JP2002248615A - Method for manufacture of concrete wherein ratio of entrained air is raised - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacture of concrete wherein entrapped air is allowed to disappear in a process for manufacture of concrete, and a target air amount is constituted by entrained air to be generated from an air entraining agent to raise a ratio of the entrained air. SOLUTION: Primary cast cement of an amount 70% to 85% of the cement amount calculated according to a specified formula based on initial design conditions is employed. Primarily kneaded ready-mixed concrete is obtained by kneading the primary cast cement together with water, a fine aggregate, a coarse aggregate, an air entraining agent and an air entraining and water reducing agent for a kneading time 2 to 4 times a specified kneading time. Then, after adding the residual amount of cement to the primarily kneaded rady-mixed concrete, the concrete is manufactured by secondarily kneading for a specific kneading time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing concrete capable of improving frost damage resistance, workability, appearance characteristics of hardened concrete, etc. by increasing the content of entrained air contained in a concrete mixture. About.

[0002]

2. Description of the Related Art Conventionally, when a target air amount is designed in cement concrete, an AE agent and an AE water reducing agent are generally used. Here, as the AE agent,
Fatty acid salts, soaps such as resin salts, sulfates, ethers, polyoxyethylene sorbitan fatty acid esters, betaines, imidazoline betaines and the like are known. As AE water reducing agents, lignin sulfonates,
Oxycarboxylates, alkylaryl sulfonates, polyol composites and the like are known. Said A
E water reducing agent is an admixture having both a water reducing function and an air entraining function. Here, the entrained air is entrained air, which is a coarse and irregular air bubble that is useless for improving the performance of the concrete composition, together with fine spherical entrained air. Therefore, when the air content of the designed value is insufficient due to the use of the AE water reducing agent, usually, the AE agent is added and entrained air is entrained to compensate for the insufficient air amount to the target value. ing.

On the other hand, Japanese Patent Application Laid-Open No. 10-259050 discloses a method for producing a highly durable cement compound having improved freeze-thaw resistance and shrinkage-reducing properties. As disclosed in
-34967 is known.

[0004] First, the gist of the cold-resistant concrete according to Japanese Patent Application Laid-Open No. 10-259050 is that a deicing agent containing lithium nitrite as a main component and an AE agent or an AE water reducing agent for generating fine bubbles are mixed. there were. Here, lithium nitrite contains 1 to 3% of lithium nitrate, contains a small amount of alkali ions, has high solubility in water, has a hygroscopic property, and suppresses an alkali-aggregate reaction. However, the mixing of the lithium nitrite increases the amount of entrapped air, and conversely reduces the amount of entrapped air, which is fine bubbles. To solve this drawback, the AE agent or the AE water reducing agent is used. So that they are mixed together
The durability of the concrete was improved by artificially entraining the entrained air into the concrete.

[0005] The gist of the method for producing a highly durable cement composition according to JP-A-11-34967 is to add an air entraining admixture (AE) to a composition containing water, cement and aggregate.
AE water reducing agent, high-performance AE water reducing agent and a compound having the same performance as the above), and after mixing and kneading, an organic shrinkage reducing agent is added and secondary mixing is performed. Met. Here, the organic shrinkage reducing agent is an additive for reducing the drying shrinkage of the cement composition, and a polyoxyalkylene compound can be used in addition to a conventionally known surfactant. The feature of the manufacturing method is that, in the case where the air entraining admixture and the shrinkage reducing agent are conventionally added at once, the freeze-thaw resistance becomes extremely poor. Separation timing of the reducing agent was added, and the air-entraining admixture was added to the cement mixture and kneaded, and then the shrinkage reducing property was ensured by a method of adding an organic shrinkage reducing agent and then secondary mixing. There.

On the other hand, at a concrete casting site,
The acceptance inspection method when the target air volume is set for the ready-mixed concrete brought into the site is JIS A1128.
(Air chamber pressure method) is generally used. This method measures the amount of air contained in a concrete composition, and the amount of air consists of both entrapped air and entrained air contained in the concrete composition. Here, the entrapped air is mainly air bubbles caused by air entrained at the time of kneading the concrete mixture, and the size of the air bubbles is 80 to 100 μm.
m or more, the shape of the cells was indeterminate and did not have a coating, and the pores were formed on the surface of the concrete after curing, so that the appearance was impaired. On the other hand, entrained air is air bubbles generated by air entrained by an AE agent, an AE water reducing agent, etc., and the size of the air bubbles is often 20 to 40 μm. In the vicinity of the fine aggregate, a ball bearing action is created to improve the fluidity of the kneaded concrete and improve workability, as well as increase the separation resistance and improve the frost damage resistance to concrete, and improve the appearance characteristics of hardened concrete It is assumed. Therefore, as described above, the JIS-A.
1128 has the disadvantage that the true functional properties of ready-mixed concrete cannot be evaluated.

Further, JIS A-5308 (Ready Mixed Concrete) specifies that the control range of the bubble content of ready-mixed concrete is ± 1.5%. For example, the target air rate is set to 4.5%. In such a case, it is necessary to control the bubble content of the ready-mixed concrete within 3.0 to 6.0%. However, the air amount measured above consists of both the entrapped air and the entrapped air. If it is high, the bubble content at the time of casting is extremely lower than the bubble content at the time of kneading, which may cause problems in workability and slump.

[0008] Further, even in the case of having both a water reducing function and an air entraining function like an AE water reducing agent, both the entrapped air and the entrapped air contain the bubble type, and the total air bubbles in the ready-mixed concrete are included. As long as the content is measured, the true functional characteristics cannot be evaluated, and the measurement results are unreliable and the performance of the product varies. In addition, even when using crushed sand among artificial aggregates used as a concrete mixture, air that forms entrapped air at the time of kneading from the irregular shape of the aggregate is easily entrained. However, the true quality characteristics of the ready-mixed concrete cannot be evaluated by measuring the total bubble content, and there is a disadvantage that the performance of the product varies.

[0009]

SUMMARY OF THE INVENTION The present invention has been made based on the knowledge obtained from the results of various studies and experiments in view of the drawbacks and the like described in the above section of the prior art. However, there is provided a concrete manufacturing method in which the ratio of entrained air is increased, in which the entrapped air is eliminated in the process of manufacturing concrete and the target air amount is constituted by the entrained air generated from the AE agent. Is to do.

[0010]

First, the present inventor has focused on the change in the ratio of the entrapped air to the entrapped air in the total amount of air contained in the ready-mixed concrete accompanying the change in the slump value. . The entrapped air in the total air content of the low-slump ready-mixed concrete indicates a high ratio, whereas the ratio of the entrapped air decreases as the slump value increases. This was presumed to be mainly due to the fact that the entrapped air entrained during the initial charging and kneading of the various components partially disappeared in a high slump state. However, according to the current concrete standard specification, the slump of concrete is a maximum of 21 cm, and those exceeding that value cannot be actually used. Therefore, the present inventors have studied the achievement of the above-mentioned object by divided kneading. In other words, the idea was to divide the amount of cement calculated by the indication blending based on the initial design conditions into the primary input and the secondary input, first, the primary input cement, water, fine aggregate, coarse aggregate, The AE agent and the AE water reducing agent are primarily kneaded and kneaded by a kneading time longer than a normal kneading time to promote defoaming of the entrapped air in the contained air and to produce a necessary amount of contained air by the entrained air. It was planned that slump primary kneaded concrete was made, then secondary cement was added to the primary kneaded ready-mixed concrete, and secondary kneading was performed to obtain ready-mixed concrete having a water-cement ratio originally designed.

The results obtained from the results of various experiments based on the above-mentioned plan, that is, the method for producing concrete with an increased ratio of entrained air according to the present invention to achieve the above-mentioned object, were originally developed. From 70% to 85% of the cement amount calculated by the indication blending based on the design conditions is used as the primary input cement amount, and water, fine aggregate, coarse aggregate, AE agent, AE
The mixture is kneaded with a water reducing agent for a kneading time of 2 to 4 times the predetermined kneading time to obtain a primary kneaded ready-mixed concrete, and then the remaining kneaded cement is added to the primary kneaded ready-mixed concrete, and then the secondary kneading is performed for a predetermined kneading time. To make concrete.

[0012]

The primary kneaded ready-mixed concrete according to the present invention is a high-slump ready-mixed concrete as compared with the ready-mixed concrete slump estimated from the total amount of each concrete mixture.
This is a state in which coarse amorphous and filmless entrapped air that is mainly involved in the charging and kneading of various compounds is easily defoamed. Furthermore, as a result of the experiment, the defoaming of the entrapped air is promoted as the kneading time is longer. However, the decrease due to the defoaming is almost finished about four times as long as the predetermined kneading time. The kneading time of the primary kneading usually needs to be specified to be 2 to 4 times the predetermined kneading time.

Further, as a result of the experiment, the primary input cement amount is
A good peak is about 80% of the cement amount calculated by the formulation based on the initial design conditions, and is approximately 85%.
If the ratio exceeds 1, the slump value of the primary kneaded ready-mixed concrete does not increase, and the entrapped air is hardly defoamed. On the other hand, if it is less than about 70%, various factors such as weather conditions are also involved, but material separation will occur. 70 cement
% To 85%.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments and comparative examples according to the present invention will be described.

Materials used in Examples and Comparative Examples are as follows. Cement (C): Normal bolt land cement (JIS
R 5210, JISR 5201, density 3.16, manufactured by Denki Kagaku Kogyo KK Fine aggregate (S): crushed sand (JIS A 5005, surface dry density 2.63, water absorption 0.88, coarse particle ratio 2.80) Coarse aggregate (G): Crushed stone (JIS A 5005, surface dry density 2.66, actual volume ratio 60.0, aggregate maximum size 2 mm, Iwaki Monster product Kanno Kosan Co., Ltd.) Admixture (Ad): AE water reducing agent, trade name PALIC Sa
(JIS A 6204) Admixture (AE) manufactured by FPC Inc .: AE agent, trade name PALIC AE200
(JIS A 6204) manufactured by FPC

Various kneadings were performed with the target slump values of 18 cm, 15 cm, and 8 cm using the above-mentioned materials. Here, the admixture was appropriately adjusted so that the air content of the concrete was 4.5% by volume.

Further, as for the method of kneading the concrete, the following kneading and split kneading were carried out using a test mixer (tilted type, 3 cut). Batch kneading: input of coarse aggregate (G), input of admixture (Ad) and (AE) dissolved in water (W), input of 1/2 aggregate of fine aggregate (S), cement (C) ), 細 amount of fine aggregate (S), and kneading by mixer for 180 seconds. Split kneading: Input of coarse aggregate (G), input of admixture (Ad) and (AE) dissolved in water (W), input of 1/2 aggregate of fine aggregate (S), primary input of cement Minutes (C1 = C ×
80%), 1/2 amount of fine aggregate (S), kneading with the above mixer for 360 seconds, temporarily stop the mixer, and put in a secondary cement (C2 = C × 20%),
Kneading for 0 seconds.

Next, the above test results are as shown in Table 1.

[0019]

[Table 1]

Next, based on the results shown in Table 1, the relationship between the target slump value and the measured air amount depending on the presence or absence of the AE agent in the same split kneading method is shown in FIG.

[0021]

FIG.

In FIG. 1, 1.8%, which is the difference between the measured air amount of 4.3% in Example 1 and the measured air amount of 2.5% in Comparative Example 3, is added by the kneading of Example 1. AE agent 0.1
It can be seen that the air is entrained air generated by 232 Kg / m3. Similarly, with the measured air amount of 4.8% in Example 2 and the measured air amount of 2.8% in Comparative Example 5, the entrained air generated by the AE agent added in the kneading of Example 2 and 0.1180 kg / m 3 was used. Is 2.0%, and is produced by the measured air amount of 4.7% in Example 3 and the measured air amount of 3.2% in Comparative Example 7, and by the AE agent added in the kneading of Example 3 by 0.0548 Kg / m3. The entrained air provided is 1.5%.

Further, based on the results of Table 1, the difference between the target slump value and the actual slump value is shown in Table 2, and the difference between the actual slump value and the target slump value in each test with respect to the target slump value is shown in FIG. It was shown to.

[0024]

[Table 2]

[0025]

FIG. 2

From the results shown in Table 2 and FIG. 2, it can be seen that the concrete manufacturing method according to the present invention has an improved slump value as compared with the conventional concrete manufacturing method by batch kneading.

On the other hand, the target slump value is 18 cm, and the kneading time at the time of primary kneading in the above-mentioned split kneading is set to one of the normally set time
20 seconds, double 240 seconds, triple 360 seconds, quadruple 48
Table 3 below shows the measured air amount when the time was set to 0 second and five times 600 seconds.

[0028]

[Table 3]

From the results shown in Table 3, the kneading time was about 24 hours.
By 0 seconds, the defoaming of the entrapped air is promoted within the content of air, and then the disappearance of the entrapped air is almost completed by about 360 seconds, indicating a nearly constant content of air. It is presumed that when the time is extended and about 480 seconds elapse, the entrained air component also defoams, and the tendency for the content air content to decrease begins to appear.

The target slump value is 18 cm, and the ratio of the primary input cement and the secondary cement input in the above-mentioned split kneading is 90% to 10%, 85% to 15%, 75% to 25%, and 70% to 30. Table 4 shows the difference between the target slump value and the measured slump value with respect to the target slump value when%, 65% and 35%.

[0031]

[Table 4]

From the results in Table 4 above, it is found that the difference between the target slump value and the measured slump value is small and the workability is improved until the ratio of the primary cement input and the secondary cement input is about 85% to 15%. Not seen, but the percentage is 85%
From 15% to 75% to 25%, the difference between the target slump value and the measured slump value is 2 to 3 cm, indicating improvement in workability. Furthermore, when the ratio reaches 65% to 35%, bleeding occurs. From the above results, the application range of the ratio of the primary cement input and the secondary cement input is 70% to 30% to 85%.
15%.

[0033]

Since the present invention is configured as described above in detail, it has the following effects.

According to the method for producing concrete with an increased ratio of entrained air according to the present invention, a conventional ready-mixed concrete plant and a secondary concrete product plant do not require the addition of a special function improving agent or the like. The raw materials improve the frost damage resistance and the workability that entrained air causes, and also prevent a significant decrease in the content of air in the process of transporting ready-mixed concrete using a ready-mixed concrete vehicle. There is an effect that a high-grade ready-mixed concrete in which a slump value lower than an allowable range due to the disappearance of air is prevented from being reduced can be manufactured.

Further, according to the method for producing concrete according to the present invention in which the ratio of entrained air is increased, since the content ratio of entrapped air is low, voids generated on the surface of hardened concrete can be reduced. It is also effective in improving the appearance of hardened concrete.

Further, according to the concrete manufacturing method of the present invention in which the ratio of the entrapped air is increased, the undesired reduction of the air content accompanying the disappearance of the entrapped air in the transporting process as described above. Since there is no problem, there is also an effect that the reliability of the measured value can be restored according to JIS A 1128 (air chamber pressure method) specified for inspecting and managing the quality of ready-mixed concrete.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a target slump value and an actually measured air amount depending on the presence or absence of an AE agent in a split kneading method.

FIG. 2 is a diagram showing a difference between an actually measured slump value and a target slump value in each test with respect to the target slump value.

Claims (1)

[Claims] 1. A primary input cement amount of 70% to 85% of the cement amount calculated by the indicated blending based on the initial design conditions, together with water, fine aggregate, coarse aggregate, AE agent, and AE water reducing agent. Kneading is performed for a kneading time of 2 to 4 times the predetermined kneading time to obtain a primary kneaded ready-mixed concrete, and then the remaining kneaded concrete is added to the primary kneaded ready-mixed concrete, and then the secondary kneading is performed for a predetermined kneading time to obtain concrete. A method for producing concrete with a higher ratio of entrained air, characterized by producing.