KR101647802B1 - Carbon nanotube composite Pretensioned Spun High Strength Concrete Pile and construction Methods thereof - Google Patents

Abstract

The present invention provides a carbon nanotube (CNT) composite pretensioned spun high strength concrete (PHC) pile and a construction method thereof. The CNT composite PHC pile comprises: a first composite PHC upper pile forming an upper portion thereof and containing a concrete pile including a CNT; and a second PHC lower pile forming a lower portion thereof. The CNT composite PHC pile aqueously disperses the CNT in centrifugally formed concrete to improve structural performance such as bending performance and shear performance. The CNT composite PHC pile can be used to provide economic efficiency and safety with respect to influence of horizontal force and bending moment such as an excessive eccentric soil pressure and an unpredicted earthquake load.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CNT synthetic high strength concrete pile and a method of constructing the CNT synthetic high purity concrete pile,

The present invention relates to a carbon nanotube (CNT) synthetic high strength concrete pile and a construction method thereof, and more particularly, to a CNT synthetic high strength concrete pile reinforced with strength and shear force and a construction method thereof.

Generally, when a building or structure is built, the foundation is reinforced to support the upper structure according to the condition of the ground or the load of the structure. Therefore, a shallow foundation or a deep foundation is performed depending on various conditions such as the load of the structure and the like depending on the load of the structure. A shallow foundation is defined as a shallow foundation and a shallow foundation is defined as a deep foundation . In the case of the shallow foundation described above, the structure is directly supported on the ground without using a file or the like,

When the ground below the structure can not support the load of the upper structure, the supporting force of the ground is reinforced by using piles and the like.

Conventional pile foundations used for deep foundation can be roughly divided into steel pipe pile and PHC pile (Pretensioned Spun High Strength Concrete Pile). In case of steel pipe pile and PHC pile having the same pile diameter, there is no significant difference in terms of the end bearing capacity due to the vertical supporting force.

However, the shear performance and bending performance differed greatly between the steel pipe pile and the PHC pile, and the pile type was determined according to the shear and bending performance. In other words, PHC pile is suitable for PHC pile due to its economical efficiency and construction workability. However, the effect of horizontal force and bending moment such as excessive biased earth pressure and unexpected seismic load is large In order to apply the PHC pile to the structure, the shear and bending performance are insufficient, and expensive steel pipe piles can not be applied.

The present invention provides a CNT synthetic PHC pile having improved shear performance and bending performance without additional investment in a conventional synthetic PHC pile manufacturing process.

Another aspect of the present invention is to provide a method of constructing the CNT synthetic PHC.

The technical problem is solved by a CNT synthetic PHC pile including a first synthetic PHC upper pile containing a concrete pile including upper carbon nanotubes and a second PHC lower pile forming a lower part .

Another object of the present invention is to provide a method for producing a carbon nanotube aqueous dispersion, comprising: dispersing a carbon nanotube in water to obtain a carbon nanotube water dispersion mixture;

Mixing the carbon nanotube water dispersion mixture with the first concrete to produce a first synthetic PHC upper pile;

Fabricating a second synthetic PHC bottom pile using a second concrete; And

And connecting the first synthetic PHC upper pile and the second synthetic PHC lower pile to form the CNT synthetic PHC pile.

The polymer CNT material containing 0.01 to 1 part by weight of the metal-nanofiber composite material based on 100 parts by weight of concrete is further added to the carbon nanotube water dispersion mixture.

The CNT synthetic PHC pile of the present invention improves structural performance such as flexural performance and shear strength by dispersing carbon nanotubes in a centrifugally formed concrete. The use of such CNT composite PHC pile is economical and has excellent safety against the effects of horizontal forces and bending moments such as excessive earth pressure and unexpected seismic load.

1 is a schematic view illustrating a CNT synthetic PHC pile according to one embodiment.
Fig. 2 is a view for explaining a process of calculating the maximum bending moment by performing a bending test according to the evaluation example 2. Fig.

Hereinafter, the CNT synthetic PHC pile and its construction method will be described in more detail.

There is provided a CNT synthetic PHC pile including a first PHC upper pile and a second PHC lower pile, the first synthetic PHC containing a concrete pile including carbon nanotubes forming the upper part.

The content of the carbon nanotubes in the first synthetic PHC is 0.01 to 3 parts by weight based on 100 parts by weight of the total weight of the first synthetic PHC upper pile. Here, when the content of carbon nanotubes is within the above range, a CNT synthetic PHC pile having excellent structural performance can be obtained.

The present invention relates to a method and apparatus for easily connecting a PHC pile synthesized by water dispersion of carbon nanotubes to an existing PHC pile, and to a depth at which a horizontal force and a bending moment such as an excessive biased earth pressure and an unexpected earthquake load are largely affected, The present invention provides a method of constructing a PHC pile that is made of a composite of a tube and a PHC pile having a smaller depth and less depth than that of a conventional PHC pile.

The depth at which the influence of horizontal forces and bending moments, such as seismic loads, largely contributes, for example, to a depth of 7 m or less, for example 5 to 7 m, from the foundation floor.

Carbon nanotubes can be single-walled carbon nanotubes (SWNTs), but double-walled carbon nanotubes (DWNTs), thin multi-walled carbon nanotubes (MWNTs) ), Multi-wall carbon nanotubes (MWNT), and the like can be used.

Double-walled carbon nanotubes and multi-walled carbon nanotubes are less expensive than single-walled nanotubes, so that CNT synthetic PHC piles can be manufactured at a lower cost.

The multiwalled carbon nanotubes have a resistance of about 0.01 to 0.2? Cm, for example 0.1? Cm, and a thermal conductivity of 1000 to 2500 W / m / K, for example about 2000 W / m / K. The tensile modulus of the multi-walled carbon nanotube is 1.0 to 1.5 TPa, for example, about 1.28 TPa, and the maximum drawing strength is 80 to 120 GPa, for example, about 100 GPa.

Carbon nanotubes (CNTs) are nanomaterials in which a sheet of graphite sheet, in which a carbon source is combined with an hexagonal honeycomb pattern, is rolled into a tube having a diameter of several nanometers to several hundreds of nanometers. Carbon nanotubes exhibit unique electrical, mechanical, and physicochemical properties due to their unique electronic structure and diameter at the nanometer level, depending on the bond type. For example, carbon nanotubes have a density of about one-half of that of aluminum, yet have a strength of more than 100 times that of steel. In addition, due to the small size, it has higher surface area per unit mass than ordinary carbon fiber, and it can produce a stable mixed material with a large energy absorption active area and a very large interaction in the mixed material. Due to the excellent properties of such carbon nanotubes, industrial applications are actively undergoing in various fields such as structural reinforcement, energy storage, fuel cell, and sensor. In particular, carbon nanotubes are known as excellent materials in terms of light absorption. In the case of a vertically grown carbon nanotube array, the total reflectance is 0.045%, which is 3 times lower than that of the material having the lowest reflectance published to date, . Considering the characteristics of the carbon nanotubes as described above, the inventors of the present invention manufactured an aqueous dispersion mixture containing carbon nanotubes having a wide surface area and an excellent light absorption rate, and used the water dispersion mixture in the preparation of synthetic PHC to improve the shear performance and the bending performance And to develop CNT synthetic PHC piles.

The water dispersion mixture containing the carbon nanotubes comprises carbon nanotubes (CNT), a dispersant, and water. The content of carbon nanotubes (CNT) in the aqueous dispersion mixture is 0.01 to 3 wt%, the content of the dispersing agent is 0.01 to 5 wt%, and the content of water is the remainder.

Carbon nanotubes are preferably subjected to a surface modification process to improve adhesion with the resin binder and dispersibility. Methods for surface modification of carbon nanotubes include liquid phase or gaseous acid treatment, ozonated water treatment, plasma treatment and the like by conventional conventional methods. These conventional carbon nanotube surface modification methods can be easily carried out by those having ordinary skill in the art to which the present invention belongs. SDB, SDSA, DTAD, CTAB, NaDDBS, Cholic Acid, Tween 85, Brij 78, Brij 700, Triton X, and the like are used as the dispersant in the carbon nanotube water dispersion mixture. , PVP, Ethyl Cellulose (EC), Nafion, Hydroxy Propyl Cellulose (HPC), Carboxy Methyl Cellulose (CMC), Hydroxy Ethyl Cellulose (HEC) and Pluronic (PEO-PPO Copolymer). They may be used alone or in the form of a mixture of two or more. The aqueous dispersion mixture may further contain at least one organic solvent selected from methanol, ethanol, ethyl acetate, acetone, methyl ethyl ketone (MEK), toluene, dimethylformamide (DMF) Various additives may be added to the water dispersion mixture in order to impart stability of the water dispersion mixture or specific functions required. Examples of the additive to be added include a dispersant, a slip agent, a flow improver, a thickener, an antistatic agent, a water repellent agent, an air / steam / perspiration agent, a friction coefficient improver and a UV stabilizer. . Of course, the additive is not necessarily limited to the above additives, and other additives may be suitably used depending on the intended use. 0.01 to 5 parts by weight of an additive may be further added to 100 parts by weight of the water dispersion mixture. The liquid multi-walled carbon nanotube (MWNT) water dispersion mixture is prepared by using an ultrasonic wave, a roll mill, a ball mill or a jet mill to prepare a liquid multi-walled carbon nanotube (MWNT) water dispersion mixture.

The first synthetic PHC upper pile may further include a polymer composite material containing a metal-nanofiber mixture. When such a metal-nanofiber mixture is further included, the shear performance and bending performance of the CNT synthetic PHC pile are further improved.

In the polymer material containing the metal-nanofiber composite, the nanofiber is composed of a tube and fiber having at least one diameter of 5 to 50 nm selected from carbon nanotubes and carbon nanofibers. Wherein the metal comprises at least one selected from the group consisting of aluminum, copper, silver, iron and titanium as fine powders of 10 to 500 μm.

As the polymer, at least one selected from thermoplastics, elastomers, thermosets, and thermoplastic elastomers may be used. Examples of the thermoplastic resin include polypropylene, polyethylene, polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA).

The metal-nanofiber composite may be, for example, a copper-carbon nanotube composite, an aluminum / copper-carbon nanotube composite, or an iron-carbon nanotube composite. The content of carbon nanotubes in the above-described copper-carbon nanotube composite, aluminum / copper-carbon nanotube composite or iron-carbon nanotube composite may be 1 vol% or more, for example, 1 to 20 vol %to be.

The content of the polymer material containing the metal-nanofiber composite is 0.01 to 50 parts by weight, for example 1 to 10 parts by weight, based on 100 parts by weight of the total weight of the first synthetic PHC upper pile. When the content of the polymer material containing the metal-nanofiber composite is within the above range, the performance of the first synthetic PHC pile is excellent.

The polymer material containing the metal-nanofiber composite may be prepared according to the following procedure. First, mechanical impact energy is applied to the metal particles and the nanofibers by mechanical milling, and the metal particles undergo elastic deformation or plastic deformation, whereby the nanofibers penetrate into the metal particles to form a metal-nanofiber mixture. Then, it is dispersed in a liquid polymer resin by a mechanical dispersion method, and then a unidirectional pressure method is used to produce a material having a specific shape. Here, the mechanical dispersion method uses ultrasonic waves, roll milling, ball milling, jet milling and the like. According to such a manufacturing method, a metal-nanofiber mixture in which a part of a nanofiber is inserted and fixed to metal particles having excellent dispersibility by applying mechanical energy is prepared and dispersed in a polymer, whereby a material having excellent mechanical properties can be obtained.

In the present invention, the first synthetic PHC upper pile forms a lower part of the CNT synthesized PHC pile and exists in an area of 5 to 7 m or less from the foundation bottom. In this way, the first synthetic PHC upper pile containing carbon nanotubes is used only in the region where the horizontal load has a great influence on the CNT synthetic PHC pile, and the synthetic PHC bottom pile using the conventional concrete is used in the region where the horizontal load has a small effect So that the PHC pile can be manufactured more economically. In order to reinforce the shear force according to the pile diameter, ECP (Engineering Cabon Plastic) is applied to the pile head and the area subjected to flexure. It is adjusted to 2mm ~ 5cm according to the size of the pile diameter. This is a structure requiring increase of bending strength, shear force reinforcement, .

In the present invention, when connecting a first synthetic PHC upper pile containing carbon nanotubes and a second synthetic PHC lower pile, the same welding connection as that of the existing PHC pile is used.

FIG. 1 schematically illustrates the structure of a CNT composite PHC pile according to one embodiment.

Referring to this, the first synthetic PHC upper pile 10 and the second synthetic PHC lower pile 11 are coupled to each other to form a CNT synthetic PHC pile. The first synthetic PHC pile (10) contains carbon nanotubes (12).

The first synthetic PHC upper pile may further include an internal stiffener including a steel bar and a spiral reinforcing bar.

Although not shown in FIG. 1, there may be a bonding structure for bonding them between the first synthetic PHC upper pile 10 and the second synthetic PHC lower pile 11.

Hereinafter, a construction method of the CNT synthetic PHC pile according to the present invention will be described.

Dispersing the carbon nanotubes in water to obtain a carbon nanotube water-dispersed mixture, mixing the carbon nanotube water-dispersed mixture with the first concrete to obtain a mixture, and manufacturing the first synthetic PHC upper pile using the mixture Preparing a second synthetic PHC bottom pile using the second concrete, and connecting the first synthetic PHC upper pile and the second synthetic PHC bottom pile to construct the CNT synthetic PHC synthetic pile .

The polymer composite material containing the metal-nanofiber composite may further be added to the carbon nanotube water dispersion mixture. The polymer composite material containing the metal-nanofiber composite is 0.01 to 50 parts by weight based on 100 parts by weight of the first concrete.

In the above process, the content of carbon nanotubes in the carbon nanotube water dispersion mixture is 0.01 to 3 parts by weight based on 100 parts by weight of concrete. In the polymer composite containing the metal-nanofiber composite, the content of the carbon nanotube is 1 vol% or more, for example, 1 to 20 vol%, based on the total volume of the composite.

The upper end of the upper pile of the first synthetic PHC is bound to the inner reinforcement of the foundation and used as a reinforcing material for the head of the PHC pile. The second synthetic PHC lower pile has a structure in which a hollow portion is formed and is connected to the lower end of the second synthetic PHC pile to be inserted into the ground.

Hereinafter, the present invention will be described with reference to the following examples, but it should be understood that the present invention is not limited to the following examples.

Example One

The water-dispersed liquid multi-walled carbon nanotube dispersion was mixed with ordinary Falkland cement and stirred to prepare first CNT synthetic PHC.

The surface of MWCNT is oxidized by using mixed solution of nitric acid and sulfuric acid (3: 1) to prepare MWCNT with improved dispersion performance. 5% by weight of the acid-treated MWCNT, 5% by weight of a dispersing agent (trade name: Triton X100), 0.2% by weight of defoamer (trade name: Surfynol 104H) and 38.8% by weight of distilled water were mixed and heated at 140 W (70% CNT was dispersed by applying ultrasonic waves to obtain a water-dispersed liquid multi-walled carbon nanotube (MWCNT) dispersion.

The content of the multi-walled carbon nanotubes in the water-dispersed liquid multi-walled carbon nanotube dispersion was about 1 part by weight based on 100 parts by weight of the Falkland cement.

The resistance of the multi-walled carbon nanotube dispersion was about 0.1 Ωcm and the thermal conductivity was about 2000 W / m / K. The multiwalled carbon nanotubes had a tensile modulus of about 1.28 TPa and a maximum draw strength of about 100 GPa.

A second synthetic PHC pile was prepared using Falkland cement.

The first synthetic PHC upper pile obtained according to Example 1 and the second synthetic PHC lower pile were connected to produce a CNT synthetic PHC pile. Wherein the first synthetic PHC upper pile is located in an area of 5 to 7 m or less from the foundation bottom and the second synthetic PHC lower pile is located in an area exceeding 7 m from the foundation bottom.

Example  2

Walled carbon nanotube dispersion in a water-dispersed liquid multi-walled carbon nanotube dispersion was changed to about 0.01 part by weight based on 100 parts by weight of Falkland cement, Piles were manufactured.

Example  3

Walled carbon nanotube dispersion in a water-dispersed liquid multi-walled carbon nanotube dispersion was changed to about 3 parts by weight based on 100 parts by weight of Falkland cement, the content of the first synthetic PHC Piles were manufactured.

Example  4

A first synthetic PHC pile was produced in the same manner as in Example 1, except that a polymer material containing a metal-nanofiber composite was further added to the aqueous dispersion of multi-walled carbon nanotubes in a liquid phase. The content of the polymer material containing the metal-nanofiber composite was 1 part by weight based on 100 parts by weight of the first synthetic PHC pile. As the polymer material containing the metal-nanofiber composite, a polymer material containing a copper-carbon nanotube composite obtained according to the following procedure was used.

A mixture of copper and carbon nanotubes was mechanically milled to obtain a copper-carbon nanotube composite. The content of carbon nanotubes in the copper-carbon nanotube composite was about 10% by volume.

30 wt% of the copper-carbon nanotube composite was added to 70 wt% of polyethylene terephthalate, and ultrasonic wave was applied thereto to perform mechanical dispersion to prepare a polymer material containing the copper-carbon nanotube composite. In the polymer material containing the copper-carbon nanotube composite thus prepared, carbon nanotubes were well inserted into the copper particles, and the mechanical properties were excellent.

A second synthetic PHC was prepared using Falkland cement.

The first synthetic pile obtained according to Example 1 and the second synthetic PHC pile were connected to produce a CNT synthetic PHC pile.

Example  5

The same procedure as in Example 4 was carried out except that the content of the polymer material containing the metal-nanofiber composite was changed to 10 parts by weight based on 100 parts by weight of the first synthetic PHC pile.

Comparative Example  One

A synthetic PHC pile was produced in the same manner as in Example 1, except that the aqueous dispersion of multi-walled carbon nanotubes in a liquid phase was not used.

Evaluation example  One

The change in compressive strength with time was measured for the CNT synthetic PHC pile manufactured according to Example 1-5 and the synthetic PHC pile manufactured according to Comparative Example 1 and is shown in Table 1 below.

The compressive strength is evaluated according to KSF 2405-79 (compressive strength test method of concrete), and the flexural strength test is conducted according to KSF 2407-79 (compressive strength test method of concrete).

division
Compressive strength (MPa) Seven days After 14 days After 28 days Example 1 5 12 30 Example 2 5 12.5 30 Example 3 6 13 32 Example 4 7 14 33 Example 5 8 15 35 Comparative Example 1 2 8 10

As shown in Table 1, the CNT synthetic PHC pile manufactured according to Example 1-5 showed an improvement in compressive strength compared with the synthetic PHC pile of Comparative Example 1. [ When the compressive strength was increased as described above, the CNT synthetic PHC pile manufactured according to Example 1-5 had excellent mechanical properties, resulting in increased strength, improved shear force and abrasion resistance.

Evaluation example  2: Bending test

1) Comparison of crack patterns

The CNT synthetic PHC piles manufactured according to Example 1-5 and the synthetic PHC piles manufactured according to Comparative Example 1 were tested according to the flexural strength test method of the KS F 4306 pretensioned centrifugal high strength concrete pile.

As shown in FIG. 2, a test was conducted by applying 3 / 5L to the total length L of the pile and applying a vertical direction concentrated load Pv to the center of the ground without introducing axial force. The vertical load was applied to the displacement control system using a pile - only tester with a maximum capacity of 1500 kN. Vertical load and center deflection were measured using a load cell attached to the tester and a displacement gauge attached to the center of the pile, and the load at which the initial crack occurred was measured by directly observing the tensile portion of the pile specimen.

As a result of examining the crack patterns of the CNT synthetic PHC pile manufactured according to Example 1-5 and the synthetic PHC pile manufactured according to Comparative Example 1, the PHC pile manufactured according to Comparative Example 1 has a large initial uniformity Whereas the CNT synthetic PHC pile manufactured according to Example 1-5 has a relatively small number of flexural cracks as the vertical load increases.

2) Maximum bending moment comparison

Based on the loads measured according to the above procedure, initial crack initiation and bending moments (M) of the ICP and dry PHC piles were calculated using the following equation (2).

[Formula 2]

What?

In Equation 2, W _PHC means the weight of the PHC pile, which is the body of the ICP pile, and is calculated using Equation 3 below. W _con means the weight of the internal filled concrete, and the unit weight of the concrete is assumed to be 2300 kg / m ³ .

[Formula 3]

In Equation 3, W _PHC is the diameter of the pile, and t is the thickness of the pile.

The flexural strength of the pile depends on the direction of the load acting on the ICP pile.

As a result of the measurement, the initial stiffness of the CNT synthetic PHC pile manufactured according to Example 1 was higher than that of Comparative Example 1. Then, the maximum load was substituted into Equation 2 through the bending test to calculate the maximum bending moment for the CNT synthetic PHC pile manufactured according to Example 1 and the synthetic PHC pile manufactured according to Comparative Example 1. The results are shown in Table 2 Respectively.

As a result of the measurement, the initial stiffness of the CNT synthetic PHC pile manufactured according to Example 1 was higher than that of Comparative Example 1. Then, the maximum load was substituted into Equation 2 through the flexural test to calculate the maximum bending moment for the CNT synthetic PHC pile manufactured according to Example 1 and the synthetic PHC pile manufactured according to Comparative Example 1.

division Maximum bending moment (kN ^. M) Example 1 252.9 Example 2 252 Example 3 254 Example 4 257 Example 5 260 Comparative Example 1 123.9

As a result of calculation of the maximum bending moment, the CNT synthetic PHC pile manufactured according to Example 1-5 showed an increase in comparison with that of Comparative Example 1. Thus, it can be seen that the CNT synthetic PHC pile manufactured according to Example 1-5 has more strength to withstand lateral forces such as earth pressure or earthquake load as the flexural performance is improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is natural to belong.

10: first synthetic PHC pile 11: second synthetic PHC pile
12: Carbon nanotubes

Claims (10)

A first synthetic PHC upper pile containing a concrete pile including upper carbon nanotubes and a second PHC lower pile forming a lower part, wherein the content of the carbon nanotubes in the first synthetic PHC Is 0.01 to 3 parts by weight based on 100 parts by weight of the total weight of the first synthetic PHC,
The first synthetic PHC upper pile further comprises a polymer composite material containing a metal-nanofiber composite,
The content of the carbon nanotubes in the polymer composite material containing the metal-nanofiber composite is 1 to 20% by volume,
Wherein the polymer composite material containing the metal-nanofiber composite comprises a carbon nanotube (CNT) composite PHC pile containing a copper-carbon nanotube composite and a polyethylene terephthalate. delete delete delete The method according to claim 1,
The first synthetic PHC upper pile is located in a region of 7 m or less from the foundation bottom. Dispersing the carbon nanotubes in water to obtain a carbon nanotube water dispersion mixture;
Mixing the carbon nanotube water dispersion mixture with concrete to produce a first synthetic PHC upper pile;
Fabricating a second synthetic PHC bottom pile using concrete;
Connecting the first synthetic PHC upper pile and the second synthetic PHC lower pile to produce the CNT synthetic PHC pile of claim 1 or 5,
The polymer composite material containing 0.01 to 1 part by weight of the metal-nanofiber composite based on 100 parts by weight of concrete is further added to the carbon nanotube water dispersion mixture,
In the step of preparing the first synthetic PHC upper pile, the content of the carbon nanotubes in the carbon nanotube water dispersion mixture is 0.01 to 3 parts by weight based on 100 parts by weight of the concrete,
The content of the carbon nanotubes in the polymer composite material containing the metal-nanofiber composite is 1 to 20% by volume,
Wherein the polymer composite containing the metal-nanofiber composite comprises a copper-carbon nanotube composite and polyethylene terephthalate. delete delete The method according to claim 6,
Wherein the upper portion of the upper pile of the first synthetic PHC is bound to the inner reinforcing portion of the foundation portion, and thus used as a reinforcing material for the head portion of the PHC pile. The method according to claim 6,
The second synthetic PHC lower pile has a hollow portion formed therein, and the second synthetic PHC pile is connected to the lower end of the second synthetic PHC pile to be inserted into the ground.

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