Ferroaluminate cement-based low-carbon concrete and preparation method thereof

Abstract

The application discloses a ferrite aluminate cement-based low-carbon concrete, and components and their dosages include: water 140-190 kg / m 3 , ferrite aluminate cement 300-450 kg / m 3 , modified silica ash 7-24 kg / m 3 , fly ash 14-48 kg / m 3 , alkali-activated mineral powder 36-57 kg / m 3 , fine aggregate 700-800 kg / m 3 , coarse aggregate 800-1200 kg / m 3 , high-slump-keeping and anti-sweating water type polycarboxylic acid superplasticizer 4-6 kg / m 3 ; the high-slump-keeping and anti-sweating water type polycarboxylic acid superplasticizer comprises a polycarboxylic acid water reducing agent, boric acid and cellulose ether. The application uses ferrite aluminate cement as a main raw material, and further combines modified silica ash, fly ash and alkali-activated mineral powder, and further combines components such as high-slump-keeping and anti-sweating water type polycarboxylic acid high-efficiency water reducing agent to retard and keep slump, so that the early strength, the elastic modulus and the working performance are high, and the application is wide.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-carbon concrete based on aluminoferrite cement and its preparation method. Background Technology

[0002] In response to the severe challenges of climate change, reducing carbon emissions from bridge construction is a crucial step in achieving dual-carbon goals in infrastructure development. Currently, concrete bridges account for 90% of all bridge projects, and cement accounts for approximately 90% of the carbon emissions from their raw materials. Therefore, a common method for reducing concrete carbon emissions is to replace a portion of silicate cement with a large amount of mineral admixtures.

[0003] In the early stages, mineral admixtures mainly play a physical filling role. Replacing cement with them can reduce the content of highly active clinker per unit volume. Their pozzolanic reaction depends on the activation of calcium hydroxide produced by cement hydration, resulting in insufficient total amount of cementitious materials in the early stages. Therefore, replacing silicate cement with a large amount of mineral admixtures will significantly reduce the early strength of concrete and slow its strength development, which cannot meet the construction requirements of early tensioning of bridge structures. This makes it difficult to apply low-carbon concrete with large amounts of mineral admixture silicate cement on a large scale.

[0004] Further exploration is needed to develop low-carbon concrete that can effectively utilize solid waste while maintaining good performance. Low-carbon cement—ferroaluminate cement, silica fume, fly ash, and mineral powder—is preferred for its preparation. Ferroaluminate cement has a rapid hydration rate and a setting time of less than 30 minutes, which is unfavorable for construction. However, commonly used slump-retaining water-reducing agents cannot effectively extend the concrete setting time. Furthermore, the adverse effects of traditional mineral admixtures on early strength limit their efficient application in low-carbon concrete and related fields. Summary of the Invention

[0005] The main objective of this invention is to provide a low-carbon concrete based on aluminoferrite cement and its preparation method. The concrete has low carbon emissions, a setting time of more than 3 hours, and can take into account the advantages of high early strength, high elastic modulus, good workability, etc., and has wide applicability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A type of low-carbon concrete based on aluminoferrite cement, the specific components and their dosages include: water 140~190 kg / m³ 3 Ferroaluminate cement 300~450 kg / m³ 3 Modified silica fume 7~24 kg / m³ 3 Fly ash content: 14~48 kg / m³ 3 Alkali-activated mineral powder 36~57kg / m³ 3 Fine aggregate 700~800 kg / m³ 3Coarse aggregate 800~1200 kg / m³ 3 High-slump-resistance and anti-bleeding water-reducing agent: 4~6 kg / m³ 3 .

[0007] Furthermore, the cementitious materials used in the low-carbon concrete include aluminoferrite cement, modified silica fume, fly ash and alkali-activated mineral powder, wherein the modified silica fume content is 1.5~5 wt%, the fly ash content is 3~10 wt%, and the alkali-activated mineral powder content is 8~12 wt%.

[0008] According to the above scheme, the aluminoferrite cement is a grade 52.5 or higher aluminoferrite cement with a specific surface area of ​​450~550 m². 2 / kg.

[0009] According to the above scheme, the modified silica fume is silica fume pre-dispersed and modified with polycarboxylate superplasticizer, with a silica content ≥90wt% and a specific surface area of ​​18000~22000m². 2 / kg; The specific preparation steps of the modified silica fume include the following: mixing silica fume with a polycarboxylate superplasticizer solution accounting for 2~5% of its mass evenly, and then drying it (such as by spray drying).

[0010] Furthermore, in the preparation of modified silica fume, the polycarboxylate superplasticizer introduced has a water reduction rate of 35-45% solid content and a water reduction rate of ≥25%.

[0011] According to the above scheme, the solid content of the high slump retention and anti-bleeding water-reducing agent is 35~45%; the water reduction rate is ≥25%; the slump retention performance is: when the initial slump is 210mm±10mm, the slump retention value after 1.5 hours is ≥90%; and the bleeding rate is ≤60%.

[0012] Furthermore, the preparation method of the high slump-retaining polycarboxylate superplasticizer includes the following steps: the polycarboxylate superplasticizer is put into a stirred tank, and a specified amount of boric acid is added. The mixture is stirred at room temperature and at a constant speed until the boric acid is completely dissolved and the system is uniform and transparent. Then, a specified amount of cellulose ether is precisely added, and the stirring temperature is controlled at 25~35℃. The mixture is stirred for 30~60 minutes to ensure that the components are fully compounded and compatible, and that their performance is synergistically coupled. After stirring, the mixture is filtered through an 80~120 mesh filter to remove trace amounts of insoluble impurities, thus obtaining the finished high slump-retaining and anti-bleeding polycarboxylate superplasticizer.

[0013] Furthermore, in the high slump retention and anti-bleeding polycarboxylate superplasticizer, the components and their weight percentages include: 100 parts of polycarboxylate superplasticizer, 5-10 parts of boric acid, and 0.05-2 parts of cellulose ether.

[0014] Furthermore, in the high-slump-resistance and anti-bleeding polycarboxylate superplasticizer, the solid content of the polycarboxylate superplasticizer is 35-45%; the water reduction rate is ≥25%.

[0015] According to the above scheme, the fly ash is Grade I fly ash that has been mechanically ground and activated, and its specific surface area is controlled at 800~1200 m². 2 / kg.

[0016] According to the above scheme, the alkali-activated mineral powder is mineral powder that has been pre-activated by an alkaline modifier, with a specific surface area of ​​400~500 m². 2 / kg.

[0017] Furthermore, the pre-activation treatment step includes: mechanically mixing the mineral powder with calcium hydroxide powder accounting for 1-3% of its mass until uniform, and then sealing and aging for 24-48 hours.

[0018] According to the above scheme, the fine aggregate is manufactured sand with a fineness modulus of 2.6 to 3.4 and a stone powder content of 8 to 14 wt%.

[0019] According to the above scheme, the coarse aggregate is ordinary crushed stone or crushed pebbles, with a continuous gradation of 5~20mm and a crushing index of 7-14%.

[0020] Furthermore, the coarse aggregate comprises coarse stone and fine stone, with the coarse stone having a particle size of ≥10mm and the fine stone having a particle size of 5~10mm (excluding 10mm).

[0021] The above-mentioned method for preparing low-carbon concrete based on aluminoferrite cement is characterized by the following steps: (1) Solution preparation: Weigh the high slump retention and anti-bleeding water-reducing agent according to the ratio and stir it evenly to obtain the water-reducing agent solution; (2) Weigh out the aluminoferrite cement, modified silica fume, fly ash, alkali-activated mineral powder, fine aggregate and coarse aggregate and put them into a concrete mixer and mix them evenly to obtain a premix. (3) Add water-reducing agent solution to the obtained premix and stir evenly to obtain the low-carbon concrete based on aluminoferrite cement.

[0022] This invention uses aluminoferrite cement to prepare low-carbon concrete, and adds modified silica fume, fly ash and alkali-activated mineral powder at a mass ratio of 12.5-27% of cementitious materials. This can effectively reduce production costs and ensure the basic mechanical properties of low-carbon concrete. In order to address the problems of rapid setting time and poor workability of aluminoferrite cement, it further combines a high-slump-retaining and anti-bleeding polycarboxylate superplasticizer to ensure good workability.

[0023] The low-carbon concrete prepared according to the above scheme is based on aluminoferrite cement and has a 3-day compressive strength ≥70MPa, a 3-day elastic modulus ≥46Gpa, an initial setting time ≥3h, a flexural strength ≥7MPa, and an electrical flux ≤1000C.

[0024] Compared with the prior art, the beneficial effects of the present invention include: (1) The carbon emission of the low-carbon concrete based on aluminoferrite cement of the present invention is 267 kg CO2 / m³. 3 <Standard limit 330kgCO2 / m 3 Carbon emissions are significantly reduced, decreasing by more than 20% compared to ordinary C50 concrete, thus achieving the low-carbonization of C50 and above concrete commonly used in bridges.

[0025] (2) The low-carbon concrete based on aluminoferrite cement described in this invention uses silica fume pre-dispersed and modified with water-reducing agent. The silica fume is pre-mixed with a small amount of water-reducing agent, so that the water-reducing agent molecules are adsorbed on the surface of silica fume particles in advance, reducing the agglomeration of silica fume, and ensuring that no additional water-reducing agent is needed after the silica fume is added to the concrete, thus ensuring that the silica fume particles are evenly distributed in the concrete. Mechanically ground and activated fly ash is used to improve the activity of fly ash. Alkali-pre-activated mineral powder is used to improve the hydration degree of mineral powder, which can effectively guarantee and improve early strength and later strength.

[0026] (3) The initial setting time of the low-carbon concrete obtained by the present invention is increased from 30 min to more than 3 h. The initial and 1.5 h slump and spread are 215 / 550 mm and 210 / 540 mm, respectively. The concrete has excellent workability and can simultaneously solve the problems of fast setting time and easy bleeding of aluminoferrite cement. It provides technical support for the application of the obtained low-carbon concrete in bridge engineering and other fields. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the invention, but the present invention is not limited to the following embodiments.

[0028] Example 1 A low-carbon concrete based on aluminoferrite cement, with the mix proportions shown in Table 1; its preparation method includes the following steps: (1) Solution preparation: Weigh the high slump retention and anti-bleeding water-reducing agent and mix it with water in a container to obtain a water-reducing agent solution; (2) Weigh out the aluminoferrite cement, silica fume, fly ash, mineral powder, manufactured sand, fine stone and coarse stone and put them into a concrete mixer and mix for 60 seconds. (3) Add the prepared water-reducing agent solution to the concrete mixer and stir for 120 seconds to obtain the low-carbon concrete.

[0029] Table 1. Mix proportions of low-carbon concrete based on aluminoferrite cement in Example 1, unit: kg / m³ 3

[0030] Wherein: the aluminoferrite cement is grade 52.5 aluminoferrite cement with a specific surface area of ​​450 m². 2 / kg; The silica fume mentioned is silica fume pre-dispersed and modified with polycarboxylate superplasticizer, with a silica content of 90 wt% and a specific surface area of ​​20,000 m². 2 / kg; the specific preparation steps include: mixing silica fume with a 3% polycarboxylate superplasticizer solution (provided by Jiangsu Subote New Material Co., Ltd., model PAC) by mass. ® The mixture (with a solid content of 40%) is thoroughly mixed and then spray-dried to obtain the final product.

[0031] The fly ash mentioned is Grade I fly ash that has been mechanically ground and activated, with a specific surface area of ​​900 m². 2 / kg; The mineral powder is S95 grade mineral powder that has undergone alkaline pre-activation treatment, with a specific surface area of ​​450 m². 2 / kg, the pre-activation process is as follows: the mineral powder and calcium hydroxide powder accounting for 2% of its mass are mechanically stirred evenly, and then sealed and aged for 24 hours; The fine aggregate is manufactured sand with a fineness modulus of 2.7 and a stone powder content of 10%. The coarse aggregate is ordinary crushed stone with a continuous gradation of 5-20mm and a crushing index of 10%. The preparation method of the high-slump-resistance and anti-bleeding polycarboxylate superplasticizer is as follows: Add 100 parts (by weight, the same below) of polycarboxylate superplasticizer to a mixing tank, add 5 parts of boric acid, and stir until completely dissolved; then add 1 part of cellulose ether, stir at a constant temperature for 30-60 minutes, and filter (using a 100-mesh filter) to obtain the final product.

[0032] Example 2 A low-carbon concrete based on aluminoferrite cement is prepared in a manner similar to that of Example 1, except that the amounts of silica fume and fly ash are different, and the mixing ratios described in Table 2 are used.

[0033] Table 2. Mix proportions of low-carbon concrete based on aluminoferrite cement in Example 2, unit: kg / m³ 3

[0034] Example 3 A low-carbon concrete based on aluminoferrite cement is prepared in a manner similar to that of Example 1, except that the total amount of mineral admixtures is different and the mixing ratio conditions described in Table 3 are used.

[0035] Table 3. Mix proportions of low-carbon concrete based on aluminoferrite cement in Example 3, unit: kg / m³ 3

[0036] Comparative Example 1 A low-carbon concrete based on aluminoferrite cement is prepared in a manner similar to that of Example 1, except that the cementitious material is aluminoferrite cement and the mixing ratio conditions described in Table 4 are used.

[0037] Table 4 shows the mix proportions of low-carbon concrete based on aluminoferrite cement in Comparative Example 1, in kg / m³. 3

[0038] Comparative Example 2 A low-carbon concrete based on aluminoferrite cement is prepared in a manner similar to that of Example 1, except that the silica fume, fly ash and mineral powder are not pretreated, and the mixing ratios described in Table 5 are used.

[0039] Table 5. Mix proportions of low-carbon concrete based on aluminoferrite cement in Comparative Example 2, unit: kg / m³ 3

[0040] Comparative Example 3 A low-carbon concrete based on aluminoferrite cement is prepared in a manner largely the same as in Example 1, except that the water-reducing agent is different and the mixing ratio conditions described in Table 6 are used.

[0041] Table 6 shows the mix proportions of low-carbon concrete based on aluminoferrite cement in Comparative Example 3, in kg / m³. 3

[0042] The water-reducing agent is a slump-retaining polycarboxylate superplasticizer, provided by Jiangsu Subote New Material Co., Ltd., model PAC. ® -1, with a solid content of 40%.

[0043] Comparative Example 4 A low-carbon concrete based on ordinary Portland cement, with mix proportions shown in Table 7 (mix proportions of C50 concrete commonly used in bridge construction), is prepared using the following methods: (1) Solution preparation: Premix the weighed water-reducing agent and water evenly in a container; (2) Weigh out the silicate cement, fly ash, mineral powder, fine aggregate and coarse aggregate and put them into a concrete mixer and mix for 60 seconds; (3) Add the prepared solution to the concrete mixer and stir for 120 seconds.

[0044] Table 7. Mix proportions of the ordinary C50 concrete described in Comparative Example 4, unit: kg / m³ 3

[0045] Wherein: the cement is PO42.5 ordinary Portland cement; The fly ash mentioned is Class I fly ash; The mineral powder mentioned is S95 grade mineral powder; The fine aggregate is manufactured sand with a fineness modulus of 2.7; The coarse aggregate is ordinary crushed stone or gravel, with a continuous gradation of 5-20mm and a crushing index of 10%. The water-reducing agent is a polycarboxylate water-reducing agent provided by Jiangsu Subote New Material Co., Ltd., with a solid content of 40% and a water reduction rate of 38%.

[0046] Comparative Example 5 A low-carbon concrete based on aluminoferrite cement is prepared in a manner largely the same as in Example 1, except that citric acid is used instead of boric acid.

[0047] Table 8 shows the mix proportions of low-carbon concrete based on aluminoferrite cement in Comparative Example 5, in kg / m³. 3

[0048] The concrete obtained from each embodiment and comparative example was tested for carbon emissions, workability, mechanical properties, electrical conductivity, etc. The specific test results are shown in Table 9.

[0049] Table 9. Performance test results of concrete obtained in Example 1 and Comparative Examples 1-5

[0050] As shown in Table 9, compared with Comparative Example 1, Example 1 of the present invention reduces the amount of aluminoferrite cement and increases the amount of mineral admixtures without reducing the concrete strength. While ensuring concrete strength (and even improving it to a certain extent), it significantly reduces raw material costs. Compared with Comparative Example 2, Example 1 changes the ratio of silica fume, fly ash, and mineral powder, which reduces the early strength of the concrete. Compared with Example 3, Example 1 uses a different water-reducing agent. The high-slump retention and anti-bleeding polycarboxylate high-efficiency water-reducing agent prepared by the present invention significantly extends the initial setting time of the concrete and significantly improves the slump spread, ensuring the workability of the concrete. Compared with Comparative Example 4, Example 1, compared with low-carbon concrete based on ordinary silicate cement, significantly reduces carbon emissions while further improving mechanical properties and impermeability. Compared with Comparative Example 5, Example 1 shows that the setting time of the concrete obtained by the present invention is greatly extended, solving the problem of rapid concrete setting time and difficulty in large-scale engineering applications, while ensuring good mechanical properties.

[0051] The embodiments of the present invention have been described above, but the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and these forms are all within the protection scope of the present invention.

Claims

1. A low-carbon concrete based on aluminoferrite cement, characterized in that, The components and their dosages include: water 140~190 kg / m³ 3 Ferroaluminate cement 300~450 kg / m³ 3 Modified silica fume 7~24 kg / m³ 3 Fly ash content: 14~48 kg / m³ 3 Alkali-activated mineral powder 36~57 kg / m³ 3 Fine aggregate 700~800 kg / m³ 3 Coarse aggregate 800~1200 kg / m³ 3 High-slump-resistance and anti-bleeding water-reducing agent: 4~6 kg / m³ 3 .

2. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The cementitious materials used in the low-carbon concrete include aluminoferrite cement, modified silica fume, fly ash and alkali-activated mineral powder, wherein the modified silica fume content is 1.5~5 wt%, the fly ash content is 3~10 wt%, and the alkali-activated mineral powder content is 8~12 wt%.

3. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The aluminoferrite cement mentioned is a grade 52.5 or higher aluminoferrite cement with a specific surface area of ​​450~550 m². 2 / kg.

4. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The modified silica fume is silica fume pre-dispersed and modified with polycarboxylate superplasticizer, with a silica content ≥90wt% and a specific surface area of ​​18000~22000 m². 2 / kg; The specific preparation steps of the modified silica fume include the following: mixing silica fume with a polycarboxylate superplasticizer solution accounting for 2~5% of its mass evenly, and then drying it.

5. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The high slump retention and anti-bleeding polycarboxylate superplasticizer comprises the following components and their respective weight percentages: 100 parts polycarboxylate superplasticizer, 5-10 parts boric acid, and 0.05-2 parts cellulose ether; the solid content of the high slump retention and anti-bleeding superplasticizer is 35-45%; and the water reduction rate is ≥25%.

6. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The preparation method of the high slump-retaining polycarboxylate superplasticizer includes the following steps: the polycarboxylate superplasticizer is put into a stirred tank, boric acid is added, and the mixture is stirred at room temperature and speed until the boric acid is completely dissolved and the system is uniform and transparent; then cellulose ether is added, and the mixture is stirred at a constant temperature. After filtration through an 80-120 mesh filter, the high slump-retaining and anti-bleeding polycarboxylate superplasticizer is obtained.

7. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The fly ash mentioned is Grade I fly ash that has been mechanically ground and activated, with a specific surface area controlled between 800 and 1200 m². 2 / kg.

8. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The alkali-activated mineral powder mentioned above is mineral powder that has been pre-activated by an alkaline modifier, with a specific surface area of ​​400~500 m². 2 / kg.

9. The low-carbon concrete based on aluminoferrite cement according to claim 1, characterized in that, The fine aggregate is manufactured sand with a fineness modulus of 2.6 to 3.4 and a stone powder content of 8 to 14 wt%; the coarse aggregate is ordinary crushed stone or gravel with a continuous gradation of 5 to 20 mm and a crushing index of 7 to 14%.

10. The method for preparing ferroaluminate cement-based low-carbon concrete according to any one of claims 1 to 9, characterized in that, Includes the following steps: (1) Solution preparation: Weigh the high slump retention and anti-bleeding water-reducing agent according to the ratio and stir it evenly to obtain the water-reducing agent solution; (2) Weigh out the aluminoferrite cement, modified silica fume, fly ash, alkali-activated mineral powder, fine aggregate and coarse aggregate and put them into a concrete mixer and mix them evenly to obtain a premix. (3) Add water-reducing agent solution to the obtained premix and stir evenly to obtain the low-carbon concrete based on aluminoferrite cement.

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