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LOW-CARBON CEMENT CLINKER AND METHOD FOR PREPARING THE SAME

20240190764 ยท 2024-06-13

    Inventors

    Cpc classification

    International classification

    Abstract

    A low-carbon cement clinker, having the following parameter ranges: alkalinity coefficient C: 1.0?C?1.5; aluminum-sulfur ratio P: P<1.92; aluminum-silicon ratio N: N<1; and limestone saturation coefficient Cs: 0.9?Cs<1.0. The specific range of each parameter value ensures an idea ratio of mineral composition in the low-carbon cement clinker. The ratio promotes a coordinated interaction among different minerals and compounds present when exposed to water, leading to improved strength development and overall performance of the final cement product.

    Claims

    1. A low-carbon cement clinker, having the following parameter ranges: alkalinity coefficient C: 1.0?C?1.5; aluminum-sulfur ratio P: P<1.92; aluminum-silicon ratio N: N<1; and limestone saturation coefficient Cs: 0.9?Cs<1.0.

    2. The low-carbon cement clinker of claim 1, wherein the low-carbon cement clinker comprises raw materials as follows: limestone or low-grade limestone; bauxite, low-grade bauxite, fly ash, alumina ash, red mud, or coal gangue; phosphogypsum, desulfurization gypsum, or anhydrite; sandstone or silica; and slag, steel slag, carbide slag, or lithium slag.

    3. A method for preparing the low-carbon cement clinker of claim 1, the method comprising: (1) measuring chemical compositions of the raw materials to identify the levels of oxides in each type of the raw materials; (2) designing the composition of the oxides in the low-carbon cement clinker using the specific ranges of alkalinity coefficient C, alumina-sulfur ratio P, alumina-silica ratio N, and limestone saturation coefficient Cs; or, using the specific ranges of alkalinity coefficient C, alumina-sulfur ratio P, alumina-silica ratio N, and limestone saturation coefficient Cs, to determine the specific values of the parameters, and deriving the composition of the oxides in the low-carbon cement clinker; (3) calculating the ratios of the raw materials in the low-carbon cement clinker according to the levels of the oxides in each type of the raw materials and the composition of the oxides in the low-carbon cement clinker; (4) weighing the raw materials according to the calculated ratios determined in 3); grinding and mixing the raw materials to obtain a raw mixture; (5) calcinating the raw mixture at 1100-1350? C. for 30-120 minutes; and (6) cooling the calcined raw mixture through a grate cooler or laboratory-based air cooling methods; adding a certain amount of gypsum to the cooled raw mixture; grinding the resulting mixture to achieve a fineness with a specific surface area of 300-350 m.sup.2/kg or a residue of below 20% on a 45 ?m sieve, thereby producing the low-carbon cement clinker.

    4. The method of claim 3, wherein in 2), the specific values of the parameters are calculated using the following formulas: C = C a O 0 . 7 3 ? ( A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 ) + 1 . 4 ? F e 2 O 3 + 1 . 8 7 ? S i O 2 , P = A l 2 O 3 - 0.64 ? F e 2 O 3 S O 3 , N = A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 S i O 2 , and Cs = C a O 0 . 7 3 ? ( A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 ) + 1.4 ? F e 2 O 3 + 1 . 8 7 ? S i O 2 + 0 .7 ? S O 3 ; where, five oxides CaO, Al.sub.2O.sub.3, SO.sub.3, SiO.sub.2, and Fe.sub.2O.sub.3 are expressed as percentages by mass; the limestone saturation coefficient Cs considers the content of SO.sub.3 to regulate the proportion of lime and silicate, and is adjusted based on the alkalinity coefficient C.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0034] FIG. 1 shows an X-ray diffraction (XRD) pattern of a low-carbon cement clinker according to Examples 1-3 of the disclosure; and

    [0035] FIG. 2 illustrates the strength of mortars made from a low-carbon cement clinker according to Examples 1-3 of the disclosure, along with the comparison to the performance of ordinary Portland cement at intervals of 1 day, 3 days, 7 days, and 28 days.

    DETAILED DESCRIPTION

    [0036] To further illustrate the disclosure, embodiments detailing a low-carbon cement clinker and a method for preparing the same are described below. It should be noted that the following embodiments are intended to describe and not to limit the disclosure.

    [0037] The composition of the low-carbon cement clinker is defined by the specific ranges of values for the following parameters: [0038] alkalinity coefficient C: 1.0?C?1.5; [0039] aluminum-sulfur ratio P: P<1.92; [0040] aluminum-silicon ratio N: N<1; and [0041] limestone saturation coefficient Cs: 0.9?Cs<1.0;

    [0042] The low-carbon cement clinker comprises five types of raw materials, comprising: [0043] limestone or low-grade limestone (limestone with a CaO content of less than 45%); [0044] bauxite, low-grade bauxite (bauxite with an Al.sub.2O.sub.3 content of less than 50%), fly ash, alumina ash, red mud or coal gangue; [0045] phosphogypsum, desulfurization gypsum or anhydrite; [0046] sandstone or silica; and [0047] slag, steel slag, carbide slag, or lithium slag.

    [0048] A method for preparing the low-carbon cement clinker, comprising: [0049] (1) measuring chemical compositions of the raw materials to identify the levels of oxides in each type of the raw materials; [0050] (2) designing the composition of the oxides in the low-carbon cement clinker using the specific ranges of alkalinity coefficient C, alumina-sulfur ratio P, alumina-silica ratio N, and limestone saturation coefficient Cs; or, using the specific ranges of alkalinity coefficient C, alumina-sulfur ratio P, alumina-silica ratio N, and limestone saturation coefficient Cs, to determine the specific values of the parameters, and deriving the composition of the oxides in the low-carbon cement clinker; [0051] (3) calculating the ratios of the raw materials in the low-carbon cement clinker according to the levels of the oxides in each type of the raw materials and the composition of the oxides in the low-carbon cement clinker; [0052] (4) weighing the raw materials according to the calculated ratios determined in 3); grinding and mixing the raw materials to obtain a raw mixture; [0053] (5) calcinating the raw mixture at 1100-1350? C. for 30-120 minutes; and [0054] (6) cooling the calcined raw mixture through a grate cooler or laboratory-based air cooling methods; adding a certain amount of gypsum to the cooled raw mixture; grinding the resulting mixture to achieve a fineness with a specific surface area of 300-350 m.sup.2/kg or a residue of below 20% (preferably below 15%) on a 45 ?m sieve, thereby producing the low-carbon cement clinker.

    [0055] In a class of this embodiment, in 2), the specific values of the parameters are calculated using the following formulas:

    [00002] C = C a O 0 . 7 3 ? ( A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 ) + 1 . 4 ? F e 2 O 3 + 1 . 8 7 ? S i O 2 , P = A l 2 O 3 - 0.64 ? F e 2 O 3 S O 3 , N = A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 S i O 2 , and Cs = C a O 0 . 7 3 ? ( A l 2 O 3 - 0 . 6 4 ? F e 2 O 3 ) + 1.4 ? F e 2 O 3 + 1 . 8 7 ? S i O 2 + 0 .7 ? S O 3 ;

    [0056] where, five oxides CaO, Al.sub.2O.sub.3, SO.sub.3, SiO.sub.2, and Fe.sub.2O.sub.3 are expressed as percentages by mass; the limestone saturation coefficient Cs considers the content of SO.sub.3 to regulate the proportion of lime and silicate, and is adjusted based on the alkalinity coefficient C.

    [0057] The requirement to define specific ranges of the parameter values for the oxide composition of the low-carbon cement clinker arises from the following considerations: the strength properties of the cement clinker depend on the interactive and cooperation of diverse minerals throughout the hydration procedure. The specific ranges ensure that the mineral composition of the low-carbon cement clinker is in an optimally balanced and well-matched state. While enhancing the reactivity of low-activity minerals such as calcium sulfoaluminate and belite in the low-carbon cement clinker, the specific ranges also ensure the optimal balance in the content ratios of crucial minerals, such as calcium sulfoaluminate, to minerals like free gypsum or belite in the low-carbon cement clinker. Moreover, the specific ranges achieve the optimal spatial and temporal coordination and collaboration between crystalline hydration products such as ettringite and gel-like hydration products like calcium silicate hydrate (CSH), ensuring excellent performance throughout the early, mid, and late-stage of the low-carbon cement clinker.

    [0058] Compared to current methods that involves a secondary calcination step for the conventional cement clinkers containing minerals like calcium sulfoaluminate, the low-carbon cement clinker requires just a single calcination step. This simplifies the process, reduces energy use, decreases emissions, lowers costs, and improves production efficiency.

    [0059] The disclosed method modifies the specific ranges of the parameter values for the cement clinker to control the mineral composition ratios in the low-carbon cement clinker. The early strength of the cement depends on rapid hydration of clinker mineral C.sub.4A.sub.3$, the mid-stage strength is aided by the hydration of C.sub.5S.sub.2$, and the later-stage strength primarily arises from the hydration of C.sub.2S. The hydration processes of various minerals in the cement clinker are interrelated rather than independent. Hence, a well-founded choice and regulation of mineral components in the cement clinker contribute to creating a low-carbon cement clinker with outstanding performance and application results.

    [0060] To clarify the disclosure and enhance understanding of the technical solutions and benefits, the following will offer a detailed description of the disclosure using examples and accompanying illustrations.

    [0061] Tables 1 show the oxide compositions of the raw materials used in the examples.

    TABLE-US-00001 TABLE 1 Oxide compositions of raw materials (wt. %) Raw material Weight Percentage (wt. %) types LOI SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 Limestone 42.64 0.61 0.05 0.19 55.9 0.01 0.42 Bauxite 16.00 21.72 52.40 7.63 / Fly ash 2.32 52.47 34.02 2.92 4.80 0.69 0.27 Phosphogypsum 6.12 1.03 0.60 0.25 38.61 2.57 49.89

    Example 1

    [0062] Tables 2 and 3 show rate values and corresponding oxide compositions for a low-carbon cement clinker prepared in the example.

    TABLE-US-00002 TABLE 2 Rate values for a low-carbon cement clinker prepared in Example 1 Rate value Cs C P N Numerical value 0.95 1.09 1.49 0.84

    TABLE-US-00003 TABLE 3 Oxide compositions of a low-carbon cement clinker prepared in Example 1 Oxide CaO Al.sub.2O.sub.3 SO.sub.3 SiO.sub.2 Fe.sub.2O.sub.3 Weight percentage wt. % 52.56 16.73 10.11 17.97 2.63

    [0063] The raw materials, comprising fly ash, phosphogypsum, limestone, and bauxite were finely ground. Following the specific rate values, the oxide compositions were established, and the raw materials are proportioned based on the oxide components. The raw materials were weighted, ground and mixed in a mill to form a raw mixture. The raw mixture was blend with a certain amount of water or alcohol, pressed into a circular thin cake with a diameter of 3 cm, and subsequently dried in a drying oven. Next, the circular thin cake was heated in a high-temperature electric furnace using a silicon molybdenum rod. The temperature was gradually increased at a rate of 5? C./min until it reached 1200? C., at which point it was held steady for 30 minutes. After heating, the circular thin cake was removed and swiftly cooled using airflow, resulting in the formation of a clinker block. The clinker block was then crushed and finely ground. Measurement revealed that the finely ground clinker left a residue of 8.9% on a 45 ?m sieve.

    Example 2

    [0064] Tables 4 and 5 show rate values and corresponding oxide compositions for a low-carbon cement clinker prepared in the example.

    TABLE-US-00004 TABLE 4 Rate values for a low-carbon cement clinker prepared in Example 2 Rate value Cs C P N Numerical value 0.947 1.16 1.08 0.95

    TABLE-US-00005 TABLE 5 Oxide compositions of a low-carbon cement clinker prepared in Example 2 Oxide CaO Al.sub.2O.sub.3 SO.sub.3 SiO.sub.2 Fe.sub.2O.sub.3 Weight percentage wt. % 51.0 16.68 13.93 15.75 2.64

    [0065] The raw materials, comprising fly ash, phosphogypsum, limestone, and bauxite were finely ground. Following the specific rate values, the oxide compositions were established, and the raw materials are proportioned based on the oxide components. The raw materials were weighted, ground and mixed in a mill to form a raw mixture. The raw mixture was blend with a certain amount of water or alcohol, pressed into a circular thin cake with a diameter of 10 cm, and subsequently dried in a drying oven. Next, the circular thin cake was heated in a high-temperature electric furnace using a silicon molybdenum rod. The temperature was gradually increased at a rate of 5? C./min until it reached 1250? ? C., at which point it was held steady for 60 minutes. After heating, the circular thin cake was removed and swiftly cooled using airflow, resulting in the formation of a clinker block. The clinker block was then crushed and finely ground. Measurement revealed that the finely ground clinker left a residue of 9.1% on a 45 ?m sieve.

    Example 3

    [0066] Tables 6 and 7 show rate values and corresponding oxide composition for a low-carbon cement clinker prepared in the example.

    TABLE-US-00006 TABLE 6 Rate values for a low-carbon cement clinker prepared in Example 3 Rate value Cs C P N Numerical value 0.949 1.08 1.53 0.78

    TABLE-US-00007 TABLE 7 Oxide composition of a low-carbon cement clinker prepared in Example 3 Oxide CaO Al.sub.2O.sub.3 SO.sub.3 SiO.sub.2 Fe.sub.2O.sub.3 Weight percentage wt. % 53.25 16.05 9.8 19.25 1.65

    [0067] The raw materials, comprising fly ash, phosphogypsum, limestone, and bauxite were finely ground. Following the specific rate values, the oxide compositions were established, and the raw materials are proportioned based on the oxide components. The raw materials were weighted, ground and mixed in a mill to form a raw mixture. The raw mixture was blend with a certain amount of water or alcohol, pressed into a circular thin cake with a diameter of 10 cm, and subsequently dried in a drying oven. Next, the circular thin cake was heated in a high-temperature electric furnace using a silicon molybdenum rod. The temperature was gradually increased at a rate of 5? C./min until it reached 1300? ? C., at which point it was held steady for 50 minutes. After heating, the circular thin cake was removed and swiftly cooled using airflow, resulting in the formation of a clinker block. The clinker block was then crushed and finely ground. Measurement revealed that the finely ground clinker left a residue of 8.7% on a 45 ?m sieve.

    X-Ray Diffraction (XRD) Analysis

    [0068] XRD analyses were performed on the low-carbon cement clinkers prepared in Examples 1 to 3. The scanning rate was set at 4?/min, using a step size of 0.01?. The results of the XRD analyses are shown in FIG. 1. FIG. 1 reveals the absence of significant diffraction peaks associated with free lime (f-CaO), indicating the complete formation of the low-carbon cement clinker at the specific temperature. In Example 1, the low-carbon cement clinker was calcined at 1200? C., while in Example 2, the low-carbon cement clinker was calcined at 1250? C. A strong diffraction peak of C.sub.5S.sub.2$ in the low-carbon cement clinker from Examples 1 and 2 confirms successful formation of C.sub.5S.sub.2$ under these experimental conditions, with a well-developed crystalline structure. Furthermore, the low-carbon cement clinker from Example 3, calcined at 1300? C., exhibits the presence of high-activity ?-C.sub.2S. The results indicate that under the specified rate values, the mineral compositions of the cement clinker achieve an optimal equilibrium. This condition allows for the cocurrent presence of the low-activity minerals like C.sub.5S.sub.2$ and coexisting-challenging minerals like C.sub.4A.sub.3$ in the low-carbon cement clinker, while maintaining heightened crystalline activity in both the low-activity minerals C.sub.5S.sub.2$ and C.sub.2S. Moreover, the rate values ensure a specific quantity of f-CaSO.sub.4 within the low-carbon cement clinker. The presence of f-CaSO.sub.4 facilitates the formation of ettringite through hydration reactions involving C.sub.4A.sub.3$, consequently enhancing the development of cement strength. Furthermore, a slightly elevated content of f-CaSO.sub.4 within the low-carbon cement clinker ensures the formation and endurance of C.sub.5S.sub.2$ in specific temperature conditions, simultaneously promoting the transformation of the low-activity mineral C.sub.2S within the low-carbon cement clinker into ?-C.sub.2S.

    Compressive Strength Testing of Cement Mortar

    [0069] In each example, the low-carbon cement clinker was supplemented with an appropriate quantity of gypsum, maintaining a water-to-binder ratio of 0.5 and a sand-to-binder ratio of 3. The resulting mixture was used for conducting a test on mortar strength. A reference cement was used for comparative purposes, undergoing the same mortar strength test while adhering to identical water-to-binder ratio and sand-to-binder ratio. The compressive strengths of both the reference cement and the cement mortars made from the low-carbon cement clinker in Examples 1-3 were evaluated at different curing periods, especially at 1 day, 3 days, 7 days, 28 days, and 90 days, as depicted in FIG. 2. FIG. 2 indicates that the cement mortar made from the low-carbon cement clinker exhibits higher strengths at 1 day and 3 days, in contrast to the reference cement. The cement mortar made from the low-carbon cement clinker achieves a strength level equivalent to the 7-day strength of the reference cement in just 3 days. The 28-day strength of the cement mortar, prepared from the low-carbon cement clinker, is comparable to that of the reference cement. Furthermore, as time progresses, the 90-day strength of the cement mortar prepared from the low-carbon cement clinker gradually exceeds that of the reference cement. The strength performance of the cement clinker is determined by the optimized combination of various minerals within the cement clinker. When exposed to the specific rate values, the cement clinker ensures the optimal mineral proportions, fostering a synergistic hydration effect among the minerals and bolstering the strength stability. Additionally, the low-carbon cement clinker exhibits comparable or even superior performance compared to the ordinary Portland cement clinker. The results suggest that the potential of the low-carbon cement clinker to replace the ordinary Portland cement clinker, ultimately contributing to a decrease in carbon emissions.

    [0070] It will be obvious to those skilled in the art that changes and modifications may be made, and therefore, the aim in the appended claims is to cover all such changes and modifications.