KR101376297B1 - ALC composition for carbonation resistance enhancement - Google Patents

Abstract

The present invention relates to a lightweight foamed concrete composition having increased carbonation resistance, 0.07 to 0.10 parts by weight of aluminum powder with respect to 100 parts by weight of a cement mixture including cement, silica sand and quicklime; 0.3 to 0.6 parts by weight of an alkali stimulant; Any one selected from the group consisting of melamine resin, silicone oil or a mixture thereof includes 1.5 to 7.0 parts by weight and mixed water, the mixed water is composed of 5.13 to 29.45 parts by weight which is 70 to 80% by weight of the total composition , The silica sand constituting the cement mixture is a silica sludge (Sand slury) having a density of 1.4 to 1.6 and content of 50 to 60% of solid content, and a return slurry of density of 1.3 to 1.4 and content of 40 to 50% of solid content ( Return slury), and the weight ratio of silica slurry: return slurry is 1: 0.4 ~ 0.6.

Description

Lightweight foamed concrete composition with increased carbonation resistance {ALC composition for carbonation resistance enhancement}

The present invention relates to a lightweight foamed concrete composition having increased carbonation resistance.

ALC (Autoclave Lightweight Concrete), a representative lightweight foam concrete, is manufactured under high temperature and high pressure conditions in an autoclave.

ALC material is a representative porous material and contains a number of pores. Bubbles of ALC are classified into macropores and micropores according to their size. These bubbles occupy 7080% of the total ALC volume, and the material itself is only 2030%. As a result, ALC exhibits low specific gravity (0.40.7), light weight, heat insulation, fire resistance, and sound absorption (sound insulation).

However, ALC is brittle and has disadvantages such as poorer strength than other competing products. This is mainly due to the formation of a large number of large pores by the blowing agent and the formation of defects due to the merging of pores, the handling during the molding aging process and the occurrence of cracks due to its own weight. Various methods have been experimented to overcome this phenomenon. Therefore, it is necessary to improve the performance of the matrix material or to control the pores to improve the mechanical properties of the ALC, and also to increase the carbonation resistance.

1. Republic of Korea Patent Publication No. 10-0802002 "Fiber reinforced lightweight foam concrete" 2. Republic of Korea Patent Publication No. 10-0653311 "Composition for preparing lightweight foamed concrete containing heavy oil ash, manufacturing method of ALC using the same" 3. Korean Unexamined Patent Publication No. 10-2012-0012615 "Alumino silicate-based lightweight foamed concrete composition and method for manufacturing lightweight foamed concrete product using the same" 4. Republic of Korea Patent Publication No. 10-1095381 "Cement mortar composition excellent in acid resistance and thermal insulation, a method of producing a floor finishing material having excellent acid resistance and thermal insulation using the same and a method of manufacturing a block" 5. Republic of Korea Patent Publication No. 1996-0004381 "Manufacturing method of high strength foam concrete by reheat water treatment"

In the present invention, by using a cement mixture of silica sand, cement and quicklime as a starting material, by mixing a melamine resin, silicone oil or a mixture thereof and an alkali stimulant in a certain weight ratio to provide a lightweight foamed concrete composition having increased carbonation resistance It's a challenge.

In addition, another object of the present invention to provide a method for producing light-weight foamed concrete with excellent carbonation resistance using the composition provided above.

0.07 to 0.10 parts by weight of aluminum powder with respect to 100 parts by weight of the cement mixture including the cement, silica sand and quicklime of the present invention which solve the above problems; 0.3 to 0.6 parts by weight of an alkali stimulant; Any one selected from the group consisting of melamine resin, silicone oil or a mixture thereof includes 1.5 to 7.0 parts by weight and mixed water, the mixed water is composed of 5.13 to 29.45 parts by weight which is 70 to 80% by weight of the total composition , The silica sand constituting the cement mixture is a silica sludge (Sand slury) having a density of 1.4 to 1.6 and content of 50 to 60% of solid content, and a return slurry of density of 1.3 to 1.4 and content of 40 to 50% of solid content ( Return slury), the weight ratio of silica slurry: return slurry is achieved by a lightweight foamed concrete composition having excellent carbonation resistance, characterized in that the weight ratio of 1: 0.4 ~ 0.6.

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The lightweight foamed concrete composition provided in accordance with the present invention can be produced in the form of lightweight foamed concrete that is significantly lower carbonation degree can provide a lightweight foamed concrete molded article excellent in carbonation resistance.

1 illustrates a TG-DTA graph for each type of additive according to an embodiment of the present invention.
Figure 2 is a photograph of the color change after 50 days after applying the phenolphthalein indicator on the specimen of lightweight foamed concrete (ALC) prepared according to an embodiment of the present invention.
Figure 3 is a photograph showing the phenolphthalein coating state of lightweight foamed concrete (ALC) added with silicone oil as an additive.
Figure 4 is a photograph showing the sound absorption performance preparation and test process according to an embodiment of the present invention.
5 is a graph illustrating sound absorption coefficients of specific gravity of ALC according to an embodiment of the present invention.
FIG. 6 is a graph illustrating sound absorption coefficients of additives of ALC according to an embodiment of the present invention. FIG.
7 is a pore observation photograph of the ALC for sound absorption test according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings.

1 is a view illustrating a TG-DTA graph for each type of additive according to an embodiment of the present invention, and FIG. 2 is a phenolphthalein indicator on a specimen of lightweight foamed concrete (ALC) prepared according to an embodiment of the present invention. 50 days after coating is a photograph of the color change, Figure 3 is a photograph showing the phenolphthalein coating state of lightweight foamed concrete (ALC) added with silicone oil as an additive, Figure 4 is an embodiment of the present invention 5 is a graph illustrating a sound absorption performance preparation and test process according to the present invention, FIG. 5 is a graph showing sound absorption coefficients for specific gravity of ALC according to an embodiment of the present invention, and FIG. Figure 7 is a graph showing the sound absorption coefficient for each type, Figure 7 is a pore observation photograph of the ALC for sound absorption test according to an embodiment of the present invention.

Hereinafter, the present invention relates to a lightweight foamed concrete composition having increased carbonation resistance, and a method for manufacturing lightweight foamed concrete using the same, which is completed according to the present invention.

Lightweight foamed concrete composition excellent in carbonation resistance provided according to the present invention is 0.07 ~ 0.10 parts by weight of aluminum powder based on 100 parts by weight of the cement mixture containing cement, silica sand and quicklime; 0.3 to 0.6 parts by weight of an alkali stimulant; Melamine resin, silicone oil, or any one selected from the group consisting of 1.5 to 7.0 parts by weight and mixed water, the mixed water is added to include 70 to 80% of the total weight of the composition.

At this time, the cement mixture is preferably mixed to include 30 to 40 parts by weight of cement and 10 to 20 parts by weight of quicklime with respect to 100 parts by weight of silica sand.

According to the present invention, the silica sand constituting the cement mixture has a certain density, and is mixed in a slurry state containing a solid content, and the silica sand in the slurry state is mixed with a silica sludge and a return slury. It is preferable to use.

At this time, the return slurry is recycled by wet crushing ALC pieces that fall off during transport or processing, or ALC determined to be defective after autoclave operation.

More preferably, sand slurries having a density of 1.4 to 1.6 and satisfying 50 to 60% of solid content, and return slury having a density of 1.3 to 1.4 and satisfying 40 to 50% of solid content are used. And, the composition ratio of silica slurry: return slurry is good to use a mixture so as to have a weight ratio of 1: 0.4 ~ 0.6.

According to the present invention, the alkali stimulant is any one selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide, more preferably sodium hydroxide or potassium hydroxide.

In addition, in the present invention, each component constituting the alkali-containing lightweight foamed concrete composition of the present invention disclosed above is added to a mixer according to the mixing ratio and mixed, and then put into a aging mold to ripen, and then molded to form the molded body by autoclave. Provided is a method for producing lightweight foamed concrete, characterized in that it is prepared by the hydrothermal synthesis reaction.

The hydrothermal synthesis reaction conditions are not particularly limited, and may be performed in the same manner as the conventional hydrothermal reaction conditions.

The conditions in the aging mold are the same as in the prior art, and more preferably, the aging mold is aged for 2 hours or more at a temperature of 50 ° C or higher.

When manufacturing lightweight foamed concrete using the alkali-containing lightweight foamed concrete composition provided in the present invention described above, it is possible to produce a lightweight foamed concrete with a significantly improved carbonation resistance.

Hereinafter, the present invention will be described in more detail with reference to preferred experimental examples for completing the present invention. However, the experimental example described below is for demonstrating this invention concretely, and does not limit this invention to the conditions of the following experimental example. Accordingly, any modification is possible without departing from the scope of the present invention.

[Experimental Example]

The present inventors compared and mixed various additives with the lightweight foamed concrete composition to prepare various methods for increasing the carbonation resistance of the lightweight foamed concrete (hereinafter referred to as 'ALC').

The present inventors have confirmed that when the high permeation type siloxane-based water repellent is used before the experiment, the carbonation resistance phase is very excellent, and also when carbon oil is mixed, the carbonation of ALC is prevented.

In addition, silicone oil is currently used in some products. The purpose of the silicone oil is to prevent corrosion of the reinforcing steel bars inside the ALC material, that is, to inhibit moisture penetration.

The carbonation degree of ALC derived by using the high-penetration siloxane-based water repellent agent that the inventors have previously confirmed is 11% or less (based on 50 days carbonation-CO ₂ concentration of 3%). It is also much lower than the degree of carbonation (around 60%).

Therefore, it is judged that the life of the building can be extended even with the result verified by the accelerated test.

However, in order to apply to high-rise buildings, it is necessary to derive more stringent results, in particular, it was judged that it is more preferable to use silicone oil which is currently used to prevent rebar corrosion.

Therefore, the present inventors have tried to increase the pH value of the ALC by mixing alkalis, thereby increasing the carbonation resistance.

In the present invention, in order to increase the pH value of ALC, reagent grade KOH, NaOH, and domestic raw waste glass powders and alkali raw materials such as ultra-light aggregates were mixed. Table 1 below shows the mixing design ratio of ALC considering KOH, NaOH, waste glass powder, and ultra-light aggregates.

As shown in Table 1, 0.3 parts by weight and 0.6 parts by weight of KOH and NaOH were added to the cement mixture including cement, quicklime, and silica sand, and 1 part by weight and 3 parts by weight of waste glass powder, and 7.5 parts by weight of ultralight aggregate. Blended.

Waste glass powder has a general flat glass composition, and ultra-light aggregates are mainly composed of SiO ₂ and alkalis. Therefore, it is believed that the alkali component of the additives will be partially eluted in the slurry state during the ALC manufacturing process.

 (Unit: g) division cement quicklime Sand slurry Return slurry Aluminum powder Mixed water Additive type
And content (parts by weight) Experimental Example 1 1060 470 3664 2073 4 600 Ultra light
aggregate 7.5 Experimental Example 2 1060 470 3664 2073 4 600 Waste glass
powder 1.0 Experimental Example 3 1060 470 3664 2073 4 600 3.0 Experimental Examples 4 and 5 1060 470 3664 2073 4 600 Melamine
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(2 parts by weight) KOH,
NaOH
0.3 each Experimental Examples 6 and 7 1060 470 3664 2073 4 600 KOH,
NaOH
0.6 each Experimental Example 8 1060 470 3664 2073 4 600 SO + M + K 7.5

NOTE 1. Density of silica slurry: 1.55; Return Slurry Density: 1.33

    2.SO + M + K = silicone oil (4.9 parts by weight) + melamine resin (2 parts by weight) + KOH (0.6 parts by weight)

    3. The content of the additives is mixed in a weight ratio to 100 parts by weight of the mixture based on the amount of cement, quicklime and silica sand (solid content of silica slurry + solid content of return slurry).

    4. The solid content of the silica slurry in terms of density is 57.66%, the solid content is 2113g, the solid content of the return slurry is 41.35%, and the solid content is 857g.

     5. Return slurry is the recycling of ALC fragments that fall off during transfer or processing, or ALC that is considered defective after autoclave operation, in the manufacture of ALC, which mostly contains silica.

According to the blending ratio of Table 1, the mixture of the mixed lightweight foamed concrete composition was charged to an autoclave to prepare a ALC specimen by hydrothermal reaction, and the prepared ALC specimen was dried at 105 ° C. for 2 hours, and then 10 mm × After cutting to 40 mm × 100 mm, the CO ₂ concentration was maintained at 3% in a carbonation tester at 20-90% relative humidity for one week. The ALC specimens were then maintained for 0, 10, 20 and 50 days in a carbonation tester with CO ₂ concentration controlled.

The amount of bound CO ₂ and CaO after carbonation is measured to calculate the degree of carbonation. TG-DTA was used to determine the amount of bound CO ₂ , with the exception of physisorbed CO ₂ and other carbonates. The calculation formula is as follows.

At this time, the amount (C) of CO ₂ for carbonation of ALC was calculated by TG-DTA as a mass reduction from 600 ° C to 800 ° C.

As shown in the TG-DTA graph of FIG. 1, the endothermic peak due to decarbonation is shown at about 700 ° C., and the exothermic peak due to the change of the tobermorite crystal to wollastonite is shown at about 830 ° C. FIG.

Therefore, in this experiment, as in the case of Fumiaki Matsushita et al., It is assumed that the mass reduction up to 600-800 ° C is the CO ₂ reduction by decarbonated (CaCO ₃ → CaO + CO ₂ ).

Figure 1 (a) is a TG-DTA graph of the additive is not added, (b) is a TG-DTA graph of the ultra-light aggregate is added as an additive (Experimental Example 1), (c) is closed as an additive TG-DTA graph of glass powder added (Experimental Example 2), (d) TG-DTA graph of silicon oil + melamine resin + potassium hydroxide (KOH) added (Experiment 8) , (e) is a TG-DTA graph of melamine resin (2 parts by weight) + KOH (0.3 parts by weight) as an additive (Experimental Example 4), and (f) is melamine resin (2 parts by weight) as an additive. It is a TG-DTA graph of what added + NaOH (0.3 weight part) (Experimental example 6).

To measure the pH of ALC, ALC was prepared into a powder, and then 10 g was sampled and mixed with 50 mL of distilled water. Sterling was followed for 30 minutes and the filtrate was collected. The collected filtrate was measured using a pH meter (Model 750P, Istek (株), Korea).

Carbonation degree results obtained according to the above experimental method are shown in Tables 2 to 4. As shown in Tables 2 to 4, Ref. In the case of the sample, 50 days of carbonation degree reached 32.5%, but when the silicone oil was added, it was confirmed that the carbonation degree was lowered to about 1/3 level by 10.96%. When alkali was added together with the silicone oil, a lower degree of carbonation was observed. The 50-day carbonation degree of ALC added 2 parts by weight of melamine resin and 0.6 parts by weight of KOH was about 24.8%. Contrast carbonation degree was found to decrease by about 7.7%. In addition, the degree of carbonation of the ALC to which 2 parts by weight of melamine resin and 0.6 parts by weight of NaOH was added was 26.5%, similar to that of KOH. It showed a lower degree of carbonation.

In particular, the 50-day carbonation degree of ALC with silicone oil, melamine resin and KOH was very low, at 7.8%. It was considered that the carbonation degree was lowered due to the carbonation resistance of silicone oil and the pH synergistic effect of KOH. That is, it is because the carbonation resistance becomes excellent by raising the initial pH value of ALC by alkali. The pH value of the initial ALC without carbonation was about 10.5 level, but was raised to 10.5 or more upon addition of alkali. The pH at the time of adding 0.3 parts by weight of KOH was 10.8 level, 11.2 when adding 0.6 parts by weight of KOH, 10.7 when adding 0.3 parts by weight of NaOH, and 11.0 when adding 0.6 parts by weight of NaOH.

In addition, when 3.0 weight part of waste glass powders were mixed, pH value was 10.8. That is, the initial pH value was found to increase with the addition of the alkali source and increase in content, it was confirmed that this may contribute to the carbonation resistance.

Table 2 below is a result of 10 days of carbonation, Table 3 is a result of 20 days, Table 4 is a result of 50 days.

division 10 days (% CO ₂ content) Carbonation degree (%) Ref. 5.54 19.37 Silicone oil 2.65 6.65 Experimental Example 1 (Ultra Light Aggregate) 4.51 14.84 Waste glass
powder Experimental Example 2
(1.0 parts by weight) 5.01 17.04 Experimental Example 3
(3.0 parts by weight) 4.55 15.02 Melamine
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(2 parts by weight) Experimental Example 4
(KOH 0.3 part by weight) 4.05 12.81 Experimental Example 5
(KOH 0.6 weight part) 3.63 10.96 Melamine
Suzy
(2 parts by weight) Experimental Example 6
(0.3 parts by weight of NaOH) 5.12 17.53 Experimental Example 7
(0.6 part by weight NaOH) 4.82 16.20 Experimental Example 7
(SO + M + K = 7.5 parts by weight) 2.15 4.45

Note) SO + M + K = silicone oil (4.9 parts by weight) + melamine resin (2 parts by weight) + KOH (0.6 parts by weight)

division 20 days (% CO ₂ content) Carbonation degree (%) R 7.20 26.68 Silicone oil 2.98 8.10 Experimental Example 1 (Ultra Light Aggregate) 5.80 20.52 Waste glass
powder Experimental Example 2
(1.0 parts by weight) 6.24 22.46 Experimental Example 3
(3.0 parts by weight) 5.75 20.30 Melamine
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(2 parts by weight) Experimental Example 4
(KOH 0.3 part by weight) 5.80 20.52 Experimental Example 5
(KOH 0.6 weight part) 5.48 19.12 Melamine
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(2 parts by weight) Experimental Example 6
(0.3 parts by weight of NaOH) 6.38 23.07 Experimental Example 7
(0.6 part by weight NaOH) 5.91 21.00 Experimental Example 7
(SO + M + K = 7.5 parts by weight) 2.57 6.30

division 50 days (% CO ₂ content) Carbonation degree (%) R 8.52 32.50 Silicone oil 3.63 10.96 Experimental Example 1 (Ultra Light Aggregate) 7.24 26.86 Waste glass
powder Experimental Example 2
(1.0 parts by weight) 7.95 29.99 Experimental Example 3
(3.0 parts by weight) 6.85 25.14 Melamine
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(2 parts by weight) Experimental Example 4
(KOH 0.3 part by weight) 7.01 25.85 Experimental Example 5
(KOH 0.6 weight part) 6.76 24.77 Melamine
Suzy
(2 parts by weight) Experimental Example 6
(0.3 parts by weight of NaOH) 7.87 29.63 Experimental Example 7
(0.6 part by weight NaOH) 7.15 26.48 Experimental Example 7
(SO + M + K = 7.5 parts by weight) 3.51 7.75

In addition, to verify the appearance of carbonation properties,

A phenolphthalein indicator was used to measure the carbonation depth of ALC. The photographs taken after applying the phenolphthalein indicator to the ALC specimens obtained before and after the carbonation progress are shown in FIGS. 2 and 3. As shown in Figure 2 Ref. The color of ALC was darker pink with the addition of alkali and melamine resin or silicone oil than ALC.

At the top of the photo shown in Figure 2 is an ALC specimen without an additive (Ref.), The center photo is an ALC specimen with melamine resin (2 parts by weight) + KOH (0.6 parts by weight) as an additive, The bottom picture is an ALC specimen with melamine resin (2 parts) + NaOH (0.6 part) added as an additive.

3 is a photograph of a specimen in which silicone oil is added as an additive.

In this experiment, the sound-absorbing performance was tested to verify the sound absorption characteristics of the prepared specimens, and the test was performed in the acoustic copper laboratory of Daewoo E & C Institute (see attached figure 4).

In this experiment, the test was carried out using the "Reverberation chamber sound absorption test method" (KS F 2805) to test the sound absorption performance. This measurement method has the advantage that the sound can be incident on the surface of the material from all directions, and the sample support condition and the back air layer can be measured according to actual field conditions. On the other hand, it has the disadvantage of having a large sample size (8.512m ² ) and a reverberation chamber capable of obtaining a sufficient diffused sound field.

Reverberation chamber method The sound absorption rate is measured by the following formula 2 from the average value of the measured reverberation time after measuring the reverberation time in the state which put the sample in and without the reverberation chamber.

과

의 측정 사이에 잔향실 내 온도는 ±5℃, 상대습도 ±10% 이상의 변화가 없어야 한다.only,

and

The temperature in the reverberation chamber shall not change more than ± 5 ° C and relative humidity ± 10% between measurements.

In this experiment, the manufactured ALC panel was analyzed by requesting Daewoo Engineering & Technology Institute (Suwon, Gyeonggi-do), a KOLAS accredited test organization. The types of ALC tested by sound absorption are as follows.

Ref. Developed before the present invention by the present inventors A total of three samples, including ALC (one of 0.48 and 0.55) and 2 parts by weight of melamine resin, were tested. A total of three samples of melamine resin prepared by this experiment and 0.6 parts of KOH were weighed. ALC panels with parts added were prepared and tested.

Sound absorption test is a test method, as shown in Figure 4, the size of the ALC panel was manufactured to 300 (width) × 3500 (length) × 200mm (thickness). The manufactured ALC was transported by truck, and then transported to the acoustic experimental sound absorbing room by using a forklift and a crane. The ALC delivered to the sound-absorbing room was assembled and installed on the bottom plate of 3.5m width and 3m length, and 6 pieces of ALC panels were used for the first test. Referring to the pre-invention test results of the present inventors (see FIG. 5), ALCs without mixing resins exhibited a characteristic that the sound absorption coefficient for each frequency was lowered as the specific gravity was increased. The sound absorption coefficient of 500Hz frequency band was ALC specific gravity 0.55 to 0.06 and specific gravity 0.48 was 0.11. In addition, the NRC values were 0.15 at specific gravity 0.55 to 0.06 and specific gravity 0.48.

This phenomenon is mainly due to the increase in pore content due to the decrease in specific gravity. In other words, it is considered that the specific gravity has a greater effect on the absorption and attenuation of sound energy in the ALC having more pores.

The specific gravity of the ALC mixed with 2 parts by weight of melamine resin was 0.50, the NRC value was 0.12, and the sound absorption coefficient at 500 Hz was 0.11. In particular, in the ALC with melamine resin, the sound absorption coefficient increased with increasing frequency. This phenomenon is believed to be due to the specific gravity of melamine resin (it varies depending on the amount of hardener, but 1.4 ~ 1.6g / cm 3) and elasticity. In particular, when sound energy flows into the melamine resin (elastic coefficient 4.5 ~ 5.5GPa), which has very good compressive strength and elasticity, compared to ALC inorganic matrix (elastic coefficient 1.5GPa), the cured melamine resin vibrates and consumes sound energy. It can play a role.

In particular, it is considered to have a better vibration effect in the high frequency region of high energy. In addition, when 2 parts by weight of melamine resin and 0.6 parts by weight of KOH were mixed at the same time, an effective sound absorption phenomenon was observed even in the low frequency region of 1500 Hz or less (see FIG. 6).

This is presumably because the porosity of the ALC increases as the melamine resin is mixed, and more acoustic energy changes to the vibration energy of the ALC matrix as the ALC intensity increases.

Table 5 shows the porosity and pore size of ALC to which Ref. And melamine resin (2 parts by weight) + KOH (0.6 part by weight) were added. As shown in Table 5, Ref. The porosity of ALC was 67.35%, average pore size was 580㎛, the porosity of melamine resin and KOH-added ALC was 75.19%, average pore size was 780㎛.

Therefore, the porosity increased by about 11.6% and the mean pore size increased by 34.5% with the use of melamine resin and KOH. This increase in porosity and pore size may have contributed to the improvement of sound absorption characteristics of ALC.

division Porosity Average pore size (1) Ref. 67.35% 580 (2) melamine resin
+ KOH 75.19% 780 (2) / (1) 100 111.64% 134.48%

As described above, when preparing an ALC panel using an ALC composition comprising an alkali stimulant provided according to the present invention and any one selected from the group consisting of melamine resins, silicone oils or mixtures thereof, an additive It can be seen that not only ALC panel having superior carbonation resistance can be manufactured compared to ALC panel without addition, but also ALC panel which can secure excellent sound absorption can be produced.

Claims (6)

0.07 to 0.10 parts by weight of aluminum powder, based on 100 parts by weight of the cement mixture including cement, silica sand and quicklime; 0.3 to 0.6 parts by weight of an alkali stimulant; Any one selected from the group consisting of melamine resin, silicone oil or a mixture thereof includes 1.5 to 7.0 parts by weight and mixed water, the mixed water is composed of 5.13 to 29.45 parts by weight which is 70 to 80% by weight of the total composition , The silica sand constituting the cement mixture is a silica sludge (Sand slury) having a density of 1.4 to 1.6 and content of 50 to 60% of solid content, and a return slurry of density of 1.3 to 1.4 and content of 40 to 50% of solid content ( Return slury), and the weight ratio of silica slurry: return slurry is 1: 0.4 ~ 0.6 weight ratio, characterized in that the lightweight foamed concrete composition excellent in carbonation resistance.
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