KR100581149B1 - Crack reducing method of mass concrete for mat foundation considering the combined addition of fly ash, limestone powder and chemical admixture - Google Patents

Abstract

A method of preventing cracks in a mass concrete foundation is provided to reduce the differences in hydration heat generation value between upper and lower concrete foundations for preventing tensile cracking of the mass concrete foundation by adding specific volume of retardant AE water reducing agent to a generic Portland cement on the upper concrete foundation and to the lower concrete foundation comprising a mixture of fly ash, fine limestone power and generic Portland cement. A method of preventing cracks in a mass concrete foundation includes dividing the mass concrete foundation into upper and lower foundations. On the upper foundation, generic Portland cement is poured and first chemical compound, comprising 0.01 to 1.5% of retardant AE water reducing agent or high AE water reducing agent by weight of the generic Portland cement, is added to the poured concrete. On the lower mass concrete foundation, concrete mixture containing 5 to 40% of fly ash and 5 to 30% of limestone powder by weight of the generic Portland cement respectively is poured, and a second chemical compound comprising 0.01 to 1.5% of retardant AE water reducing agent or high retardant AE water reducing agent by weight of the lower mass concrete mixture is added to the poured concrete. The first chemical compound includes 0.01 to 1.5% of generic or high generic AE water reducing agent by weight of the generic Portland cement, whereas second chemical compound includes 0.01 to 1.5% of retardant AE or high retardant AE water reducing agent by weight of the lower concrete mixture. The first chemical compound includes 0.01 to 1.5% of accelerator or high accelerator AE water reducing agent by weight of the generic Portland cement, and the second chemical compound includes 0.01 to 1.5% of retardant or high retardant AE water reducing agent by the weight of lower concrete mixture.

Description

Crack Reducing Method of Mass Concrete for Mat Foundation Considering the Combined Addition of Fly Ash, Limestone Powder 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 cracking of basic mass concrete according to a combination of fly ash, limestone fine powder, and chemical admixture, and in particular, in the case of construction foundation mass concrete which is poured in two or more layers for the purpose of preventing settlement cracking, etc. In order to prevent the tensile crack caused by the temperature difference between the upper and lower concrete caused by the difference between the time of placing the 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 the cracking of basic mass concrete according to a combination of fly ash, limestone fine powder and chemical admixture form for removing and controlling 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 Placement

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 substitutes fly ash (hereinafter referred to as "FA") and limestone fine powder (hereinafter referred to as "LSP") with low hydration calorific value By lowering the hydration calorific value and delaying the condensation by the use of the delayed form of AE reducing agent and high performance AE reducing agent, and reducing the total heat of hydration, the maximum temperature is lowered.The upper layer concrete has a higher heat generation than the lower layer concrete. Pour concrete using the accelerated form of AE reducing agent and high performance AE reducing agent to match the hydration heating time of upper and lower concrete, ultimately reducing the heat difference between upper and lower concrete to eliminate the temperature difference Fly ash, limestone powder and chemical admixtures to control cracking The purpose of the present invention is to provide a method for reducing the cracking of basic mass concrete according to concrete combinations.

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 is mixed, and the lower layer is poured 0.01 ~ 20% by weight of the mixed concrete while pouring 5 ~ 40% by weight of fly ash and 5 ~ 30% by weight of limestone fine powder in comparison with the weight of ordinary Portland cement. Fly ash and limestone fine powder and chemicals that reduce the hydration calorific difference between the upper and lower layers by combining a second admixture composed of 1.5 wt% delayed AE water reducing agent or delayed high performance AE water reducing agent to vary the setting time. Provided is a method for reducing cracking of mass concrete according to a combination of 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 of reducing the cracks of the basic mass concrete according to the combination of fly ash, limestone fine powder and chemical admixture form is equally divided into the upper and lower layers in the mass concrete, and in the case of the lower layer concrete, the ordinary portland cement Substitute 5% to 40% of fly ash (FA) and 5% to 30% of limestone fine powder (LSP) as weight percent to (OPC) and use only plain Portland cement (OPC) for top 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 and fly ash, which are added while pouring mixed concrete mixed with 5 to 40% by weight of fly ash (FA) and 5 to 30% by weight of limestone fine powder (LSP), are added to the weight of ordinary portland cement. And a second admixture composed of 0.01 to 1.5% by weight of a delayed AE sensitizer or a delayed high performance AE sensitizer relative to the weight of the mixed concrete mixed with limestone fine powder.

<Example 2>

In the second embodiment of the present invention, in the method of the first embodiment, the first 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 ordinary portland cement added to the upper layer. The lower layer 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 ordinary Portland cement, fly ash and limestone powder are mixed.

<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 reducing agent or a delayed 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 in which ordinary Portland cement, fly ash and limestone fine powder are mixed.

<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. In the lower 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, fly ash, and limestone powder.

Referring to Figure 1, the crack reduction method of the basic mass concrete according to the combination of fly ash, limestone fine powder and chemical admixture according to the present invention, in the case of the conventional method (A) in FIG. As it is placed in place, the temperature crack occurs due to the generation of high heat of hydration and the temperature difference between the upper and lower concrete from the early age.

However, the method (B) according to the present invention uses fly ash (FA) and limestone fine powder (LSP) to reduce the calorific value of the lower layer of concrete to integrate the upper and lower temperatures to control the temperature cracking, that is, between the upper and lower concrete The temperature crack can be controlled by reducing the calorific value difference.

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 15% by weight of limestone 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.

According to the present invention, the method of reducing the cracks of the basic mass concrete according to the combination of the fly ash and the limestone fine powder and the chemical admixture form reduces the environmental load by effectively using the industrial ash by fly ash and the limestone fine powder. By reducing the amount of), global warming can be reduced, and in economic terms, the economy can be secured 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 the fly ash, the limestone fine powder and the chemical admixture according to the present invention lowers the maximum temperature due to the heat of hydration of the mass concrete and controls the cracks of the hydration heat, so It can reduce crack repair cost and ensure durability by securing quality, and can reduce environmental load by reducing ordinary Portland cement (OPC) usage through effective use of industrial by-products. It is effective in shortening the air 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 5 to 40% by weight of fly ash and 5 to 30% by weight of limestone powder compared to the weight of the ordinary portland cement in the lower layer, By reducing the hydration calorific value difference between the upper layer and the lower layer by combining the second admixture composed of a delayed AE water sensitizer or a delayed high performance AE water sensitizer of 0.01 to 1.5% by weight based on the weight of the mixed concrete Reduction of Cracking of Mass Concrete by Combination of Fly Ash, Limestone Fine Powder and Chemical Admixture Way. 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 Combination form of fly ash, limestone fine powder and chemical admixture, comprising 0.01 ~ 1.5% by weight of delayed AE water reducing agent or delayed high performance AE water reducing agent, based on the weight of mixed concrete mixed with ordinary Portland cement, fly ash and limestone fine powder Reduction of cracks in mass concrete according to 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 limestone 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 relative to the weight of the mixed concrete is mixed with the ordinary Portland cement and fly ash and limestone 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. The combination of fly ash and limestone 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 relative to the weight of the mixed concrete is mixed with the ordinary portland cement and fly ash and limestone fine powder Reduction of cracks in mass concrete according to

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