KR20230036643A - Flowable concrete composition with excellent workability and resistance to material separation - Google Patents

Abstract

The present invention provides a concrete composition capable of controlling the decrease in strength even when a shrinkage reducing agent is applied so as to ameliorate workability and resistance to material separation as well as resistance to cracks. A low-shrinkage and middle-fluidity concrete composition with excellent workability and resistance to material separation of the present invention includes a cement-containing binder, water, a polycarboxylic acid-based water reducing agent, a cellulose thickener, and a shrinkage reducing agent.

Description

Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation {Flowable concrete composition with excellent workability and resistance to material separation}

The present invention relates to a concrete composition that can simultaneously satisfy workability and resistance to material separation, and can control strength reduction while improving crack resistance by adding a shrinkage reducing agent.

A cement composition such as concrete or cement mortar is a hydraulic reactant hardened by a reaction between cement and water, and physical properties such as compressive strength after hardening may change depending on the amount of water used. In general, increasing the amount of water added improves workability, but decreases compressive strength and may cause cracking. Therefore, the amount of water used in cement compositions is limited, and admixtures are additionally added to overcome the weakening of physical properties.

In general, as admixtures, AE agents (air entraining admixture), water reducing agents (water reducing admixture), and high range water reducing admixture (high range water reducing admixture) are used. Among them, the AE water reducing agent is mixed with a water reducing agent or a high performance water reducing agent and is classified into an AE water reducing agent and a high performance AE water reducing agent.

On the other hand, there are four major mechanisms that affect the shrinkage of cement hardened bodies: surface free energy, capillary tension, water movement and separation pressure. Among these theories, the most supported theories in drying shrinkage are the capillary tension theory and the water transport theory. In this drying shrinkage process, when the concrete is placed under dry conditions, moisture movement occurs on the surface, and as the surface becomes dry, internal moisture moves to the surface due to surface tension, and moisture movement is accelerated due to pressure in the concrete capillaries. As the process progresses, the volume occupied by the internal moisture is reduced, which causes tensile stress in the concrete, and when the allowable stress is exceeded, drying shrinkage cracks occur.

As an example of a technology for improving resistance to drying shrinkage cracking, Korean Patent Registration No. 1568765 adds trehalose to cement, sand and water, but the cement: 30 to 40% by weight and sand: 60 to 70 A binder containing % by weight, water added at 10 to 20 parts by weight and trehalose added at 0.1 to 0.6 parts by weight based on 100 parts by weight of the binder, the cement, Portland cement: 25 to 30% by weight, Silica sand: 35 to 45% by weight, calcium carbonate: 15 to 25% by weight, antifoaming agent: 0.05 to 0.10% by weight, shrinkage reducing agent: 0.1 to 5% by weight, methyl cellulose: 0.1 to 0.3% by weight, and Methyl ethyl cellulose: contains 0.1 to 0.2% by weight, and the silica sand has an average diameter of 0.01 to 0.3 mm, and proposes a concrete composition for preventing drying shrinkage and cracking.

However, when a shrinkage reducing agent is added to improve crack resistance such as drying shrinkage cracking, there is a problem in that unfavorable effects are expressed in terms of initial strength as well as long-term strength. There is a problem that it is not easy to satisfy the resistance to separation.

Republic of Korea Patent Registration No. 1568765

Therefore, the present invention is to provide a concrete composition capable of controlling the decrease in strength even when a shrinkage reducing agent is applied in order to improve workability and resistance to material separation as well as resistance to cracking.

In order to achieve the above object, the low shrinkage medium flow concrete composition (hereinafter referred to as the "composition of the present invention") excellent in workability and resistance to material separation of the present invention is a binder containing cement, water, and a polycarboxylic acid-based water reducing agent. , A cellulose thickener, and a shrinkage reducing agent are included.

As an example, the shrinkage reducing agent is one or two of butyldiglycol, butyltriglycol, methyldiglycol, butylpolyglycol, ethylpolyglycol, methyltriglycol, ethylglycol, monoethylene glycol, polyethylene glycol, and polyalkylene glycol. Characterized in that it is a mixture of phases.

One example is characterized in that an amine-based additive and sodium persulfate are further included.

As an example, polyethylene oxide and magnesium aluminum silicate are further included.

One example is characterized in that sodium polyacrylate starch is further included.

One example is characterized in that magnesium hydroxide is further included.

As an example, bentonite coated with itaconic acid on the surface is further included.

The concrete composition of the present invention has improved workability and resistance to material separation, and in particular, has the advantage of not reducing strength while improving crack resistance by adding a shrinkage reducing agent.

Hereinafter, embodiments and experimental examples of the present invention will be described in more detail with reference to the accompanying drawings.

The composition of the present invention is characterized in that it includes a cement-containing binder, water, a polycarboxylic acid-based water reducing agent, a cellulose thickening agent, and a shrinkage reducing agent.

The present invention includes a binder containing cement and water in an admixture containing a polycarboxylic acid-based water reducing agent, a cellulose thickener, and a shrinkage reducing agent described below, wherein the binder may include fly ash, blast furnace slag, etc. in addition to cement.

The cement is not limited to the type as long as it is included in mortar or concrete in the art, and is preferably general Portland cement, early-strength Portland cement, ultra-high-strength Portland cement, medium heat Portland cement, sulfate-resistant Portland cement, white Portland cement, and zinnia Any one of hard cement or a mixture thereof may be used, but is not limited thereto, and cement powder form as well as clinker form may be used. However, when using cement clinker, it is preferable to use a cement clinker that has undergone a firing and grinding process as a pretreatment.

The water is not limited to the type, but it is preferable to use purified water without impurities. In addition, water and binder (W/B) are values that determine the strength and durability of concrete, such as design standard strength and mixing strength. It is preferable under the condition that the etc. do not occur.

The blast furnace slag is finely pulverized granulated slag, which is a by-product of the pig iron manufacturing process, and serves to increase the long-term strength of cement and increase water tightness and seawater resistance. The blast furnace slag has a powder degree of 2,000 to 15,000 cm 2 / g, preferably 4,000 to 8,000 cm 2 / g, so that the strength development of the concrete composition is not reduced while maintaining the fluidity of the concrete composition. In addition, the blast furnace slag preferably contains 2 to 6% by weight of sulfuric anhydride (SO ₃ ) out of 100% by weight, preferably 2 to 3% by weight. The anhydrous sulfuric acid is added when blast furnace slag is pulverized, and serves as a co-stimulant.

The fly ash serves to enhance the long-term strength of concrete by a pozzolanic reaction and to enhance the watertightness, durability, and chemical resistance of the concrete structure, and is completely burned as coal ash remaining after using coal in a thermal power plant and has a specific gravity of 2.0 to 2.4 , Preferably it is preferable to use one in the range of 2.1 to 2.2, and it is preferable to use one with a fineness of 3,500 to 4,500 cm 2 / g and an ignition loss of less than 5%.

In addition, although not mentioned above, the composition of the present invention further includes coarse aggregate and fine aggregate. The coarse aggregate is generally referred to as gravels, and is not limited to the type as long as it is commonly used in the art. It is preferable to use crushed aggregate or natural aggregate as the coarse aggregate, preferably one that satisfies KS F 2502 or KS F 2527.

The fine aggregate is generally referred to as sand, and both fine aggregate and coarse aggregate can be used. The fine aggregate is preferably a material that passes almost completely through the No. 4 sieve (ASTM C125, 4.75 mm), and it is preferable to use silica sand or the like. The coarse aggregate is a material mainly remaining in sieve No. 4 (ASTM C125, 4.75mm), for example, other durable aggregates such as silica sand, quartz, marble, granite, limestone, calcite, feldspar, alluvial sand, and other sand, or their The mixture is good. In addition, in the present invention, in order to determine the fluidity of concrete, it is preferable that the fine aggregate ratio (S / a) satisfies 35 to 55% by volume, which is the volume ratio of sand (S) to the total aggregate (sand + gravel, a) volume can be calculated

In the case of the polycarboxylic acid-based water reducing agent, it not only exhibits excellent water reducing performance compared to previously used admixtures, but also has a small slump loss and has excellent kneading properties. This polycarboxylate system is composed of one main chain and side chains, and the main chain serves to increase the water reducing effect of concrete by widening the interval between cement particles so that the mixing water effectively contacts cement and facilitates the hydration reaction. It serves to increase workability, that is, fluidity, by delaying the flow characteristics of concrete, which decrease over time.

In addition, the cellulose thickener is to improve resistance to material separation. Workability is improved by the addition of a polycarboxylate-based water reducing agent, but it may be vulnerable to material separation, so in the present invention, a cellulose thickener is further added. Here, the cellulose thickener is not limited in its type, but examples thereof include methyl-based cellulose such as methyl cellulose, hydroxymethyl cellulose, and carboxymethyl cellulose; ethyl cellulose such as ethyl cellulose, hydroxyethyl cellulose, and carboxyethyl cellulose; A cellulose-based thickener selected from propyl-based cellulose such as hydroxypropyl cellulose may be used.

The shrinkage reducing agent is an organic admixture characterized in that it changes the physical properties of water, and dissolves in the capillary condensate that governs shrinkage to reduce the surface tension, thereby reducing the capillary tension during drying so that the function of reducing shrinkage is expressed. .

The shrinkage reducing agent is one or a mixture of two or more of butyldiglycol, butyltriglycol, methyldiglycol, butylpolyglycol, ethylpolyglycol, methyltriglycol, ethylglycol, monoethylene glycol, polyethylene glycol, and polyalkylene glycol. characterized by

On the other hand, the shrinkage reducing agent may have a problem ⁱⁿ that initial and long-term strength is lowered by affecting the Ca ²⁺ concentration of concrete.

Accordingly, in the present invention, an example in which a mixture of sodium persulfate and an amine-based additive is further added is presented in order to control the decrease in initial and long-term strength according to the addition of a shrinkage reducing agent or the like.

The sodium persulfate acts as an early strength additive. The early-strength additive serves as a stimulus to break the impermeable film formed on the surface of the blast furnace slag when blast furnace slag is included in the binder, and has an effect of activating the reaction of cement. Describing this in detail, ions and reactive radicals generated during thermal decomposition react with the main component of cement to greatly improve reactivity. As a result, initial hydration and setting reactions are promoted, and the early strength of concrete can be improved.

In addition to this, the amine-based additive is to compensate for the initial and long-term strength that can be reduced according to the addition of the shrinkage reducing agent, as mentioned above. As the amine-based additive promotes the hydration reaction inside the concrete, it prevents deterioration in initial and long-term strength that may accompany the addition of the shrinkage reducing agent. These amine-based additives have a lower strength development effect than sodium persulfate described below, but have excellent strength development stability. The reason is that sodium persulfate is greatly affected by the internal conditions of concrete, but amine-based additives are relatively less affected. Therefore, the reduction in initial strength by sodium persulfate is prevented, but by further mixing amine-based additives, concrete can stably exhibit initial and long-term strength. The amine-based additive is not particularly limited, but preferably, one or a mixture of two or more selected from the group consisting of TIPA, TEA, form urea, and hydroxyethyl urea may be used.

That is, the present invention is to add a mixture of sodium persulfate and amine-based additives as a strength enhancer, sodium persulfate is to supplement the initial strength that can be reduced by the addition of blast furnace slag, and the amine-based additive is added It is to compensate for the initial and long-term strength degradation that can be reduced by

However, when a large amount of polycarboxylic acid is added to secure high fluidity in low-powder concrete, material separation occurs, and as mentioned above, a cellulose-based thickener is further added, but the cellulose-based thickener uses blast furnace slag as a binder In this case, there is a problem in that the amount of suspended matter increases because the cellulose-based thickener does not catch the blast furnace slag, unlike the cement particles.

Accordingly, the present invention suggests an example in which polyethylene oxide is further included in order to improve the resistance to material separation in the case of cement particles as well as blast furnace slag particles.

However, when only polyethylene oxide is added as an additive, it is effective in preventing material separation, but when such an admixture is mixed and used in a concrete composition, water is generated in the carboxymethyl reaction. Since a phenomenon occurs, there is a case where a problem in which workability is deteriorated due to such a phenomenon occurs.

Accordingly, in the present invention, an example is provided in which magnesium aluminum silicate is further included in addition to polyethylene oxide as an additive. The magnesium aluminum silicate is added to the concrete composition as an admixture to absorb water generated in the carboxymethyl reaction when mixed, By removing it, it serves to prevent the reactants from clumping, so that material separation is prevented by the addition of polyethylene oxide, and in addition, workability is prevented from being deteriorated by the addition of magnesium aluminum silicate.

In addition to this, as magnesium aluminum silicate is added to the additive, as mentioned above, it absorbs water generated in the carboxymethyl reaction, so that the function as a moisturizer is also expressed. That is, the function of crack resistance is also expressed.

In addition to the above compositions, an example in which sodium polyacrylate starch is further included is presented. As mentioned above, polyethylene oxide is included as an additive in the admixture to prevent material separation, but when viscosity is expressed too early by polyethylene oxide, there is a problem in that sufficient workability and filling properties are not secured.

Accordingly, the additive includes sodium polyacrylate starch in addition to the above compositions, so that workability is maintained until the pouring process after mixing by including sodium polyacrylate starch. In other words, the formulation is in the form of a gel by polyethylene oxide, and by the addition of sodium polyacrylate starch, this formulation is changed to a sol form by mechanical collision during the mixing process so that workability is maintained over time After that, when the energy such as mechanical collision is removed after casting, it is to be in the form of gel again.

On the other hand, when the composition of the present invention is used for purposes such as particularly large structures, cracks due to moisture evaporation, etc., can be controlled by the action of magnesium aluminum silicate as mentioned above, but cracks due to temperature contraction during the curing process cannot be controlled. However, as a composition for controlling such temperature cracking, an example in which magnesium hydroxide is further included in the additive in addition to the above compositions is presented. In the case of the magnesium hydroxide, it is to absorb the curing heat generated during the curing process of the paste to control the temperature crack.

Preferably, the admixture contains 20 to 80 parts by weight of a cellulose thickener, 20 to 80 parts by weight of a shrinkage reducing agent, 1 to 10 parts by weight of a mixture of an amine additive and sodium persulfate, and 1 to 10 parts by weight of polyethylene oxide, based on 100 parts by weight of a polycarboxylic acid water reducing agent. It is reasonable to include 1 to 10 parts by weight of magnesium aluminum silicate, 1 to 10 parts by weight of sodium polyacrylate starch, and 1 to 10 parts by weight of magnesium hydroxide. Preferably, the amine-based additive and the sodium persulfate mixture are formulated in a weight ratio of (7:3) to (9:1).

On the other hand, although drying shrinkage cracks and temperature cracks can be controlled as described above by the addition of the admixture, there may be a lack of control of cracks caused by various causes such as cracks due to paste shrinkage accompanying securing early strength. , In addition to the above compositions, the additive presents an example in which bentonite coated on the surface of itaconic acid is further included. It is appropriate to mix 1 to 10 parts by weight of bentonite coated with itaconic acid based on 100 parts by weight of the polycarboxylate-based water reducing agent.

Bentonite is intended to improve resistance to cracking by compensating for shrinkage of the paste during curing by absorbing moisture and expanding its volume.

In addition to this, the bentonite is coated with itaconic acid on the surface so that only cations such as sodium ions are selectively adsorbed in the water absorption process of the bentonite.

In the composition of the present invention, sodium persulfate is included in the composition of the admixture to secure early rigidity. When sodium persulfate is added, sodium ions are eluted to the surface by capillarity or metal ions present in the paste are removed from the surface by capillarity. eluted to form voids on the surface, and these surface voids act as points of surface cracks. This is to control surface cracking by selectively adsorbing sodium ions.

When only bentonite is added for expansion, both positive and negative ions are adsorbed during the water absorption process. By adding conic acid-coated bentonite to the surface, only cations such as sodium ions are selectively adsorbed.

The itaconic acid is an anionic polymer, and a method for coating the surface of bentonite with itaconic acid may be prepared by impregnating bentonite in an aqueous solution of itaconic acid having a (-) charge and then drying it.

Examples of the present invention will be described through experimental examples below.

Each sample in this experiment was prepared by the formulation shown in Table 1 below. The composition of the admixture (AD) was varied in each sample, and Example 1 contained 20 parts by weight of a cellulose thickener, 20 parts by weight of a shrinkage reducing agent, and 5 parts by weight of polyethylene oxide based on 100 parts by weight of a polycarboxylic acid-based water reducing agent in the admixture. Example, Example 2 is the same as Example 1, but further includes 5 parts by weight of an amine-based additive and a sodium persulfate mixture (8: 2 in weight ratio), Example 3 is the same as Example 2, but magnesium aluminum silicate 5 An example in which parts by weight are further included, and Example 4 is the same as Example 3 but further includes 5 parts by weight of sodium polyacrylate starch, and Example 5 is the same as Example 4 but further includes 3 parts by weight of magnesium hydroxide. Example 6 is the same as Example 5, but an example in which 5 weight ratio of bentonite coated on the surface of itaconic acid is further included.

combination
division W/B
(%) S/a
(%) Combination Table (Kg/m ³ ) AD
(%/B) note W OPC FA BS S CS G 49.4 53.0 168 238 68 34 282 666 914 1.1

division length change rate
(%)
Slump flow
(mm)
Compressive strength ( MPa ) immediately 60 minutes 1 day 7 days 28 days Example 1 -0.039 510 470 2.23 23.26 35.19 Example 2 -0.042 505 460 2.53 23.71 37.50 Example 3 -0.028 515 475 2.51 23.77 37.52 Example 4 -0.027 520 485 2.54 23.01 37.03 Example 5 -0.019 520 480 2.52 24.52 37.82 Example 6 -0.011 515 485 2.51 25.21 38.70

Although not shown in Table 2, it is determined that the resistance to material separation is satisfied in light of the material amount standard (the Korean Society of Civil Engineers standard does not exceed 150 mg / l) as a result of the experiment.

It can be seen that Example 2 exhibits a slightly disadvantageous effect compared to Example 1 in terms of the length change rate. Able to know.

In addition, it can be seen that the case of Example 3 is more advantageous than Examples 1 and 2, and this seems to be due to the magnesium aluminum silicate controlling cracks caused by moisture evaporation as mentioned above.

In addition, it can be seen that Example 5 exhibits an advantageous effect in terms of length change rate compared to other Examples, which is due to the improvement of resistance to temperature cracking by the addition of magnesium hydroxide in Example 5. judged In addition, it can be seen that Example 6 exhibits the most advantageous effect, which is determined to be due to the addition of bentonite coated with itaconic acid on the surface in Example 6 to control the expansion and surface cracking of the paste.

On the other hand, it can be seen that the case of Example 2 exhibits a somewhat disadvantageous effect in terms of fluidity compared to Example 1. It can be seen that the fluidity is slightly lowered.

In addition, it can be seen that in the case of Example 3, more favorable results were obtained in fluidity after time elapsed (60 minutes) than in Example 1 as well as in Example 2. This is because in Example 3, magnesium aluminum was added to polyethylene oxide as an additive. It is believed that this is due to the addition of silicate, and as mentioned above, magnesium aluminum silicate absorbs and removes water generated in the carboxymethyl reaction, thereby preventing the reactant from clumping, resulting in a decrease in workability. It is judged to be due to the expression of the function to prevent it. As shown in Example 2, workability is somewhat deteriorated by the addition of sodium persulfate, but as shown in Example 3, magnesium aluminum silicate is further added to ensure early strength and workability. there is.

In addition, it can be seen that in the case of Example 4, more favorable results are obtained in fluidity after time elapsed (60 minutes) than in the case of Example 3, which is due to the addition of sodium polyacrylate starch as an additive in the case of Example 4. As mentioned above, it is judged that the addition of sodium polyacrylate starch is due to the change in the form of sol by mechanical collision in the mixing process, etc., and workability is maintained despite the passage of time. do.

On the other hand, in terms of strength, it can be seen that Example 2 exhibits a somewhat advantageous effect in terms of initial strength, etc. , It is to supplement the initial strength that can be reduced by the addition of blast furnace slag by sodium persulfate, and to supplement the initial and long-term strength deterioration that can be reduced by the addition of a shrinkage reducing agent by the amine additive.

In addition, it can be seen that the case of Example 5 is relatively advantageous in terms of strength compared to Examples 1 to 4. In this case, as mentioned above, the addition of magnesium hydroxide resulted in the improvement of resistance to various cracks. It is judged to be In addition, it can be seen that Example 6 exhibits the most advantageous effect in terms of strength, which is also believed to be due to the addition of bentonite coated with itaconic acid on the surface to control the expansion and surface cracking of the paste.

Through the above description, those skilled in the art will understand that various changes and modifications are possible without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims (7)

A low-shrinkage, medium-flow concrete composition with excellent workability and resistance to material separation, characterized in that it contains a binder containing cement, water, a polycarboxylic acid-based water reducing agent, a cellulose thickener, and a shrinkage reducing agent.
According to claim 1,
The shrinkage reducing agent is one or a mixture of two or more of butyldiglycol, butyltriglycol, methyldiglycol, butylpolyglycol, ethylpolyglycol, methyltriglycol, ethylglycol, monoethylene glycol, polyethylene glycol, and polyalkylene glycol. Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that.
According to claim 1,
Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that it further contains an amine-based additive and sodium persulfate.
According to claim 1,
Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that it further contains polyethylene oxide and magnesium aluminum silicate.
According to claim 3,
Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that it further contains sodium polyacrylate starch.
According to claim 4,
Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that magnesium hydroxide is further included.
According to claim 1,
Low shrinkage medium flow concrete composition with excellent workability and resistance to material separation, characterized in that it further comprises calcium sulfoaluminate, gypsum, and bentonite coated on the surface of itaconic acid.