Portland cement clinker, and preparation method therefor and use thereof

Abstract

The present invention provides a Portland cement clinker, and a preparation method therefor and a use thereof. Mineral components of the Portland cement clinker comprise dicalcium silicate and calcium sulfate, and the sum of masses of dicalcium silicate and calcium sulfate is not less than 68% of the total mass of the Portland cement clinker. Additionally, the mass ratio of calcium sulfate to dicalcium silicate is not less than 0.13. The present invention also provides various cements prepared on the basis of the Portland cement clinker, a method for preparing the Portland cement clinker, and a method for preparing the cements. The Portland cement clinker of the present invention has the advantages of high early strength, sustained growth of long-term strength, and low CO2 emissions.

Description

[Revised according to Detailed Rule 26, 2002.06.2025] A low-calcium, high-sulfur silicate cement clinker, its preparation method and application Technical Field

[0001] This invention belongs to the field of inorganic building materials, specifically relating to a silicate cement clinker, its preparation method, and its application. Background Technology

[0002] Cement is an indispensable raw material for infrastructure construction and plays a vital role in national economic development. Silicate cement, with its inexpensive and readily available raw materials, stable performance, and mature production process, is one of the most widely used inorganic cementitious materials. However, the production of silicate cement consumes a large amount of natural resources and generates high CO2 emissions; producing one ton of silicate cement clinker emits approximately 0.87 tons of CO2. Currently, global cement production exceeds 4 billion tons, and its CO2 emissions account for about 7% of the global total. The International Energy Agency's low-carbon cement technology roadmap indicates a 34% carbon reduction potential in the clinker production stage and a 10% carbon reduction potential from performance improvements in the cement application stage. Therefore, there is an urgent need to develop a new type of low-carbon cement clinker to replace traditional silicate cement clinker on a large scale.

[0003] Silicate cement clinker typically consists of 40%–60% tricalcium silicate, 15%–35% dicalcium silicate, 5%–14% tricalcium aluminate, and 10%–16% tetracalcium aluminoferrite. The order of CO2 emissions from clinker minerals, from highest to lowest, is tricalcium silicate > tricalcium aluminate > dicalcium silicate > tetracalcium aluminoferrite. One effective way to reduce CO2 emissions from silicate cement clinker is to reduce the tricalcium silicate content and correspondingly increase the content of the low-calcium mineral dicalcium silicate. However, dicalcium silicate in silicate cement clinker is predominantly β-type, and its activity is much lower than that of tricalcium silicate. High-belite silicate cement with dicalcium silicate as the main mineral suffers from problems such as low early strength and slow strength development in later stages. Although ion doping and other methods can alter the crystal structure of dicalcium silicate to improve its activity, the early strength of activated high-belite silicate cement still falls short of the levels of traditional silicate cement.

[0004] Therefore, it is necessary to develop a new type of cement clinker that not only has lower carbon emissions but also can produce silicate cement products with higher early strength. Summary of the Invention

[0005] The primary objective of this invention is to provide a new type of cement clinker that not only has low carbon emissions but also provides higher early strength for silicate cement.

[0006] Another object of the present invention is to provide a method for preparing the cement clinker.

[0007] Another object of the present invention is to provide the application of the cement clinker in the preparation of building materials.

[0008] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0009] In a first aspect, the present invention provides a silicate cement clinker, the mineral composition of which includes dicalcium silicate and calcium sulfate, and the sum of their masses is not less than 68% of the total mass of the silicate cement clinker, preferably not less than 73%, and more preferably not less than 79%; at the same time, the mass ratio of calcium sulfate to dicalcium silicate is not less than 0.13, preferably not less than 0.26, and more preferably not less than 0.33.

[0010] In the silicate cement clinker of the present invention, the dicalcium silicate is preferably a mixture of highly active α'-type dicalcium silicate and highly active β-type dicalcium silicate dissolved in sulfur trioxide.

[0011] In the silicate cement clinker of the present invention, the calcium sulfate portion preferably exists in an amorphous form.

[0012] In the preferred silicate cement clinker of the present invention, the dicalcium silicate content is 49% to 81% by weight, more preferably 53% to 77%, and even more preferably 57% to 73%.

[0013] In the preferred silicate cement clinker of the present invention, the calcium sulfate content, by weight percentage, is 8% to 26%, more preferably 11% to 23%, and even more preferably 14% to 20%.

[0014] In the preferred silicate cement clinker of the present invention, the mineral composition further includes anhydrous calcium sulfoaluminate; by weight percentage, the content of anhydrous calcium sulfoaluminate in the silicate cement clinker is 5% to 25%, preferably 10% to 25%, and more preferably 10% to 20%.

[0015] In the preferred silicate cement clinker of the present invention, the mineral composition further includes an iron phase; by weight percentage, the iron phase content in the silicate cement clinker is 1%-15%.

[0016] In a further preferred embodiment of the present invention, the silicate cement clinker further comprises free calcium oxide; the free calcium oxide content is 0.01% to 3.9% of the total weight of the silicate cement clinker by weight percentage.

[0017] The mineral composition content of the silicate cement clinker mentioned above is obtained through theoretical calculation based on the oxide content in the clinker.

[0018] The silicate cement clinker of this invention includes dicalcium silicate and calcium sulfate as essential components. The mechanism of action of calcium sulfate includes: ① Calcium sulfate exists in a liquid phase at high temperatures, which can accelerate the diffusion rate of reactants, promote the formation of clinker minerals such as dicalcium silicate, and lower the clinker firing temperature, thereby significantly reducing CO2 emissions from the clinker. ② During clinker firing, dicalcium silicate and calcium sulfate react to form calcium sulfosilicate. As the temperature further increases, calcium sulfosilicate decomposes into amorphous calcium sulfate, highly active α'-type dicalcium silicate, and highly active β-type dicalcium silicate with dissolved sulfur trioxide. These two types of dicalcium silicate have high hydration activity, solving the problem of low early strength in high-belite silicate cement. ③ During clinker cooling, the liquid phase formed by calcium sulfate helps stabilize the highly active α'-type dicalcium silicate. Furthermore, in the traditional silicate cement clinker preparation process, calcium and aluminum usually react to form tricalcium aluminate. In this invention, calcium, aluminum, and calcium sulfate react in the presence of calcium sulfate to form anhydrous calcium sulfoaluminate. Anhydrous calcium sulfoaluminate exhibits high early hydration activity, further ensuring the early strength development of high-belite silicate cement.

[0019] In the preferred silicate cement clinker of this invention, the mechanism of action of free calcium oxide mainly includes: the free calcium oxide in the clinker of this invention is highly active after being calcined at a low temperature of 1250±100℃. The free calcium oxide in the clinker can be used to regulate the dissolution rate of minerals such as anhydrous calcium sulfoaluminate, calcium sulfate, and dicalcium silicate, as well as the precipitation rate of hydration products such as ettringite, thereby regulating the setting and hardening rate of the clinker.

[0020] In a second aspect, the present invention also provides a method for preparing the silicate cement clinker described in the first aspect, comprising: grinding and homogenizing a mixed raw material containing silicon, aluminum, sulfur, calcium, and iron elements according to the content of each mineral component of the silicate cement clinker described in the first aspect, followed by a high-temperature reaction to obtain the silicate cement clinker. Preferably, the high-temperature reaction is high-temperature calcination; more preferably, the high-temperature calcination temperature is 1250℃±100℃; and even more preferably, the high-temperature calcination temperature is 1250℃±50℃.

[0021] In the method for preparing silicate cement clinker according to the first aspect of the present invention, the mixed raw material containing silicon, aluminum, sulfur, calcium, and iron is any one of a variety of compositions composed of various substances, including limestone, alkali slag, steel slag, carbide slag, bauxite, high-iron bauxite, waste fly ash, red mud, aluminum ash, bauxite tailings, coal gangue, kaolin, fluidized bed slag, clay, sandstone, natural anhydrous gypsum, natural dihydrate gypsum, desulfurized gypsum, hemihydrate gypsum, phosphogypsum, fluorogypsum, desulfurized ash, aluminum sulfate, industrial waste rich in gypsum, iron ore, selected iron ore powder, fly ash, granulated blast furnace slag, or gasification slag. Preferably, the mixed raw material containing silicon, aluminum, sulfur, calcium, and iron is composed of limestone, steel slag, fly ash, desulfurized gypsum, phosphogypsum, and sandstone.

[0022] The method for preparing the clinker of this invention is similar to the traditional method for preparing silicate cement clinker, and can be industrialized using a traditional silicate cement clinker production line. However, the advantages of the preparation method of this invention are: lower firing temperature and lower requirements for raw material quality.

[0023] Thirdly, the present invention also provides the following various cements prepared based on the silicate cement clinker described in the first aspect of the present invention:

[0024] A type of cement with high early strength is prepared by weight from the following raw materials: 80-100 parts of silicate cement clinker as described in the first aspect of the present invention, 0-20 parts of gypsum, and 0-20 parts of cement admixture.

[0025] A high-strength cement is prepared from the following raw materials by weight: 50-80 parts of silicate cement clinker as described in the first aspect of the present invention, 0-20 parts of gypsum, and 20-50 parts of cement admixture.

[0026] A cement with low heat of hydration is prepared by weight from the following raw materials: 5-50 parts of silicate cement clinker as described in the first aspect of the present invention, 0-20 parts of gypsum, and 50-95 parts of cement admixture.

[0027] The cement of the present invention, which is a high-early-strength cement, a high-strength cement, or a cement with low heat of hydration, wherein the gypsum in its raw materials is any one or a combination of at least two of natural dihydrate gypsum, natural anhydrite, hemihydrate gypsum, α-type high-strength gypsum, desulfurized gypsum, phosphogypsum, or fluorogypsum; preferably, the gypsum is any one or a combination of at least two of natural dihydrate gypsum, natural anhydrite, hemihydrate gypsum, or desulfurized gypsum.

[0028] The cement of the present invention, which has high early strength, high strength, or low heat of hydration, is made of any one of the following: granulated blast furnace slag, fly ash, silica fume, steel slag, gasification slag, limestone, dolomite, pozzolanic mixture, or sandstone, or a combination of at least two of these.

[0029] The present invention preferably includes any one of the following: cement with high early strength, cement with high strength, or cement with low heat of hydration. 0.1 to 5 parts by weight of setting-regulating and strength-promoting components may also be added to the raw materials.

[0030] The setting and strength-promoting component is selected from any one or a combination of at least two of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium sulfate, sodium sulfate, potassium sulfate, aluminum sulfate, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium silicate, lithium chloride, citric acid, sodium citrate, or sodium gluconate; preferably, the setting and strength-promoting component includes any one or a combination of at least two of lithium hydroxide, sodium hydroxide, lithium sulfate, sodium sulfate, aluminum sulfate, lithium carbonate, citric acid, sodium citrate, or sodium gluconate; more preferably, the setting and strength-promoting component further includes any one or a combination of at least two of silicate cement, silicate cement clinker, quicklime, hydrated lime, industrial calcium oxide, industrial calcium hydroxide, carbide slag, calcium oxide-based expansion agent, and ettringite-based expansion agent.

[0031] Fourthly, the present invention also provides a method for preparing any of the above-mentioned cements, comprising: mixing the raw materials according to the raw material proportions of any of the above-mentioned cements and then grinding them together to a specific surface area of ​​200-800 m². 2 The cement is obtained by mixing the raw materials in powder form of / g; preferably, the raw materials are mixed and then ground together to a specific surface area of ​​300-600m². 2 The cement is obtained by grinding each raw material into powder with a specific surface area of ​​200-1000 m² / g; or by grinding each raw material separately to a specific surface area of ​​200-1000 m² / g. 2 / g of powder, and then mixed to obtain the cement.

[0032] Fifthly, the present invention also provides the application of the silicate cement clinker described in the first aspect of the present invention in the preparation of building materials.

[0033] Compared with existing technologies, the present invention has the following beneficial effects:

[0034] This invention innovatively uses dicalcium silicate and calcium sulfate as the main minerals to prepare silicate cement clinker. Dicalcium silicate and calcium sulfate first react at high temperatures to form calcium sulfosilicate. As the temperature further increases, calcium sulfosilicate decomposes into amorphous calcium sulfate, highly active α'-type dicalcium silicate, and highly active β-type dicalcium silicate with dissolved sulfur trioxide. This process significantly enhances the hydration activity of dicalcium silicate and calcium sulfate, ensuring the early and later strength development of high-belite silicate cement. Calcium sulfate can also react rapidly with another highly active mineral in the clinker, anhydrous calcium sulfoaluminate, and water, further improving early strength. Furthermore, calcium sulfate exists in a liquid phase at high temperatures, which not only stabilizes the highly active crystal form of dicalcium silicate but also accelerates the diffusion rate of reactants, promotes the formation of clinker minerals, and lowers the clinker firing temperature (approximately 200°C lower than traditional silicate cement clinker). Therefore, compared with existing high-belite silicate cement clinker, the silicate cement clinker of this invention has advantages such as high early strength, continuous strength growth in later stages, and low CO2 emissions. Using this clinker, cement with high early and later strength and low heat of hydration can be prepared, making it suitable for construction, transportation, water conservancy, and other fields. Attached Figure Description

[0035] Figure 1 shows the X-ray diffraction patterns of the silicate cement clinker of the present invention and the conventional silicate cement clinker. Detailed Implementation

[0036] Although the invention has been described in detail, it should be understood that the invention is not limited to the specific methods, schemes, and reagents described herein, as these can vary. It should also be understood that the terminology used herein is not intended to limit the scope of the invention, which is limited only by the appended claims. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0037] The elements of the invention will be described below. These elements are set forth along with specific embodiments; however, it should be understood that they can be combined in any manner and in any number to produce other embodiments. The various examples and preferred embodiments described should not be construed as limiting the invention to only the explicitly described embodiments. This description should be understood to support and cover embodiments that combine the explicitly described embodiments with any number of the disclosed and / or preferred elements. Furthermore, unless the context otherwise indicates, the description of this application should be considered to disclose any permutation and combination of all the elements described herein.

[0038] Throughout this specification and the appended claims, unless the context otherwise requires, the term "comprise" and its variations such as "comprises" and "comprising" shall be understood to mean including the stated members, integers, or steps, but not excluding any other unstated members, integers, or steps. The term "consist of" is a specific embodiment of the term "comprise," in which any other unstated members, integers, or steps are excluded. In the context of this invention, the term "comprise" encompasses the term "consist of." Therefore, the term "comprising" covers both "including" and "consisting," for example, a composition "comprising" X may consist of only X, or may include additional elements, such as X+Y.

[0039] In this invention, unless otherwise indicated, different features of alternatives and implementations may be combined with each other.

[0040] For clarity and readability, the following descriptions of Chinese terminology, chemical symbols, and calculation methods are provided. Any technical features mentioned in connection with these definitions can be interpreted in each embodiment of the invention. Additional definitions and explanations may be provided in the context of these embodiments.

[0041] (I) The present invention relates to the correspondence between the Chinese names of mineral compositions and their chemical symbols as follows:

[0042] Dicalcium silicate (C2S), calcium sulfate (CaSO4), anhydrous calcium sulfoaluminate Iron phase (C4AF), perovskite (CT), free calcium oxide (f-CaO).

[0043] (II) The mineral composition of the clinker in this invention is calculated based on oxide composition, and the calculation methods are as follows:

[0044] w(C2S)=2.87w(SiO2)

[0045] w(C4AF)=3.04w(Fe2O3)

[0046] w(CT) = 1.7w(TiO2)

[0047] w(f-CaO)=w(CaO)-0.55[w(Al2O3)-0.64w(Fe2O3)]-1.87w(SiO2)-1.4w(Fe2O3)-

[0048] 0.7[w(TiO2)+w(SO3)]

[0049] In this invention, the amorphous phase composition of the clinker is inferred from the oxide calculation results and X-ray diffraction (XRD) test results.

[0050] (III) The terms used in this invention are defined as follows:

[0051] "α'-type dicalcium silicate" refers to a metastable dicalcium silicate formed under high temperature conditions. It belongs to the monoclinic or orthorhombic crystal system and has higher hydration activity than β-type dicalcium silicate.

[0052] "β-type dicalcium silicate" refers to a monoclinic dicalcium silicate that is widely found in silicate cement clinker and makes an important contribution to the mid-to-late stage strength development of cement.

[0053] "Highly active β-type dicalcium silicate with sulfur trioxide solution" refers to a solid solution formed by β-type dicalcium silicate and a small amount of sulfur trioxide, which has higher hydration activity than β-type dicalcium silicate.

[0054] "Amorphous form" refers to a solid form of matter that does not have a long-range ordered arrangement in its microstructure, that is, it does not have a clear crystal structure or lattice periodicity.

[0055] "Iron phase" refers to a mineral in cement clinker, mainly composed of tetracalcium aluminoferrite.

[0056] "Free calcium oxide" refers to calcium oxide that exists in cement clinker in a free state without reacting with other oxides to form silicate, aluminate or other minerals.

[0057] "High-iron bauxite" refers to bauxite with a ferric oxide content generally above 10%.

[0058] "Fly ash from waste" refers to a byproduct of the waste incineration process.

[0059] "Fluidized bed slag" refers to the waste residue produced during combustion in a fluidized bed boiler.

[0060] "Gasification slag" refers to the solid waste generated during the coal gasification process.

[0061] "Cement admixtures" refer to artificial or natural mineral materials that are added to the mill along with clinker and gypsum during cement grinding to improve cement performance, adjust cement grade, and increase cement production.

[0062] "Setting and strength-enhancing components" refer to chemical substances added during the cement production process to adjust the setting time and strength of cement.

[0063] "α-type high-strength gypsum" refers to hemihydrate gypsum with an α-type crystal form.

[0064] "Volcanic ash composite material" refers to natural and artificial mineral raw materials with silicon dioxide and aluminum oxide as the main components. When ground into fine powder and mixed with water, it does not harden. However, when mixed with lime and then further mixed with water, it can harden not only in the air but also continue to harden in water.

[0065] "Industrial calcium hydroxide" refers to calcium hydroxide that can be used in industrial production.

[0066] "Industrial calcium oxide" refers to calcium oxide that can be used in industrial production.

[0067] "Calcium oxide-based expansive agents" refer to concrete expansive agents that produce calcium hydroxide through a hydration reaction when mixed with cement and water.

[0068] "Calcium alum stone-based expansion agent" refers to a concrete expansion agent that generates calcium alum stone through a hydration reaction after being mixed with cement and water.

[0069] The present invention will be further described in detail below by way of examples and comparative examples.

[0070] Examples 1-25

[0071] A series of silicate cement clinker were prepared using raw materials including limestone, fly ash, desulfurized gypsum, and sandstone. The chemical composition of each raw material is shown in Table 1 below.

[0072] Table 1: Chemical Composition of Raw Materials Required for the Production of Silicate Cement Clinker

[0073] After mixing the raw materials in Table 1 according to the proportions listed in Table 2, they were ground to below 80μm, homogenized, and then calcined at a high temperature of 1250℃ to obtain a series of silicate cement clinker in Examples 1-25.

[0074] Table 2: Raw material proportions used in the production of silicate cement clinker for Examples 1-25

[0075] The chemical and mineral compositions of the above series of clinkers were analyzed. The mineral composition was obtained through chemical composition calculations, and the results are shown in Table 3 below:

[0076] Table 3: Chemical and mineral composition of silicate cement clinker in Examples 1-25

[0077] The mineral composition of the silicate cement clinker of Example 10 was characterized by XRD, and the XRD pattern is shown in Figure 1. The quantitative analysis results are shown in Table 4. In Figure 1, the blue curve at the bottom represents the silicate cement clinker of Example 10, and the red curve at the top represents the conventional silicate cement clinker. As can be seen from Figure 1, in addition to the diffraction peaks corresponding to dicalcium silicate, calcium sulfate, and anhydrous calcium sulfoaluminate, the blue curve at the bottom also shows obvious "bun peaks," indicating that the silicate cement clinker contains a large amount of amorphous phase. As can be seen from Table 4, dicalcium silicate mainly exists in the highly active α' type. In addition, the XRD measured values ​​of calcium sulfate and dicalcium silicate are lower than the XRF calculated values, which suggests that a large amount of calcium sulfate and some dicalcium silicate exist in amorphous form.

[0078] Table 4: Calculated and measured values ​​of mineral composition of silicate cement clinker in Example 10

[0079] The physical and mechanical properties of a series of clinkers from Examples 1 to 25 were determined according to ISO 9597:2008 "Cement—Test methods—Determination of setting time and soundness" and ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 5.

[0080] Table 5: Physical and mechanical properties of silicate cement clinker from Examples 1 to 25

[0081] As shown in Table 5, the strength and setting time of clinker are mainly determined by the mass ratio of calcium sulfate to dicalcium silicate and the total mass. Generally speaking, the higher the mass ratio and the lower the total mass, the faster the clinker sets and hardens, and the higher its flexural and compressive strengths.

[0082] Comparative Examples 1-5

[0083] A series of silicate cement clinker were prepared by mixing the raw materials in Table 6-1 according to the listed proportions, grinding them to below 80 μm, homogenizing them, and then calcining them at a high temperature of 1250℃ to obtain a series of silicate cement clinker of Comparative Examples 1 to 5.

[0084] Table 6-1. Raw material proportions used in the production of silicate cement clinker for Comparative Examples 1-5

[0085] The chemical and mineral compositions of the above series of clinkers were analyzed. The mineral composition was obtained through chemical composition calculations, and the results are shown in Table 6-2 below:

[0086] Table 6-2: Chemical and mineral composition of silicate cement clinker in Comparative Examples 1-5

[0087] The mineral composition of the silicate cement clinker in Comparative Example 2 was further characterized by XRD, and the quantitative analysis results are shown in Table 7.

[0088] Table 7: Mineral composition of silicate cement clinker in Comparative Example 2

[0089] As can be seen from Table 7, the crystal form of dicalcium silicate is mainly determined by the mass ratio of calcium sulfate to dicalcium silicate. When the mass ratio of calcium sulfate to dicalcium silicate is less than 0.13, the clinker dicalcium silicate is mainly of the β type; when the mass ratio of calcium sulfate to dicalcium silicate exceeds 0.13, a large amount of α' type dicalcium silicate begins to appear.

[0090] The physical and mechanical properties of a series of clinkers from Comparative Examples 1 to 5 were determined according to ISO 9597:2008 "Cement—Test methods—Determination of setting time and soundness" and ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 8.

[0091] Table 8: Physical and mechanical properties of silicate cement clinker from Comparative Examples 1-5

[0092] As can be seen from Table 8, if the mass ratio of calcium sulfate to dicalcium silicate is less than 0.13, the setting and hardening rate of silicate cement clinker will be slowed down, and the flexural strength and compressive strength will be significantly reduced.

[0093] The hydration activity of dicalcium silicate in the silicate cement clinker of Comparative Example 2 and Examples 6-10 was quantitatively analyzed by XRD. To reduce interference from other factors, an appropriate amount of calcium sulfate was added to the clinker, and the mass ratio of calcium sulfate to anhydrous calcium sulfoaluminate was controlled at 1.78. The results of the XRD quantitative analysis are shown in Table 9.

[0094] Table 9: Degree of dicalcium silicate hydration in silicate cement clinker of Comparative Example 2 and Examples 6-10 at 28 days

[0095] As shown in Table 9, if the mass ratio of calcium sulfate to dicalcium silicate is less than 0.13, the 28-day hydration degree of dicalcium silicate in silicate cement clinker is only 30.5%. If the mass ratio of calcium sulfate to dicalcium silicate exceeds 0.13, the 28-day hydration degree of dicalcium silicate in silicate cement clinker increases significantly, reaching over 50%, and the hydration degree of dicalcium silicate gradually increases with the increase of the mass ratio.

[0096] Examples 26-30

[0097] A series of silicate cement clinkers with different free calcium oxide contents were prepared, and their chemical and mineral compositions are shown in Table 10 below:

[0098] Table 10: Chemical and mineral composition of silicate cement clinker in Examples 26-30

[0099] The physical and mechanical properties of a series of clinkers from Examples 26 to 30 were determined according to ISO 9597:2008 "Cement—Test methods—Determination of setting time and soundness" and ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 11.

[0100] Table 11: Physical and mechanical properties of silicate cement clinker from Examples 26-30

[0101] As shown in Table 11, with the increase of free calcium oxide content, the setting time of silicate cement clinker shows a trend of first shortening and then lengthening. This indicates that a small amount of free calcium oxide can accelerate the setting and hardening rate of clinker, while excessive free calcium oxide content slows down the setting and hardening rate. Furthermore, free calcium oxide has a significant impact on the 6-hour strength of silicate cement clinker, but a smaller impact on the 3-day and 28-day strength.

[0102] Examples 31-37

[0103] Using clinker from Example 12 and one or more of anhydrite, slag, gasification slag, or aluminum sulfate as raw materials, a series of silicate cements with high early strength were prepared. The specific raw material ratios are shown in Table 12 below:

[0104] Table 12: Raw material proportions of silicate cement

[0105] The physical and mechanical properties of a series of silicate cements from Examples 31 to 37 were determined according to ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 13.

[0106] Table 13: Mechanical properties of silicate cement in Examples 31-37

[0107] As can be seen from Table 13, with the increase of anhydrite content, the strength of silicate cement shows a trend of first increasing and then decreasing. Adding an appropriate amount of aluminum sulfate, a setting regulator and strength promoter, is beneficial to the early and later strength development.

[0108] Examples 38-45

[0109] Using clinker from Example 5 and one or more of anhydrite, slag, calcined clay, limestone powder, or sodium sulfate as raw materials, a series of silicate cements with high strength were prepared. The specific raw material ratios are shown in Table 14 below:

[0110] Table 14: Raw material proportions of silicate cement

[0111] The physical and mechanical properties of a series of silicate cements from Examples 38 to 45 were determined according to ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 15.

[0112] Table 15: Mechanical properties of silicate cement from Examples 38-45

[0113] As shown in Table 15, reducing the clinker content in cement and correspondingly increasing the amount of admixtures is detrimental to the early strength development of silicate cement, but promotes the later strength development. Adding an appropriate amount of sodium sulfate, a setting regulator and strength-promoting component, can promote both early and later strength development. Adding a small amount of limestone powder can promote cement strength development, but excessive limestone powder content has a negative impact on strength.

[0114] Examples 46-53

[0115] A series of silicate cements were prepared using clinker from Example 18 and one or more of anhydrite, slag, fly ash, or citric acid as raw materials. The specific raw material proportions are shown in Table 16 below.

[0116] Table 16: Raw material proportions of silicate cement

[0117] The physical and mechanical properties of a series of silicate cements from Examples 46 to 53 were determined according to ISO 679:2009 "Cement—Test methods—Determination of strength". The results are shown in Table 17.

[0118] Table 17: Physical and mechanical properties of silicate cement in Examples 46-53

[0119] As shown in Table 17, the heat of hydration and strength of silicate cement both decrease with increasing fly ash content. Increasing clinker content increases the heat of hydration and early strength of cement, but has little effect on later strength.

Claims

1. A silicate cement clinker, characterized in that: Its mineral composition includes dicalcium silicate and calcium sulfate, and the sum of their masses is not less than 68% of the total mass of the silicate cement clinker; meanwhile, the mass ratio of calcium sulfate to dicalcium silicate is not less than 0.

13.

2. The silicate cement clinker as described in claim 1, characterized in that: The sum of the masses of dicalcium silicate and calcium sulfate shall not be less than 73% of the total mass of the silicate cement clinker; at the same time, the mass ratio of calcium sulfate to dicalcium silicate shall not be less than 0.

26.

3. The silicate cement clinker as described in claim 1, characterized in that: The sum of the masses of dicalcium silicate and calcium sulfate shall not be less than 79% of the total mass of the silicate cement clinker; at the same time, the mass ratio of calcium sulfate to dicalcium silicate shall not be less than 0.

33.

4. The silicate cement clinker as described in claim 1, characterized in that: The dicalcium silicate is a mixture of highly active α'-type dicalcium silicate and highly active β-type dicalcium silicate dissolved in sulfur trioxide.

5. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The calcium sulfate portion exists in an amorphous form.

6. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The dicalcium silicate content is 49%–81% by weight.

7. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The dicalcium silicate content is 53%–77% by weight.

8. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The dicalcium silicate content is 57%–73% by weight.

9. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The calcium sulfate content ranges from 8% to 26% by weight.

10. The silicate cement clinker according to any one of claims 1-4, characterized in that: The calcium sulfate content is 11%–23% by weight.

11. The silicate cement clinker according to any one of claims 1-4, characterized in that: The calcium sulfate content is 14%–20% by weight.

12. The silicate cement clinker according to any one of claims 1-4, characterized in that: The mineral composition also includes anhydrous calcium sulfoaluminate; the content of anhydrous calcium sulfoaluminate is 5% to 25% by weight.

13. The silicate cement clinker as described in claim 12, characterized in that: The anhydrous calcium sulfoaluminate content is 10% to 25% by weight percentage.

14. The silicate cement clinker as described in claim 12, characterized in that: The anhydrous calcium sulfoaluminate content is 10% to 20% by weight percentage.

15. The silicate cement clinker as described in any one of claims 1-4, characterized in that: The mineral composition also includes an iron phase; by weight percentage, the iron phase content in the silicate cement clinker is 1%-15%.

16. The silicate cement clinker according to any one of claims 1-4, characterized in that: The mineral composition also includes free calcium oxide; by weight percentage, the free calcium oxide content is 0.01% to 3.9% of the total weight of silicate cement clinker.

17. A method for preparing silicate cement clinker according to any one of claims 1-16, comprising: According to any one of claims 1-16, the silicate cement clinker is obtained by grinding and homogenizing a mixed raw material containing silicon, aluminum, sulfur, calcium and iron elements, followed by high-temperature calcination at 1250℃±100℃.

18. The method as described in claim 17, characterized in that: The high-temperature calcination temperature is 1250℃±50℃.

19. The method according to any one of claims 17-18, characterized in that: The mixed raw material containing silicon, aluminum, sulfur, calcium and iron is any one of a variety of compositions composed of various substances from limestone, alkali slag, steel slag, carbide slag, bauxite, high-iron bauxite, waste fly ash, red mud, aluminum ash, bauxite tailings, coal gangue, kaolin, fluidized bed slag, clay, sandstone, natural anhydrous gypsum, natural dihydrate gypsum, desulfurized gypsum, hemihydrate gypsum, phosphogypsum, fluorogypsum, desulfurized ash, aluminum sulfate, industrial waste rich in gypsum, iron ore, selected iron ore powder, fly ash, granulated blast furnace slag or gasification slag.

20. The method according to any one of claims 17-18, characterized in that: The mixed raw material containing silicon, aluminum, sulfur, calcium and iron is composed of limestone, steel slag, fly ash, desulfurized gypsum, phosphogypsum and sandstone.

21. An application of a silicate cement clinker, characterized in that: A composition comprising one or more of the silicate cement clinker as described in any one of claims 1-16, gypsum, cement admixtures, and setting and strength-promoting components.

22. A cement with high early strength, prepared by weight from the following raw materials: 80-100 parts of silicate cement clinker as described in any one of claims 1-16, 0-20 parts of gypsum, and 0-20 parts of cement admixture.

23. A type of cement, prepared by weight from the following raw materials: 50-80 parts of silicate cement clinker as described in any one of claims 1-16, 0-20 parts of gypsum, and 20-50 parts of cement admixture.

24. A type of cement, prepared by weight from the following raw materials: 5-50 parts of silicate cement clinker as described in any one of claims 1-16, 0-20 parts of gypsum, and 50-95 parts of cement admixture.

25. The cement as described in any one of claims 22-24, characterized in that: The gypsum is any one or a combination of at least two of the following: natural dihydrate gypsum, natural anhydrite, hemihydrate gypsum, α-type high-strength gypsum, desulfurized gypsum, phosphogypsum, or fluorogypsum.

26. The cement according to any one of claims 22-24, characterized in that: The gypsum is any one or a combination of at least two of the following: natural dihydrate gypsum, natural anhydrite, hemihydrate gypsum, and desulfurized gypsum.

27. The cement according to any one of claims 22-24, characterized in that: The cement admixture is any one or a combination of at least two of the following: granulated blast furnace slag, fly ash, silica fume, steel slag, gasification slag, limestone, dolomite, pozzolanic admixture, or sandstone.

28. The cement according to any one of claims 22-24, characterized in that: The raw materials also contain 0.1 to 5 parts by weight of a coagulation-regulating and strength-promoting component; the coagulation-regulating and strength-promoting component is any one or a combination of at least two of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium sulfate, sodium sulfate, potassium sulfate, aluminum sulfate, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium silicate, lithium chloride, citric acid, sodium citrate or sodium gluconate.

29. The cement as described in claim 28, characterized in that: The regulating and strengthening components include any one or a combination of at least two of lithium hydroxide, sodium hydroxide, lithium sulfate, sodium sulfate, aluminum sulfate, lithium carbonate, citric acid, sodium citrate, or sodium gluconate.

30. The cement as described in claim 29, characterized in that: The setting and strength-promoting components also include any one or a combination of at least two of silicate cement, silicate cement clinker, quicklime, hydrated lime, industrial calcium oxide, industrial calcium hydroxide, carbide slag, calcium oxide-based expansive agents, and ettringite-based expansive agents.

31. A method for preparing the cement according to any one of claims 22-30, comprising: According to the raw material proportioning of the cement as described in any one of claims 22-30, the raw materials are mixed and then ground together to form a specific surface area of ​​200-800 m². 2 The cement is obtained by dissolving / g of powder.

32. A method for preparing the cement according to any one of claims 22-30, comprising: According to the raw material proportions of the cement as described in any one of claims 22-30, the raw materials are mixed and then ground together to form a specific surface area of ​​300-600 m². 2 The cement is obtained by dissolving / g of powder.

33. A method for preparing the cement according to any one of claims 22-30, comprising: According to the raw material proportions of the cement as described in any one of claims 22-30, the various raw materials are respectively ground to a specific surface area of ​​200-1000 m². 2 / g of powder, and then mixed to obtain the cement.

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