KR20220016637A - Concrete composition for revealing early strength - Google Patents

Abstract

The present invention relates to an early strength expression type concrete composition which comprises: a binding material comprising cement; and a mixing agent comprising a nitrate, sodium thiocyanate, and triethanolamine.

Description

Early strength expression type concrete composition {Concrete composition for revealing early strength}

The present invention relates to a concrete composition capable of exhibiting workability and crack resistance while exhibiting crude stiffness.

In the concrete frame work, if certain quality standards are satisfied in terms of strength, etc. after pouring concrete, the formwork is dismantled and the subsequent process is carried out. Therefore, in order to satisfy the quality standards and at the same time reduce the time required for the entire process, it is required to develop an early hardening concrete composition that can shorten the time required to reach a certain standard strength after pouring concrete.

In the concrete standard specification, the minimum strength standard for dismantling the formwork in concrete framing work is 5 MPa (50 kgf/㎠) for vertical members, and 2/3 or more of the design standard strength for horizontal members or 14 Mpa (140 kg) f/cm2). These regulations not only serve as a strength standard for dismantling formwork in concrete framing work, but also play an important role in securing quality to prevent early freezing during construction in Korea and China.

Concrete generally used in construction sites has a design strength of 21 to 35 MPa (210 to 350 kgf/㎠), and in the case of conventional technology, the standard for dismantling the formwork is 5 Mpa (50 kgf/㎠). It must take at least 2 days or more after concrete pouring.

However, in practice, in order to shorten the construction period, the formwork of the structure is indiscriminately removed before the strength of the concrete reaches the standard strength for dismantling the formwork, resulting in deterioration of the quality of the concrete structure. In order to overcome these problems and to speed up the dismantling of the formwork while satisfying the quality standards, a method of using high-strength concrete (design standard strength of 40Mpa or more), a method of using crude steel cement, or a method of improving the curing method, etc. have been proposed. have.

However, for early demolding of the formwork, the method of using the high-strength concrete, the method of using the crude steel cement, or the method of improving the curing method is not simple, and there is a problem in that economical efficiency is lowered.

In addition, in the case of the existing crude steel type concrete composition, crude strength can be secured, but there is a problem that workability is lowered. There is an impossible problem.

Republic of Korea Patent Publication No. 2000-64260

The present invention has been devised to solve the above problems, and it is an object to provide a concrete composition that can secure roughness while maintaining workability for early demolding of a formwork, and also improve crack resistance.

As a means for solving the above problems, the early strength expression type concrete composition of the present invention (hereinafter referred to as "composition of the present invention") includes: a binder including cement; An admixture comprising nitrate, sodium thiocyanate, and triethanolamine; characterized in that it is included.

As an example, the admixture is characterized in that it further comprises tartaric acid.

As an example, the admixture may further include polyethylene oxide and magnesium aluminum silicate.

As an example, the admixture is characterized in that it further comprises sodium polyacrylate starch.

As an example, the admixture further comprises bentonite coated with itaconic acid on the surface.

As described above, the composition of the present invention exhibits early strength and secures workability, thereby shortening the time required for dismantling the formwork, etc., while also satisfying crack resistance. There are advantages to making this possible.

Hereinafter, the configuration and operation of the present invention will be described in more detail based on the accompanying drawings. In describing the present invention, the terms or words used in the present specification and claims are based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention. It should be interpreted as meaning and concept consistent with the technical idea of

The composition of the present invention, a binder comprising cement; An admixture comprising nitrate, sodium thiocyanate, and triethanolamine; characterized in that it contains. Preferably, the admixture includes 50 to 150 parts by weight of sodium thiocyanate and 50 to 150 parts by weight of triethanolamine based on 100 parts by weight of nitrate. The admixture may be formulated so that the above-mentioned compositions are further included in the existing admixture, or may be formulated only with the above-mentioned compositions.

The present invention includes a binder including cement and water in the admixture 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 preferably, general Portland cement, crude steel Portland cement, ultra-hard Portland cement, medium heat Portland cement, sulfate-resistant Portland cement, white Portland cement, and ultra-velocity cement. Any one of hard cement or a mixture thereof may be used, but the present invention is not limited thereto, and not only cement powder form but also clinker form may be used. However, when using cement clinker, it is preferable to use the one that has been calcined and pulverized as a pretreatment.

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

The blast furnace slag is finely pulverized water slag, which is 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 expression 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 ) based on 100% by weight of the total, and preferably 2 to 3% by weight is added. The anhydrous sulfuric acid is added when pulverizing blast furnace slag, and serves as a secondary irritant.

The fly ash serves to enhance the long-term strength of concrete by the pozzolan reaction and to strengthen the watertightness, durability, and chemical resistance of the concrete structure. , preferably in the range of 2.1 to 2.2, the fineness is 3,500 to 4,500 cm2/g, and the loss on ignition is preferably less than 5%.

In addition, although not mentioned above, the composition of the present invention further includes coarse aggregates and fine aggregates. The coarse aggregates are generally also called gravels, and the types are not limited as long as they are generally used in the art. The coarse aggregate is preferably crushed aggregate or natural 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 almost completely passes 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, 4.75 mm), for example, silica sand, quartz, marble, granite, limestone, calcite, feldspar, alluvial sand, other durable aggregates such as 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 volume %, which is the volume ratio of sand (S) to the total aggregate (sand + gravel, a) volume. can be calculated

Hereinafter, admixtures added to improve physical properties in the composition of the present invention will be described.

First of all, the nitrate not only allows a certain strength to be initially expressed, but also enables the setting promotion performance at low temperature to be expressed, so that early formwork demolding strength can be expressed in a low temperature environment.

In addition, since the nitrate can ensure a certain degree of fluidity even though the early strength is expressed, it is to make it easier to express the early form demolding strength in a low-temperature environment.

It is reasonable to mix the nitrate in the above mixing range, but if it is less than the above content, the crude steel effect and the setting promoting effect may be insignificant, and if the content is exceeded, there is a problem of reducing the fluidity of concrete will be.

In addition, the present invention allows sodium thiocyanate (NaSCN) to be included for the expression of crude rigidity. The crude stiffness is further doubled by the addition of sodium thiocyanate (NaSCN).

When the content of sodium thiocyanate (NaSCN) is less than the above mixing range, there is a problem in that sufficient crude strength cannot be obtained. There is a problem and it is limited as described above.

The triethanolamine is also for improving the crude stiffness, and as shown in the following experimental example, the sodium thiocyanate improves the crude stiffness, but there is a problem that the workability is somewhat lowered, and in the case of the triethanolamine, the crude stiffness is slightly improved. However, there is an advantageous mechanism of action in terms of workability, so that triethanolamine is added in addition to sodium thiocyanate, so that workability and crude rigidity are further improved by complementing each other.

Meanwhile, the present invention provides an example in which 1 to 10 parts by weight of tartaric acid are further included with respect to 100 parts by weight of nitrate in addition to the above composition.

The reason that tartaric acid is added is that, when the paste is rapidly hardened, temperature cracks may occur. The tartaric acid absorbs heat and thus does not delay the curing speed. is to control it. That is, it is to improve physical properties such as durability and strength by controlling temperature cracks and the like.

In addition, the present invention provides an example in which 1 to 10 parts by weight of sodium polyacrylate starch is further included with respect to 100 parts by weight of nitrate in addition to the above composition. It should be doubled. If the concrete, which has not hardened due to the addition of the above-mentioned compositions, is gelled at an early stage due to the securement of crude rigidity, of course the workability will be lowered and the formwork will not be tightly filled, resulting in adverse effects in terms of durability and strength. can

Therefore, in the present invention, sodium polyacrylate starch is to be doubled to the above compositions to prevent premature gelation.

However, fluidity can be secured by the addition of sodium polyacrylate starch, etc., but when a large amount is added, there is a problem that material separation occurs. In order to improve resistance to material separation, polyethylene oxide is further included in the present invention. make it possible When only polyethylene oxide is added, it is effective in preventing material separation, but when such an additive is mixed with the concrete composition, water is generated in the carboxymethyl reaction, and the water produced in this way strengthens the cohesive force between particles and causes agglomeration. As a result, such a phenomenon may cause a problem in which workability is lowered.

Accordingly, the present invention provides an example 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 additive and absorbed water generated in the carboxymethyl reaction when blended, This is to prevent agglomeration of the reactant by removing it, so that material separation is prevented by the addition of polyethylene oxide, and in addition, to prevent deterioration of workability by the addition of magnesium aluminum silicate.

In addition, by adding magnesium aluminum silicate to the additive, as mentioned above, water generated in the carboxymethyl reaction is absorbed so that the function as a moisturizing agent is also expressed.

Preferably, it is appropriate that the mixture of polyethylene oxide and magnesium aluminum silicate be blended in an amount of 1 to 10 parts by weight based on 100 parts by weight of nitrate in addition to the above compositions.

On the other hand, as seen above, drying shrinkage cracking and temperature cracking can be controlled by the addition of the additives, but there may be insufficient control of cracks caused by various causes such as cracking due to paste shrinkage accompanying early strength assurance. , the additive provides an example of further including bentonite coated on the surface of itaconic acid in addition to the above compositions.

The bentonite absorbs moisture and expands the volume, thereby compensating for the shrinkage of the paste during the curing process to improve the resistance to cracking.

In addition to this, the bentonite is to be coated on the surface of itaconic acid 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 thiocyanate, etc. is contained in order to secure crude rigidity, and sodium thiocyanate is added to the surface by capillary action to elute sodium ions or metal ions present in the paste to the surface by capillary action. It is eluted to form pores on the surface, and these surface pores act as a point of surface cracks. In the present invention, bentonite coated with itaconic acid is added to the surface to be present in the paste during the expansion process by water absorption of bentonite. This is to control surface cracks by selectively adsorbing sodium ions, etc.

When only bentonite is added for the expansion action, cations as well as anions are adsorbed during the water absorption process. It is to selectively adsorb only cations such as sodium ions by adding bentonite coated with conic acid on the surface.

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

Preferably, the bentonite coated on the surface of the itaconic acid is preferably formulated in an amount of 1 to 10 parts by weight based on 100 parts by weight of nitrate.

Hereinafter, preferred examples are presented through experimental examples of the present invention.

<Experiment 1>

An experiment was performed for comparative evaluation of the performance of the concrete composition added with a general admixture and the concrete composition added with the conventional admixture for early strength expression. and the experimental results are shown in Table 3.

As shown in Table 3 above, target fluidity and air volume were secured by controlling the amount of admixture and air entraining agent usage. As a result of checking the change over time of slump, large slump loss occurred in all formulations.

As a result of measuring the compressive strength, when the crude admixture was applied, it showed a compressive strength higher than 2 MPa compared to general admixtures and showed a compressive strength of 5 MPa or more at 21 hours.

In Table 3, the slump loss was large, indicating high initial compressive strength in all formulations. In Table 4 above, an experiment was conducted to improve the retention performance of the admixture, and the results are shown. As a result of the experiment, the amount of admixture used was slightly increased, and the target fluidity was secured after 60 minutes.

As a result of measuring the compressive strength in this experiment, the formulation to which the crude admixture was applied showed a higher initial strength compared to the general admixture, but did not reach the target compressive strength of 5 MPa for 21 hours. Therefore, as shown in Tables 3 and 4, it is determined that workability and crude rigidity cannot be satisfied at the same time in the case of the existing crude admixture.

<Experiment 2>

In this experiment, it is intended to conduct an experiment on workability and crude stiffness when each additive is added to the existing crude admixture. , The concrete mix of each sample is shown in Table 2 above, and the experimental results are shown in Table 7.

In all samples, the initial target fluidity and air volume were secured, and there was a difference in the change of slump over time according to the type of additive. Samples-2,4,7 showed the same level of maintenance as Plain, but in the case of Sample-1,3,5,6, the slump loss is large, so it is judged that it is difficult to use.

As a result of measuring the compressive strength, the compressive strength showed a tendency to increase when the additive was used, but the target compressive strength of 5 MPa or more was not secured for 21 hours. That is, in the case of samples with nitrate added (Sample-2, 4, 7), when added to the existing crude steel type admixture, crude strength is secured while workability is maintained, but it is judged that sufficient crude strength is not expected.

<Experiment 3>

In this experiment, it is intended to conduct an experiment on workability and crude stiffness when adding other additives to the existing crude admixture than in Experiment 2, and the experimental plan of this experiment is shown in Table 8 below, and Table 9 shows the additives and The amount used is shown, and the concrete mixing details of each sample are shown in Table 2 above, and the experimental results are shown in Table 10.

As a result of the experiment, the initial target fluidity and air volume were secured in all samples. The sodium thiocyanate (Sample-8) improves the crude strength, but there is a problem that the workability is somewhat lowered, and in the case of the triethanolamine (Sample-9), the workability is maintained, but a slight effect is expressed in terms of the improvement of the crude stiffness. On the other hand, in the case of the sample (Sample-9) containing both sodium thiocyanate and triethanolamine, it can be seen that workability and roughness are further improved by mutual complementation, but even in this case, the target compressive strength of 21 It was not possible to secure more than 5 MPa based on time.

That is, in the case of the sample (Sample-10) to which both sodium thiocyanate and triethanolamine are added, it is determined that the crude rigidity is secured while the workability is maintained, but sufficient crude rigidity is not expected.

<Experiment 4>

In this experiment, nitrate, sodium thiocyanate, and triethanolamine were added to the existing crude admixture (Sample-11), and in addition, tartaric acid and sodium polyacrylate starch were added (Sample-12, 13, 14, 15), the experimental plan of this experiment is shown in Table 11 below, and Table 12 shows the additives and usage in each sample, and the concrete mix of each sample The details are shown in Table 2, and the experimental results are shown in Table 13.

As shown in Table 13, in the case of the sample (Sample-11) to which nitrate, sodium thiocyanate, and triethanolamine were all added, the initial strength was 1 MPa or more higher than that of the existing crude admixture, and the target compressive strength of 5 MPa or more was secured for 21 hours. In addition, in the case of the sample (Sample-12) to which tartaric acid was further added, it was found that a more advantageous effect was expressed in terms of roughness, which is considered to be due to the reduction of temperature cracks.

In addition, in the case of the sample (Sample-13) to which sodium polyacrylate starch is further added, it can be seen that the workability is more improved than that of Sample-11.

In addition, it can be seen that in the case of the sample (Sample-14) to which a mixture of polyethylene oxide and magnesium aluminum silicate is further added, a somewhat more favorable result is obtained in terms of compressive strength than Sample-11, which improves the resistance to material separation by polyethylene oxide. It can be seen that somewhat similar results are obtained in terms of workability, which is judged to be the result of preventing deterioration of workability despite the resistance to material separation by adding more magnesium aluminum silicate.

In addition, it can be seen that in the case of the sample (Sample-15) to which bentonite coated on the surface of itaconic acid is further added, a more advantageous effect is expressed in terms of roughness, which is due to improving the resistance to cracking by inducing expansion of the paste. is considered to have been

Those skilled in the art from the above description will be able to see that various changes and modifications are possible without departing from the technical spirit of the present invention. Accordingly, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be defined by the claims.

Claims (5)

binders including cement; An admixture comprising nitrate, sodium thiocyanate, and triethanolamine; Early strength expression type concrete composition comprising a.
The method of claim 1,
The early strength expression type concrete composition, characterized in that the admixture further comprises tartaric acid.
The method of claim 1,
The early strength expression type concrete composition, characterized in that the admixture further comprises a mixture of polyethylene oxide and magnesium aluminum silicate.
The method of claim 1,
The early strength expression type concrete composition, characterized in that the admixture further comprises sodium polyacrylate starch.
The method of claim 1,
The early strength expression type concrete composition, characterized in that the admixture further comprises bentonite coated on the surface of itaconic acid.