WO2008056927A1

WO2008056927A1 - Method for manufacturing cement having minute particle by chemical synthesis and method for manufacturing concrete using thereof

Info

Publication number: WO2008056927A1
Application number: PCT/KR2007/005575
Authority: WO
Inventors: Byung Wan Jo
Original assignee: Iucf-Hyu (Industry-University Cooperation Foundation Hanyang University)
Priority date: 2006-11-06
Filing date: 2007-11-06
Publication date: 2008-05-15
Also published as: KR100761452B1

Abstract

A method for producing particulate cement is provided. The method includes the steps of : preparing a sol containing 100 parts by weight of water and 50 parts by weight or less of sodium aluminate arid a gel containing 8 to 40 parts by weight of a silica powder and 100 parts by weight of water, and separately aging the sol and the gel; mixing the aged sol with the aged gel; and adding at least one additive to the mixture, followed by cleaning and drying. Further provided is a method for producing concrete using cement produced by the cement production method. The concrete production method includes the steps of adding 10 to 150 parts by weight of a chemical activator and 50 to 500 parts by weight of aggregates to 100 parts by weight of the cement, and curing the mixture.

Description

[ DESCRIPTION J

[ Invention Title ]

METHOD FOR MANUFACTURING CEMENT HAVING MINUTE PARTICLE BY CHEMICAL SYNTHESIS AND METHOD FOR MANUFACTURING CONCRETE USING THEREOF

[ Technical Field ]

The present invention relates to a method for producing cement and a method for producing concrete using cement produced by the cement production method . More particularly, the present invention relates to a method for producing environmentally friendly cement having fine particles and a method for producing concrete with excellent physical properties .

[ Background Art ]

Portland cement is general ly used in the current construction industry. Since the invention of Portland cement in Britain in 1824 by Joseph Aspdin, a great deal of progress has been made in the cement industry year after year . A large quantity of energy is consumed in the cement industry and it is est imated that 700 kg of CO2 is released per ton of cement produced. Since the Kyoto protocol was adopted to prevent global warming as a result of increased greenhouse gas emissions , the cement industry has been faced with difficulties arising from environmental problems , such as natural resource consumpt ion and global warming, and release of substances harmful to humans . Recent rapid development of nat ional economy in Korea has led to an improvement in the standard of Korean l i fe. Under these circumstances , high functionality, ecologically friendly, high value-added construction materials have received considerable attention. In advanced countries, numerous studies have focused on trying to improve the performance of concrete, for example, by the addition of one or more additives selected from slag powder, silica fume, nanosilica, etc. Despite these studies, traditional calcination processes of limestone for the production of Portland cement are still employed.

Environmental destruction problems such as deforestation are inevitable due to the exploitation of natural resources (e.g., limestone) and considerable cost is incurred in calcining for the production of conventional cement. Global warming arising from atmospheric emission of carbon dioxide (CO2) during cement production causes unusual climate change. For these reasons, the cement production industry is considered as one that involves serious environmental pollution problems.

Cement has substantial disadvantages in terms of its materials. For example, cement-based concrete suffers from many problems, such as incidence of skin diseases (e.g., atopy) due to hexavalent chromium ions (Cr⁶⁺) and strong alkalinity of the concrete, and structural defects due to drying shrinkage and cracks caused after hydration.

These problems will be discussed in greater detail below.

Firstly, exploitation of natural resources such as limestone, clay, gypsum and aggregates leads to the destruction of natural environment.

Secondly, much energy corresponding to a temperature of about l,450°C is consumed for the calcination of clinker such as limestone [CaCQs ^→ CaO + CO2 Tl.

Thirdly, CO2 is released to cause serious global environmental problems such as global warming and unusual climate change. Fourthly, Ca(OH)₂, a hydration product, is strongly alkaline (pH 13.5-13.8) and hexavalent chromium ions (Cr⁶⁺) are formed, thus posing hazards to human health. Fifthly, defects {e.g., cracks) of concrete are formed due to adverse

factors, e.g., drying shrinkage and heat of hydration of a cured product resulting

from the hydration of cement with water. These defects may negatively affect the

solidity of concrete structures such as buildings.

[Disclosure]

[ Technical Problem ]

In view of this situation, the present inventor has undertaken extensive studies, and as a result, found that the above problems can be solved by applying chemical synthesis to produce cement having fine particles whose size is in the nanometer (HT⁹ m) range. Thus, it is a first object of the present invention to provide a method for producing particulate cement having nanometer-sized particles.

It is a second object of the present invention to provide a method for

applying cement produced by the cement production method to produce concrete.

[ Technical Solution]

In order to accomplish the first object of the present invention, there is provided a method for producing particulate cement, the method including the steps of: preparing a sol containing 100 parts by weight of water and 50 parts by weight or less of sodium aluminate and a gel containing 8 to 40 parts by weight of a silica powder and 100 parts by weight of water, and separately aging the sol and the gel; mixing the aged sol with the aged gel; and adding at least one additive to the mixture, followed by cleaning and drying.

In order to accomplish the second object of the present invention, there is provided a method for producing concrete, the method including the steps of: adding 10 to 150 parts by weight of a chemical activator and 50 to 500 parts by weight of aggregates to 100 parts by weight of cement produced by the cement production method; and curing the mixture.

[Advantageous Effects]

Calcination of limestone and pulverization into clinker are used to produce

_Portland cement in conventional methods, whereas chemical synthesis is used to produce particulate cement in the cement production method of the present invention. The cement production method of the present invention offers the following effects: i) Environmental destruction due to the exploitation of natural resources necessary for the production of conventional cement is prevented; ii) High energy cost is avoided; iii) Environmental pollution resulting from the emission of CO2 is prevented; iv) Incidence of skin diseases {e.g., atopy) due to hexavalent chromium ions (Cr⁶⁺) is prevented; and v) Various adverse factors, e.g., drying shrinkage and cracks formed after hydration, which pose threats to the stability of concrete structures, are removed.

In addition, according to the cement production method of the present invention, constituent chemical substances of cement are used without undergoing calcination to produce cement at markedly reduced cost in an effective and simple manner.

Furthermore, cement having nanometer-sized particles produced by the cement production method of the present invention is mixed with suitable amounts of a chemical activator and aggregates and_'. is then dry-cured by alkali activation to produce a cured product having desired strength. Therefore, the cement is suitable for use as a replacement for conventional cement.

[Description of Drawings] FIG.1 is view illustrating the processes of a method for producing cement according to the present invention.

FIG.2 is a graph showing the results of energy dispersive x-ray (EDX) analysis for cement produced by a method of the present invention. FIG.3 is a graph showing the particle size distribution of cement produced by a method of the present invention.

FIG.4 is a scanning electron microscopy (SEM) image (30,000 x) of cement produced by a method of the present invention.

FIG. 5 is a graph showing the variation in the compressive strength of concrete produced by a method of the present invention as a function of aging time.

[Best Mode]

Exemplary embodiments of the present invention will now be described in greater detail. The present invention provides a method for producing cement by chemical synthesis. A detailed explanation of the_^method will be provided below.

First, 100 parts by weight of water and 50 parts by weight or less of sodium aluminate are used to prepare a sol. When the sodium aluminate is used in an amount exceeding 50 parts by weight, it may remain undissolved {i.e. supersaturated) in the water. The sol may further contain 100 parts by weight of water and 60 parts by weight or less of sodium hydroxide. The use of the sodium hydroxide in an amount greater than 60 parts by weight may allow the sodium hydroxide to be in a supersaturated state in the water.

The sodium aluminate is used in an amount of 3 to 30 parts by weight and the sodium hydroxide is used in an amount of 5 to 40 parts by weight. The use of both sodium aluminate and sodium hydroxide is most preferred from the viewpoint of economic efficiency. Thereafter, 100 parts by weight of water and 8 to 40 parts by weight of a silica powder are mixed together to prepare a gel.

The use of the silica powder in an amount of less than 8 parts by weight may cause a reduction in the purity of the final cement powder, while the use of the silica powder in an amount of more than 40 parts by weight may lead to a risk of supersaturation.

The water is preferably distilled water in terms of the purity of the final cement, but is not limited to distilled water.

The sol and the gel are separately aged and mixed together. Then, at least one additive is added to the mixture and allowed to react for a specified time. Then, the reaction mixture is cleaned and dried.

The aging is preferably conducted in the temperature range of room temperature to 90°C for 24 to 36 hours tp disperse the sol and gel particles. There is no particular limitation on the aging conditions so long as the particles can be dispersed.

The additive is selected from SiC, ZrU2, TiU2, Ag, MgO, carbon nanotubes (CNTs), Fe2θ3, and TEA(triethanolamine). The most effective amount of the additive is from about 0.003 to about 5 parts by weight, based on the weight of the mixture.

In addition to the aforementioned materials, any additive that is already known to improve the performance of cement may be used in the present invention. Too large an amount of the additive may bring about various problems such as brittle fracture. Therefore, the content of the additive is preferably limited to 5 parts by weight.

The resulting mixture is dried and pulverized to prepare a powder. The powder preferably includes fine particles having a size of about 100 to about 200 nm. The size of the fine particles is not necessarily limited to this range. The particles preferably make up 90% or more of the volume of the powder. The pulverization is based on the concept of dispersing the particles. Any known technique, such as milling, may be^:employed to pulverize the mixture. The present invention also provides a method for producing concrete. Specifically, the method includes the steps of adding 10 to 150 parts by weight of a chemical activator and 50 to 500 parts by weight of aggregates to 100 parts by weight of cement produced by the cement production method, and curing the mixture. The chemical activator is preferably selected from the group consisting of sodium hydroxide, sodium suicide, sodium carbonate, sodium sulfate, and mixtures thereof. Any alkaline activator that can replace the chemical activator may be used. The addition of the chemical activator in an amount of less than 10 parts by weight causes problems such as poor workability. Meanwhile, the addition of the chemical activator in an amount of more than 150 parts by weight may induce the separation of the materials, causing problems during the construction of the final concrete. The aggregates may be selected from sand, gravel, broken gravel, and other natural materials. Artificial materials selected from recycled and advanced materials may be used as the aggregates. The use of the aggregates in an amount of less than 50 parts by weight with respect to the weight of the cement extremely increases the construction cost of the final concrete. Meanwhile, the use of the aggregates in an amount of more than 500 parts by weight with respect to the weight of the cement may cause poor adhesion of the aggregates to the cement, resulting in a decrease in the strength of the final concrete.

The mixture may be insufficiently cured at a temperature lower than 20°C. A curing temperature as high as 250°C is economically undesirable. Therefore, the curing temperature is preferably limited to 20 to 250°C, but is not limited to this range.

[Mode for Invention] Hereinafter, the methods of the present invention will be explained in more detail with reference to the following preferred examples. However, these examples are given for the purpose of illustration and are not intended to limit the present invention.

EXAMPLES

40 parts by weight of sodium aluminate was mixed with 100 parts by weight of water to prepare a sol.30 parts by weight of a silica powder was mixed with 100 parts by weight of water to prepare a gel.

Thereafter, the gel and sol were separately aged and mixed together. Triethanolamine (TEA) as an additive was added to the mixture, cleaned and dried to produce cement. This production procedure is illustrated in FIG.1.

FIG.2 shows the results of energy dispersive x-ray (EDX) analysis for the cement, FIG.3 is a graph showing the particle size distribution of the cement, and FIG.4 is a scanning electron microscopy (SEM) image (30,000 x) showing the shape of the cement particles.

The cement was analyzed to have a specific gravity of 2.11 and a specific surface area of 358.24 m²/g. In contrast, typical Portland cement was measured to have a specific gravity of 3.15. Particularly, the specific surface area of the cement produced in Example 1 was about 1,150 times larger than that (3,112 cm²/g) of the Portland cement. From these results, it can be estimated that the smaller size of the cement particles produced in Example 1 led to the increased specific surface area of the cement particles to enable the production of larger numbers of hydrated or cured products around the aggregates and the pore size of the cement particles was decreased, indicating that the cement particles were densified as a whole. Therefore, the cement is expected to show high compressive strength and improved mechanical properties when' compared to conventional cement products.

The proportions of the constituent ingredients of the cement increased according to the following order: Siθ2 > AI2O3 > CaO > Fe2θ3. Particularly, the content of CaO in the cement was much lower than the Portland cement. The cement produced in Example 1 was essentially composed of Siθ2 and AI2O3, which are known as ingredients contributing to the pozzolanic activity. The fact that the AI2O₃ content of the cement produced in Example 1 was higher than that of the _Portland cement represents the formation of a slight amount of C3A, which contributes to an improvement in the strength of the cement. The cement produced in Example 1 was measured to have an average particle size (D50) of 168 nm. Most of the cement particles had a particle size ranging from 120 to 170 nm. The increased specific surface area of the nanometer-sized particles due to their smaller size, which is one of typical characteristics of nanoparticles, enables the production of a highly densified cured product.

30 and 60 parts by weight of sodium aluminate were separately mixed with 100 parts by weight of water to prepare two different sols.30 parts by weight of silica was mixed with 100 parts by weight of water to prepare a gel. Thereafter, the procedure of Example 1 was repeated to produce two kinds of cement.

Supersaturation occurred when the sodium aluminate was used in an amount of 60 parts by weight, which is outside the content range of the sodium aluminate defined above.

50 and 70 parts by weight of sodium hydroxide were separately mixed with 100 parts by weight of water to prepare two different sols.30 parts by weight of silica was mixed with 100 parts by weight of water to prepare a gel. Thereafter, the procedure of Example 1 was repeated to produce two kinds of cement .

The sodium hydroxide used in an amount of 70 parts by weight was not completely dissolved {i.e. supersaturated) in the water.

20 parts by weight of sodium aluminate and 40 parts by weight of sodium hydroxide were mixed with 100 parts by weight of water to prepare a sol.30 parts by weight of silica was mixed with 100 parts by weight of water to prepare a gel. Thereafter, the procedure of Example 1 was repeated to produce cement.

The cement showed satisfactory results in terms of size and composition and material characteristics {e.g., specific_^gravity and fineness) of the particles.

<Example 5> 30 parts by weight of sodium aluminate was mixed with 100 parts by weight of water to prepare a sol.5, 20 and 50 parts by weight of silica were separately mixed with 100 parts by weight of water to prepare three different gels. Thereafter, the procedure of Example 1 was repeated to produce three kinds of cement.

The cement produced using 5 parts by weight of the sodium aluminate, which is outside the content range of the sodium aluminate defined above, showed low purity of the cement powder. Supersaturation occurred when the sodium aluminate was used in an amount of 50 parts by weight, which is also outside the content range of the sodium aluminate defined above.

< Example 6>

In this example, the cement produced in Example 1 was used to produce concrete. The optimal composition of the concrete was determined by varying the amounts of aggregates and a chemical activator used to produce the concrete.

(1) 80 parts by weight sodium hydroxide was separately added to 100 parts by weight of the cement.30, 100 and 550 parts by weight of aggregates were mixed with the cement mixture and cured at 90°C to produce three kinds of concrete. The concrete produced using 30 parts by weight of the aggregates was disadvantageous in terms of its material costs. The concrete produced using 550 parts by weight of the aggregates showed a low strength.

(2) 5, 50 and 160 parts by weight of sodium suicide were separately added to 100 parts by weight of the cement. Each of the cement mixtures was mixed with 150 parts by weight of aggregates and cured at 90°C to produce concrete.

The concrete produced using 5 parts by weight of the sodium suicide and the concrete produced using 160 parts by weight of the sodium suicide showed insufficient strength.

(3) 50 parts by weight of sodium carbonate and 50 parts by weight of sodium sulfate were separately added to 100 parts by weight of the cement to obtain two different mixtures. Each of the mixtures was mixed with 150 parts by weight of aggregates and cured at 90°C to produce₍ concrete.

The two kinds of concrete satisfied the desired specifications.

The concrete produced using 100 parts by weight of the aggregates was measured for compressive strength at a curing temperature of 90°C with varying aging times. The results are shown in FIG.5.

After aging for 7 days, the strength of the concrete produced in Example 6 and Portland cement was measured. As a result, the concrete produced in Example 6 had a strength of 54 MPa with an increment of 128% when compared to that (42 MPa) of the Portland cement.

Claims

[CLAIMS] [Claim 1]

A method for producing particulate cement by chemical synthesis, the method comprising the steps of'■ preparing a sol containing 100 parts by weight of water and 50 parts by weight or less of sodium aluminate and a>-,gel containing 8 to 40 parts by weight of a silica powder and 100 parts by weight of water, and separately aging the sol and the gel; mixing the aged sol with the aged gel; and adding at least one additive to the mixture, followed by cleaning and drying.

[Claim 2]

The method according to claim 1, wherein the sol contains 100 parts by weight of water and 30 parts by weight or less of sodium aluminate.

[Claim 3]

The method according to claim 1, wherein the sol further contains 100 parts by weight of water and 60 parts by weight or less of sodium hydroxide.

[Claim 4]

The method according to claim 3, wherein the sodium hydroxide is present in an amount of 5 to 40 parts by weight in the sol.

[Claim 5]

The method according to claim 1, wherein the aging is conducted in the temperature range of room temperature to 90°C for 24 to 36 hours.

[Claim 6]

The method according to claim 1_> -wherein the additive is selected from SiC, ZrCb, T1O2, Ag, MgO, carbon nanotubes (CNTs), Fe2θ3 and TEA is added in an amount of 0.003 to 5 parts by weight with respect to 100 parts by weight of the water.

[Claim 7]

The method according to claim 1, further comprising the step of pulverizing the dried mixture to prepare a powder including fine particles whose size is 100 to 200 ran wherein the particles make up 90% or more of the volume of the powder.

[Claim 8]

A method for producing concrete, the method comprising the steps of: adding 10 to 150 parts by weight of a chemical activator and 50 to 500 parts by weight of aggregates to 100 parts by weight of particulate cement produced by the method according to any one of claims 1 to 7; and curing the mixture.

[Claim 9] The method according to claim 8, wherein the chemical activator is selected from the group consisting of sodium hydroxide, sodium suicide, sodium carbonate, sodium sulfate, and mixtures thereof.

[Claim 10] The method according to claim 9, wherein the curing is conducted in the temperature range of 20 to 250°C.