KR102662384B1 - Flowable concrete composition with excellent workability and resistance to material separation - Google Patents

Abstract

The present invention relates to a low-shrinkage, medium-flow concrete composition with excellent workability and resistance to material separation, characterized by containing a binder containing cement, 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 simultaneously satisfies workability and resistance to material separation and is capable of controlling strength decline while improving crack resistance by adding a shrinkage reducing agent.

Cement compositions such as concrete or cement mortar are hydraulic reactants that harden through a reaction between cement and water, and physical properties such as compressive strength may change after hardening depending on the amount of water used. In general, increasing the amount of water added improves workability, but it can reduce compressive strength and cause cracks, so the amount of water used in cement compositions is limited, and additional admixtures are sometimes added to overcome this weakening of physical properties.

In general, admixtures include AE agents (air entraining admixture), water reducing agents (water reducing admixture), and high range water reducing admixtures. Among these, AE agents are mixed with water reducing agents or high-performance water reducing agents and are classified as AE water reducing agents and high-performance AE water reducing agents.

Meanwhile, there are four main types of mechanisms that affect the shrinkage of cement hardening bodies: surface free energy, capillary tension, moisture movement, and separation pressure. Among these theories, the theories that receive the most support for drying shrinkage are the capillary tension theory and the moisture movement theory. This drying shrinkage process occurs when concrete is placed under dry conditions, moisture moves to the surface, and as the surface dries, internal moisture moves to the surface due to surface tension, and moisture movement accelerates due to pressure within the concrete capillaries. As the process progresses, the volume occupied by the internal moisture decreases, causing tensile stress in the concrete and drying shrinkage cracks occurring when the allowable stress is exceeded.

As an example of a technology to improve resistance to drying shrinkage cracks, in Republic of Korea Patent Registration No. 1568765, trehalose is added to cement, sand and water, where the cement: 30 to 40% by weight and sand: 60 to 70% by weight. % by weight of a binder, water added in an amount of 10 to 20 parts by weight and trehalose added in an amount of 0.1 to 0.6 parts by weight based on 100 parts by weight of the binder, and the cement includes: Portland cement: 25 to 30 parts 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 reducer: 0.1 to 5% by weight, methyl cellulose: 0.1 to 0.3% by weight, and A concrete composition for preventing drying shrinkage and cracking is proposed, which contains 0.1 to 0.2% by weight of methyl ethyl cellulose, and the silica sand has an average diameter of 0.01 to 0.3 mm.

However, when a shrinkage reducing agent is added to improve crack resistance such as drying shrinkage cracking, there is a problem that unfavorable effects appear not only in initial strength but also in long-term strength, and the high sensitivity and sufficient fluidity and material required in recent years by the above technology. There is a problem in that it is not easy to satisfy resistance to separation.

Republic of Korea Patent Registration No. 1568765

Accordingly, the present invention aims to provide a concrete composition that can control strength reduction even with the application of a shrinkage reducing agent to improve workability and resistance to material separation as well as improve resistance to cracking.

In order to achieve the above object, the low-shrinkage heavy fluid concrete composition of the present invention with excellent workability and resistance to material separation (hereinafter referred to as "composition 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.

As an example, the shrinkage reducing agent is one or a mixture of two or more of butyl diglycol, butyl triglycol, methyl diglycol, butyl polyglycol, methyl triglycol, ethyl glycol, monoethylene glycol, and polyalkylene glycol. .

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

One example is that polyethylene oxide and magnesium aluminum silicate are further included.

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

One example is that magnesium hydroxide is further included.

One example is characterized in that bentonite coated on the surface with itaconic acid 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 improving crack resistance by adding a shrinkage reducing agent without reducing strength.

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

The composition of the present invention is 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.

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. Here, 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 strong Portland cement, ultra early strong Portland cement, medium heat Portland cement, sulfate resistant Portland cement, white Portland cement, and high speed Portland cement. Any one of light cements or a mixture thereof can be used, but it is not limited to this, and not only cement powder form but also clinker form can be used. However, when using cement clinker, it is preferable to use one that has undergone a pre-treatment process of firing and grinding.

The type of water is not limited, but it is recommended to use clean, purified water without impurities. In addition, water and binder (W/B) are values that determine the strength and durability of concrete, such as the design standard strength and mixing strength. W/B should be 30 to 55% by weight to prevent drying shrinkage of concrete and material separation. It is desirable under the condition that such things do not occur.

The blast furnace slag is made by finely pulverizing granulated slag, a by-product of the pig iron manufacturing process, and serves to increase the long-term strength of cement and increase watertightness and seawater resistance. The blast furnace slag has a fineness of 2,000 to 15,000 cm2/g, preferably 4,000 to 8,000 cm2/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 anhydrous sulfuric acid (SO ₃ ) based on the total 100% by weight, and preferably 2 to 3% by weight. The anhydrous sulfuric acid is added when finely pulverizing blast furnace slag, and serves as an auxiliary stimulant.

The fly ash plays a role in improving the long-term strength of concrete through pozzolanic reaction and strengthening the watertightness, durability, and chemical resistance of the concrete structure. It is a coal ash left over from the use of coal in a thermal power plant and is completely burned to have a specific gravity of 2.0 to 2.4. , preferably in the range of 2.1 to 2.2, with a powder degree of 3,500 to 4,500 cm2/g and a loss on ignition 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 also called gravel, and is not limited to the type as long as it is commonly used in the art. It is recommended to use crushed aggregate or natural aggregate as the coarse aggregate, and 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 almost completely passes through a No. 4 sieve (ASTM C125, 4.75 mm), and it is recommended to use silica sand, etc. The coarse aggregate is the material mainly remaining in No. 4 (ASTM C125, 4.75mm), such as silica sand, quartz, marble, granite, limestone, calcite, feldspar, alluvial sand, other sand, and other durable aggregates or these. The mixture is good. In addition, in the present invention, in order to determine the fluidity of concrete, it is recommended that the fine aggregate ratio (S/a) satisfies 35 to 55% by volume, which is the volume ratio of sand (S) to the volume of the total aggregate (sand + gravel, a). It can be calculated.

In the case of the polycarboxylic acid-based water reducing agent, it not only exhibits superior water reducing performance compared to previously used admixtures, but also has the characteristics of low slump loss and excellent kneading properties. This polycarboxylic acid system is composed of one main chain and one side chain. The main chain widens the spacing between cement particles and allows the mixed water to effectively contact the cement to facilitate the hydration reaction. It mainly plays a role in increasing the water-reducing effect of concrete, and the side chain It plays a role in improving workability, or fluidity, by delaying the flow characteristics of concrete that decrease over time.

Additionally, the cellulose thickener is used to improve resistance to material separation. The addition of a polycarboxylic acid-based water reducing agent improves workability, but it may be vulnerable to material separation, so in the present invention, a cellulose thickener is added. Here, the type of cellulose thickener is not limited, but examples include methyl 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 hydroxypropylcellulose can be used.

The shrinkage reducing agent is an organic admixture characterized by changing the physical properties of water. It dissolves in capillary condensate, which dominates shrinkage, to reduce surface tension, thereby reducing shrinkage by reducing capillary tension during drying. .

The shrinkage reducing agent is characterized in that it is one or a mixture of two or more of butyl diglycol, butyl triglycol, methyl diglycol, butyl polyglycol, methyl triglycol, ethyl glycol, monoethylene glycol, and polyalkylene glycol.

Meanwhile, the shrinkage reducing agent may affect the ^{Ca 2+} concentration of concrete, causing a decrease in initial and long-term strength.

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

The sodium persulfate acts as a crude strength additive. When the binder includes blast furnace slag, the early strength additive acts as a stimulant to break the impermeable film formed on the surface of the blast furnace slag and has the effect of activating the reaction of cement. To explain this in detail, ions and reactive radicals generated during thermal decomposition react with the main components of cement, greatly improving reactivity. As a result, the initial hydration and setting reactions are promoted, and the crude strength of concrete can be improved.

In addition, the amine-based additive is intended to compensate for the initial and long-term strength that may decrease due to the addition of a shrinkage reducing agent, as mentioned above. The amine-based additive promotes the hydration reaction inside the concrete, thereby preventing the initial and long-term strength decrease that may occur due to the addition of a shrinkage reducing agent. Although these amine-based additives have a lower strength development effect than sodium persulfate described below, they have excellent strength development stability. This is because sodium persulfate is greatly affected by the internal conditions of concrete, but amine-based additives are relatively less affected. Therefore, sodium persulfate prevents the initial strength from being lowered, but by adding amine-based additives, the concrete can maintain stable initial and long-term strength. There is no need to specifically limit the amine additive, but preferably one or a mixture of two or more selected from the group consisting of TIPA, TEA, formal urea, and hydroxyethyl urea can be used.

That is, the present invention adds a mixture of sodium persulfate and an amine-based additive as a strength enhancer. The sodium persulfate is used to compensate for the initial strength that may be lowered by the addition of blast furnace slag, and the amine-based additive is the addition of a shrinkage reducing agent. This is to compensate for the initial and long-term decrease in strength that may be caused by .

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

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

However, when only polyethylene oxide is added as an additive, it is effective in preventing material separation, but when such an admixture is mixed with the concrete composition, water is generated in the carboxymethyl reaction. As this phenomenon occurs, there are cases where workability is reduced due to this phenomenon.

Accordingly, the present invention presents an example in which magnesium aluminum silicate is further included in addition to polyethylene oxide as an additive. When the magnesium aluminum silicate is added to the concrete composition as an admixture and mixed, it absorbs water generated in the carboxymethyl reaction, By removing it, it plays a role in preventing the reactant from clumping, preventing material separation due to the addition of polyethylene oxide, and further preventing a decrease in workability due to the addition of magnesium aluminum silicate.

In addition, by adding magnesium aluminum silicate to the additive, as mentioned above, it absorbs the water produced in the carboxymethyl reaction and functions as a moisturizer. In other words, the function of crack resistance is also expressed.

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

Accordingly, in addition to the above compositions, the additive further includes sodium polyacrylate starch. By including sodium polyacrylate starch, workability is maintained until the pouring process after mixing. In other words, the mixture is in the form of a gel due to polyethylene oxide, but by adding sodium polyacrylate starch, this mixture changes into a sol form due to mechanical collision during the mixing process, so that workability is maintained over time. After pouring, when energy such as mechanical collision is removed, it returns to the form of a gel.

Meanwhile, when the composition of the present invention is used especially for 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 shrinkage during the curing process cannot be controlled. However, an example is presented in which the additive further contains magnesium hydroxide in addition to the above compositions as a composition for controlling such temperature cracking. In the case of the magnesium hydroxide, it is used to control temperature cracking by absorbing the curing heat generated during the curing process of the paste.

Preferably, the admixture includes 20 to 80 parts by weight of a cellulose thickener, 20 to 80 parts by weight of a shrinkage reducer, 1 to 10 parts by weight of an amine additive and sodium persulfate mixture, and 1 to 10 parts by weight of polyethylene oxide, based on 100 parts by weight of polycarboxylic acid-based 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 blended in a weight ratio of (7:3) to (9:1).

Meanwhile, drying shrinkage cracks and temperature cracks can be controlled as seen above by adding the admixture, but there may be a lack of control of cracks caused by various causes such as cracks due to paste shrinkage accompanying securing early strength. , an example is presented in which the additive further includes bentonite coated on the surface with itaconic acid in addition to the above compositions. It is appropriate to mix 1 to 10 parts by weight of bentonite coated with itaconic acid on the surface with respect to 100 parts by weight of polycarboxylic acid-based water reducing agent.

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

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

This is because the composition of the present invention contains sodium persulfate as an admixture to ensure early strength. When sodium persulfate is added, sodium ions are eluted to the surface by capillary action or metal ions present in the paste are leached to the surface by capillary action. It is eluted to form voids on the surface, and these surface voids act as points of surface cracks. In the present invention, itaconic acid is added to the bentonite coated on the surface, so that itaconic acid is present in the paste during the expansion process due to moisture absorption of the bentonite. This is to control surface cracks by selectively adsorbing sodium ions, etc.

When only bentonite is added for the expansion effect, not only positive ions but also negative ions are adsorbed during the moisture absorption process. In this case, OH- for generating calcium hydroxide in the cement hydration reaction is adsorbed and may inhibit the hydration reaction. Therefore, in the present invention, Bentonite coated with conic acid is added to the surface so that only cations such as sodium ions are selectively adsorbed.

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

Hereinafter, embodiments of the present invention will be described through experimental examples.

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

combination
division W/B
(%) S/a
(%) Formulation table (Kg/m ³ ) AD
(%/B) note W OPC FA B.S. S C.S. G 49.4 53.0 168 238 68 34 282 666 914 1.1

division rate of change in length
(%)
Slump flow
(mm)
Compressive strength ( MPa ) immediately 60 minutes 1 day 7 days 28th 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 above, it is judged from the experimental results that Examples 1 to 6 all satisfy the resistance to material separation in light of the material amount standard (not to exceed 150 mg/l according to the Korean Society of Civil Engineers standard).

In terms of length change rate, it can be seen that Example 2 has a somewhat disadvantageous effect compared to Example 1. This is because in Example 2, as sodium persulfate is added as an additive, early strength is developed and crack resistance is somewhat lowered. Able to know.

In addition, it can be seen that Example 3 is more advantageous than Examples 1 and 2, which appears to be due to the magnesium aluminum silicate controlling cracking due to moisture evaporation, as mentioned above.

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

Meanwhile, it can be seen that Example 2 has a somewhat disadvantageous effect in terms of fluidity compared to Example 1. This is because in Example 2, sodium persulfate is added as an additive, and as shown below, early strength is developed. It can be seen that liquidity is somewhat reduced.

In addition, it can be seen that Example 3 produces more favorable results in terms of fluidity over time (60 minutes) than Example 1 as well as Example 2. This is because in Example 3, magnesium aluminum is used as an additive in addition to polyethylene oxide. This is believed to be due to the addition of silicate. As mentioned above, magnesium aluminum silicate plays a role in preventing the reactants from clumping by absorbing and removing water generated in the carboxymethyl reaction, which reduces workability. It is believed that this is due to the emergence of a function to prevent this. As shown in Example 2, the addition of sodium persulfate slightly reduces workability, but as shown in Example 3, the addition of magnesium aluminum silicate ensures crude strength and ensures workability. there is.

In addition, it can be seen that Example 4 produces more favorable results in terms of fluidity over time (60 minutes) than Example 3. This is due to the addition of sodium polyacrylate starch as an additive in Example 4. It is believed that, as mentioned above, the addition of sodium polyacrylate starch changed the mixture into a sol form due to mechanical collision during the mixing process, and workability was maintained despite the passage of time. do.

Meanwhile, in terms of strength, it can be seen that Example 2 has a somewhat more advantageous effect than Example 1 in terms of initial strength, etc., which is due to the addition of a mixture of sodium persulfate and amine-based additives as a strength enhancer in Example 2. , Sodium persulfate compensates for the initial strength that can be lowered by the addition of blast furnace slag, and amine-based additives compensates for the decrease in initial and long-term strength that can be lowered by the addition of shrinkage reducing agent.

In addition, it can be seen that 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 improves resistance to various cracks. It is judged that In addition, it can be seen that Example 6 has the most advantageous effect in terms of strength, and in this case, it is believed that this is due to the addition of bentonite coated on the surface of itaconic acid to control expansion of the paste and surface cracks.

Through the above-described content, those skilled in the art will be able to see that various changes and modifications can be made without departing from the technical idea of the present invention. Therefore, the technical scope of the present invention should not be limited to what is described in the detailed description of the specification, but should be defined by the scope of the patent claims.

Claims (7)

It contains a binder containing cement, water, a polycarboxylic acid-based water reducing agent, a cellulose thickener, and a shrinkage reducing agent, and further contains bentonite coated on the surface with itaconic acid, controlling shrinkage cracks through expansion by moisture absorption of the bentonite. A low-shrinkage, medium-flow concrete composition with excellent workability and resistance to material separation, which controls surface cracks due to the formation of surface voids by selectively adsorbing sodium ions present in the paste during the expansion process.
According to clause 1,
The shrinkage reducing agent is one or a mixture of two or more of butyl diglycol, butyl triglycol, methyl diglycol, butyl polyglycol, methyl triglycol, ethyl glycol, monoethylene glycol, and polyalkylene glycol. A low-shrinkage, medium-flow concrete composition with excellent resistance to material separation.
According to clause 1,
A 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 clause 1,
A 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 clause 4,
A 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 clause 5,
A low-shrinkage, medium-flow concrete composition with excellent workability and resistance to material separation, characterized in that it further contains magnesium hydroxide. delete