JPH09309754A - Cement admixture and cement composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject admixture capable of promoting a coagulation rate of mortar and concrete, shortening a prefaced curing time and suppressing cracking caused by thermal expansion in a heat-curing by allowing to contain gypsum, aluminum sulfate and/or alunite and a specific material. SOLUTION: This cement admixture contains gypsum (e.g. anhydrous gypsum of type II), aluminum sulfate and/or alunite and activated silica (e.g. silica fume), further preferably one or more of an alkaline metal aluminate (e.g. anhydrous sodium aluminate) or an alkaline metal silicate (e.g. anhydrous sodium silicate) and/or one or more of pozzolan materials (e.g. a baked product of a clay mineral) or latent hydraulic materials (e.g. a blast furnace slag). By using the admixture, short time strengths in a heat curing are enhanced, a production cycle from mixing and kneading of mortar or concrete to releasing it from a former can be shortened and production efficiency is improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cement admixture and a cement composition, and more specifically, to promoting the setting promotion of mortar or concrete and the development of short-term strength in heating curing such as steam curing. Used for early demolding of products.

[0002]

2. Description of the Related Art Conventionally, there are many types of secondary concrete products, many types of them, and they are sold in large quantities. It is necessary to have a large number of equipment, and a vast product yard (site) is also required. Therefore, various early demolding methods are being studied in order to increase production efficiency with as few molds as possible. Common methods of early demolding include raising the curing temperature, using highly hydraulic cements, or using strong cements such as chlorides, nitrates, and rhodanates to accelerate the setting and hardening of concrete. The use of setting accelerators is conceivable.

[0003] However, the demolding strength in a short time by the method of forcibly promoting the hydration reaction of such cement (depending on the shape and weight of the secondary product, the demolding strength of a large and heavy product is generally 8 N / mm ^{2 to} 15 N / mm ² ) can be obtained, but the subsequent strength development is suppressed, and there is a problem that it is necessary to increase the amount of unit cement etc. to secure the design strength. there were.

[0004] In order to cover the above-mentioned drawbacks caused by the conventional setting accelerating method, the present inventor contains gypsum and a sulfate band or alumite and sub-, bi-, or pyrosulfite. An admixture utilizing the production of ettringite (JP-A-4-160042) was proposed.

[0005] However, in this proposal, although the demolding strength can be obtained by short-time heat curing and the long-term strength can be prevented, a rapid hydration reaction of aluminum sulfate or the like is suppressed by sulfite or the like. In order to increase the production cycle, shorten the pre-curing time until heat curing,
In addition, there is a problem in that the effect of suppressing the occurrence of cracks due to thermal expansion that occurs when the heating rate is increased is poor.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have reasonably promoted condensation while shortening the pre-curing time, while securing a workable time. The inventors have found an excellent early demolding method that does not cause thermal expansion even if the heating and curing rate is increased, and completed the present invention.

[0007]

Means for Solving the Problems That is, the present invention provides (1)
A cement admixture characterized by containing gypsum, aluminum sulfate and / or alum, and activated silica, (2) Furthermore, an alkali metal aluminate or an alkali metal silicate. Alternatively, the cement admixture according to (1), which contains two or more kinds.
(3) A cement admixture according to (1) or (2), containing one or more of a pozzolanic substance and a latent hydraulic substance, (4) cement, and (1) to (3). A cement composition containing the cement admixture according to any one of 1.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The gypsum used in the present invention includes type II anhydrous gypsum called insoluble or sparingly soluble, as well as dihydrate gypsum, hemihydrate gypsum, and soluble type III anhydrous gypsum, which are effective in developing long-term strength. And, the blending amount is at most 6 parts by weight in terms of CaSO _{4 with} respect to 100 parts by weight of cement, more preferably 5 parts by weight or less, and the most preferable range is 0.1 part.
It is 2 to 4.0 parts by weight. If it is less than 0.2 parts by weight, the elongation of long-term strength will be small, and if it exceeds 6 parts by weight, the long-term strength development will be good, but the retardation of setting will be large and the effect of shortening the pre-curing time and thermal expansion will be caused. It is not preferable because the crack suppressing effect becomes small. In addition, it is most preferable to use type II anhydrous gypsum, which is called insoluble or sparingly soluble in gypsum, and the specific surface area by the Blaine method is not particularly limited and 2500 cm ² / g or more is sufficient.

As the aluminum sulfate and alumite (alnite) used in the present invention, those which are sold on the market are used, and they have an effect of promoting condensation and an effect of developing short-time strength by heat curing, but they are not affected by thermal expansion. The effect of suppressing is small. Both those containing water of crystallization and those which are calcined to give anhydrous salts are used. These are blended at a maximum of 2.5 parts by weight with respect to 100 parts by weight of cement, in terms of the total amount of each anhydride, whether they are used alone or in combination at an arbitrary ratio. It is preferable that the amount is 2.0 parts by weight or less, and the most preferable range is 0.1.
It is 1.5 parts by weight. If the amount is less than 0.1 parts by weight, the effect of shortening the finishing time and the strength for a short time are small, and if the amount exceeds 2.5 parts by weight, the workability necessary for molding cannot be secured or the composition is rapidly consolidated. There is no such thing. In addition, since these are highly reactive, the fineness and particle size are not particularly limited, and commercially available granules or coarse grains may be used as they are, or they may be crushed and used. It is a good one.

Further, the activated silica used in the present invention is, for example, silica fume, fly ash fume, metakaolin, incinerated ash of silicified wood, and Aerosil. And, these are ultrafine powders that are one order finer than cement, and when used in combination with gypsum, aluminum sulfate and / or alum stones, the amount is very small and the setting is promoted further to shorten the pre-curing time and the thermal expansion cracking. It is effective in suppressing.

Preferably, the active silica is compounded in an amount of at most 2.0 parts by weight based on 100 parts by weight of cement.
1.5 parts by weight or less is more preferable, and the most preferable range is 0.05 to 1.0 parts by weight. If the amount is less than 0.05 parts by weight, the effect of shortening the finishing time becomes small, and 2.
Even if added in an amount of more than 0 parts by weight, the effect of shortening the pre-curing time does not become large.

In the present invention, in order to promote the effect of promoting the setting by the combination of gypsum, aluminum sulfate and / or alum, and activated silica, the effect of shortening the precuring curing time and the effect of suppressing thermal expansion cracks is exhibited. , An alkali metal aluminate or an alkali metal silicate is used in combination. The alkali metal means sodium, potassium and lithium.

The content of these components is preferably at most 1.0 part by weight, more preferably 0.8 part by weight or less, and most preferably 0.04 part by weight based on 100 parts by weight of cement.
~ 0.6 parts by weight. If it is less than 0.04 part by weight, the effect of promoting setting is small, and if it exceeds 1.0 part by weight, it may cause rapid setting depending on the lot and type of cement, which is not preferable.

Further, in the present invention, the strength development effect is promoted by the combination of gypsum, aluminum sulfate and / or alum, activated silica and / or alkali metal aluminate or alkali metal silicate. For this purpose, a pozzolanic active substance and a latent hydraulic substance are used in combination.

The pozzolanic substance is composed mainly of SiO ₂ and Al ₂ O ₃ and reacts with lime for a long period of time to form a cement hydrate. It contains various clay minerals such as bentonite, acid clay and zeolite. Shown is fly ash produced as a by-product from a thermal power plant that uses fired products or carbonaceous materials as fuel.
The latent hydraulic material refers to blast furnace slag that is hardened by an alkali stimulus.

These are different from the above-mentioned activated silica,
The order of particle size is the same as that of cement, and the fineness (Blaine method, porosity 0.5) is 3000 cm ² / g
The powder is about 8500 cm ² / g, and the fineness is not particularly limited as long as it is within this range.

Even though they have a small hydration activity, they can be added together with aluminum sulfate and / or an alkali metal aluminate, ultrafine silica activated silica and the like to give short-term strength and long-term strength. Promotes strength. The reason for this is not clear, but one is that when it is premixed with activated silica or the like, which easily aggregates and is difficult to disperse, such as aluminum sulfate having an extremely fast hydration reactivity or an aluminate of an alkali metal, it may enhance the dispersion effect. It is guessed that
Mixing cement or the like instead of the pozzolanic substance does not show a strong effect, and it is speculated that some chemical interaction is involved between the pozzolanic substance and other components.

If the amount of these pozzolanic substances added is more than 2 parts by weight with respect to 100 parts by weight of cement, no further increase in the effect can be expected. Is something you cannot expect.

In the present invention, the mortar and concrete containing the admixture of the present invention are molded into a mold and heat-cured. Heating and curing methods include steam, electric heat, and hot water.
There is no limitation on the means, but since the concrete secondary product factory already has steam curing equipment, the method by steam curing is preferable. The heating temperature is 100 ° C at the highest, and the higher the curing temperature, the shorter the time. Although the strength obtained is high, on the contrary, if it is too high, cracking due to thermal expansion tends to occur, so 50 ° C or higher is preferable, and 65 to 95 ° C is more preferable. If the temperature is lower than 40 ° C, the strength development is delayed, so that the time until demolding becomes longer and the purpose of early demolding is not met, and the temperature over 100 ° C is difficult to obtain by heating with steam, so existing steam curing equipment cannot be used. In addition, if the heating rate is increased, cracks due to thermal expansion are more likely to occur, which is not preferable.

The type of cement used in the present invention is various portland cements, belite cements and mixed cements obtained by mixing various portland cements with slag, fly ash, silica or the like. It is not preferable to use because it is only shortened and no strong effect can be expected.

Further, the method of adding the cement admixture of the present invention to concrete and the method of kneading may be conventional methods, and there is no particular limitation, but the method of adding the cement admixture is
Each powder component may be mixed, or the mixture may be added as a suspension to a mixer when mixing mortar or concrete, or each component may be added separately and mixed. Good thing.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 As a unit amount, 360 g of water, 1000 g of cement, 1 sand
Using a mortar formulation consisting of 500 g and a water reducing agent,
By changing the type and amount of plaster, aluminum sulfate, alum, activated silica, etc., and adjusting the amount of water reducing agent so that the flow value immediately after kneading falls within the range of 200 ± 5 mm, knead the mortar. The coagulation 60 minutes after the water injection and the compressive strength at the time of demolding after heating and curing were measured. The results are shown in Tables 1 to 3. As a result, the amount of water reducing agent is 5 to 2
Although the flow rate was adjusted within the range of 0 g, the amount of the water reducing agent increased as the blending amount of aluminum sulfate, alum stone and activated silica increased. The mixing method of mortar is JIS R
5201 mechanical kneading, put water in a kneading bowl, stir at low speed, add each mixture of components and cement and stir for 30 seconds, then add sand and mix at low speed for 3
The mixture was stirred for 0 seconds and further kneaded at high speed for 60 seconds. The condensation was measured by using a Proctor penetration tester according to ASTM C403, mortar was molded into a container of 6 W x 6 L x 7 Hcm, and the value of the pressure gauge when the penetration needle of φ1.6 cm penetrated 1 cm was measured. Then, the mixing and setting test of the mortar were conducted in a room at 20 ± 3 ° C. and RH of 80% or more.
Specimens for compressive strength test were molded with 4x4x16cm triple molds using a piercing rod, and after 60 minutes of pre-curing (the time from kneading to the start of heat curing) was set in a steam curing tank. The mixture was put in, heated to 65 ° C. in 30 minutes, heated and cured with steam for 2.5 hours, taken out and demolded, and immediately the demolding strength (4 hours from kneading) was measured while hot. The demolded specimen was air-dried in a room at 20 ° C. and RH 60%, and the 28-day-old strength was measured.

<Materials used> (1) Cement: ordinary Portland cement manufactured by Denki Kagaku Kogyo Co., Ltd. (2) Sand: River sand produced by Himekawa water system in Niigata prefecture (3) Water reducing agent: Naphthalene sulfonate type by Denki Kagaku Kogyo ( Liquid) A. Gypsum A-1: Type II anhydrous gypsum (hydrofluoric acid generated by-product gypsum, Blaine specific surface area 4000 cm ² / g) A-2: Gypsum dihydrate (reagent, specific surface area 3800 cm ² / g) A-3: Hemihydrate gypsum (Heat treatment of di-water at 150 ° C, Blaine specific surface area 8000 cm ² / g) A-4: Soluble anhydrous gypsum (heat treatment of semi-water at 200 ° C, Blaine specific surface area 12000 cm ² / g) B. Aluminum sulphate, etc. B-1: Aluminum sulphate 18-hydrate (for industrial use) B-2: Calcined alum stone from Shokozan, Hiroshima Prefecture at 650 ° C (crushed to a Blaine specific surface area of 6800 cm ² / g, purity 90%) C.I. Active silica, etc. C-1: Silica fume (BET method specific surface area of ^{25m 2 / g) C-2} : fly ash fumes (BET method specific surface area of 30 m ² /
g) C-3: metakaolin (BET method specific surface area of ^{1.4m 2 / g) c-4} : Aerosil (BET method specific surface area of ^{160m 2 / g) c-5} : chaff ash (BET method specific surface area of 1.5 m ² / g)

From Tables 1 and 2, when the content of gypsum and aluminum sulfate etc. was kept constant and the content of active silica was increased, the larger the content, the more the setting was promoted. The 4-hour intensity also increases. And the effect of the active silica is shown from 0.01 parts by weight, and 0.8 to 1.
Up to 0 parts by weight promotes the setting and the increase in the strength for 4 hours, but if it exceeds it, the effect is not changed, or the setting amount of the water reducing agent is increased to obtain the same flow and the setting and the setting are increased. The 4-hour strength tends to slightly decrease (see Experiment Nos. 1-6 to 1-37).

From Table 2, when the content of gypsum was changed, an improvement in long-term strength was recognized from 0.2 parts by weight, regardless of the type, and up to 4 parts by weight, there was a large degree of setting and 4 hour strength. Increases long-term strength without affecting. And when it exceeds it, setting tends to be delayed and the strength tends to decrease for 4 hours (see Experiment Nos. 1-39 to 1-55).

Table 3 shows that aluminum sulfate and the like, regardless of the type, show a remarkable acceleration of the condensation and an increase in the 4-hour strength from 0.1 part by weight. The more the addition amount, the more remarkable. If it exceeds 1.5 parts by weight, the elongation of long-term strength tends to be suppressed (Experiment No. 1-5).
6 to 1-68). In addition, even if aluminum sulfate and alum stone are combined, if they are the same and the total amount of the combination amount and the combination amount are the same, similar setting acceleration and 4
Time intensity is obtained (comparison between Experiment No. 1-65, 1-66 and 1-69, 1-70).

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

Example 2 Experiment No. 3 shown in Table 3. Using 1-71, 1-72, and 1-73 mortar, the same test as in Example 1 was conducted by changing the type and addition amount of the alkali metal aluminate or alkali metal silicate. Table 4 shows the results. <Materials used> D-1: Anhydrous sodium aluminate (reagent) D-2: Anhydrous potassium aluminate (reagent) D-3: Sodium silicate anhydrous (reagent)

From Table 4, in the present invention, the effect of promoting the setting of alkali metal salts such as aluminate and the effect of increasing the 4-hour strength are remarkably shown (Experiment Nos. 2-1, 2-2 and 2-).
3, 2-4 comparison). Then, the effect of promoting the setting of alkali metal salts such as aluminate and the effect of increasing the strength for 4 hours is 0.04.
It is recognized from the parts by weight, and becomes more remarkable as the blending amount increases, but when it exceeds 0.6 parts by weight, the long-term strength tends to decrease (see Experiment Nos. 2-5 to 2-12).

[0032]

[Table 4]

Example 3 Using the concrete composition shown in Table 5, as gypsum A-
1, aluminum sulphate B-1, alum B-2, activated silica C-1 and alkali metal aluminate D-1 in any combination, mix concrete with different mixing amount, φ15 × 30 cm Concrete was molded in the mold of No. 2, and the pre-curing time (time from the mixing after mixing to the start of heating and curing) was changed, and the test for occurrence of thermal expansion cracks was performed when rapid heating was performed with steam. For rapid heating, set the steam curing tank to 75 ° C in advance,
It was cured by steam for 2.5 hours, demolded, and examined for the occurrence of thermal expansion. Furthermore, the compressive strength at the time of demolding was also measured in part.
Table 6 shows the results. The concrete has a capacity of 20
10 using a 0 liter planetary forced kneading mixer
0 liters of concrete was mixed in a room at 20 ± 3 ° C. Various components such as gypsum and the like are premixed and placed in cement, and kneading water is added while kneading with crushed stone or sand, and the water reducing agent used in the examples is arbitrarily added so that the slump falls within the specified range. It was adjusted and adjusted by the post-addition method. In addition,
The kneading time was 120 seconds after the kneading water was added.

[0034]

[Table 5]

From Table 6, it can be seen that the cracks caused by thermal expansion were heated while soft,
It means that work such as driving is possible.
In the present invention, while ensuring a work time of at least about 30 minutes, thermal expansion cracks due to rapid heat curing are suppressed,
It is shown to enhance strength for a short time.

[0036]

[Table 6]

Example 4 Experiment No. 1 in Table 1 1-1, 1-7 and the experiment No. of Table 4.
The same test as in Example 1 was conducted using 2-8 mortar and changing the types and addition amounts of the pozzolanic substance and the latent hydraulic substance. The results are shown in Table 7. However, the measurement items were 4-hour intensity and 28-day intensity. <Materials used> E-1: Bentonite is fired at 1200 ° C and fineness is 4500 cm ² / g
Those E-2 was pulverized to: those that have been ground to 5000 cm ² / g acid clay and fired at 800 ° C. E-3: Commercially available fly ash (fineness ^{4500cm 2 / g) E-4} : blast furnace slag (fineness (4500 cm ² / g)

[0038]

[Table 7]

From Table 7, Experiment No. in which only the pozzolanic substance was added was used. Since 4-1 has a small addition amount, almost no strong addition effect is exhibited. On the other hand, in the present invention, the effect of addition is shown from 0.1 parts by weight, and the strength is gradually increased as the addition amount is increased. However, even if the addition amount exceeds 2 parts by weight, the strength is not further increased. It shows that you can't expect it.

[0040]

[Effect of the Invention] The cement admixture of the present invention containing gypsum, aluminum sulphate and / or alum, and activated silica as main components is blended with mortar or concrete to accelerate the setting speed of mortar or concrete. Further, it is possible to further shorten the pre-curing time, suppress thermal expansion cracks in heat curing and increase short-time strength, and it is possible to manufacture mortar and concrete without long-term strength reduction. Further, by using an alkali metal aluminate or an alkali metal silicate together, the setting time can be further shortened, and the effect of suppressing thermal expansion cracks and enhancing short-term strength can be promoted. In addition, short-term strength and long-term strength can be increased by using a pozzolanic substance and a latent hydraulic substance together. Therefore, in the secondary concrete product factory, the production cycle from mixing and removing mortar and concrete to demolding can be shortened, and the production efficiency can be further increased.

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Claims (4)

[Claims] 1. A cement admixture containing gypsum, aluminum sulfate and / or alum, and activated silica. 2. The cement admixture according to claim 1, further comprising one or more alkali metal aluminates or alkali metal silicates. 3. A pozzolanic substance or a latent hydraulic substance, or one or more types thereof are contained.
Cement admixture described. 4. A cement composition comprising cement and the cement admixture according to any one of claims 1 to 3.