CN114940604A - Nano-silica modified high-tensile-strength strain hardening cement-based composite material and preparation method thereof - Google Patents
Nano-silica modified high-tensile-strength strain hardening cement-based composite material and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- 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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- 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
- C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B14/02—Granular materials, e.g. microballoons
- C04B14/04—Silica-rich materials; Silicates
- C04B14/06—Quartz; Sand
- C04B14/062—Microsilica, e.g. colloïdal silica
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- C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
- C04B40/0028—Aspects relating to the mixing step of the mortar preparation
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- 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
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- 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
- C04B2201/52—High compression strength concretes, i.e. with a compression strength higher than about 55 N/mm2, e.g. reactive powder concrete [RPC]
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Abstract
A nano silicon dioxide modified high tensile strength strain hardening cement-based composite material and a preparation method thereof are disclosed, wherein the raw materials of the composite material comprise the following components by mass: 780 parts of cement 720-containing materials, 190 parts of fly ash 170-containing materials, 190 parts of silica ash 170-containing materials, 980 parts of quartz sand 940-containing materials, 240 parts of steel fiber 220-containing materials, 20-40 parts of nano silicon dioxide, 25-30 parts of water reducing agent and 180 parts of water 170-containing materials, and the raw materials are stirred and mixed according to the parts by mass and then cured by steam to obtain the material; the cement-based composite material prepared by the invention has the advantages of compressive strength of more than 200MPa, tensile strength of more than 10MPa, strain hardening property, and capability of obviously improving the toughness of the material and reducing the tensile failure degree of the structure.
Description
Technical Field
The invention belongs to the technical field of building materials, and particularly relates to a nano-silica modified high-tensile-strength strain hardening cement-based composite material and a preparation method thereof.
Technical Field
Ultra-high performance concrete (UHPC) has been widely used in civil and defense engineering fields as a cement-based composite material having high strength and high durability. Although the compressive strength is high, the strength is low under the action of tensile load and the strain softening characteristic is mostly presented, in some national defense engineering protection structures, the structure can generate coupling failure modes such as tensile, bending and shearing due to the strong dynamic load generated by explosion, and in order to enable the structure to have higher anti-striking capability and reduce the structural damage degree, the tensile strength and the toughness of the engineering protection material need to be further improved.
Various fiber reinforced materials are commonly used in concrete materials, but most fibers show pull-out failure characteristics in the tensile failure process, rather than tensile failure, which indicates that the bonding strength of the fibers and a matrix is low, the anchoring force is insufficient, and the high tensile strength of the fibers cannot be fully utilized in the tensile failure process. Furthermore, with the increase of tensile strain, the tensile stress is reduced after the initial crack is generated on the material matrix, the strain softening phenomenon is shown, and the energy absorption in the tensile failure process is less. According to the theory related to fiber bridging, the key condition for the fiber reinforced material to generate the strain hardening characteristic is that the complementary energy of the fiber bridging is larger than the energy released by the matrix due to cracking in the stretching process, wherein the complementary energy is provided by the energy consumed by bonding and slipping between the fibers and the matrix. When the tensile strength of the matrix is improved, the energy released during cracking is increased, and higher fiber bridging and energy complementing are needed to enable the material to have the strain hardening characteristic, so that the energy absorbed in the tensile failure process is increased, and the capacity of the material for resisting external load is improved. At present, in order to realize the high tensile strength and the strain hardening characteristic of the cement-based composite material, the bridging performance between the fiber and the matrix is generally further improved, for example, the epoxy resin-nano graphite coating is used for modifying the surface of the polyvinyl alcohol fiber in the chinese patent CN108298853A, on one hand, the PVA fiber is used for the high-strength concrete, the bridging stress is insufficient, the tensile strength cannot be further improved, on the other hand, the epoxy resin-nano graphite coating process is complex, and the epoxy resin influences the hydration degree of the cement. For example, in chinese patent CN111333377A, NaOH is used to improve the intermixing effect between the steel fibers and the carbon fibers, so as to improve the bridging performance with the matrix, on one hand, the intermixing fibers can disturb the uniformity of the bulk material in the concrete and reduce the compactness of the matrix, on the other hand, the carbon fibers can generate an agglomeration effect during the blending process, and the stability cannot be ensured.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a nano-silica modified high-tensile-strength strain hardening cement-based composite material, the compactness of a matrix and the surface roughness of steel fibers are increased through the nano-silica, the peak stress of the steel fibers in the pulling-out process can be improved, the nano-silica is uniformly dispersed in the matrix through a mechanical and ultrasonic combined dispersion mode, and the bonding strength and the sliding energy consumption of the steel fibers and the matrix can be improved while the basic proportion of the cement-based composite material is not changed; so that the tensile strength of the composite material is improved and the strain hardening characteristics are exhibited.
In order to realize the purpose, the following technical scheme is adopted:
the nano-silica modified high-tensile-strength strain hardening cement-based composite material comprises the following raw materials in parts by mass: 720-780 parts of cement, 190 parts of fly ash 170-190 parts, 980 parts of silica ash 170-190 parts, 940-980 parts of quartz sand, 240 parts of steel fiber 220-40 parts, 20-30 parts of nano silicon dioxide, 25-30 parts of a water reducing agent and 180 parts of water 170-180.
Furthermore, the cement is P.O 52.5.5 type ordinary portland cement, and the technical indexes meet the requirements of the current national standards.
Further, the fly ash is grade I ash meeting the requirements of GB/T1596 fly ash for cement and concrete.
Furthermore, the average particle size of the silica fume is 0.1-0.3um, and the specific surface area is more than or equal to 15000m 2 /kg。
Furthermore, the quartz sand is refined quartz sand with the particle size of 0.1-0.3 mm.
Furthermore, the steel fiber is straight or end hook type copper-plated steel fiber, the diameter is 0.18-0.22mm, the length is 12-18mm, and the tensile strength is more than or equal to 2500 MPa.
Further, the water reducing agent is a polycarboxylate high-performance water reducing agent, and the water reducing rate is more than or equal to 30%.
Further, the particle size of the nano silicon dioxide is 20-50nm, the content of the silicon dioxide is more than or equal to 99 percent, and the specific surface area is more than or equal to 200000m 2 /kg。
A preparation method of a nano-silica modified high tensile strength strain hardening cement-based composite material comprises the following steps:
(1) the raw materials are mixed according to the mass part ratio: 780 parts of cement 720-containing materials, 190 parts of fly ash 170-containing materials, 190 parts of silica ash 170-containing materials, 980 parts of quartz sand 940-containing materials, 240 parts of steel fiber 220-containing materials, 20-40 parts of nano silicon dioxide, 25-30 parts of water reducing agent and 180 parts of water 170-containing materials, and weighing the raw materials of the components;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2000r/min-2800r/min for 5-8min, and then dispersing for 10-15min by using ultrasonic dispersion equipment with the vibration frequency of 15-20kHz to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 60-90 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 5-10min to obtain a composite material mixture;
(6) injecting the composite material mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 22-26h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 70-80 h by using steam with the temperature of 90-95 ℃, and then curing to a specified age by using a standard concrete curing method to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the nano-silica is low in price, has excellent filling effect and nucleation effect, and can be secondarily reacted with calcium hydroxide generated by cement hydration to generate calcium silicate hydrate, so that the compactness of a matrix is increased, the matrix is adhered to the surface of steel fiber, the roughness is increased, and the friction force is increased;
2. the invention selects a mechanical and ultrasonic combined dispersion mode to uniformly disperse the nano silicon dioxide in the matrix, and can improve the matrix strength and the fiber and matrix bonding performance without changing the basic proportion of the cement-based composite material. The nano silicon dioxide is used for improving the compactness of a matrix and the surface roughness of the steel fiber, improving the interface performance between the steel fiber and the cement-based composite material matrix, and improving the peak stress of the steel fiber in the pulling-out process, so that the tensile strength of the composite material is improved, and the composite material has the strain hardening characteristic.
Drawings
FIG. 1 is a stress-displacement curve under uniaxial tensile load for cement-based composites of examples and comparative examples.
FIG. 2 is a load-displacement curve of an end hook type steel fiber pulled out from an un-doped nano silica matrix monofilament.
FIG. 3 is a load-displacement curve of the end hook type steel fiber pulled out from the nano silica doped matrix monofilament.
FIG. 4 is a micro-topography of steel fibers after being pulled out of an undoped nano-silica matrix.
FIG. 5 is a micro-topography of steel fibers after being pulled out of a nano-silica doped matrix.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In all the embodiments of the invention, the cement is ordinary portland cement type P.O 52.5.5, and the technical index meets the national standard requirement. The fly ash is I-grade ash meeting the national standard requirements. The silica fume has an average particle diameter of 0.1-0.3um and a specific surface area of no less than 15000m 2 In terms of/kg. The quartz sand is refined quartz sand with the particle size of 0.1-0.3 mm. The steel fiber is copper-plated steel fiber, the diameter is 0.18-0.22mm, the length is 13-20mm, and the tensile strength is more than or equal to 2500 MPa. The water reducing agent is a polycarboxylate high-performance water reducing agent, and the water reducing rate is more than or equal to 30 percent. The particle diameter of the nano silicon dioxide is 20-50nm, the silicon dioxide content is more than or equal to 99 percent, and the specific surface area is more than or equal to 200000m 2 /kg。
Example 1
The nano-silica modified high-tensile-strength strain hardening cement-based composite material comprises the following raw materials in parts by mass: 745 parts of cement, 170 parts of fly ash, 170 parts of silica fume, 980 parts of quartz sand, 235 parts of short straight steel fibers, 23 parts of nano silicon dioxide, 25 parts of a water reducing agent and 175 parts of water.
The preparation method of the nano-silica modified high-tensile-strength strain hardening cement-based composite material specifically comprises the following steps:
(1) weighing the raw materials of the components in parts by mass: 745 parts of cement, 170 parts of fly ash, 170 parts of silica fume, 980 parts of quartz sand, 235 parts of short and straight steel fibers, 23 parts of nano silicon dioxide, 25 parts of a water reducing agent and 175 parts of water;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2000r/min for 5min, and then performing ultrasonic dispersion at the vibration frequency of 15kHz for 10min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 60 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 5min to obtain a composite material mixture; (ii) a
(6) Injecting the mixture obtained in the step (5) into a mold, covering a plastic film after vibrating and compacting to prevent water evaporation;
(7) standing for 22h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 72h by using steam with the temperature of 90 ℃, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
Example 2
The nano-silica modified high-tensile-strength strain hardening cement-based composite material comprises the following raw materials in parts by mass: 726 parts of cement, 170 parts of fly ash, 180 parts of silica fume, 970 parts of quartz sand, 235 parts of short straight steel fiber, 40 parts of nano silicon dioxide, 28 parts of water reducing agent and 175 parts of water.
The preparation method of the nano-silica modified high-tensile-strength strain hardening cement-based composite material specifically comprises the following steps:
(1) weighing the raw materials of the components in parts by mass: 726 parts of cement, 170 parts of fly ash, 180 parts of silica fume, 970 parts of quartz sand, 235 parts of short and straight steel fibers, 40 parts of nano silicon dioxide, 28 parts of a water reducing agent and 175 parts of water;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2800r/min for 8min, and then performing ultrasonic dispersion at the vibration frequency of 20kHz for 15min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 60 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 8min to obtain a composite material mixture;
(6) injecting the mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 24h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 75h by using 93 ℃ steam, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
Example 3
The nano-silica modified high-tensile-strength strain hardening cement-based composite material comprises the following raw materials in parts by mass: 745 parts of cement, 180 parts of fly ash, 180 parts of silica fume, 960 parts of quartz sand, 235 parts of end hook steel fiber, 23 parts of nano silicon dioxide, 28 parts of water reducing agent and 175 parts of water.
The preparation method of the nano-silica modified high-tensile-strength strain hardening cement-based composite material specifically comprises the following steps:
(1) weighing the raw materials of the components in parts by mass: 745 parts of cement, 180 parts of fly ash, 180 parts of silica fume, 960 parts of quartz sand, 235 parts of end hook steel fiber, 23 parts of nano silicon dioxide, 28 parts of water reducing agent and 175 parts of water;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2000r/min for 5min, and then performing ultrasonic dispersion at the vibration frequency of 15kHz for 10min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 90 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 10min to obtain a composite material mixture;
(6) injecting the mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 24h in an environment with the temperature of 20 +/-5 ℃, removing a mold, curing for 72h by using steam with the temperature of 90 ℃, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
Example 4
The nano-silica modified high-tensile-strength strain hardening cement-based composite material comprises the following raw materials in parts by mass: 726 parts of cement, 190 parts of fly ash, 190 parts of silica fume, 940 parts of quartz sand, 235 parts of end hook steel fiber, 40 parts of nano silicon dioxide, 30 parts of water reducing agent and 180 parts of water.
The preparation method of the nano-silica modified high-tensile-strength strain hardening cement-based composite material specifically comprises the following steps:
(1) weighing the raw materials of the components in parts by mass: 726 parts of cement, 190 parts of fly ash, 190 parts of silica fume, 940 parts of quartz sand, 235 parts of end hook steel fiber, 40 parts of nano silicon dioxide, 30 parts of water reducing agent and 180 parts of water;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2800r/min for 8min, and then performing ultrasonic dispersion at the vibration frequency of 20kHz for 15min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 90 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 6min to obtain a composite material mixture;
(6) injecting the mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 24h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 80h by using steam with the temperature of 95 ℃, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
Comparative example 1: the components are basically the same as those in example 1, but the nano-silica is not added, and the mass portion of the nano-silica is changed into the equivalent cement portion.
Comparative example 2: the components are basically the same as those in example 3, but the nano-silica is not added, and the mass portion of the nano-silica is changed into the equivalent cement portion.
The performance test results of the nano silica modified cement-based composite materials prepared in examples 1-4 and comparative examples 1-2 are shown in table 1 by referring to the test in the relevant regulations in the basic performance and test method for ultra-high performance concrete (T/CBMF 37-2018).
TABLE 1 basic Performance test results for Cement-based composites
| Compressive strength/MPa | Tensile strength/MPa | |
| Example 1 | 218 | 10.5 |
| Example 2 | 220 | 11.7 |
| Example 3 | 226 | 13.1 |
| Example 4 | 230 | 14.8 |
| Comparative example 1 | 188 | 8.6 |
| Comparative example 2 | 195 | 10.2 |
As can be seen from the data in Table 1, the compressive strength of the nano-silica modified cement-based composite material prepared by the method reaches more than 200MPa in 28d, and the tensile strength reaches more than 10 MPa. Fig. 1 is a stress-displacement curve under uniaxial tensile load of cement-based composites of examples and comparative examples, and it can be seen that the effects of examples 1-4 are significantly better than those of comparative examples 1-2. Comparing example 1 with comparative example 1, and example 3 with comparative example 2, it can be seen that after part of cement in the material components is replaced by nano-silica, both the compressive strength and the tensile strength are improved, the compressive strength is improved by about 15%, and the tensile strength is improved by more than 20%. The uniaxial tension process of the material in comparative example 1 shows a strain softening phenomenon, and the uniaxial tension process of the material in example 1 shows a strain hardening phenomenon due to the addition of the nano silica.
In order to further compare the improvement effect of the nano-silica on the bonding performance of the steel fiber and the matrix, fiber drawing tests are carried out aiming at the example 3 and the comparative example 2, the load and the displacement of the end hook type steel fiber in the process of drawing out the steel fiber from the matrix when the bonding length of the end hook type steel fiber and the matrix is 5mm are tested, a method of simultaneously drawing out 4 steel fibers is adopted for reducing errors during the test, the matrix materials are prepared according to the example 3 and the comparative example 2 respectively, and the steel fibers are removed during the preparation.
FIG. 2 is a load-displacement curve of steel fibers as they are pulled from the matrix material of comparative example 2, FIG. 3 is a load-displacement curve of steel fibers as they are pulled from the matrix material of example 3, FIG. 4 is a microstructure of steel fibers as they are pulled from the matrix material of comparative example 2, and FIG. 5 is a microstructure of steel fibers as they are pulled from the matrix material of example 3. Comparing fig. 2 and fig. 3, it can be seen that the peak load is effectively increased when the steel fiber is pulled out from the matrix after the nano-silica is doped. Comparing fig. 4 and fig. 5, it can be seen that a part of the nano silica is attached to the surface of the steel fiber, and the chemical adhesion and the friction of the interface can be improved after the hydration reaction.
Claims (10)
1. A nano-silica modified high tensile strength strain hardening cement-based composite material is characterized in that: the material comprises the following raw materials in parts by mass: 780 parts of cement, 190 parts of fly ash, 190 parts of silica ash, 980 parts of quartz sand, 240 parts of steel fiber, 20-40 parts of nano silicon dioxide, 25-30 parts of a water reducing agent and 180 parts of water 170.
2. The nano-silica modified high tensile strength strain hardening cement-based composite material as claimed in claim 1, wherein the cement is P.O 52.5.5 type ordinary portland cement, and the technical index meets the current national standard requirements; the fly ash is I-grade ash meeting the requirements of GB/T1596 fly ash for cement and concrete.
3. The nano-silica modified high tensile strength strain hardening cement-based composite material as claimed in claim 1, wherein the silica fume has an average particle size of 0.1-0.3um and a specific surface area of 15000m or more 2 /kg。
4. The nano-silica modified high tensile strength strain hardening cement-based composite material as claimed in claim 1, wherein the quartz sand is refined quartz sand, and the particle size is 0.1-0.3 mm.
5. The nano-silica modified high tensile strength strain hardening cement-based composite material of claim 1, wherein the steel fiber is a straight or end-hooked copper-plated steel fiber, the diameter is 0.18-0.22mm, the length is 12-18mm, and the tensile strength is more than or equal to 2500 MPa.
6. The nano-silica modified high tensile strength strain hardening cement-based composite material as claimed in claim 1, wherein the water reducing agent is a polycarboxylate high performance water reducing agent, and the water reducing rate is not less than 30%.
7. The nano-silica modified high tensile strength strain hardening cement-based composite material as claimed in claim 1, wherein the nano-silica has a particle size of 20-50nm, a silica content of 99% or more, and a specific surface area of 200000m or more 2 /kg。
8. A preparation method of a nano-silica modified high tensile strength strain hardening cement-based composite material is characterized by comprising the following steps:
(1) the raw materials are mixed according to the mass part ratio: 780 parts of cement 720-containing materials, 190 parts of fly ash 170-containing materials, 190 parts of silica ash 170-containing materials, 980 parts of quartz sand 940-containing materials, 240 parts of steel fiber 220-containing materials, 20-40 parts of nano silicon dioxide, 25-30 parts of water reducing agent and 180 parts of water 170-containing materials, and weighing the raw materials of the components;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2000r/min-2800r/min for 5-8min, and then dispersing for 10-15min by using ultrasonic dispersion equipment with the vibration frequency of 15-20kHz to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 60-90 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 5-10min to obtain a composite material mixture;
(6) injecting the composite material mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 22-26h in an environment with the temperature of 20 +/-5 ℃, then removing the mold, curing for 70-80 h by using steam with the temperature of 90-95 ℃, and then curing to a specified age by using a standard curing method of concrete to obtain the nano silicon dioxide modified high tensile strength strain hardening cement-based composite material.
9. The method for preparing the nano-silica modified high tensile strength strain hardening cement-based composite material according to claim 8, is characterized by comprising the following steps:
(1) the raw materials are mixed according to the mass part ratio: 745 parts of cement, 170 parts of fly ash, 170 parts of silica fume, 980 parts of quartz sand, 235 parts of short and straight steel fibers, 23 parts of nano silicon dioxide, 25 parts of a water reducing agent and 175 parts of water, and weighing raw materials of the components;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2000r/min for 5min, and then performing ultrasonic dispersion at the vibration frequency of 15kHz for 10min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 60 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 5min to obtain a composite material mixture;
(6) injecting the composite material mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 22h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 72h by using steam with the temperature of 90 ℃, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
10. The method for preparing the nano-silica modified high tensile strength strain hardening cement-based composite material according to claim 8, is characterized by comprising the following steps:
(1) the raw materials are mixed according to the mass part ratio: 726 parts of cement, 190 parts of fly ash, 190 parts of silica fume, 940 parts of quartz sand, 235 parts of end hook steel fiber, 40 parts of nano silicon dioxide, 30 parts of water reducing agent and 180 parts of water, and weighing raw materials of the components;
(2) performing magnetic dispersion on the weighed nano silicon dioxide and water at the rotating speed of 2800r/min for 8min, and then performing ultrasonic dispersion at the vibration frequency of 20kHz for 15min to prepare a nano silicon dioxide aqueous solution;
(3) adding the weighed water reducing agent into the nano silicon dioxide aqueous solution obtained in the step (2), and slowly and uniformly stirring to obtain a mixed solution;
(4) sequentially adding the weighed cement, silica fume, fly ash and quartz sand into a concrete mixer for stirring for 90 s;
(5) adding the mixed liquid obtained in the step (3) and the weighed steel fibers into a concrete mixer, and stirring for 6min to obtain a composite material mixture;
(6) injecting the composite material mixture obtained in the step (5) into a mould, and covering a plastic film after the mixture is vibrated to be dense to prevent water evaporation;
(7) standing for 24h in an environment with the temperature of 20 +/-5 ℃, removing the mold, curing for 80h by using steam with the temperature of 95 ℃, and then curing to the age of 28d by using a standard curing method for concrete to obtain the nano-silica modified high-tensile-strength strain hardening cement-based composite material.
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