Low-calcium silicate cement clinker, cement and preparation method

Abstract

The present invention discloses a low-calcium Portland cement clinker, cement, and preparation method. The cement clinker comprises the following mineral components, measured by mass percentage: 5-20% C3S, 50-60% C2S, 10-20% C6AF2, 0-7% C3A, and 0.1-15% C4A3$. By designing a high silicon content, the present invention increases the C2S content in the cement clinker, thereby improving the late-stage performance of the clinker. Simultaneously, the early strength generated by the rapid hydration of C4A3$ compensates for the insufficient early hydration activity of the clinker caused by the increased C2S content, resulting in excellent cement performance in the early, mid, and late stages.

Description

Technical Field

[0001] The present invention relates to the field of building materials, and in particular to a low-calcium silicate cement clinker, cement and a preparation method thereof. Background Art

[0002] my country is a major cement producer and carbon emitter. Due to its massive output, the cement industry has become the second-largest carbon emitter in my country's industrial sector, facing immense pressure to reduce carbon emissions. Portland cement is the dominant product in my country's cement industry, emitting an average of 0.97 tons of CO2 per ton produced. The main mineral components of Portland cement clinker include tricalcium silicate (C3S), dicalcium silicate (C2S), tetracalcium aluminoferrite (C4AF), and tricalcium aluminate (C3A). Among these, C3S has the highest calcium content and contributes to high carbon emissions. Significantly reducing C3S content and developing new low-calcium Portland cement clinkers are urgently needed to reduce carbon emissions from the cement industry.

[0003] Patent application number 201310138543.5 discloses a high-strength Portland cement clinker containing calcium sulfoaluminate. Its mineral composition includes 50-75% C3S, 2-25% C2S, 2-8% C4AF, 2-25% C3A, 2-9% C4A3$, 0.5-3% free calcium oxide (f-CaO), 1-6% periclase (MgO), and 0-3% gypsum (CaSO4). The patent utilizes a two-step calcination process: the Portland cement clinker is first calcined at 1400-1500°C, then heated to 1000-1300°C for a secondary calcination, followed by rapid cooling. The clinker achieves 3d and 28d strengths of 42-44 MPa and 65-72 MPa, respectively. This invention utilizes a two-step calcination process to introduce C4A3$ into the Portland cement clinker, which improves the clinker's compressive strength. However, the clinker has a high C3S content, resulting in higher carbon emissions, and the secondary burning process will further consume a large amount of energy.

[0004] Patent application number 202210843960.9 provides a highly sulfur-resistant Portland cement clinker. The clinker's mineral composition includes 35-60% C3S, 15-35% C2S, 0-7% C3A, and 10-23% C6AF2. The clinker is produced by holding the mixture at 1350-1420°C for 30-40 minutes. The introduction of C6AF2 significantly improves the cement clinker's resistance to sulfate attack and can reduce cement production costs and energy consumption. However, this approach focuses solely on sulfur resistance and fails to guarantee the early and late strength properties required for engineering construction. Summary of the Invention

[0005] The present invention provides a low-calcium Portland cement clinker, cement, and a preparation method. A high silicon content is designed in the Portland cement clinker to ensure the later strength of the clinker; a high iron content is designed to improve the wear resistance of the clinker; and sulfur is introduced during the clinker firing process so that the sulfur in the clinker exists in the form of C4A3$, thereby ensuring the early performance of the clinker.

[0006] The technical solution of the present invention is: a low-calcium silicate cement clinker, which includes the following mineral components by mass percentage: C3S: 5-20%, C2S: 50-60%, C6AF2: 10-20%, C3A: 0-7%, and C4A3$: 0.1-15%.

[0007] The raw materials of cement clinker include: iron raw materials, silicon-aluminum raw materials, calcium raw materials and gypsum.

[0008] The chemical composition of the raw materials is 50%~64% CaO, 15%~23% SiO2, 3%~15% Al2O3, 3%~12% Fe2O3, and 0.1%~24% SO3.

[0009] The iron raw materials include any one or more of steel slag, iron tailings, iron bauxite, and red mud.

[0010] The silicon-alumina raw materials include any one or more of fly ash, coal gangue, bauxite, clay, and sandstone.

[0011] The calcareous raw materials include any one or more of limestone, marble, dolomite, steel slag, and carbide slag.

[0012] The gypsum includes any one or more of dihydrate gypsum, anhydrite, desulfurized gypsum, and phosphogypsum.

[0013] A low-calcium silicate cement comprises, by mass percentage, 95% to 97% of the low-calcium silicate cement clinker and 3% to 5% of anhydrite.

[0014] A method for preparing low-calcium Portland cement clinker, characterized in that it comprises the following steps:

[0015] (1) Raw material pretreatment

[0016] Dry the various raw materials separately, crush them and grind them into fine powder;

[0017] (2) Raw material premixing and tableting

[0018] The raw materials obtained by grinding in step (1) are mixed uniformly to obtain raw material;

[0019] (3) Clinker calcination

[0020] The raw material is calcined at a high temperature of 1300-1370°C; after the calcination, the clinker is taken out and rapidly cooled to room temperature, and then rapidly cooled by a fan to obtain low-calcium silicate cement clinker.

[0021] The present invention has the following effects:

[0022] (1) The present invention increases the C2S content in cement clinker by designing a high silicon content, thereby improving the late performance of the clinker. At the same time, the early strength formed by the rapid hydration of C4A3$ will compensate for the problem of insufficient early hydration activity of the clinker caused by the increase in C2S content, so that the cement has good performance development in the early, middle and late stages.

[0023] (2) By increasing the iron content in the clinker mineral composition, the present invention causes the iron-phase mineral in the silicate clinker to form C6AF2, which has a higher hydration rate than C4AF. C6AF2 hydrates in the presence of gypsum to form iron-containing ettringite, which forms a dense structure that fills the voids within the cement paste. Increasing the C6AF2 content can make the cement hydrated paste structure denser, improving the clinker's erosion resistance and wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of XRD detection of Example 1. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to embodiments, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0026] The raw materials and chemical compositions used in Examples 1 to 3 are shown in Table 1.

[0027] Table 1 Chemical composition of raw materials

[0028]

[0029] Example 1:

[0030] The design mineral composition of cement clinker is shown in Table 2. According to the design mineral composition and material balance principle, the raw materials are configured by mass percentage. Limestone is selected as the calcareous raw material, accounting for 60.54%; bauxite and sandstone are selected as the siliceous and aluminous raw materials, accounting for 6.55% and 10.99% respectively, desulfurized gypsum is 0.94%, and steel slag is 20.98%. After thorough mixing, 1 kg of the uniformly mixed raw material is weighed and ground in a vibration mill to a 0.075 mm square hole sieve residue of less than 5% to obtain powdered cement raw material.

[0031] Add 8% water by mass to the powdered cement raw meal (i.e., the mass of water is 8% of the mass of the raw meal), stir evenly, and press into a tablet press to form 235mm diameter tablets. Dry at 105°C for 12 hours. Adding water facilitates tableting.

[0032] The material was taken out and placed in a muffle furnace preheated to 900°C for calcination for 30 minutes to fully decompose the CaCO3 in the raw material into CaO. It was then transferred to an electric furnace at 1350°C and kept warm for 1 hour. The clinker was taken out and quickly cooled to room temperature with a fan to obtain clinker blocks.

[0033] After the cooled cement clinker is crushed, it is ground into powder using a ball mill until the specific surface area is 400±20m 2 / kg, to obtain cement clinker.

[0034] Table 2 Mineral composition of cement clinker (wt%)

[0035]

[0036] The XRD pattern of the clinker in Example 1 is shown in the attached Figure 1 As shown: The crystal diffraction peaks of C3S, C2S, C6AF2, and C4A3$ can be clearly observed in the XRD pattern, indicating that the clinker minerals are well formed.

[0037] Example 2:

[0038] The design mineral composition of cement clinker is shown in Table 3. According to the design mineral composition and material balance principle, the raw materials are configured by mass percentage: limestone 61.71%, bauxite 3.83%, sandstone 12.50%, steel slag 21.77%, and anhydrite 0.19%. After thorough mixing, 1 kg of the mixed raw material is weighed and ground in a vibration mill to a residue on a 0.075 mm square hole sieve of less than 5% to obtain powdered cement raw material.

[0039] 8% by mass of water is added to the powdered cement raw meal, stirred evenly, pressed into dense raw meal sheets, and thoroughly dried. This step promotes the solid-phase reaction during clinker formation. The material is then calcined at 900°C for 30 minutes, then heated to 1350°C for 1 hour. The material is then removed and rapidly cooled to room temperature using a fan.

[0040] After the cooled cement clinker blocks are crushed, they are ground into powder using a ball mill until the specific surface area is 400±20m 2 / kg cement clinker is obtained.

[0041] Table 3 Mineral composition of cement clinker (wt%)

[0042]

[0043] Example 3:

[0044] The design mineral composition of cement clinker is shown in Table 4. According to the design mineral composition and material balance principle, the raw materials are configured according to mass percentage: limestone 63.33%, bauxite 6.59%, sandstone 13.50%, steel slag 14.71%, and anhydrite 1.87%. After thorough mixing, 1 kg of the mixed raw material is weighed and ground in a vibration mill until the residue on a 0.075 mm square hole sieve is less than 5% to obtain powdered cement raw material.

[0045] Add 8% by mass of water to the powdered cement raw meal, stir thoroughly, press into dense raw meal sheets, and thoroughly dry. Remove the material and calcine it at 900°C for 30 minutes, then increase the temperature to 1350°C and hold for 1 hour. Remove the material and rapidly cool it to room temperature using a fan.

[0046] After the cooled cement clinker blocks are crushed, they are ground to a specific surface area of ​​400 ± 20 m 2 / kg, and obtain cement clinker.

[0047] Table 4 Mineral composition of cement clinker (wt%)

[0048]

[0049] Example 4:

[0050] The clinker produced in Examples 1, 2, and 3 was used to prepare cements in a ratio of clinker: anhydrite = 95:5, labeled HFC1, HFC2, and HFC3. Cement mortar strength tests were conducted according to GB / T 17671-1999, "Test Method for Cement Mortar Strength," with a mortar-to-cement ratio of 1:3. Mortar specimens were formed using 40 mm × 40 mm × 160 mm test molds. The performance of the new clinker was also compared to a benchmark cement designated P.O.42.5 to observe its performance. The strength results are shown in Table 5.

[0051] Table 5

[0052]

[0053] By comparison, the strength of the cement in Examples 1-3 of the present invention is higher than the strength of the P.O.42.5 benchmark cement.

[0054] In the cement clinker of this invention, C3S has high gelling activity; a reduction in its content will directly lead to a significant reduction in cement strength. C2S has low early activity but exhibits good late-stage strength. Calcium sulfoaluminate (C4A3$) features a low calcium content and excellent early performance. Introducing sulfur into Portland cement to form C4A3$ effectively compensates for the insufficient early strength caused by reduced C3S content and increased C2S content. Even if C4A3$ is introduced, its content should be kept as low as possible. To ensure stable clinker performance, the content of iron phases with high gelling activity, such as C6AF2, should be further adjusted to achieve widespread industrial application of low-calcium Portland cement clinker.

[0055] Furthermore, iron-phase minerals such as hexacalcium aluminoferrate (C6AF2), in addition to their high strength and early-strength properties, are also highly effective in improving the toughness and sulfate corrosion resistance of Portland cement. Increasing the C6AF2 content in Portland cement significantly enhances its advantages in erosion and wear resistance.

[0056] The present invention aims to achieve the contradictory needs of further reducing calcium and carbon and high performance by simultaneously introducing C4A3$ and increasing the content of C2S and high gelled iron phase, thereby achieving the coordinated development of the early and late performance of the clinker, and preparing excellent performance cement clinker with properties such as wear resistance.

Claims

1. A low-calcium Portland cement clinker, characterized in that: The cement clinker comprises the following mineral components by mass percentage: C3S: 5-20%, C2S: 50-60%, C6AF2: 10-20%, C3A: 0-7%, C4A3$: 0.1-15%; The raw materials of cement clinker include: iron raw materials, silicon-aluminum raw materials, calcium raw materials and gypsum. The chemical composition of the raw material is 50% to 64% CaO, 15% to 23% SiO2, 3% to 15% Al2O3, 3% to 12% Fe2O3, and 0.1% to 24% SO3; C6AF2 hydrates in the presence of gypsum to form iron-containing calcium sulfide, which forms a dense structure to fill the voids inside the cement paste.

2. A low-calcium Portland cement clinker according to claim 1, characterized in that The iron raw materials include any one or more of steel slag, iron tailings, iron bauxite, and red mud.

3. A low-calcium Portland cement clinker according to claim 1, characterized in that: The silicon-alumina raw materials include any one or more of fly ash, coal gangue, bauxite, clay, and sandstone.

4. A low-calcium Portland cement clinker according to claim 1, characterized in that: The calcareous raw materials include any one or more of limestone, marble, dolomite, steel slag, and carbide slag.

5. A low-calcium Portland cement clinker according to claim 1, characterized in that: The gypsum includes any one or more of dihydrate gypsum, anhydrite, desulfurized gypsum, and phosphogypsum.

6. A low-calcium silicate cement, characterized in that Calculated by mass percentage, it comprises 95% to 97% of the low-calcium Portland cement clinker according to any one of claims 1 to 5 and 3% to 5% of anhydrite.

7. A method for preparing low-calcium Portland cement clinker according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Raw material pretreatment Dry the various raw materials separately, crush them and grind them into fine powder; (2) Raw material premixing and tableting The raw materials obtained by grinding in step (1) are mixed uniformly to obtain raw material; (3) Clinker calcination The raw material is calcined at a high temperature of 1300-1370°C; after the calcination, the clinker is taken out and rapidly cooled to room temperature, and then rapidly cooled by a fan to obtain low-calcium silicate cement clinker.

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