Multi-element low-carbon less clinker composite cement and preparation method thereof

Abstract

The application discloses a kind of multi-element low carbon less clinker composite cement and its preparation method.The composite cement contains the following ingredients according to weight percentage: Portland cement clinker: 25%-50%, activated kaolin material: 15%-30%, slag: 0-50%, limestone: 2-15%, gypsum: 0-5%.The activated kaolin material is natural clay or industrial solid waste coal gangue (kaolin content ≥30%), by crushing, grinding and low-temperature calcination 600-800℃ to stimulate activity, then by batching, homogenization and grinding to prepare composite cement.Based on the synergistic effect of kaolin-limestone-slag hydration, the multi-element low carbon less clinker composite cement clinker dosage can be as low as 25%, while having the advantages of fast strength development, good late performance and dense microstructure, which can solve the technical defects of high carbon emission of existing ordinary Portland cement and poor performance of less clinker cement, while effectively disposing solid waste, reducing cement cost, and conducive to the low-carbon sustainable development of cement industry.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a multi-element low-carbon clinker composite cement and its preparation method. Background Technology

[0002] The cement production process generates significant amounts of carbon dioxide, a greenhouse gas, through fuel consumption and limestone decomposition. Using admixtures to replace cement clinker can reduce cement costs, energy consumption, and carbon dioxide emissions, representing a current trend towards low-carbon, green, and sustainable development in the cement industry. Statistics show that the average clinker replacement rate in my country is currently approximately 32.2%. Based on the hydration and multi-component synergistic reaction mechanisms of cement, as well as physicochemical theories such as setting and hardening, developing low-clinker, multi-component, low-carbon composite cement can effectively improve the performance of composite cement, enhancing the microstructure and mechanical properties of cement concrete. Under the same performance requirements, it can significantly increase the clinker replacement rate, demonstrating a clear advantage in energy conservation and emission reduction.

[0003] In recent years, researchers both at home and abroad have generally believed that calcined clay-limestone composite cement system (i.e., LC) 3 Cement, with its widely available and abundant raw materials, has significant potential. European patent EP2253600A1, "Portland Limestone calcined clay cement," discloses a ternary composite cement system composed of calcined clay, limestone, and cement. This system exhibits comparable late-stage mechanical properties and durability to ordinary Portland cement, with a clinker replacement rate of up to 50%. However, it suffers from slow strength development and low early strength, which somewhat limits its application in engineering. Furthermore, when the cement content in the ternary composite cement system is further reduced, a large amount of unreacted calcined clay and limestone remains, leading to a significant decrease in its mechanical properties, failing to meet engineering requirements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a low-carbon, low-clinker composite cement and its preparation method. The cement is characterized by having a lower clinker content than existing technologies, faster strength development, and better later-stage mechanical properties.

[0005] To achieve the above objectives, this invention utilizes the synergistic hydration-promoting effect of metakaolin, slag, and limestone to form a low-carbon, low-clinker composite cement technology solution:

[0006] A multi-element, low-carbon, low-clinker composite cement, comprising the following components by weight percentage: 25-50% silicate cement clinker, 15%-30% activated kaolin material, 0-50% slag, 2-15% limestone, and 0-5% gypsum.

[0007] In the aforementioned multi-element low-carbon clinker composite cement, the activated kaolin material is either activated natural clay or industrial solid waste coal gangue, preferably with a kaolin content of ≥30%.

[0008] In the aforementioned multi-component low-carbon clinker composite cement, the proportion of metakaolin, an active component in the limestone and activated kaolin material, is 0.25-1.00.

[0009] In the aforementioned multi-component low-carbon clinker composite cement, the slag is granulated blast furnace slag, preferably with a specific surface area ≥300 m². 2 / kg, 28-day activity index ≥95%.

[0010] The aforementioned multi-element, low-carbon, low-clinker composite cement is prepared by the following steps:

[0011] Step 1) The activated kaolin material is crushed to a particle size of less than 10-20 mm, ball-milled at 450 r / min for 5-40 min until less than 10% remains after passing through an 80 μm square hole sieve, and then heated to 600-800 °C in a muffle furnace at a rate of 5-20 °C / min and held for 1-2 h to activate its activity, thus obtaining activated kaolin material containing metakaolin.

[0012] Step 2) The 25%-50% silicate cement clinker, 15%-30% activated kaolin material, 0-50% slag, 2-15% limestone and 0-5% gypsum are mixed, homogenized and ground to obtain the multi-element low-carbon clinker composite cement.

[0013] The batching, homogenization, and grinding steps of the multi-element low-carbon clinker-less composite cement in step 2) above can be carried out according to one of the following methods:

[0014] Method 1) Grinding and mixing: According to the weight ratio, take finely ground silicate cement clinker, activated kaolin material, slag, limestone and gypsum and mix them evenly to obtain multi-element low-carbon low-clinker composite cement. The fineness of the multi-element low-carbon low-clinker composite cement should pass through an 80μm square hole sieve with a residue of less than 10%.

[0015] Method 2) Mixing and grinding: According to the weight ratio, take the unground silicate cement clinker, activated kaolin material, slag, limestone and gypsum and mix and grind them to obtain multi-element low carbon low clinker composite cement. The fineness of the multi-element low carbon low clinker composite cement should pass through an 80μm square hole sieve with a residue of less than 10%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. This invention uses a variety of admixtures to prepare low-carbon cement. While meeting performance requirements, the amount of cement clinker can be reduced by 75%, which significantly reduces cement production costs and carbon dioxide emissions.

[0018] 2. The active kaolin material used in this invention has a wide range of raw material sources and can effectively utilize solid waste, such as coal gangue and slag, which is conducive to the reduction and resource utilization of solid waste.

[0019] 3. The multi-element low-carbon clinker composite cement prepared by this invention has the advantages of high early strength, rapid strength development, and high flexural and compressive strength in the later stage, and can be widely used in structural materials such as buildings and pavements. Attached Figure Description

[0020] Figure 1 Thermogravimetric analysis diagrams of multi-component low-carbon clinker-less composite cement and activated kaolin-limestone composite cement.

[0021] Figure 2 X-ray diffraction analysis diagrams of multi-component low-carbon clinker-less composite cement and activated kaolin-limestone composite cement;

[0022] Figure 3 Isothermal hydration calorimetry results for multi-component low-carbon clinker-less composite cement and activated kaolin-limestone composite cement. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be provided below in conjunction with specific embodiments.

[0024] Example 1: A multi-element low-carbon clinker composite cement with a clinker replacement rate of 65%, comprising the following components by weight percentage: 35% silicate cement clinker, 15% activated kaolin material, 3.8% limestone, 41.2% slag, and 5% gypsum.

[0025] The activated kaolin material is calcined coal gangue, with a kaolin content of 98%.

[0026] The silicate cement clinker is a concrete admixture testing standard cement conforming to GB 8076-2008, with a strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg, the slag is S95 grade granulated blast furnace slag powder, 300 mesh, and the limestone and gypsum are analytical grade reagents.

[0027] The aforementioned method for preparing a multi-element, low-carbon, low-clinker composite cement includes the following steps:

[0028] Step 1) After crushing the activated kaolin material to a diameter ≤20mm, grind it for 30min at 450r / min using a planetary ball mill. Then, place it in a corundum crucible and calcine it at 800℃ for 2h using a muffle furnace with a heating rate of 10℃ / min. The specific surface area of ​​the activated kaolin material is 450m². 2 / kg.

[0029] Step 2) Prepare silicate cement clinker, activated kaolin material, limestone, slag and gypsum according to the aforementioned weight percentages, and mix them for 2 hours using a dry powder premixer until the raw materials are uniform to obtain multi-element low-carbon low-clinker composite cement.

[0030] Example 2: A multi-element low-carbon clinker composite cement with a clinker replacement rate of 75%, comprising the following components by weight percentage: 25% silicate cement clinker, 15% activated kaolin material, 3.8% limestone, 51.2% slag, and 5% gypsum.

[0031] The activated kaolin material is calcined coal gangue, with a kaolin content of 98%.

[0032] The silicate cement clinker is a concrete admixture testing standard cement conforming to GB 8076-2008, with a strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg, the slag is S95 grade granulated blast furnace slag powder, 300 mesh, and the limestone and gypsum are analytical grade reagents.

[0033] The aforementioned method for preparing a multi-element, low-carbon, low-clinker composite cement includes the following steps:

[0034] Step 1) After crushing the activated kaolin material to a diameter ≤20mm, grind it for 30min at 450r / min using a planetary ball mill. Then, place it in a corundum crucible and calcine it at 800℃ for 2h using a muffle furnace with a heating rate of 10℃ / min. The specific surface area of ​​the activated kaolin material is 450m². 2 / kg.

[0035] Step 2) Prepare silicate cement clinker, activated kaolin material, limestone, slag and gypsum according to the aforementioned weight percentages, and mix them for 2 hours using a dry powder premixer until the raw materials are uniform to obtain multi-element low-carbon low-clinker composite cement.

[0036] The principle of this invention is as follows: limestone and the aluminum phase in cement will produce a synergistic effect, promoting the conversion of the hydration product calcium sulfoaluminate into calcium carboaluminate, which is more thermodynamically stable and has a lower density. At the same time, it indirectly stabilizes the content of ettringite and densifies the microstructure of cement stone in the later stage. Meanwhile, the activity of mineral powder is rapidly activated in the early stage of hydration in the composite cement system (1-3 days), which enables the early strength of multi-element low-carbon low-clinker composite cement to develop rapidly. In addition, the synergistic effect of high terre monoxide-limestone-mineral powder enhances the cementing effect between micro-products, effectively improving its microstructural mechanical properties, macroscopic flexural strength and compressive strength.

[0037] To verify the technical effects of the embodiments, comparative examples 1, 2, and 3 were set up. Comparative example 1 was pure cement, comparative example 2 was slag cement with a clinker replacement rate of 65%, and comparative example 3 was activated kaolin-limestone composite cement, which had the same activated kaolin material and limestone content as example 1. In example 1, the slag was replaced with an inert admixture, quartz. The superior performance characteristics of the multi-element, low-carbon, low-clinker composite cement proposed in this paper are illustrated by comparing the performance of different cements.

[0038] Comparative Example 1: Pure cement containing 100% silicate cement clinker, wherein the silicate cement clinker is the concrete admixture testing standard cement conforming to GB8076-2008, with a strength grade of 42.5.

[0039] Comparative Example 2: Slag cement with a clinker replacement rate of 65%, containing the following components by weight percentage: 35% silicate cement clinker, 60% slag, and 5% gypsum.

[0040] The silicate cement clinker is a concrete admixture testing standard cement conforming to GB 8076-2008, with a strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg, the slag is S95 grade granulated blast furnace slag powder, 300 mesh, and the gypsum is an analytical grade reagent.

[0041] The aforementioned method for preparing slag cement includes the following steps:

[0042] Step 1) Prepare silicate cement clinker, slag and gypsum according to the aforementioned weight percentages, and mix them for 2 hours using a dry powder premixer until the raw materials are uniform to obtain slag cement.

[0043] Comparative Example 3: An activated kaolin material-limestone composite cement with a clinker replacement rate of 65% contains the following components by weight percentage: 35% silicate cement clinker, 15% activated kaolin material, 3.8% limestone, 41.2% quartz, and 5% gypsum.

[0044] The silicate cement clinker is a concrete admixture testing standard cement conforming to GB 8076-2008, with a strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg, 300 mesh, quartz, limestone, and gypsum are analytical grade reagents.

[0045] The aforementioned method for preparing activated kaolin-limestone composite cement includes the following steps:

[0046] Step 1) After crushing the activated kaolin material to a diameter ≤20mm, grind it for 30min at 450r / min using a planetary ball mill. Then, place it in a corundum crucible and calcine it at 800℃ for 2h using a muffle furnace with a heating rate of 10℃ / min. The specific surface area of ​​the activated kaolin material is 450m². 2 / kg.

[0047] Step 2) Prepare silicate cement clinker, activated kaolin material, limestone, quartz, and gypsum according to the aforementioned weight percentages, and mix them for 2 hours using a dry powder premixer until the raw materials are uniform to obtain activated kaolin material-limestone composite cement.

[0048] According to GB / T 17671-1999, the test method for cement mortar strength was used to prepare 40mm×40mm×160mm prismatic cement mortar specimens with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The cast specimens were cured in a standard curing chamber (temperature 20±1℃, relative humidity 95%) for 24 hours. After demolding, they were placed back in the standard curing chamber for further curing until the specified age. The mechanical properties of the cement in the examples and comparative examples were tested, and the test results are shown in Table 1. The hydration and microstructure research results of Example 1 and Comparative Example 3 are as follows: Figure 1-3 As shown.

[0049] Table 1

[0050]

[0051]

[0052] As shown in Table 1, the multi-element low-carbon, low-clinker composite cement described in this patent exhibits significantly improved early-age strength and later-age compressive and flexural strength compared to slag cement (Comparative Example 2) and activated kaolin-limestone composite cement (Comparative Example 3), and its strength approaches or even exceeds that of pure cement specimens (Comparative Example 1). Furthermore, with a clinker substitution rate of 75%, the multi-element low-carbon, low-clinker composite cement described in this patent achieves a 3-day compressive strength of 24.2 MPa and a 28-day compressive strength of 50.7 MPa, demonstrating its applicability in practical industrial applications and significant carbon reduction potential.

[0053] Figure 1 ,2 Figures 3 and 4 show the thermogravimetric analysis, X-ray diffraction analysis, and isothermal hydration exothermic results of the multi-component low-carbon clinker-reduced composite cement (Example 1) and the activated kaolin-limestone composite cement, respectively. The results indicate that the activity of the mineral powder in the multi-component low-carbon clinker-reduced composite cement is rapidly activated in the early hydration stage (1-3 days). Simultaneously, the aluminum phase in the composite cement and limestone exhibit a synergistic effect, generating low-density calcium aluminate, which promotes the refinement of the cement's micropores. This results in the multi-component low-carbon clinker-reduced composite cement exhibiting superior characteristics compared to existing low-carbon clinker-reduced cements, including a high substitution rate, early strength, and high strength.

[0054] The above description is merely a preferred embodiment of the present invention and 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 all fall within the scope of protection of the present invention. The scope of protection of this patent should be determined by the appended claims.

Claims

1. A multi-element low-carbon less-clinker composite cement, characterized by, The composite cement contains the following components by weight percentage: 25%-35% silicate cement clinker, 15%-30% activated kaolin material, 41.2%-50% slag, 2%-3.8% limestone, and 5% gypsum; the proportion of active component predominantly kaolin in the limestone and activated kaolin material is 0.

25.

2. The multi-element low-carbon less-clinker composite cement according to claim 1, characterized in that, The activated kaolin material is either natural clay or industrial solid waste coal gangue, and its active ingredient, metakaolin content, is ≥30%.

3. The multi-element low-carbon less-clinker composite cement according to claim 1, characterized in that, The slag is granulated blast furnace slag, specific surface area ≥ 300 m 2 / kg, 28-day activity index ≥ 95%.

4. A method for preparing a multi-element low-carbon and less-clinker composite cement according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1) The activated kaolin material is crushed to a particle size of 10-20 mm, ball-milled at 450 r / min for 5-40 min to form powder, and then heated to 600-800℃ in a muffle furnace at a rate of 5-20℃ / min and held for 1-2 h to activate its activity, thus obtaining activated kaolin material containing metakaolin. Step 2) The 25%-35% silicate cement clinker, 15%-30% activated kaolin material, 41.2-50% slag, 2-3.8% limestone and 5% gypsum are mixed, homogenized and ground to obtain the multi-element low-carbon clinker composite cement.

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