Erosion-resistant cement clinker with ultralow aluminum rate as well as preparation method and application of erosion-resistant cement clinker

Abstract

The invention discloses an ultralow-aluminum-rate erosion-resistant cement clinker as well as a preparation method and application thereof, and belongs to the technical field of Portland cement. The clinker is prepared from the following mineral components in percentage by mass: 55 to 65 percent of C3S, 15 to 25 percent of C2S, less than or equal to 2 percent of C3A and 17 to 21 percent of C4AF, the aluminum ratio IM is 0.50 to 1.00, the lime saturation coefficient KH is 0.910 to 0.930, and the silicon ratio SM is 1.90 to 2.10. The preparation method comprises the steps of S1, raw material preparation and S2, sintering. According to the invention, a new mineral system of'high iron phase-optimized silicate phase 'is constructed, and a specific sintering process is matched, so that the aluminum rate is remarkably reduced, the burnability of the clinker is improved, the energy consumption is reduced, the obtained clinker has excellent sulfate corrosion resistance, and the 3-day and 28-day compressive strength of the clinker is equivalent to that of common silicate clinker; after 60 days, the strength increase rate is obviously improved compared with that of common clinker, the hydration heat is obviously reduced, the comprehensive performance is excellent, and the clinker is suitable for engineering construction in a harsh sulfate environment.

Description

Technical Field

[0001] This invention relates to the field of silicate cement materials technology, specifically to a cement clinker with ultra-low alumina ratio and high resistance to sulfate attack, its preparation method, and its application. Background Technology

[0002] Silicate cement is one of the most important building materials today. However, in harsh conditions rich in sulfates, such as marine environments, saline-alkali land, and underground engineering projects, traditional cement concrete is prone to sulfate attack and damage. Sulfates react with calcium aluminate and other products in cement hydration to form expansive crystals, leading to cracking, spalling, and strength loss in concrete structures, seriously threatening the durability and safety of engineering structures.

[0003] The classic method to improve the sulfate resistance of cement is to produce sulfate-resistant silicate cement. The core technology lies in strictly controlling the content of tricalcium aluminate (C3A) minerals in the clinker, which have high hydration activity and are susceptible to sulfate attack. For example, the national standard GB / T 748-2005 stipulates that the C3A content in medium-sulfate-resistant cement clinker should not exceed 5.0%, and the C3A content in high-sulfate-resistant cement clinker should not exceed 3.0%. To achieve this goal, traditional production methods typically employ a medium-to-high alumina ratio (IM, usually greater than 0.9) in the batching scheme. This limits the total amount of C3A while ensuring sufficient aluminum and iron phases to form appropriate flux minerals, maintaining normal clinker firing and a certain early strength.

[0004] However, this traditional technical approach has significant limitations: First, its improvement in sulfate resistance mainly relies on the "passive restriction" of C3A, which has a performance ceiling and cannot meet the ultra-long service life requirements under extremely harsh environments. Second, the medium-to-high alumina ratio formulation is highly dependent on high-quality alumina raw materials (such as bauxite), resulting in higher costs and contradicting the green development trend of utilizing low-grade raw materials and conserving mineral resources. Third, and most importantly, simply attempting to further reduce the alumina ratio to pursue better corrosion resistance or economy will lead to insufficient liquid phase, resulting in clinker firing difficulties (increased free calcium oxide f-CaO content), insufficient silicate mineral formation, and consequently, serious performance imbalances such as slow early strength development and abnormal setting time. Therefore, developing a cement clinker and its production technology that can simultaneously achieve high sulfate resistance and excellent comprehensive mechanical properties at ultra-low alumina ratios is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an ultra-low alumina ratio corrosion-resistant cement clinker, its preparation method, and its application. The specific technical solution of this invention is as follows:

[0006] This invention provides an ultra-low alumina ratio corrosion-resistant cement clinker. The mineral composition of the cement clinker, by mass percentage, includes: C3S 55-65%, C2S 15-25%, C3A ≤ 2%, and C4AF 17-21%. The alumina ratio IM of the clinker is 0.50-1.00, the lime saturation coefficient KH is 0.910-0.930, and the silicon ratio SM is 1.90-2.10.

[0007] Preferably, the aluminum content (IM) of the clinker is 0.65-0.85.

[0008] Preferably, the aluminum content (IM) of the clinker is 0.65-0.77.

[0009] Preferably, the C3A content of the clinker is ≤ 1.5%.

[0010] Preferably, the C4AF content of the clinker is 18-20%.

[0011] The present invention also provides a method for preparing the ultra-low alumina ratio erosion-resistant cement clinker, comprising the following steps: S1. Raw material preparation: Weigh limestone, sandstone, copper ore powder and fly ash according to the proportion, mix and grind to the specified fineness to obtain raw meal; S2. Sintering: The raw materials prepared in step S1 are sintered at a maximum temperature of 1230-1270℃, and the cement clinker is obtained after cooling.

[0012] Preferably, in step S1, by controlling the raw material ratio, the raw material ratio is made to meet the following requirements: lime saturation coefficient KH = 0.92-1.02, silicon ratio SM = 2.00-2.10, and aluminum ratio IM = 0.65-0.80.

[0013] Preferably, in step S1, the raw materials, by mass percentage, include: limestone 82.5-85.0%, sandstone 8.5-11.0%, copper ore powder 2.0-7.5%, and fly ash 0-3.0%.

[0014] The present invention also provides a cement comprising the aforementioned cement clinker.

[0015] The application of the aforementioned cement clinker in the preparation of sulfate-resistant cement.

[0016] Compared with the prior art, the beneficial technical effects of this invention are reflected in: Excellent resistance to sulfate attack: By reducing the clinker aluminate ratio (IM) to 0.50-1.00 and controlling the C3A content to ≤2% (as low as 0.24%), the main reactive phase for sulfate attack is fundamentally and significantly reduced. Simultaneously, the high C4AF content (15-21%) and optimized silicate mineral structure further enhance the compactness and erosion resistance of the clinker paste, resulting in sulfate resistance far exceeding the national standard requirements for high sulfate-resistant cement (C3A ≤ 3.0%).

[0017] Excellent comprehensive mechanical properties: Despite a significant reduction in aluminum content, through precise matching and optimized sintering of KH and SM, the compressive strength of the clinker at all ages is comparable to that of ordinary silicate clinker. Test data shows that its 3-day compressive strength remains at 30.5-31.9 MPa, and its 28-day compressive strength reaches 58.8-60.3 MPa, fully meeting engineering application requirements. Simultaneously, the clinker setting time is normal, and the standard consistency water requirement is stable.

[0018] The formula, characterized by ultra-low alumina ratio and high ferric phase, combined with a specific sintering temperature, improves the burnability of the raw materials. Industrial production data shows that when using this invention, key process parameters such as the preheater outlet temperature, decomposition furnace outlet temperature, and kiln tail temperature are significantly lower than when producing ordinary clinker (for example, the kiln tail flue temperature decreases by approximately 120°C). The system negative pressure is also reduced, indicating a lighter thermal load on the calcination system, which helps reduce coal consumption and overall energy consumption.

[0019] Low heat of hydration and good volume stability: The heat of hydration of the clinker of this invention is significantly lower than that of ordinary silicate clinker, with a decrease of approximately 16.36 KJ / kg after 7 days. The low heat of hydration helps to reduce the internal temperature rise of large-volume concrete, reduce the risk of temperature cracks, and improve the volume stability and durability of concrete.

[0020] Significant advantages in resources and economy: The low-alumina formula reduces dependence on high-priced bauxite and allows for the extensive use of iron-rich industrial by-products or low-grade raw materials such as copper ore powder. This not only reduces production costs but also achieves comprehensive utilization of resources, which aligns with the green and sustainable development direction of the cement industry. Attached Figure Description

[0021] Figure 1 and Figure 2 Lithofacies photographs of the fourth-stage low-alumina clinker prepared for embodiments of the present invention in different observation areas; Figure 3 This is a comparison chart of heat flow-time curves between low-aluminum clinker and ordinary clinker in the fourth stage of this invention. Figure 4 This is a comparison chart of the hydration heat release-time curves of low-aluminum clinker and ordinary clinker in the fourth stage of the present invention. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Example 1: Preparation of raw materials and raw meal The chemical composition of the raw materials used in this invention is shown in Table 1.

[0027] Table 1 Chemical composition of raw materials (mass percentage, %)

[0028] Four raw material formulations with different aluminum ratio targets were designed. The design ratio values ​​and corresponding clinker mineral composition targets are shown in Table 2. Based on the designs in Table 2, the specific raw material proportions were calculated and are shown in Table 3.

[0029] Table 2 Design ratio values ​​and mineral composition of raw and cooked materials

[0030] Table 3 Specific raw material ratios (mass percentage, %)

[0031] Example 2: Clinker Calcination and Industrial Production Experiment On a 5,000-ton-per-day cement clinker production line (Kiln #7), following the proportioning scheme in Table 3, a continuous industrial trial was conducted for 7 days (October 27 to November 2, 2025), gradually transitioning from clinker of stage 1 (first stage, high-alumina ordinary clinker) to clinker of stage 4 (fourth stage, ultra-low-alumina clinker of this invention). During production, the operation of the calcination system was strictly controlled to ensure that the maximum calcination temperature of the fourth stage material was controlled within the range of 1250±20℃.

[0032] Samples were taken daily during production to test the clinker's chemical composition, yield value, mineral composition, physical properties, and heat of hydration. The test results are shown in Table 4. The testing method was as follows: (1) f-CaO determination. f-CaO was detected in clinker at different calcination temperatures using the ethanol-ethylene glycol method with phenolphthalein as an indicator. Benzoic acid was used to titrate until the red color in the solution disappeared, and the amount of benzoic acid solution consumed was recorded. The f-CaO content in cement clinker was calculated from this.

[0033] (2) Phase composition. Phase analysis was performed using an X-ray diffractometer from Panaco GmbH, Germany. The X-ray tube power was 3kW, the detector was a NaI scintillation counter, the operating voltage and current were 40kV and 40mA, respectively, the scanning angle (2θ) was 5° to 70°, and the step scan size and time were 0.02° and 0.5s, respectively. Qualitative analysis was performed using Jade9 software, and quantitative analysis was performed using Topas-V6 software to fit the XRD results to the full spectrum (Rietveld) to obtain the content of each phase in each sample.

[0034] (3) Mechanical property testing. Cement paste specimens were formed with a water-cement ratio (w / c) of 0.5. The mixed cement paste was poured into a 40mm×40mm×160mm mold, and the mold was placed in a standard curing room for curing. After 24 hours, the specimens were demolded, and then the specimens were cured for 3d, 7d, 14d, 28d, 45d, and 60d. The compressive strength was tested according to the cement process performance test method.

[0035] (4) Heat of hydration test. According to GB / T12959-2024 "Determination of heat of hydration of cement".

[0036] Table 4

[0037] Core production data trend analysis: Aluminum content (IM) and mineral composition: From October 27th to November 2nd, the clinker IM was successfully reduced from 1.52-1.57 (Phase 1) to 0.65-0.77 (Phase 4). Correspondingly, the C3A content decreased significantly from 8.10-8.60% to 0.24-1.98% (mostly below 1%), while the C4AF content increased significantly from 10.67-11.00% to 17.95-19.54%.

[0038] Burnability and Process Parameters: The system process parameters were significantly optimized during the transition to low-alumina clinker. Compared to producing ordinary clinker (stage one), producing the clinker of this invention (stage four) resulted in a preheater outlet temperature decrease of approximately 11°C, a system negative pressure decrease of approximately 0.21 kPa, a decomposition furnace outlet temperature decrease of approximately 32°C, a chute temperature decrease of 23°C compared to ordinary clinker production, a significant decrease in kiln tail flue gas temperature of approximately 120°C, and a secondary air temperature decrease of 40°C compared to ordinary clinker production. This indicates improved burnability of the raw material and a significant reduction in system thermal load.

[0039] Clinker quality and mechanical properties: f-CaO: Throughout the transition period, the f-CaO content remained within a reasonable range of 0.67-2.03%, indicating that the firing was sufficient and the clinker quality was stable.

[0040] During the production of low-alumina clinker, the clinker KH was between 0.910 and 0.925, the MgO and R2O indices remained basically stable, and the clinker particle size distribution did not change significantly.

[0041] Compressive strength: Despite drastic changes in aluminum ratio and C3A, the compressive strength of clinker remained stable at all ages. The 3-day compressive strength of the clinker of this invention (fourth stage data) was 30.5-31.1 MPa, the 28-day compressive strength was 58.8-60.1 MPa, the 45-day compressive strength was 60.0-60.5 MPa, and the 60-day compressive strength was 61.5-64.2 MPa. These values ​​are not significantly different from the strength levels of ordinary clinker in the first stage (3d: 31.9 MPa, 28d: 60.2 MPa, 45d: 61.0 MPa, 60d: 62.1 MPa) at 3d, 28d, and 45d. The strength improvement rate after 60d is significantly higher than that of ordinary clinker in the first stage, fully meeting the national standard requirements.

[0042] Setting time and standard consistency: The setting time is normal, with initial setting in 93-130 minutes and final setting in 142-183 minutes; the standard consistency water requirement is between 24.2-25.2%, with very little fluctuation.

[0043] Heat of hydration: The clinker of this invention (fourth stage sample) and ordinary clinker (first stage sample) were respectively prepared into PI type cement and subjected to heat of hydration testing. The results are as follows: Figure 3-4 As shown, the 7-day heat of hydration of the cement of this invention is 228.29 KJ / kg, which is about 16.36 KJ / kg lower than that of ordinary cement (244.65 KJ / kg), a significant reduction.

[0044] Example 3: Microstructure analysis of clinker (lithology and XRD) X-ray diffraction (XRD) and petrographic analysis were performed on the clinker samples produced in the fourth stage of this invention. The XRD analysis data are shown in Table 5.

[0045] Table 5

[0046] XRD quantitative analysis confirmed that the main mineral contents of the clinker were: C3S 64.11%, C2S 13.51%, and C3A 0.75%, which is consistent with the values ​​calculated by chemical methods.

[0047] The total C3S content in this clinker is 64.11% (the sum of M3 and M1), which is normal. C3S is the main contributor to strength and has a relatively high promoting effect on clinker strength.

[0048] The overall C2S content in this clinker was 13.51%, which is normal. C2S can be classified into α', α, β, and γ types, among which γ-type C2S has an adverse effect on clinker strength. No γ-type C2S was found in this sample.

[0049] The overall C3A content in this clinker is 0.75%, which is normal. C3A exists in two crystal forms: cubic (tricalcium aluminate-cubic) and orthorho (tricalcium aluminate-orthorho). C3A-orthorho forms when the alkali content or aluminum phase content is relatively high. In this sample, the C3A-orthorho content is 0.60%, which is relatively low and will significantly reduce the standard consistency of the clinker.

[0050] Lithofacies analysis: The fourth-stage low-alumina clinker sample prepared according to the embodiments of the present invention was cut, inlaid, coarsely ground, finely ground, and polished to prepare a standard polished sheet. The surface of the polished sheet was etched with a 1% (volume fraction) nitric acid ethanol solution for approximately 2-5 seconds. Immediately after etching, it was rinsed with anhydrous ethanol and dried. The treated sample was placed under a reflective polarizing microscope at 200x magnification, and a representative field of view was selected for observation and photography to obtain the following results: Figure 1 and Figure 2 The shown petrographic photograph. From Figure 1-2The petrographic photographs of the ultra-low alumina clinker of this invention show that its dominant mineral, A-ore (tricalcium silicate, C3S), exhibits the following key microstructural characteristics: moderate and uniform grain size, minimal inclusions of impurities or intermediate phases in the cross-section, and clear, regular grain boundaries. This microstructure fully demonstrates that by employing the specific ratio synergistic scheme of this invention (KH: 0.910-0.930, SM: 1.90-2.10, IM: 0.50-1.00) and a suitable firing process, uniform and full development and crystallization of clinker minerals (especially C3S) can still be achieved under conditions of extremely low alumina. The uniformity of the grains reflects the stability and rationality of the firing regime; the "few inclusions" directly confirm that the batching reaction is complete, and harmful components such as free calcium oxide (f-CaO) are effectively absorbed; the clear and regular grain boundaries indicate that the clinker microstructure is dense and complete. These features together constitute the microstructure basis for the clinker of this invention to possess excellent mechanical strength and high corrosion resistance potential, intuitively refuting the traditional technical prejudice that "ultra-low aluminum ratio inevitably leads to poor firing and loose structure".

[0051] Comparative Example The comparative example is the ordinary silicate cement clinker produced in the first stage of Example 2, which has an aluminum ratio IM of approximately 1.55, a C3A content of approximately 8.35%, and a C4AF content of approximately 10.8%.

[0052] The performance of the clinker obtained in the fourth stage of Example 2 of the present invention was compared with that of the comparative clinker, and the results are summarized as follows: Corrosion resistance basis: The C3A content of the clinker of this invention (≤2%) is much lower than that of the comparative example (8.35%) and the national standard for high sulfate resistance cement (≤3%), thus possessing inherently superior resistance to sulfate attack.

[0053] Strength performance: The compressive strength of both after 3 days and 28 days is comparable, indicating that the present invention does not sacrifice mechanical properties while greatly improving corrosion resistance potential.

[0054] Heat of hydration: The clinker of this invention has a lower heat of hydration, making it suitable for large-volume concrete projects.

[0055] Energy consumption during production: When producing the clinker of this invention, the key temperatures of the kiln system are generally reduced, indicating lower coal consumption for firing.

[0056] In summary, this invention, through a specific design of ultra-low alumina ratio and high-iron phase mineral composition, coupled with a precisely matched sintering process, successfully produces an innovative cement clinker with excellent sulfate resistance, superior comprehensive mechanical properties, and lower production energy consumption. This method breaks through the technical framework of traditional sulfate-resistant cement and has significant industrial application value and environmental and economic implications.

[0057] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

[0058] It should be particularly noted that the various embodiments listed in this specification and accompanying drawings are intended to illustrate the technical solutions and advantages of the present invention, and not to limit the scope of protection of the present invention. Without departing from the core ideas and technical effects of the present invention, those skilled in the art can make any form of improvement, substitution, combination, or modification to the structural arrangement, process parameters, material selection, control logic, etc., of the described embodiments; any obvious changes based on the same concept should be considered equivalent solutions of the present invention and should be included within the scope of protection defined by the claims of the present invention. The actual scope of protection of the present invention is determined by the appended claims and should be correctly understood in conjunction with the specification and accompanying drawings.

Claims

1. A corrosion-resistant cement clinker with ultra-low alumina ratio, characterized in that, The mineral composition of the cement clinker, by mass percentage, includes: C3S 55-65%, C2S 15-25%, C3A ≤ 2%, C4AF 17-21%; the alumina ratio IM of the clinker is 0.50-1.00, the lime saturation coefficient KH is 0.910-0.930, and the silica ratio SM is 1.90-2.

10.

2. The cement clinker according to claim 1, characterized in that, The aluminum content (IM) of the clinker is 0.65-0.

85.

3. The cement clinker according to claim 2, characterized in that, The aluminum content (IM) of the clinker is 0.65-0.

77.

4. The cement clinker according to any one of claims 1-3, characterized in that, The C3A content of the clinker is ≤1.5%.

5. The cement clinker according to any one of claims 1-3, characterized in that, The clinker has a C4AF content of 18-20%.

6. A method for preparing ultra-low alumina ratio erosion-resistant cement clinker as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material preparation: Weigh limestone, sandstone, copper ore powder and fly ash according to the proportion, mix and grind to the specified fineness to obtain raw meal; S2. Sintering: The raw materials prepared in step S1 are sintered at a maximum temperature of 1230-1270℃, and the cement clinker is obtained after cooling.

7. The method according to claim 6, characterized in that, In step S1, by controlling the raw material ratio, the raw material ratio is made to meet the following requirements: lime saturation coefficient KH = 0.92-1.02, silicon ratio SM = 2.00-2.10, and aluminum ratio IM = 0.65-0.

80.

8. The method according to claim 6, characterized in that, In step S1, the raw materials, by mass percentage, include: limestone 82.5-85.0%, sandstone 8.5-11.0%, copper ore powder 2.0-7.5%, and fly ash 0-3.0%.

9. A type of cement, characterized in that, The cement comprises cement clinker as described in any one of claims 1-5.

10. The use of the cement clinker as described in any one of claims 1-5 in the preparation of sulfate-resistant cement.

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