JPH05279096A - Production of concrete - Google Patents

Abstract

PURPOSE:To hardly generate breathing at the time of producing concrete. CONSTITUTION:A surfactant and defoaming agent are added into the concrete. The concrete is so formed that the average cell diameter of the surface area of the open cells in the concrete attains 20 to 400mum. The concrete is preferably so formed that the number of the open cells having 20 to 300mum surface area cell diameter attains >=90% of the total number of the open cells. An anionic surfactant is preferably used as the surfactant. An emulsion which consists essentially of dimethyl polysiloxane and is subjected to a heating treatment in the presence of a cement water-reducing agent and in which 30 to 70% number of emulsion particles having 0.5 to 40mum grain sizes and 70 to 30% number of emulsion particles having 40 to 300mum grain sizes coexist is preferably used as the defoaming agent. The cement water-reducing agent, slowly releasable dispersant, setting accelerator and setting retarder are preferably used alone or in combination as the other admixture at the time of using the surfactant and the defoaming agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing concrete in which breathing hardly occurs.

[0002]

2. Description of the Related Art Conventionally, river sand has been used as an aggregate when manufacturing concrete. However, in recent years, river sand has been depleted, and sea sand has been used instead of river sand. However, sea sand contains a small amount of fine particles having a particle size of 0.3 mm or less, which is contained in river sand in a large amount, and therefore, breathing is likely to occur in concrete. That is, since the amount of fine particles in the concrete is insufficient, the surface area capable of absorbing water is reduced, and the water in the concrete is separated on the surface. And, there is a drawback that hardened concrete with good performance is difficult to be obtained due to separation of water.

In order to prevent breathing, it has been attempted to add a water-absorbing substance such as a water-absorbing polymer to concrete to remove excess water in the concrete.
However, when the water content in concrete decreases,
There is a drawback that the initial fluidity is hindered, the deformability of concrete is lowered, and the workability and handleability are deteriorated.

[0004]

Therefore, the inventors of the present invention have conducted various studies on a method in which breathing is less likely to occur even when sea sand having a small amount of fine particles is used as an aggregate. As a result, by entraining fine air bubbles in concrete, the surface of the fine air bubbles was made to retain water to prevent the occurrence of breathing. And
As a result of earnest research on a method of entraining fine air bubbles in concrete, an admixture using a surfactant and an antifoaming agent in combination,
The present inventors have found that a relatively large amount of fine bubbles can be entrained by being added to concrete, and have reached the present invention. Incidentally, JP-A-61-270247 and JP-A-4-264
Japanese Patent No. 1 discloses a technique in which a surfactant and an antifoaming agent are added together in concrete, but since the defoaming agent used is not devised, fine bubbles are entrained in the concrete. It has not been done. That is, JP-A-61-270
In the technology described in Japanese Patent No. 247, since the defoaming agent is easily deteriorated, and in the technology described in Japanese Patent Laid-Open No. 4-26441, the antifoaming agent is easily hydrolyzed, so that the present invention can be used in concrete. It is not possible to entrain such fine bubbles.

[0005]

Means for Solving the Problems The present invention, which was made based on the above findings, provides a method for producing concrete using an admixture containing a surfactant and an antifoaming agent as essential components. The present invention relates to a method for producing concrete, characterized in that the average surface area bubble diameter is 20 to 400 μm. It also relates to defoamers and admixtures suitable for use in the production of this concrete.

The surfactant used in the present invention may be any of those conventionally used as a foaming agent (AE agent). That is, synthetic surfactants,
Both resinate-based surfactants and protein-based surfactants can be used. As the kind of the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant are used alone or in combination. In particular, anionic surfactants are preferable because they easily entrain fine bubbles having a small particle size in concrete. A nonionic surfactant or the like may be difficult to entrain fine bubbles in concrete, but by using together with an anionic surfactant, coarse bubbles can be made into fine bubbles. When a surfactant and a cement water reducing agent are used in combination, since the cement water reducing agent is generally anionic, an anionic surfactant, a nonionic surfactant or an amphoteric surfactant is used as the surfactant. Preference is given to using.

The amount of the surfactant used is preferably adjusted so that the amount of air in the standard concrete is 6 to 20%. That is, the amount of air in the reference concrete can be made 6 to 20% by adding about 0.005 to 0.25% by weight of the surfactant to the amount of cement using the reference concrete. Here, the reference concrete is JI.
SA 6204 refers to the concrete mixture specified in "Chemical admixture for concrete". That is, the unit cement amount is 30
The unit water amount is 0 kg / m (320 kg / m when using crushed aggregate), the amount of slump when kneading is 18 ± 1 cm, and the fine aggregate ratio is 40 to 50%. A predetermined amount of a surfactant is added to the concrete so that the amount of air in the reference concrete is 6 to 20%. here,
The amount of air in the standard concrete is calculated by the following calculation formula. That is, the air amount (%) = [(A−B) /
A] × 100. However, A is the unit volume weight (kg / m) calculated from the composition, and B is the measured unit volume weight (kg / m).
m). If the amount of air in the concrete is less than 6%, the absolute number of fine bubbles in the concrete is small, the surface area capable of retaining water decreases, and breathing tends to occur easily. On the contrary, when the air content in the concrete exceeds 20%, when the defoaming agent is added, the air content tends to increase and the strength of the hardened concrete tends to decrease.

The defoaming agent used in the present invention includes
Lower alcohol antifoaming agents such as methanol and ethanol,
Organic polar compound-based defoaming agent such as oleic acid, tributyl phosphate, metal soap, sorbitan lauric acid monoester, polyethylene glycol derivative, and mineral oil-based defoaming agent in which mineral oil and a surfactant such as fatty acid metal salt are mixed. ，
A silicone-based defoaming agent such as a dimethylpolysiloxane emulsion or a dimethylpolysiloxane-modified self-emulsifying type can be used.

In the present invention, it is particularly preferable to use the following defoaming agents. That is, an antifoaming agent obtained by heating an emulsion containing dimethylpolysiloxane as a main component in the presence of a cement water reducing agent,
It is preferable to use an antifoaming agent in which the number of emulsion particles having a particle size of 0.5 to 40 μm is 30 to 70% and the number of emulsion particles having a particle size of 40 to 300 μm is 70 to 30%. Such an antifoaming agent can be easily produced by the method described below. That is, dimethylpolysiloxane having a viscosity of about 100 to 100,000 centistokes at 25 ° C. is prepared. In addition, the viscosity of dimethylpolysiloxane is measured by using a Labelose viscometer when the viscosity is about 5000 centistokes or less, and by using a B or BM type rotational viscometer when the viscosity is about 5000 centistokes or more. To do. Examples of such dimethylpolysiloxane include "SH5561" and "SH873" manufactured by Toray Dow Corning Silicone Co., Ltd.
0 ”,“ SH5505 ”or“ SM5573 ”, Shin-Etsu Chemical Co., Ltd.“ KM72F ”or“ KM75 ”, Toshiba Silicone Co., Ltd.“ TSA ”
770 ”or the like can be used. Then, the dimethylpolysiloxane was treated at a temperature of 60 ° C in the presence of a cement water reducing agent.
~ 98 ° C, preferably 90 ° C or more, time 5 to 48 hours, preferably 10 hours or more, and heat treatment under the condition of temperature × time = 500 ° C · hrs. Or more, preferably 800 to 1400 ° C · hrs. Can be obtained by doing. It may be heated at a temperature lower than this condition, but it is not practical because the reaction takes a long time. Further, when the heat treatment is performed for a long time, the emulsion is decomposed or aggregated, and it tends to be difficult to obtain a stable defoaming agent. Further, the amount of the cement water reducing agent used is about 20 to 1000 parts by weight with respect to 1 part by weight of the emulsion containing dimethylpolysiloxane as a main component. Without using a cement water reducing agent, it becomes difficult to obtain an antifoaming agent having emulsion particles of the above-mentioned particle size,
The emulsion particles may become coarse and adversely affect the hardened concrete. As the cement water reducing agent, various known compounds or compositions can be used. The use of the defoaming agent as described above is preferable because fine bubbles can be favorably carried in the concrete.

The amount of defoamer used is influenced by the amount of surfactant used, and the amount of air in the standard concrete is 3 to 5% by using both the surfactant and the defoamer. It is preferable to adjust to. That is, in the same manner as in the case of determining the amount of the surfactant used, by using the reference concrete, by adding about 0.005 to 0.25% by weight of the defoaming agent to the cement amount, the air in the reference concrete is reduced. Quantity 3-5
% Can be adjusted. As described above, the amount of surfactant used is preferably such that the amount of air in the standard concrete is 6 to 20%, but a predetermined amount of defoaming agent is further added to the amount of air in the standard concrete. Is 3
It is good to adjust it to be ~ 5%. Also, the amount of surfactant used is 6-20% of the amount of air in the standard concrete.
Even if it is not adjusted to fall within the range, it is preferable to add a predetermined amount of antifoaming agent so that the amount of air in the reference concrete becomes 3 to 5%. When the amount of air in the concrete is less than 3%, the absolute number of fine bubbles in the concrete is small, and the surface area capable of retaining water decreases,
Breathing tends to occur easily. vice versa,
If the amount of air in the concrete exceeds 5%, the amount of air is too large, and the strength of the hardened concrete tends to decrease.

A predetermined amount of the above-mentioned surfactant and defoaming agent is added to the concrete to adjust the average surface area bubble diameter of the entrained bubbles in the concrete to 20 to 400 μm.
This surface area average cell diameter is also determined by the following method using standard concrete. The standard concrete in this case may contain a cement water reducing agent (which may be any of standard type, delayed type and accelerated type). First, mortar is separated from a standard concrete to which a surfactant and a defoaming agent are added in a predetermined amount with a 5 mm diameter sieve and poured into a mold having a diameter of 5 cm and a height of 10 cm. Then, after curing, a cutter is used to horizontally cut at a height of 5 cm. After polishing the cut surface, fine powder of calcium carbonate, titanium oxide, zinc oxide, calcined gypsum, etc. having a particle size of 1 μm or less is embedded in the pores. Then, 1 cm ^{2 of} this embedded surface is analyzed by an image analyzer (LUZEX III, manufactured by Nireco Co., Ltd.) to measure the diameter of each bubble. The diameter of this bubble is called the surface area bubble diameter, and the average value of the surface area bubble diameter is the surface area average bubble diameter in the present invention. Therefore, the bubbles appearing on the cut surface are those in which any part of the spherical bubble was cut, but the measurement was performed assuming that the center of the spherical bubble was cut. And the average value is the surface area average bubble diameter. As described above, the reference concrete is used to produce the concrete in such an amount that the surfactant and the defoaming agent are added such that the surface area average bubble diameter of the entrained bubbles is 20 to 400 μm. It is difficult and unrealistic to make the surface area average bubble diameter of entrained bubbles in concrete less than 20 μm. On the other hand, if the surface area average cell diameter exceeds 400 μm, the amount of water retained on the surface of the cell becomes small and breathing easily occurs, which is not preferable.

Further, in the present invention, the surface area bubble diameter is
It is preferable that the number of entrained bubbles of 20 to 300 μm is 90% or more of the total number of entrained bubbles. The number of entrained bubbles is also determined by the same method as described above. That is, the cut surface of the hardened concrete treated in a predetermined manner, and analyzed by an image analyzer to measure the number of cells per 1 cm ^2, in all its bubbles in, the surface area cell diameter of 20 to 300
It suffices to count the number of μm bubbles. If the number of fine bubbles having a surface area bubble diameter of 20 to 300 μm is less than 90%, the amount of water retained on the surface of the bubbles is reduced, and breathing tends to occur easily.

According to the present invention, as described above, a surfactant and an antifoaming agent are added to concrete so that the average surface area bubble diameter of the entrained bubbles in the concrete is 20 to 400 μm. The following may be used in combination as an admixture other than the surfactant and the defoaming agent, although it reduces breathing. That is, the cement water reducing agent, the sustained-release dispersant, the setting accelerator, the setting retarder, and the waterproofing agent may be used alone or in combination. In particular, when a cement water reducing agent is used together, breathing can be further reduced, which is preferable. As a cement water reducing agent, a naphthalene sulfonic acid formaldehyde high condensation product water reducing agent, a methylnaphthalene sulfonic acid formaldehyde high condensation product water reducing agent, a sulfonated melamine resin water reducing agent,
A lignin sulfonic acid type water reducing agent, a phenol-formaldehyde condensate type water reducing agent, a polycarboxylic acid type water reducing agent, a partial ester water reducing agent of polycarboxylic acid, an aniline sulfonic acid type water reducing agent and the like can be used. When the cement water reducing agent is used in combination, the surfactant is preferably about 0.05 to 60 parts by weight, and the antifoaming agent is preferably about 0.01 to 0.1 part by weight, relative to 100 parts by weight of the water reducing agent. Further, in the present invention, blast furnace slag, fly ash, silica fume and the like may be mixed in concrete in addition to ordinary cement or the like which is usually used.

[0014]

【Example】

1. Surfactants Used First, Table 1 shows the surfactants used in the examples.

[Table 1]

2. Cement water reducing agent used Next, the cement water reducing agent used in the examples is shown in Table 2.

[Table 2]

3. Concrete mix and used materials The concrete mix and used materials used in the examples are as follows.・ Water cement ratio ・ ・ ・ 59.7% ・ Unit cement amount ・ ・ ・ 320kg / m (Osaka, Ube, Onoda ordinary Portland cement equivalent amount mixed) ・ Fine aggregate rate… 49% ・ Fine aggregate… Murogijima sea sand (Kagawa Prefecture) , Coarse grain ratio = 3.23, Specific gravity = 2.57, Maximum size = 5 mm or less ・ Coarse aggregate ... Utada-cho Jintsusan (Wakayama Prefecture), Coarse grain ratio = 6.65, Specific gravity = 2.61, Maximum size = 20 mm or less

4. Adjustment of the amount of surfactant used A standard concrete (slump = 18 cm, air content = 2% or less) specified in JIS A 6204 "Chemical admixture for concrete" was manufactured. The surfactant shown in Table 1 was added to this concrete, and the amount of air in the concrete was measured. Then, the addition amount of the surfactant was determined so that the air amount was 6 to 20%. This is shown in Table 3. The addition amount in Table 3 is the addition amount to the cement weight.

[Table 3]

5. Preparation of Defoaming Agent 2 parts by weight of a commercially available defoaming agent shown in Table 4 was mixed with 98 parts by weight of a naphthalenesulfonic acid formaldehyde highly condensed water reducing agent (Mighty Na salt, manufactured by Kao Corporation), and the mixture was added at 90 ° C. The antifoaming agent was adjusted by heating for an hour. This defoaming agent was in the form of emulsion, and its particle size distribution was as shown in Table 4.

[Table 4]

6. Manufacturing of concrete 3. The cement water reducing agent shown in Table 2 was added to the concrete composition shown in Table 2 so that the slump value would be 18 cm. Then, the surfactant shown in Table 1 was added to 4. It is added so that the preferable usage amount adjusted and determined in (Example). On the other hand, in the comparative example, an amount outside the preferred range of use was added. Furthermore, 5. The defoaming agent prepared in 1. is added so that the air content in the reference concrete is 3 to 5%. In addition, in the comparative example, the defoaming agent was not added. As described above, the cement water reducing agent, the surfactant,
The concrete to which the defoaming agent was added in the proportions shown in Tables 5 and 6 was stirred for 3 minutes (rotation speed 25 rpm) with a tilting mixer.

[Table 5]

[Table 6]

The slump value of the concrete stirred as described above was measured according to JIS A 1101. Also,
The amount of air in the concrete was measured according to JIS A 1128, and the breathing was measured according to JIS A 1123. Further, mortar was sampled from this concrete with a 5 mm sieve, filled in a mold having a diameter of 5 cm and a height of 10 cm to be hardened, and then a portion having a height of 5 cm was cut by a cutter. This cross section was polished by a polishing machine. And on the polishing surface,
Finely pulverized calcium carbonate (particle size 1 μm or less) was embedded in the pores. This was analyzed by the image analyzer described above, and the surface area average bubble diameter and the ratio of bubbles having a surface area bubble diameter of 300 μm or less (fine bubble rate) to the total number of bubbles were measured. The above measurement results are shown in Tables 7 and 8.

[Table 7]

[Table 8]

7. Storage stability of a composition comprising a cement water reducing agent, a surfactant and an antifoaming agent A cement water reducing agent, a surfactant and an antifoaming agent are blended in the proportions shown in Examples 1, 8, 14, 19, and 23. , Concrete admixture (concrete admixture corresponding to Example 1
31 and the same as Examples 32, 33, 34 and 35 hereinafter. ) Was adjusted. The solid content of this concrete admixture was adjusted to 30% by weight, and the mixture was stored in a thermostatic chamber at 35 ° C. for 6 months. And, this concrete admixture, after one month, 3
After 6 months and 6 months, it was applied to the reference concrete and the amount of air in the concrete was measured. Also, for comparison, instead of the defoaming agent used in Examples 31, 32, 33, 34 and 35, 5. In Example, except that the corresponding commercially available antifoaming agent which was not subjected to the heat treatment shown in Table 1 was used, and the mixing ratio was set to the ratio shown in Table 9 and the solid content concentration was 35% by weight. 31-35 in the same manner as the concrete admixture (a concrete admixture corresponding to Example 31
31 and hereinafter Comparative Examples 32, 33, 34 and 35. ) Was adjusted. After this concrete admixture was stored in the same manner as above, it was applied to concrete and the amount of air in the concrete was measured. The results are shown in Table 9.

[Table 9]

As is clear from the comparison between Examples 1 to 25 and Comparative Examples 1 to 15, when a surfactant and an antifoaming agent are used in combination with concrete, entrained bubbles in the concrete become fine. It can be seen that as a result, breathing of concrete can be reduced. In addition, Example 31
~ 35 and Comparative Examples 31-35 are clear, as an antifoaming agent, an emulsion containing dimethylpolysiloxane as a main component, in the presence of a cement water reducing agent, when heat-treated is used, It can be seen that the storage stability of the admixture in which the cement water reducing agent, the surfactant and the defoaming agent are mixed is improved as compared with the case where the one which is not heat-treated is used.

[0023]

[Function] By adding a surfactant and an antifoaming agent to the concrete in combination, the entrained cells in the concrete can be made finer, and the reason why the surface area average cell diameter can be 20 to 400 μm is not clear. It can be inferred as follows. First, it is known that the internal pressure of the bubble, the surface tension of the liquid, and the bubble diameter have the following relationship. That is,
P _i = P _a + (4γ / R). However, P _i is the internal pressure of the bubble, P _a is the external pressure, γ is the surface tension of the liquid, and R is the diameter of the bubble. On the other hand, the surface tension in cement-saturated water is 40 to 60 dyne / cm in the amount of surfactant added so that the amount of air in concrete is 3 to 6%.
Is. Further, the surface tension in the saturated water of cement in the suitable addition amount range of the surfactant in the present invention is usually 35 ~
It is 55 dyne / cm. By adding an antifoaming agent such as a silicone antifoaming agent to the surface tension of 28 to 35 dyne / cm
Can be lowered. From the above formula, when the internal pressure of the bubble is calculated when the external pressure is constant (1 atm) and the bubble diameter is 100 μm, it becomes 0.029 atm when the surface tension is 73 dyne / cm, whereas the surface tension is 0.029 atm. Is 30 dyne / cm
Is 0.009 atm. That is, it is assumed that fine bubbles are stably present by reducing the surface tension.

From the physical point of view, it can be inferred as follows. Concrete with a surfactant added entraps air from the gas-liquid interface due to shearing force. It is considered that coarse bubbles are present at the gas-liquid interface, relatively small bubbles sheared by the shearing force are present inside the slurry, and the bubbles become finer as the shearing force further increases. At this time, if the defoaming agent is present, the coarse bubbles present at the gas-liquid interface are defoamed. Therefore, it is presumed that only minute bubbles are present inside the concrete.

[0025]

As described above, in the method for producing concrete according to the present invention, a surfactant and a defoaming agent are used together and applied to the concrete so that the entrained bubbles in the concrete have a constant fine diameter. As a result, the surface area of the bubbles in the concrete can be increased, and a large amount of water can be retained on the surface of the bubbles. Therefore, the method according to the present invention has an effect of reducing breathing of concrete. When a defoaming agent obtained by heat-treating an emulsion mainly composed of dimethylpolysiloxane in the presence of a cement water reducing agent is used, the composition containing the defoaming agent and another admixture is stored. An effect that stability can be improved is exhibited.

[Table 8]

[Table 8]

Claims (9)

[Claims] 1. A method for producing concrete using an admixture containing a surfactant and an antifoaming agent as essential components, wherein the surface area average cell diameter of entrained cells in the concrete is
The method for producing concrete is characterized in that it is 20 to 400 μm. 2. The method for producing concrete according to claim 1, wherein the number of entrained bubbles having a surface area bubble diameter of 20 to 300 μm is 90% or more of the total number of entrained bubbles. 3. The method for producing concrete according to claim 1, wherein the surfactant is an anionic surfactant. 4. The method for producing concrete according to claim 1, wherein the amount of the surfactant used is adjusted so that the amount of air in the reference concrete is 6 to 20%. 5. The method for producing concrete according to claim 1, 2, 3 or 4, wherein the use amounts of the surfactant and the defoaming agent are adjusted so that the air amount in the reference concrete is 3 to 5%. 6. An antifoaming agent obtained by heat-treating an emulsion containing dimethylpolysiloxane as a main component in the presence of a cement water-reducing agent, wherein the number of emulsion particles having a particle diameter of 0.5 to 40 μm is 30 to 70%, The method for producing concrete according to claim 1, 2, 3, 4 or 5, wherein an antifoaming agent mixed with 70 to 30% of emulsion particles having a diameter of 40 to 300 µm is used. 7. A combination use of at least one admixture selected from the group consisting of a cement water reducing agent, a sustained release dispersant, a setting accelerator and a setting retarder. Or the method for producing concrete according to 6. 8. An antifoaming agent obtained by heat-treating an emulsion containing dimethylpolysiloxane as a main component in the presence of a cement water-reducing agent, wherein the number of emulsion particles having a particle size of 0.5-40 μm is 30-70%. A defoaming agent for concrete, characterized by mixing 70 to 30% of emulsion particles having a diameter of 40 to 300 μm. 9. The defoaming agent for concrete according to claim 7, wherein at least one selected from the group consisting of a surfactant, a cement water reducing agent, a sustained release dispersant, a setting accelerator and a setting retarder. An admixture for concrete characterized by using an admixture together.