KR100645546B1 - Crack reducing method of mass concrete for mat foundation considering the combined addition of limestone powder and chemical admixture - Google Patents

Abstract

A method of reducing crack of foundation mass concrete according to the configuration combination of limestone granule and chemical admixture is provided to reduce the crack repair cost and the hardening time by lowering the maximum temperature of the mass concrete and completely controlling the hydration heat crack according to the pouring of the mixing concrete with the limestone granule and the common portland cement. A method of reducing crack of foundation mass concrete according to the configuration combination of limestone granule and chemical admixture divides upper and lower layers by evenly dividing the section height of the mass concrete, pours the common portland cement at the upper layer, mixes a first admixture comprising a delaying AE water reducing agent or a delaying high AE water reducing agent of 0.01~1.5 weight% for the weight of the common portland cement, pours the mixing concrete mixed with the limestone granule and the common portland cement of 5~40 weight% for the weight of the common portland cement at the lower layer, mixes a second admixture comprising the both water reducing agents of 0.01~1.5 weight% for the weight of the mixing cement, and reduces the hydration heating value difference of the upper and lower layers by the combination of the admixture.

Description

Crack Reducing Method of Mass Concrete for Mat Foundation Considering the Combined Addition of 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 the cracking of basic mass concrete according to the combination of limestone fine powder and chemical admixture, and in particular, the casting of the lower concrete during the construction of building foundation mass concrete, which is poured in two or more layers for the purpose of preventing settlement cracking. In order to prevent the tensile cracking caused by the temperature difference between the upper and lower concrete caused by the difference between the timing and the time of placing 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 eliminate the temperature difference. The present invention relates to a method for reducing cracking of basic mass concrete according to a combination of limestone fine powder and chemical admixture to control 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 way to separate and place 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 lowers the hydration calorific value by replacing the limestone fine powder (hereinafter referred to as "LSP") with low amount of hydration heat, AE water reducing agent, high performance AE The use of delayed form of water reducing agent delays condensation and reduces the heat of hydration at the same time, and lowers the maximum temperature.The upper layer concrete is composed of ordinary portland cement (hereinafter referred to as "OPC"), which generates more heat than lower layer concrete, AE water reducing agent, and high performance AE water reducing agent. Pour concrete using accelerated form to match the heating time of hydration of upper and lower concrete, and ultimately reduce the calorific value difference between upper and lower concrete to eliminate the temperature difference, and to combine the limestone powder and chemical admixture type to control temperature cracking. Crack Reduction Method of Foundation Mass Concrete The purpose is to provide.

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 ~ 1.5 weight to the weight of the mixed concrete while placing 5 ~ 40% by weight of limestone fine powder (LSP) and the mixed concrete of ordinary portland cement, compared to the weight of the ordinary portland cement By mixing the second admixture composed of% delayed AE water reducing agent or delayed high performance AE water reducing agent and varying the setting time, the limestone fine powder and the chemical admixture type combination which reduces the calorific value of hydration of upper layer and lower layer Provides a method for reducing cracks in mass concrete.

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.

The method of reducing the cracks of the basic mass concrete according to the combination of the limestone fine powder and the chemical admixture according to the present invention divides the height of the pouring layer evenly into the upper and lower layers in the mass concrete, and in the case of the lower layer concrete, the ordinary portland cement (OPC) Limestone fine powder (LSP) 5 to 40% is used as a weight% of the weight), and in the case of upper layer concrete, only ordinary portland cement (OPC) is used. 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, the lower layer is placed 5 to 40% by weight of the limestone fine powder (LSP) and the mixed concrete mixed with the ordinary portland cement, while the ordinary portland cement and limestone fine powder mixed with the mixed concrete 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.

<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 mixed with ordinary Portland cement and limestone fine powder.

<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 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 limestone fine powder.

<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 in which ordinary portland cement and limestone fine powder are added.

Referring to Figure 1 illustrates the crack reduction method of the basic mass concrete according to the combination of the limestone fine powder and the chemical admixture according to the present invention, in the case of the conventional method (A) in FIG. As it is poured, temperature cracking occurs 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 is a method of controlling the temperature cracking by integrating the upper and lower temperatures by reducing the calorific value of the lower concrete layer by using limestone fine powder (LSP), that is, by reducing the calorific value difference between the upper and lower concretes. Can control the crack

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 and the limestone powder of 20% by weight relative to the weight of ordinary Portland cement and Ordinary portland cement was poured with mixed concrete, and the upper layer was poured using only ordinary 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.

The method of reducing the cracks of the basic mass concrete according to the combination of the limestone fine powder and the chemical admixture according to the present invention reduces the environmental load by effectively using the limestone fine powder (LSP) which is an industrial by-product from the environmental point of view, and uses the ordinary portland cement (OPC). By reducing the global economy, global warming can be reduced, and economically, the economy can also 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 limestone fine powder and the chemical admixture according to the present invention is to lower the maximum temperature by the heat of hydration of the mass concrete and to control the cracks of the heat of hydration to ensure the good quality of the concrete. It can reduce crack repair cost and secure durability, and reduce the 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, and upper concrete It is effective for shortening the curing period by shortening the curing period by expressing the strength of fast.

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. Mixing the first admixture consisting of, and in the lower layer is poured 5 to 40% by weight of limestone fine powder (LSP) and the mixed concrete mixed with the ordinary portland cement, 0.01 to the weight of the mixed concrete Limestone fine powder and chemical admixture form to reduce the difference in hydration calorific value of the upper and lower layers by combining a second admixture composed of ~ 1.5% by weight of delayed AE water reducing agent or delayed high performance AE water reducing agent Reduction of cracking of mass concrete by combination 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 Cracking of the mass concrete according to the combination of limestone fine powder and chemical admixture form, comprising 0.01 to 1.5% by weight of delayed AE water reducing agent or delayed high performance AE water reducing agent compared to the weight of mixed concrete mixed with ordinary portland cement and limestone fine powder Reduction Method. 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 port cement cement to the upper layer, the second admixture is the lower layer According to the combination of limestone fine powder and chemical admixture form, 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 compared to the weight of the mixed concrete mixed with the ordinary portland cement and limestone fine powder Reduction of cracks in mass concrete. 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. Reduction of cracking of the mass concrete according to the combination of limestone fine powder and chemical admixture form, characterized in that composed of 0.01 to 1.5% by weight of standard AE water reducing agent or standard high performance AE water reducing agent Way.

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