KR100698759B1 - Cement composition for concrete having superhigh compressive strength and manufactruing method thereof - Google Patents

Abstract

Provided is a cement composition for concrete having super high compressive strength greater than 120MPa yet ensuring sufficient fluidity and capable of controlling heat of hydration at a low level. The cement composition comprises 55-75 wt% of cement; 10-30 wt% of slag granules(SG); 5-15 wt% of silica fume; and 2-10 wt% of anhydrite. Desirably, the slag granules(SG) and the anhydrite are mixed at a weight ratio of 4:1. Each of the elements is mixed in a high-efficiency powder mixer. The silica fume is obtained by collecting SiO2 gas, and has an average particle size of 0.2-0.5 micrometers. The slag granules are used as a mixing agent for suppressing temperature increase in concrete and for delaying the generation of heat of hydration to control the occurrence of cracks.

Description

Cement composition for concrete having superhigh compressive strength and manufactruing method

1 is a graph showing the compressive strength and the paste flow according to the addition amount of silica fume.

2 is a graph showing the compressive strength and the paste flow according to the mixing ratio of the slag fine powder (SG) and anhydrous gypsum (GY).

3 is a graph showing the compressive strength and the paste flow according to the total amount of addition of the slag fine powder (SG) and anhydrous gypsum (GY).

Figure 4 is a graph showing the amount of agglomeration according to the mixing method of the cement binder for ultra-high strength concrete of the present invention.

Figure 5 is a SEM photograph of the binder after mixing of cement binder for ultra-high strength concrete of the present invention.

6 is a graph showing the hydration heating pattern of the cement binder (UHPC) and cement (OPC) for ultra-high strength concrete of the present invention.

7 is a graph comparing the pore structure of the cement binder (UHPC) and cement (OPC) for ultra-high strength concrete of the present invention.

8 is a graph showing the compressive strength of each age of the ultra-high strength concrete using the cement binder (UHPC) for ultra-high strength concrete of the present invention.

The present invention relates to a cement binder composition used for producing ultra high strength concrete.

As construction technology advances, buildings are gradually becoming higher, larger, and more specialized, and in recent years, interest in high-rise buildings has been increasing. Therefore, concrete is also evolving from high strength concrete to ultra high strength.

Ultra high-strength concrete generally means concrete with a compressive strength of 120 MPa or more, and it is expected to be applied to high-rise buildings due to various advantages such as lengthening of building span, reduction of cross section of vertical members, improvement of durability, and shortening of air.

There are various means to increase the strength and ultra high strength of concrete, of which the most important is to increase the strength of the binder. Accordingly, a method of lowering the water cement ratio using a high performance admixture or increasing the amount of hydrate using a special admixture such as silica fume is used.

However, in order to manufacture ultra-high strength concrete with a compressive strength of 120MPa or more, it is necessary to use a very low water cement ratio, which is difficult to manufacture and cast concrete with high viscosity. In addition, the amount of unit cement is large, and the desired strength expression cannot be expected due to defects in the cured product due to high heat of hydration. Therefore, technical measures for cement binders such as securing workability and reducing heat of hydration are required.

In the manufacturing method of the ultra-high strength cement polymer composite material of Patent No. 1996-004596, it introduces the ultra-high strength concrete compounding technology in which polymer, fiber, and fine silica are mixed, but it is used as a new material application technology rather than the structural material of buildings. Patent application No. 1997-039330, high strength concrete composition of the patent application No. 2001-0065531 cement high strength composite composition of the invention, but the technology applied to the factory concrete by steam curing or autoclave curing method is limited in actual ready-mixed concrete factory There is a problem in the manufacturing supply of the resin.

On the other hand, the production of high-strength concrete in the ready-mixed concrete factory has a track record of placing the actual structure up to 80MPa by the general high-strengthening method, but more than 120MPa has not yet overcome workability, pumping property and material defects in the ultra-high strength region.

The present invention has been made to solve the problems of the prior art as described above, the object of the present invention is to provide a high strength suitable for the production of ultra-high strength concrete with a compressive strength of 120MPa or more, ultra-high fluidity and low heat of hydration is controlled It is to provide a cement binder composition for high strength concrete.

Still another object of the present invention is to provide a cement binder composition for ultra high strength concrete, which makes it easy to manufacture a super high strength concrete of 120 MPa or more in a ready-mixed concrete plant.

In order to achieve the above technical problem, the present invention is 55 to 75% by weight of cement; 10-30% by weight of slag powder; 5-15% by weight of silica fume; And 2 to 10% by weight of anhydrous gypsum; provides a cement binder composition for ultra-high strength concrete comprising a.

 In addition, the present invention provides a cement binder composition for ultra-high strength concrete, characterized in that the material of the composition ratio is prepared by stirring with a high efficiency powder mixer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1. Cement for ultra high strength concrete Binder  Composition

The present invention relates to a cement binder composition for ultra high strength concrete comprising cement, slag powder, silica fume and anhydrous gypsum.

(1) The use range of cement is preferably 55 to 75% by weight. The amount of cement depends on the minimum and maximum amount of auxiliary binder added. That is, the lower limit of the amount of cement is to maintain the minimum amount of the main binder (cement) to express strength alone when the auxiliary binder is the maximum addition amount. In addition, when the cement is used in excess of 75% by weight may cause a problem that the heat of hydration rises.

In the manufacture of high strength or ultra high strength concrete with a high unit cement content, there are many cases where a medium heat of low hydration heat and a low heat type cement are used. However, in the present invention, when considering economical efficiency, ease of application, and initial strength as a material for a super high strength concrete binder, One good cement can be used. This is because the admixture such as the slag fine powder controls the heat of hydration. On the other hand, the heat of hydration of cement may increase the reactivity of the slag fine powder, which may lead to mutual synergy of the compressive strength.

(2) Slag fine powder is a mixed material obtained by finely crushing quenching slag produced in steel mills and is a latent hydraulic material. It is preferable to use a high powder material which is finely ground to a specific surface area of 6,000 cm 2 / g or more.

In general, ultra high-strength concrete has a cement content of 1,000 kg / ㎥, so a large amount of cement binder is used. Therefore, the heat of hydration increases due to the hydration reaction between water and cement binder, and the increased heat of hydration is caused by the temperature difference between the inside and the outside of the structure. Causes volume change. As a result, the temperature stress exceeds the tensile strength, cracks, and decreases the compressive strength.

At this time, by using the slag powder as a mixed material, it is possible to control the occurrence of cracks by the heat of hydration by reducing the temperature rise of the concrete, delaying and controlling the hydration heat. In addition, by using a high-molecular weight material with a specific surface area of 6,000 cm 2 / g or more, the reaction activity of the slag fine powder can be increased, thereby compensating for the initial strength drop and increasing the compressive strength of the later age group, thereby contributing to the production of super high strength concrete. Slag fine powder is also a multi-purpose material that can prevent the deterioration of workability due to the drop in fluidity which is a problem when placing concrete by improving the flowability of cement binder.

The use range of the slag fine powder is preferably 10 to 30% by weight. If the slag powder is less than 10% by weight, the initial reactivity is lowered to improve the fluidity and workability, and the heat of hydration is hard to be obtained.If the slag powder is used at more than 30% by weight, the strength is reduced by reducing the amount of cement as the main binder. A problem arises.

(3) Silica fume is a material collected by condensation of ferrosilicon used as a deoxidizer for steelmaking and SiO ₂ gas generated during the production of metal silicon for semiconductors. It is spherical in shape and has an average particle diameter of 0.2 to 0.5 µm and a specific surface area of 200,000. It is an ultrafine particle which is cm <2> / g, and is a pozzolanic material.

Silica fume contains 85% or more of SiO ₂ , and is classified in its original form in the form of powder (undensified), compacted (densified), and suspended in water. At this time, it is preferable to use powdered silica fume for mixing with other powders.

Since silica fume is ultra fine particles having a particle diameter of 0.2 μm, it fills the gap between water and cement particles in the hardened concrete to lower the viscosity of the concrete. In addition, in hardened concrete, it acts as a micro filler to fill the pores of the hydrate to improve the compressive strength and durability. Meanwhile, the silica component (SiO ₂ ) of the silica fume reacts with calcium hydroxide (Ca (OH) ₂ ) produced by cement hydration to produce CSH hydrate, thereby improving compressive strength.

The use range of the silica fume is preferably 5 to 15% by weight. 1 is a graph showing the compressive strength and the paste flow according to the amount of silica fume added as a result of a test for determining an appropriate use range of silica fume. In Figure 1, the total amount of slag powder (SG) and anhydrous gypsum (GY) is 30% by weight, and these were used in a mixing ratio of 7: 3. And, cement was used to satisfy the percentage according to the amount of silica fume used.

As shown in FIG. 1, when the silica fume is increased from 12% by weight to 16% by weight, the compressive strength slightly increases, but it can be seen that the paste flow is greatly reduced. In other words, silica fume should be used in less than 16% by weight to provide proper paste flow. When using less than 5% by weight of silica fume it is difficult to secure the strength performance due to the filling of the microporous hydrate.

(4) In the present invention, anhydrous gypsum (CaSO ₄ ) reacts with C ₃ A in cement or Al ₂ O ₃ in slag powder to produce ethrinzite (C ₃ A · 3CaSO ₄ · 32H ₂ O) to form a cured product. It compensates for shrinkage, forms dense tissue, and contributes to increased compressive strength. In addition, anhydrous gypsum plays a role of an adjuvant that enhances the strength by increasing the reactivity of the slag powder by acting as a stimulant in the latent hydraulic reaction which is a characteristic of the slag powder.

The use range of the anhydrous gypsum is preferably 2 to 10% by weight. The range of anhydrous gypsum was determined in consideration of the appropriate mixing ratio with the slag fine powder.

(5) At this time, it is preferable that the slag powder and the anhydrous gypsum are mixed in a weight ratio of 4: 1.

2 is a graph showing the compressive strength and the paste flow according to the mixing ratio of the slag fine powder (SG) and anhydrous gypsum (GY). Slag fine powder (SG) and anhydrous gypsum (GY) were mixed in a total amount of 30% by weight, silica fume (SF) was used as 12% by weight, cement was used as 58% by weight.

As shown in FIG. 2, as the mixing ratio of anhydrous gypsum was increased, the paste flow was almost unchanged, but the compressive strength was slightly increased to show the maximum strength in the 8: 2 (4: 1) formulation. That is, considering the increase in long-term intensity expression rate, the mixing ratio of slag fine powder (SG): anhydrous gypsum (GY) is preferably 4: 1.

In addition, the slag fine powder (SG) and the anhydrous gypsum (GY) is preferably a total amount of the two materials are mixed in 23 ~ 28% by weight.

3 is a graph showing the compressive strength and the paste flow according to the total amount of addition of the slag powder (SG) and anhydrous gypsum (GY). Silica fume (SF) was used at 12% by weight, and cement was used to satisfy the percentage according to the change in the total amount of the slag powder (SG) and the anhydrous gypsum (GY).

As shown in Figure 3, the experimental results showed that the compressive strength was greatest when the total amount of the slag fine powder (SG) and anhydrous gypsum (GY) was 25% by weight, and slightly decreased at 30% by weight. In addition, the paste flow tended to increase slightly with increasing total amount. That is, in view of the increase in the paste flow and the compressive strength, the total amount of the slag powder (SG) and the anhydrous gypsum is preferably mixed at 23 to 28% by weight.

2. Cement for ultra high strength concrete Binder  Preparation of the composition

The materials constituting the composition of the present invention can be uniformly mixed in the composition ratio of (1) to (5) to produce a cement binder composition for ultra-high strength concrete of the present invention.

At this time, preferably the composition of the present invention may be prepared by stirring with a high efficiency powder mixer.

Cement binders for ultra-high strength concrete are important to secure fluidity and workability with the development of ultra-high strength, but in practice, mixed materials are added together with cement at the stage of ready-mixed concrete production. Problems have been pointed out. In addition, the workability was found to be reduced even in the simple mixing. In the present invention, this problem is solved by mixing the binder in advance with a high-efficiency powder mixer.

In the case of preparing the binder of the composition ratio by mixing in advance with the high-efficiency powder mixer, the dispersion and particle coating of ultra-fine particles are made, which greatly improves fluidity and workability. In practice, it becomes possible to manufacture ultra-high strength concrete of 120MPa or more in the ready-mixed concrete stage.

The binder mixed as described above appears to have a homogeneous particle size of 5,000 ~ 12,000 cm 2 / g powder.

4 is a graph showing the amount of agglomeration when the raw materials of the cement binder for ultra-high strength concrete are simply mixed and premixed with a high-efficiency powder mixer, and FIG. 5 is a SEM photograph of the binder after mixing. The binder was prepared using 63 wt% cement, 20 wt% slag powder, 5 wt% anhydrous gypsum, 12 wt% silica fume, and a rotary mixer was used as the high-efficiency powder mixer.

In FIG. 4, A represents a case of simple mixing, and B represents a case of pre-mixing with a high-efficiency powder mixer. B1, B3, B5, and B10 indicate that the mixture was stirred with a high efficiency powder mixer for 1 minute, 3 minutes, 5 minutes, and 10 minutes, respectively. Each of five samples were taken and analyzed, and ① to ⑤ in FIG. 4 represent sample numbers.

As a result of measuring the lump content of 600 ㎛ or more by simple sieve as shown in Figure 4 it can be seen that the lump content is drastically reduced compared to the case of simple mixing when mixed in advance with a high efficiency powder mixer. That is, it can be confirmed that the dispersion effect of the binder is excellent when mixed in advance with the high efficiency powder mixer.

In addition, in the case of simple mixing through the SEM image of FIG. 5, the silica fume is non-uniform while forming a lump, whereas in the case of pre-mixing with the high-efficiency powder mixer, the spherical silica fume adheres to the cement particle surface and is well dispersed. You can see that. That is, it can be confirmed that the mixing and dispersion of the binder is excellent.

On the other hand, as shown in Figure 4, when stirring with the high-efficiency powder mixer, when the mixture is stirred for 3 minutes or more compared to the lump content when stirred for 1 minute, it can be seen that the lump content is significantly reduced, excellent dispersion effect In order to obtain, it is preferable to stir for 3 minutes or more. On the other hand, stirring for 10 minutes or more is uneconomical in manufacturing economy. It is preferable to stir for 3 to 10 minutes with a high efficiency powder mixer.

As the high-efficiency powder mixer, a zero gravity mixer or a mixer of the mixer body and the stirring blades may be used as a reverse rotation method.

The zero gravity mixer is a device for forming and mixing a zero gravity region by using a rotational force, for example, a Twin Shaft Batch Type Mixer. When a plurality of arms are fixed to two parallel main shafts and paddles are mounted on each of them, the paddles are mixed by the rotational force in which both axes rotate at constant speed in the opposite direction. Spread up to the upper middle layer of the yarn, the effective volume increases, and a zero gravity region is formed in a flash. The paddles are designed to overlap each other, so that the transport zone and the mixing zone of the raw materials are formed by the constant speed rotation, and the fluidized bed in the zero gravity state is formed regardless of the particle size, specific gravity, and shape of the raw materials. As a result, uniform mixing is possible in a short time.

On the other hand, it is possible to use a rotary mixer in which the mixer body and the stirring blade is a reverse rotation method, for example, a stirring blade rotating in a direction opposite to the rotating cylinder that rotates in a state inclined at a predetermined angle (Rotating Mixing Pan) Powerful cross flow and counter flow are generated by the tool, which enables uniform mixing in a short time, and is a batch mixer or a rotary mixer capable of continuous operation.

Test Example

The cement binder for the ultra-high strength concrete of the present invention was prepared and tested for its physical properties and the compressive strength of the concrete prepared as follows.

The composition ratio of ultra high strength cement binder (UHPC) prepared for this test is 63% by weight of ordinary ordinary Portland cement, 20% by weight of slag powder, 5% by weight of gypsum anhydrous, and 12% by weight of silica fume. Stirred for a minute.

(1) physical and chemical properties

The physical properties and chemical properties of the ultra high strength concrete cement binder (UHPC) were examined in comparison with cement (OPC).

First, looking at the chemical composition and physical properties of each material constituting the binder (UPHC) is shown in Table 1.

TABLE 1

Material division Chemical composition (%) Physical properties ig-loss SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO Average particle size (㎛) Fertilizer Area (㎠ / g importance cement 0.77 22.05 5.30 3.63 62.93 2.12 14.3 3,220 3.14 Slag powder -0.34 34.56 13.80 0.66 40.53 4.98 6.0 7,516 3.01 Anhydrous gypsum 3.62 3.23 0.79 0.38 36.17 0.13 5.9 - 2.87 Silica fume 2.22 92.40 1.42 0.59 - 1.30 0.2 200,000 2.36

Physical and chemical properties of the binder (UHPC) and cement (OPC) can be found in Tables 2 and 3.

TABLE 2 Physical Properties

Material division Particle size distribution (%) Average particle size (㎛) Specific surface area (㎠ / g) importance Less than 1㎛ 1.5 ~ 12㎛ 16 ~ 32㎛ More than 48㎛ Cement (OHC) 6.5 36.0 41.8 15.1 14.3 3,220 3.14 Ultra High Strength Cement Binder for Concrete (UHPC)  6.5  47.7  35.5  9.6  10.7  8,340  2.89

TABLE 3 Chemical Properties

Material division ig-loss SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO SO ₃ K ₂ O Na ₂ O Cement (OPC) 0.77 22.05 5.30 3.63 62.93 2.12 2.05 1.00 0.15 Ultra High Strength Cement Binder for Concrete (UHPC)  0.71  31.15  6.28  2.82  50.02  2.25  5.63  0.99  0.15

(2) hydration characteristics

6 is a graph showing the heat generation pattern of the ultra-high strength concrete cement binder (UHPC) compared with cement (OPC).

As shown in FIG. 6, the binder (UHPC) has a low first exothermic peak, a second exothermic peak is delayed, and a high peak is low. That is, it is confirmed that there is a characteristic that the heat of hydration is controlled as a whole, it can be seen that the binder of the present invention controls the occurrence of cracking by the heat of hydration, and prevents the decrease in compressive strength.

(3) void structure

FIG. 7 is a graph showing the pore structure of the ultra high strength concrete cement binder (UHPC) compared with cement (OPC).

As shown in FIG. 7, the pore structure of the binder (UHPC) may be reduced as compared with cement (OPC). In addition, when looking at the distribution of pore sizes, it can be seen that in the case of the binder (UHPC), large pores decrease and small voids increase. Silica fume subdivides the pores to form dense tissue, which increases the compressive strength.

(4) compressive strength by age of super high strength concrete

The ultra high strength concrete was prepared using the ultra high strength cement binder (UHPC) to test the compressive strength of each age.

The formulation for the manufacture of ultra-high strength concrete with a design strength of 150MPa is shown in Table 4.

TABLE 4

Design standard strength W / B (%) S / a (%) Admixture (B ×%) Unit material amount (㎏ / ㎥) W UPHC Fine aggregate Coarse aggregate 150 MPa 14 40 3.0 140 1,000 520 813

W / B: water-binding ratio, S / a: fine aggregate ratio (S: fine aggregate, a: total aggregate)

Admixture: Polycarboxylic acid high performance water reducing agent, W: Water

8 is a graph showing the compressive strength for each age of the ultra-high strength concrete by the combination of Table 4. When using the binder of the present invention as shown in Figure 8 it can be confirmed that the production of ultra-high strength concrete that exceeds 150MPa of design strength in the hardened concrete when manufacturing the super-high strength concrete.

As described above, the cement binder for ultra-high strength concrete according to the present invention has a low heat of hydration as a whole and has a small amount of pore structure. It solves the unforeseen problems and provides high compressive strength because compact structure can be formed by reducing the pore structure.

In addition, the cement binder for ultra-high strength concrete according to the present invention is prepared by stirring with a high-efficiency powder mixer in advance, so that the dispersion and particle coating of ultra-fine particles is greatly improved, the fluidity and workability are greatly improved, so that the preparation of ultra-high strength concrete of 120 MPa or more can be easily performed in ready-mixed concrete factory. Makes it possible.

Claims (7)

55 to 75 weight percent cement; 10-30% by weight of slag powder; 5-15% by weight of silica fume; And 2-10% by weight of anhydrite; Cement binder composition for ultra-high strength concrete comprising a. In claim 1, The slag powder and the anhydrous gypsum is cement binder composition for ultra-high strength concrete, characterized in that mixed in a weight ratio of 4: 1. In claim 2, The total amount of the slag powder and the anhydrous gypsum is 23 ~ 28% by weight cement binder composition for ultra high strength concrete, characterized in that. In claim 1, The binder composition is a cement binder composition for ultra high strength concrete, characterized in that the homogeneous particle size of 5,000 ~ 12,000 cm 2 / g powder. Method for producing a cement binder composition for ultra-high strength concrete, characterized in that the composition of any one of claims 1 to 4 by stirring with a high efficiency powder mixer. In claim 5, The high-efficiency powder mixer is a method for producing a cement binder composition for ultra-high strength concrete, characterized in that the gravity-free mixer or mixer mixer and the stirring blade is a rotary mixer of the reverse rotation method. In claim 5, Method for producing a cement binder composition for ultra-high strength concrete, characterized in that for 3 to 10 minutes stirring with the high-efficiency powder mixer.

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