CN110526608B

CN110526608B - Nano silicon dioxide-carbon nano tube composite material with core-shell structure, cement containing nano silicon dioxide-carbon nano tube composite material and preparation method of cement

Info

Publication number: CN110526608B
Application number: CN201910514387.5A
Authority: CN
Inventors: 李�浩; 师永民; 陈佳辉; 焦智奕; 王忠宇
Original assignee: Shaanxi University of Science and Technology
Current assignee: Shaanxi University of Science and Technology
Priority date: 2019-06-14
Filing date: 2019-06-14
Publication date: 2022-03-01
Anticipated expiration: 2039-06-14
Also published as: CN110526608A

Abstract

The invention utilizes nano-silica, carbon nano-tube and trifluoropropyl trimethyl siloxane to prepare an elastic nano-silica-carbon nano-tube core-shell structure; the structure is added into the existing cement material to prepare the high-performance cement-based composite material. The main mechanism is as follows: the activated nano silicon dioxide can promote the hydrolysis of trifluoropropyl trimethyl siloxane and the condensation reaction with the trifluoropropyl trimethyl siloxane, so that a nano silicon dioxide-carbon nano tube core-shell structure is formed by uniformly attaching the nano silicon dioxide-carbon nano tube core-shell structure on the surface of the carbon nano tube, and the nano silicon dioxide-carbon nano tube core-shell structure is an irregular ellipsoid with the length of 3-12 mu m and the diameter of 2-10 mu m. The cement-based composite material containing the activated nano silicon dioxide-carbon nanotube core-shell structure has higher mechanical strength, dielectric constant and contact angle, better durability and corrosion resistance and lower resistivity; the chemical characterization reveals the appearance and nucleation mode of the core-shell structure and the influence mechanism of the core-shell structure on the cement hydration structure and hydration products.

Description

Nano silicon dioxide-carbon nano tube composite material with core-shell structure, cement containing nano silicon dioxide-carbon nano tube composite material and preparation method of cement

Technical Field

The invention relates to the technical field of silicate materials, in particular to a high-performance cement-based composite material containing a nano silicon dioxide-carbon nano tube elastic core-shell structure and a forming method.

Background

At present, the concrete material is used as a building material with the largest use amount and the widest application range in the world, and is widely applied to engineering construction of bridges, tunnels, dams, railways, wharfs and the like due to the excellent structural performance of the concrete material. The preparation of high environmental protection performance and intelligent materials by using concrete is more and more concerned by the scientific community, the strength, durability, corrosion resistance and heat conduction and electric conductivity of the materials become technical problems to be solved urgently, and higher requirements are provided for the freeze-thaw resistance of the concrete in high and cold regions. Nanomaterials have the property of improving the above properties, and nanomaterials with particle sizes in the range of 1-100nm are now commercially used in many applications. The large surface area of the nanomaterial makes it highly reactive and highly impact to improve cement slurry properties such as good early strength, reduced permeability, accelerated cement hydration and control of fluid loss. Indeed, due to the large surface area of the nanoparticles, the production of more Calcium Silicate Hydrate (CSH) and less calcium hydroxide is promoted in the presence of the nanoparticles. This effect makes the concrete material more dense and compact. Professor Mehta, a cement concrete expert well known as early as 90 s in the 20 th century, has pointed out that chloride ion corrosion from marine environments, salinized soil areas and deicing is one of the main causes of concrete reinforcement corrosion. The corrosion of chloride ions can damage the steel bar passive film to cause the corrosion of the steel bars, so that the performance of the steel bars is degraded, and the service life of the reinforced concrete structure is further shortened. At present, the main mature technologies for improving the durability of a concrete structure in a chloride corrosion environment comprise the steps of adopting low water-cement ratio, high-performance concrete and the like, improving the thickness of a concrete protective layer, spraying the protective layer on a concrete surface layer, and using corrosion-resistant reinforcing steel bars. Furthermore, carbon nanotubes have a high thermal conductivity and a relatively low density, which has led to the attention of researchers to optimize the thermal performance of buildings and outdoor thermal comfort conditions for the thermal performance of concrete materials. In cold regions, freezing and thawing of the residual water in the concrete pores can lead to swelling, cracking, scaling and fragmentation of the road concrete. Road ice formed by rainfall in freezing environments creates almost zero friction conditions for vehicle tires, increasing injury and mortality, and thus, the freeze-thaw resistance of concrete materials is particularly important. In addition, the further potential of these materials, such as electrical properties for strain sensing applications, to enable direct crack sensing capability and provide distributed strain data for Structural Health Monitoring (SHM), is currently rapidly evolving.

The volume of the nanomaterial is small and many researchers report that the addition of nanosilica (nanosilica) is known₂) And nano titanium dioxide (nano TiO)₂)、Nano iron (nano Fe)₂O₃) Nano alumina (nano Al)₂O₃) And nano materials such as carbon nano tubes and nano clay particles have the function of improving the performance of the concrete. The functions of nano silicon dioxide and carbon nano tubes are particularly remarkable in the materials. Nanosilica is one of the most common and important cement admixtures in the oil field, building and civil industries. Nanosilica is an extremely fine silica particle; it is composed of highly fine vitreous particles, is nearly 1000 times smaller than ordinary cement particles, and has high pozzolanic activity. Therefore, nano silica is widely used to improve the impermeability of the slurry and the mechanical properties of the hardened material. In addition, the addition of the nano silicon dioxide curing slurry can shorten the setting time; it has therefore been used as a popular additive in the oilfield industry. The carbon nano tube is used as a nano material, has light weight, has super-strong mechanical property (tensile strength of 50-200 GPa; bending strength of 14GPa), extremely high aspect ratio (diameter nano-scale, length micro-scale and aspect ratio of 100-²) And can be modified without damage, and the like, and the materials are very hopeful to be used for producing the next generation of high-performance structure and multifunctional nano composite materials. Due to the size effect and the filling effect of the carbon nano tubes, the functions of bridging and the like can be better played in each matrix, and the pores and the mechanical property of the cement-based composite material can be improved by doping a small amount of the carbon nano tubes. Their positive impact on the performance of cement-based composites is mainly influenced by two phenomena: hydration nucleation effect and filling effect. However, the problems of compatibility and dispersibility of the nanomaterial and the cement have been important issues involved in the application of the nanomaterial to the cement. The existing method mostly adopts a physical method: mainly comprises mechanical force dispersion and ultrasonic dispersion, and a chemical method comprises the following steps: mainly adds a modifier to lead the modifier to be mixed with the nano SiO₂The hydroxyl on the surface has chemical action to reduce SiO₂The number of hydroxyl groups on the surface reduces agglomeration, so that the nano particles are dispersed.

Furthermore, grafting certain functional groups on the surface of nanosilica and CNTs allows them to interact chemically with cement particles, thus positively influencing the hydration process. However, some authors report that surface treatment of CNTs by chemical modification may reduce the mechanical strength of the CNTs, thereby reducing the final properties of the composite. This is because the chemicals used for CNT functionalization negatively affect the kinetics of the hydration process. The binding of CNTs to NS has an accelerating effect on the hydration kinetics, thus leading to higher C-S-H production. Due to the chemical compatibility of nanosilica and the C-S-H matrix, the silica molecules located on the surface of the carbon nanotubes can participate in matrix-forming polymerization. Thus, enhanced load transfer capability may be achieved due to improved bonding between CNTs and NS in the matrix.

Disclosure of Invention

According to the research, firstly, nano silicon dioxide is activated at 80 ℃, the activated nano silicon dioxide can accelerate the hydrolysis of trifluoropropyltrimethylsiloxane to form more silanol, -OH on the surface of the nano silicon dioxide and the silanol are subjected to dehydration condensation reaction, a carbon nano tube and the carbon nano tube are added to form a nano silicon dioxide-carbon nano tube core-shell structure, and the silanol can continue to undergo dehydration condensation reaction with a cement hydration product calcium hydroxide, so that the nano silicon dioxide-carbon nano tube core-shell structure and the calcium hydroxide are combined more closely to fill pores. In addition, NMR (nuclear Magnetic Resonance spectroscopy), FT-IR (Fourier Transform induced spectroscopy) proves that the hydrothermally activated nano-silica can accelerate the hydrolysis of the trifluoropropyltrimethylsiloxane and generate dehydration condensation with the trifluoropropyltrimethylsiloxane; the surface element distribution was demonstrated by XPS; XRD (X-ray diffraction) and hydration heat (TA/TAM-AIR-8) experiments prove that the core-shell structure of the nano silicon dioxide-carbon nano tube promotes hydration products Ca (OH)₂Further reacting with nano silicon dioxide to generate hydrated calcium silicate; thermogravimetric analysis of TG (Thermogravimetric) proves that the core-shell structure of the activated nano-silica-carbon nanotube can accelerate the hydration products Ca (OH)₂Converted into hydrated calcium silicate and enables the concrete material to have better temperature resistance; the nano-silica is confirmed to be uniformly adsorbed by SEM (scanning Electron microscope) and BET physical adsorption methodA tighter interface is formed on the CNT surface and fills the voids between the cement hydration products. The dielectric constant-resistivity test proves that the silicon dioxide-carbon nanotube core-shell structure can greatly reduce the resistivity of the concrete material and improve the dielectric constant; cement freeze thawing-electrochemical corrosion experiments prove that the silicon dioxide-carbon nanotube core-shell structure has good corrosion resistance and freeze thawing resistance on concrete materials, and the durability of the concrete is improved; mechanical property tests prove that the compressive strength and the tensile strength are respectively improved by 102.04 percent and 140.47 percent compared with a control group, and are respectively improved by 53.51 percent and 71.43 percent compared with a non-hydrothermal activation treatment group.

The main mechanism of the invention is as follows: according to the research, firstly, nano silicon dioxide is activated at 80 ℃, the activated nano silicon dioxide can accelerate the hydrolysis of trifluoropropyltrimethylsiloxane to form more silanol, -OH on the surface of the nano silicon dioxide and the silanol carry out dehydration condensation reaction, a carbon nano tube and the carbon nano tube are added to form a nano silicon dioxide-carbon nano tube core-shell structure, the silanol on the surface of the nano silicon dioxide can continue to carry out dehydration condensation reaction with calcium hydroxide which is a cement hydration product, so that the nano silicon dioxide-carbon nano tube core-shell structure is combined with the calcium hydroxide more tightly to fill pores, and the mechanical property, the freeze-thaw resistance, the corrosion resistance, the waterproofness and the electrical conductivity of the cement-based composite material are improved.

Compared with the prior art, the invention has the beneficial effects that:

the existing cement-based composite materials have the characteristics of low mechanical property, freeze thawing resistance, corrosion resistance, poor waterproofness, low conductivity and the like, have great defects in the aspects of sustainable use and intelligent building material use, and have higher mechanical property, freeze thawing resistance, corrosion resistance and conductivity compared with the existing cement-based composite materials; mechanical property tests prove that the compressive strength and the tensile strength are respectively improved by 102.04 percent and 140.47 percent compared with a control group, and are respectively improved by 53.51 percent and 71.43 percent compared with a non-hydrothermal activation treatment group; the freeze-thaw resistance mass loss ratio is reduced from 8.35% to 3.39%; the corrosion resistance is more intuitive and obvious; resistivity from1.82×10¹⁰Reduced to 1.14 × 10⁸The dielectric constant is increased from 8.41 to 24.88; the contact angle increases from 41 ° to 92.5 °. Has wide application in the aspects of later industrial and civil construction, intelligent building and traffic.

Drawings

FIG. 1 is a NMR nuclear magnetic spectrum of an example group and a control group, and an FTIR infrared spectrum of the example group and the control group; (a) nuclear magnetic H spectra of trifluoropropyltrimethylsiloxane in deuterated chloroform; (b) nuclear magnetic H spectrum of non-activated nano silicon dioxide and trifluoropropyltrimethylsiloxane in deuterated chloroform; (c) nuclear magnetic H spectrum of the activated nano silicon dioxide and trifluoropropyltrimethylsiloxane in deuterated chloroform; (d) infrared analysis charts of G-CNT10.8+ NS7.2, S-WMNT10.8+ NS7.2, WMNT10.8+ NS7.2 and control groups 5 and 6.

FIG. 2 is an XPS scanning electron micrograph of an example group and a control group; (a) distributing O elements on the surface of the cement composite material containing the activated nano silicon dioxide-carbon nano tubes; (b) c element distribution on the surface of the cement composite material containing the activated nano silicon dioxide-carbon nano tubes; (c) distributing Ca elements on the surface of the cement composite material containing the activated nano silicon dioxide-carbon nano tubes; (d) the Si element distribution on the surface of the cement composite material containing the activated nano silicon dioxide-carbon nano tube.

FIG. 3 is an XRD X-ray diffraction analysis chart of the working group and the control group; (a) XRD patterns of G-CNT and Nano silica; (b) XRD patterns of OH-G-CNT and Nano silica; (c) XRD analysis patterns of S-MWNT and Nano silica; (d) XRD analysis patterns of OH-S-MWNT and Nano silica; (e) XRD patterns of controls 5, 6; (f) the surface element distribution of the cement composite material containing the activated nano silicon dioxide-carbon nano tube.

FIG. 4 is a TG thermogram of the working group and the control group; (a) (a') TG and TGA profiles of G-CNT and Nano silica; (b) (b') TG and TGA profiles of OH-G-CNT and Nano silica; (c) (c') TG and TGA profiles of S-MWNT and Nano silica; (d) (d') TG and TGA profiles of OH-S-MWNT and Nano silica; (e) (e') TG and TGA profiles of control groups 5, 6.

FIG. 5 is a thermogram of hydration of an example group and a control group; (ii) a (a) Accumulating the heat release; (b) the rate of heat generation.

FIG. 6 is SEM scanning electron micrographs of the examples and the control; (a) SEM image of the structure of the nano silica-carbon nano tube which is not activated; (b) SEM image of the structure of the activated nano silicon dioxide-carbon nano tube; (c) the structure of the unactivated nano silicon dioxide-carbon nano tube in the cement; (d) the nano silicon dioxide-carbon nano tube core-shell structure after the activation treatment; (e) control group 5; (f) the core-shell structure of the activated nano silicon dioxide-carbon nano tube forms an ellipsoid shape; (h) the shape of the nano silicon dioxide-carbon nano tube core-shell structure which is not subjected to activation treatment in cement; (i) the shape of the activated nano silicon dioxide-carbon nano tube core-shell structure in cement.

FIG. 7 is a BET porosity profile of an example versus a control; (a) a physical adsorption desorption curve; (b) a porosity curve.

FIG. 8 is a graph showing the effect of freeze-thaw experiments of the working group and the control group; (a) comparing the freeze-thaw loss of the experimental group 1 with that of the control groups 5 and 6; (b) comparing the freeze-thaw loss of the experimental group 2 with that of the control groups 5 and 6; (c) comparing the freeze-thaw loss of the experimental group 3 with that of the control groups 5 and 6; (d) the freeze-thaw loss of the experimental group 4 was compared with the control groups 5 and 6.

FIG. 9 is a graph of the electrochemical corrosion and contact angle experimental apparatus for the test group and the control group and the experimental effect of the control group; (a) an experimental device; (b) all experimental groups; (c) the corrosion resistance effect and the contact angle size of the control group 5 after electrochemical corrosion; (d) the corrosion resistance effect and the contact angle size of the control group 6 after electrochemical corrosion.

FIG. 10 is a graph showing the effects of electrochemical corrosion and contact angle tests on the control group and the test group; (a) the corrosion resistance effect and the contact angle of the experimental group 1 after electrochemical corrosion are high; (b) the corrosion resistance effect and the contact angle of the experimental group 2 after electrochemical corrosion are high; (c) the corrosion resistance effect and the contact angle of the experimental group 3 after electrochemical corrosion are high; (d) the corrosion resistance effect and the contact angle size of the experimental group 4 after the electrochemical corrosion.

Detailed Description

The invention is further illustrated with reference to specific embodiments below.

Example 1

Experimental groups 1-1 to 4-4: adding nano silicon dioxide into trifluoropropyltrimethylsiloxane, heating to 80 ℃, continuously stirring for 2h, accelerating hydrolysis of the trifluoropropyltrimethylsiloxane (hydrolysis is carried out by utilizing water contained in the trifluoropropyltrimethylsiloxane or water absorbed in the environment) and carrying out dehydration condensation on the activated nano silicon dioxide, then adding the carbon nano tube, continuously keeping the temperature of 80 ℃, and continuously stirring for 2h, so that the nano silicon dioxide is uniformly attached to the surface of the carbon nano tube to form a nano silicon dioxide-carbon nano tube core-shell structure. 16 groups of experimental groups (experimental group 1 is graphitized carbon nano-tube (G-CNT) added, experimental group 2 is graphitized carbon nano-tube (OH-G-CNT) added with hydroxyl, experimental group 3 is short-arm carbon nano-tube (S-MWNT) added, and experimental group 4 is short-arm carbon nano-tube (OH-S-MWNT)) are configured according to the mixing ratio in the table 1; adding the mixed cement paste into a JSF-550 type stirrer produced by Shunno instruments ltd of Kunshan city according to a water-cement ratio of 0.38, rotating at 800r/min for 20min, taking out the paste after uniform stirring, putting the paste into a grinding tool (a cement triple die 40mm multiplied by 160mm is adopted in a mechanical property test, a 20mm multiplied by 20mm is adopted in a freeze-thaw test, a die with the diameter of 50mm and the height of 30mm is adopted in an electrochemical corrosion test, an iron rod with the diameter of 10mm and the length of 80mm is inserted (the surface is smooth and has no corrosion), a die with the diameter of 15mm and the thickness of 5mm is adopted in a dielectric constant analysis, a square die with the length of 10mm and the width of 0.5mm is adopted in a resistivity test, and all samples are continuously maintained for 28 days at the temperature of 25 ℃ and the humidity of 98 percent in a constant temperature and humidity box.

The main content of the invention is the required materials, the formula and the operation method, and the mass formula is as follows:

composition of different mixtures of Table1 and its name

The composite material adopted by the invention is as follows: the nano silicon dioxide and the carbon nano tube are purchased from Beijing German island gold science and technology limited, and relevant material parameters are shown in Table 1; g-grade oil well cement and superfine portland cement are produced by Shandong Kangjing new material science and technology limited company, and relevant parameters are shown in a table 2; trifluoropropyltrimethylsiloxane is a chemical analysis pure reagent produced by Meclin corporation, and the concentration is 96 percent; the defoaming agent is a mortar defoaming agent purchased from Jingqi chemical technology Limited company in Foshan; the water reducing agent is a polycarboxylic acid high-performance water reducing agent purchased by Qin fountain building materials Co., Ltd, Shaanxi province; the fresh water is tap water for life; the content of each component (see table 2);

table 2 properties of carbon nanotubes.

G, graphitized OH, hydroxyl S, short-walled CNT, carbon nanotube MWCNT, and multi-walled carbon nanotube

TABLE 3 chemical oxide and mineral phase composition of the cements

The operation method adopted by the invention is as follows: adding the required composite material into a JSF-550 type stirrer (any stirrer of other brands) produced by Shunno instruments ltd, Kunshan city according to a formula proportion, rotating at 800r/min for 20min, taking out the paste after uniform stirring, putting the paste into a grinding tool (40mm multiplied by 160mm), and maintaining the temperature at 25 ℃ and the humidity at 98% in a constant temperature and humidity box for 28 days for maintenance.

Comparative example 1

Control group 5: pure cement without any additive is prepared into a group 5 control group according to the mixing ratio in the table 1; adding the mixed cement paste into a JSF-550 type stirrer produced by Shunno instruments ltd of Kunshan city according to a water-cement ratio of 0.38, rotating at 800r/min for 20min, taking out the paste after uniform stirring, putting the paste into a grinding tool (a cement triple die 40mm multiplied by 160mm is adopted in a mechanical property test, a 20mm multiplied by 20mm is adopted in a freeze-thaw test, a die with the diameter of 50mm and the height of 30mm is adopted in an electrochemical corrosion test, an iron rod with the diameter of 10mm and the length of 80mm is inserted (the surface is smooth and has no corrosion), a die with the diameter of 15mm and the thickness of 5mm is adopted in a dielectric constant analysis, a square die with the length of 10mm and the width of 0.5mm is adopted in a resistivity test, and all samples are continuously maintained for 28 days at the temperature of 25 ℃ and the humidity of 98 percent in a constant temperature and humidity box.

Comparative example 2

Control group 6: adding nano silicon dioxide into trifluoropropyltrimethylsiloxane, continuously stirring for 2h at room temperature, adding carbon nanotubes, continuously keeping the room temperature, continuously stirring for 2h, and preparing a 6 th group of control groups according to the mixing ratio in the table 1;

adding the mixed cement paste into a JSF-550 type stirrer produced by Shunno instruments ltd of Kunshan city according to a water-cement ratio of 0.38, rotating at 800r/min for 20min, taking out the paste after uniform stirring, putting the paste into a grinding tool (a cement triple die 40mm multiplied by 160mm is adopted in a mechanical property test, a 20mm multiplied by 20mm is adopted in a freeze-thaw test, a die with the diameter of 50mm and the height of 30mm is adopted in an electrochemical corrosion test, an iron rod with the diameter of 10mm and the length of 80mm is inserted (the surface is smooth and has no corrosion), a die with the diameter of 15mm and the thickness of 5mm is adopted in a dielectric constant analysis, a square die with the length of 10mm and the width of 0.5mm is adopted in a resistivity test, and all samples are continuously maintained for 28 days at the temperature of 25 ℃ and the humidity of 98 percent in a constant temperature and humidity box.

The mechanical property testing method adopted by the invention comprises the following steps: the well-maintained cement composite material is subjected to a fracture and compression test according to the fracture strength and compression strength in GB/T17671-1999 by using a TYE-300D type cement mortar fracture and compression tester produced by Wuxi instrument machinery Co. The test results were as follows:

table 4 Compressive strand and tensile strand of specimens.

And (3) mechanism analysis:

analysis of mechanical Properties

The sample size is 40mm multiplied by 160mm, and the fracture and compression resistance test is carried out by utilizing a TYE-300D type cement mortar fracture and compression resistance tester produced by the stannless construction instrument mechanical company Limited. The test shows that the compressive strength and the tensile strength are respectively improved by 102.04 percent and 140.47 percent compared with the control group and are respectively improved by 53.51 percent and 71.43 percent compared with the non-hydrothermal activation treatment group.

NMR, FT-IR, XPS analysis

NMR has shown that activated nanosilica can accelerate hydrolysis and condensation of trifluoropropyltrimethylsiloxane, and fig. 1a shows a 1H NMR spectrum of a specific formula of trifluoropropyltrimethylsiloxane, and three H species were observed as standard peaks at 1H (δ ═ 3.52 ppm, d, J ═ 1.2Hz),2H (δ ═ 2.12 to 1.99ppm, m),3H (δ ═ 0.81 to 0.72ppm, m) in order to avoid hydrolysis and determine the original formula of trifluoropropyltrimethylsiloxane; FIG. 1b shows the 1H NMR spectrum of trifluoropropyltrimethylsiloxane without activated nanosilica, -O-CH₃As 1H, a distinct peak was observed at (δ — 3.78-3.41 ppm, m), whereas peaks were detected at 2H (δ — 2.25-2.05 ppm, m),3H (δ — 0.99-0.78 ppm, m), and splits in the spectrum may be due to sample concentration; fig. 1c shows the 1H NMR spectrum of trifluoropropyltrimethylsiloxane containing activated nanosilica, and it was observed that either-O-CH 3 was observed as a peak at (δ ═ 3.46ppm, s) 2H (δ ═ 2.11, q, J ═ 9.2,8.1Hz),3H (δ ═ 0.95 to 0.74ppm, m) as 1H, or further at (δ ═ 4.99 to 4.69ppm, m, OH) due to-O-CH₃A large number of-OH peaks resulting from hydrolysis; the nano-silica after activation is proved to accelerate the hydrolysis of the trifluoropropyltrimethylsiloxane.

In order to characterize the nano-silica p-trifluoropropyl trimethyl siliconAcceleration of hydrolysis and condensation of siloxane and acceleration of hydration of cement by nanosilica-carbon nanotube core-shell structure IR analysis was performed on G-CNT10.8+ NS7.2, OH-G-CNT10.8+ NS7.2, S-WMNT10.8+ NS7.2, OH-S-WMNT10.8+ NS7.2 and controls 5 and 6 using FT-IR (FIG. 1 d). The results show that: the cement composite material containing the activated nano silicon dioxide-carbon nanotube structure is 3600cm^-1The left and right contain free hydroxyl groups which do not form hydrogen bonds, and when hydrogen bonds are formed, the absorption peak shifts to 3300cm at low frequency^-1To 3500cm^-1Strong and wide-OH stretching vibration absorption bands are formed, which shows that the activated nano-silica promotes the hydrolysis of trifluoropropyltrimethylsiloxane, and due to hydrogen bonds, the hydrolyzed Si-OH is successfully subjected to dehydration condensation with-OH on the surface of the nano-silica, and the phenomenon is that the length of the silicon dioxide is 1000 cm^-1-1200cm^-1The obvious increase of the Si-O-Si peak is further proved; while control 5 contained no free hydroxyl groups and control 6 contained only a small amount of free hydroxyl groups; the obvious peak area of the hydroxyl peak of the control group 6 is larger than that of the control group 5 and is further larger than that of the experimental group, and the research of B Pang et al proves that 3300cm^-1To 3500cm^-1The peak at (A) is the-OH peak of calcium hydroxide. 1630cm^-1The absorption peak of the expansion vibration of the CC double bond corresponding to the carbon nanotube skeleton is caused by the expansion vibration of the CC double bond generated by the five-membered ring or seven-membered ring at the CNT turning point or the sealing point. Due to the uniform adhesion of the nano-silica, the carbon nano-tube has corresponding SP3 hybridization on the surface, and the defects are increased, which is shown in that the core-shell structure of the nano-silica-carbon nano-tube subjected to the hydrothermal treatment is 2923cm^-1、2853cm^-1The peak (these peaks correspond to the C-H bond stretching vibration absorption peak in-CH, -CH 2), while the control group 5 showed substantially no such peak, and the control group 6 showed a weak peak, which proves that only a small portion of the nanosilica was attached to the surface of the carbon nanotube to cause weak defects.

The surface elemental analysis of the cement composite was verified using XPS and at the binding energy of O-1200eV, FIG. 3f shows the presence of C, O, Ca and Si elements in the composite cement material. FIG. 2a allows to observe a main peak of Si2P evident at a binding energy of 102.3eV, indicating the presence of Si-O; XPS peaks for C1s centered on binding energies of 286.2, 288.7, 293.2, 296.0eV were assigned to-CF 2, -CF3 (fig. 2b), respectively, demonstrating that particles on cement were successfully coated with trifluoropropyltrimethylsiloxane; the Ca2p XPS spectrum with binding energy 344-352eV shows that in FIG. 2c, the Ca2p3/2 and Ca2p1/2 spectra show two distinguishable main peaks at binding energies 347.0 and 351.1eV, indicating the presence of the hydration product CaOH as well as calcium silicate hydrate. The XPS peak of C1s centered on the binding energy of 284.6eV was assigned to CC/CH/C-Si, respectively, and it is clear that most of the carbon atoms are sp2 hybridized, while the C-C peak is dominant, corresponding to the phase of graphene, demonstrating that carbon nanotubes are contained and have been successfully coated on the surface of cement particles; FIG. 2a shows a main peak of O1S evident at 532.6eV binding energy, which proves that the composite cement material contains Si-O, Si-O-Si bonds.

XRD, TG, Isotermal calorimetric analysis

The phase composition of the cement composite was investigated using XRD techniques. In fig. 3, a, b, C and d are XRD diffractograms of the experimental group and the control group, and the atlases show that characteristic peaks of Calcium Hydroxide (CH), Calcium Silicate Hydrate (CSH), tricalcium silicate (C3S), dicalcium silicate (C2S) and tricalcium aluminate (C3A), which are main products of cement hydration, all appear in the atlases, which proves that the core-shell structure of the nano silica-carbon nanotube does not promote the cement hydration to generate new crystalline phase; the same characteristic peak can be found in fig. 3e, but the more obvious Calcium Hydroxide (CH) peak at 2-Theta ═ 18 ° disappears with the addition of the nano silica-carbon nanotube core-shell structure, and compared with the characteristic peak which is not subjected to hydrothermal treatment, although the Calcium Hydroxide (CH) peak disappears, the characteristic peak values of the hydrothermally treated tricalcium silicate (C3S), dicalcium silicate (C2S) and tricalcium aluminate (C3A) are all obviously improved, and the atlas confirms that the hydrothermally treated nano silica-carbon nanotube core-shell structure can further accelerate the further hydration of the cement hydration product calcium hydroxide to generate hydrated calcium silicate due to the self nucleation effect of the hydrothermal nano silica-carbon nanotube core-shell structure; the XRD patterns of four different carbon nanotubes are compared and doped: the four carbon nanotubes and the nano-silica can form a nano-silica-carbon nanotube core-shell structure with the nano-silica to promote further hydrolysis of Calcium Hydroxide (CH), and the four different carbon nanotubes do not show particularly different XRD (X-ray diffraction) patterns, so that the categories of the carbon nanotubes cannot influence the crystalline phase of the cement composite material, and the optimal ratio of the carbon nanotubes to the nano-silica is 10.8+ 7.2.

Thermal analysis research is carried out, and the influence of the nano silicon dioxide-carbon nano tube core-shell structure on the thermal stability of the cement is further analyzed. FIG. 4 shows the results of TG-DTG analysis of the experimental group and the control group, and the first broad endothermic peak is located in the temperature range of 49.8 to 130 ℃, which is related to the evaporation of free water. The second endothermic peak is located at 400.2-472.5 ℃, which is associated with the dehydration of Calcium Hydroxide (CH). FIG. 4e is a thermogravimetric analysis of control 5 and control 6, and the analysis in conjunction with FIGS. 4a-d reveals that: the two characteristic peaks both appear, and the fact that the hydration reaction is not influenced by adding the nano silicon dioxide-carbon nano tube core-shell structure is proved, because the same hydration product is formed. However, it is clear that the presence of CNTs may affect the kinetics of hydration of the cement, since the total loss of the controls 5, 6 was 9.8%, 8.92%, and a decrease in the mass loss ratio of both peaks of the experimental group compared to the control group was observed, demonstrating that Calcium Hydroxide (CH) has been converted to another hydration product. FIG. 4a is a thermogravimetric analysis of G-CNT and nanosilica at four different mix ratios showing a total loss of G-CNT14.4+ NS3.6 of at most 9.58% and a cooling loss of at most 6.45% at the second peak, a loss of G-CNT10.8+ NS7.2 of at least 7.78% and a loss of at least 5.59% at the second peak; this loss amount reaction accelerates the conversion of more Calcium Hydroxide (CH) to the hydration product calcium silicate when the mix ratio is G-CNT10.8+ NS7.2, and is further reflected in the compressive strength as well as the tensile strength; FIG. 4b is a thermogravimetric analysis of OH-G-CNT and nanosilica at four different mix ratios showing that the overall loss of OH-G-CNT3.6+ NS14.4 is 9.19% maximum, and the loss of cooling is 6.79% maximum at the second peak, the loss of OH-G-CNT10.8+ NS7.2 is 7.69% minimum, and the loss is 5.57% minimum at the second peak; this loss amount is reflected in the acceleration of more calcium hydroxide (Ca (OH) when the mix ratio is OH-G-CNT10.8+ NS 7.2)₂) Conversion to calcium silicate hydrate; FIG. 4c is a thermogravimetric analysis of S-WMNT and nanosilica at four different blend ratios showing a maximum total loss of 8.88% for S-WMNT3.6+ NS14.4, a maximum cooling loss at the second peak of 6.52%, a minimum loss of 7.46% for S-WMNT10.8+ NS7.2, and a minimum loss of 5.17% at the second peak; the loss amount is reflected by accelerating more calcium hydroxide (Ca (OH) when the mixing ratio is S-WMNT10.8+ NS7.2₂) Conversion to calcium silicate hydrate; FIG. 4d is a thermogravimetric analysis of OH-S-WMNT and nanosilica at four different mix ratios showing a maximum total OH-S-WMNT3.6+ NS14.4 loss of 7.88%, a minimum OH-S-WMNT10.8+ NS7.2 loss of 7.58%, and a minimum loss of 5.37% at the second peak; the loss amount is reflected by accelerating more calcium hydroxide (Ca (OH) when the mixing ratio is S-WMNT10.8+ NS7.2₂) Conversion to calcium silicate hydrate;

cement hydration kinetics are affected by particle surface reactions and particle surface area or particle size. It is well known that the addition of nanomaterials to cement stimulates nucleation processes that occur during early hydration of the cement, and that the faster the nuclei are formed, the earlier they grow into larger crystals, thereby accelerating the hydration of the cement. The nano material has small volume, large surface area and strong reactivity, and plays a nucleating role in the cement hydration process. Figure 5a shows the cumulative thermal evolution and heat generation rate (up to 72h) of the composite cement slurry during hydration, depending on the additive materials used. The first peak is usually associated with wetting of the cement powder, dissolution of silicates and gypsum, and formation of ettringite. After the induction period, the second peak is mainly due to hydration, leading to the formation of C-S-H and Calcium Hydroxide (CH), which also corresponds to the acceleration band associated with sulfate formation. The larger the dispersion degree of the cement particles is, the better the cement hydration effect is. In most cases, with the addition of the nano silicon dioxide and the carbon nano tube, the influence of the nano silicon dioxide-carbon nano tube core-shell structure leads to the reduction of the dormancy stage, which shows that the hydration of cement is accelerated by taking the core-shell structure particles as nucleation sites due to the larger surface area of the core-shell structure particles; this acceleration effect can be identified by the following parameters: (a) the slope of the curve changes in the acceleration period; (b) time to reach extremum dominant peak; (c) the exotherm of the main peak; as can be seen from fig. 5a, in the heat release of the main peak, G-CNT is the highest in a series of nanoparticle modified slurries, and the acceleration periods of different nanosilicon dioxide-carbon nanotube core-shell structures are different, but have similar slopes overall, and are both higher than those of the control groups 5 and 6; meanwhile, the accumulated heat release of the core-shell structure containing the activated nano silica-carbon nano tube is greater than that of the cement containing the nano silica-carbon nano tube structure which is not activated, and further greater than that of the control group 5 which does not contain any additive material. Fig. 5b shows that the group with the fastest heating rate is the experimental group containing activated G-CNTs, and then the experimental group containing other types of carbon nanotubes, and the non-activated nano silica-carbon nanotube control group 6 is between the experimental group and the control group 5, which proves that the activated nano silica-carbon nanotube core-shell structure accelerates cement hydration.

SEM-BET analysis

The combination of SEM and BET physical pore adsorption further proves that the activated nano-silica can accelerate the hydrolysis of trifluoropropyltrimethylsiloxane and the dehydration condensation of trifluoropropyltrimethylsiloxane, and the activated nano-silica is uniformly attached to the surface of CNT so as to fill the gaps between cement hydration products to form a tighter interface and reduce the porosity. FIG. 6a is a mixture of unactivated nanosilica and trifluoropropyltrimethylsiloxane, showing that only a small amount of nanosilica is distributed on the surface of trifluoropropyltrimethylsiloxane; FIG. 6b is the mixture of nano-silica and trifluoropropyl trimethyl siloxane after activation treatment, and it is evident that the nano-silica is uniformly distributed on the surface of the trifluoropropyl trimethyl siloxane because Si-OH generated after hydrolysis of the trifluoropropyl trimethyl siloxane is dehydrated and condensed with-OH on the surface of the nano-silica, so that the nano-silica is more tightly bonded; FIG. 6c shows the structure of the nano-silica-carbon nanotube without activation, which means that only a small amount of nano-silica is attached to the surface of the carbon nanotube; FIG. 6d is a SEM image of the structure of activated nano-silica-carbon nanotubes, nano-silicaSilicon is uniformly attached to the surface of the carbon nano tube, and the carbon nano tubes are tightly linked under the hydrolysis and condensation action of trifluoropropyl trimethyl siloxane; FIG. 6e is control 5, where only the presence of the cement hydration products calcium hydroxide and calcium silicate hydrate can be observed; FIG. 6f shows that the nano-silica on the surface of the carbon nanotube forms irregular ellipsoids with the particle size of about 3-12 μm long and 2-10 μm diameter under the hydrolysis and condensation of trifluoropropyltrimethylsiloxane; FIG. 6h shows the structure of the unactivated nanosilica-carbon nanotubes in cement with few ellipsoid formations and only a few voids are simply filled; FIG. 6i shows the structure of activated nano silica-carbon nanotubes in cement, since the size range of the core-shell structure is substantially within the pore range of the cement, and the surface of the core-shell structure contains nano silica, Si-OH generated by hydrolysis of trifluoropropyltrimethylsiloxane can be further reacted with CH (Ca (OH)₂) Dehydration and condensation, so that the core-shell structure can be well filled in the pores of the cement hydration product and well combined with the cement hydration product CH; FIG. 7a is a cement physical adsorption and desorption curve of each component content, wherein the adsorption amount and desorption amount of the control group 5 are larger than those of the control group 6; the adsorption and desorption amounts of the experimental group are minimum, which shows that the relative pore space of the experimental group is smaller; FIG. 7b is a plot of the porosity distribution of cement with respect to the content of each component, the cement with the nanosilica-carbon nanotube structure exhibiting lower porosity and the pore size distribution being primarily in the 10-100nm range; the BET result further proves that the core-shell structure of the nano silicon dioxide-carbon nano tube fully reduces the porosity and the specific surface area of the cement after hydration, the core-shell structure after activation shows better effect, and the further action is reflected in the compressive and tensile strength.

Freezing and thawing experiment, electrochemical corrosion and contact angle test

In order to further verify the influence of the nano-silica-carbon nanotube core-shell structure on the freeze-thaw resistance, the durability and the corrosion resistance of the cement material, a cement freeze-thaw resistance experiment and an electrochemical corrosion experiment are performed, wherein the main reason of freeze-thaw damage is that the volume of cement expands when water is converted into ice, and the water remaining on the surface of the cement freezes and freezes when the water is cooled and freezes, so that the freeze-thaw damage can be performed on the surface of the cement after the water is thawed. Fig. 8a, b, c, d are graphs comparing the freeze-thaw quality loss of the experimental and control groups 5, 6, respectively. The experimental results show that: the total loss after 210 cycles of controls 5, 6 with increasing number of freeze-thaw cycles was 8.35%, 6.87%; the loss of the experimental group is maintained between 3.39% and 5.90%, wherein G-CNT3.6+ NS14.4, G-CNT7.2+ NS10.8 and S-WMNT10.8+ NS7.2 show the best freeze-thaw resistance, and the total loss is 3.56%, 3.61% and 3.39%; the experimental group only observes 0.13 to 0.26 percent of mass loss after the freeze-thaw cycle is performed for 120 times, and the fourth group of the experimental group has no mass loss after the freeze-thaw cycle is performed for 210 times, so that the nano silicon dioxide-carbon nanotube core-shell structure is proved to have the effect of enhancing the freeze-thaw resistance of the cement material; corrosion resistance test the test block was subjected to electrochemical corrosion in 3.5 wt% NaCl at 26V for 20 seconds and then the block was broken to observe the corrosion at the contact between the test block and the iron rod, fig. 9a shows the test operation method and the test apparatus, fig. 9b shows the general graph after all the tests, fig. 9c and d show the results after the electrochemical corrosion of the control groups 5 and 6, respectively, and fig. 10a, b, c and d show the effects and the contact angle after the electrochemical corrosion of the test groups. The experimental results show that: the surfaces of the experimental group copper rods containing the activated nano silicon dioxide-carbon nanotube structures are not corroded, and the contact angles are 76.5-92.5 degrees, wherein the third experimental group shows the best contact angle; and the surface of the control group 5 is corroded in a large area, the contact angle is 41 degrees, the surface of the control group 6 is not corroded, the contact angle is 71 degrees between the surface of the experimental group and the surface of the control group 5, and the activated nano silicon dioxide-carbon nanotube structure is proved to have the effect of improving the corrosion resistance of the cement material, and the activated nano silicon dioxide-carbon nanotube structure and trifluoropropyl trimethylsiloxane provide the cement material with waterproofness and corrosion resistance.

Dielectric constant-resistivity analysis

The dielectric constant-resistivity test basis adopted by the invention is as follows:

an Agilent E498OLCR tester is adopted for dielectric constant analysis, the upper surface and the lower surface are ground by a grinding machine, silver is uniformly coated as a conductive contact surface, the testing frequency is 1KHz-1MHz, and the relative dielectric constant is calculated by a formula by utilizing the capacitance at 1 KHz; the resistivity analysis adopts a rated ATI-212 volume surface resistivity tester produced by Beijing Zhonghang time instrument and equipment Limited, the voltage is 10KV, and the resistivity of the material is tested.

Table 5 dielectric constant and resistivity.

As the carbon nano tube has good conductivity, the composite cement material is further tested for dielectric constant and resistivity, all samples are dried in an oven at 50 ℃ for 24 hours for testing, and the experimental results of the table 5 show that: G-CNT10.8+ NS7.2, OH-G-CNT10.8+ NS7.2, S-WMNT10.8+ NS7.2, WMNT10.8+ NS7.2 have dielectric constants of 24.88, 23.35, 23.32, 21.87, and resistivities of 1.14 × 108 Ω · m, 1.77 × 108 Ω · m, 1.81 × 108 Ω · m, 1.84 × 108 Ω · m, respectively; the dielectric constant of comparative group 5 was 8.41, and the resistivity was 1.82 × 1010 Ω · m; the dielectric constant of the control 6 was 18.33, and the resistivity was 1.96X 108. omega. m; the experimental group successfully grafted the activated nano silica-carbon nanotube core-shell structure to the hydration product Calcium Hydroxide (CH) to fill the pores and form a communicated conductive path, so that the dielectric constant is increased and the resistivity is reduced, while the control group 5 shows low dielectric constant and high resistivity due to the absence of the core-shell structure, and the control group 6 grafted a small amount of the core-shell structure to the hydration product Calcium Hydroxide (CH) so that the dielectric constant and the resistivity are between those of the experimental group and the control group 5, thereby proving that the activated nano silica-carbon nanotube core-shell structure can effectively increase the dielectric constant of the cement composite material, reduce the resistivity and improve the conductivity.

Claims

1. A preparation method of a nano silicon dioxide-carbon nanotube composite material with a core-shell structure is characterized by comprising the following steps:

adding 3.6-14.4 parts of nano silicon dioxide into 13.5 parts of trifluoropropyltrimethylsiloxane by mass, heating to 80 ℃, stirring, and activating; the activated nano silicon dioxide accelerates the hydrolysis of trifluoropropyltrimethylsiloxane and generates a dehydration condensation reaction with the hydrolysate of the trifluoropropyltrimethylsiloxane;

and then adding 3.6-14.4 parts of carbon nano tube, keeping the temperature of 80 ℃ and continuously stirring, and completely reacting to form the nano silicon dioxide-carbon nano tube composite material with the core-shell structure.

2. A nanosilica-carbon nanotube composite prepared by the method of claim 1.

3. Use of the nanosilica-carbon nanotube composite material of claim 2 for the preparation of high performance cement.

4. The high-performance cement containing the nano silicon dioxide-carbon nano tube elastic core-shell structure is characterized by comprising the following components in percentage by mass:

450 portions of G-grade cement

450 parts of superfine portland cement

342 portions of domestic water

9 portions of water reducing agent

1.8 portions of defoaming agent

31.5 parts of the composite material of claim 2.

5. The method for forming the high-performance cement with the nano-silica-carbon nanotube elastic core-shell structure according to claim 4, wherein the high-performance cement with the nano-silica-carbon nanotube elastic core-shell structure according to claim 4 is prepared by mixing the raw materials according to a formula ratio, adding water, uniformly stirring, mixing, and stirring at 800r/min for 20min to obtain a composite cement slurry; the curing condition of the composite cement slurry is that the temperature is 25 ℃ and the humidity is 98 percent and the continuous curing is carried out for 28 days.

6. A high-performance concrete material containing a nano-silica-carbon nanotube elastic core-shell structure is characterized by being obtained by curing the high-performance cement containing the nano-silica-carbon nanotube elastic core-shell structure in claim 4.