KR101988770B1 - A method of selecting and recovering al deoxidized slags in the slag generated during sts production using blast furnace pig iron and converter and its recycling - Google Patents

Abstract

The present invention provides a method for selectively treating Al-deoxidized slag from molten slag generated in the production of stainless steel, and a method for recycling the raw material for cement admixture or concrete shrinkage reducing material using wet-selected Al deoxidized slag.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method and apparatus for sorting Al-deoxidized slag from molten converter slag generated in the production of stainless steel using a furnace wire and a converter, CONVERTER AND ITS RECYCLING}

The present invention relates to a method for selectively concentrating and selecting Al-deoxidized slag included in a molten transfer slag generated in the process of producing stainless steel using a furnace brick and a converter, and a method for selectively and concentrating the concentrated and Al-deoxidized slag as a raw material for a shrinkage reducing material To a method for recycling.

STS steel is produced by using Si-based de-oxidation material or Al-based de-oxidation material to remove impurities such as oxygen contained in molten steel and molten steel, according to the STS steel grade produced in the blast furnace and converter.

In the deoxidation treatment, the transfer slag in a molten state is generated by using the Si-based de-oxidation material or the Al-based de-oxidation material, and the converter slag is deoxidized into silicon (Si) It is generally distinguished by slag, but most of the generated slag is mixed and processed.

Particularly, when the slag is used as a concrete aggregate or as a road aggregate, 3CaOAl ₂ O ₃ and 12CaO 7Al ₂ O ₃ components react with water in the hydration process. An etching ring is formed. The etring zite generated in the hydration process has an expandability. When the etring zite is produced in a large amount, the curing agent contained in the concrete aggregate or the road aggregate expands and the durability of the aggregate drops.

That is, because the expansion characteristics of the Al-deoxidation converter slag are extremely limited, the natural curing is required for at least one year in order to reduce the swelling phenomenon.

Accordingly, in order to solve such a problem, Korean Patent Publication No. 10-2012-0112619 provides a method of efficiently recovering and recycling 2CaO · SiO ₂ contained in the sludge from wet quenching steelmaking sludge generated during a steelmaking process have.

However, even in this case, a method for enriching and sorting the Al-deoxidized slag from the mixed slag is not disclosed, and a method capable of efficiently selecting and recycling the Al-deoxidized slag is required.

Therefore, one aspect of the present invention is to provide a method for producing molten slag from stainless steel, which comprises melting slag generated during the production of stainless steel, And a method of recycling the concentrated and sorted Al-deacid slag as a raw material for a cement composition and a shrinkage reducing material.

According to one aspect of the present invention, there is provided a method for producing a slag comprising the steps of cooling a mixed slag of an Al-deoxidized slag and a Si-deoxidized slag, a crushing step of crushing the cooled mixed slag and removing the present slag, And a wet screening step for wet screening the Al deoxidized slag from the mixed slag of the Si deacid slag, and a method for concentrating and sorting the Al deacid slag from the mixed slag of the Si deacidified slag.

The cooling may be cooled to 20 to 40 占 폚.

The crushing step comprises crushing the cooled slag to an average particle size of 200 mm or less and then removing a large amount of base metal, crushing the crushed slag to a mean particle size of 80 mm or less, A second crushing step of crushing the crushed slag from which the present crushed material is removed to an average particle size of not more than 40 mm and a wet crushing step of wet crushing an average particle size of not more than 5 mm, And removing the ternary complex.

In the wet screening step, the mixed slag may be supplied at 35 to 45 ton / h, and the process water may be supplied at 100 to 140 ton / h to concentrate and sort the Al deacid slag.

And filtering the slurry from which the wet-selected Al deoxidized slag is removed to use the filtrate as the process water.

According to another aspect of the present invention, there is provided a shrinkage reducing material comprising the concentrated and sorted Al-deoxidized slag.

The Al-deoxidized slag may have an average particle size of 15 to 100 mu m.

The shrinkage reducing material may include Al-deoxidized slag and anhydrous gypsum at a weight ratio of 1: 2: 2 to 1: 1.

 According to another aspect of the present invention, there is provided a cement composition comprising 3 to 6% by weight of a mixture of the concentrated and selected Al deoxidized slag and anhydrous gypsum and the balance cement or slag cement.

The mixture may be an Al-deacid slag and anhydrous gypsum mixed at a weight ratio of 1: 2: 2 to 1: 1.

The Al-deoxidized slag may have an average particle size of 15 to 100 mu m.

According to the present invention, it is possible to selectively concentrate and select the Al-deoxidized slag by cooling the mixed slag of the Al-deoxidized slag and Si-deoxidized slag as molten slag generated in the manufacturing process of stainless steel and then performing the wet fractionation treatment.

Furthermore, the concentrated and sorted Al-deoxidized slag can be mixed with anhydrous gypsum, which can be used as a raw material for a cement composition and a concrete shrinkage reducing material.

FIG. 1 is a view showing one embodiment of a process for concentrating and sorting an Al-deoxidized slag by wet-sorting a mixed slag of an Al-deoxidized slag and a Si-deoxidized slag generated in a stainless steel manufacturing process according to the present invention.
FIG. 2 is a graph showing the composition and compressive strength of an Al-deoxidized slag obtained according to an embodiment of the present invention.
FIG. 3 is a graph showing the components and compressive strength of the Si-deacidified slag sludge separated according to an embodiment of the present invention.

One aspect of the present invention provides a method for selecting Al deoxidized slag from mixed slag of Al deoxidized slag and Si deoxidized slag, which are molten slag produced in the production of stainless steel.

FIG. 1 is a view showing a preferred embodiment in which a mixed slag of an Al-deoxidized slag and a Si-deoxidized slag generated in a stainless steel manufacturing process according to the present invention is cooled and then subjected to wet fractionation to concentrate and sort the Al-deoxidized slag from the mixed slag.

More particularly, the present invention relates to a method for producing a slag comprising the steps of: cooling a mixed slag of an Al-deoxidized slag and a Si-deoxidized slag as a molten slag generated in a stainless steel manufacturing process, a crushing step of crushing the cooled mixed slag, And a wet screening step of wet-screening the Al deacid slag from the mixed slag of the removed Al deacid slag and the Si deacid slag.

According to one embodiment of the present invention, cooling molten slag produced in the manufacture of stainless steel can be performed. The molten slag is a mixed slag containing Si-deacidified slag and Al-deacidified slag, and the mixing ratio of the mixed slag may be different depending on the ratio of the generated slag. For example, mixed slag mixed with Si deacidified slag and Al deacidified slag at a ratio of 6 to 8: 2 to 4 can be used.

The Si-deoxidized slag contained in the mixed slag undergoes phase transformation of β-2CaOSiO ₂ (hereinafter referred to as C ₂ S) to γ-C ₂ S at around 500 ° C. during cooling, resulting in differentiation and formation of fine powder. On the other hand, in the Al-deacid slag, the Al component is oxidized to Al ₂ O ₃ , and this component has the effect of suppressing the phase transition phenomenon and forms a lump without being differentiated. Therefore, the shape of the Al-deoxidized slag and the Si-deoxidized slag included in the mixed slag are different depending on the phase transition due to the cooling of the Si-deacidized slag and the Al-deacidized slag. Therefore, the Al-deoxidized slag and the Si-deoxidized slag of the different shapes may be selectively concentrated by wet fractionation.

The cooling step may include cooling the mixing slag in the port and cooling it in a port cooling zone as shown in FIG. After the cooling, additional cooling may be performed in the house cooling field depending on whether phase transition of the Al-deoxidized slag and the Si-deoxidized slag is performed (103).

The cooling may be carried out at 20 to 40 占 폚. When the cooling temperature is lower than 20 ° C, the cooling rate of the slag is too fast, so that the phase transition of the slag due to the phase transition may be difficult, and when the cooling rate is higher than 40 ° C, cooling may be difficult. Therefore, due to the cooling in the temperature range, the Al-deoxidized slag can be obtained as agglomerated slag with phase transition suppressed, and the Si-deoxidized slag can be obtained as the undifferentiated slag due to the occurrence of aging due to phase transition. At this time, it may further include a step of spraying water to improve the cooling rate and to reduce the generation of scattered dust in the crushing process.

When the cooling is completed, the cooled mixed slag can be crushed. The components can now be removed for recycling of the slag after the crushing process. More specifically, the cooling can be performed as follows. The slag cooled first is crushed to a mean particle size of 200 mm or less and then the base metal is removed, crushed to an average particle size of 80 mm or less (104) And crushing to an average particle size of 40 mm or less (step 106).

The crushed pieces can be crushed to a mean particle size of not more than 80 mm and crushed to an average particle size of not more than 40 mm by a crusher such as a jaw crusher after crushing the cooled slag to an average particle size of 200 mm or less. The metal components may be selectively removed from the crushed mixed slag in order to prevent contamination in the process of recycling into the cement composition and the shrinkage reducing material after each crushing.

The slag crushed to a size of 40 mm or less may be wet-pulverized to have an average particle size of about 5 mm or less, and the slurry may be sorted by floating to separate the components. At this time, wet crushing using a rod mill can be performed (107) in order to make the particle size of the slag thinner so as to facilitate separation of the components present in the mixed slag. When the average particle size of the crushed slag is more than 5 mm, there is a problem that the separation efficiency is lowered when the magnetic particles are mixed with the slag and the metal.

In order to separate the present components contained in the wet-crushed slag having an average particle size of 5 mm or less, the wet flotation can be selected. By separating the wet flotation into a slag component having a high specific gravity and a slag component having a low specific gravity, (108). In order to more effectively prevent the metal component from floating and contaminating when used as a cement composition and a shrinkage reducing material, a step of separating the residual carbonaceous material by magnetic force separation may be additionally performed (109).

The Al-deoxidized slag contained in the wet crushed slag from which the complex is removed can be concentrated and selected. The process may be carried out to separate the Al-deoxidized slag from the coarse-grained Al-deoxidized slag (110), and the wet fractionation method is not particularly limited. For example, the mixed slag of the Al-deoxidized slag and the Si-deoxidized slag from which the sintered material has been removed after crushing is introduced into the wet-type spiral screw to obtain the Si deoxidized slag slurry 112 in which the lumpy Al- Can be selectively separated.

At this time, the wet slag may be supplied at a flow rate of 35 to 45 ton / h, and the process water may be supplied at a flow rate of 100 to 140 ton / h. When the flow rate of the slag is less than 35 ton / h, the selective separation effect of the Al deoxidized slag may be deteriorated. If the flow rate exceeds 45 ton / h, the Si deoxidized slag may be mixed when the Al deoxidized slag is selected .

When the flow rate of the process water is less than 100 ton / h, the screening efficiency of the thick Al-deoxidized slag and the Si-deoxidized slag having a small particle size may be deteriorated. When the flow rate exceeds 140 ton / h, Is not preferable because it can be mixed.

By mixing the introduced process water and slag, the agglomerated Al-deoxidized slag forms slag of coarse particles (111) and the undifferentiated Si deacid slag forms a slurry (112) The Al-deoxidized slag can be selected by wet fractionation from the mixed slag of the slag. Therefore, it is possible to concentrate and select only the Al-deoxidized slag from the mixed slag mixed with the Al-deoxidized slag and the Si-deoxidized slag by the wet fractionation treatment according to the present invention without any additional equipment.

After completion of the concentration and selection of the Al-deacidified slag from the mixed slag, the step of filtering the Si-deacidified slag slurry is further performed (113), and the filtered liquid can be reused as the process water (115). The filtration step is not particularly limited as long as the filtrate can be separated from the slurry.

Another aspect of the present invention provides a cement composition and a shrinkage reducing material comprising the concentrated and sorted Al-deoxidized slag.

The concentrate screening Al deoxidized slag which is the main crystal phase 3CaOAl ₂ O _3, 12CaO7Al a ₂ O _3, 3CaOAl ₂ O ₃ and 12CaO7Al ₂ O ₃ component is to produce a ring eth- ZUID hydrate as the expression below.

3CaOAl ₂ O ₃ + 3CaSO ₄ 2H ₂ O + 26H ₂ O -> 3CaOAl ₂ O ₃ 3CaSO ₄ 32H ₂ O

[Equation _{2] 12CaO7Al 2 O 3 + 3Ca} (OH) 2 + 5CaSO 4 + 57H 2 O

-> 5 (3CaOAl ₂ O ₃ CaSO ₄ 12H ₂ O) + 2Al (OH) ₃ (monosulfate, Monosulphate)

[Formula 3] Al ₂ O ₃ CaSO ₄ 12H ₂ O + 2CaSO ₄ + 20H ₂ O

- > 3CaOAl ₂ O ₃ 3CaSO ₄ 32H ₂ O (Ettringite)

The amorphous CaO-Al ₂ O ₃ -H ₂ O hydrate formed on the surface of the slag when the Al deoxidized slag is wet-treated as described above is formed by the hydration reaction of the slag containing 3CaOAl ₂ O ₃ and 12CaO 7Al ₂ O ₃ components .

Since the hydrate is an intermediate product formed before the Etring zeite is formed, the hydrate may act as seed nuclei in the actual reaction step to promote the production of Etring zeite. In addition, the etching ring formed in the hydration process of 3CaOAl ₂ O ₃ and 12CaO 7Al ₂ O ₃ has swelling property, so that the cured product may expand when mass production is made. Therefore, when the wet-screened Al-deoxidized slag is used as a raw material for a cement composition and a concrete shrinkage reducing material, it can be used as a functional additive excellent in initial strength improvement.

However, when the concentrated and sorted Al-deoxidized slag has an average particle size of about 5 mm or less and an Al-deoxidized slag of 5 mm or less for the fine aggregate, the Al-deoxidized slag may hydrate and expand on the concrete surface due to the hydration reaction . Therefore, the hydration reaction of the Al-deacid slag is slowed and the performance of the cement composition and the shrinkage reducing agent can be slowed down. In order to prevent this, the average particle size of the Al-deoxidized slag is preferably 75um or less.

The Al-deoxidized slag having an average particle size of 75um or less can be used as a raw material for a cement composition and a shrinkage reducing material. At this time, in order to improve the mortar compressive strength of the cement composition and the shrinkage reducing material and to reduce the shrinkage ratio, it is preferable to mix anhydrous gypsum with the Al deoxidized slag to form a mixed paste of anhydrous gypsum in the Al deoxidized slag.

At this time, the mixed paste may contain the Al deacid slag and the anhydrous gypsum at a weight ratio of 1: 2: 2 to 1: 1. In the case where the weight ratio of the alumoxane slag is less than 0.5 based on the weight ratio of the anhydrous gypsum, it is not preferable because the amount of the ettringite generated when used as a shrinkage reducing material may be lowered. If the weight ratio is more than 2, Lt; / RTI >

The Al-deoxidized slag having an average particle size of 75um or less may be a raw material for the cement composition. The Al deacid slag may form a mixture mixed with anhydrous gypsum, and the mixture may be blended with common cement or slag cement to form a cement composition.

The mixed paste of the Al-deacid slag and the anhydrous gypsum as a raw material of the cement composition may be 3 to 6% by weight based on 100% by weight of the total cement composition. When the mixing paste is less than 3% by weight, it is difficult to form an ettringite so that shrinkage reduction effect is difficult to be exhibited. When the mixing paste is more than 6% by weight, compressive strength development is less preferable than general cement.

As described above, according to the present invention, there is provided a method of concentrating and sorting Al-deoxidized slag without any additional facility by performing a wet fractionation after completely cooling the molten slag generated in the manufacturing process of stainless steel and a method of concentrating and sorting the cement composition containing the concentrated and selected Al- And a shrinkage reducing material.

Hereinafter, preferred embodiments of the present invention will be described with reference to various embodiments. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

Example

Wet sorting of Al-deoxidation converter slag and Si deoxidation converter slag and manufacture of composition for cement and concrete using Al-deoxidation converter slag

Si deoxidation converter slag and Al deoxidation converter slag were used for blast furnace slag and Si deoxidation converter slag and Al deoxidation converter slag obtained in the process of producing 400 series stainless steel (main component of Fe-Cr alloy) Was mixed at a ratio of 7: 3.

The mixed slag 101 was placed in the port and cooled in a port cooling zone for 24 hours (102), and the cooled slag was cooled (103) for 24 hours in a house cooling zone. Through this cooling, a mixed slag of the Al deoxidation converter slag in the lump state and the Si deoxidation converter slag in the fine powder state was obtained. At this time, spraying treatment was performed to prevent scattering dust.

The fully cooled mixed slag was crushed using a braking machine so that the average particle size was less than about 200 mm, and the crushed slag was now removed from the crushed slag. The slag crushed to a size of about 200 mm or less was subjected to primary crushing through a jaw crusher to a size of about 80 mm or less (104), and the slag was separated at 105 by a magnetic separator. Thereafter, an additional secondary crushing treatment was carried out by using a jaw crusher to a depth of about 40 mm or less (106).

The slag crushed to a size of 40 mm or less was crushed (107) so that the average particle size of the slag was 5 mm or less in a wet-milled road mill crusher (107). The slag was crushed using a wet floating separator, After separation into low slag, the ingredients are now removed (108). Thereafter, the adduct was removed with a magnetic separator (109).

Then, the slag from which the adduct-free slag was removed was charged at a rate of 40 tons per hour for 1 hour, and the process water was added at 120 tons per hour for 1 hour to obtain a mixture.

The mixture was introduced into a wet spiral screw to separate the Si deoxidation converter slag slurry having a large particle size and the Al deoxidation converter slag 111 and the fine powder into a lumpy state. The slurry was then filtered 113 to remove the sludge 114 and the filtrate was reused 115 as process water. The concentrated and sorted Al-deoxidation converter slag (111) was obtained, and the main chemical components contained in the slag were analyzed by X-ray fluorescence spectrometer (XRF).

division Al ₂ O ₃ SiO ₂ CaO MgO Fe ₂ O ₃ Cr ₂ O ₃ Aluminum deasphalted slag 10.8 19.2 48.7 6.6 5.9 4.4 Si deoxidation sludge 5.6 21.3 58.0 7.4 2.1 2.3

(unit: %)

Table 1 shows the components and contents of the Si deoxidation converter slag sludge 114 in which the Al deoxidation converter slag 111 and the fine powder are mixed. From the results shown in Table 1, it was confirmed that the content of Al ₂ O ₃ contained in the Al deacid slag was about twice that of the content of Al ₂ O ₃ contained in the Si deacidified slag sludge.

From the results of FIG. 2, it can be seen that the Al slag is cooled by the cooling of the mixed slag, and phase transition is suppressed so that the Al ₂ O ₃ component is concentrated in the subsequent wet sorting step, and the slag is converted into 3CaOAl ₂ O ₃ , 12CaO 7Al ₂ O ₃ and amorphous CaO-Al ₂ O ₃ -H ₂ O were formed on the surface of the slag.

While Fig. From the results of the third and the state of the fine powder to the Si deoxidation converter slag phase transfer sludge to the Si deoxidation converter slag of the pulverized is already hydration reaction proceeds in a wet screening step include most 2CaOSiO ₂ and Ca (OH) ₂ .

In order to produce a cement or slag cement composition and a shrinkage reducing material using the property of expanding the hydration reaction of the obtained Al deoxidation converter slag, the Al deoxidation converter slag was pulverized using a ball mill so that the average particle size was about 75 μm . Then, 200 g of the Al-deoxidized transfer slag having a size of less than 75 μm was granulated using a steel having a diameter of less than 75 μm.

200 g of the Al-deoxidation converter slag powder thus obtained was mixed with 200 g of anhydrous gypsum in an amount of 2% by weight and 2% by weight to prepare 400 g of a mixed paste. 400 g of the mixed paste, 4000 g of common portland cement, and 5600 g of blast furnace fine powder were mixed at 40% by weight and 56% by weight to prepare 10,000 g of a composition.

Comparative Example

Comparative Example 1

Cement was prepared under the same conditions as in Example except that a mixture of 55 wt% of common portland cement and 45 wt% of blast furnace slag fine powder not containing the mixed powder of Al deoxidized slag and anhydrous gypsum was used.

Comparative Example 2

Cement was prepared by mixing 4 wt% of the Al-deoxidation converter slag concentrated and sorted under the same conditions as those of Example except for the natural anhydrous gypsum.

Comparative Example 3

Cement was prepared under the same conditions as in Example except that 4% by weight of natural anhydrous gypsum was mixed except for the Al-deoxidation converter slag.

Comparative Example 4

Cement was prepared under the same conditions as in Example except that the Al-deoxidation converter slag and anhydrous gypsum were mixed in an excess amount of 10 wt% in total of 5 wt% each.

division OPC Blast furnace
Fine powder Al-deoxidation converter slag natural
Anhydrous plaster Compressive strength (MPa) 28 day shrinkage length change
([mu] m / m) 3 days 28th Experimental Example 1 40 56 2 2 24 55 510 Comparative Example 1 55 45 - - 22 52 780 Comparative Example 2 40 56 4 - 19 50 770 Comparative Example 3 40 56 - 4 20 51 750 Comparative Example 4 40 52 5 5 15 40 300

Table 2 above shows the results of the above Examples and Comparative Examples

In Comparative Example 1, it was confirmed that the shrinkage length change at the time of 28 days from the experiment was the largest at 780 um / m, and the shrinkage reduction effect was not large.

In Comparative Example 2, the compressive strengths were measured at 19 MPa and 51 MPa at 3 days and 28 days after the experiment, respectively, and the compressive strengths were measured to be about 5 MPa smaller than those of the experimental examples (24 MPa and 55 MPa). This confirms that the compressive strength of Comparative Example 2 is relatively weak compared with the compressive strength of the preferred embodiment of the present invention.

Further, in Comparative Examples 2 and 3, the compressive strength on the third day after the test was conducted was measured to be less than about 5 MPa as compared with Example 1, and the shrinkage length change was measured to be about 350 um / m. And the shrinkage reduction effect was remarkably decreased.

In Comparative Example 4, the compressive strength at the third day after the test was 15 MPa, which was about 9 MPa less than that in the Experimental Example. Compared with the Examples, the compressive strength was relatively weak.

As described above, when the method of concentrating and sorting Al-deoxidation transfer slag according to the present invention and recycling it as a raw material for a cement admixture and a concrete shrinkage reducing material, there is an effect of not only improving the initial strength but also reducing the shrinkage length change and thus having excellent compressive strength.

Claims (11)

A cooling step of cooling the mixed slag of the Al deoxidized slag and the Si deoxidized slag;
A crushing step of crushing the cooled mixed slag and removing the component now; And
A wet sorting step of wet-sorting the Al-deoxidized slag from the mixed slag of the Al-deoxidized slag and the Si-deoxidized slag,
A method for producing a shrinkage reducing material by concentrating and selecting an Al deoxidized slag from a mixed slag of an Al-deacid slag and a Si-deacid slag. The method according to claim 1,
Wherein the cooling is performed at a temperature of 20 to 40 캜, wherein the Al-deoxidized slag and the Si-deacidified slag are concentrated and selected from the mixed slag of the Si-deacidified slag to produce a shrinkage reducing material. The method according to claim 1,
The shredding step
Crushing the cooled slag to an average particle size of 200 mm or less and removing a large base metal;
A first crushing step of crushing the above-mentioned crushed slag removed at an average particle size of not more than 80 mm and sorting out the magnetic force to remove the crust now;
A second crushing step of crushing the crushed slag from which the crumb component has been removed to an average particle size of 40 mm or less;
A wet crushing step of wet crushing an average particle size of 5 mm or less to select a wet suspended particle for the present component; And
Removing the residual zeolite;
A method for producing a shrinkage reducing material by concentrating and selecting an Al deoxidized slag from a mixed slag of an Al-deacid slag and a Si-deacid slag. The method according to claim 1,
The wet screening step comprises concentrating and selecting the Al deacid slag from the mixed slag of Al deacid slag and Si deacid slag, feeding the mixed slag at 35 to 45 ton / h and supplying the process water at 100 to 140 ton / h, A method for manufacturing a reducing agent. The method according to claim 1,
Further comprising the step of filtering the slurry from which the wet-selected Al deoxidized slag has been removed and using the filtrate as the process water to concentrate and sort the Al deoxidized slag from the mixed slag of the Al deoxidized slag and the Si deoxidized slag to produce a shrinkage reducing material How to. A shrinkage reducing material comprising an Al-deoxidized slag concentrated and selected according to claim 1. The method according to claim 6,
Wherein the Al deoxidized slag has an average particle size of 15 to 75 占 퐉. The method according to claim 6,
Wherein the shrinkage reducing material comprises Al-deoxidized slag and anhydrous gypsum at a weight ratio of 1: 2: 2 to 1: 1. 9. The shrinkage reducing material according to any one of claims 6 to 8, And residual cement or slag cement. 10. The cement composition of claim 9, wherein the shrinkage reducing material comprises from 3 to 6% by weight based on the total weight of the cement composition.
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