Cement and method of manufacture

Abstract

The application relates to the field of building materials, in particular to cement and a preparation method. The cement provided by the application comprises a cementing component and an auxiliary activator; the cementing component comprises 10-60 parts of red mud and 20-70 parts of slag in terms of weight percentage; the auxiliary activator accounts for 0.1-8% of the mass of the cementing component. The cement prepared by the joint use of the red mud and the slag in the specific proportion and the use of the auxiliary activator with the specific mass percentage has obviously improved the bending strength and the compressive strength.

Description

Technical Field

[0001] This invention relates to the field of building materials, specifically to a type of cement and its preparation method. Background Technology

[0002] Red mud is a solid waste discharged from the alumina industry. Depending on the alumina production process, it is classified into sintering red mud, Bayer process red mud, and combined process red mud. Its color is brown or red due to its high Fe2O3 content. Because of its high Na2O content, its pH value can generally reach 10-13, thus classifying it as a strongly alkaline industrial waste and listing it as a major industrial waste in 2010. Depending on the type of bauxite and the production process, approximately 0.8-2.5 tons of red mud are discharged for every ton of alumina produced. After natural dehydration and weathering in the stockpile, red mud enters the atmosphere with air currents, causing dust pollution. The alkaline substances and heavy metals in red mud seep into the soil with precipitation, causing soil salinization and polluting groundwater and surrounding farmland. Due to its low volcanic ash activity at room temperature, red mud is commonly used as a supplementary cementitious material (SCM) in concrete, in the preparation of ceramics and microcrystalline glass, in the recovery of valuable metals, and in the preparation of adsorbents and novel functional materials. Due to market demand, red mud is widely used in civil engineering and building materials, but its dosage as an admixture in actual projects is relatively low, generally not exceeding 10%.

[0003] With increasing concern about global warming and greenhouse gas emission reduction, the research and development of low-carbon technologies has become an urgent need for the cement industry. Over the past 20 years, researchers have proposed various novel low-carbon cementitious materials. Among them, alkali-activated cementitious materials are derived from industrial solid waste containing aluminosilicate glass. These materials not only offer similar performance to silicate cement-based cementitious materials but also reduce the industry's clinker consumption, dispose of solid waste, and alleviate environmental pressure, thus achieving green and low-carbon development. Therefore, the research and development of alkali-activated cementitious materials has become a hot topic in the field of cement concrete science and technology. Furthermore, red mud contains high levels of SiO2 and Al2O3 and is a typical aluminosilicate solid waste. Therefore, the development of alkali-activated cementitious materials offers hope for the large-scale application of red mud in alkali-activated cement.

[0004] The feasibility of preparing alkali-activated slag cement using red mud as a raw material has been confirmed. However, most studies require high-temperature treatment of the red mud to loosen its silicon-oxygen tetrahedral and aluminum-oxygen tetrahedral structures, forming a metastable aluminosilicate structure, thereby improving the red mud's activity. Currently, the performance of red mud-based silica-alumina low-carbon cement is still relatively poor, with low hardness. Therefore, it is necessary to provide a cement with high flexural strength and compressive strength. Summary of the Invention

[0005] This invention addresses the problem of low flexural and compressive strength in cement prepared using existing technologies by proposing a new type of cement and its preparation method. Cement prepared using the method of this invention exhibits significantly improved flexural and compressive strength.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a cement comprising a cementitious component and an auxiliary activator; the cementitious component comprises 10-60 parts of red mud and 20-70 parts of slag by weight; the auxiliary activator accounts for 0.1-8% of the mass of the cementitious component.

[0007] The auxiliary activator is selected from one or more of calcium formate, calcium lignosulfonate, sodium sulfate, calcium chloride, sodium carbonate, sodium hydroxide, and sodium silicate; preferably, the auxiliary activator comprises calcium formate, sodium hydroxide, and sodium silicate in a mass ratio of 0.4-0.6:0.5-6:4-6.

[0008] The cementitious component further includes at least one of 0-30 parts by weight of steel slag, 0-20 parts by weight of cement clinker, and 0-5 parts by weight of gypsum; preferably, the cementitious component further includes 0-20 parts by weight of lithium slag.

[0009] The cementitious component comprises, by weight, 10-30 parts red mud, 5-15 parts steel slag, 10-20 parts lithium slag, 30-70 parts blast furnace slag, 5-10 parts cement clinker, and 1-5 parts gypsum; preferably, the cementitious component comprises 10-15 parts red mud, 5-15 parts steel slag, 10-15 parts lithium slag, 50-70 parts blast furnace slag, 5-10 parts cement clinker, and 1-5 parts gypsum.

[0010] The cementitious components, by weight, include 10-15 parts red mud, 5-15 parts steel slag, 10-15 parts lithium slag, 50-70 parts blast furnace slag, 5-10 parts cement clinker, 1-5 parts gypsum, and 1-10 parts fly ash.

[0011] The red mud is sintered red mud; preferably, the red mud has an Al2O3 mass content ≥6.0%, a SiO2 mass content ≥10.0%, and a 28-day compressive strength activity index >60%; more preferably, the chemical composition of the red mud, by mass percentage, includes: Al2O3: 8.0-25%, SiO2: 15.0-30%, Fe2O3: 5-15%, CaO: 5-50%, MgO: 0.1-2%, K2O: 0.001-1%, Na2O: 2-8%, SO3 ≤5%.

[0012] The steel slag contains 30-60% CaO, 10-30% SiO2, 2-20% MgO, and 10-40% Fe2O3 by mass. Preferably, the chemical composition of the steel slag, by mass percentage, includes: CaO: 38-50%, Fe2O3: 25-35%, SiO2: 14-20%, MgO: 4.5-12%, MnO: ≤5%, Al2O3: 1-10%, CaF2 ≤2%, and SO3 ≤5%.

[0013] The lithium slag is the residue obtained by leaching and washing after calcining spodumene and extracting lithium carbonate clinker using the sulfuric acid method.

[0014] The lithium slag contains 30-50% CaO, 10-30% Fe2O3, 10-25% SiO2, 2-10% MgO, 1-8% Al2O3, ≤6% MnO, and ≤5% SO3 by mass.

[0015] The slag is water-quenched slag or air-cooled granulated blast furnace slag.

[0016] The cement clinker is silicate cement clinker, which meets the requirements of GB / T21372 "Silicate Cement Clinker".

[0017] The fly ash is either Class C or Class F fly ash, conforming to the requirements of GB / T1596 "Fly Ash for Cement and Concrete".

[0018] The gypsum is selected from one or more of desulfurized gypsum, mirabilite gypsum, phosphogypsum, and titanium gypsum.

[0019] The present invention also provides a method for preparing cement, wherein the components are weighed according to the weight parts, mixed and ground, or the components other than the auxiliary activator are weighed according to the weight parts, mixed and ground, and the auxiliary activator is added before use.

[0020] The solid content of the auxiliary activator is 95-100%;

[0021] Furthermore, the cementitious components and auxiliary activators are dried before weighing to ensure that the total moisture content of the cementitious components and auxiliary activators is less than 1%. Cement clinker and fly ash are dry materials, and commercially available products have a moisture content of less than 1%, so drying is not required. The auxiliary activator is in solid form, mainly containing water of crystallization and chemically bound water, and the dosage is also very low, so drying is not required.

[0022] The water content refers to the sum of physically adsorbed water and free water, excluding chemically bound water and water of crystallization.

[0023] Furthermore, the ground powder needs to be sieved through a 60-100μm square-hole sieve, and the residue of the powder on the sieve is 0-10%.

[0024] The present invention also provides a method for preparing cement.

[0025] The technical solution of the present invention has the following beneficial effects:

[0026] (1) The present invention provides a cement comprising a cementitious component and an auxiliary activator; the cementitious component comprises 10-60 parts of red mud and 20-70 parts of slag by weight; the auxiliary activator accounts for 0.1-8% of the mass of the cementitious component. By using the above-mentioned specific ratio of red mud and slag in combination, and with the use of a specific mass percentage of auxiliary activator, the flexural strength and compressive strength of the prepared cement are significantly improved.

[0027] (2) The cement provided by this invention, while maintaining the same total mass of cementitious components, adds steel slag, lithium slag, cement clinker, and gypsum to the cementitious components based on red mud and slag. The flexural and compressive strength of the prepared cement is significantly improved. Its cementitious components include 10-30 parts by weight of red mud, 5-15 parts by weight of steel slag, 10-20 parts by weight of lithium slag, 30-70 parts by weight of slag, 5-10 parts by weight of cement clinker, and 1-5 parts by weight of gypsum. Further adjustments to the component weights... Through optimization, the performance of cement has been further improved, with flexural strengths of 7.1-8.2 MPa and 8.5-9.6 MPa at 3 days and 28 days, respectively, and compressive strengths of 36.1-38.8 MPa and 55.1-61.6 MPa at 3 days and 28 days, respectively. Its cementitious components include 10-15 parts by weight of red mud, 5-15 parts by weight of steel slag, 10-15 parts by weight of lithium slag, 50-70 parts by weight of slag, 5-10 parts by weight of cement clinker, and 1-5 parts by weight of gypsum.

[0028] (3) The cement provided by the present invention uses an auxiliary activator selected from one or more of calcium formate, calcium lignosulfonate, sodium sulfate, calcium chloride, sodium carbonate, sodium hydroxide and sodium silicate, preferably calcium formate, sodium hydroxide and sodium silicate in a mass ratio of 0.4-0.6:0.5-6:4-6. This auxiliary activator combination can better promote the reaction between cementitious components, thereby further improving the flexural strength and compressive strength of the cement.

[0029] (4) The cement provided by the present invention, by controlling the chemical composition and content of red mud, steel slag and lithium slag, promotes the chemical substances in the cementitious components to be in a better proportion, thereby further improving the flexural strength and compressive strength of the cement.

[0030] (5) The present invention provides a cement and a preparation method. The preparation method is simple and has low energy consumption, and belongs to a low-carbon and environmentally friendly preparation technology. The cement hardened body prepared by the present invention exhibits good mechanical properties in both the early and late stages, has good stability, and has a wide range of applications, which will bring huge benefits to society, economy and environment. Detailed Implementation

[0031] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0032] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] Examples 1-9

[0034] Examples 1-9 each provide a type of cement, the formulation of which is shown in Table 1. The cement in each example is prepared according to the following steps:

[0035] The cementitious components and auxiliary activators are dried, and each raw material is weighed according to Table 1. The prepared cementitious components and auxiliary activators are mixed evenly and then ground into powder. The powder is ground until the residue on an 80μm square hole sieve does not exceed 10%, and then the silica-alumina low-carbon cement based on red mud is obtained.

[0036] Table 1 Cement Formulation (kg)

[0037]

[0038] The chemical composition of red mud, steel slag, and lithium slag used in Examples 1-9 and Comparative Examples 1-2 is shown in Tables 2-4 below, and the information of slag, cement clinker, gypsum, and fly ash is shown in Table 5 below.

[0039] Table 2 Chemical composition of red mud (%)

[0040]

[0041] Table 3 Chemical composition of steel slag (%)

[0042] materials CaO <![CDATA[SiO2]]> MgO <![CDATA[Fe2O3]]> <![CDATA[CaF2]]> MnO <![CDATA[Al2O3]]> <![CDATA[SO3]]> Loss on ignition steel slag 38.71 15.55 5.9 26.48 0.02 2.29 3.72 0.32 3.11

[0043] Table 4 Chemical composition (%) of lithium slag

[0044]

[0045]

[0046] Table 5 Information on slag, cement clinker, fly ash, and gypsum

[0047] materials factory model slag Shanghai Bio-Heng New Materials Co., Ltd. Water-quenched slag powder - S95 cement clinker Jiahua Special Cement Co., Ltd. Ordinary silicate cement clinker fly ash Shanghai Bio-Heng New Materials Co., Ltd. Class F: Grade I fly ash plaster Shanghai Bio-Heng New Materials Co., Ltd. Desulfurized gypsum

[0048] Example 10

[0049] This embodiment provides a cement with a formula shown in Table 1. The difference from Example 9 lies in the type of red mud used; the chemical composition of the red mud is shown in Table 6 below. All other materials are the same as in Example 9. The cement was prepared according to the preparation methods of Examples 1-9.

[0050] Table 6 Chemical composition of red mud (%)

[0051]

[0052] Example 11

[0053] This embodiment provides a cement with a formula shown in Table 1. The difference from Example 9 lies in the type of steel slag used. The chemical composition of the steel slag is shown in Table 7 below. All other materials are the same as in Example 9. The cement was prepared according to the preparation methods of Examples 1-9.

[0054] Table 7 Chemical composition (%) of steel slag

[0055] materials CaO <![CDATA[SiO2]]> MgO <![CDATA[Fe2O3]]> <![CDATA[CaF2]]> MnO <![CDATA[Al2O3]]> <![CDATA[SO3]]> Loss on ignition steel slag 40.44 13.89 11.1 24.27 0.3 4.6 1.5 0.1 3.12

[0056] Comparative Examples 1-2

[0057] Comparative Examples 1-2 each provided a type of cement, the formulation of which is shown in Table 1. The cements in each comparative example were prepared according to the preparation methods of Examples 1-9.

[0058] Experimental Example 1

[0059] The flexural strength and compressive strength of the cements prepared in Examples 1-11 and Comparative Examples 1-2 were determined. The method was as follows: the cement was mixed and molded according to GB / T17671 "Test Method for Strength of Cement Mortar (ISO Method)" to prepare mortar specimens. The mortar specimens were cured in a curing box at 20℃±2℃ and relative humidity not less than 90% for 1 day, and then demolded. The demolded specimens were placed in water at 20℃±1℃ for 3 days and 28 days. The flexural strength and compressive strength at 3 days and 28 days were tested according to the method in GB / T17671.

[0060] The measurement results are shown in Table 8 below.

[0061] Table 8 Results of Flexural Strength and Compressive Strength Tests

[0062]

[0063] As can be seen from Table 8, the flexural strength of the cement prepared in Examples 1-11 reached 2.0-8.2 MPa on the 3rd day, 5.5-9.6 MPa on the 28th day, 12.0-38.8 MPa on the 3rd day, and 35.1-61.6 MPa on the 28th day, all of which showed good cement performance.

[0064] With the total mass of cementitious components remaining constant, Examples 2-3, compared to Example 1, added gypsum and cement clinker, resulting in improved flexural and compressive strength. Based on Example 3, Example 4 added steel slag, further improving flexural and compressive strength. Furthermore, based on Example 4, lithium slag and fly ash were added, as in Examples 5-11, significantly improving flexural and compressive strength. Examples 6-11 exhibited the best cement performance, with flexural strength reaching 7.1-8.2 MPa on day 3, 8.5-9.6 MPa on day 28, and compressive strength reaching 36.1-38.8 MPa on day 3 and 55.1-61.6 MPa on day 28.

[0065] With the cementitious components and mass remaining unchanged, compared with Example 9, the flexural strength and compressive strength of the cement mortar in Examples 10-11 are lower than those in Example 9. Therefore, using the preferred chemical composition of the red mud of the present invention, which by mass percentage includes Al2O3: 8.0-25%, SiO2: 15.0-30%, Fe2O3: 5-15%, CaO: 5-50%, MgO: 0.1-2%, K2O: 0.001-1%, Na2O: 2-8%, SO3≤5%; and using the preferred chemical composition of the steel slag of the present invention, which by mass percentage includes CaO: 38-50%, Fe2O3: 25-35%, SiO2: 14-20%, MgO: 4.5-12%, MnO: ≤5%, Al2O3: 1-10%, CaF2≤2%, SO3≤5%, can further improve the flexural strength and compressive strength of cement.

[0066] Compared to Example 2, the cement prepared in Example 3 using the combined auxiliary activators calcium formate, sodium hydroxide, and sodium silicate exhibits superior performance, particularly a significantly improved 28-day compressive strength. Furthermore, the cement prepared in Example 7 also demonstrates better performance compared to Example 6. Therefore, the combined use of the auxiliary activators calcium formate, sodium hydroxide, and sodium silicate yields the best results.

[0067] Experiment Example 2

[0068] According to the "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T1346-2011), the soundness of cement paste in Examples 1-11 was tested using the Le Chatelier clamp method. The results are shown in Table 9. The results show that Examples 1-11 all meet the requirements of the national standard GB175-2020 for cement.

[0069] Table 9 Results of setting time and stability determination

[0070]

[0071] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A type of cement, characterized in that, Includes gelling components and auxiliary activators; The cementitious components, by weight, include 10-60 parts red mud, 20-70 parts slag, 5-10 parts cement clinker, and 1-5 parts gypsum. The auxiliary activator accounts for 0.1-8% of the mass of the gelling component; The auxiliary activator comprises calcium formate, sodium hydroxide, and sodium silicate in a mass ratio of 0.4-0.6:0.5-6:4-6.

2. The cement according to claim 1, characterized in that, The cementitious components also include 0-30 parts by weight of steel slag and 0-20 parts by weight of lithium slag.

3. The cement according to claim 1 or 2, characterized in that, The cementitious components, by weight, include 10-30 parts red mud, 5-15 parts steel slag, 10-20 parts lithium slag, 30-70 parts blast furnace slag, 5-10 parts cement clinker, and 1-5 parts gypsum.

4. The cement according to claim 1 or 2, characterized in that, The cementitious components, by weight, include 10-15 parts red mud, 5-15 parts steel slag, 10-15 parts lithium slag, 50-70 parts blast furnace slag, 5-10 parts cement clinker, and 1-5 parts gypsum.

5. The cement according to claim 1 or 2, characterized in that, The cementitious components, by weight, include 10-15 parts red mud, 5-15 parts steel slag, 10-15 parts lithium slag, 50-70 parts blast furnace slag, 5-10 parts cement clinker, 1-5 parts gypsum, and 1-10 parts fly ash.

6. The cement according to claim 1 or 2, characterized in that, The red mud mentioned is sintered red mud.

7. The cement according to claim 6, characterized in that, The red mud contains Al2O3 mass content ≥6.0%, SiO2 mass content ≥10.0%, and 28-day compressive strength activity index >60%.

8. The cement according to claim 7, characterized in that, The chemical composition of the red mud, by mass percentage, includes: Al2O3: 8.0-25%, SiO2: 15.0-30%, Fe2O3: 5-15%, CaO: 5-50%, MgO: 0.1-2%, K2O: 0.001-1%, Na2O: 2-8%, SO3≤5%.

9. The cement according to claim 2, characterized in that, The steel slag contains 30-60% CaO, 10-30% SiO2, 2-20% MgO, and 10-40% Fe2O3 by mass.

10. The cement according to claim 9, characterized in that, The chemical composition of the steel slag, by mass percentage, includes: CaO: 38-50%, Fe2O3: 25-35%, SiO2: 14-20%, MgO: 4.5-12%, MnO: ≤5%, Al2O3: 1-10%, CaF2 ≤2%, SO3 ≤5%.

11. The cement according to claim 2, characterized in that, The lithium slag contains 30-50% CaO, 10-30% Fe2O3, 10-25% SiO2, 2-10% MgO, 1-8% Al2O3, ≤6% MnO, and ≤5% SO3 by mass.

12. The cement according to claim 5, characterized in that, The slag is water-quenched slag or air-cooled granulated blast furnace slag; and / or, the cement clinker is silicate cement clinker; and / or, the fly ash is Class C fly ash or Class F fly ash; and / or, the gypsum is selected from one or more of desulfurized gypsum, mirabilite gypsum, phosphogypsum and titanium gypsum.

13. A method for preparing cement according to any one of claims 1-12, characterized in that, The mixture is prepared by weighing and grinding each component according to the specified weight proportions, or by weighing and grinding each component except for the auxiliary activator according to the specified weight proportions, and then adding the auxiliary activator before use.

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