A low-temperature calcining, low-heat silicate cement and its preparation method

Abstract

This invention discloses a low-temperature calcined, low-heat silicate cement and its preparation method, comprising the following steps: 1) calcining dicalcium silicate monoore using calcium carbonate, silicon dioxide, barium carbonate, and calcium sulfate as raw materials and grinding it. 2) mixing the dicalcium silicate monoore powder from step 1) with α-type alumina powder with a particle size of 0.5-1.5 μm to prepare clinker seed crystals. 3) preparing raw meal using limestone and sandstone, mixing 0.8-1.2% clinker seed crystals by weight of the raw meal, and calcining at 1100℃ to produce dicalcium silicate cement clinker. 4) grinding 35-45 parts by weight of dicalcium silicate cement clinker, 50-60 parts by weight of silicate cement clinker, and 3-8 parts by weight of gypsum together to prepare low-heat silicate cement. By weight percentage, the dicalcium silicate content in the dicalcium silicate clinker is greater than 95%, and the dicalcium silicate content in the prepared low-temperature calcined, low-heat silicate cement is greater than 40%. The firing method according to the present invention can reduce the firing temperature of cement clinker with high dicalcium silicate content by 400°C, thereby achieving low carbonization of the production process.

Description

Technical Field

[0001] This invention relates to the field of cement technology, and more particularly to a low-temperature calcined, low-heat silicate cement and its preparation method. Background Technology

[0002] As the world's most widely used traditional building material, cement is in huge demand. However, the production of 1 ton of cement will emit about 0.88 tons of CO2, making the carbon emissions and energy consumption problems of the cement industry serious.

[0003] Compared to ordinary Portland cement, low-heat Portland cement, with dicalcium silicate as the dominant mineral, has relatively lower carbon emissions, and its value has long been widely recognized both domestically and internationally. Firstly, it has a lower production enthalpy, reducing energy consumption during cement firing, and secondly, it requires less limestone during production, thus reducing carbon emissions to some extent. Furthermore, low-heat Portland cement exhibits higher later-stage strength, better erosion resistance, and superior volume stability than ordinary Portland cement, effectively improving the durability of building structures.

[0004] The key research areas for low-heat cement are, on the one hand, its performance improvement and engineering applications, and on the other hand, its preparation methods.

[0005] Existing patent literature includes, for example, invention patent CN1193613, which discloses a high-belite cement clinker and its preparation process. The cement described in this invention uses dicalcium silicate as the main mineral and has advantages such as low heat of hydration, low water demand, high fluidity, high strength, and high durability. Invention patent CN104788032A introduces a small amount of anhydrous calcium sulfoaluminate mineral into belite cement clinker, which significantly improves the early strength of belite cement without changing its advantages such as low calcium content, low energy consumption, and low requirements for raw material quality. Invention patent CN115417609A discloses an early-strength, low-shrinkage, low-heat silicate cement and its preparation method, which uses raw materials such as iron slag, copper slag, and vanadium ore slag to prepare cement, thereby improving the crack resistance and early strength of the cement.

[0006] Currently, the firing temperature of industrially produced low-heat cement clinker is about 100°C lower than that of ordinary silicate cement clinker. However, as a low-carbon emission cement, the firing temperature of low-heat cement clinker can still be lowered. Typically, the main mineral in low-heat cement, dicalcium silicate, can be formed at firing temperatures exceeding 800°C, which provides a theoretical possibility for low-temperature firing of low-heat cement clinker.

[0007] The concept of seed crystals is widely used in the cement industry. On the one hand, it can lower the nucleation barrier of cement mineral crystals during cement production, altering the cement firing process; on the other hand, it can accelerate cement hydration and improve early strength. Currently, seed crystal technology has achieved considerable success and application in the field of concrete hydration regulation. Invention patent CN113105148B discloses a PCE composite seed crystal type early strength agent, which uses PCE combined with seed crystals to produce an early strength agent with good early strength effect, high stability, and a simple synthesis process. Invention patent CN115557723B forms a colloid of hydrated calcium silicate in a complexing agent alkyd solution, utilizing the seed crystal effect of the hydrated calcium silicate colloid to accelerate cement hydration. Research on using seed crystals to promote firing in the field of cement clinker firing is relatively limited. Patent CN115043604A uses cement seed crystals and tetracalcium aluminoferrite whiskers combined with high-magnesium raw materials to produce low-background cement, confirming the role of seed crystals in cement clinker firing.

[0008] In summary, low-heat silicate cement is a type of low-carbon-emission cement. Currently, its production methods are similar to those of ordinary silicate cement. It utilizes the low firing temperature of dicalcium silicate and employs seed crystals to promote the nucleation and growth of clinker minerals, which can effectively reduce the firing temperature during the preparation of low-heat cement. Summary of the Invention

[0009] To address the above problems, this invention provides a method for preparing low-temperature fired low-heat silicate cement and a method for reducing the firing temperature of low-heat cement and promoting the production of low-carbon cement.

[0010] The technical solution of this invention is:

[0011] A method for preparing low-temperature calcined, low-heat silicate cement utilizes a mixture of dicalcium silicate and α-alumina to prepare clinker seed crystals, thereby improving the calcination efficiency of dicalcium silicate and achieving low-temperature calcination of dicalcium silicate cement clinker. The method is implemented according to the following steps:

[0012] Step 1: Dicalcium silicate monoore is produced by calcining calcium carbonate, silicon dioxide, barium carbonate, and calcium sulfate, and then grinding it to a specific surface area greater than 360 m². 2 / kg, the raw materials include, by weight: 65-75 parts calcium carbonate, 18-24 parts silicon dioxide, 4-7 parts barium carbonate, and 2-4 parts calcium sulfate, wherein the total weight percentage of the dicalcium silicate monominerals α'-type dicalcium silicate and α-type dicalcium silicate is greater than 65%;

[0013] Step 2: Mix the dicalcium silicate monomineral powder from Step 1 with α-alumina powder with a particle size of 0.5-1.5 μm to prepare mature seed crystals. The mature seed crystals include, by weight, 70-80 parts of dicalcium silicate monomineral powder and 70-80 parts of α-alumina powder.

[0014] Step 3: Prepare raw meal using limestone and sandstone, mix in 0.8-1.2% clinker seed crystals by weight of the raw meal, and calcine at 1100℃ to produce dicalcium silicate cement clinker;

[0015] Step 4: By weight, 35-45 parts of dicalcium silicate cement clinker, 50-60 parts of silicate cement clinker, and 3-8 parts of gypsum are ground together to produce low-heat silicate cement.

[0016] Specifically, the total weight percentage of dicalcium silicate monominerals α'-type dicalcium silicate and α-type dicalcium silicate in step 1 is greater than 65%.

[0017] Specifically, in step 2, the total weight percentage of α'-type dicalcium silicate and α-type dicalcium silicate in the seed crystals is greater than 50%.

[0018] Specifically, in the dicalcium silicate cement clinker described in step 3, the weight of the seed crystals during the firing of the dicalcium silicate cement clinker is 0.8-1.2% of the weight of the raw meal.

[0019] Specifically, the low-heat silicate cement described in step 4 comprises 35-45 parts by weight of dicalcium silicate cement clinker, 50-60 parts by weight of silicate cement clinker, and 3-8 parts by weight of gypsum.

[0020] Specifically, a low-temperature calcined, low-heat silicate cement obtained by any one of the methods described.

[0021] A low-temperature calcined, low-heat silicate cement, wherein the low-heat silicate cement contains more than 40% dicalcium silicate and less than 5% tricalcium aluminate by weight fraction.

[0022] Specifically, the low-heat silicate cement has a 3-day heat of hydration of less than 200 J / g, a 7-day heat of hydration of less than 250 J / g, and a 28-day compressive strength of greater than 45 MPa.

[0023] The beneficial effects of this invention are:

[0024] 1) This invention is based on the principle of crystal nucleation-growth. It utilizes α-alumina to provide nucleation attachment points in the dicalcium silicate nucleation process, thereby reducing the crystal nucleation barrier and improving the crystal sintering efficiency.

[0025] 2) The clinker seed crystals used in this invention contain a large amount of highly active α'-type dicalcium silicate and α-type dicalcium silicate, which can induce newly generated dicalcium silicate minerals to form in α' and α crystal forms, effectively improving clinker activity and ensuring that the prepared cement achieves low heat of hydration while exhibiting good strength, with a 3-day heat of hydration of less than 200 J / g, a 7-day heat of hydration of less than 250 J / g, and a 28-day compressive strength of greater than 45 MPa. Attached Figure Description

[0026] Figure 1This is a flowchart of the preparation process of the present invention. Detailed Implementation

[0027] Based on the low energy consumption, high performance, and durability of low-heat silicate cement production, and combining the key mechanism that seed crystals can reduce the crystal nucleation barrier and improve firing efficiency during the cement firing process, this invention discloses a method for preparing low-temperature fired low-heat silicate cement. This method lowers the firing temperature of low-heat cement and promotes the low-carbonization of low-heat cement production.

[0028] The applicant discovered that the α-alumina crystal transformation temperature is 900℃, and the initial formation temperature of dicalcium silicate is approximately 800℃. α-alumina particles can provide nucleation attachment sites for dicalcium silicate formation before the transformation occurs, thus improving the nucleation efficiency of dicalcium silicate. α'-crystal dicalcium silicate and α-crystal dicalcium silicate grains, as nuclei in the nucleation process, can induce dicalcium silicate to transform towards α'-crystal and α-crystal forms, thereby improving the activity of cement clinker. Using α'-crystal dicalcium silicate, α-crystal dicalcium silicate combined with α-alumina as clinker seed crystals can effectively improve the calcination efficiency of dicalcium silicate clinker and ensure clinker activity.

[0029] The present invention will be described in detail below with reference to specific implementation examples, but the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] A method for preparing low-temperature calcined, low-heat silicate cement. By weight, 70 parts calcium carbonate, 21 parts silicon dioxide, 7 parts barium carbonate, and 2 parts calcium sulfate are used as raw materials to calcine dicalcium silicate monomineralize, which is then ground to a specific surface area of ​​360 g / cm³. 3 Dicalcium silicate single mineral powder and α-alumina were mixed at a weight ratio of 4:1 to prepare clinker seed crystals. 1% of the seed crystals by weight were added to a raw meal mixture of limestone and sandstone and calcined at 1100℃ to produce dicalcium silicate clinker. Low-heat silicate cement was prepared by grinding 40% dicalcium silicate clinker, 55% silicate cement clinker, and 5% gypsum together. The cement mineral composition of this embodiment is shown in Table 1.

[0032] Example 2

[0033] A method for preparing low-temperature calcined, low-heat silicate cement. By weight, 68 parts calcium carbonate, 20 parts silicon dioxide, 7 parts barium carbonate, and 5 parts calcium sulfate are used as raw materials to calcine dicalcium silicate monomineralize, which is then ground to a specific surface area of ​​360 g / cm³. 3Dicalcium silicate single mineral powder and α-alumina were mixed at a weight ratio of 7:3 to prepare clinker seed crystals. 1% of the seed crystals by weight were added to a raw meal mixture of limestone and sandstone and calcined at 1100℃ to produce dicalcium silicate clinker. Low-heat silicate cement was prepared by grinding 40% dicalcium silicate clinker, 55% silicate cement clinker, and 5% gypsum together. The cement mineral composition of this embodiment is shown in Table 1.

[0034] Example 3

[0035] A method for preparing low-temperature calcined, low-heat silicate cement. By weight, 70 parts calcium carbonate, 21 parts silicon dioxide, 7 parts barium carbonate, and 2 parts calcium sulfate are used as raw materials to calcine dicalcium silicate monomineralize, which is then ground to a specific surface area of ​​360 g / cm³. 3 Dicalcium silicate single mineral powder and α-alumina were mixed at a weight ratio of 4:1 to prepare clinker seed crystals. 0.8% of the seed crystals by weight of the raw meal (limestone and sandstone) were added and calcined at 1100℃ to produce dicalcium silicate clinker. Low-heat silicate cement was prepared by grinding 45% dicalcium silicate clinker, 50% silicate cement clinker, and 5% gypsum together. The cement mineral composition of this embodiment is shown in Table 1.

[0036] Example 4

[0037] A method for preparing low-temperature calcined, low-heat silicate cement. By weight, 68 parts calcium carbonate, 20 parts silicon dioxide, 7 parts barium carbonate, and 5 parts calcium sulfate are used as raw materials to calcine dicalcium silicate monomineralize, which is then ground to a specific surface area of ​​360 g / cm³. 3 Dicalcium silicate single mineral powder and α-alumina were mixed at a weight ratio of 7:3 to prepare clinker seed crystals. 0.8% of the seed crystals by weight of the raw meal (limestone and sandstone) were added and calcined at 1100℃ to produce dicalcium silicate clinker. Low-heat silicate cement was prepared by grinding 45% dicalcium silicate clinker, 50% silicate cement clinker, and 5% gypsum together. The cement mineral composition of this embodiment is shown in Table 1.

[0038] Cement mortar strength specimens were prepared and physical performance tests were conducted in accordance with GB / T 17671-1999 Cement Mortar Strength Test Method (ISO Method). The physical performance results of each implementation case are shown in Table 2.

[0039] Table 1. Cement mineral composition in Examples 1-4

[0040] Tricalcium silicate Dicalcium silicate Tricalcium aluminate Tetracalcium aluminoferrite Example 1 36.3 45.1 3.5 10.1 Example 2 35.3 45.6 3.6 10.5 Example 3 30.7 51.2 3.5 9.6 Example 4 31.1 50.8 3.8 9.3

[0041] Table 2. Heat of hydration and mechanical properties of cement in the examples

[0042]

[0043] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for producing a low-temperature fired low-heat portland cement, characterized by, The application discloses a method for improving the sintering efficiency of dicalcium silicate by mixing dicalcium silicate and alpha type aluminum oxide to prepare a clinker seed, and realizes low-temperature sintering of dicalcium silicate cement clinker. Step 1: sintering dicalcium silicate single mineral from calcium carbonate, silicon dioxide, barium carbonate and calcium sulfate and grinding the dicalcium silicate single mineral, wherein the total weight ratio of alpha type dicalcium silicate and alpha type dicalcium silicate is greater than 65%; Step 2: mixing the dicalcium silicate single mineral powder in step 1 with alpha type aluminum oxide powder to prepare a clinker seed; Step 3: preparing raw meal from limestone and sandstone, mixing the raw meal with 0.8-1.2% of the clinker seed by weight, and sintering at 1100 DEG C to obtain dicalcium silicate cement clinker; Step 4: grinding 35-45 parts of the dicalcium silicate cement clinker, 50-60 parts of Portland cement clinker and 3-8 parts of gypsum to obtain low-heat Portland cement.

2. The method of claim 1, wherein the low-temperature sintering low-heat portland cement is prepared by mixing and sintering the mixture of the raw materials at a temperature of 1,100°C or lower. The total weight ratio of alpha type dicalcium silicate and alpha type dicalcium silicate in the clinker seed in step 2 is greater than 50%.

3. The method of claim 1, wherein the low-temperature sintered low-heat portland cement is characterized by, The raw materials in step 1 include: 65-75 parts of calcium carbonate, 18-24 parts of silicon dioxide, 4-7 parts of barium carbonate and 2-4 parts of calcium sulfate.

4. The method of claim 1, wherein the low-temperature sintered low-heat portland cement is characterized by, The clinker seed in step 2 includes: 70-80 parts of dicalcium silicate single mineral powder and 70-80 parts of alpha type aluminum oxide powder.

5. The low-temperature sintered low-heat Portland cement obtained by the method in any one of claims 1-4.

6. A low temperature fired low heat Portland cement according to claim 5, characterized in that, The content of dicalcium silicate in the low-heat Portland cement is greater than 40% by weight, and the content of tricalcium aluminate is less than 5%.

7. A low temperature fired low heat Portland cement according to claim 5 or 6, characterized in that, The 3d hydration heat of the low-heat Portland cement is less than 200 J / g, the 7d hydration heat is less than 250 J / g, and the 28d compressive strength is greater than 45 MPa.

Images