Clinker step calcination and powder multi-level matching composite cement and preparation method thereof

Abstract

The present application relates to a kind of clinker step calcination and powder multi-level matching composite cement and its preparation method, by mass fraction, including the following raw materials: low-temperature calcined clinker 40-60 parts, high-temperature calcined clinker 5-15 parts, gypsum 4-6 parts, joint grinding admixture 15-30 parts, other admixture 10-15 parts, grinding aid 0.02-0.2 parts.The present application controls low-temperature calcined clinker by high-temperature calcined clinker to make composite system have the characteristics of early strength, high strength and stable strength development, and there are joint grinding admixture and other admixture and the like, which can increase the hourly output, improve production efficiency, reduce production energy consumption, reduce the proportion of production clinker, reduce cost;In the preparation method, part of the joint grinding admixture participates in the grinding process, so that the entire powder system forms a good particle size distribution and grading composite, better play the hydration characteristics of each part, improve the strength.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of cement production, and particularly relates to a composite cement prepared by step-by-step calcination of clinker and multi-level matching of powder and a preparation method thereof. BACKGROUND

[0002] The C3S (tricalcium silicate) component accounts for 35%-45% in the low-temperature calcined clinker, and the C3S component accounts for 50%-60% in the ordinary Portland cement clinker. Although reducing the content of C3S contributes greatly to carbon reduction in cement production, the C3S in the clinker mineral is the main source of early strength of cement, which leads to the disadvantage of early strength of the cement prepared by using the low-temperature calcined clinker alone. How to further improve the early mechanical properties of the low-temperature calcined clinker becomes a problem to be solved.

[0003] The high-temperature calcined clinker has good early strength of the cement prepared by virtue of the early strength mineral components C 12 A7 (dodecacalcium heptatitanate) and C4A3 (calcium sulphoaluminate) in it, but the high calcination temperature brings about great energy consumption. At the same time, high-alumina raw materials such as bauxite are needed in the preparation of the high-temperature calcined clinker, which is high in price, which also leads to high cost of the cement prepared by using the high-temperature calcined clinker alone, and limits the application space of the cement to some extent. How to exert the early strength advantage of the high-temperature calcined clinker and increase the application space thereof becomes a problem to be solved.

[0004] The size and particle size distribution of cement particles and mixed material particles have a direct relationship with the hydration speed and hydration degree of cement. In the cement production grinding process, the mineral powder and fly ash do not participate in the grinding process, but are directly mixed at the end, which leads to the fact that the particle size distribution and grading of cement particles and mixed material particles cannot be well controlled in the actual production process. How to regulate and control the particle size distribution and grading of each component powder of cement in the actual production process becomes a problem to be solved. SUMMARY

[0005] The application aims to overcome the above technical deficiencies, and provides a composite cement prepared by step-by-step calcination of clinker and multi-level matching of powder and a preparation method thereof, which solves the technical problems of poor early mechanical properties of the low-temperature calcined clinker, high cost of the cement prepared by using the high-temperature calcined clinker alone, and uncontrollable particle size distribution and grading of cement in the prior art.

[0006] To achieve the above technical purposes, the technical solution provided by the application is as follows:

[0007] In a first aspect, the present application provides a clinker step calcination and powder multi-level composite cement, comprising the following raw materials in parts by mass: low-temperature calcined clinker 40-60 parts, high-temperature calcined clinker 5-15 parts, gypsum 4-6 parts, joint grinding admixture 15-30 parts, other admixture 10-15 parts, and grinding aid 0.02-0.2 parts.

[0008] In a second aspect, the present application provides a preparation method of a clinker step calcination and powder multi-level composite cement, comprising the following steps: mixing low-temperature calcined clinker, high-temperature calcined clinker, gypsum, first joint grinding admixture, other admixture, and grinding aid, and performing joint grinding to obtain a first powder; wherein the mass of the first joint grinding admixture is more than 12.5% of the total mass of the joint grinding admixture; and mixing the remaining part of the joint grinding admixture with the first powder and stirring uniformly to obtain the clinker step calcination and powder multi-level composite cement.

[0009] Compared with the prior art, the present application has the following advantages:

[0010] (1) The present application controls the low-temperature calcined clinker by the high-temperature calcined clinker to make the composite system have the characteristics of early strength, high strength, and stable strength development, avoids the shortcomings of poor early mechanical properties of using all low-temperature calcined clinker, and avoids the shortcomings of high energy consumption and high price of using all high-temperature calcined clinker; the composite system of the two cement clinkers guarantees their respective advantages and increases the application space; at the same time, the joint grinding admixture and other admixture and the like are added, and the grinding aid is added, which can increase the hourly output, improve the production efficiency, and reduce the production energy consumption in a certain amount. The addition of the multiple joint grinding admixtures and other admixtures and the like reduces the proportion of the produced clinker, and is beneficial to reducing the clinker production energy consumption and reducing the cost.

[0011] (2) In the preparation method of the present application, part of the joint grinding admixture which does not participate in the grinding process is involved in the grinding process, which is adjusted with other components to form a good particle size distribution and grading composite of the entire powder system, better play the hydration characteristics of each part, so as to obtain a cement product with good performance and improve the strength. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0013] In a first aspect, the present application provides a kind of clinker step calcination and powder multi-level composite cement, by mass fraction, including the following raw materials: low temperature calcined clinker 40-60 parts, high temperature calcined clinker 5-15 parts, gypsum 4-6 parts, joint grinding mixed material 15-30 parts, other mixed material 10-15 parts, grinding aid 0.02-0.2 parts.

[0014] Preferably, by mass percentage, the mineral composition of low temperature calcined clinker includes: 35%-45% of C3S (tricalcium silicate), 20%-30% of C2S (dicalcium silicate), 16%-26% of C4AF (tetracalcium aluminoferrite), 1%-3% of C3A (aluminum tri-calcium).

[0015] Further preferably, the preparation steps of low temperature calcined clinker include: uniformly mixing 70-80 parts of limestone, 10-15 parts of sandstone and 5-10 parts of iron ore by mass fraction, calcining at 1200-1300 ℃ for 30-40 min to obtain low temperature calcined clinker, which is a clinker mainly composed of C3S, C2S, C4AF and C3A.

[0016] Preferably, by mass percentage, the mineral composition of high temperature calcined clinker includes: 10%-15% of C 12 A7 (dodecacalcium heptatitanate), 30%-50% of C4A3 (calcium sulphoaluminate) and 15%-25% of C2S (dicalcium silicate).

[0017] Further preferably, the preparation steps of high temperature calcined clinker include: taking 40-50 parts of limestone, 30-40 parts of bauxite and 10-30 parts of anhydrite as main raw materials, calcining at a temperature of 1350-1450 ℃ for 30-40 min to obtain high temperature calcined clinker, which is a clinker mainly composed of C 12 A7, C4A3 and C2S.

[0018] Preferably, the joint grinding mixed material includes fly ash and mineral powder in a mass ratio of (5-10):(10-20); that is, by mass fraction, it includes the following raw materials: low temperature calcined clinker 40-60 parts; high temperature calcined clinker 5-15 parts; gypsum 4-6 parts; fly ash 5-10 parts; mineral powder 10-20 parts, other mixed material 10-15 parts; grinding aid: 0.02-0.2 parts.

[0019] Further preferably, the specific surface area of fly ash is 400-600 m 2 / kg. In the present application, first grade fly ash is selected, which has high activity. In the present application, the amount of fly ash is relatively small, which can play the role of grinding aid, increase the hourly output, and avoid the significant reduction of cement strength caused by the addition of a large amount of fly ash.

[0020] Further preferably, the specific surface area of the mineral powder is 380-480 m 2 / kg; in the present application, the mineral powder is beneficial to the cement hydration process, accelerates the hydration, and the amount of ettringite and C-S-H gel is larger, thereby improving the compressive strength and flexural strength of the cement.

[0021] In the present application, part of the fly ash and mineral powder is ground together with the cement clinker, and the remaining part is mixed finally.

[0022] Preferably, the other mixed materials include limestone; in the present application, the limestone is used as a cement mixed material, which has good grindability, small water requirement for cement standard consistency, and is beneficial to improve the particle distribution of the cement and the compatibility with the admixture. In the present application, the limestone directly participates in the grinding process of the cement clinker and gypsum.

[0023] Preferably, in the present application, the gypsum is a mixture of natural gypsum and desulfurization gypsum at a mass ratio of 1:1, and the gypsum in the present application participates in the grinding process.

[0024] Preferably, the grinding aid has triethanolamine as the main component.

[0025] In a second aspect, the present application provides a preparation method of a clinker step calcination and powder multi-level composite cement, comprising the following steps:

[0026] The low-temperature calcined clinker, the high-temperature calcined clinker, the gypsum, the first joint grinding mixed material, the other mixed materials and the grinding aid are mixed and ground to obtain a first powder; wherein the mass of the first joint grinding mixed material is more than 12.5% of the total mass of the joint grinding mixed material;

[0027] The remaining part of the joint grinding mixed material is mixed with the first powder and stirred uniformly to obtain the clinker step calcination and powder multi-level composite cement.

[0028] Preferably, the first joint grinding mixed material accounts for 12.5%-60% of the total mass of the joint grinding mixed material, such as 12.5%, 15%, 18%, 20%, 25%, 30%, 35%, 38%, 41%, 42%, 45%, 50%, 55% or 48%.

[0029] More preferably, the combined grinding mixture includes fly ash and mineral powder, and the first combined grinding mixture includes first fly ash and first mineral powder, wherein the first fly ash accounts for 30% to 60% of the total mass of fly ash, and the first mineral powder accounts for 30% to 60% of the total mass of mineral powder. More preferably, the first fly ash accounts for 38% to 48% of the total mass of fly ash, such as 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, or 48%; and the first mineral powder accounts for 35% to 45% of the total mass of mineral powder, such as 35%, 37%, 39%, 40%, 41%, 42%, or 45%.

[0030] Preferably, the combined grinding conditions are: grinding in a ball mill at a speed of 50-60 rpm for 28-35 minutes.

[0031] Preferably, the remaining fly ash and mineral powder are mixed with the first powder and stirred at a speed of 20-40 rpm for 3-5 minutes.

[0032] In this invention, 30% to 60% of the mineral powder and 30% to 60% of the fly ash are added to the mill in advance, so that they participate in the grinding process with cement clinker, gypsum, and other admixtures. At the same time, grinding aids are added. Finally, the powder coming out of the mill is mixed with the remaining mineral powder and fly ash that did not participate in the joint grinding, so that the entire powder system forms a complete and continuous multi-graded composite, and finally obtains a cement product with good performance.

[0033] Preferably, in this invention, the powder particle size is divided into: d < 3 μm, 3 μm ≤ d < 30 μm, 30 μm ≤ d < 65 μm, and 65 μm ≤ d, wherein the proportion of powder with d < 3 μm is 2-4%, the proportion of powder with 3 μm ≤ d < 30 μm is 56-76%, the proportion of powder with 30 μm ≤ d < 65 μm is 17-30%, and the proportion of powder with 65 μm ≤ d is 2-12%; the gradation of different ranges is controlled by combined grinding and final mixing to achieve a continuous and complete multi-gradation composite; thus forming a multi-gradation composite cement product with good performance.

[0034] In this invention, low-temperature calcined clinker and high-temperature calcined clinker are obtained through stepwise calcination. Stepwise calcination here refers to calcining separately to obtain the two types of clinker, without emphasizing the order in which they are obtained. The various material components are then compounded, with a portion of the mineral powder and fly ash participating in the grinding process with the clinker, gypsum, and limestone for joint grinding, while the remaining portion is mixed together after grinding is complete. The main mechanism of action of this invention includes:

[0035] 1. The content of C3S in the clinker mineral composition of low-temperature calcined clinker is about 35%-45%, and the early mechanical properties are not ideal during separate use. At this time, a small amount of high-temperature calcined clinker is introduced, and the early strength effect of the whole system is achieved by virtue of the regulation of two early-type minerals, i.e., dodecacalcium heptatitanium oxide (C 12 A7) and anhydrous calcium sulphoaluminate (C4A3 ), and the high energy consumption and high price caused by the use of all high-temperature calcined clinker are avoided, and the application space is increased to a certain extent. At the same time, due to the large amount of C4AF and C2S in the system, the long-term mechanical property development of the system is stable.

[0036] 2. By using two kinds of clinker and introducing a plurality of admixtures, the energy consumption and carbon emission can be saved at a low clinker ratio, and the development of the mechanical properties of the cement can be maintained.

[0037] 3. In the cement production grinding process, the mineral powder and fly ash do not participate in the grinding process and are directly mixed at the end, which cannot well guarantee that the cement powder system has a good particle size matching. The size of the cement particles and the admixture particles has a direct relationship with the hydration speed and degree of the cement. By adding a small amount of mineral powder and fly ash and clinker and other components in the early stage for joint grinding, and then mixing with the remaining mineral powder and fly ash, the various components can be adjusted together to make the whole powder system have a good particle size distribution and grading composition. At the same time, a small amount of mineral powder and fly ash can increase the hourly output and reduce the production energy consumption and improve the production efficiency by virtue of the grinding effect and the addition of grinding aids.

[0038] The present application obtains a cement product with good performance by the step-by-step calcination method of cement clinker and the multi-level grading composition of the powder formed by joint grinding. The following will be further described in detail by specific examples. In order to avoid redundancy, the preparation methods of the low-temperature calcined clinker and the high-temperature calcined clinker used in the following examples and comparative examples are described as follows:

[0039] Taking 80 parts of limestone, 10 parts of sandstone and 10 parts of iron ore as main raw materials, calcining at 1250 DEG C for 35 min, a low-temperature calcined clinker mainly composed of C3S, C2S, C4AF and C3A is obtained;

[0040] Taking 40 parts of limestone, 40 parts of bauxite and 20 parts of anhydrite as main raw materials, calcining at 1400 DEG C for 35 min, a high-temperature calcined clinker mainly composed of C 12 A7, C4A3 and C2S is obtained.

[0041] Example 1

[0042] The cement is prepared according to the following components by mass fraction: low-temperature calcined clinker 50 parts, high-temperature calcined clinker 10 parts, gypsum 4 parts, fly ash 7 parts, mineral powder 17 parts, limestone 10 parts, and grinding aid 0.05 parts, which is mainly composed of triethanolamine.

[0043] First, 7 parts of mineral powder and 3 parts of fly ash are added into the mill in advance to participate in the joint grinding process of the low-temperature calcined clinker, high-temperature calcined clinker, gypsum, and limestone, and the grinding aid is added at the same time. The grinding conditions are 55 rpm for 30 min. At this time, the first joint grinding mixture added in advance accounts for 41.7% of the total mass of the joint grinding mixture.

[0044] The final powder from the mill is mixed with the remaining mineral powder and fly ash that did not participate in the joint grinding, and stirred at 30 rpm for 4 min to form a complete and continuous multi-level composite system, and finally a good performance cement product is obtained.

[0045] Example 2

[0046] The difference from Example 1 is only that the mass of the joint grinding mixture added in advance into the mill is adjusted, and the other steps and conditions are the same as those of Example 1. The difference is that 0 parts of mineral powder and 3 parts of fly ash are added into the mill in advance, and the first joint grinding mixture added in advance accounts for 12.5% of the total mass of the joint grinding mixture.

[0047] Example 3

[0048] The difference from Example 1 is only that the mass of the joint grinding mixture added in advance into the mill is adjusted, and the other steps and conditions are the same as those of Example 1. The difference is that 7 parts of mineral powder and 0 parts of fly ash are added into the mill in advance, and the first joint grinding mixture added in advance accounts for 29.2% of the total mass of the joint grinding mixture.

[0049] Example 4

[0050] The difference from Example 1 is only that the mass of the joint grinding mixture added in advance into the mill is adjusted, and the other steps and conditions are the same as those of Example 1. The difference is that 17 parts of mineral powder and 7 parts of fly ash are added into the mill in advance, and the first joint grinding mixture added in advance accounts for 100% of the total mass of the joint grinding mixture.

[0051] Comparative Example 1

[0052] The cement is prepared according to the following components by mass fraction: low-temperature calcined clinker 60 parts, high-temperature calcined clinker 0 parts, gypsum 4 parts, fly ash 7 parts, mineral powder 17 parts, limestone 10 parts, and grinding aid 0.05 parts.

[0053] Firstly, 7 parts of mineral powder and 3 parts of fly ash are added into the mill in advance, so that they participate in the joint grinding process of low-temperature calcined clinker, gypsum and limestone, and grinding aids are added at the same time, and the grinding condition is 55 rpm for 30 min.

[0054] Finally, the powder from the mill is mixed with the remaining mineral powder and fly ash which do not participate in the joint grinding, and stirred at 30 rpm for 4 min, so that the entire powder system forms a complete and continuous multi-level composite, and finally a good performance cement product is obtained.

[0055] Comparative Example 2

[0056] The cement composition is as follows: low-temperature calcined clinker 0 parts, high-temperature calcined clinker 60 parts, gypsum 4 parts, fly ash 7 parts, mineral powder 17 parts, limestone and other mixed materials 10 parts, and grinding aids 0.05 parts.

[0057] Firstly, 7 parts of mineral powder and 3 parts of fly ash are added into the mill in advance, so that they participate in the joint grinding process of low-temperature calcined clinker, gypsum and limestone, and grinding aids are added at the same time, and the grinding condition is 55 rpm for 30 min.

[0058] Finally, the powder from the mill is mixed with the remaining mineral powder and fly ash which do not participate in the joint grinding, and stirred at 30 rpm for 4 min, so that the entire powder system forms a complete and continuous multi-level composite, and finally a good performance cement product is obtained.

[0059] Performance test

[0060] The 3-day and 28-day compressive strength is tested according to GB / T17671-1999 standard, and the particle size distribution in four intervals of d<3 μm, 3 μm≤d<30 μm, 30 μm≤d<65 μm and 65 μm≤d is tested by a laser particle size analyzer. The particle size distribution is shown in Table 1, and the strength performance test results are shown in Table 2.

[0061] Table 1 Particle size distribution of cement products obtained in each example and comparative example

[0062]

[0063] Table 2 Compressive strength of cement products obtained in each example and comparative example

[0064]

[0065] The low-temperature calcined clinker and the high-temperature calcined clinker of each embodiment and the comparative example in the application maintain consistent raw material proportions and preparation processes; wherein the proportions of each component of embodiment 1 are within the optimal range; embodiment 2 is not added with mineral powder for joint grinding in the early stage, and other proportions are the same as those of embodiment 1; embodiment 3 is not added with fly ash for joint grinding in the early stage, and other proportions are the same as those of embodiment 1; embodiment 4 is added with all mineral powder and fly ash for joint grinding in the early stage, and other proportions are the same as those of embodiment 1; comparative example 1 is removed with high-temperature calcined clinker, and the low-temperature calcined clinker is added to make the total amount of clinker 60 parts, and other proportions are the same as those of embodiment 1; and comparative example 2 is removed with low-temperature calcined clinker, and the high-temperature calcined clinker is added to make the total amount of clinker 60 parts, and other proportions are the same as those of embodiment 1.

[0066] It can be found by comparing the particle size distribution data of each embodiment and comparative example that the particle size distribution of each interval of embodiment 1 is the most reasonable, and the cement strength brought by such gradation is better; the large particle size distribution in the powder particle size distribution of embodiments 2-4 increases, and the intermediate particle size distribution decreases; and the particle size distribution is not greatly affected in comparative examples 1-2 because the proportions of the joint grinding part are not changed.

[0067] It can be found by comparing the strength data of each embodiment and comparative example that embodiment 1 with the optimal particle size distribution has good early mechanical properties and the best development of late mechanical properties. The mechanical properties of embodiments 2-4 are relatively reduced compared with those of embodiment 1, especially embodiment 4 in which all mineral powder and fly ash are added to the joint grinding process has the relatively worst mechanical properties. Comparative example 1 is removed with high-temperature calcined clinker, and without the regulation of high-temperature calcined clinker, the mechanical properties are not ideal; comparative example 2 is removed with low-temperature calcined clinker, although the early mechanical properties are the best, the late mechanical properties are not as good as those of embodiment 1, and the use of all high-temperature calcined clinker brings huge energy consumption, which is not conducive to ecological production.

[0068] Therefore, the application combines two kinds of clinkers (low-temperature calcined clinker and high-temperature calcined clinker) in the optimal range, and 30%-60% of the mass of mineral powder and 30%-60% of the mass of fly ash are added to the mill in advance to participate in the joint grinding with the two kinds of clinker, gypsum, limestone and other materials, and the addition of a grinding aid, so that the advantages of the two kinds of clinker can be brought into play, and complete and continuous multi-gradation combination and optimal particle size distribution are formed, which has good performance in improving the performance of cement.

[0069] Compared with the prior art, the application obtains two kinds of clinker by the cement clinker step-by-step calcination method, combines the two kinds of clinker, and then participates in the joint grinding by part of the mineral powder and fly ash to form multi-gradation combination and good particle size distribution of the powder, and finally obtains a cement product with good performance, and the advantages specifically include:

[0070] 1. By controlling low-temperature sintered clinker with high-temperature sintered clinker, the composite system has the characteristics of early strength, high strength and stable strength development, avoiding the shortcomings of using low-temperature sintered clinker which has poor early mechanical properties, and avoiding the shortcomings of using high-temperature sintered clinker which has high energy consumption and high price. The composite system of the two cement clinkers guarantees their respective advantages and increases the application space.

[0071] 2. A part of the mineral powder and fly ash which originally does not participate in the grinding process is involved in the grinding process, so that it is adjusted with other components to bring good particle size distribution and grading composite to the whole powder system, and better play the hydration characteristics of each part to obtain good performance of the cement product.

[0072] 3. The mixed material with grinding effect such as mineral powder and limestone is added, and the grinding aid is also added, which can increase the hourly output, improve the production efficiency and reduce the production energy consumption under certain amount. The addition of various combined grinding mixed materials reduces the proportion of sintered clinker production, and is also beneficial to reduce the energy consumption of sintered clinker production and reduce the cost.

[0073] The specific embodiments of the application described above do not constitute a limitation on the protection scope of the application. Any various other corresponding changes and modifications made according to the technical concept of the application shall be included in the protection scope of the claims of the application.

Claims

1. A composite cement with clinker staged calcination and powder multi-gradation, characterized in that, By weight, it includes the following raw materials: 40-60 parts of low-temperature calcined clinker, 5-15 parts of high-temperature calcined clinker, 4-6 parts of gypsum, 15-30 parts of combined grinding mixture, 10-15 parts of other mixtures, and 0.02-0.2 parts of grinding aid. The combined grinding mixture comprises fly ash and mineral powder in a mass ratio of (5-10):(10-20); The gradation distribution range of the composite cement is as follows: the proportion of powder with a particle size of d < 3μm is 4% or 5%, the proportion of powder with 3μm ≤ d < 30μm is 61-76%, the proportion of powder with 30μm ≤ d < 65μm is 17-25%, and the proportion of powder with 65μm ≤ d is 2-10%. The method for preparing clinker-based stepwise calcination and powder-based multi-grade composite cement includes the following steps: Low-temperature calcined clinker, high-temperature calcined clinker, gypsum, a first combined grinding mixture, other mixtures, and grinding aids are mixed and combined grinding to obtain a first powder; wherein, the mass of the first combined grinding mixture is 12.5% ​​to 41.7% of the total mass of the combined grinding mixture; The remaining combined grinding mixture is mixed with the first powder and stirred evenly to obtain clinker step-calcination and powder multi-grade composite cement. The mineral composition of the low-temperature calcined clinker, by mass percentage, includes: 35%–45% C3S, 20%–30% C2S, 16%–26% C4AF, and 1%–3% C3A. The mineral composition of the high-temperature calcined clinker, by mass percentage, includes: 10%–15% C. 12 A7, 30%–50% C4A3 And 15%–25% C2S.

2. The clinker-step calcination and powder multi-grade composite cement according to claim 1, characterized in that, The specific surface area of ​​the fly ash is 400-600 m². 2 / kg; the specific surface area of ​​the mineral powder is 380-480m². 2 / kg; The other mixed materials include limestone; The gypsum is a mixture of natural gypsum and desulfurized gypsum in a mass ratio of 1:

1.

3. The clinker-step calcination and powder multi-grade composite cement according to claim 1, characterized in that, The combined grinding mixture includes fly ash and mineral powder. The first combined grinding mixture includes first fly ash and first mineral powder. The first fly ash accounts for 30% to 60% of the total mass of fly ash, and the first mineral powder accounts for 30% to 60% of the total mass of mineral powder.

4. The clinker-step calcination and powder multi-grade composite cement according to claim 1, characterized in that, The preparation steps of the low-temperature calcined clinker include: mixing 70-80 parts by mass of limestone, 10-15 parts by mass of sandstone and 5-10 parts by mass of iron ore, and calcining at 1200-1300℃ for 30-40 minutes to obtain low-temperature calcined clinker.

5. The clinker-based stepwise calcination and powder-based multi-grade composite cement according to claim 1, characterized in that, The preparation steps of the high-temperature calcined clinker include: mixing 40-50 parts limestone, 30-40 parts bauxite and 10-30 parts anhydrite by mass, and calcining at 1350-1400 ℃ for 30-40 min to obtain high-temperature calcined clinker.

6. The clinker-step calcination and powder multi-grade composite cement according to claim 1, characterized in that, The combined grinding conditions are: grinding in a ball mill at a speed of 50-60 rpm for 28-35 minutes; The remaining combined grinding mixture is mixed with the first powder and stirred at a speed of 20-40 rpm for 3-5 minutes.

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