A method for improving early activity of cement by activating belite minerals through refinement

Abstract

The application provides a method for improving early activity of cement by refining activated belite minerals, and belongs to the field of building materials. In the clinker calcination process, the first step is to control the firing temperature to be 1100-1200 DEG C, and the holding time is 1-2 h, so that a large amount of C5S2$ minerals are generated; the second step is to increase the calcination temperature to 1280-1320 DEG C, and the holding time is 1-2 h, so that the C5S2$ minerals are not completely decomposed, and most of them are converted into alpha'-C2S and C$ clinker minerals with small grain size. In addition, the mineralization technology is used to promote the generation of a large amount of C3S at about 1300 DEG C, the ion doping is used to distort the C2S mineral lattice and the C3S mineral lattice, and the crystal defects of the high belite cement clinker minerals are increased, so that the grain size of the clinker minerals is refined. The above-mentioned methods work together, the grain size of the high belite cement clinker is refined, and the early activity of the high belite cement is improved. The preparation method solves the problems of low early activity of the high belite cement, and the prepared high belite cement clinker has the characteristics of small grain size and containing alpha'-C2S minerals.

Description

Technical Field

[0001] This invention belongs to the field of building materials and relates to a method for activating the early activity of cement by refining clinker mineral belite. Background Technology

[0002] To achieve low-carbon and environmentally friendly goals such as reducing energy consumption and carbon dioxide emissions in the domestic cement industry, there is increasing attention being paid to new low-carbon cement clinker systems. Belite cement clinker (C2S) is a low-carbon cement clinker with a firing temperature 150℃–250℃ lower than traditional silicate cement clinker and a lower limestone content. This results in a reduction of over 25% in both energy consumption and CO2 emissions, characterized by low calcium, low emissions, and low energy consumption. Based on these advantages, cement clinker systems with belite as the main component have gradually developed. For example, the sulfoaluminate cement clinker (CSA) developed by the China Building Materials Academy, whose main minerals are calcium sulfoaluminate (C4A3$, ye'elimite) and belite, is prepared by calcining limestone, bauxite, and gypsum at 1300-1350℃. The Aether cement clinker proposed by Lafarge in France, whose main minerals are C4A3$, belite, and C2(A,F), can be produced at 1200-1300℃. The belite-calcium sulfoaluminate-calcium sulfosilicate system cement clinker (BCT cement clinker) proposed by Heidelbergcement in Germany, whose main minerals are C4A3$, C2S, C2(A,F) and calcium sulfosilicate (C5S2$), can be produced at 1250-1300℃.

[0003] While the aforementioned novel cement clinker systems utilize a certain amount of belite as the main clinker component, thus lowering the clinker's firing temperature, they often contain a large amount of calcium sulfoaluminate minerals. This is primarily because belite in clinker exists mainly in the β-C2S form, exhibiting low early hydration activity and slow hydration reactions. Introducing a large amount of calcium sulfoaluminate minerals can improve the early hydration activity of the cement clinker system. Currently, both domestic and international methods utilize the introduction of large amounts (>30%) of C4A3 to enhance the activity of the C4A3-C2S clinker system. However, the raw material cost for C4A3 is high. Using large amounts of bauxite as a raw material would inevitably increase the cost of these clinker systems and would not comply with my country's environmental protection policies. Unlike existing methods that heavily incorporate C4A3 into belite cement systems, this invention proposes a method to refine the belite grain size to improve the early activity of high-belite clinker, thereby achieving high-belite cement with enhanced early activity. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for refining belite grain size using industrial waste raw materials, thereby preparing high-belite cement clinker with good early hydration activity.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for enhancing the early-stage activity of cement by refining and activating belite minerals, the method is as follows:

[0007] Raw materials are calcined in a high-temperature kiln. During clinker calcination, the first step controls the calcination temperature to 1100–1200℃ and holds it for 1–2 hours, generating a large amount of calcium sulfosilicate (C5S2$) minerals. The second step raises the calcination temperature to 1280–1320℃ and holds it for 1–2 hours, thereby controlling the incomplete decomposition of C5S2$ minerals and converting most of them into fine-grained α'-C2S and C$ clinker minerals. In addition, mineralization technology promotes the large-scale generation of C3S at around 1300℃, and ion doping distorts the crystal lattices of C2S and C3S minerals, increasing crystal defects in the high-belite cement clinker minerals and refining the clinker mineral grain size. The synergistic effect of these methods refines the grain size of the high-belite cement clinker and improves the early activity of high-belite cement.

[0008] Furthermore, the raw material is composed of the following raw material components by mass percentage:

[0009] Limestone: 55%–70%, clay or silica fume: 15%–25%, phosphogypsum or desulfurized gypsum: 8%–15%, mineralized component A: 3%–8%, the sum of the mass percentages of the above components is 100%.

[0010] Furthermore, the mineralized component A is composed of the following raw material components by mass percentage: fluorite 20-50%, magnesite tailings 5-20%, strontium slag 10-60%, barium slag 10-60%, and steel slag 0-20%. The sum of the mass percentages of the above components is 100%.

[0011] Furthermore, the clinker mineral composition is as follows: C2S (including β-C2S and α'-C2S): 40-60%, C3S: 15-30%, C5S2S: 0-5%, C4A3S: 10-15%, C2S: 6-10%, with the remainder being unavoidable impurities.

[0012] The technical solution of this invention is also characterized by,

[0013] A method for preparing refined Belite clinker minerals includes the following steps:

[0014] Step (1) Raw material batching calculation and preparation

[0015] Calculate the raw material composition of high belite cement clinker based on the chemical composition of each raw material.

[0016] Step (2) Raw material grinding and premixing homogenization

[0017] Limestone, clay or silica fume, phosphogypsum, and component A are crushed and ground according to the mass fraction ratio. The fineness of the raw material is controlled to pass through a 0.08mm square hole sieve, and qualified raw material is obtained after pre-homogenization.

[0018] Step (3) Calcination of clinker:

[0019] The raw material prepared in step (2) is put into the kiln for calcination. During the calcination process of clinker, the first step is to control the calcination temperature at 1100-1200℃ and the holding time is 1-2h; the second step is to raise the calcination temperature to 1280-1320℃ and the holding time is 1-2h; after rapid cooling, high belite cement clinker with refined grain size is obtained.

[0020] In application, the high-Belite cement clinker from step (3) is ground to a Blaine specific surface area of ​​350–400 m². 2 / kg, which is used to make high belite cement.

[0021] The beneficial effects of this invention are as follows:

[0022] Adding large amounts of phosphogypsum or desulfurized gypsum and mineralizing component A to high-belite cement raw materials enables C2S to form a large amount of intermediate mineral C5S2$ at 1100-1200℃. Further heating to 1280-1350℃ decomposes calcium sulfosilicate to obtain refined α'-C2S highly active belite minerals and C$. Component A promotes the formation of a large amount of fine-grained C3S and C2S minerals at around 1300℃ through mineralization technology, maximizing activity. Barium and strontium ions in component A can distort the belite and allit lattices, increasing clinker crystal defects and refining clinker grain size. The synergistic effect of these methods results in a belite grain size of approximately 10μm in the clinker minerals, far lower than the traditional belite grain size of approximately 20μm. The above methods work synergistically to refine the grain size of high belite cement clinker, including the α'-C2S crystal form with higher grain activity, thereby effectively improving the early hydration activity and early strength of high belite cement. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention as described above or otherwise will become clearer.

[0024] Appendix Figure 1 SEM image of Belite cement clinker for comparison example 1

[0025] Appendix Figure 2 These are SEM images of representative high-Belitt cement clinker obtained in Examples 1-3. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail through the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] For the raw materials and their chemical composition in the following examples, please refer to Table 1:

[0028] Table 1 Chemical composition of raw materials

[0029] Types of raw materials <![CDATA[SiO2]]> CaO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[P2O5]]> <![CDATA[CaF2]]> SrO BaO Loss total limestone 0.72 53.24 0.72 0.13 1.52 / / / / / 42.83 99.16 clay 74.22 0.35 18.34 2.11 0.45 / / / / / 4.26 99.73 phosphogypsum 3.28 29.84 0.61 0.55 / 42.11 1.68 / / / 20.21 98.28 fluorite 37.89 7.54 5.12 2.33 3.79 5.21 / 23.61 / / 13.09 98.58 Strontium residue 11.91 12.91 6.43 2.12 1.43 17.92 / / 44.29 / 1.22 98.23 Magnesite tailings 6.10 4.85 0.75 0.52 42.70 / / / / / 44.32 99.24 steel slag 14.77 46.73 5.52 18.42 6.27 / 1.67 / 2.76 2.21 98.35 Barium slag 15.34 16.99 3.44 2.34 5.29 15.58 / / / 36.54 4.1 99.70

[0030] Example 1

[0031] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground until they could pass through a 0.08mm square-hole sieve. The following weight percentages were then weighed: limestone 65.6%, clay 20.7%, phosphogypsum 9.8%, and component A 3.9%, where component A was composed of: fluorite 45%, magnesite tailings 5%, strontium slag 10%, barium slag 30%, and steel slag 10%. The weighed raw materials were placed in a planetary ball mill and mixed thoroughly for 30 minutes to obtain a uniformly mixed powdered raw meal. 8% water was added to the powdered cement raw meal, and the mixture was stirred evenly before being pressed into round sheets with a diameter of approximately 50mm and a thickness of approximately 5mm using a tablet press. After drying the raw material discs, they were placed in a high-temperature kiln. The kiln temperature was raised to 900℃ and held for 0.5 hours, then increased to 1100℃ and held for 2 hours, and finally raised to 1300℃ and held for 1.5 hours. After calcination, the Belite cement clinker was removed and rapidly cooled to room temperature using a fan. The Belite cement clinker was then ground to a Blaine specific surface area of ​​393 m². 2 / kg.

[0032] Example 2

[0033] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground until they passed through a 0.08mm square-hole sieve. The following weight percentages were then weighed: limestone 63.4%, clay 21.1%, phosphogypsum 10.2%, and component A 5.3%, where component A was composed of: fluorite 35%, magnesite tailings 7%, strontium slag 12%, barium slag 35%, and steel slag 11%. The weighed raw materials were placed in a planetary ball mill and mixed thoroughly for 30 minutes to obtain a uniformly mixed powdered raw meal. 8% water was added to the powdered cement raw meal, and the mixture was stirred evenly before being pressed into round discs with a diameter of 50mm and a thickness of 5mm using a tablet press. After drying the raw material discs, they were placed in a high-temperature kiln. The kiln temperature was raised to 900℃ and held for 0.5 hours, then increased to 1150℃ and held for 1.5 hours, and finally raised to 1280℃ and held for 2 hours. After calcination, the Belite cement clinker was removed and rapidly cooled to room temperature using a fan. The Belite cement clinker was then ground to a Blaine specific surface area of ​​367 m² / g. 2 / kg.

[0034] Example 3

[0035] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground until they passed through a 0.08mm square-hole sieve. The following weight percentages were then weighed: limestone 66.4%, clay 19.1%, phosphogypsum 8.7%, and component A 5.8%, where component A is composed of: fluorite 50%, magnesite tailings 10%, strontium slag 20%, barium slag 12%, and steel slag 8%. The weighed raw materials were placed in a planetary ball mill and mixed thoroughly for 30 minutes to obtain a uniformly mixed powdered raw meal. 8% water was added to the powdered cement raw meal, and the mixture was stirred evenly and pressed into round discs with a diameter of 50mm and a thickness of 5mm using a tablet press. After drying the raw meal discs, they were placed in a high-temperature kiln. The kiln temperature was raised to 900℃ and held for 0.5 hours, then raised to 1200℃ and held for 1 hour, and finally raised to 1320℃ and held for 1 hour. After calcination, the Belite cement clinker was removed and rapidly cooled to room temperature using a fan. The Belite cement clinker was then ground to a Blaine specific surface area of ​​381 m². 2 / kg.

[0036] Comparative Example 1

[0037] The above-mentioned raw materials, limestone and clay, were dried at 105°C for 24 hours. Then, all raw materials were crushed and ground until they passed through a 0.08 mm square-hole sieve. The following weight percentages were then weighed: limestone 73.4%, clay 21.1%, and phosphogypsum 5.5%. To eliminate the influence of C4A3S and C3S minerals on the early hydration activity of Belite cement, the gypsum content in the raw materials of Comparative Example 1 was consistent with the gypsum content required for calcium sulfoaluminate minerals in Examples 1-3, and the ratio of calcareous to siliceous raw materials was consistent with the ratio of calcareous to siliceous raw materials in Comparative Example 3. The weighed raw materials were placed in a planetary ball mill and mixed thoroughly for 30 minutes to obtain a uniformly mixed powdered raw meal. 8% by mass of water was added to the powdered cement raw meal, and the mixture was stirred evenly and then pressed into round discs with a diameter of 50 mm and a thickness of 5 mm using a tablet press. After drying the raw material discs, they were placed in a high-temperature kiln. The kiln temperature was raised to 900℃ and held for 0.5 hours, then raised to 1300℃ and held for 3 hours. After calcination, the Belite cement clinker was removed and rapidly cooled to room temperature using a fan. The Belite cement clinker was then ground to a Blaine specific surface area of ​​379 m². 2 / kg.

[0038] The early (3-day) compressive strength of the belite cement clinker prepared in Examples 1-3 and Comparative Example 1 was tested according to the national standard GB17671-1999, and the specific results are shown in Table 2. After black-and-white binarization of the SEM images of the clinker, the grain size of the cement clinker minerals was statistically analyzed using ImagePro software, and the statistical results are shown in Table 3. Representative SEM images of the clinker from Comparative Example 1 and Examples 1-3 are attached. Figure 1 and attached Figure 2 (Specifically, as shown in Example 3).

[0039] Table 2. 3d compressive strength of Belite cement

[0040] Example Example 1 Example 2 Example 3 Comparative Example 1 3D compressive strength (MPa) 23.3 19.7 25.8 18.3

[0041] Table 3. Average grain size (μm) of minerals in high belite clinker.

[0042]

[0043] From the appendix Figure 1 Appendix Figure 2 As can be seen from Table 3, the representative clinker mineral grain size of Examples 1-3 is significantly smaller than that of Comparative Example 1, indicating that the belite clinker mineral grain size is refined. Table 2 shows that by refining the belite cement grain size, the 3-day compressive strength of Examples 1-3 is significantly higher than that of Comparative Example 1, indicating a significant improvement in the early-stage activity of belite cement.

[0044] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for enhancing the early-stage activity of cement by refining and activating belite minerals, characterized in that, The method is as follows: Raw materials are calcined in a high-temperature kiln. During the clinker calcination process, the first step controls the calcination temperature to 1100~1200℃ and the holding time to 1~2h, generating a large amount of calcium sulfosilicate minerals, abbreviated as C5S2$. The second step raises the calcination temperature to 1280~1320℃ and holds it for 1~2h, thereby controlling the incomplete decomposition of C5S2$ minerals and converting most of them into α'-C2S and C$ clinker minerals with fine grain size. The raw meal is composed of the following raw material components by mass percentage: limestone: 55%~70%, clay or silica fume: 15%~25%, phosphogypsum or desulfurized gypsum: 8%~15%, mineralized component A: 3~8%, and the sum of the mass percentages of the above components is 100%. The mineralized component A is composed of the following raw material components by mass percentage: fluorite 20-50%, magnesite tailings 5-20%, strontium slag 10-60%, barium slag 10-60%, and steel slag 0-20%; the sum of the mass percentages of the above components is 100%.

2. The method for enhancing the early-stage activity of cement by refining and activating belite minerals according to claim 1, characterized in that, C3S is generated in the temperature range of 1280~1320℃ by mineralization technology. The crystal defects of high belite cement clinker minerals are increased and the grain size of clinker minerals is refined by ion doping to distort the C2S mineral lattice and C3S mineral lattice.

3. The method for enhancing the early-stage activity of cement by refining and activating belite minerals according to claim 1, characterized in that, The clinker mineral composition is C2S: 40-60%, C3S: 15-30%, C5S2S: 0-5%, C4A3S: 10-15%, C2S: 6-10%, with the remainder being unavoidable impurities, wherein C2S includes β-C2S and α'-C2S.

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