Negative temperature cement composite material based on nano-alumina and modified magnesium-aluminum hydrotalcite

Abstract

This invention discloses a negative-temperature cement composite material based on nano-alumina and modified magnesium-aluminum hydrotalcite, belonging to the field of building materials technology. The composite material is composed of ordinary silicate cement, industrial aluminum ash, silica fume, nano-alumina, magnesium-aluminum hydrotalcite, sodium aluminate, triethanolamine, polycarboxylate superplasticizer, tartaric acid, and water. This invention solves the problems of existing negative-temperature cement materials that rely on external heating or the addition of traditional antifreeze agents such as nitrites, resulting in high costs, environmental risks, and limited early strength improvement. This invention achieves normal hydration and hardening of cement at temperatures ranging from -15℃ to -5℃ through the synergistic effect of heterogeneous nucleation of nano-alumina and the locking of free water by modified magnesium-aluminum hydrotalcite, without the need for traditional antifreeze agents. It features high early strength, good freeze-thaw resistance, environmental friendliness, and benefits from the resource utilization of industrial solid waste.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a cement composite material suitable for use in negative temperature environments from -15℃ to -5℃ and its preparation method. Background Technology

[0002] In low-temperature winter environments, the hydration reaction of cement slows down, limiting early setting and hardening processes, which directly impacts construction progress and early strength development. Currently, there are two main types of cement materials used under sub-zero temperatures. The first type is based on sulfoaluminate cement, with the addition of conventional antifreeze agents such as calcium nitrite, lithium carbonate, and urea to form a rapid-hardening, early-strength system. For example, patent CN121318326A discloses a sulfosilicate cement product for sub-zero temperatures, using sulfosilicate cement in combination with a specific antifreeze agent; patent CN118420310A discloses a sub-zero grouting material that utilizes modified calcium oxide to achieve self-heating. However, this type of material typically suffers from high raw material costs, a relatively concentrated technological approach, and limited formula options. The second type involves adding antifreeze agents, such as nitrite, calcium chloride, and potassium formate, to ordinary silicate cement. However, some antifreeze agents may cause steel corrosion and pose certain environmental and safety risks. Furthermore, the mechanism of action of these antifreeze agents mainly relies on lowering the freezing point of the solution; under even lower temperature conditions, their effect on promoting early hydration and strength improvement is limited.

[0003] In recent years, the application of nanomaterials in cement-based materials has attracted attention, and related patents have begun to emerge. Patent CN116283100A discloses a method for modifying the fracture properties of geopolymer concrete with nano-SiO2, utilizing the pozzolanic effect of nano-SiO2 to improve concrete strength. Patent CN108467215A discloses an early-strength cement admixture reinforced with nano-CSH seed crystals for building concrete. In these patents, nanomaterials are mainly used to enhance the strength of cement materials, not for frost protection. Furthermore, methods for using nanomaterials as seed crystals to induce hydration have been extensively studied, leaving little room for innovation. Patents on the application of layered bimetallic hydroxides (hydrotalcite) in the building materials field are relatively few. Patent CN100595174C discloses a method for using calcium aluminum hydrotalcite as an early-strength agent in concrete to improve concrete strength. Patent CN110255963B discloses a modified hydrotalcite-like concrete anti-sulfate corrosion agent. Currently, in the publicly available patents, hydrotalcite is mainly used as an early strength agent or as a corrosion inhibitor. No patents use it in negative temperature antifreeze systems, nor do any patents disclose the use of hydrotalcite combined with nano-alumina in negative temperature cement. Summary of the Invention

[0004] The purpose of this invention is to provide a negative temperature cement composite material that can hydrate and harden normally without external heating in a negative temperature environment of -15℃ to -5℃, and without adding conventional chemical antifreeze agents such as nitrite, urea, and formate.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite, comprising the following components in parts by weight:

[0007] 600-750 parts of ordinary silicate cement, 150-250 parts of industrial aluminum ash, 40-60 parts of silica fume, 5-15 parts of nano alumina, 10-25 parts of magnesium aluminum hydrotalcite, 5-15 parts of sodium aluminate, 2-5 parts of triethanolamine, 4-8 parts of polycarboxylate superplasticizer, 1-3 parts of tartaric acid, and 230-260 parts of mixing water.

[0008] The nano-alumina is α-phase nano-alumina;

[0009] The magnesium-aluminum hydrotalcite underwent organic modification, specifically intercalation modification using triethanolamine.

[0010] In the formulation of the negative-temperature cement composite material of this invention, nano-alumina and magnesium aluminum hydrotalcite are simultaneously added to exert a synergistic effect and improve the freeze-thaw resistance of the cement material. This solves the problem that existing negative-temperature cement materials rely on external heating or the addition of traditional antifreeze agents such as nitrite, resulting in high costs, environmental risks, and limited early strength improvement. Nano-alumina accelerates the formation of hydration products through heterogeneous nucleation, while the modified magnesium aluminum hydrotalcite layered structure locks in free water, reducing the content of freezeable water from both physical and chemical dimensions to achieve the purpose of freeze protection. Nano-alumina provides rigid nucleation sites, and modified magnesium aluminum hydrotalcite provides layered nucleation sites, forming a dual heterogeneous nucleation system, which significantly accelerates the formation of ettringite and CSH gel, exhibiting higher early strength.

[0011] As a further explanation of the present invention, in order to ensure that the nano-alumina overcomes agglomeration in the cement system to achieve uniform dispersion and provide a sufficient number of nucleation interfaces, the nano-alumina preferably has a particle size of 20-50 nm and a specific surface area ≥ 50 m². 2 / g. The α-phase nano-alumina has a stable structure and a high heterogeneous nucleation capacity, which can accelerate the formation of hydration products.

[0012] As a further explanation of the present invention, to ensure structural stability and prevent free water from freezing, the magnesium-aluminum molar ratio of the magnesium-aluminum hydrotalcite is 2:1 to 3:1. The magnesium-aluminum hydrotalcite undergoes organic modification treatment, specifically intercalation modification using triethanolamine, which can improve its dispersibility and compatibility in cement systems.

[0013] Magnesium aluminum hydrotalcite, also known as magnesium aluminum carbonate hydrate, is a layered double hydroxide mineral composed of magnesium, aluminum, hydroxide and carbonate ions, and its crystal structure has a layered feature.

[0014] As a further explanation of the present invention, the industrial aluminum ash contains ≥70% Al2O3 and has a fineness ≤200 mesh; the industrial aluminum ash undergoes pretreatment before use, including sieving, alkali washing or water washing to remove impurities, drying and re-grinding, in order to reduce the impact of impurities / harmful components and realize resource utilization.

[0015] As a further explanation of the present invention, the ordinary silicate cement is P·O 42.5 grade; the silica fume contains ≥95% SiO2 and has a specific surface area ≥20m². 2 / g.

[0016] As a further explanation of the present invention, the polycarboxylate superplasticizer is a powder with a solid content of 40% and a water reduction rate of ≥30%; the sodium aluminate is industrial grade with an Al2O3 content of ≥45%.

[0017] This invention also provides a method for preparing the above-mentioned negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite, comprising the following steps:

[0018] (1) Mix the formulated amount of nano-alumina with polycarboxylate superplasticizer and part of the mixing water, and disperse in an ultrasonic dispersion device for 10-15 minutes to prepare a nano-alumina dispersion suspension;

[0019] (2) Mix the magnesium aluminum hydrotalcite of the formula with triethanolamine and deionized water, heat to 60~80℃, stir and react for 1~2 hours, filter, dry the filter cake at 80~100℃ for 12~24 hours, grind through a 200-mesh sieve to obtain organic modified magnesium aluminum hydrotalcite.

[0020] (3) In a cold environment of -5℃ to 0℃, put the formula amount of ordinary silicate cement, industrial aluminum ash, silica fume, all the organic modified magnesium aluminum hydrotalcite obtained in step (2), sodium aluminate and tartaric acid into the mixer and mix for 10~15 minutes to obtain dry mix.

[0021] (4) Add the dry mixture obtained in step (3) to the mixer, slowly add all the nano alumina dispersion suspension obtained in step (1) and the remaining mixing water, stir quickly for 2-3 minutes, let stand for 1 minute, and then stir slowly for 1 minute to obtain cement paste, and cure at negative temperature.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention accelerates the formation of hydration products through heterogeneous nucleation of nano-alumina and simultaneously locks in free water using the layered structure of modified magnesium aluminum hydrotalcite, reducing the content of freezeable water from both physical and chemical perspectives to achieve antifreeze properties. Nano-alumina provides rigid nucleation sites, while modified magnesium aluminum hydrotalcite provides layered nucleation sites, forming a dual heterogeneous nucleation system that significantly accelerates the formation of ettringite and CSH gel, exhibiting high early strength. The combination of nano-alumina and modified magnesium aluminum hydrotalcite for use in negative-temperature cement has not been publicly reported. Aluminum-containing solid industrial byproducts are used as the high-alumina component, and pretreatment reduces the impact of impurities / harmful components, achieving resource utilization. The dual nanomaterials synergistically optimize the pore structure, reducing the most probable pore size and improving the freeze-thaw resistance of concrete. This enables normal hydration and hardening of cement at temperatures ranging from -15℃ to -5℃ without the need for traditional antifreeze agents, exhibiting high early strength, good freeze-thaw resistance, environmental friendliness, and facilitating the resource utilization of industrial solid waste. The raw materials are widely available, the preparation process is compatible with existing concrete production processes, requires no special equipment, and is easy to promote and apply. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0025] All raw materials used in the embodiments of the present invention are commercially available, and their specific specifications and pretreatment methods are as follows:

[0026] 1. Ordinary Portland cement: P·O 42.5 grade.

[0027] 2. Industrial aluminum ash: Al2O3 content 72%, ground to 200 mesh.

[0028] 3. Silica fume: SiO2 content ≥ 95%, specific surface area ≥ 20m² 2 / g.

[0029] 4. Nano-alumina: α-Al₂O₃, particle size 30nm, specific surface area 60m² 2 / g.

[0030] 5. Magnesium aluminum hydrotalcite: magnesium aluminum molar ratio 2.5:1, industrial grade.

[0031] 6. Sodium aluminate: Industrial grade, Al2O3 content ≥45%.

[0032] 7. Triethanolamine: Industrial grade, purity ≥85%.

[0033] 8. Polycarboxylate superplasticizer: powder, 40% solid content, water reduction rate ≥30%.

[0034] 9. Tartaric acid: Industrial grade, purity ≥99%.

[0035] Example 1

[0036] 1. Formula composition:

[0037] 700 kg of ordinary silicate cement, 200 kg of industrial aluminum ash, 50 kg of silica fume, 10 kg of nano alumina, 18 kg of magnesium aluminum hydrotalcite, 10 kg of sodium aluminate, 4 kg of triethanolamine, 6 kg of polycarboxylate superplasticizer, 2 kg of tartaric acid, and 240 kg of mixing water.

[0038] 2. Preparation process:

[0039] (1) Mix 10 kg of nano alumina with 6 kg of polycarboxylate superplasticizer and 25 kg of mixing water, and ultrasonically disperse for 12 minutes to obtain a nano alumina dispersion suspension.

[0040] (2) Mix 18 kg of magnesium aluminum hydrotalcite with 4 kg of triethanolamine and 40 kg of deionized water, heat to 70 °C, stir and react for 1.5 hours, filter, dry the filter cake at 90 °C for 18 hours, grind through a 200 mesh sieve to obtain organic modified magnesium aluminum hydrotalcite.

[0041] (3) In a -3℃ cold room, 700kg of ordinary silicate cement, 200kg of industrial aluminum ash, 50kg of silica fume, all the organic modified magnesium aluminum hydrotalcite obtained in step (2), 10kg of sodium aluminate and 2kg of tartaric acid are put into a mixer and mixed for 12 minutes to obtain dry mix.

[0042] (4) Add the dry mixture to the mixer, slowly add the nano-alumina dispersion suspension obtained in step (1) and the remaining 215 kg of mixing water, stir quickly for 2.5 minutes, let stand for 1 minute, stir slowly for 1 minute to obtain negative temperature cement paste. After testing the workability, form 40 mm × 40 mm × 160 mm test blocks and cure at -10℃.

[0043] 3. Performance test results:

[0044] Table 1 Performance test results of Example 1

[0045] Initial flowability Jumping table method 215mm 30-minute flowability Jumping table method 175mm Condensation time -5℃ environment Initial setting time: 85 minutes; final setting time: 210 minutes compressive strength -10℃ 24h 7.2MPa compressive strength -10℃ 3d 17.8MPa compressive strength -10℃ 28d 32.5MPa Late game strength -10℃ for 28 days + standard care for 28 days 48.6MPa Freezeable water content DSC test at -10℃ 35% lower than ordinary cement Most possible aperture MIP testing 12.5nm (42% lower than ordinary cement) Freeze-thaw resistance 300 freeze-thaw cycles Mass loss: 3.2%; Strength loss: 16.8%

[0046] Example 2

[0047] 1. Formula composition:

[0048] 650 kg of ordinary silicate cement, 220 kg of industrial aluminum ash, 45 kg of silica fume, 12 kg of nano alumina, 20 kg of magnesium aluminum hydrotalcite, 12 kg of sodium aluminate, 5 kg of triethanolamine, 7 kg of polycarboxylate superplasticizer, 2 kg of tartaric acid, and 245 kg of mixing water.

[0049] 2. Preparation process:

[0050] The ultrasonic dispersion time was adjusted to 15 minutes, the magnesium aluminum hydrotalcite modification temperature was adjusted to 75°C, the reaction time was 1 hour, and the rest was the same as in Example 1.

[0051] 3. Performance test results:

[0052] Table 2 Performance test results of Example 2

[0053] compressive strength -10℃ 24h 7.8MPa compressive strength -10℃ 3d 18.5MPa compressive strength -10℃ for 28 days + standard care for 28 days 50.2MPa Freeze-thaw resistance 300 freeze-thaw cycles Mass loss 2.8%, strength loss 15.2%.

[0054] Example 3

[0055] 1. Formula composition:

[0056] 720 kg of ordinary silicate cement, 180 kg of industrial aluminum ash, 55 kg of silica fume, 8 kg of nano alumina, 15 kg of magnesium aluminum hydrotalcite, 8 kg of sodium aluminate, 3 kg of triethanolamine, 5 kg of polycarboxylate superplasticizer, 3 kg of tartaric acid, and 235 kg of mixing water.

[0057] 2. Preparation process:

[0058] The ultrasonic dispersion time was 10 minutes, the magnesium-aluminum hydrotalcite modification temperature was 65°C, the reaction time was 2 hours, and the rest was the same as in Example 1.

[0059] 3. Performance test results:

[0060] Table 3 Performance test results of Example 3

[0061] compressive strength -10℃ 24h 6.5MPa compressive strength -10℃ 3d 16.2MPa compressive strength -10℃ for 28 days + standard care for 28 days 46.8MPa Freeze-thaw resistance 300 freeze-thaw cycles Mass loss: 3.5%; Strength loss: 18.2%

[0062] Comparative Example 1

[0063] 1. Formulation composition: Remove magnesium aluminum hydrotalcite, adjust the amount of cement to 718kg, and the rest is the same as in Example 1.

[0064] 2. Performance test results:

[0065] Table 4 Performance test results of Comparative Example 1

[0066] compressive strength -10℃ 24h 4.2MPa compressive strength -10℃ 3d 11.5MPa compressive strength -10℃ for 28 days + standard care for 28 days 38.2MPa Freezeable water content Under -10℃ conditions 12% lower than ordinary cement Freeze-thaw resistance 300 freeze-thaw cycles Mass loss was 6.8%, and strength loss was 28.5%.

[0067] Comparative Example 2

[0068] 1. Formulation composition: Remove nano-alumina, adjust the amount of cement to 710kg, and the rest is the same as in Example 1.

[0069] 2. Performance test results:

[0070] Table 5 Performance test results of Comparative Example 2

[0071] compressive strength -10℃ 24h 3.8MPa compressive strength -10℃ 3d 10.2MPa compressive strength -10℃ for 28 days + standard care for 28 days 35.6MPa Most possible aperture MIP testing 18.6nm Freeze-thaw resistance 300 freeze-thaw cycles Mass loss was 7.2%, and strength loss was 31.4%.

[0072] Comparative Example 3

[0073] 1. Formulation composition: Triethanolamine is removed, and the magnesium aluminum hydrotalcite is not subjected to triethanolamine organic modification treatment; the rest is the same as in Example 1.

[0074] 2. Performance test results:

[0075] Table 6 Performance test results of Comparative Example 3

[0076] Initial flowability Jumping table method 180mm (poor dispersion) compressive strength -10℃ 24h 5.6MPa compressive strength -10℃ 3d 14.8MPa compressive strength -10℃ for 28 days + standard care for 28 days 42.3MPa

[0077] Results Analysis

[0078] A comparison of Examples 1-3 and Comparative Examples 1-3 shows that:

[0079] The early and later strengths of Comparative Example 1 (without magnesium aluminum hydrotalcite) and Comparative Example 2 (without nano alumina) were significantly lower than those of the Example, and their freeze-thaw resistance was significantly reduced, proving that nano alumina and magnesium aluminum hydrotalcite have a synergistic effect and that neither can be omitted.

[0080] Comparative Example 3 (magnesium aluminum hydrotalcite without organic modification) had lower workability and strength than Example 1, indicating that organic modification can improve the dispersibility of magnesium aluminum hydrotalcite in cement systems.

[0081] The reduction in the freezeable water content in Comparative Example 1 was limited, demonstrating that the layered structure of magnesium aluminum hydrotalcite locking in free water is one of the key antifreeze mechanisms of this invention; while the most probable pore size in Comparative Example 2 was larger, indicating that nano-alumina has a significant effect on pore structure optimization.

[0082] In summary, this invention achieves good hydration hardening of cement under negative temperature conditions through the synergistic effect of nano-alumina and modified magnesium aluminum hydrotalcite, exhibiting excellent early strength and freeze-thaw resistance, without the need for traditional antifreeze agents.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite, characterized in that, It is composed of the following components in parts by weight: 600-750 parts of ordinary silicate cement, 150-250 parts of industrial aluminum ash, 40-60 parts of silica fume, 5-15 parts of nano alumina, 10-25 parts of magnesium aluminum hydrotalcite, 5-15 parts of sodium aluminate, 2-5 parts of triethanolamine, 4-8 parts of polycarboxylate superplasticizer, 1-3 parts of tartaric acid, and 230-260 parts of mixing water. The nano-alumina is α-phase nano-alumina; The magnesium-aluminum hydrotalcite underwent organic modification, specifically intercalation modification using triethanolamine.

2. The negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite according to claim 1, characterized in that, The nano-alumina has a particle size of 20-50 nm and a specific surface area ≥50 m². 2 / g.

3. The negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite according to claim 1, characterized in that, The magnesium-aluminum hydrotalcite has a magnesium-aluminum molar ratio of 2:1 to 3:

1.

4. The negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite according to claim 1, characterized in that, The industrial aluminum ash contains ≥70% Al2O3 and has a fineness ≤200 mesh. Before use, the industrial aluminum ash undergoes pretreatment such as sieving, alkali washing or water washing to remove impurities, drying, and re-grinding.

5. The negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite according to claim 1, characterized in that, The ordinary Portland cement is P·O 42.5 grade; the silica fume contains ≥95% SiO2 and has a specific surface area ≥20m². 2 / g.

6. The negative-temperature cement composite material based on nano-alumina and modified hydrotalcite according to claim 1, characterized in that, The polycarboxylate superplasticizer is a powder with a solid content of 40% and a water reduction rate of ≥30%; the sodium aluminate is industrial grade with an Al2O3 content of ≥45%.

7. A method for preparing a negative-temperature cement composite material based on nano-alumina and modified magnesium aluminum hydrotalcite as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Mix the formulated amount of nano-alumina with polycarboxylate superplasticizer and part of the mixing water, disperse in an ultrasonic dispersion device to prepare a nano-alumina dispersion suspension; (2) Mix the prescribed amount of magnesium aluminum hydrotalcite with triethanolamine and deionized water, heat to 60~80℃, stir to react, filter, dry the filter cake, grind and sieve to obtain organic modified magnesium aluminum hydrotalcite. (3) In a cold environment of -5℃ to 0℃, the formula amount of ordinary silicate cement, industrial aluminum ash, silica fume, all the organic modified magnesium aluminum hydrotalcite, sodium aluminate and tartaric acid obtained in step (2) are put into a mixer and mixed evenly to obtain dry mix. (4) Add the dry mixture obtained in step (3) to the mixer, slowly add all the nano alumina dispersion suspension obtained in step (1) and the remaining mixing water, stir quickly for 2-3 minutes, let stand for 1 minute, and then stir slowly for 1 minute to obtain cement paste, and cure at negative temperature.

8. The preparation method according to claim 7, characterized in that, In step (1), the ultrasonic dispersion time is 10-15 minutes.

9. The preparation method according to claim 7, characterized in that, In step (2), the stirring reaction time is 1 to 2 hours; the drying temperature is 80 to 100°C and the drying time is 12 to 24 hours; the sieve mesh number for grinding and sieving is 200 mesh.

10. The preparation method according to claim 7, characterized in that, In step (3), the mixing time is 10 to 15 minutes.