JP2014136424A - Method for producing concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing concrete where the flowability of the concrete is kept and the reduction effect of bleeding is high.SOLUTION: In a method for producing concrete including a primary kneading step to make mortar by kneading cement, a fine aggregate and primary water and a secondary kneading step to knead the concrete by charging a coarse aggregate and secondary water to the mortar, the primary water and/or the secondary water contains preferably a water-reducing agent and more preferably kneading continues for 60 seconds or more after the mortar becomes a capillary state in the primary kneading step.

Description

  The present invention relates to a method for producing concrete with less bleeding.

Concrete mainly consists of water, cement, aggregate, and the like, and the specific gravity of these constituent materials is different from about 1, 3.2, and 2.5, respectively. Therefore, the concrete kneaded material from kneading to hardening is likely to cause material separation (hereinafter referred to as “bleeding”) in which water rises while cement and aggregate settle. If this bleeding is large, voids are formed at the cement paste / aggregate interface and the concrete / rebar interface, etc., and the adhesive strength of the interface decreases. .
In addition, the amount of floating water generated by bleeding (hereinafter referred to as “bleeding amount”), even for concrete of the same composition using cement having the same characteristic values such as cement mineral composition, fineness, and gypsum content. Unlikely, sometimes the amount of bleeding is excessive.

Thus, as means for reducing bleeding, a specific admixture added to concrete, a method for producing concrete in which the constituent materials of concrete are kneaded in a specific order, and the like have been proposed.
For example, Patent Document 1 proposes an admixture for preventing separation of concrete, which is made of a microbial fermentation polysaccharide produced by a bacterial species having a cell number of Alcaligenes ATTC 31961, as the admixture. However, the admixture increases the viscosity of the concrete and suppresses the bleeding, but on the other hand, the fluidity and pumpability of the concrete are lowered, and the strength is lowered due to poor filling and the concrete surface is easily roughened. Such a problem is remarkable in high fluidity concrete. Further, since the admixture is a natural product produced by a specific bacterial species, there are concerns about quantitative restrictions and high costs in mass production of concrete.
In Patent Document 2, the kneaded water is divided into a first kneaded water (hereinafter referred to as “primary water”) and a second kneaded water (hereinafter referred to as “secondary water”), and the primary water is added to the cement. A concrete preparation method is proposed in which after adjusting the cement paste by kneading and adding secondary water to the paste, the mixture is kneaded again to adjust the second cement paste, and then the aggregate is added to the second cement paste and kneaded. Has been. However, this method may not have a sufficient bleeding reduction effect as shown in a comparative example described later.

JP-A-5-306153 JP 2010-222171 A

  Therefore, an object of the present invention is to provide a method for producing concrete having a high effect of reducing bleeding while maintaining good fluidity.

The inventor has studied a method for producing concrete that meets the above-mentioned object, and has found that the object can be achieved by kneading the constituent materials of the concrete in a specific order, thereby completing the present invention.
That is, this invention is a manufacturing method of the concrete which has the following structure.
[1] A primary kneading step of kneading cement, fine aggregate, and primary water to produce a mortar, and a secondary kneading step of adding coarse aggregate and secondary water to the mortar and kneading concrete. A method for producing concrete.
[2] The method for producing concrete according to [1], wherein the primary water and / or secondary water includes a water reducing agent.
[3] The method for producing concrete according to [1] or [2], wherein in the primary kneading, the kneading is continued for 60 seconds or more after the mortar is in a capillary state.

  The concrete production method of the present invention maintains good fluidity of the concrete even when the water-cement ratio of the concrete varies, and has a high effect of reducing bleeding.

It is a figure which shows the presence state of the liquid phase between granular materials.

Hereinafter, the concrete production method of the present invention will be described by dividing it into a primary kneading step and a secondary kneading step.
1. Primary kneading step This step is a step of kneading cement, fine aggregate, and primary water to produce mortar, and will be described in detail below in the order of cement, fine aggregate, primary water, and primary kneading method.
(1) Cement The above cements are ordinary Portland cement, early-strength Portland cement, ultra-early strong Portland cement, medium heat Portland cement, low heat Portland cement, sulfate-resistant Portland cement, blast furnace cement, fly ash cement, coal ash-containing cement, One or more types selected from silica cement, white cement, eco-cement and the like can be mentioned. Among these, a cement that easily causes bleeding is preferable. Here, the cement in which bleeding is likely to occur is, for example, using the cement paste prepared in accordance with JIS R 5201 “Physical testing method of cement”, and the Japan Society of Civil Engineers standard “pre-packed concrete injection mortar breathing rate and expansion. This refers to a cement having a breathing rate (bleeding rate) measured in accordance with “rate test method” of 4.0% or more. The bleeding rate is a value representing the ratio of the mass of floating water by breathing to the mass of the total water amount as a percentage.

(2) Fine Aggregate Examples of the fine aggregate include one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, dredged sand, slag fine aggregate, lightweight fine aggregate, and the like. In addition to natural aggregate, recycled aggregate can be used as the fine aggregate.

(3) Primary water The primary water can be used as long as it does not adversely affect the physical properties of concrete such as strength and fluidity. For example, from tap water, sewage treated water, and supernatant of fresh concrete. One or more selected may be mentioned. Further, since the water reducing agent lowers the water / cement ratio and increases the torque at the time of mixing, the aggregated particles of the cement are crushed and the bleeding rate is reduced. Therefore, the primary water is preferably a high-performance AE. It contains one or more water reducing agents selected from water reducing agents, high performance water reducing agents, AE water reducing agents and the like. Here, the kind of the water reducing agent includes at least one selected from polycarboxylic acid, naphthalenesulfonic acid formalin condensate, melamine sulfonic acid formalin condensate, lignin sulfonic acid, and salts thereof.

(4) Primary kneading method As the method,
(i) After the fine aggregate and primary water are added and kneaded, the cement is charged and kneaded again.
(ii) Cement and primary water are added and kneaded, then fine aggregate is added and kneaded again.
(iii) After fine aggregate and cement are added and kneaded, primary water is added and kneaded, and
(iv) A method in which cement, fine aggregate, and primary water are added and kneaded in a lump. Among these, the method (i) is preferable because a mortar having a uniform and low bleeding can be obtained by forming a shell-forming layer by adhering the cement to the wet surface of the fine aggregate. The kneading apparatus is not particularly limited, and a forced kneading mixer, a gravity mixer, or the like can be used.
The kneading time in the primary kneading step is preferably 80 to 220 seconds, more preferably 100 to 160 seconds, from the viewpoint of the production efficiency of concrete and the effect of reducing bleeding.
Moreover, the primary water amount is preferably 28 to 35%, more preferably 28 to 33%, when containing a water reducing agent, preferably 20 to 33%, when containing a water reducing agent, in terms of water-cement ratio. More preferably, it is 23 to 30%.

The mortar obtained in the primary kneading step is preferably in a capillary state. Here, as shown in FIG. 1 (d), the capillary state is almost completely filled with a liquid phase such as water, and a gas phase such as voids and bubbles is substantially present. The state that does not. The mortar in this state has the strongest bond between the granular materials and maximizes the kneading energy (torque).
The primary water amount for obtaining the mortar in the capillary state is preferably 28 to 32%, more preferably 28 to 30% in the water / cement ratio conversion, and includes the water reducing agent. In the case, it is preferably 23 to 30%, more preferably 23 to 28%. If the primary water amount is out of the above range, it is difficult to obtain capillary mortar, and the effect of reducing bleeding may be reduced.
However, for the sake of more accuracy, the primary water amount may be determined by, for example, the following (a) to (c).
(A) A mixture of cement and fine aggregate is put into a Hobart mortar mixer.
(B) Water is gradually added to the mixture and kneaded, and the load current applied to the mixer motor at that time is measured as the load resistance.
(C) In the relationship between the mass ratio of water / the mixture and the load current value, the mass ratio at which the load current value is maximized is determined, and this value is determined as the primary water amount.

In addition, when kneading mortar in a capillary state in the primary kneading step, kneading is preferably continued as it is for 60 seconds or more after the mortar is in a capillary state. If the time is less than 60 seconds, the effect of reducing bleeding may be reduced. The upper limit of the time is preferably 120 seconds, more preferably 100 seconds. If the upper limit exceeds 120 seconds, the concrete production efficiency and bleeding reduction effect may be reduced.
The time when the mortar enters the capillary state can be grasped as the time when the kneading torque becomes maximum.

2. Secondary kneading step This step is a step of adding coarse aggregate and secondary water to the mortar and kneading them to produce concrete. The following is the procedure for coarse aggregate, secondary water, concrete, and secondary It demonstrates in detail in order of the next kneading | mixing method.
(1) Coarse aggregate The coarse aggregate includes one or more selected from gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, and the like. As the coarse aggregate, similar to the fine aggregate, regenerated aggregate can be used in addition to natural aggregate.

(2) Secondary water Similar to the primary water, secondary water can be used as long as it does not adversely affect physical properties such as strength and fluidity of concrete. For example, tap water, treated sewage water, Examples include fresh concrete supernatant. The secondary water is preferably selected from a high performance AE water reducing agent, a high performance water reducing agent, an AE water reducing agent and the like in order to increase the strength of the concrete by reducing the fluidity of the concrete and the water / cement ratio. Contains one or more water reducing agents. Here, the kind of the water reducing agent includes at least one selected from polycarboxylic acid, naphthalenesulfonic acid formalin condensate, melamine sulfonic acid formalin condensate, lignin sulfonic acid, and salts thereof.

(3) Concrete The concrete to which the production method of the present invention is applied is, for example, ordinary concrete, summer concrete, cold concrete, mass concrete, fluidized concrete, high fluid concrete, high strength concrete, low heat concrete, expanded concrete, prestressed Concrete, low shrinkage concrete, fiber reinforced concrete, lightweight concrete, polymer concrete and the like can be mentioned. Among these, ordinary concrete, high-strength concrete, high-fluidity concrete, and the like, in which the strength and fluidity of concrete are more important, are preferable.

(4) Secondary kneading method As the method, for the mortar,
(i) After the coarse aggregate is charged and kneaded, the secondary water is charged and kneaded again.
(ii) after adding secondary water and kneading, then adding coarse aggregate and kneading again, and
(iii) After adding the coarse aggregate and secondary water, a method of kneading in a lump may be used. Here, the kneading apparatus used for the secondary kneading is not particularly limited, and a forced kneading mixer, a gravity mixer, or the like can be used.
The lower limit of the kneading time in the secondary kneading step is preferably 60 seconds, and the upper limit is 120 seconds, more preferably 100 seconds. If the lower limit is less than 60 seconds, it is difficult to produce homogeneous concrete, and if the upper limit exceeds 120 seconds, the production efficiency of concrete decreases.
The secondary water amount is a mass obtained by subtracting the primary water amount from the total water amount obtained based on the water cement ratio satisfying the design strength of the concrete.
The secondary kneading is performed in the same place (same mixer) as the primary kneading. For example, after the primary kneading in a batcher plant mixer, it is transported to a concrete placement place (on-site) by a transport means such as a truck agitator car. Then, it may be performed at the placement site. Further, the secondary kneading may be performed while the concrete is being transported by a transporting means having a mixing function such as a truck agitator vehicle.

3. Others The primary water and secondary water used in the present invention may contain admixtures such as a shrinkage reducing agent, an AE agent, a hydration heat inhibitor, a whitening inhibitor, a retarder, and a curing accelerator in addition to the water reducing agent. Good. The concrete produced according to the present invention can contain admixtures such as blast furnace slag, fly ash, coal ash, silica fume, limestone powder, and siliceous powder. The total amount of the admixture is preferably charged in the primary kneading step. Thereby, this admixture becomes easy to disperse | distribute more uniformly in mortar.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Materials used (1) Cement: Medium heat Portland cement A and B. As shown in Table 1 below, the size of bleeding is excessive for cement A and standard for cement B.
(2) Fine aggregate: Land sand (produced in Kakegawa City, Shizuoka Prefecture)
(3) Coarse aggregate: Sandstone crushed stone (produced by Sakuragawa City, Ibaraki Prefecture)
(4) Water reducing agent: lignin sulfonate (Pozoris No. 70 [registered trademark], manufactured by BASF Japan), polycarboxylate (Reobuild SP8SV [registered trademark], manufactured by BASF Japan)
(5) Water: Tap water

2. Measurement and results of flow value and bleeding rate of cement paste After preparing a cement paste having a water cement ratio (W / C) shown in Table 1 using a polycarboxylate as a water reducing agent, the flow value of the paste and The bleeding ratio was measured in accordance with JIS R 5201 “Physical testing method of cement” and “Journal of the pre-packed concrete, mortar breathing rate and expansion rate testing method”, respectively. The results are shown in Table 1.
As shown in Table 1, the bleeding rate of cement A was significantly higher than that of cement B, although the flow value was similar at any water cement ratio.

3. Manufacture of concrete (1) Concrete of Examples 1 to 3 According to the formulation shown in Table 2, fine aggregate, cement, and primary water are collectively charged into a kneading mixer and kneaded, and the mortar becomes a capillary state. After that, the mixture was further kneaded for 60 seconds to prepare a mortar (total kneading time was about 100 seconds).
Next, according to the formulation shown in Table 2, coarse aggregate and secondary water were all added to the mortar and then kneaded for 60 seconds to produce concrete.
In addition, in each Example, the content rate of the water reducing agent in primary water and secondary water was made the same.

(2) Concrete of Comparative Examples 1, 3, and 5 In order to compare with the concrete production method described in Patent Document 2, according to the production method, cement and primary water were mixed into a forced kneading mixer according to the formulation shown in Table 2. After adding all at once, the mixture was kneaded for 60 seconds, and then secondary water was added thereto and kneaded for 60 seconds to prepare a cement paste. Next, according to the composition shown in Table 2, coarse aggregate and fine aggregate were put together into the paste and kneaded for 60 seconds to produce concrete.
In addition, in each comparative example, the content rate of the water reducing agent in primary water and secondary water was made the same.

(3) Concrete of Comparative Examples 2 and 4 Concrete was manufactured by batch kneading for 160 seconds according to the formulation shown in Table 2 in order to compare with batch kneading, which is a normal kneading method of concrete.

4). Measurement of concrete slump flow, slump, and bleeding rate Concrete slump flow, slump, and bleeding rate are measured according to JIS A 1150 “Concrete slump flow test method”, JIS A 1101 “Concrete slump test method”, and JIS A, respectively. It was measured according to A 1123 “Concrete Bleeding Test Method”. The results are shown in Table 2.

As shown in Table 2, the slump flows of Example 1, Comparative Example 1, and Comparative Example 2 are about the same, and the slumps of Example 2, Comparative Example 3, and Comparative Example 4 are also about the same. The kneading method does not affect the fluidity of the concrete.
On the other hand, regarding the bleeding, as shown in Table 2, the bleeding amount and bleeding rate when the water-cement ratio of the concrete is 35% (total) are 0.24 and 5.72 in Comparative Example 1 and in Comparative Example 2, respectively. In contrast to 0.44 and 10.2, in Example 1, they are 0.09 and 2.18, respectively, which are much smaller. The same applies to Comparative Example 3, Comparative Example 4, and Example 2 in which the water cement ratio is as high as 55% (total).
Therefore, it can be seen that the concrete production method of the present invention has a high effect of reducing bleeding while maintaining good fluidity even if the water-cement ratio varies.

Claims (3)

  Manufacture of concrete including a primary kneading step of kneading cement, fine aggregate and primary water to produce mortar, and a secondary kneading step of adding coarse aggregate and secondary water to the mortar and kneading concrete. Method.   The method for producing concrete according to claim 1, wherein the primary water and / or secondary water contains a water reducing agent.   The method for producing concrete according to claim 1 or 2, wherein in the primary kneading, the kneading is continued for 60 seconds or more after the mortar is in a capillary state.

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