WO2003093191A1

WO2003093191A1 - Method for manufacturing recycle cement

Info

Publication number: WO2003093191A1
Application number: PCT/KR2003/000475
Authority: WO
Inventors: Sang-Gyun Oh; Sang-Keun Lee; Byeung-Hee Kang; Jung-Kil Kim; Jae-Cheol Ahn
Original assignee: Re-Form System Co., Ltd.
Priority date: 2002-05-06
Filing date: 2003-03-12
Publication date: 2003-11-13
Also published as: KR100379697B1; AU2003221198A1

Abstract

The present invention relates to a method for manufacturing a recycle cement, and more particularly, to a method for manufacturing cement in which waste concrete or waste mortar is recycled for reuse thereof.

Description

METHOD FOR MANUFACTURING RECYCLE CEMENT

TECHNICAL FIELD

The present invention relates to a method for manufacturing recycle cement, and more particularly, to a method for manufacturing cement in which waste concrete or waste mortar is recycled for reuse thereof.

BACKGROUND ART

Generally, cement is a kind of base material for architecture or engineering work, and is being used with outstanding importance compared with other materials at present as well as the past and is anticipated to be used widely in future.

Cement has advantages in that it is easy to purchase, has a high compressive strength and has outstanding fire resistance and durability, The cement, however, has the largest disadvantage in that it is difficult to reuse.

To this end, most of waste concrete or waste mortar is restricted in its reuse to crushed aggregate or roadbed material for reclamation.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method for manufacturing recycle cement that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method for manufacturing recycle cement in which waste concrete or waste mortar is reprocessed to enable the reuse of hardened cement portions as well as aggregate.

Another object of the present invention is to provide a method for manufacturing recycle cement in which waste concrete and waste mortar are reused to sole problems such as processing of architecture waste, resource production, environment destroy due to the processing of waste, exhaustion of aggregate resource or limestone resource, exhaust of carbon dioxide (C0₂) gas or the like.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings. To achieve the object, there is provided a method for manufacturing recycle cement. The method comprises the steps of: first crushing waste concrete or waste mortar; preheating hardened cement pieces obtained through the first crushing at a temperature ranged from 200 °C to 300 °C for a time interval of 1 hr to 3 hrs; secondly crushing the preheated hardened cement pieces; separating fine pieces having a diameter of 0.15 mm or less from the secondly crushed hardened cement pieces; heating the separated fine pieces at a temperature range of 500 - 900 °C for a time interval of 1 hr to 3 hrs; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS0₄-2H₂0) with the cooled fine pieces. In an aspect of the present invention, the calcium sulfate dehydrate is mixed by an amount of 2 - 6 % in weight.

In an aspect of the present invention, the aforementioned method further comprises the step of mixing at least one selected from a group consisting of blast furnace slag, fly-ash and high range water reducer, along with the calcium sulfate dehydrate.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic view illustrating the concept of recycle cement; FIG. 2 is a schematic view illustrating a method for manufacturing recycle cement according to a preferred embodiment of the present invention; FIG. 3 is a grain size distribution graph depending on sieve size of fine aggregate, and table 3 show weight percents of fine aggregates that have passed screen;

FIG. 4 illustrates the mixture ratio of recycle cement and 28-days compressive strength depending on main heating temperature; FIG. 5 illustrates 28-days compressive strength of recycle cement not containing aggregate depending on main heating temperature;

FIG. 6 illustrates 28-days compressive strength of recycle cement containing aggregate depending on main heating temperature; and

FIG. 7 illustrates 28-days compressive strength depending on main heating temperature in a method for manufacturing recycle cement of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

First, the principle for manufacturing a general cement will be described.

Cement is obtained by heating limestone (CaCOs). In other words, when limestone is heated, cement (CaO) is obtained and dioxide carbon (CO2) is generated. This reaction can be expressed by the following chemical formula 1 : Formula 1

Heat CaC0₃ → Cao + C0₂

As will be seen in the above formula 1 , cement (CaO) is obtained by heating the limestone. The obtained cement reacts with water to generate hardened cement calcium dihydroxide, which can be expressed by the following chemical formula 2: Formula 2 CaO + H₂0 → Ca(OH)₂

In a method for manufacturing recycle cement according to the present invention, the hardened cement (Ca(OH)₂) obtained by the formula 2 is recycled to manufacture cement (CaO), which can be expressed by the following chemical formula 3:

Formula 3 Ca(OH)₂ + Heat → CaO + H₂0

In other words, in the method for manufacturing recycle cement according to the present invention, the hardened cement (Ca(OH)₂) separated from waste concrete or waste mortar is heated to recover the reaction capability with water and thus manufacture recycle cement.

At this time, the heating time and temperature influence several properties of the recycle cement, which will be described in detail in the below.

FIG. 1 is a schematic view illustrating the concept of recycle cement, Referring to FIG. 1 , a building is made by using natural resources such as limestone, aggregate and the like. After an elapse of a long term period, as the life span of the building is ended, it is disassembled. If necessary, its rebuilding is carried out.

At this time, a part of the building waste generated in the disassembling procedure are reclaimed for its treatment, and another part is separated to waste concrete or waste mortar utilized in the invention.

The waste concrete or waste mortar is divided into recycle aggregate and hardened cement pieces through a crushing process. The cement- hardened pieces are reused through a sintering and a chemical treatment as provided in the present invention.

The recycle cement is again mixed recycle aggregate or the like and the mixture is used as the material for the building.

Thus, the present invention enables the reuse of architecture wastes and can solve many problems such as environment destroy, exhaust of resource, waste processing and the like.

FIG. 2 is a schematic view illustrating a method for manufacturing recycle cement according to a preferred embodiment of the present invention.

As shown in FIG. 2, in a method for manufacturing recycle cement, hardened cement pieces that was impossible to reuse, are separated from building waste, along with reusable aggregate and reinforcing bar.

The cement-hardened pieces are subject to a crushing process. In a first crushing step, the cement-hardened pieces are crushed to have a diameter of 5 mm by a crusher. The first crushed hardened cement pieces are subject to a preheating step at a temperature of approximately 250 °C for a time interval of 1 to 3 hrs.

The preheating step is performed to facilitate a second crushing.

After the preheating is completed, the second crushing step is carried out by a ball mill, and fine pieces having a diameter of 0.3 mm or less are separated from the crushed hardened cement pieces.

It is preferable that the fine pieces separated from the cement-hardened pieces have a diameter of 0.15 mm or less.

After that, a main heating of the separated fine pieces is carried out at a temperature range of 500 °C to 900 °C for a time interval of 1 hr to 3 hrs. By the main heating, reacting property of the cement-hardened pieces with water is recovered as described in the above chemical formula 3.

Lastly, the cement-hardened pieces are mixed with cement mixture to manufacture recycle cement.

In more detail, the first crushing step is a step to separate reusable aggregate from the cement-hardened pieces and crush the cement- hardened pieces into fine pieces having a diameter of approximately 5 mm or less.

The preheating step is carried out to enhance an efficiency of the second crushing, by which a difference in the heat expansion rate between the aggregate and the fine pieces is caused, so that aggregate and fine pieces are separated easily.

The cement-hardened pieces are divided into fine pieces having a diameter of 0.15 mm or less by the second crushing step.

The aforementioned first crushing step, preheating step and second crushing step may be replaced by once crushing step. The twice crushing steps and the preheating step are used for easier separation of the fine pieces.

The main heating step is carried out at a temperature range of 500 -

900 °C for a time interval of 1 hr to 3 hrs. Through the main heating, the reacting property of the cement-hardened pieces with water is recovered and the recovered reacting property allows the recycle cement to combine with water and a recycle hardened cement piece to be produced.

Preferably, the main heating temperature is in a range of 650 - 750 °C. In particular, since the hardened cement pieces obtained from aged waste concrete or waste mortar is in a neutralized state, it is more desirable that the main heating temperature be kept in a temperature range of 800 - 900 °C.

From the above facts, it is desirable that the main heating of the cement-hardened pieces be in a temperature range of 500 - 900 °C.

It is necessary to cool the main-heated fine pieces. The cooling step can be rapidly carried out by a separate cooler. Upon considering saving of the manufacturing costs, the main-heated fine pieces may be cooled in an air atmosphere. A predetermined amount of calcium sulfate dehydrate (CaS0₄-2H₂0) is added to the cooled fine pieces to control the reaction rate of the recycle cement with water.

Preferably, the calcium sulfate dehydrate is mixed by an amount of 2 - 6 % in weight. Also, a variety of mixtures may be added to the recycle cement. For instance, the mixture includes blast furnace slag, fly-ash and high range water reducer.

In other words, in order to complement the lowering in the strength of the recycle cement, it is preferable to add predetermined amounts of blast furnace slag and fly-ash.

. Also, in order to complement the fast condensation rate and lowering in the fluidity of the recycle cement, it is preferable to add blast furnace slag, fly-ash and high range water reducer.

Hereinafter, there will be described experimental factors and methods and results to elicit the method for manufacturing recycle cement according to the present invention.

Table 1 illustrates experimental factors and levels, and table 2 illustrates physical properties and symbols of used materials. Table 1

Table 2

As seen in tables 1 and 2, Normal Portland cement is used as the powder, and ratios of used fine aggregate are 30%, 45%, and 55% respectively.

The used Portland cement has a specific gravity of 3.15, and a specific surface area of 3,400 (cm²/g). The polycarboxylic acid-based SP- 8N has a specific gravity of 1.05 ± 0.02.

FIG. 3 is a grain size distribution graph depending on sieve size of fine aggregate, and table 3 show weight percents of fine aggregates that have passed screen. Table 3

Table 4 illustrates mix proportion of water, cement and aggregate and symbols of mixed materials in an experiment for illustrating the effects of the invention.

Table 4

In table 4, to discriminate recycle paste and recycle mortar from original powder and original mortar, symbols of OP, RP, OM, RM are used, mix proportions of water (W) and cement (C) are classified into two indexes of 45 and 55, and proportions of aggregate are classified into indexes of S3, S4 and S5.

Table 5 illustrates chemical components according to main heating temperature of the recycle cement, and represents respective chemical components when the main heating temperature is 0 °C (TO), 400 °C (T4), 700 °C (T7) and 1 ,000 °C (T10).

Table 5

As seen in table 5, according to the main heating temperature, there are shown differences in the specific gravity, fineness and chemical component.

Upon considering that the specific gravity of the natural cement is 3.15 and fineness is 3200 (cm²/g), if the main heating temperature is about 700 °C, it is forecasted that the specific gravity of the recycle cement is lowered than that of the normal cement.

In other words, since the recycle cement is lower in the specific gravity than the natural cement, it has an advantage contributable to the lightweight of the normal cement.

FIG. 4 illustrates the mixture ratio of recycle cement and 28-days compressive strength depending on main heating temperature.

As shown in FIG. 4, there appear differences in the compressive strength of the recycle cements according to the mix proportions. However, when considering variations with the main heating temperature, the compressive strength has the highest value when the main heating temperature is 700 °C.

FIG. 5 illustrates 28-days compressive strength of recycle cement not containing aggregate depending on main heating temperature, and FIG. 6 illustrates 28-days compressive strength of recycle cement containing aggregate depending on main heating temperature.

As shown in FIG. 5, RP45 and RP55 show a difference in the compressive strength according to the mix proportion. However, when the main heating temperature is 700 °C, it is confirmed that they commonly have the highest compressive strength of 370 kg/cm² and 290 kg/cm².

Also, as shown in FIG. 6, in case that aggregate is included in, there is a difference in the compressive strength. However, when the main heating temperature is 700 °C, it is confirmed that they have the highest compressive strength.

As seen in FIG. 7, it is confirmed that the compressive strength increases abruptly as the main heating time increases to 90 minutes but its increasing degree slows down according to the elapse of time.

As seen in FIG. 7, it is desirable to maintain the main heating temperature for a time interval of 1 - 3 hrs for the strength development of the recycle cement. Also, since the main heating time influences the manufacturing costs of the recycle cement directly, it is desirable to properly control the main heating time according to the strength of the recycle cement.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention.

Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and there equivalents.

Industrial Applicability

According to the method for manufacturing recycle cement of the invention, used waste concrete or waste mortar is reprocessed to enable reuse of hardened cement pieces as well as aggregate. Also, the invention reuses waste concrete and waste mortar to solve processing problem of building waste, resource production and environment destroy problem due to the processing of waste and help to protect the environment.

In addition, exhaust problems of aggregate resource or limestone, and public petition caused by the construction of waste processing facilities, exhaust problem of carbon dioxide gas can be solved.

Claims

1 . A method for manufacturing recycle cement, the method comprising the steps of: first crushing waste concrete or waste mortar; preheating hardened cement pieces obtained through the first crushing at a temperature ranged from 200 °C to 300 °C for a time interval of 1 hr to 3 hrs; secondly crushing the preheated hardened cement pieces; separating fine pieces having a diameter of 0.15 mm or less from the secondly crushed hardened cement pieces; heating the separated fine pieces at a temperature range of 500 - 900 °C for a time interval of 1 hr to 3 hrs; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS0₄-2H₂0) with the cooled fine pieces.

2. The method of claim 1 , wherein the calcium sulfate dehydrate is mixed by an amount of 2 - 6 % in weight.

3. The method of claim 1 , further comprising the step of mixing at least one selected from a group consisting of blast furnace slag, fly-ash and high range water reducer, along with the calcium sulfate dehydrate.

4. A method for manufacturing recycle cement, the method comprising the steps of: crushing waste concrete or waste mortar; separating fine pieces having a diameter of 0.15 mm or less from the crushed hardened cement pieces; heating the separated fine pieces at a temperature range of 500 - 900

°C for a predetermined time interval; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS0₄-2H₂0) with the cooled fine pieces.

5. The method of claim 4, wherein the crushing step comprises the steps of: first crushing waste concrete or waste mortar; preheating hardened cement pieces obtained through the first crushing; and secondly crushing the preheated hardened cement pieces.

6. The method of claim 5, wherein the preheating step is performed at a temperature range of 200 - 300 °C for a time period of 1 - 3 hrs.

7. The method of claim 4, wherein the heating step of the separated fine pieces is performed for a time period of 1 - 3 hrs.

8. The method of claim 4, wherein the calcium sulfate dehydrate is mixed by an amount of 2 - 6 % in weight.

9. The method of claim 4, further comprising the step of mixing at least one selected from a group consisting of blast furnace slag, fly-ash and high range water reducer, along with the calcium sulfate dehydrate.

10. A method for manufacturing recycle cement, the method comprising the steps of: crushing waste concrete or waste mortar; separating fine pieces having a diameter of 0.3 mm or less from the crushed hardened cement pieces; heating the separated fine pieces at a temperature rang of 500 - 900 °C for a time period of 1 - 3 hrs; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS04-2H20) of 2 -6 % in weight with the cooled fine pieces.

1 1 . The method of claim 10, wherein the crushing step comprises the steps of: first crushing waste concrete or waste mortar; preheating hardened cement pieces obtained through the first crushing; and secondly crushing the preheated hardened cement pieces.

12. The method of claim 1 1 , wherein the preheating step is performed at a temperature range of 200 - 300 °C for a time period of 1 - 3 hrs.

13. The method of claim 10, further comprising the step of mixing at least one selected from a group consisting of blast furnace slag, fly-ash and high range water reducer, along with the calcium sulfate dehydrate.

14. A method for manufacturing recycle cement, the method comprising the steps of: crushing waste concrete or waste mortar; separating fine pieces having a diameter of 0.15 mm or less from the crushed hardened cement pieces; heating the separated fine pieces at a temperature range of 650 - 750 °C for a predetermined time period; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS04-2H20) with the cooled fine pieces.

15. A method for manufacturing recycle cement, the method comprising the steps of: crushing waste concrete or waste mortar to form fine pieces; heating the fine pieces at a temperature range of 500 - 900 °C for a predetermined time period; and cooling the heated fine pieces.

16. The method of claim 15, wherein the fine pieces have a diameter of 0.15 mm or less.

17. The method of claim 15, further comprising the step of mixing calcium sulfate hydrate with the cooled fine pieces.

18. The method of claim 17, wherein the calcium sulfate dehydrate is mixed by an amount of 2 - 6 % in weight.

19. The method of claim 17, further comprising the step of mixing at least one selected from a group consisting of blast furnace slag, fly-ash and high range water reducer, along with the calcium sulfate dehydrate.

20. The method of claim 15, wherein the step of forming the fine pieces comprises the steps of: first crushing the waste concrete or the waste mortar; preheating hardened cement pieces obtained from the first crushing; and secondly crushing the preheated hardened cement pieces.

21. The method of claim 20, wherein the preheating is performed at a temperature range of 200 - 300 °C for a time period of 1 - 3 hrs.

22. A method for manufacturing recycle cement, the method comprising the steps of: crushing waste concrete or waste mortar; separating fine pieces having a diameter of 0.15 mm or less from the crushed hardened cement pieces; heating the separated fine pieces at a temperature range of 500 - 900 °C for a predetermined time period according to a neutralized degree of the separated fine pieces; cooling the heated fine pieces; and mixing calcium sulfate dehydrate (CaS0 -2H₂0) with the cooled fine pieces.