JPH0617260B2 - Method for producing cementitious composition - Google Patents

Description

The present invention relates to a method for producing an uncured cementitious composition such as cement paste, mortar and concrete admixture, especially after admixture having an effect of reducing material separation. The present invention relates to a method for producing a cementitious composition that enables addition and improves workability at the time of setting.

[Conventional technology and its problems] Conventionally, as a method for producing ready-mixed concrete to which a separation reducing agent is added, the separation reducing agent is added at the same time as the cement, the aggregate and the water in the plant, or the cement, the aggregate and the dry material are added in advance. After blending, water is often added and kneaded,
The method of post-adding the separation reducing agent to the once-kneaded concrete is not generally adopted. The reason for this is that this admixture is a water-soluble polymer, and when post-added as a powder, viscosity develops in a state in which the dispersion is non-uniform, so kneading is uniform in truck mixer trucks with poor stirring efficiency. This is because it is not carried out and the quality of concrete is adversely affected.

In addition, as a method of adding a separation reducing agent in the production of cement paste for injection method, even if water is added by pre-blending the cement and the separation reducing agent, the effect of grinding and dispersing the separation reducing agent by the aggregate is small. Therefore, lumps occur and it is difficult to form a uniform paste, which causes a quality problem. Further, when the separation reducing agent is added as powder to the cement paste, the dispersion becomes worse.
As described above, the conventional separation reducing agent is restricted in the addition method or causes a problem in quality.

In the actual construction, there is a restriction on the addition in the plant, so when it is necessary to add it after the site or in the manufacturing process,
In some cases, it has to be added afterward, and development of an admixture and a kneading system that can evenly disperse even after adding and exert the effect sufficiently has been advanced.

In the case of adding the separation reducing agent as a powder afterwards, in order to carry out the kneading uniformly, a method by improving the kneading machine such as a batch type mixer or a continuous mixer has been studied, but the kneading is still uniform by these methods. Labor required to bring a mixer etc. to the scene,
There is a problem in securing the place.

On the other hand, as a method of improving the admixture, a method of adding a separation reducing agent blended with a filler and a method of adding it as a slurry dispersed in water have been considered and studied.

The former method has a tentative effect depending on the selection of an appropriate extender, its amount, and the addition method, but there remains a problem that the powder adheres to the wall surface of the mixer and the working environment is bad.

In the latter method of adding in the form of a slurry, in general, when dispersed in water, the viscosity develops quickly and the one treated with an aldehyde such as glyoxal in order to handle the poor dispersion accompanying the increase in viscosity and delay the solubility of the admixture It is used. However, when the amount of this admixture added is small, it is possible to add a completely dissolved one, but when adding a large amount to the cement composition, a large amount of water is added to maintain the fluidity of the slurry. When it is spent, the amount of remaining water that can be added to the cement composition becomes too small, so that the kneading and transportation of the cement composition cannot be performed properly, and a large amount of labor is required to prepare and add a large amount of slurry liquid. Therefore, the slurry concentration must be increased. In the conventional technology, the limit of the slurry concentration when using a high viscosity type admixture is about 4%, and if it exceeds that, it becomes a paste with poor fluidity, and the transportation and charging to the mixer cannot be performed well. Even dispersion in the cement composition was not possible. For this reason, the advent of an admixture that can be slurried at a high concentration has been strongly desired.

[Means for Solving Problems] The inventors of the present invention have conducted extensive studies to develop an admixture that can meet the above-mentioned requirements, and as a result, have adopted an admixture containing cellulose ether as a main component. in case of,
Aldehyde treatment of cellulose ether, combined use of aliphatic carboxylic acid or oxycarboxylic acid in this treatment, apparent density of powder of the resulting admixture, pH adjustment in slurry, kind of cellulose ether, etc. preparation of high concentration slurry or Be an important factor for stabilization;
That is, (1) if the amount of the aldehyde of the cross-linking agent is increased, the slurry concentration increases to some extent, but if the powder particles are soft and the apparent density is low, they easily swell in water, and there is a limit to making a high-concentration slurry. . (2) Aldehydes and aliphatic carboxylic acids and /
Alternatively, by treating the oxycarboxylic acid, the acetal reaction proceeds uniformly and efficiently, and absorption swelling of water from the surface of the particles hardly occurs, so that the concentration of the slurry can be increased. (3) The acetal bond is easily broken on the alkali side and dissolution is promoted, but it is stable on the acidic side and has the effects of increasing the concentration of the slurry and extending the slurry life. (4) Hydroxyalkylalkylcellulose (MS0.1 to 2.0, DS0.5 to 2.5) with heat gelling property is a powder of the final product due to its characteristics in the process of heating and washing during manufacturing → cooling → heating and drying. The inventors have found that there is a relationship such as the effect of increasing the density and increasing the apparent density, and arrived at the present invention.

Therefore, in the method for producing a cementitious composition according to the present invention, an admixture having an alkali-soluble acetalized cellulose ether as a main component is dispersed in a lower aliphatic carboxylic acid acidic water to give a high-concentration slurry of 4% or more. The gist is to post-add to the uncured cement composition.

The present invention will be described in more detail below.

First, the material separation prevention of the uncured cement-based composition targeted by the present invention, methylcellulose (MC) and ethyl cellulose (EC) as a cellulose ether that is a raw material of an alkali-soluble acetalized cellulose ether effective in preventing bleeding. Hydroxyalkyl cellulose such as alkyl cellulose, hydroxypropyl cellulose (HPC) and hydroxyethyl cellulose (HEC), and further hydroxypropyl methyl cellulose (HPMC), hydroxyethyl methyl cellulose (HEMC), hydroxyethyl ethyl cellulose (HEEC), etc. Cellulose etc. are mentioned.

These water-soluble cellulose ethers were added to M.M.
S. 0.1-2.0 (preferably 0.15-1.5), DS 0.5-2.
It is advantageous to choose a hydroxyalkylalkylcellulose of 5 (preferably 1.0 to 2.0).

When the temperature of the solution increases, the hydroxyalkylalkylcelluloses with the above-mentioned degree of substitution have a certain temperature or higher (MS, DS
The phenomenon in which the alkyl group in the highly substituted portion crystallizes and the solution gels occurs depending on the value), and this phenomenon occurs when other cellulose ethers [HEC, HPC that does not have thermal gelation properties] are used in the cooling gelation process during manufacturing. Such as hydroxyalkyl cellulose, which has a heat gelation property but MC whose gelation temperature is too low, and hydroxyalkyl alkyl cellulose which has a low MS and a high DS, and a hydroxyalkyl alkyl cellulose which has heat gelation property but has a too high gelation temperature (M.
S. is high and DS is low)], but it has the effect of increasing the apparent density of the powder of the final product.

Glyoxal, succinaldehyde, etc. are mentioned as an aliphatic dialdehyde used at the time of the acetalization of the above-mentioned cellulosic ether. The addition amount that enables high-concentration slurry formation is preferably 1 to 10% by weight with respect to the above water-soluble cellulose ether. When this is sprayed onto the surface of the admixture and heat-treated, a reaction occurs and the surface partially becomes insoluble. To do. If the particles of the admixture used at this time are hard and the apparent density is large, the swelling property with respect to water is small, and a slurry having a high concentration can be formed.

On the other hand, examples of the aliphatic carboxylic acid or oxycarboxylic acid used for promoting the reaction of aldehyde uniformly and efficiently include formic acid, acetic acid, glycolic acid, lactic acid, succinic acid, etc., and formaldehyde or aliphatic dialdehyde. It is possible to achieve a slurry with a higher concentration than when used alone.
It is desirable to add 0.1 to 5% by weight to the admixture.

The apparent density of the obtained acetalized powder is preferably 0.25 or more, but when it exceeds 0.6, a high concentration slurry is realized, but since the particles are too hard, dissolution after addition to the cementitious composition is delayed and limited. It will prevent complete dissolution in the kneading time.

The weight average molecular weight of such an acetalized product of cellulose ether is also an important factor for preventing material separation,
When the amount is 3 × 10 ⁵ g / mol or more, the effect is large. This addition amount is adjusted depending on the application, target performance, construction conditions, etc., but is used in the range of about 0.1 to 2% by weight with respect to water.

If a lower aliphatic carboxylic acid, preferably acetic acid, is added to the admixture in advance so that the pH of the slurry becomes 4 to 6.5, a high-concentration slurry having a long slurry life can be obtained. There are various types that make the pH of the solution acidic, but since hydrochloric acid and sulfuric acid, which are inorganic acids, are strong acids, it is difficult to control the pH and the pH is low.
In the case of pH, it causes a decrease in viscosity of the water-soluble cellulose ether. Further, C ion and SO ₄ ion are unfavorable components for the durability of the cement composition. Oxycarboxylic acids such as succinic acid and citric acid are not desirable because they have an effect on the setting of cement. In this respect, acetic acid is a weak acid and pH
Is the most desirable acidic substance because it is relatively easy to control and has little effect on the cement composition.

In carrying out the present invention, an antifoaming agent may be used in combination if it is desired to reduce the amount of air entrained. Examples of the defoaming agent include silicone type, tributyl phosphate, and polyoxyethylene polyoxypropylene block polymerization type defoaming agent.

Further, a fluidizing agent may be used in combination for improving fluidity and strength. Examples of the fluidizing agent include those containing a sulfonate of an aromatic polycyclic condensate as a main component, those containing a sulfonate of a melamine formalin condensate as a main component, and those containing a polycarboxylate as a main component. used. Further, when it is necessary to adjust the hardening of cement, a hardening accelerator and a retarder may be used in combination.

Next, specific embodiments of the present invention will be described with reference to examples.

Example 1 Hydroxypropyl methylcellulose (HPMC) was sprayed with glyoxal, acetic acid, or glycolic acid as shown in Table 1 and heat-treated at 75 ° C. for 2 hours to obtain a powdery admixture. This was used as a concrete mortar having the following composition.

When the limiting slurry concentration for the admixture, the slump of concrete before the addition of the slurry, and the separation resistance in water of the obtained concrete mortar were tested, the results shown in Table 1 were obtained.

The types of HPMC in the table, addition methods, and test methods are shown below.

(1) Types of HPMC HPMC-1: MS = 0.23, DS = 1.45, viscosity 30000cps at 2% HPMC-2: MS = 0.85, DS = 1.38, viscosity 30000cps at 2% (2) Method of addition ・ Simultaneous addition of raw plant : A powder admixture was added together with cement, aggregate and water and kneaded.

・ Post-addition of powder for truck mixer: Concrete mixed with green concrete is transported by truck mixer (10 ton), and powder is added little by little from the upper opening of the truck mixer at the site and stirred at high speed for 10 minutes.
An underwater separation resistance test was conducted.

・ Truck mixer truck slurry post-addition: Kneaded ready-mixed concrete is carried by a truck mixer truck (10 ton), leaving water necessary for making the slurry of the admixture, and a slurry of the limit slurry concentration is bucketed from the upper port of the truck mixer on site. , And stirred at high speed for 10 minutes, and then subjected to a separation resistance test in water.

(3) Test method ・ Limited slurry concentration: The limit concentration at which fluidity can be maintained in a slurry state at 20 ° C for 30 minutes.

・ Separation resistance in water: Ratio of compressive strength (strength ratio) of underwater-produced specimen (molded by free-falling concrete in mold with 50 cm depth of water) to compressive strength of specimen in air using 10φ × 20cm ).

-Apparent density: Shows looseness of powder and apparent density as measured by a powder tester (manufactured by Hosokawa Iron Works).

In Table 1, Experiment No. 2 (Comparative Example) is a case where the separation reducing agent was post-added as a powder, but the separation reducing agent was not sufficiently dispersed, so that the strength ratio in the underwater separation resistance test was 70%. %, The performance of concrete is inferior.

When the separation reducing agent is slurried and added later, a large amount of water is required to make the slurry when the slurry concentration is low, and the amount of water used for the base concrete before adding the slurry must be reduced. It becomes hard-mixed (small slump) concrete (this limit slurry concentration is 4%).

In Experiment No. 6 (Comparative Example), the limit slurry concentration was 3.8%.
As the base concrete was too hard to drain from the mixer.

Experiment No. 3 (invention) has a lower slurry concentration than Experiments Nos. 4, 5 and 7 (invention), and the base concrete becomes hard, but unlike Experiment No. 6, it cannot be discharged from the mixer. It is not so hard concrete.

Therefore, the concrete by the method of the present invention (Experiment Nos. 3 to 5 and 7) in which the slurry was post-added to the base concrete was uniformly kneaded and the effect as the separation reducing agent was developed, and the separation resistance in water was The strength ratio of the sex test is high.

Example 2 As the hydroxyethyl methyl cellulose (HEMC), HEMC-3000 (MS = 0.16, DS = 1.49) manufactured by Shin-Etsu Chemical Co., Ltd. was used and sprayed with glyoxal, glycolic acid, or acetic acid as shown in Table 2. Then, the mixture was heated at 75 ° C. for 2 hours to obtain a powdery admixture.

Next, water / cement ratio of 1: 1, admixture: 1% (to water), tributyl phosphate (antifoaming agent): 0.2% (to water) was used as a cement paste to improve the stability and uniformity of kneading. Upon evaluation, the results shown in Table 2 were obtained.

The addition method and each test method in the table are shown below.

(1) Addition method ・ Dry blend: 10 kg cement and admixture using 20 Hobart type mixer
100g was dry blended for 1 minute, and when uniform, water was added and kneaded for 3 minutes.

1% slurry + cement: 100 g of the admixture was added to 10 kg of water, stirred for 1 minute, added with cement, and kneaded for 3 minutes.

-Cement paste + 8% slurry: 10 kg of cement and 9.1 kg of water were kneaded for 1 minute, and after addition of a slurry of 10% of the admixture (100 g of admixture + 900 g of water) after 30 minutes had elapsed, another 3 minutes Kneaded

(2) Test method-Slurry life: Time at which a fluid slurry state continues at 20 ° C.

・ Amount of lumps: 20 kg of the kneaded cement paste was passed through a sieve with an opening of 1 mm, and the amount of substances remaining on the sieve was measured.

Breathing rate: A value (%) expressed as a percentage of breathing water after allowing the cement paste placed in the graduated cylinder 1 to stand for 24 hours.

[Effects of the Invention] According to the method for producing a cementitious composition according to the present invention, it is possible to add a high slurry concentration of 4% or more as compared with the conventional production method, it is not necessary to adjust the water content in the cement composition, and the amount of slurry is large. A small amount is needed, the labor of adjusting and inputting labor is saved, the homogeneity after dispersion of the admixture in the cement composition and the dissolution in cement alkali is maintained, and the increase in the mechanical strength of the concrete after placing is exhibited. Give good results.

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Claims (5)

[Claims] 1. An admixture containing an alkali-soluble acetalized cellulose ether as a main component is dispersed in lower aliphatic carboxylic acid acidic water to obtain a high-concentration slurry of 4% or more, which is then added to an uncured cement composition. A method for producing a cementitious composition, which comprises adding. 2. A patent in which an alkali-soluble acetalized cellulose ether is an acetalized product of water-soluble cellulose ether with formaldehyde or an aliphatic dialdehyde, and the apparent density of the powder is 0.25 to 0.6 g / cm ³ . A method for producing the cementitious composition according to claim 1. 3. An alkali-soluble acetalized cellulose ether is a treatment product of formaldehyde or an aliphatic dialdehyde of a water-soluble cellulose ether and an aliphatic carboxylic acid and / or an oxycarboxylic acid,
The method for producing a cementitious composition according to claim 1, wherein the apparent density of the powder is 0.25 to 0.6 g / cm ³ . 4. The water-soluble cellulose ether has an average degree of substitution (MS) of hydroxyalkyl groups per glucose unit of cellulose of 0.1 to 2.0 and an average degree of substitution of alkyl groups.
The method for producing a cementitious composition according to claim 2 or 3, which is a water-soluble hydroxyalkylalkylcellulose having a thermogelation property (DS) of 0.5 to 2.52. 5. The method for producing a cementitious composition according to any one of claims 1 to 4, wherein the high-concentration slurry is an acidic dispersion liquid of a lower aliphatic carboxylic acid having a pH of 4 to 6.5.