KR102372277B1 - Carbon Nanotube Intermixed Cement and preparation method thereof - Google Patents

Abstract

The present invention relates to a carbon nanotube agglutination mixed cement comprising pretreated carbon nanotubes and a method for manufacturing the same. Through this, by introducing the step of mixing carbon nanotubes in the dry process and functionalizing the carbon nanotube surface to induce chemical bonding, it was confirmed that the pretreated carbon nanotubes agglomerated with cement particles can be dispersed in the nanoscale in concrete, It was confirmed that the concrete prepared by blending the carbon nanotube agglutination cement also had significantly improved strength compared to general cement.

Description

Carbon nanotube intermixed cement and preparation method thereof

The present invention relates to a carbon nanotube agglutination mixed cement comprising pretreated carbon nanotubes and a method for manufacturing the same.

Since 2010, technological development in the ultra-fine structure field of cement composites including concrete has expanded and achieved rapid development. Concrete as a construction material is evaluated as a core material, which is used over 11 billion tons per year around the world. In order to more comprehensively understand and manage the macro-scale properties of concrete materials, a lot of research has focused on the ultra-microstructure field in the nano-scale range beyond the micro-metric range. number is in progress. However, despite many existing studies related to NT, brittle fracture, which is an essential weakness of concrete, low fracture toughness, and cracking due to shrinkage are still pointed out as unavoidable disadvantages.

Meanwhile, as a new material in the NT field, carbon nanotubes (hereinafter, CNTs) have emerged, attracting attention in various fields such as ceramics, fibers, and wearable devices, and research in related fields is increasing. Carbon nanotube refers to a new material manufactured in the form of a tube having a nano-scale diameter by rolling up a graphene film made of only carbon atoms. It is divided into single-walled carbon nanotubes (SWCNTs) using single membranes and multi-walled carbon nanotubes (MWCNTs) using multiple membranes, and multi-walled carbon nanotubes (MWCNTs) are mainly used in related industries.

The building technology program of MIT University in the US predicted and reported that when carbon nanotubes are applied to concrete, ultra-high strength concrete with a compressive strength of 200 MPa or more can be easily produced. In addition, nano-scale carbon nanotubes control various matrix cracks occurring in the concrete matrix in the lowest scale range, so it is expected to be able to significantly control cracks caused by enhancement of fracture toughness and shrinkage of concrete. .

In order to produce ultra-high-strength concrete capable of exerting a compressive strength of 200 MPa or to produce carbon nanotube-mixed concrete capable of suppressing cracking, intorsion and agglomeration, which are considered the biggest issues by domestic and foreign researchers, are Resolving the problem is of the utmost priority. In order to solve this problem, many advanced countries are already promoting the development of source technology, and related fields are also pointing out this as one of the biggest technology issues.

In existing domestic and foreign studies, the technique of adding a solvent such as acetone or ethanol in the mixing process of materials (fresh concrete), which is the stage before hardening of cement, and the simultaneous mixing of a surfactant and carbon nanotubes in the mixed water. Various efforts have been made to change the physical properties of nanomaterials through techniques and ultrasonic treatment, which is a physical external force. However, within a few minutes after application of the dispersion effect of carbon nanotubes, precipitation caused by the difference in density between mixed water, surfactant, and carbon nanotubes, as well as pretreatment problems in various processes and excessive mixing of carbon nanotubes (the amount of mixing It attempts to solve the dispersion problem by increasing the In particular, carbon nanotubes mixed to improve strength, that is, to reduce the amount of cement, actually increase the overall unit cost of concrete, which revealed a problem in field applicability.

As a result of diligent research efforts to efficiently improve cement strength while mixing a small amount of carbon nanotubes, the present inventors solve the agglomeration phenomenon in water by mixing with dry cement raw materials, unlike the existing carbon nanotube mixed cement manufacturing method. The present invention was completed by improving the dispersibility by chemically colliding with the cement raw material through pretreatment of the nanotubes.

One object of the present invention is to provide a method for producing a pretreated carbon nanotube agglutination mixed cement.

Another object of the present invention is a carbon nanotube having an oxidized surface; And to provide a carbon nanotube agglutination mixed cement comprising a cement raw material.

This will be described in detail as follows. Meanwhile, each description and embodiment disclosed in the present invention may be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be considered that the scope of the present invention is limited by the specific descriptions described below.

A first aspect of the present invention is a first step of preparing a pre-treated carbon nanotube by putting the carbon nanotube in an acidic solution; a second step of preparing a cement material by mixing the raw material for cement and the pretreated carbon nanotubes in a solvent; a third step of calcining the cement material mixed in the second step under an inert gas condition to produce clinker; and a fourth step of mixing gypsum with the clinker produced in the third step, to provide a method for producing carbon nanotube agglutination cement.

As used herein, the term “carbon nanotube” may refer to a new material manufactured in the form of a tube having a nano-scale diameter by rolling up a graphene film made of only carbon atoms. It may be divided into single-walled carbon nanotubes (SWCNTs) using single membranes and multi-walled carbon nanotubes (MWCNTs) using multiple membranes, respectively, but is not limited thereto.

The first step of the present invention is a step introduced to solve the carbon nanotube aggregation phenomenon (FIG. 1) by using the deformation of the defect site on the surface of the carbon nanotube. The 'modification of the defect site' may mean introducing a functional group into the defect site on the surface of the carbon nanotube. Specifically, the first step may mean a step of functionalizing the carbon nanotube (FIG. 2) to have a functional group containing oxygen on the surface of the carbon nanotube through an oxidation process in which the carbon nanotube is put into an acidic solution and refluxed. . The pH of the acidic solution may be about 2 or less. This is because the low pH serves as a reaction pathway to form oxidation of the CNTs surface.

The first step may be to reflux the carbon nanotubes for about 1 hour to about 24 hours. If the carbon nanotubes are refluxed for less than about 1 hour, the amount of oxygen introduced to the surface of CNTs may be insufficient. there is

The second step of the present invention is a step of preparing a cement material by mixing the raw material for cement and the pretreated carbon nanotubes in a solvent. This is different from the prior art in which the final cement material in a wet state is prepared from cement raw materials and then carbon nanotubes are put in, the present invention is manufactured by putting the pretreated carbon nanotubes in the state of the raw cement raw material that has not been dry post-treated. There is a marked difference in points. When carbon nanotubes are injected into cement materials in a wet state, carbon nanotubes are non-polar and hydrophobic materials that have a greater affinity for oily materials than water-based materials. Therefore, when carbon nanotubes are put into a material containing water, a Van der Waals force between the particles is applied to cause entanglement and agglomeration. In the case of input to the material, there was a problem in that a significantly large amount of carbon nanotubes had to be input because the input effect was insignificant due to agglomeration. Therefore, the problem can be solved through the second step of the present invention.

In performing the second step, the pretreated carbon nanotubes may be mixed in an amount of about 0.5 wt% to about 1.5 wt% based on the weight of the cement raw material. If it is less than 0.5 wt%, there is a problem in that the effect of adding the pretreated carbon nanotubes is insignificant, and if it is more than 1.5 wt%, the increase rate of cement strength is not improved any more, so there is a problem of inefficiency. This is significant because the cement compressive strength can be maximized even when a small amount of the pretreated carbon nanotubes is added compared to the prior art.

The solvent of the second step may be an organic solvent or an aqueous solvent. For example, the solvent may be a hydrocarbon-based, halogenated hydrocarbon, alcohol, aldehyde, ether, ester, ketone, glycol derivative, or the like. According to an embodiment, the solvent may be ethanol, but is not limited thereto.

The third step of the present invention is an essential step for manufacturing cement by mixing carbon nanotubes in a dry process. Specifically, it may mean that the mixed cement material is manufactured into dumplings with a diameter of 20 to 40 nm and calcined in an inert gas condition in a high-temperature sintering furnace (furnace).

When carbon nanotubes are exposed to air, there is a problem in that the weight may be reduced by causing an oxidation reaction with carbon dioxide, oxygen, and moisture as shown in Scheme 1 below.

[Scheme 1]

C + CO ₂ (g) → 2CO (g)

2C + O ₂ (g) → 2CO (g)

C + H ₂ O(g) → CO(g) + H ₂ (g)

According to the prior art, since the raw material for cement is calcined in the air, after the second step of the present invention, when calcined in the air as in the prior art, the weight reduction of the carbon nanotubes is remarkable, and there is a problem that an excessive amount of the carbon nanotubes is added. Therefore, in order to maximize the carbon nanotube input effect by minimizing the weight reduction, the present invention applied the step of calcining in an inert gas state, not in a general atmospheric state containing oxygen. In an embodiment of the present invention, it was confirmed that the weight reduction was significantly reduced through a comparison experiment of the weight reduction rate during firing in the argon gas state compared to the general atmospheric state.

The sintering temperature of the third step may be about 1250°C to about 1450°C. This may mean a process for the phase change of the cement raw material. It can be confirmed from an embodiment of the present invention that the weight reduction can be maintained at the lowest even in the high temperature range. At a temperature lower than about 1250°C, there is a problem that a phase change does not occur, and when it exceeds about 1450°C, there is a problem of inefficiency.

In the fourth step of the present invention, the first rotary cup milling and the second jar ball milling are performed by mixing gypsum to prevent flash set of cement. is a manufacturing step.

In performing the fourth step, the gypsum may be mixed in an amount of about 2.5 wt% to about 4 wt% based on the weight of the clinker. When the mixing amount of gypsum is less than about 2.5 wt%, there is a slight problem in preventing the rapid setting, and when the mixing amount of gypsum is more than about 4 wt%, there is a problem in that the setting time of the final product, the mixed cement, is excessively delayed.

A second aspect of the present invention is a carbon nanotube having an oxidized surface; and a cement raw material, wherein the carbon nanotube having the oxidized surface and the cement raw material are chemically crosslinked, to provide a carbon nanotube agglutination mixed cement.

The 'carbon nanotube having an oxidized surface' of the present invention may mean the 'pretreated carbon nanotube' mentioned in the first aspect of the present invention. More specifically, the step of refluxing carbon nanotubes after the input into an acidic solution; filtering the acid-treated refluxed carbon nanotubes; and drying the filtered carbon nanotubes may mean pre-treatment. By the pretreatment, carboxylic acid (COOH) or hydroxyl (OH) functionalization on the surface of CNTs can obtain carbon nanotubes with significantly improved separation of CNTs. Accordingly, the 'oxidized surface' according to an embodiment of the present invention may mean that a carboxylic acid functional group (-COOH) and/or a hydroxyl functional group (-OH) is provided on the surface of the carbon nanotube. In particular, according to an embodiment, the 'oxidized surface' may mean that the oxygen content in the carbon nanotube is 10% to 20% compared to the carbon content.

The 'cement raw material' of the present invention may include limestone, silica stone, copper slag, and clay, but is not limited thereto. Raw material chemical constituents may include, but are not limited to, SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO, Na ₂ O, K ₂ O, SO ₃ .

In the present invention, the 'agglutination' may mean chemical bonding between the carbon nanotubes and the cement raw material. A carboxyl group (COOH) and a hydroxyl group (OH) group are highly compatible with ceramic materials such as aluminum oxide (Al ₂ O ₃ ) or silicon oxide (SiO ₂ ). In the present invention, a raw material for cement having a composition similar to that of ceramics can also achieve chemical agglutination with carbon nanotubes. A reaction example is as follows (Scheme 2).

[Scheme 2]

CaO + 2(COOH-R) = Ca(COO-R) + H ₂ O

SiO ₂ + 2(COOH-R) = SiO(COO-R) + H ₂ O

Al ₂ O ₃ + 6(COOH-R) = 2Al(COO-R) ₃ + 3H ₂ O

Therefore, using this point, it can be confirmed that the effect of improving the cement strength of the carbon nanotubes is improved by allowing the nanoscale carbon nanotubes, which are difficult to see with the naked eye, to have the maximum dispersibility without their own agglomeration.

The specific surface area of the carbon nanotubes may be about 70 m ² /g to about 150 m ² /g. Specifically, the outer diameter may be about 20 nm to about 30 nm, and the length may be about 10 um to about 30 um. More specifically, the inner diameter may be from about 5 nm to about 10 nm, and the bulk density may be from about 0.2 g/cm ³ to about 0.5 g/cm ³ . It may have excellent physical and mechanical properties as a cement reinforcing material. The specific surface area of the carbon nanotube may mean a nitrogen adsorption specific surface area measured according to the BET method. When the specific surface area of the carbon nanotubes is about 70 m ² /g or more, the contact area with the acid can be increased, so that a dispersion having further excellent dispersibility of the carbon nanotubes can be obtained. If the specific surface area of the carbon nanotube is about 150 m ² /g or less, it is possible to suppress damage to characteristics such as conductivity, thermal conductivity, and strength of the fibrous carbon nanostructure.

The oxygen content of the carbon nanotube having the oxidized surface may be about 10% to about 20% relative to the carbon content. The above-described oxygen content may refer to a value obtained by calculating the ratio of the abundance of oxygen atoms (O) to 100% of the total atomic weight constituting the surface of the carbon nanotube. When the oxygen content is less than about 10%, a sufficient number of chemical agglomerations with the cement raw material may not occur, and when the oxygen content is less than about 20%, the dispersibility may exhibit a maximum value.

Through the present invention, it was confirmed that the conventional problem that was limited in the production of high-strength concrete due to agglomeration during the production of carbon nanotube-mixed concrete could be solved. Specifically, the pre-treated carbon nanotubes were mixed with the cement raw material in a dry process in the previous stage of cement manufacturing and chemical bonding with the cement raw material was induced, so that the cement strength improvement effect could be maximized even by the input of a small amount of carbon nanotubes. Therefore, the present invention can be usefully used in the manufacture of multi-functional concrete in the construction field.

1 is a scanning electron microscope (SEM) photograph of a commercial multi-wall carbon nanotube according to an embodiment of the present invention.
2 shows a schematic diagram of carbon nanotube functionalization.
Figure 3 shows a multi-wall carbon nanotube acid treatment reflux process according to an embodiment of the present invention.
4 is a schematic diagram of the production of carbon nanotube agglutination mixed cement.
5 is a graph showing the weight reduction rate of multi-wall carbon nanotubes by TGA.
6 is a photograph of a multi-wall carbon nanotube agglutination mixed cement clinker prepared in an embodiment of the present invention.
7 is a contrast photograph of multi-walled carbon nanotube agglutination mixed cement and ordinary portland cement (OPC).
8 is a graph showing the specific gravity test results of agglutination cement and ordinary cement (OPC) according to the mixing rate of the multi-wall carbon nanotubes in FIG. 7 .
9 is a graph showing the results of a fineness test of cement.
10 is a graph showing the results of the cement stability test.
11 is a graph showing the cement setting time test results.
12 is a graph showing the mortar compressive strength test results for each blend of multi-wall carbon nanotube agglutination cement prepared in an embodiment of the present invention.
13 is a graph showing the improvement rate of mortar compressive strength for each compounding.
14 is a graph showing the mortar flexural strength test results for each compounding.
15 is a graph showing the improvement rate of mortar flexural strength for each compounding.
16A is a SEM image of P-MWCNTs (MWCNTs without pretreatment) agglomerated cement paste.
16b and 16c are SEM images of F-MWCNTs (pre-treated MWCNTs) agglomerated cement paste with different imaging times.
17 is a graph showing the results of measuring the compressive strength of concrete designed for mixing in an example of the present invention.
18 is a graph showing the measurement result of splitting tensile strength of concrete designed by mixing in one embodiment of the present invention.
19 is a graph showing the results of measurement of the flexural strength of concrete mixing designed in an example of the present invention.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example 1. Pretreatment of carbon nanotubes through acid treatment reflux

Multi-walled carbon nano tubes (MWCNTs) used in the experiment were manufactured by CHEAPTUBES Inc. (Grafton, Vermont, USA) with a purity of 99% or more. The estimated diameter and length of the initial multi-walled carbon nanotubes from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements performed by the manufacturer ranged from about 28 nm to about 22.5 μm on average. The characteristics of the multi-wall carbon nanotubes used in the experiment are shown in Table 1 below.

Outer diameter / nm 20-30 Inside diameter / nm 5-10 Length / μm 10-30 Purity/% 95 or more Minutes (Ash) / % less than 1.5 Specific surface area / m ² /g 110 Electrical conductivity / (S/cm) over 100 Bulk density / g/cm ³ 0.28 True density / g/cm ³ 2.1

Nitric acid (HNO ₃ ) and sulfuric acid (H ₂ SO ₄ ) manufactured by The Science Company (Lakewood, Colorado, USA) were used as oxidizing agents for acid treatment of multi-wall carbon nanotubes, respectively, and each physical · Chemical properties are shown in Table 2 below.

classification Nitric acid (NITRIC ACID) SULFURIC ACID Chemical formula HNO ₃ H ₂ SO ₄ Concentration / % 68-70 58-98 Appearance colorless transparent liquid colorless transparent liquid Hydrogen ion concentration (pH at 20℃) 1 or more 0.3 or more Solubility Can be diluted in water Can be diluted in water Specific gravity 1.41 1.48-1.84

1 is an SEM photograph of a commercialized multi-walled carbon nanotube, which is a carbon nanotube, before acid treatment, and agglomeration of the multi-walled carbon nanotube could be observed. To solve such agglomeration, as shown in FIG. 2, CNTs having an oxygen-functionalized surface were pretreated with an acidic solution. 3 shows an acid treatment process. About 2 g of multi-wall carbon nanotubes were put into about 200 ml of an oxidizing solution in which sulfuric acid and nitric acid were mixed at a ratio of 3:1 (volume ratio), and then refluxed at about 70°C. Then, the CNTs extracted through the filter paper were dried at about 100° C. or less for about 24 hours.

Example 2. Carbon nanotubes (CNTs) chemical agglutination cement production

Figure 4 shows a schematic diagram of the carbon nanotube agglutination mixed cement production. As an embodiment of the present invention, among carbon nanotubes, multi-wall carbon nanotubes were used. In order to prepare the multi-wall carbon nanotube agglutination type mixed cement, the multi-wall carbon nanotubes pretreated according to Example 1 were first added to the raw material supplied from G Cement of the United States in about 0.25 wt%, about 0.5 wt%, compared to the raw material of cement. , about 0.75 wt %, about 1 wt %, about 1.25 wt %, and about 1.5 wt %, respectively, and then primary grinding was performed to a size of about 75 μm using a rotary cup milling device. Thereafter, secondary dispersion of MWCNTs of MWCNTs is induced along with secondary grinding of the same raw material for cement using a jar ball milling device. The pulverized cement raw material containing MWCNTs is mixed evenly with ethanol. This is to prevent the movement of water-soluble substances in the raw material of cement, and the raw material for cement containing MWCNTs evenly mixed with ethanol is made into dumplings with a diameter of about 20 mm to about 30 mm in an argon gas environment of a high-temperature furnace. Firing was performed up to 1450°C. Thereafter, multi-wall carbon nanotube agglutination cement clinker (FIG. 6) and gypsum for preventing flash set of cement are mixed with about 2.5% to about 4% compared to clinker, and primary rotary cup milling (rotary cup milling) ) and secondary jar ball milling were performed again to prepare cement having a target specific surface area. As shown in FIG. 7 , it was confirmed that the multi-wall carbon nanotube agglutination cement exhibited an even black color compared to ordinary portland cement (OPC). It can be considered that the dispersed multi-walled carbon nanotubes are evenly distributed in the cement.

division SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO Na ₂ O K ₂ O SO ₃ Ratio limestone(%) 0.05 0.04 0.01 53.79 0.30 0.57 0.08 0.43 78.52 Quartzite (%) 92.85 3.95 1.25 0.10 0.00 0.00 0.95 0.00 11.12 Copper slag (%) 33.20 5.00 60.60 2.80 1.60 0.00 0.90 1.20 2.98 clay (%) 45.40 38.10 0.87 0.10 0.05 0.03 0.25 0.01 7.37 MWCNTs (%) Cement raw material * 0.5, 0.75, 1, 1.25, 1.5 %

Table 3 shows the chemical composition and mixing ratio of raw materials for manufacturing the multi-wall carbon nanotube agglomerated mixed cement. However, the reason that the sum of the chemical components of limestone does not reach 100% is because gas components such as CO ₂ are excluded.

Example 3. CNTs agglomerated concrete mix design

Concrete mixing design was performed using the multi-wall carbon nanotube agglutination mixed cement prepared in Example 2. Table 4 below shows the concrete formulation used.

w/b
(%) S/a
(%) Air
(%) W
(kg/m ³ ) Unit weight (kg/m ³ ) SP
(BΥ%) w/b
(%) S/a
(%) Air
(%) W
(kg/m ³ ) C S G SP
(BΥ%) 55 48.2 4.5 165 300 871 947 0.8

(In Table 4, w/b: water binder ratio, S/a: fine aggregate ratio, Air: air quantity, W: unit quantity C: unit cement quantity S: unit fine aggregate quantity G: unit coarse aggregate quantity, SP: superplasticizer ) can mean

Test Example 1. Differential Thermal Analysis of Pretreated Multi-Walled Carbon Nanotubes

Two different environments were applied to the pretreated multi-wall carbon nanotubes: a normal atmospheric condition containing oxygen and an inert gas, argon gas. reviewed.

5 shows the results of the TGA experiment. It can be seen that the weight of differential heat carried out in air was rapidly reduced at about 550 °C, and most of the multi-walled carbon nanotubes were oxidized at about 650 °C. On the other hand, it was confirmed that about 20% of the multi-wall carbon nanotubes were oxidized in an inert gas argon gas environment. This result indicates that about 20% of carbon nanotubes can be lost when carbon nanotube agglutination mixed cement is fired.

In general, the cement manufacturing process goes through a high-temperature firing process (about 1250°C to about 1450°C) for the phase change of raw materials for cement. In this process, multi-walled carbon nanotubes, whose main element is carbon, are produced with carbon dioxide, oxygen, and moisture as shown in the following formula. There is a problem that may cause an oxidation reaction to cause weight loss (Equation 1).

(Equation 1)

C + CO ₂ (g) → 2CO (g)

2C + O ₂ (g) → 2CO (g)

C + H ₂ O(g) → CO(g) + H ₂ (g)

In the present invention, since carbon nanotubes undergo a firing process together with cement raw materials in the dry process, it was confirmed that introducing argon gas during firing in order to solve the problem of weight reduction is most effective.

Test Example 2. Evaluation of properties of carbon nanotube agglutination mixed cement

1.1 Cement specific gravity test

8 shows the results of the specific gravity test of agglutination cement and general cement (OPC) for each mixing rate of multi-wall carbon nanotubes. As a result of the experiment, the average specific gravity value of three times of general cement was about 3.17, and in the case of multi-wall carbon nanotube agglomerated cement, the specific gravity value was from about 3.15 to about 3.17 at the maximum by mixing rate. Accordingly, it was confirmed that the multi-wall carbon nanotube agglutination mixed cement prepared in Example 2 had an appropriate specific gravity.

1.2 Cement fineness test

In order to measure the fineness of the mixed cement prepared in Example 2, a test method using an air permeation device was performed. The air permeable device used in this method sucks a certain amount of air through a cement bed having a constant porosity, and determines the fineness of the air according to the speed of the air flowing through the bed. The fineness test was conducted frequently to determine the first and second milling times of cement clinker, and the optimal milling time was determined to exceed the KS standard value of about 2800 cm ² /g. As shown in FIG. 9 , it was confirmed that all three test results exceeded the KS regulation value.

1.3 Stability test by autoclave expansion of cement

Calcium oxide (CaO) and magnesium oxide (MgO) contained in the multi-walled carbon nanotube agglutination mixed cement material prepared in Example 2, or autoclave expansion degree to determine the index of potential expansion due to these two components The test was carried out. The experimental results are shown in FIG. 10 . The cement stability (%) described in FIG. 10 shows the difference in volume before and after expanding the cement sample in the autoclave. As shown in FIG. 7 , it was confirmed that all specimens exhibited a value of about 0.8% or less as stipulated in KS.

1.4 Mortar setting time test

In general, in order to measure the setting time of cement, the method of measuring the cement setting time by a Gilmore needle is adopted. The present invention aims to compare the setting characteristics between cement containing simple multi-walled carbon nanotubes and OPC, and in order to more quantitatively confirm the setting characteristics according to elapsed time, MWCNTs agglutination cement and standard sand according to KS F 2436 The setting time according to the penetration resistance of the mortar was measured, and the experimental results are shown in FIG. As shown in FIG. 11 , it was confirmed that all specimens including multi-walled carbon nanotubes exhibited very similar coagulation properties to OPC.

1.5 Compressive strength test of mortar

In order to measure the compressive strength of the multi-walled carbon nanotube agglomerate mixed cement prepared in Example 2, a test was performed according to the KS standard prescribed in the compressive strength test method of hydraulic cement mortar. An about 50 mm Х about 50 mm Х about 50 mm cubic mold was used to prepare the test specimen. After the specimen was stored in a humid room for about 24 hours, it was demolded and cured in water at about 23±2℃. The compressive strength of each compound by age is shown in FIG. 12, and the compressive strength enhancement rate is shown in FIG. 13. Compared with OPC, all specimens including multi-walled carbon nanotubes showed a strength value that exceeded this, and in particular, the highest strength ratio (143% ) was shown. Unlike the prior art, which showed high compressive strength as the mixing rate of carbon nanotubes increased, it was found that the maximum compressive strength expression rate was exhibited with sufficient dispersibility even at about 1 wt%.

1.6 Flexural strength test of mortar

The multi-wall carbon nanotube agglutination mixed cement mortar flexural strength test specimen prepared in Example 2 was molded using a mold having a cross section of about 25.4 mm Х about 25.4 mm and an effective gage distance of about 254 mm used in the cement stability test. The measuring equipment was pressurized with a force of about 890 N to about 1800 N per second using an electro-hydraulic servo universal test device capable of applying a maximum load of 1000 kN until the specimen was destroyed. Fig. 14 shows the flexural strength for each formulation at 28 days of age, and Fig. 15 shows the flexural strength enhancement rate. As shown in the figure, compared with OPC, all specimens including multi-walled carbon nanotubes showed flexural strength that exceeded OPC. It showed an improvement rate of 158%.

Comparative Example 1. Preparation of mixed cement by physical mixing of carbon nanotubes

Cement clinker was prepared by calcining the raw material of cement at about 1450° C. in the air without pretreatment of the carbon nanotubes of Example 1. After gypsum was mixed with the clinker in the same manner as in Example 2, the clinker in which the wet gypsum was added was pulverized. About 1 wt%, about 1.5 wt%, about 2 wt%, about 5 wt%, about 10 wt%, and about 20 wt% of the carbon nanotubes prepared in the pulverized clinker were added and mixed with respect to the weight of the cement raw material. As a result, unlike Examples 1 and 2, it was shown that the compressive strength of the mortar would be 150% or more only when the degree of improvement in the strength of the final cement was 10 wt% or more based on the weight of the cement raw material. In comparison with the results of Test Example 1.5, it is inferred that, in the case of physical mixing in a wet process rather than chemical agglomeration of carbon nanotubes and cement raw materials, the aggregation phenomenon of carbon nanotubes is affected and the strength enhancement efficiency compared to the addition amount is significantly reduced. Could.

Therefore, combining Test Examples 1.1 to 1.6 and Comparative Example 1, it can be seen that carbon nanotubes are evenly dispersed in the cement composite by showing superior results despite a relatively low incorporation rate of carbon nanotubes. Moreover, the results of analyzing the cement paste using a scanning electron microscope (SEM) to determine whether such dispersion is actually visually confirmed is shown in FIG. 16 . As a result, it was confirmed that the agglomeration phenomenon was confirmed in the case of the carbon nanotube mixed cement that was not pretreated in FIG. 16A, but it was confirmed that the pretreated carbon nanotube agglutination mixed cement of FIGS. 16B and 16C was evenly dispersed without agglomeration.

Test Example 2. Performance evaluation of mixed-designed carbon nanotube agglomerated concrete

2.1 Performance evaluation of unhardened concrete

Table 5 shows the results of the evaluation of the physical properties of the concrete to which the multi-wall carbon nanotube agglutination mixed cement prepared in Example 3 was applied.

Combination items Slump (mm) air (%) setting time (hour) wet density
(kg/m ³ ) Initial Final OPC(a) 120 5.4 8.0 10.5 2,246 OPC(b) 115 5.0 8.5 10.5 2,237 MWC 0.25 wt% 125 5.5 7.5 10.0 2,251 MWC 0.50 wt% 120 5.2 7.5 9.0 2,245 MWC 0.75 wt% 120 5.4 7.0 8.5 2,252 MWC 1.00 wt% 120 5.6 7.5 8.5 2,251

(In Table 5 above, MWC: MWCNTs, slump: (slump) concrete slump measurement value, air: (air) concrete air amount measurement value, setting time: (setting time), wet density: (Wet density) means the unit volumetric weight of concrete. ) Because there is a risk of differences in physical properties manufactured on the market, commercially available general cement (OPC(a)) and laboratory-produced general cement without CNTs (OPC(b)) were selected as standard formulations for each experiment.

As a result, there was almost no change in the properties of non-hardened concrete such as slump, air volume, and setting time. In the setting time, the higher the carbon nanotube mixing rate, the higher the setting rate was, but the fluidity results were all within the error range. This may be due to the difference from the existing method of mixing carbon nanotubes separately when mixing concrete. It can be seen that the carbon nanotubes, which have already been physically and chemically agglomerated with cement, are not separated by forced mixing with water or aggregate, but are integrated with the cement particles, and thus do not affect the physical properties before hardening. In particular, after mixing, which is pointed out as a problem with concrete mixed with CNTs, there was no phenomenon that the carbon nanotube particles floated on the surface together with the bleed water or precipitated under the mold, and there was no phenomenon that the bleed water appeared black after mixing.

2.2 Hardened concrete strength properties

In order to directly or indirectly evaluate the dispersibility of multi-wall carbon nanotube agglomerated cement, mechanical properties such as compressive strength, splitting tensile strength, and flexural strength were evaluated. The experimental method followed each KS standard, and underwater curing was performed until the age of measurement.

17 to 19 and Table 6 show the strength characteristics evaluation results of the concrete to which the mixed cement obtained by interlocking the multi-wall carbon nanotubes prepared in Example 3 is applied, and through this, it can be seen that the multi-wall carbon nanotubes have dramatically superior strength characteristics. could

strength increase rate
(%) OPC (a) OPC (b) MWC 0.25 wt% MWC 0.50 wt% MWC 0.75 wt% MWC 1.00 wt% MWC 1.50 wt% compressive strength 100 95.0 118.7 128.4 126.4 128.8 124.1 Splitting Tensile Strength 100 94.1 123.5 144.9 158.1 155.4 156.6 flexural strength 100 98.8 120.2 145.7 160.7 154.8 153.6

(The OPC (a) in Table 6 refers to the existing commercially available carbon nanotube-free Falkland cement, and the OPC (b) refers to the carbon nanotube-free Falkland cement manufactured at the laboratory level.) As shown in Table 6, the increase in strength due to the incorporation rate of carbon nanotubes is clearly shown in all strength characteristics. At a mixing ratio of about 0.25%, the strength improvement rate is about 120% compared to OPC(a), and in other mixing ratios of about 0.5 wt% or more, the compressive strength improvement ratio is about 125% or more, and the bending and tensile strength improvement ratio is about A value of 145% or more is shown at almost all ages. In particular, when the mixing ratio is about 0.5% wt% or more, almost similar results are shown at all ages. It can be inferred that the dispersion has already been sufficiently completed at the mixing ratio of about 0.5 wt% to about 1.50 wt%, reaching a limit that can be enhanced by the bridging effect of carbon nanotubes. It was confirmed that the optimal mixing ratio of the multi-walled carbon nanotube agglomerate mixed cement produced through this was within about 0.5 wt% to about 1.50 wt% of the weight of the raw material of cement, and the oxidation rate of carbon nanotubes at the cement firing temperature of about 1450 ° C. Considering that it was about 20%, it was found that sufficient strength improvement could be achieved even with about 0.4 wt% to about 1.20 wt% of carbon nanotubes relative to the weight of cement. Therefore, even in the synthesis of Test Example 2, an amount much less than the weight of carbon nanotubes required for physical mixing of carbon nanotubes through the wet process as in Test Example 1, specifically, about 0.5 wt% to about 1.50 wt. It was confirmed that even within %, it can bring about superior strength improvement.

Claims (9)

A first step of preparing a pre-treated carbon nanotube by putting the carbon nanotube into an acidic solution;
a second step of preparing a cement material by mixing the raw material for cement and the pretreated carbon nanotubes in a solvent;
a third step of calcining the cement material mixed in the second step to produce clinker; and
A method for producing carbon nanotube agglutination cement, comprising a fourth step of mixing gypsum with the clinker produced in the third step,
In performing the third step, the cement material is fired under an inert gas condition to prevent oxidation of the pretreated carbon nanotubes.
The method of claim 1,
The first step is a method for producing carbon nanotube agglutination cement comprising the step of refluxing for 1 hour to 24 hours.
delete The method of claim 1,
In performing the second step, the pretreated carbon nanotubes are mixed in a ratio of 0.5 wt% to 1.5 wt% based on the weight of the raw material for cement, a method for producing carbon nanotube agglutination mixed cement.
The method of claim 1,
The sintering temperature of the third step is 1250 ° C to 1450 ° C.
The method of claim 1,
In performing the fourth step, the gypsum is mixed in a ratio of 2.5 wt% to 4 wt% based on the weight of the clinker, a method for producing carbon nanotube agglutination cement.
carbon nanotubes having an oxidized surface; and
containing cement raw materials;
As a carbon nanotube agglutination mixed cement, wherein the carbon nanotube having the oxidized surface and the cement raw material are chemically crossed,
Wherein the carbon nanotubes are mixed in a ratio of 0.5 wt% to 1.5 wt% based on the weight of the cement raw material, carbon nanotube agglutination cement.
8. The method of claim 7,
The carbon nanotubes have a specific surface area of 70 m ² /g to 150 m ² /g, the carbon nanotube agglutination cement.
8. The method of claim 7,
The oxygen content of the carbon nanotube having the oxidized surface is 10 atomic% to 20 atomic% relative to the carbon content, the carbon nanotube agglutination cement.

Images