown in Comparative Examples 3-5.

[0050] Figure 15 The XRD patterns of BYT cement hydrated for 28 days are shown in Comparative Examples 3-5.

[0051] Figure 16 The XRD patterns of BYT cement hydrated for 90 days are shown in Comparative Examples 3-5. Detailed Implementation

[0052] To further understand the present invention, the following detailed description of a paste preparation method for high-precision thin-layer photopolymerization printing provided by the present invention is provided in conjunction with embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0053] In the following examples, the chemical composition of the raw materials is shown in Table 1.

[0054] Table 1 Chemical composition of raw materials (wt.%)

[0055]

[0056] Before use, bauxite undergoes fine grinding and activation pretreatment. The specific steps include: first, adding low-grade bauxite to a citric acid solution (concentration of 50-80 g / L) and stirring (100-300 r / min) for 30-40 min, then soaking at room temperature for 2.5-3.5 h, and then fully drying at 80-110℃. Next, finely grinding the bauxite in a pulverizer at a speed of 2700-3000 r / min with the addition of triethanolamine grinding aid (0.05-0.2% of the bauxite mass) for 20-25 min, so that it passes through a 150-mesh sieve.

[0057] Example 1

[0058] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 78.39 parts, bauxite 24.58 parts, desulfurized gypsum 20.49 parts, and fly ash 26.82 parts; the specific preparation steps are as follows:

[0059] 1) Add low-grade bauxite to a citric acid solution with a concentration of 50 g / L, stir continuously at 100 r / min for 30 min, soak at room temperature for 2.5 h, and then dry the bauxite thoroughly at 105 °C; then grind the bauxite in a pulverizer at 2700 r / min with the addition of triethanolamine grinding aid (0.05% of the bauxite mass) for 20 min, so that it passes through a 150 mesh sieve;

[0060] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0061] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0062] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1210°C at a rate of 10°C / min and held for 0.5 hours. Then, the temperature was lowered to 1150°C at a rate of 10°C / min and held for 0.5 hours. After calcination, the cake was rapidly cooled to room temperature using a blowing method for 28–33 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0063] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 28.6 wt.% calcium sulfosilicate, 37.0 wt.% calcium sulfoaluminate, 7.7 wt.% tetracalcium aluminoferrite (iron phase), 23.0 wt.% dicalcium silicate (belite), and 2.0 wt.% calcium sulfate (anhydrite).

[0064] After the calcined cement clinker is crushed and ground, 5% anhydrous gypsum by weight is added, mixed evenly, and passed through a 200-mesh sieve. The residue on the sieve is less than 3%, and the finished cement product is made.

[0065] Example 2

[0066] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 74.53 parts, bauxite 27.95 parts, desulfurized gypsum 24.56 parts, and fly ash 22.85 parts; the specific preparation steps are as follows:

[0067] 1) Add low-grade bauxite to a citric acid solution with a concentration of 60 g / L, stir continuously at 150 r / min for 32 min, and soak at room temperature for 2.7 h. After soaking, dry the bauxite thoroughly at 105 °C. Then, grind the bauxite in a pulverizer at 2800 r / min with the addition of triethanolamine grinding aid (0.05% of the bauxite mass) for 21 min, so that it passes through a 150 mesh sieve.

[0068] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0069] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0070] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1220°C at a rate of 9°C / min and held for 0.7 hours. Then, the temperature was lowered to 1140°C at a rate of 8°C / min and held for another 0.7 hours. After calcination, the cake was rapidly cooled to room temperature using a blowing method for 28–32 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0071] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 30.2 wt.% calcium sulfosilicate, 38.5 wt.% calcium sulfoaluminate, 7.2 wt.% tetracalcium aluminoferrite (iron phase), 18.1 wt.% dicalcium silicate (belite), and 3.5 wt.% calcium sulfate (anhydrite). The calcined cement clinker is pulverized and ground, then 5% anhydrous gypsum is added, mixed thoroughly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0072] Example 3

[0073] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 69.66 parts, bauxite 31.32 parts, desulfurized gypsum 29.66 parts, and fly ash 16.86 parts; the specific preparation steps are as follows:

[0074] 1) Add low-grade bauxite to a citric acid solution with a concentration of 70 g / L, stir continuously at 200 r / min for 34 min, and soak at room temperature for 2.9 h. After soaking, dry the bauxite thoroughly at 105 °C. Then, grind the bauxite in a pulverizer at 2900 r / min with the addition of triethanolamine grinding aid (0.1% of the bauxite mass) for 22 min to make it pass through a 150 mesh sieve.

[0075] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0076] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0077] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1230°C at a rate of 8°C / min and held for 0.8 hours. Then, the temperature was lowered to 1130°C at a rate of 7°C / min and held for another 0.8 hours. After calcination, the cake was rapidly cooled to room temperature using a blowing method for 28–32 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0078] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 33.8 wt.% calcium sulfosilicate, 39.2 wt.% calcium sulfoaluminate, 7.6 wt.% tetracalcium aluminoferrite (iron phase), 13.5 wt.% dicalcium silicate (belite), and 4.3 wt.% calcium sulfate (anhydrite).

[0079] After the calcined cement clinker is crushed and ground, 4% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. The residue on the sieve is less than 3%, and the finished cement product is made.

[0080] Example 4

[0081] A BYT composite cement clinker uses the following raw materials and their respective weight percentages: limestone 67.81 parts, bauxite 31.68 parts, desulfurized gypsum 31.74 parts, and fly ash 15.90 parts; the specific preparation steps are as follows:

[0082] 1) Add low-grade bauxite to a citric acid solution with a concentration of 75 g / L, stir continuously at 250 r / min for 36 min, and soak at room temperature for 3.2 h. After soaking, dry the bauxite thoroughly at 105℃. Then, grind the bauxite in a pulverizer at 3000 r / min with the addition of triethanolamine grinding aid (0.15% of the bauxite mass) for 23 min, so that it passes through a 150 mesh sieve.

[0083] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0084] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0085] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1240°C at a rate of 7°C / min and held for 0.9 hours. Then, the temperature was lowered to 1120°C at a rate of 6°C / min and held for another 0.9 hours. After calcination, the cake was rapidly cooled to room temperature using a blowing method for 28–32 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0086] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 33.5 wt.% calcium sulfosilicate, 39.8 wt.% calcium sulfoaluminate, 7.4 wt.% tetracalcium aluminoferrite (iron phase), 11.4 wt.% dicalcium silicate (belite), and 6.3 wt.% calcium sulfate (anhydrite).

[0087] After the calcined cement clinker is crushed and ground, 3% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0088] Example 5

[0089] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 65.93 parts, bauxite 32.05 parts, desulfurized gypsum 33.83 parts, and fly ash 14.91 parts; the specific preparation steps are as follows:

[0090] 1) Add low-grade bauxite to a citric acid solution with a concentration of 80 g / L, stir continuously at 300 r / min for 40 min, soak at room temperature for 3.5 h, and then dry the bauxite thoroughly at 105 °C; then grind the bauxite in a pulverizer at 3000 r / min with the addition of triethanolamine grinding aid (0.2% of the bauxite mass) for 25 min, so that it passes through a 150 mesh sieve;

[0091] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0092] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0093] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1250°C at a rate of 5°C / min and held for 1 hour. Then, it was lowered to 1100°C at a rate of 5°C / min and held for another hour. After calcination, it was rapidly cooled to room temperature using a blowing fan for 27–31 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0094] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 38.8 wt.% calcium sulfosilicate, 40.6 wt.% calcium sulfoaluminate, 4.7 wt.% tetracalcium aluminoferrite (iron phase), 6.5 wt.% dicalcium silicate (belite), and 7.1 wt.% calcium sulfate (anhydrite).

[0095] After the calcined cement clinker is crushed and ground, 3% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0096] Comparative Example 1

[0097] A rapid-hardening CSA cement is composed of the following raw materials in parts by weight: 90 parts sulfoaluminate cement clinker, 13 parts phosphate building gypsum, and 12 parts limestone powder; its preparation steps are as follows:

[0098] The various raw materials are ground separately and then mixed in a forced mixer according to the proportions to obtain cement.

[0099] Comparative Example 2

[0100] A low-alkali CSA cement is composed of the following raw materials in parts by weight: 85 parts sulfoaluminate cement clinker, 11 parts phosphate building gypsum, and 11 parts limestone powder; its preparation steps are as follows:

[0101] The various raw materials are ground separately and then mixed in a forced mixer according to the proportions to obtain cement.

[0102] Comparative Example 3

[0103] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 65.93 parts, bauxite 32.05 parts, desulfurized gypsum 33.83 parts, and fly ash 14.91 parts; the specific preparation steps are as follows:

[0104] 1) Add low-grade bauxite to a citric acid solution with a concentration of 80 g / L, stir continuously at 300 r / min for 40 min, soak at room temperature for 3.5 h, and then dry the bauxite thoroughly at 105 °C; then grind the bauxite in a pulverizer at 3000 r / min with the addition of triethanolamine grinding aid (0.2% of the bauxite mass) for 25 min, so that it passes through a 150 mesh sieve;

[0105] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0106] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0107] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The temperature was raised from room temperature to 1200°C at a rate of 5°C / min and held for 1 hour. Then, the temperature was lowered to 1120°C at a rate of 5°C / min and held for calcination for another hour. After calcination, the cake was rapidly cooled to room temperature by blowing air for 27–32 minutes to obtain the cement clinker. The calcined cement clinker was then crushed, ground, and passed through a 200-mesh sieve to obtain the final product.

[0108] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 48.7 wt.% calcium sulfosilicate, 30.0 wt.% calcium sulfoaluminate, 5.9 wt.% tetracalcium aluminoferrite (iron phase), 5.3 wt.% dicalcium silicate (belite), and 8.9 wt.% calcium sulfate (anhydrite).

[0109] After the calcined cement clinker is crushed and ground, 3% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0110] Comparative Example 4

[0111] A BYT composite cement clinker uses the following raw materials and their weight percentages: limestone 65.93 parts, bauxite 32.05 parts, desulfurized gypsum 33.83 parts, and fly ash 14.91 parts; the specific preparation steps are as follows:

[0112] 1) Add low-grade bauxite to a citric acid solution with a concentration of 80 g / L, stir continuously at 300 r / min for 40 min, soak at room temperature for 3.5 h, and then dry the bauxite thoroughly at 105 °C; then grind the bauxite in a pulverizer at 3000 r / min with the addition of triethanolamine grinding aid (0.2% of the bauxite mass) for 25 min, so that it passes through a 150 mesh sieve;

[0113] 2) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0114] 3) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0115] The obtained raw meal cake is placed in a high-temperature furnace for calcination. The temperature is raised from room temperature to 1300℃ at a rate of 5℃ / min and held for 1 hour. Then, the temperature is lowered to 1150℃ at a rate of 5℃ / min and held for calcination for 1 hour. After calcination, the cake is rapidly cooled to room temperature by blowing air for 28-33 minutes to obtain the cement clinker. The calcined cement clinker is then crushed, ground, and passed through a 200-mesh sieve to obtain the final product.

[0116] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 5.2 wt.% calcium sulfosilicate, 45.2 wt.% calcium sulfoaluminate, 6.3 wt.% tetracalcium aluminoferrite (iron phase), 19.6 wt.% dicalcium silicate (belite), and 20.5 wt.% calcium sulfate (anhydrite).

[0117] After the calcined cement clinker is crushed and ground, 3% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0118] Comparative Example 5

[0119] A BYT composite cement clinker uses the following raw materials and their weight proportions: limestone 65.93 parts, bauxite 32.05 parts, desulfurized gypsum 33.83 parts, and fly ash 14.91 parts. The low-grade bauxite in this group undergoes a simple fine grinding and activation pretreatment before use. The grinding mill speed is 3000 r / min, and the grinding time is 25 min. The specific preparation steps are as follows:

[0120] 1) After crushing the raw materials according to the mass ratio, premix them manually for 10 minutes, and then mix them again in a planetary ball mill at a rate of 2400 r / min for 12 hours to ensure that the raw materials are mixed evenly. Finally, use a 200 mesh sieve to screen the raw material to obtain the raw material.

[0121] 2) Add 15wt.% water to the obtained raw material and stir thoroughly. Use a steel mold to press the raw material into small test cakes of Φ50mm×8mm at 20MPa and place them in an oven to dry at 105℃ for firing.

[0122] The obtained raw meal cake was placed in a high-temperature furnace for calcination. The furnace temperature was first raised from room temperature to 1250°C at a rate of 5°C / min and held for 1 hour. Then, it was lowered to 1100°C at a rate of 5°C / min and held for another hour. After calcination, it was rapidly cooled to room temperature using a blowing fan for 27–31 minutes, yielding the cement clinker. The calcined cement clinker was then pulverized, ground, and passed through a 200-mesh sieve.

[0123] According to Rietveld quantitative analysis, the main mineral composition of cement clinker is 40.5 wt.% calcium sulfosilicate, 34.6 wt.% calcium sulfoaluminate, 4.1 wt.% tetracalcium aluminoferrite (iron phase), 12.4 wt.% dicalcium silicate (belite), and 5.6 wt.% calcium sulfate (anhydrite).

[0124] After the calcined cement clinker is crushed and ground, 3% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. If the residue is less than 3%, the finished cement product is produced.

[0125] The compressive strength of the new BYT cement obtained in Examples 1-5 and the cement obtained in Comparative Examples 1-5 was tested at a water-cement ratio of 0.5. The specific testing method is as follows: Cement specimens with a size of 40mm×40mm×40mm were prepared according to GB / T 17671-2021 standard, and then placed in a standard curing box. After 6 hours, they were demolded and transferred to a constant temperature water bath for curing. When the specimens reached the corresponding age, the compressive strength test was carried out according to the specification. The test results are shown in Table 2.

[0126] Table 2. Test results of compressive strength (cement paste strength) of cement specimens obtained in Examples 1-5 and Comparative Examples 1-4.

[0127]

[0128] As shown in Table 2, the 28-day compressive strength of both rapid-hardening and low-alkali sulfoaluminate cement hardened bodies showed an increasing trend. Comparative Example 1 exhibited higher strength at all ages than Comparative Example 2, demonstrating superior mechanical properties, but both showed shrinkage at 90 days. Comparative Examples 3 and 4, based on the formulation of Example 5, modified the calcination temperature and holding time. The results showed that the compressive strength of Comparative Example 3 was lower than that of Example 5 at all ages. Although the compressive strength of Comparative Example 4 was higher than that of Example 5 in the early stages, its compressive strength was lower than that of Example 5 after 28 days, and even showed shrinkage at 90 days.

[0129] The test results of Examples 1-5 show that the novel low-carbon BYT obtained in this invention... The highest compressive strength of the cement clinker system reached 43.6 MPa and 48.8 MPa at 28 days and 90 days, respectively. Although the early strength (1-7 days) was lower than that of traditional sulfoaluminate cement, Examples 3-5 achieved a strength reversal at 28 days and the strength at 90 days was higher than that of sulfoaluminate cement in all aspects, which solved the problem of strength reduction in the later stage of sulfoaluminate cement. This also proves that the system has a significant late-stage strengthening effect.

[0130] The compressive strength of Comparative Examples 1-2 was higher than that of the Example Group during the early hydration stage. This is because the calcium sulfoaluminate and gypsum content in the sulfoaluminate cement is very high, allowing for rapid hydration upon contact with water and the formation of a large amount of calcium vanadate. Since the gypsum content in BYT cement clinker is inherently low, and the amount of gypsum added to the clinker later is only 2-5%, far lower than the gypsum content in sulfoaluminate cement, the hydration process is slower in the early stages, resulting in a lower amount of calcium vanadate generated compared to sulfoaluminate cement. Since calcium vanadate primarily contributes to strength, the compressive strength is lower than that of sulfoaluminate cement. From the 28-day hydration age, the compressive strength of Examples 3, 4, and 5 was higher than that of the comparative examples. This is mainly due to two factors. First, the calcium sulfosilicate in the cement system plays a role, namely, the hydration synergy effect between calcium sulfosilicate and calcium sulfoaluminate. Calcium sulfosilicate hydrates in the later stages to form dihydrate gypsum, providing additional gypsum to the system. This gypsum continues to react with unreacted calcium sulfoaluminate, continuously generating calcium vanadate, thus increasing strength. Secondly, the belite in the system undergoes later hydration to form hydrated calcium aluminum feldspar (C2ASH8). Due to the complex layered crystal structure of C2ASH8, namely bitetrahedral and octahedral layers, studies have shown that it helps improve the compressive strength of sulfoaluminate cements, providing additional support. At a 90-day hydration age, the compressive strength of Examples 1-5 was higher than that of the comparative example, which is also related to the two factors mentioned above.

[0131] In summary, the BYT cement described in this invention exhibits higher compressive strength in the later stages compared to sulfoaluminate cement. This invention utilizes industrial solid waste to replace traditional raw materials, employing fine grinding and activation pretreatment of low-grade bauxite. This achieves a 12-18% increase in 28-day strength and a 30-55% increase in 90-day strength while lowering the calcination temperature (1100-1250℃). Compared to traditional processes, this technology offers advantages such as wider raw material adaptability, reduced carbon emissions, and superior durability in the later stages, demonstrating broad prospects for development in the building materials industry.

[0132] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A BYT composite cement clinker, characterized in that, The raw materials used and their weight percentages include: 60-79 parts limestone, 24-39 parts low-grade bauxite, 20-38 parts desulfurized gypsum, and 9-27 parts fly ash.

2. The BYT composite cement clinker according to claim 1, characterized in that, The limestone contains 45–55 wt.% CaO; the desulfurized gypsum contains 30–42 wt.% SO3; and the fly ash contains 46–60 wt.% SiO2 and 20–25 wt.% Al2O3.

3. The BYT composite cement clinker according to claim 1, characterized in that, The low-grade bauxite contains 40–60 wt.% Al2O3, 16–27 wt.% SiO2, 3–8% Fe2O3, and 2–4% TiO2; the aluminum-silicon ratio is <7, and the LOI is >12%.

4. The method for preparing BYT composite cement clinker according to any one of claims 1 to 3, characterized in that, Includes the following steps: 1) Mix and grind the raw materials weighed according to the proportion to obtain cement raw meal; 2) Place the cement raw meal obtained in step 1) in a high-temperature furnace, heat it to the target calcination temperature and keep it at the temperature for calcination, and then perform staged cooling. The specific steps are as follows: First, slowly cool it down to 1100-1150℃ for heat preservation treatment, and then rapidly cool it to room temperature under directional airflow conditions to obtain the BYT composite cement clinker.

5. The preparation method according to claim 4, characterized in that, The target calcination temperature is 1210–1250℃, and the holding time is 0.5–1h.

6. The preparation method according to claim 4, characterized in that, The cooling rate used for slow cooling is 5–10 °C / min.

7. The preparation method according to claim 4, characterized in that, The heat preservation treatment time is 0.5 to 1 hour.

8. The preparation method according to claim 4, characterized in that, Before use, the low-grade bauxite undergoes fine grinding and activation pretreatment. The specific steps include: first, adding the low-grade bauxite to a citric acid solution and stirring for 30-40 minutes; then, soaking at room temperature for 2.5-3.5 hours; drying; and then fine grinding the bauxite in a pulverizer at a speed of 2700-3000 r / min with the addition of grinding aids for 20-25 minutes, so that it passes through a 150-mesh sieve.

9. The preparation method according to claim 4, characterized in that, In step 2), the rapid cooling rate is 35-40°C / min.

10. The preparation method according to claim 4, characterized in that, In step 2), the calcined cement clinker is crushed and ground, 2-5% anhydrous gypsum is added, mixed evenly, and passed through a 200-mesh sieve. The residue on the sieve is less than 3%, thus obtaining the BYT cement product.

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