Environment-friendly green cement as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of cement, and particularly relates to environment-friendly green cement as well as a preparation method and application thereof. The cement provided by the invention is prepared from the following components in parts by weight: 180 to 240 parts of cement; 120 to 160 parts of silica fume; 40 to 80 parts of quartz sand; 6 to 12 parts of a MgAl-LDH (at) CNTs composite material; 15 to 25 parts of a halloysite nanotube; 4 to 8 parts of acid modified silicon nitride nanofiber; 8-12 parts of a water reducing agent; 4-8 parts of a dispersant; and 160 to 200 parts of water. The MgAl-LDH is loaded on the surfaces of the CNTs in situ, agglomeration caused by excessive winding between the CNTs is reserved, dispersion of the MgAl-LDH and the CNTs in the cement is promoted, improvement of the mechanical property of the cement is promoted, meanwhile, the halloysite nanotubes and the acid-modified silicon nitride nanofibers are matched, the comprehensive performance of the cement is effectively improved, and the cement has the good application prospect. Therefore, the composite material can be widely applied to building exterior walls.

Description

Technical Field

[0001] This invention belongs to the field of cement technology. More specifically, it relates to an environmentally friendly green cement, its preparation method, and its application. Background Technology

[0002] Cement-based materials are characterized by low cost, abundant raw materials, simple production, and excellent compressive strength, making them a core material in modern construction engineering. However, traditional cement concrete materials have limited functionality and poor toughness, and are prone to plastic deformation and shrinkage during curing and use, leading to defects such as cracking and outer layer peeling, accelerating material corrosion and aging, and affecting the lifespan of projects. To address this, researchers have developed various fiber-reinforced cement-based composite materials (FRCs) using ordinary cement as the matrix and various fibers as reinforcements through a composite process, to meet the new material requirements of modern construction.

[0003] Hydrotalcite-like materials are two-dimensional nanomaterials. In recent years, there has been increasing research on the application of hydrotalcite-like materials as a novel admixture in cement. Adding hydrotalcite to cement can improve the porosity of cement paste by promoting cement hydration and filling effect. It can promote early hydration of cement and improve early strength, and can also act as a filler to optimize the pore structure of cement paste and thus improve later strength. In other words, it can improve the compressive strength and flexural strength of cement as a whole.

[0004] CN117209228A discloses a high-ductility cement-based composite material, comprising, by weight, 20-30 parts silicate cement, 25-45 parts fly ash, 10-20 parts mineral powder, 1-2 parts PP fiber, 0.5-1 part polycarboxylate superplasticizer, 1-10 parts 40-70 mesh quartz sand, 5-10 parts 70-100 mesh quartz sand, 0.1-0.5 parts polyacrylamide, and 15-20 parts water; wherein the modified PP fiber is produced by nano-calcium carbonate, nano-... PP fibers modified with silica and coupling agents; the preparation method includes the following steps: weighing silicate cement, fly ash, mineral powder, quartz sand and polyacrylamide respectively and mixing them in proportion to obtain a dry mixture; then adding polycarboxylate high-performance water-reducing agent and water to the dry mixture in at least two portions and stirring; finally adding modified PP fibers and continuing to stir to obtain a cement-based composite material; it not only has excellent mechanical properties, which can improve the strength and durability of the structure, but also has high ductility and high strength.

[0005] CN120535224A discloses a low-carbon emission masonry cement made entirely from solid waste and its preparation method. The method includes: first, finely grinding iron tailings, carbide slag, fly ash, and silica fume, and proportioning them according to a design to obtain cement raw materials; second, forming the cement raw materials into briquettes or pellets, and calcining them at a designed temperature to obtain cement clinker; and third, mixing the cement clinker with a certain proportion of gypsum and grinding it to the target fineness to obtain masonry cement. This invention utilizes all solid waste to prepare masonry cement, with the calcium source mainly provided by low-carbon emission carbide slag. Compared to cement made from calcium sources such as calcium carbonate, carbon emissions are significantly reduced. This invention achieves the goal of high-value and green utilization of various solid wastes, including iron tailings. The prepared masonry cement meets the national standards for compressive strength, sulfur trioxide content, and sieve residue. Furthermore, using all solid waste raw materials to prepare masonry cement reduces the preparation cost.

[0006] CN120535279A discloses a method for preparing low-carbon magnesium phosphate cement, comprising the following raw materials in the following percentage proportions: 40-50 parts magnesium oxide, 20-30 parts phosphate, 1-2 parts retarder, 6-8 parts quartz powder, 1-3 parts glass fiber, 0.5-1.5 parts polypropylene fiber, 1-3 parts steel fiber, 10-20 parts slag powder, 5-15 parts silica fume, 1-2 parts nano-silica, 0.5-1.5 parts nano-alumina, and 4-6 parts additives. This method for preparing low-carbon magnesium phosphate cement reduces the need for high-cost raw materials by introducing cheaper mineral admixtures or industrial waste as partial substitutes. It allows the use of waste materials such as fly ash and slag to replace some expensive raw materials, thus reducing production costs and promoting resource recycling. Furthermore, to overcome the problem of strength reduction in water in traditional low-carbon magnesium phosphate cement, special retarder, stabilizer, and other modifying materials are added to effectively inhibit the dissolution of hydration products in water.

[0007] CN119859028A discloses a high-strength, retarded magnesium phosphate cement, its preparation method, and its application, belonging to the field of magnesium phosphate cement technology. The high-strength, retarded magnesium phosphate cement provided by this invention comprises, by weight, the following raw materials: 60-95 parts of reburned magnesium oxide powder, 20-50 parts of phosphate, 3-15 parts of composite retarder, 5-20 parts of admixture, 8-14 parts of fly ash microspheres, 1-2 parts of carbon nanotubes, 1-5 parts of carbon fiber, and 5-30 parts of water; the composite retarder includes sodium tripolyphosphate, zinc acetate, disodium EDTA, and polyacrylic acid; the admixture includes phosphorus slag powder and silica fume. The results of the embodiments show that the setting time of the high-strength, retarded magnesium phosphate cement provided by this invention is controllable between tens of minutes and tens of hours, while the 28-day compressive strength of the magnesium phosphate cement is >90 MPa, exhibiting excellent mechanical properties.

[0008] Adding fibers to cement can improve its mechanical properties. Based on the above, this invention provides an environmentally friendly green cement with excellent mechanical properties. Summary of the Invention

[0009] The technical problem this invention aims to solve is to overcome the defects and shortcomings of existing technologies and provide an environmentally friendly green cement, its preparation method, and its application. By weight, the cement comprises the following components: 180-240 parts cement; 120-160 parts silica fume; 40-80 parts quartz sand; 6-12 parts MgAl-LDH@CNTs composite material; 15-25 parts halloysite nanotubes; 4-8 parts acid-modified silicon nitride nanofibers; 8-12 parts water-reducing agent; 4-8 parts dispersant; and 160-200 parts water. This invention, by in-situ loading MgAl-LDH onto the surface of CNTs, preserves the excessive entanglement and agglomeration caused by CNTs while promoting the dispersion of MgAl-LDH and CNTs in the cement, thereby improving the mechanical properties of the cement. Simultaneously, the combination of halloysite nanotubes and acid-modified silicon nitride nanofibers effectively improves the overall performance of the cement, enabling its widespread application in building exterior walls.

[0010] The purpose of this invention is to provide an environmentally friendly green cement.

[0011] Another objective of this invention is to provide a method for preparing environmentally friendly green cement.

[0012] Another objective of this invention is the application of environmentally friendly green cement in building exterior walls.

[0013] The above-mentioned objective of this invention is achieved through the following technical solution:

[0014] An environmentally friendly green cement, by weight, comprises the following components:

[0015] 180-240 parts cement;

[0016] 120-160 parts silica fume;

[0017] 40-80 parts of quartz sand;

[0018] 6-12 parts of MgAl-LDH@CNTs composite material;

[0019] 15-25 parts of halloysite nanotubes;

[0020] 4-8 parts of acid-modified silicon nitride nanofibers;

[0021] 8-12 parts of water-reducing agent;

[0022] 4-8 parts of dispersant;

[0023] 160-200 parts water.

[0024] In this invention, in a preferred embodiment, the silica fume has a particle size of 60~120μm; the silicon nitride nanofibers are 4~8mm in diameter and have an aspect ratio of 100~200:1.

[0025] In a further preferred embodiment of the present invention, the preparation method of the MgAl-LDH@CNTs composite material includes the following steps:

[0026] (1) CNTs were ultrasonically dispersed in nitric acid solution, treated in a water bath, cooled to room temperature, filtered, washed, and dried to obtain acid-modified CNTs;

[0027] (2) Disperse the acid-modified CNTs, magnesium salt and aluminum salt obtained in step (1) into deionized water, stir, then add urea, continue stirring, then carry out hydrothermal reaction, cool to room temperature, filter, wash and dry to obtain MgAl-LDH@CNTs composite material.

[0028] Furthermore, in step (1), the concentration of the nitric acid solution is 2-4 mol / L; the water bath treatment is performed at 30-50°C for 1-3 hours; and the drying is performed at 80-100°C for 12-18 hours.

[0029] Furthermore, in step (2), the magnesium salt is at least one of magnesium nitrate, magnesium chloride, and magnesium acetate; the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum acetate; and the ratio of the acid-modified CNTs, magnesium salt, aluminum salt, and urea is 100g:1 mol; 1~3mol:10~14mol.

[0030] Furthermore, in step (2), the stirring time is 20-40 min, the continued stirring time is 10-30 min, the hydrothermal reaction conditions are 120-140℃ for 3-7 h, and the drying is 80-100℃ for 12-18 h.

[0031] In a further preferred embodiment of the present invention, the method for preparing the acid-modified silicon nitride nanofibers includes the following steps: ultrasonically dispersing CNTs in a nitric acid solution, water bath treatment; cooling to room temperature, filtering, washing, and drying to obtain acid-modified silicon nitride nanofibers.

[0032] Furthermore, the concentration of the nitric acid solution is 2–4 mol / L; the water bath treatment conditions are water bath treatment at 40–60℃ for 2–4 hours; and the drying is drying at 80–100℃ for 10–20 hours.

[0033] Based on the above-described method for preparing environmentally friendly green cement, the preparation method includes the following steps:

[0034] Cement, silica fume, quartz sand, water-reducing agent, and dispersant are dispersed in water and stirred at 400-600 rpm for 30-50 minutes. Then, MgAl-LDH@CNTs composite material, halloysite nanotubes, and acid-modified silicon nitride nanofibers are added, and stirring is continued for 10-30 minutes to obtain environmentally friendly green cement.

[0035] The above describes the application of environmentally friendly green cement in building exterior walls.

[0036] The present invention has the following beneficial effects:

[0037] This invention loads MgAl-LDH onto the surface of CNTs in situ, thus preserving the excessive entanglement and agglomeration caused by CNTs while promoting the dispersion of MgAl-LDH and CNTs in cement, thereby improving the mechanical properties of cement. Compared with physical mixing, the performance is superior. MgAl-LDH can improve the porosity of cement paste by promoting cement hydration and filling effect, thus improving the mechanical properties of cement. At the same time, combined with halloysite nanotubes and acid-modified silicon nitride nanofibers, the overall performance of cement is effectively improved, making it widely used in building exterior wall applications. Detailed Implementation

[0038] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0039] The cement used in this invention is PII52.5 cement; the water-reducing agent is H-4005 type polycarboxylate superplasticizer; and the dispersant is B193.

[0040] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0041] Example 1

[0042] An environmentally friendly green cement, by weight, comprises the following components:

[0043] 220 parts cement;

[0044] 140 parts of silica fume; the particle size of the silica fume is 100 μm.

[0045] 60 parts of quartz sand; the particle size of the quartz sand is 8 μm;

[0046] 10 parts of MgAl-LDH@CNTs composite material;

[0047] 20 portions of halloysite nanotubes;

[0048] Six parts of acid-modified silicon nitride nanofibers; the silicon nitride nanofibers are 6 mm in diameter and have an aspect ratio of 150:1.

[0049] 10 parts water-reducing agent;

[0050] 6 parts dispersant;

[0051] 180 portions of water;

[0052] The preparation method of MgAl-LDH@CNTs composite material includes the following steps:

[0053] (1) 100g of CNTs were ultrasonically dispersed in 100mL of 3mol / L nitric acid solution and treated in a water bath at 40℃ for 2h; cooled to room temperature, filtered, washed, and dried at 90℃ for 16h to obtain acid-modified CNTs;

[0054] (2) Disperse 100g of acid-modified CNTs obtained in step (1), 1mol of magnesium nitrate and 2mol of aluminum chloride into 250mL of deionized water, stir for 30min, then add 12mol of urea, continue stirring for 20min, then hydrothermally react at 130℃ for 5h, cool to room temperature, filter, wash, and dry at 90℃ for 14h to obtain MgAl-LDH@CNTs composite material.

[0055] The preparation method of the acid-modified silicon nitride nanofibers includes the following steps: 100g of CNTs are ultrasonically dispersed in 100mL of 3mol / L nitric acid solution, and treated in a water bath at 50℃ for 3h; cooled to room temperature, filtered, washed, and dried at 90℃ for 16h to obtain acid-modified silicon nitride nanofibers.

[0056] A method for preparing environmentally friendly green cement includes the following steps:

[0057] PII52.5 cement, silica fume, quartz sand, water-reducing agent and dispersant are dispersed in water and stirred at 500 rpm for 40 min. Then, MgAl-LDH@CNTs composite material, halloysite nanotubes and acid-modified silicon nitride nanofibers are added and stirred for another 20 min to obtain environmentally friendly green cement.

[0058] Example 2

[0059] An environmentally friendly green cement, by weight, comprises the following components:

[0060] 240 parts cement;

[0061] 120 parts silica fume; the particle size of the silica fume is 60 μm.

[0062] 80 parts of quartz sand; the particle size of the quartz sand is 12 μm;

[0063] Six parts of MgAl-LDH@CNTs composite material;

[0064] 25 portions of halloysite nanotubes;

[0065] Four parts of acid-modified silicon nitride nanofibers; the silicon nitride nanofibers are 4 mm in diameter and have an aspect ratio of 100:1.

[0066] 12 parts water-reducing agent;

[0067] 4 parts dispersant;

[0068] 200 parts water;

[0069] The preparation method of MgAl-LDH@CNTs composite material includes the following steps:

[0070] (1) 100g CNTs were ultrasonically dispersed in 100mL of 4mol / L nitric acid solution and treated in a water bath at 50℃ for 1h; cooled to room temperature, filtered, washed, and dried at 100℃ for 12h to obtain acid-modified CNTs;

[0071] (2) Disperse 100g of acid-modified CNTs obtained in step (1), 1mol of magnesium chloride and 3mol of aluminum acetate into 250mL of deionized water, stir for 20min, then add 14mol of urea, continue stirring for 10min, then hydrothermally react at 140℃ for 3h, cool to room temperature, filter, wash, and dry at 100℃ for 12h to obtain MgAl-LDH@CNTs composite material.

[0072] The preparation method of the acid-modified silicon nitride nanofibers includes the following steps: 100g of CNTs are ultrasonically dispersed in 100mL of 4mol / L nitric acid solution and treated in a water bath at 60℃ for 2h; cooled to room temperature, filtered, washed, and dried at 100℃ for 10h to obtain acid-modified silicon nitride nanofibers.

[0073] The preparation method of an environmentally friendly green cement is the same as that in Example 1.

[0074] Example 3

[0075] An environmentally friendly green cement, by weight, comprises the following components:

[0076] 180 parts cement;

[0077] 160 parts of silica fume; the particle size of the silica fume is 120 μm.

[0078] 40 parts of quartz sand; the particle size of the quartz sand is 4 μm;

[0079] 12 parts of MgAl-LDH@CNTs composite material;

[0080] 15 portions of halloysite nanotubes;

[0081] Eight parts of acid-modified silicon nitride nanofibers; the silicon nitride nanofibers are 8 mm in diameter and have an aspect ratio of 200:1.

[0082] 8 parts water-reducing agent;

[0083] 8 parts dispersant;

[0084] 160 portions of water;

[0085] The preparation method of MgAl-LDH@CNTs composite material includes the following steps:

[0086] (1) 100g of CNTs were ultrasonically dispersed in 100mL of 2mol / L nitric acid solution and treated in a water bath at 30℃ for 3h; cooled to room temperature, filtered, washed, and dried at 80℃ for 18h to obtain acid-modified CNTs;

[0087] (2) Disperse 100g of acid-modified CNTs obtained in step (1), 1 mol of magnesium acetate and 1 mol of aluminum nitrate into 250mL of deionized water, stir for 40min, then add 10mol of urea, continue stirring for 30min, then hydrothermally react at 120℃ for 7h, cool to room temperature, filter, wash, and dry at 80℃ for 18h to obtain MgAl-LDH@CNTs composite material.

[0088] The preparation method of the acid-modified silicon nitride nanofibers includes the following steps: 100g of CNTs are ultrasonically dispersed in 100mL of 2mol / L nitric acid solution and treated in a water bath at 40℃ for 4h; cooled to room temperature, filtered, washed, and dried at 80℃ for 20h to obtain acid-modified silicon nitride nanofibers.

[0089] The preparation method of an environmentally friendly green cement is the same as that in Example 1.

[0090] Comparative Example 1

[0091] Except for the differences, Comparative Example 1 is the same as Example 1, except that the preparation method of the MgAl-LDH and CNTs composite material includes the following steps:

[0092] (1) 100g of CNTs were ultrasonically dispersed in 100mL of 3mol / L nitric acid solution and treated in a water bath at 40℃ for 2h; cooled to room temperature, filtered, washed, and dried at 90℃ for 16h to obtain acid-modified CNTs;

[0093] (2) Disperse 1 mol magnesium nitrate and 2 mol aluminum chloride into 250 mL of deionized water, stir for 30 min, then add 12 mol urea, continue stirring for 20 min, then hydrothermally react at 130 °C for 5 h, cool to room temperature, filter, wash, and dry at 90 °C for 14 h to obtain MgAl-LDH composite material;

[0094] (3) 100g of acid-modified CNTs obtained in step (1) and MgAl-LDH composite material obtained in step (2) were ultrasonically dispersed into 100mL of deionized water, filtered, and dried at 90℃ for 14h to obtain MgAl-LDH and CNTs composite material.

[0095] Comparative Example 2

[0096] Except for the differences, Comparative Example 2 is the same as Example 1, except that an equal amount of acid-modified CNTs is used to replace the MgAl-LDH@CNTs composite material, wherein the acid-modified CNTs are exactly the same as the acid-modified CNTs in Example 1.

[0097] Comparative Example 3

[0098] Except for the differences, Comparative Example 3 is the same as Example 1, except that an equal amount of basalt fiber is used to replace the CNTs in Example 1, and a MgAl-LDH@basalt fiber composite material is prepared.

[0099] Comparative Example 4

[0100] Except for the differences, Comparative Example 4 is the same as Example 1, except that the acid modification of silicon nitride nanofibers is omitted.

[0101] Comparative Example 5

[0102] Except for the differences, Comparative Example 5 is the same as Example 1, except that an equal amount of halloysite nanotubes are used to replace the MgAl-LDH@CNTs composite material.

[0103] Comparative Example 6

[0104] Except for the differences, Comparative Example 6 is the same as Example 1, except that an equal amount of halloysite nanotubes are used to replace the acid-modified silicon nitride nanofibers.

[0105] The performance of Examples 1-3 and Comparative Examples 1-6 was tested, and the specific test results are shown in Table 1:

[0106] In particular, according to (GB / T 50081-2019), the 28-day compressive strength and flexural strength of high-performance concrete were measured.

[0107] Table 1:

[0108] Compressive strength / MPa Flexural strength / MPa Example 1 157.9 15.1 Example 2 155.8 14.6 Example 3 156.2 14.9 Comparative Example 1 150.3 13.8 Comparative Example 2 145.3 13.2 Comparative Example 3 154.5 14.4 Comparative Example 4 153.6 14.2 Comparative Example 5 139.8 12.5 Comparative Example 6 141.3 12.7

[0109] As shown in Table 1, the environmentally friendly green cement prepared by this invention possesses strong mechanical properties, with a maximum compressive strength of 157.9 MPa and a maximum flexural strength of 15.1 MPa. In summary, the cement prepared by this invention exhibits excellent comprehensive performance, making it widely applicable in building exterior wall applications.

[0110] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An environmentally friendly green cement, characterized in that: The cement comprises the following components in parts by weight: 180-240 parts cement; 120-160 parts silica fume; 40-80 parts of quartz sand; 6-12 parts of MgAl-LDH@CNTs composite material; 15-25 parts of halloysite nanotubes; 4-8 parts of acid-modified silicon nitride nanofibers; 8-12 parts of water-reducing agent; 4-8 parts of dispersant; 160-200 parts water.

2. The environmentally friendly green cement according to claim 1, characterized in that: The silica fume has a particle size of 60~120μm; the silicon nitride nanofibers are 4~8mm in diameter and have an aspect ratio of 100~200:

1.

3. The environmentally friendly green cement according to claim 1, characterized in that: The preparation method of the MgAl-LDH@CNTs composite material includes the following steps: (1) CNTs were ultrasonically dispersed in nitric acid solution, treated in a water bath, cooled to room temperature, filtered, washed, and dried to obtain acid-modified CNTs; (2) Disperse the acid-modified CNTs, magnesium salt and aluminum salt obtained in step (1) into deionized water, stir, then add urea, continue stirring, then carry out hydrothermal reaction, cool to room temperature, filter, wash and dry to obtain MgAl-LDH@CNTs composite material.

4. The environmentally friendly green cement according to claim 3, characterized in that: In step (1), the concentration of the nitric acid solution is 2-4 mol / L; the water bath treatment is performed at 30-50℃ for 1-3 hours; and the drying is performed at 80-100℃ for 12-18 hours.

5. The environmentally friendly green cement according to claim 3, characterized in that: In step (2), the magnesium salt is at least one of magnesium nitrate, magnesium chloride, and magnesium acetate; the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum acetate; and the ratio of the acid-modified CNTs, magnesium salt, aluminum salt, and urea is 100g:1 mol; 1~3mol:10~14mol.

6. The environmentally friendly green cement according to claim 3, characterized in that: In step (2), the stirring time is 20-40 min, the continued stirring time is 10-30 min, the hydrothermal reaction conditions are 120-140℃ for 3-7 h, and the drying is 80-100℃ for 12-18 h.

7. The environmentally friendly green cement according to claim 1, characterized in that: The method for preparing the acid-modified silicon nitride nanofibers includes the following steps: ultrasonically dispersing CNTs in a nitric acid solution, water bath treatment; cooling to room temperature, filtering, washing, and drying to obtain acid-modified silicon nitride nanofibers.

8. The environmentally friendly green cement according to claim 7, characterized in that: The concentration of the nitric acid solution is 2-4 mol / L; the water bath treatment is carried out at 40-60℃ for 2-4 hours; and the drying is carried out at 80-100℃ for 10-20 hours.

9. A method for preparing environmentally friendly green cement according to any one of claims 1-8, characterized in that: The preparation method includes the following steps: Cement, silica fume, quartz sand, water-reducing agent, and dispersant are dispersed in water and stirred at 400-600 rpm for 30-50 minutes. Then, MgAl-LDH@CNTs composite material, halloysite nanotubes, and acid-modified silicon nitride nanofibers are added, and stirring is continued for 10-30 minutes to obtain environmentally friendly green cement.

10. The application of an environmentally friendly green cement as described in any one of claims 1-8 in building exterior walls.