KR100581148B1 - Crack reducing method of mass concrete for mat foundation considering the combined addition of fly ash, blast furnace slag and chemical admixture - Google Patents

Abstract

In the case of building-based mat concrete, the lower concrete is required to reduce the heat of hydration and prevent temperature cracking, which is essential for concrete to be constructed with mass concrete. Disclosed is a method for preventing temperature cracking by pouring concrete using higher port heat cement, which ultimately reduces the calorific value difference between upper and lower concrete. According to the present invention, the subsequent process is accelerated due to the rapid development of the strength of the upper layer concrete, and material cost savings due to the use of the admixture, and the occurrence of cracks can reduce the maintenance cost and secure the durability.

Description

Crack Reducing Method of Mass Concrete for Mat Foundation Considering the Combined Addition of Fly Ash, Blast Furnace Slag and Chemical Admixture}

1 is a view for showing the concept of the crack reduction method of the basic mass concrete according to the present invention.

2 is a graph showing the temperature history of the basic mass concrete structure according to the present invention.

The present invention relates to a method for reducing the cracking of basic mass concrete according to a combination of fly ash, blast furnace slag powder, and chemical admixture type, and in particular, in construction-based mass concrete construction that is poured in two or more layers for the purpose of preventing settlement cracking. In order to prevent tensile cracking caused by the temperature difference of upper and lower concrete caused by the difference between the time of placing the lower concrete and the upper concrete, different chemical admixtures are added to the upper and lower concrete to reduce the heat difference between the upper and lower concrete to reduce the temperature difference. The present invention relates to a method for reducing cracking of basic mass concrete according to a combination of fly ash, blast furnace slag fine powder and chemical admixture form for controlling the temperature cracking.

In general, the construction of matt concrete is inevitable due to the increase in land prices and the development of construction technology, which leads to the increase in size, height, and depth. However, mass concrete with a thickness of more than 800 mm causes quality degradation of concrete, such as cracks, if it does not adequately cope with temperature stress caused by hydration heat.

Currently, the building foundation mass concrete construction in Korea is divided into two or more floors for the purpose of preventing settlement cracks. The time difference between the upper and lower parts varies depending on the site, but it is usually about 4 to 12 hours. Therefore, since the upper concrete is placed at the time when the hydration heat of the lower concrete is activated, the temperature difference of the upper and lower concrete becomes very large from this time, and the tensile stress is generated by the heat of hydration on the upper surface part after about 10 hours after the initial casting. It appears as a tensile crack.

Existing methods for solving such a problem have been proposed as shown in Table 1 below.

<Table 1> Crack Prevention and Control Measures in Conventional Mass Concrete Placing

Measures Concrete measures Combination Reduction of calorific value Use of low heat cement Reduction of Cement Use of high quality mixed materials Make the slump smaller Increase aggregate size Use of fine aggregate Extension of the strength judgment period City ball Minimization of temperature change Curing temperature control Insulation (Sheet, Insulation) Heating Curing Formwork period adjustment Adjusting the spacing time of concrete Control of setting time for each lift by using super delay agent Reduce the temperature rise during construction Cooling of materials  Strictly control planned temperature design Design consideration Installation of crack-induced joints Disperses cracks with rebar Separate waterproof reinforcement

That is, in order to prevent cracking caused by the temperature difference between the upper and lower concrete placed with a time difference when placing conventional concrete, the curing temperature is controlled or thermal insulation curing such as sheet insulation material is adjusted, the length of the mold surviving period and concrete casting The physical change method such as time interval adjustment is generally used, but there is no method of separating and placing the admixture variable between upper and lower concrete.

The present invention has been invented to solve such a conventional problem, the lower-layer concrete in the building-based mass concrete to lower the hydration calorific value by using a fly ash (hereinafter referred to as "FA") and a fine blast furnace slag fine powder, The delayed condensation of the AE water reducing agent and the high performance AE water reducing agent reduces the heat of hydration and lowers the maximum temperature. By pouring concrete using the accelerated form of high-performance AE water reducing agent, the coincidence time of hydration of upper and lower concrete is coincided, and ultimately, the fly ash to control the temperature crack and control the temperature crack by reducing the heat difference between upper and lower concrete Depending on the blast furnace slag fine powder and chemical admixture form combination The purpose is to provide a crack reduction method for other basic mass concrete.

The present invention for performing such an object,

The cross section height of the mass concrete is divided equally to separate the upper and lower layers, and only the upper portland cement is placed on the upper layer, and the delayed AE water reducer or delayed high performance AE water reducing agent is 0.01 ~ 1.5 wt% based on the weight of the ordinary portland cement. The first admixture, which is composed, and the lower layer is poured into the mixed concrete mixed with 5 to 30% by weight of fly ash and 5 to 60% by weight of blast furnace slag fine powder to the weight of ordinary portland cement, 0.01 to the weight of the mixed concrete Fly ash and blast furnace slag fine powder which reduces the hydration calorific difference between the upper layer and the lower layer by combining the second admixture composed of delayed AE water reducing agent or delayed high performance AE water reducing agent of ~ 1.5% by weight. The present invention provides a method for reducing cracking of mass concrete according to a combination of chemical and admixture forms.

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

1 is a view illustrating a concept of a method for reducing cracking of basic mass concrete according to the present invention, and FIG. 2 is a graph illustrating a temperature history of the basic mass concrete structure according to the present invention.

According to the present invention, the method for reducing the cracking of the basic mass concrete according to the combination of the fly ash, the blast furnace slag fine powder and the chemical admixture form is equally divided into the upper and lower layers in the mass concrete. 5% to 30% of fly ash and 5% to 60% of blast furnace slag fine powder are used as the weight% of the cement (OPC), and only ordinary Portland cement (OPC) is used for the upper layer concrete. In addition, the condensation time between the upper and lower layers controls the temperature cracking by reducing the hydration calorific difference between the upper and lower concrete by adjusting the form of the AE reducing agent and the high performance AE reducing agent.

<Example 1>

When placing mass concrete, the cross-sectional height of the mass concrete is divided equally to distinguish the upper and lower layers, and only the upper portland cement is placed on the upper layer, and the delayed AE water reducing agent of 0.01 to 1.5% by weight to the weight of the ordinary portland cement is added. Or a first admixture composed of a delayed high performance AE reducing agent. In addition, in the lower layer, ordinary Portland cement, fly ash and blast furnace are added while placing mixed concrete in which 5 ~ 30% by weight of fly ash (FA) and 5 ~ 60% by weight of blast furnace slag fine powder are added. A second admixture composed of 0.01 to 1.5% by weight of the delayed AE sensitizer or the delayed high performance AE sensitizer is mixed with the weight of the mixed concrete in which the fine slag powder is mixed.

<Example 2>

In the second embodiment of the present invention, the first admixture is composed of 0.01 to 1.5% by weight of the standard AE water reducing agent or the standard high performance AE water reducing agent based on the weight of the ordinary portland cement added to the upper layer in the method of the first embodiment. The lower layer is composed of delayed AE water reducing agent or delayed high performance AE water reducing agent of 0.01 to 1.5% by weight based on the weight of the mixed concrete in which ordinary Portland cement, fly ash and blast furnace slag fine powder are injected.

<Example 3>

In the third embodiment of the present invention, the first admixture in the method of the first embodiment comprises 0.01 to 1.5% by weight of the promoted AE water reducing agent or the accelerated high performance AE water reducing agent, based on the weight of the ordinary portland cement added to the upper layer. The admixture is composed of a delayed AE water reducer or a delayed high performance AE water reducer of 0.01 to 1.5% by weight, based on the weight of the mixed concrete in which the ordinary portland cement, fly ash, and blast furnace slag fine powder are added to the lower layer.

<Example 4>

In the fourth embodiment of the present invention, the first admixture in the method of the first embodiment comprises 0.01 to 1.5% by weight of the accelerated AE sensitizer or the accelerated high performance AE sensitizer relative to the weight of the ordinary portland cement added to the upper layer. The admixture is composed of a standard AE water reducing agent or a standard high performance AE water reducing agent in an amount of 0.01 to 1.5% by weight based on the weight of the mixed concrete mixed with ordinary Portland cement and fly ash and blast furnace slag powder.

The crack reduction method of the basic mass concrete according to the combination of fly ash, blast furnace slag fine powder and chemical admixture according to the present invention with reference to Figure 1, in the case of the conventional construction method (A) in Figure 1 is usually between the upper and lower concrete As it is placed over time, temperature cracks occur due to the generation of high heat of hydration and the temperature difference between the early age and the upper and lower concrete.

However, the method (B) according to the present invention uses a fly ash and blast furnace slag fine powder (BS) to reduce the calorific value of the lower layer of concrete by integrating the upper and lower temperatures to control the temperature cracking, that is, the calorific value difference between the upper and lower concretes By reducing the temperature control can be controlled.

Figure 2 shows the temperature history of the structure according to the invention measured at the actual construction site. In Figure 2, the conventional method (A) is usually cast concrete integrally with a time difference between the upper and lower parts, in the case of the method (A) according to the present invention, the lower layer is 20% by weight of fly ash with respect to the weight of ordinary portland cement and The mixed concrete in which 30% by weight of blast furnace slag fine powder is mixed is poured, and the upper layer is usually poured using only Portland cement.

In the case of the conventional construction method (A) in FIG. 2, the high temperature of hydration heat and the temperature difference between the upper and lower concretes are generated as the concrete is integrally placed with time difference between the upper and lower parts, but in the case of the construction method (B) according to the present invention. In the upper layer and the lower layer, simultaneous hydration and heat generation did not occur.

Fly ash and blast furnace slag fine powder according to the present invention, the method of reducing the cracks of the basic mass concrete according to the combination of chemical admixtures in terms of environmental aspects to reduce the environmental load by effectively using the industrial ash fly ash and blast furnace slag fine powder, ordinary portland cement Reducing the use of (OPC) can reduce global warming, and in economic terms, it can also secure economic efficiency by reducing the use of expensive ordinary Portland cement (OPC).

In addition, in the case of the method according to the present invention, since the upper concrete expresses strength early, the subsequent work can be quickly performed, thereby reducing the air compared to other methods.

As described above, the method for reducing the cracking of the basic mass concrete according to the combination of fly ash, blast furnace slag fine powder and chemical admixture according to the present invention lowers the maximum temperature by the heat of hydration of the mass concrete and controls the crack of the heat of hydration completely. It can reduce crack repair cost and ensure durability by securing good quality, and can reduce environmental load by reducing the use of ordinary Portland cement (OPC) through effective use of industrial by-products, which can have a great effect on environmental problems such as global warming. In addition, it is effective in shortening the curing period by shortening the curing period by expressing the strength of the upper concrete.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto and may be improved or modified by those skilled in the art within the scope of the technical idea of the present invention.

Claims (4)

The cross-sectional height of the mass concrete is divided equally to separate the upper and lower layers, and only the upper portland cement is poured into the upper layer, while the delayed AE water reducing agent or delayed high performance AE water reducing agent is 0.01 to 1.5% by weight based on the weight of the ordinary portland cement. While mixing the first admixture consisting of, the lower layer is poured concrete mixed with 5 ~ 30% by weight of fly ash and 5 ~ 60% by weight of blast furnace slag fine powder relative to the weight of the ordinary portland cement By mixing a second admixture composed of a delayed AE sensitizer or a delayed high-performance AE sensitizer with a delayed AE sensitizer or a delayed high performance AE sensitizer relative to the weight of the mixed concrete, the calorific value difference between the upper and lower layers Mass concrete according to combination of shrinking fly ash, blast furnace slag fine powder and chemical admixture form Crack Reduction Method. According to claim 1, wherein the first admixture is composed of a standard AE water reducing agent or a standard high performance AE water reducing agent of 0.01 to 1.5% by weight relative to the weight of the ordinary portland cement to the upper layer, wherein the second admixture is added to the lower layer Fly ash and blast furnace slag fine powder and chemical admixture, characterized in that composed of 0.01 to 1.5% by weight of delayed AE water sensitizer or delayed high performance AE water sensitizer to the weight of the mixed concrete, which is usually a mixture of Portland cement, fly ash and blast furnace slag fine powder Crack Reduction Method of Mass Concrete According to Morphological Combination. According to claim 1, wherein the first admixture is composed of 0.01 to 1.5% by weight of the accelerated AE water reducing agent or accelerated high performance AE water reducing agent relative to the weight of the ordinary portland cement to the upper layer, the second admixture is added to the lower layer. Fly ash and blast furnace slag fine powder, characterized in that composed of 0.01 to 1.5% by weight of delayed AE water reducing agent or delayed high performance AE water reducing agent with respect to the weight of the mixed concrete is mixed with the ordinary portland cement and fly ash and blast furnace slag fine powder Reduction of cracking of mass concrete according to the combination of chemical admixtures. According to claim 1, wherein the first admixture is composed of 0.01 to 1.5% by weight of the accelerated AE water reducing agent or accelerated high performance AE water reducing agent relative to the weight of the ordinary portland cement to the upper layer, the second admixture is added to the lower layer. Fly ash and blast furnace slag fine powder and chemical admixture, characterized in that composed of 0.01 to 1.5% by weight of a standard AE water reducing agent or a standard high performance AE water reducing agent with respect to the weight of the mixed concrete is mixed with the ordinary portland cement and fly ash and blast furnace slag fine powder Crack Reduction Method of Mass Concrete According to Morphological Combination.

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