CN113149550B - Nano carbon fiber cement-based toughened and reinforced composite material and preparation method thereof - Google Patents
Nano carbon fiber cement-based toughened and reinforced composite material and preparation method thereof Download PDFInfo
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- CN113149550B CN113149550B CN202110390779.2A CN202110390779A CN113149550B CN 113149550 B CN113149550 B CN 113149550B CN 202110390779 A CN202110390779 A CN 202110390779A CN 113149550 B CN113149550 B CN 113149550B
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
- C04B28/04—Portland cements
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
- C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength
Abstract
The invention discloses a nano carbon fiber cement-based toughening and reinforcing composite material and a preparation method thereof, wherein the composite material comprises 30.0-40.0 wt% of Portland cement, 10.5-23.0 wt% of fly ash, 8.5-14.5 wt% of silica fume, 6.2-15.0 wt% of composite expanding agent, 30.0-40.0 wt% of fine aggregate, 0.8-2.0 wt% of modified spiral nano carbon fiber and 0.1-0.5 wt% of water reducing agent. According to the invention, the methyl cellulose, the polyvinylpyrrolidone and the silane coupling agent are used for modifying the spiral nano carbon fiber, so that the spiral nano carbon fiber has better dispersibility in a cement-based material, the toughness of the cement-based material is effectively enhanced, and the generation and development of early plastic shrinkage, dry shrinkage and other non-structural cracks are controlled.
Description
Technical Field
The invention relates to the field of building materials, in particular to a nano carbon fiber cement-based toughening and reinforcing composite material and a preparation method thereof.
Background
Cement is the most common inorganic cementing material in the building material industry at present, and has excellent performances such as low price, durability, safety and stability, but the cement-based material belongs to a brittle material with large self-weight, has low tensile strength and poor toughness, is easy to generate cracks in structural engineering, and influences the service life of the material structure, so how to enhance the toughness of the cement-based material, and the improvement of the safety and the durability of cement and concrete structures is a problem that researchers in the field of building materials need to pay major attention. At present, the commonly used measure is to add materials such as fiber and polymer in the cement-based material to compound the cement-based material, thereby improving the mechanical property and controlling the cracking of the structure, but the macroscopic fiber also belongs to a brittle material, only can inhibit the development of the micro-cracks of the structure, can not inhibit the formation of the cracks on a microscopic scale, and has no obvious toughening effect on the cement-based material.
CN104446264A discloses a cement-based nanocomposite and a preparation method thereof, wherein the cement-based nanocomposite comprises the following raw materials: 1 part of Portland cement; 0.15-0.25 parts of silica fume; 0.003-0.006 part of nano CaO; nano CaCO30.01-0.02 part; nano Al2O30.005-0.01 part; 0.01 to 0% of fibrous nano calcium silicate02 parts or 0.001-0.002 part of nano carbon fiber; 325 mesh quartz powder or glass powder: 0.3-0.4 part; 0.45-0.55 part of 0.4-0.6 mm quartz sand; 0.4-0.6 parts of steel fiber; 0.015-0.025 parts of a high-performance water reducing agent; 0.18-0.25 part of water. The method mainly improves the mechanical property of the cement base material by adding fibrous nano calcium carbonate or nano carbon fiber and steel fiber. However, the steel fiber has the problems of poor construction workability in the process, fiber agglomeration or fiber breakage during stirring and vibrating, the bonding property needs to be improved and the like; and are more expensive in price than the same type of product.
Disclosure of Invention
In order to improve the comprehensive mechanical property of a cement base material on the basis of not increasing the cost, the invention provides a nano carbon fiber cement-based toughening and reinforcing composite material and a preparation method thereof. In order to achieve the purpose, the nano carbon fiber cement-based toughening and reinforcing composite material provided by the invention comprises the following components in percentage by mass: 30.0 to 40.0 percent of Portland cement, 10.5 to 23.0 percent of fly ash, 8.5 to 14.5 percent of silica fume, 6.2 to 15.0 percent of composite expanding agent, 30.0 to 40.0 percent of fine aggregate, 0.8 to 2.0 percent of modified spiral nano carbon fiber and 0.1 to 0.5 percent of water reducing agent.
The preparation method of the modified spiral carbon nanofiber comprises the following steps:
A. selecting 304 stainless steel as a substrate, taking a tin nitrate aqueous solution with the mass fraction of 50-70% as a catalyst, taking methanol or ethanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 0.9-1.5 cm, firstly controlling the temperature of the flame to be 400-500 ℃, heating for 10-15 min, and scraping off black substances by using a nonmetal appliance to obtain the single-spiral carbon nanofibers; controlling the flame temperature to be 550-650 ℃, heating for 10-15 min, and scraping black substances by using a nonmetal tool to obtain the double-helix carbon nanofibers;
B. uniformly mixing the single-spiral carbon nanofibers and the double-spiral carbon nanofibers obtained in the step A according to any mass ratio to obtain a mixture, adding the mixture into a methyl cellulose aqueous solution with the mass fraction of 5% according to the solid-to-liquid ratio of 0.03-0.05 g/mL to obtain a solution a, ultrasonically dispersing the solution a, slowly dropwise adding the solution a into a mixed solution b prepared from polyvinylpyrrolidone and a silane coupling agent according to the mass ratio of 1 (8-12), magnetically stirring for 20-24 hours at 30-50 ℃, centrifuging, and collecting solids to obtain modified spiral carbon nanofibers; wherein the mass ratio of the solution a to the mixed solution b is 1 (15-20).
The non-metal tool in the step A can be a bamboo knife, a wood knife, a ceramic knife or a high-temperature resistant plastic knife. The metal cutter is easy to melt at high temperature to generate metal scraps which are mixed into the single-spiral carbon nanofibers and the double-spiral carbon nanofibers, and the performance of the spiral carbon nanofibers is adversely affected. In the step B, the surface grafting modification effect is generated between the activated group of the polyvinylpyrrolidone and the surface of the spiral carbon nanofiber, so that the surface polarity of the spiral carbon nanofiber is increased, the self-aggregation of the spiral carbon nanofiber is reduced, and the dispersibility and the stability of the spiral carbon nanofiber in cement slurry are higher.
Preferably, the mass ratio of the single-spiral carbon nanofibers to the double-spiral carbon nanofibers is (6-1): 1.
Further preferably, the mass ratio of the single-helix nano carbon fiber to the double-helix nano carbon fiber is 3: 1.
Preferably, the diameters of the single-spiral carbon nanofiber and the double-spiral carbon nanofiber are both 60-80nm, and the screw pitches are both 120-150 nm.
Preferably, the composite expanding agent comprises a calcium sulphoaluminate-calcium oxide expanding agent and a magnesium oxide expanding agent, and the mass ratio of the calcium sulphoaluminate-calcium oxide expanding agent to the magnesium oxide expanding agent is (3:7) - (4: 1).
Preferably, the activity of the magnesium oxide expanding agent is 90 s-220 s.
Preferably, the silane coupling agent is gamma-aminopropyltriethoxysilane and/or gamma- (2, 3-glycidoxy) propyltrimethoxysilane.
Preferably, the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent.
The preparation method of any one of the carbon nanofiber cement-based toughening and reinforcing composite material comprises the following steps:
s1, stirring and mixing the portland cement, the fly ash, the silica fume, the composite expanding agent and the fine aggregate uniformly, adding the water reducing agent and the water, stirring at the rotating speed of 30-60 rpm, adding the modified spiral carbon nanofibers 3-5 times in the stirring process, increasing the stirring speed to 120-150 rpm, and stirring until the materials are uniformly mixed to obtain cement mortar containing the modified spiral carbon nanofibers;
and S2, performing mould reversing, vibration molding, curing and demoulding on the cement mortar obtained in the step S1 to obtain the nano carbon fiber cement-based toughening and reinforcing composite material.
The invention has the beneficial effects that: according to the nano carbon fiber cement-based toughening and reinforcing composite material provided by the invention, the performance of a cement-based material is improved by adding the modified spiral nano carbon fibers, and the spiral nano carbon fibers are pretreated by using methyl cellulose, a silane coupling agent and polyvinylpyrrolidone, so that the spiral nano carbon fibers have good dispersion, the crack resistance of the cement-based material can be obviously enhanced, a larger external force is required for the initial growth of cracks in concrete, and the formation of the cracks is delayed. The proper spiral carbon nanofibers matched with the silica fume can bridge the nanometer cracks in the cement-based material and fill the holes, so that the cement hydration products are better connected, and the bending strength of the cement-based material is improved.
Detailed Description
The technical solution of the present invention is described in detail and fully with reference to the following examples, it is obvious that the described examples are only a part of the examples of the present invention, and not all of the examples. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention. Any equivalent changes or substitutions by those skilled in the art according to the following embodiments are within the scope of the present invention.
Drawings
FIG. 1 is a cement-based material prepared according to a baseline control example of the present invention;
FIG. 2 is a nano carbon fiber cement-based toughened and reinforced composite material prepared in example 1;
FIG. 3 is a nano carbon fiber cement-based toughened and reinforced composite material prepared in example 5.
Example 1
The nano carbon fiber cement-based toughened and reinforced composite material comprises the following raw materials in percentage by mass: 30.0 percent of Portland cement, 10.5 percent of fly ash, 10.0 percent of silica fume, 7.5 percent of composite expanding agent, 40.0 percent of fine aggregate, 1.5 percent of modified spiral carbon nanofiber and 0.5 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 1: 1.
The modified spiral carbon nanofiber is prepared by the following method:
A. selecting 304 stainless steel with the thickness of 2cm as a substrate, taking 70% by mass of tin nitrate aqueous solution as a catalyst, taking ethanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 1.5cm, controlling the flame temperature to be 450 ℃, heating for 12min, and scraping black substances by using a bamboo knife to obtain single-spiral carbon nanofibers; and then heating to 600 ℃, heating for 12min, and scraping black substances by using a bamboo knife to obtain the double-helix carbon nanofiber.
B. Selecting 0.45g of single-spiral carbon nanofibers with the diameter of 60-80nm and the pitch of 120-150nm from the step A, selecting 0.15g of double-spiral carbon nanofibers with the diameter of 60-80nm and the pitch of 120-150nm, uniformly mixing the two fibers, adding the two fibers into 12mL of methyl cellulose aqueous solution with the mass fraction of 5% to obtain solution a, ultrasonically dispersing the solution a, slowly dripping the solution a into mixed solution b prepared from 23g of polyvinylpyrrolidone and 230g of silane coupling agent, magnetically stirring the solution b at 30 ℃ for 24 hours, centrifuging the solution, and collecting solids to obtain the modified spiral carbon nanofibers.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material comprises the following steps:
s1, stirring and mixing the portland cement, the fly ash, the silica fume, the composite expanding agent and the fine aggregate uniformly, adding the water reducing agent and the water, stirring at the rotating speed of 50rpm, adding the modified spiral carbon nanofibers for 4 times in the stirring process, increasing the stirring speed to 140rpm, and stirring until the materials are uniformly mixed to prepare cement-based slurry containing the modified spiral carbon nanofibers;
and S2, performing reverse molding, vibration molding, curing and demolding on the cement-based slurry of the modified spiral carbon nanofibers obtained in the step S1 to obtain the carbon nanofiber cement-based toughening and reinforcing composite material.
Example 2
The nano carbon fiber cement-based toughened and reinforced composite material comprises the following raw materials in percentage by mass: 30.0 percent of Portland cement, 23.0 percent of fly ash, 8.5 percent of silica fume, 6.2 percent of composite expanding agent, 30.0 percent of fine aggregate, 2.0 percent of modified spiral carbon nanofiber and 0.3 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 2: 1.
The preparation method of the modified spiral carbon nanofiber is the same as that in the embodiment 1, and the preparation method of the carbon nanofiber cement-based toughened and reinforced composite material is the same as that in the embodiment 1.
Example 3
The nano carbon fiber cement-based toughened and reinforced composite material comprises the following raw materials in percentage by mass: 40.0 percent of Portland cement, 12.0 percent of fly ash, 8.5 percent of silica fume, 8.5 percent of composite expanding agent, 30.0 percent of fine aggregate, 0.9 percent of modified spiral carbon nanofiber and 0.1 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 3: 7.
The preparation method of the modified spiral carbon nanofiber is the same as that in the embodiment 1, and the preparation method of the carbon nanofiber cement-based toughened and reinforced composite material is the same as that in the embodiment 1.
Example 4
The nano carbon fiber cement-based toughened and reinforced composite material comprises the following raw materials in percentage by mass: 35.0 percent of Portland cement, 13.0 percent of fly ash, 14.5 percent of silica fume, 6.2 percent of composite expanding agent, 30.0 percent of fine aggregate, 0.8 percent of modified spiral carbon nanofiber and 0.5 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 4: 1.
The preparation method of the modified spiral filamentous nanocarbon is the same as that of example 1.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
Example 5
The nano carbon fiber cement-based toughened and reinforced composite material comprises the following raw materials in percentage by mass: 30.0 percent of Portland cement, 10.5 percent of fly ash, 8.5 percent of silica fume, 15.0 percent of composite expanding agent, 34.5 percent of fine aggregate, 1.0 percent of modified spiral carbon nanofiber and 0.5 percent of water reducing agent. The composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 3:1, and the mass ratio of the modified single-helix carbon nanofibers to the modified double-helix carbon nanofibers in the modified spiral carbon nanofibers is 3: 1.
The preparation method of the modified spiral filamentous nanocarbon is the same as that of example 1.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
Example 6
The composition of the nano carbon fiber cement-based toughened and reinforced composite material in the embodiment is the same as that in the embodiment 1, except that:
the preparation method of the modified spiral carbon nanofiber comprises the following steps:
A. selecting 304 stainless steel with the thickness of 2cm as a substrate, taking a tin nitrate aqueous solution with the mass fraction of 50% as a catalyst, taking methanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 0.9cm, controlling the flame temperature to be 400 ℃, heating for 15min, and scraping off black substances by using a wood knife to obtain single-spiral carbon nanofibers; and then heating to 550 ℃, heating for 15min, and scraping black substances by using a wood knife to obtain the double-helix carbon nanofiber.
B. And B, uniformly mixing 0.6g of single-helix carbon nanofibers and 0.1g of double-helix carbon nanofibers obtained in the step A, adding the mixture into 21mL of methyl cellulose aqueous solution with the mass fraction of 5% to obtain solution a, ultrasonically dispersing the solution a, slowly dropwise adding the solution a into mixed solution b prepared from 36.5g of polyvinylpyrrolidone and 289g of silane coupling agent, magnetically stirring the solution b at 50 ℃ for 20 hours, centrifuging the mixture, and collecting solids to obtain the modified spiral carbon nanofibers.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is different from the preparation method of the embodiment 1 in that the nano carbon fiber cement-based toughened and reinforced composite material is stirred at the rotating speed of 30rpm in the step S1, the modified spiral nano carbon fiber is added for 5 times in the stirring process, and the stirring speed is increased to 150rpm and stirred until the mixture is uniformly mixed.
Example 7
The composition of the nano carbon fiber cement-based toughened and reinforced composite material in the embodiment is the same as that in the embodiment 1, except that:
the preparation method of the modified spiral carbon nanofiber comprises the following steps:
A. selecting 304 stainless steel with the thickness of 2cm as a substrate, taking a tin nitrate aqueous solution with the mass fraction of 60% as a catalyst, taking ethanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 1.2cm, controlling the flame temperature to be 500 ℃, heating for 10min, and scraping black substances by using a ceramic knife to obtain single-spiral carbon nanofibers; and then heating to 650 ℃, heating for 10min, and scraping black substances by using a wood knife to obtain the double-helix carbon nanofiber.
B. And B, uniformly mixing 0.25g of single-helix carbon nanofibers and 0.25g of double-helix carbon nanofibers obtained in the step A, adding the mixture into 12.5mL of methyl cellulose aqueous solution with the mass fraction of 5% to obtain a solution a, ultrasonically dispersing the solution a, slowly dropwise adding the solution a into a mixed solution b prepared from 25g of polyvinylpyrrolidone and 300g of silane coupling agent, magnetically stirring for 22 hours at 40 ℃, centrifuging, and collecting solids to obtain the modified spiral carbon nanofibers.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is different from the preparation method of the embodiment 1 in that the nano carbon fiber cement-based toughened and reinforced composite material is stirred at the rotating speed of 60rpm in the step S1, the modified spiral nano carbon fiber is added for 3 times in the stirring process, and the stirring speed is increased to 120rpm and stirred until the mixture is uniformly mixed.
Reference control example
The cement-based material of the reference comparison example comprises the following raw materials in percentage by mass: 31.5% of Portland cement, 10.5% of fly ash, 10% of silica fume, 7.5% of composite expanding agent, 40% of fine aggregate and 0.5% of water reducing agent; wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 1: 1. That is, in this comparative example, the modified helical filamentous nanocarbon was not added, compared to example 1.
The cement-based material is prepared according to the following method:
(1) after the portland cement, the fly ash, the silica fume, the expanding agent and the fine aggregate are stirred and mixed uniformly, the water reducing agent and the water are added, the mixture is stirred at the rotating speed of 50rpm for the same time as that in the embodiment 1, the stirring speed is increased to 140rpm, and the mixture is stirred until the mixture is mixed uniformly, so that cement-based slurry is prepared;
(2) and (4) performing reverse molding, vibration molding, maintenance and demolding on the cement-based slurry, and maintaining to a corresponding age according to the standard.
Comparative example 1
The nano carbon fiber cement-based toughening and reinforcing composite material of the comparative example comprises the following raw materials in percentage by mass: 30.0 percent of Portland cement, 10.5 percent of fly ash, 9.0 percent of silica fume, 7.5 percent of composite expanding agent, 40.0 percent of fine aggregate, 2.5 percent of modified spiral carbon nanofiber and 0.5 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 1: 1. That is, the present comparative example increased the amount of the modified helical filamentous nanocarbon to 2.5% as compared to example 1.
The preparation method of the modified spiral filamentous nanocarbon is the same as that of example 1.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
Comparative example 2
The nano carbon fiber cement-based toughening and reinforcing composite material of the comparative example comprises the following raw materials in percentage by mass: 31.0 percent of Portland cement, 10.5 percent of fly ash, 10.0 percent of silica fume, 7.5 percent of composite expanding agent, 40.0 percent of fine aggregate, 0.5 percent of modified spiral carbon nanofiber and 0.5 percent of water reducing agent. Wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 1: 1. That is, the present comparative example reduces the amount of the modified helical filamentous nanocarbon to 0.5% as compared to example 1.
The preparation method of the modified spiral filamentous nanocarbon is the same as that of example 1.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
Comparative example 3
The nano carbon fiber cement-based toughening and reinforcing composite material of the comparative example comprises the following raw materials in percentage by mass: 30.0% of Portland cement, 10.5% of fly ash, 10.0% of silica fume, 7.5% of composite expanding agent, 40.0% of fine aggregate, 1.5% of linear type carbon nanofiber and 0.5% of water reducing agent; wherein the composite expanding agent is formed by mixing calcium sulphoaluminate-calcium oxide and magnesium oxide according to the mass ratio of 1: 1. Namely, the linear type carbon nanofibers are used in the present comparative example instead of the modified spiral carbon nanofibers.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
Comparative example 4
The composition of the nano carbon fiber cement-based toughened and reinforced composite material of the comparative example is the same as that of the example 1. The difference is that the preparation method of the modified spiral nano carbon fiber comprises the following steps:
A. selecting 304 stainless steel with the thickness of 2cm as a substrate, taking 70% by mass of tin nitrate aqueous solution as a catalyst, taking ethanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 1.5cm, controlling the flame temperature to be 450 ℃, heating for 12min, and scraping black substances by using a bamboo knife to obtain single-spiral carbon nanofibers; and then heating to 600 ℃, heating for 12min, and scraping black substances by using a bamboo knife to obtain the double-helix carbon nanofiber.
B. And B, selecting 0.45g of single-helix nano carbon fiber with the diameter of 60-80nm and the pitch of 120-150nm from the step A, selecting 0.15g of double-helix nano carbon fiber with the diameter of 60-80nm and the pitch of 120-150nm, uniformly mixing the two fibers, adding the two fibers into 12mL of methyl cellulose aqueous solution with the mass fraction of 5%, ultrasonically dispersing, slowly dropwise adding the mixture into 253g of silane coupling agent, magnetically stirring for 24 hours at 30 ℃, centrifuging, and collecting solids to obtain the modified spiral nano carbon fiber.
The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material is the same as that of the embodiment 1.
The cement-based composite materials prepared in the embodiments 1-5, the reference control examples and the comparative examples 1-4 are subjected to performance tests, and the strength tests refer to GB/T50081-2002 Standard of mechanical property test methods of common concrete; the crack reduction coefficient evaluation is according to T/CECS 10001-2019 anti-cracking and anti-permeability composite material used in concrete, and the test results are shown in Table 1 and figure 1.
TABLE 1 Cement-based composites Performance test results
From the test results in the table, it can be seen that, compared with the reference comparison example, the modified spiral carbon nanofibers added in the examples 1 to 5 can significantly improve the compressive strength and the flexural strength of the cement-based composite material and greatly reduce cracks. Compared with comparative examples 1 and 2, the addition amount of the modified spiral carbon nanofibers is controlled within a proper range, so that the compression resistance can be improved, the breaking strength can be improved, and the crack coefficient can be reduced; when the addition amount of the modified spiral carbon nanofibers is too much, although the crack coefficient can be obviously reduced, the adverse effect on the resistance to pressure is also generated; when the addition amount of the modified spiral carbon nanofibers is too small, the adverse effect on the compressive strength is controlled, but the improvement on the flexural strength and the crack resistance is not obvious. Compared with the comparative example 3, the modified spiral carbon nanofibers of the example have more obvious comprehensive improvement effect on the compressive strength, the breaking strength and the cracking resistance of the cement-based composite material. Compared with the comparative example 4, the modified spiral carbon nanofibers prepared by adding polyvinylpyrrolidone in the example have more remarkable improvement on the comprehensive mechanical properties of the cement-based composite material. This shows that only the spiral carbon nanofibers prepared by the modification method of the present invention can achieve the best effect on the improvement of the comprehensive mechanical properties of the cement-based composite material when used within the scope of the present invention. As can be seen from FIGS. 1 to 3, the cement-based composite materials prepared in examples 1 and 5 have almost no macroscopic cracks, while the cement-based composite materials prepared in the reference control example have more obvious macroscopic cracks.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The present invention may be subject to various modifications and changes by any person skilled in the art. Any simple equivalent changes and modifications made in accordance with the protection scope of the present application and the content of the specification are intended to be included within the protection scope of the present invention.
Claims (9)
1. The nano carbon fiber cement-based toughened and reinforced composite material is characterized by comprising the following components in percentage by mass: 30.0 to 40.0 percent of Portland cement, 10.5 to 23.0 percent of fly ash, 8.5 to 14.5 percent of silica fume, 6.2 to 15.0 percent of composite expanding agent, 30.0 to 40.0 percent of fine aggregate, 0.8 to 2.0 percent of modified spiral nano carbon fiber and 0.1 to 0.5 percent of water reducing agent;
the preparation method of the modified spiral carbon nanofiber comprises the following steps:
A. selecting 304 stainless steel as a substrate, taking a tin nitrate aqueous solution with the mass fraction of 50-70% as a catalyst, taking methanol or ethanol flame as a heat source and a carbon source, controlling the distance between the substrate and the flame to be 0.9-1.5 cm, firstly controlling the temperature of the flame to be 400-500 ℃, heating for 10-15 min, and scraping off black substances by using a nonmetal appliance to obtain the single-spiral carbon nanofibers; controlling the flame temperature to be 550-650 ℃, heating for 10-15 min, and scraping black substances by using a nonmetal tool to obtain the double-helix carbon nanofibers;
B. uniformly mixing the single-spiral carbon nanofibers and the double-spiral carbon nanofibers obtained in the step A according to any mass ratio to obtain a mixture, adding the mixture into a methyl cellulose aqueous solution with the mass fraction of 5% according to the solid-to-liquid ratio of 0.03-0.05 g/mL to obtain a solution a, ultrasonically dispersing the solution a, slowly dropwise adding the solution a into a mixed solution b prepared from polyvinylpyrrolidone and a silane coupling agent according to the mass ratio of 1 (8-12), magnetically stirring for 20-24 hours at 30-50 ℃, centrifuging, and collecting solids to obtain modified spiral carbon nanofibers; wherein the mass ratio of the solution a to the mixed solution b is 1 (15-20).
2. The nano carbon fiber cement-based toughening and reinforcing composite material as claimed in claim 1, wherein the mass ratio of the single-helix nano carbon fiber to the double-helix nano carbon fiber is (6-1): 1.
3. The nano carbon fiber cement-based toughening and reinforcing composite material as claimed in claim 2, wherein the mass ratio of the single-helix nano carbon fiber to the double-helix nano carbon fiber is 3: 1.
4. The nano carbon fiber cement-based toughening and reinforcing composite material as claimed in claim 1, wherein the diameters of the modified single-helix nano carbon fiber and the modified double-helix nano carbon fiber are both 60-80nm, and the screw pitches are both 120-150 nm.
5. The nanocarbon fiber cement-based toughening and reinforcing composite material according to claim 1, wherein the composite expanding agent comprises a calcium sulphoaluminate-calcium oxide expanding agent and a magnesium oxide expanding agent, and the mass ratio of the calcium sulphoaluminate-calcium oxide expanding agent to the magnesium oxide expanding agent is (3:7) - (4: 1).
6. The nano carbon fiber cement-based toughening and reinforcing composite material as claimed in claim 5, wherein the activity of the magnesia expansive agent is 90 s-220 s.
7. The nano carbon fiber cement-based toughening and reinforcing composite material as claimed in claim 1, wherein the silane coupling agent is gamma-aminopropyltriethoxysilane and/or gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane.
8. The nano carbon fiber cement-based toughening and reinforcing composite material according to claim 1, wherein the water reducing agent is a polycarboxylic acid type high-efficiency water reducing agent.
9. The preparation method of the nano carbon fiber cement-based toughened and reinforced composite material as claimed in any one of claims 1 to 8, characterized in that the preparation method comprises the following steps:
s1, stirring and mixing the portland cement, the fly ash, the silica fume, the composite expanding agent and the fine aggregate uniformly, adding the water reducing agent and the water, stirring at the rotating speed of 30-60 rpm, adding the modified spiral carbon nanofibers 3-5 times in the stirring process, increasing the stirring speed to 120-150 rpm, and stirring until the materials are uniformly mixed to obtain cement mortar containing the modified spiral carbon nanofibers;
and S2, performing mould reversing, vibration molding, curing and demoulding on the cement mortar obtained in the step S1 to obtain the nano carbon fiber cement-based toughening and reinforcing composite material.
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