KR100704869B1 - Highly efficient shot-crete composition mixed Metakaolin and Silica Fume - Google Patents

Abstract

The present invention relates to a shotcrete composition which is used as a temporary support member for stabilizing an excavation section immediately after excavation of a tunnel / ground space and also as a permanent support material after completion of the tunnel / ground space, and is a fine powder admixture. ) And silica fume in combination with a high performance shotcrete composition considering the mechanical properties such as compressive strength and flexural strength, as well as long-term durability and economic feasibility.

High-performance shotcrete composition of the present invention is a coarse aggregate of 500 ~ 700kgf weight having a maximum dimension of 10 ~ 15mm per 1m ³ shotcrete; Fine aggregate weighing 1,000-1,200 kgf; 300 to 450 kgf weight cement; Water having a water-cement ratio of 40 to 60% by weight; A fastener of 4 to 10% of the weight of the cement; And, 4 to 8% of a blended material of the cement weight. The blended material is characterized by mixing and mixing metakaolin and silica fume.

Metakaolin, Silica Fume, Shotcrete, High Performance, High Strength, Durable

Description

Highly efficient shot-crete composition mixed Metakaolin and Silica Fume}

1 is a graph showing the particle size distribution of the fine aggregate used in the embodiment of the present invention.

2 is a graph comparing the setting time of the Examples and Comparative Examples of the present invention.

3 is a graph comparing the compressive strength of the embodiment of the present invention and the comparative example.

Figure 4 is a graph comparing the bending strength of the embodiment of the present invention and the comparative example.

5 is a graph comparing the chlorine ion permeability of the Examples and Comparative Examples of the present invention.

Figure 6 is a graph comparing the resistance to freezing and thawing of the examples of the present invention and the comparative example.

The present invention relates to a shotcrete composition used as a temporary support member for stabilizing an excavation section immediately after excavation of a tunnel / underground space and also as a permanent support material after completion of the tunnel / underground space. The present invention relates to a high performance shotcrete composition in which mechanical properties such as compressive strength and flexural strength are increased by increasing the long-term durability as well as economic efficiency by mixing and mixing metakaolin and silica fume.

In the tunnel / underground construction shotcrete is most important jibojae being, though, the compressive strength based on domestic shotcrete from 28 days to date as 180kgf / cm ² or 210kgf / cm ² in Norway, more than 300kgf / cm ² being applied, etc., Switzerland Compared to the strength criterion is quite low. Due to the low strength level of domestic shotcrete, the thickness of shotcrete for stabilizing tunnels / underground spaces is inevitably thickened, which leads to an increase in construction speed and construction cost, thereby degrading the efficiency and economic efficiency of shotcrete construction. .

Moreover, no technical considerations have been made in the long term durability of shotcrete in Korea. In addition, high-strength and high durability of shotcrete, which are well-known for the long-term stability of tunnels / underground spaces, is required.In addition to the current construction method for additional secondary concrete lining after the shotcrete is placed, the secondary concrete lining is omitted and In order to apply the single-shell tunneling method to apply high performance shotcrete with permanent lining, shotcrete high performance technology is essential.

In foreign countries, silica fume, which is a fine powder admixture, is essentially used for high performance of shotcrete. However, since the production of silica fume consumes a lot of power, production is not carried out in Korea, where the cost of electricity is expensive, and the price itself is up to 10 times higher than the unit price of cement. Moreover, when a large amount of silica fume is used, the unit quantity increases in order to obtain the same dough kneader, and there is a problem such as initial cracking.In the case of incorporation of silica fume, the amount of retained water is large because the bleeding is small. The use of high-performance water reducing agents, which are large in shrinkage and also expensive, has a disadvantage in that they increase proportionally.

On the other hand, metakaolin is a mixed material produced by thermally activating high quality kaolin, and because of the abundant kaolin resources, which are raw materials of metakaolin in Korea, the unit price is low and there is no big difference from the cement unit price. Moreover, unlike industrial fume silica fume, metakaolin is a stable material because it is produced by good management control (650-800 ° C.) with very little change in physical and chemical properties. However, to date, metakaolin to replace silica fume remains in some applications in the concrete field, and there has been no application to shotcrete.

The present invention takes advantage of each of the advantages of metakaolin and silica fume by mixing and mixing metakaolin and silica fume, and the use of shotcrete and the use of metakaolin and silica fume according to the characteristics required for shotcrete so that the use of shotcrete Its purpose is to provide a high performance shotcrete composition with improved performance and economics.

The present invention for achieving the above object is coarse aggregate weight of 500 ~ 700kgf per shotcrete 1m ³ , the maximum dimension of 10 ~ 15mm; Fine aggregate weighing 1,000-1,200 kgf; 300 to 450 kgf weight cement; Water having a water-cement ratio of 40 to 60% by weight; A fastener of 4 to 10% of the weight of the cement; And, 4 to 8% of a blended material of the cement weight. The blended material provides a high performance shotcrete composition, characterized in that the mixed mixture of metakaolin and silica fume.

The present invention has a technical feature to replace some of the amount of silica fume with metakaolin which is cheaper than silica fume. This technical feature reduces the production cost than the shotcrete using only silica fume, and enhances the rigidity of the shotcrete microstructure by metakaolin having a larger particle diameter than silica fume, and fills the micropores between the metakaolin particles with silica fume as a result of the composition Improve the overall mechanical properties and durability of shotcrete. In addition, the amount of the mixed use of metakaolin and silica fume can be selectively changed according to the strength / durability criteria required for the tunnel / underground space, thereby increasing the applicability of the present invention.

Hereinafter, the present invention will be described in detail by way of examples.

Example 1 Shotcrete Formulation

Formulation design in the present invention is shown in Table 1. In the formulation, the slump was fixed at 10 ± 2cm, the air volume was 4 ± 1%, the water cement ratio was 45%, and the residual aggregate rate was 68%. The substitution rates of silica fume and metakaolin were 4 and 8% of the cement content and 2 and 4% respectively in the case of the mixture containing both admixtures (ie MK + SF = 4% and 8 of the cement weight). %).

combination Maximum size of coarse aggregate (mm) Slump range (cm) Air volume range (%) W / C (%) Residual rate (%) Unit material amount (㎏ / ㎥) water Cement (C) Silica fume (SF) Meta kaolin (MK) Fine aggregate Coarse aggregate Glidant (g / ㎥) A quick payment P 13 10 ± 2 4 ± 1 49 68 205.8 420 - - 1124 545 3360 21 SF4 403.2 16.8 (= 4% × C) - 4200 SF8 386.4 33.6 (= 8% × C) - SM4 403.2 8.4 (= 2% × C) 8.4 (= 2% × C) SM8 386.4 16.8 (= 4% × C) 16.8 (= 4% × C)

1. Material used

(1) cement

For shotcrete cement, portland cement is usually used. If it is necessary to generate strength early after construction, or the curing period cannot be sufficient after construction, crude steel portland cement or superhard cement may be used. In this example, one H type ordinary portland cement suitable for commercially available KS L 5201 is used and physical properties are shown in Table 2.

Powder level (cm ² / g) importance Stability (%) Compressive strength (MPa) 3 days 7 days 28 days Class 1 cement 3,488 3.15 0.08 22 ± 2 30 ± 2 38 ± 3 KS L 5201 2,800 - 0.8 ↓ 13 ↑ 20 ↑ 29 ↑

(2) aggregate

 The coarse aggregate was crushed stone with maximum size of 13mm, and the fine aggregate was specific gravity 2.6 and the absorption was 0.67. The particle size of the fine aggregate did not deviate from the KS particle size standard range as shown in FIG. 1, and the assembly rate was 2.86 instructor used within the range of 2.3-3.1 assembly rate of the fine aggregate of KS F 2526.

(3) Payment

The quickener may be a liquid quickener such as an alkali-free quickener or a powdery quickener such as a cement mineral quickener. In the present embodiment, a C ₁₂ A ₇ -based mineral fastener developed in Korea was used, and the basic physical properties are shown in Table 3 below. The greater the amount of cement mineral quickener used, the faster the strength expression and the lower the strength, the better the workability, the W / C reduction effect, and the faster the curing, the stronger the water part.

Main component shape Heavy weight Volume specific gravity pH Calcium Aluminate Light gray powder 2.76 0.93 11.7

(4) mixed materials

In the present invention, silica fume and metakaolin, which are mineral admixtures, were used.

Silica fume has an average particle diameter and the content of SiO ₂ was satisfied at least 85% 0.2㎛, the powder shown in the ASTM C 1240-95 was about 240,000cm ₂ / g. Chemical composition of the silica fume is shown in Table 4 below.

SiO ₂ Al ₂ O ₃ K ₂ O + Na ₂ O CaO + MgO Min.90 Max.2 Max.2 Max.5

 In addition, metakaolin is a product produced domestically, the physical and chemical properties of metakaolin are shown in Table 5 below.

Physical properties Powder importance Particle Size [44㎛ Pass (%)] Moisture content (%) 10000 (㎠ / g) 2.53 90 0 Chemical properties Chemical component (%) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ TiO ₂ 52 40 3 0.4 K ₂ O Na ₂ O CaO MgO 0.6 0.4 1.2 0.5

Experimental Example 1 Condensation Time

1. Experimental method

The setting time test was performed by KS F 2436 <Test method of setting time of concrete by penetration resistance needle>. Settling times for the five formulations shown in Table 1 were measured.

2. Experimental results

Condensation time test results of each shotcrete according to the admixture mixture conditions are shown in FIG. Looking at the setting time of the blended composition of Figure 2 regardless of the type and mixing of the mixed material showed a similar setting time and there was no delay effect of the setting time according to the mixing conditions of the mixed material. This is because the fastening property of the fastener which forms the net structure and promotes the hydration reaction of the cement by the formation and development of the needle-shaped ethrinzite from the beginning of the reaction with the portland cement and the mixing water determines the setting time of the shotcrete.

Experimental Example 2 Compressive Strength

1. Experiment Method

The compressive strength test was carried out according to KS F 2405 <Concrete compressive strength test method>. Φ100 × 200mm specimens were prepared and repeated three times for 1, 3, 7 and 28 days of age. In the universal testing machine, the specimen was placed in the center of the test plate, and the specimen was pressurized until the specimen was destroyed at a constant speed. The average load of the specimen was divided by the cross-sectional area, and the average value was defined as the compressive strength. The specimens were cured under water at 23 ± 2 ℃ in a constant temperature condition of 23 ± 2 ℃ in a curing room with 23 ± 2 ℃ and 50% relative humidity.

2. Experimental Results

Compressive strength test results of each shotcrete according to the admixture mixing conditions are as shown in FIG.

The compressive strength test results showed that the compressive strength of the blend containing admixtures did not show a significant difference in the early age compared to the formulation (P) containing only the fastener, but the strength was higher and the compressive strength was higher with increasing age. appear. This is due to the reaction characteristics of silica fume and metakaolin, which react with calcium hydroxide produced during cement hydration to form an additional CSH gel to cause a pozzolanic reaction.

In the case of mixing and mixing metakaolin and silica fume, the 28-day compressive strength showed a strength improvement effect of up to 50% or more compared to the formulation without mixing admixture (P) and compared with the formulation containing only silica fume (SF4 and SF8). A maximum strength increase of at least 30% was shown.

In the case of mixing and mixing silica fume and metakaolin (SM4 and SM8), metakaolin having a larger particle size than silica fume enhances the rigidity of shotcrete microstructure and fills the micropores between the metakaolin particles with silica fume, resulting in the composition The compressive strength of shotcrete seems to increase.

Experimental Example 3 Flexural Strength

1. Experiment Method

In order to evaluate the bending performance according to the admixture, it was carried out by KS F 2408 <Test method of bending strength of concrete>. Two specimens were prepared for 1 day, 3 days, 7 days, and 28 days by casting directly into a square mold of 150 × 150 × 550㎜. After initial curing, they were cured under constant temperature of 23 ± 2 ℃. The experiment was conducted.

2. Experimental results

In the case of mixing and mixing metakaolin and silica fume, the 28-day flexural strength increased up to 40% more than the compound (P) containing no admixture, and the maximum compared with the compound containing only silica fume (SF4 and SF8). An increase in strength of at least 25% was shown (FIG. 4).

Experimental Example 4 Chloride Ion Permeation Test

1. Experiment Method

Permeability in shotcrete is important not only in strength but also in durability. The increase in permeability not only lowers the strength by the expansion of the crack, but also worsens the durability such as freezing and thawing. Tests for indirect permeability of shotcrete include permeation test using air, permeation test using water, and permeation test using specific gas. In this example, in order to determine the indirect permeability of the shotcrete according to the type of admixture, it was carried out according to the method of ASTM C 1202 (Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration).
Coulombs Chloride ion permeability Typical of > 4000 400 ~ 2000 2000 ~ 1000 1000 ~ 100 <100 High Moderate Low Very low Negligible High W / c-ratio 0.4 ~ 0.5 W / C-ratio W / C-ratio <0.4 Latex modif. concrete Polymer concrete

2. Experimental results

The permeability of the shotcrete without the admixture was found to be "high permeability" according to the preceding criteria, but the permeability of the admixture with the admixture was less than "usually permeable". 5).

In particular, the average particle diameter of silica fume is 0.1 μm, which is about 100 times smaller than that of cement particles (10 μm). Thus, due to the micro-filter effect of filling these pores between cement particles, silica fume is used when the amount of the mixture is the same. In the case of single mixing (SF4 and SF8), it showed low permeability.

Since the average particle diameter of metakaolin is smaller than cement particles (10 μm) but about 1-2 μm larger than silica fume (0.1 μm), the permeability of metakaolin single mixed shotcrete compared to the same permeability of silica fume mixed shotcrete It will show a somewhat large result, in the present invention, by mixing and mixing (meta kaolin and silica fume (SM4 and SM8) to induce a micro filter effect of the silica fume will be able to induce a significant permeability lowering effect. In the experimental results, the blended shotcrete of metakaolin and silica fume was able to obtain almost the same level of water permeability as compared with the silica fume-only shotcrete.

Therefore, the metakaolin and silica fume mixed shotcrete show the same permeability-related durability as the expensive silica fume mixed shotcrete, and as described above, the mechanical properties (compressive strength, flexural strength, etc.) can be obtained. It is expected.

However, lower permeability improves the durability of shotcrete. However, if the permeability of shotcrete is too low, the groundwater pressure that shotcrete must support increases, so the strength of shotcrete is increased or the thickness of shotcrete is increased. There is a problem that needs to be increased. Accordingly, it is desirable to meet the durability performance criteria while changing the mixing ratio of metakaolin and silica fume according to the durability (eg water permeability) of the shotcrete required for the tunnel / underground space.

Experimental Example 5 Freeze-thawing Test

1. Experiment Method

Shotcrete may be subjected to repeated freezing and thawing with changes in winter temperature. The repetitive action of freeze-thawing freezes the free water in the shotcrete and expands the volume, causing tensile stress due to the large expansion pressure inside the shotcrete to destroy the shotcrete.

In this example, in order to measure the freeze-thawing resistance of shotcrete according to the type of admixture mixture, 100 × 100 × 400㎜ square specimens were prepared and cured in a curing bath at 23 ° C. for 14 days, followed by KS F 2456 < Freeze-thawing test was performed according to Method B of the test method for the resistance of concrete in Korea. Standard specimens were prepared to repeat the freezing action of dropping the temperature at the center of the specimen from 4 ° C. to −18 ° C. and the fusion effect of raising it to 4 ° C. Relative dynamic modulus was measured every 30 cycles, and the test results were made from two specimens and averaged.

2. Experimental results

The freeze-thaw resistance showed a great difference according to the use of the admixture as in the previous chlorine ion passing charge, and the greater the amount of admixture used (8% of the cement weight), the higher the freeze-thaw resistance (Fig. 6).

Freeze-thawing resistance of shotcrete mixed with metakaolin and silica fume was the highest when the amount of admixtures was the same.

According to the present invention as described above, compared with the current shotcrete, the improvement of the short- and long-term stability of the tunnel / underground space through the improvement of the mechanical properties and durability of the shotcrete, the construction properties due to the reduction of the thickness of the shotcrete casting, the shotcrete lining permanent Various effects such as the application to the single-shell tunnel method can be expected.

In addition, the present invention will be able to significantly reduce the production cost through the mixing and mixing of the metakaolin and silica fume as compared to the conventional shot of the silica fume single shot shotcrete as well as the performance of the shotcrete.

Claims (2)

Shotcrete per 1m ^3, Coarse aggregate of 500 to 700 kgf weight with a maximum dimension of 10 to 15 mm; Fine aggregate weighing 1,000-1,200 kgf; 300 to 450 kgf weight cement; Water having a water-cement ratio of 40 to 60% by weight; A fastener of 4 to 10% of the weight of the cement; And, 4-8% of the admixture of the weight of the cement; It includes, The admixture is high performance shotcrete composition, characterized in that the mixed mixture of metakaolin and silica fume. In claim 1, The fastener is a high performance shotcrete composition, characterized in that the cement mineral filler.

Images