JPH0813695B2 - Cement admixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a cement admixture, more specifically, reduction or prevention of alkali-aggregate reaction of mortar and concrete, improvement of durability such as salt resistance and sulfate resistance. Cement admixture capable of achieving

<Conventional technology and its problems> In recent years, due to depletion of high-quality cement raw materials, changes in the firing method of cement, and the change to pulverized coal as the burning fuel, the amount of alkali in the cement has increased, but due to the depletion of aggregates. There was a problem that an alkali-aggregate reaction occurs together with the deterioration of quality.

Also, the durability of mortar and concrete such as salt resistance and sulfate resistance is beginning to be emphasized due to the progress of ocean development, but simply improving the strength by lowering the water-cement ratio will not result in a significant improvement. There was a problem that it was not recognized.

The use of blast furnace slag cement is recommended as a way to solve these problems all at once.

The reason why the blast furnace slag cement reduces or prevents the alkaline aggregate reaction is not clear, but it has been recognized in the laboratory that it has a preventive effect. Further, regarding the durability such as salt resistance and sulfate resistance, the property that the Al component in the blast furnace slag is chemically adsorbed to the permeating chlorine ions and sulfate ions is utilized.

The amount of blast furnace slag used is 40 parts by weight or more is recommended for the total 100 parts by weight of cement and blast furnace slag, regardless of whether the alkali reaction is suppressed, salt resistance, sulfate resistance, etc. The slag content of blast furnace slag type B cement was generally 30 to 35% by weight, but it has recently been 40%.
It has been raised to ~ 55% by weight.

Also, the slag used for blast furnace slag cement has a coarseness (Blaine value) of around 4,000 cm ² / g, while recently it has a high strength and, for example, salt resistance and alkali-aggregate reaction prevention. 10,0 in fineness for high durability
It has been proposed to use ultrafine slag having a maximum particle size of about 10 μm and a diameter of around 00 cm ² / g (JP-A-61-281057).

However, probably because blast furnace slag is produced as a by-product from the reducing atmosphere, chemical analysis of each component and conversion into oxides results in a considerable weight increase in total, which is considered to be oxygen deficiency. When such blast furnace slag is hydrated with cement or slaked lime, a large amount of blast furnace slag
Despite containing the Al component, almost no calcium aluminate hydrate was detected by X-ray diffraction. However, when chlorine ions and sulfate ions permeate there, they quickly become Friedel salts (3CaO ・ Al ₂ O ₃・ CaCl ₂・ 1OH ₂ O) and ethrin guide (3CaO ・ Al ₂ O ₃・ 3CaSO _4).・ 32H ₂ O) is generated to prevent permeation, but it is easy to adsorb carbon dioxide and oxygen, which easily leads to deterioration of the hardened body due to neutralization and oxidation and rusting of the reinforcing bar. The problem remains in the durability of.

On the other hand, aluminum hydroxide is commercially available for industrial use, and although it looks fine, it has a Blaine value of 1,00.
It is about 0 cm ² / g. If this aluminum hydroxide is used as it is for mortar and concrete, it will not react at all under normal temperature curing and atmospheric pressure steam curing conditions, and it has an alkaline aggregate reaction suppression effect and durability such as salt resistance and sulfate resistance. No sexual effect is observed.

The present invention provides a cement admixture that reduces or prevents alkali-aggregate reaction and improves durability such as salt resistance and sulfate resistance without using any conventional blast furnace slag.

In order to solve the above problems, the present inventors have conducted diligent studies, and as a result, usually, aluminum hydroxide, which is said to be inactive or poor in activity, has a specific Blaine value or more, at room temperature or normal temperature. The present invention has been completed based on the knowledge that it reacts under a pressure steam curing condition to reduce or prevent alkali-aggregate reaction and improve durability such as salt resistance and sulfate resistance.

<Means for Solving the Problem> That is, the present invention is a cement admixture containing aluminum hydroxide as a main component and having a Blaine value of 3,500 cm ² / g or more.

 Hereinafter, the present invention will be described in detail.

The Blaine value of the aluminum hydroxide used in the present invention is 3,
It is 500 cm ² / g or more.

When the Blaine value is less than 3,500 cm ² / g, the reactivity of aluminum hydroxide is small and its use effect is negligible. The finer the aluminum hydroxide, the higher its use effect, but it is most preferable that the particle size is 10 to 12 μm and the Blaine value is around 10,000 cm ² / g according to the industrial pulverization and classification technology. In consideration of economic efficiency, it is preferably 4,000 cm ² / g or more, more preferably 5,000 to 9,000 cm ² / g.

The amount of the cement admixture mainly composed of aluminum hydroxide having a Blaine value of 3,500 cm ² / g or more is 0.5 part by weight or more as aluminum hydroxide with respect to 100 parts by weight of cement in concrete. The greater the amount of aluminum hydroxide used, the greater the effect of its use. However, if it exceeds 5 parts by weight, the amount of crystalline calcium aluminate hydrate will increase, and the strength will gradually increase. Since it decreases, it is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight.

The cement in which the cement admixture of the present invention is used is various portland cements such as normal, early strength, super early strength, moderate heat, white, etc., as well as fly ash cement and silica cement mixed cement.

Further, various kinds of commercially available water reducing agents, AE agents, retarders, accelerators, expansive agents, etc., which are usually used, can be used together in the production of mortar and concrete. In particular, it is preferable to use a high-performance water reducing agent in combination, and by reducing the water / cement ratio and increasing the solidification,
It promotes the effects of reducing or preventing alkali-aggregate reaction and improving durability such as salt resistance and sulfate resistance.

A high-performance water-reducing agent is a surfactant with a large dispersibility that does not cause excessive delay of condensation or excessive air entrainment even when added in a large amount. Condensate salts, high-molecular-weight lignin sulfonates, polycarboxylates, and the like as main components, and specifically include, for example, Kao Corporation's trade name “Mighty 150”, Electrochemical Industry ( Product name "FT-500" manufactured by Bozoris Bussan Co., Ltd. and product name "NL-4000" manufactured by Bozoris Bussan.

The amount of the high-performance water reducing agent is not particularly limited, but is preferably about 0.2 to 2 parts by weight based on 100 parts by weight of cement in terms of solid content.

Also, with mortar and concrete using expansive materials, the amount of micropores increases due to expansion,
It is particularly preferable to use the cement admixture of the present invention together, since chlorine ions and sulfate ions easily penetrate.

Expansive material is Denka CSA, trade name manufactured by Denki Kagaku Kogyo Co., Ltd.
# 20 "and other Etlin guide systems and Onoda Cement Co., Ltd.
It is roughly classified into lime series such as product name "Onoda Expan".

As a method for adding the cement admixture of the present invention, any method such as adding powder as it is when kneading mortar or concrete, dispersing it in kneading water and adding it, and mixing it with preliminarily cement can be used.

<Example> Hereinafter, the present invention will be described with reference to an example.

Example 1 A cement containing 800 parts by weight of cement, 1,600 parts by weight of sand, 8 parts by weight of a water reducing agent and 320 parts by weight of water was used, and the Blaine value of aluminum hydroxide was changed to change the addition amount based on 100 parts by weight of cement. To prepare a mortar, and a 4 × 4 × 16 cm mortar specimen was prepared. And about 5 hours after molding, capping and 15 ℃ / hr
The temperature was raised to 65 ° C. at the rate of, the temperature was maintained for 4 hours, the steam valve was stopped, and the mixture was naturally cooled in the steam curing tank. The next day, the mold was removed and immersed in a 3% NaCl aqueous solution to quantify the amount of chlorine permeated for each age group. The results are shown in Table 1.

Although aluminum hydroxide is for industrial use, it is assumed that it does not contain a large amount of impurities that may affect the amount to be added, etc., and the total amount of aluminum hydroxide was added as sand by weight replacement with sand.

The Blaine value was measured by setting the specific gravity of aluminum hydroxide to 2.43 (air-comparison specific gravity meter) and the porosity to 0.
50 was set. However, when the fineness of powder was too fine to be compressed into the volume of the bed, the porosity was increased so that the volume of the bed could be compressed.

Further, the quantitative determination of chlorine was carried out by fluorescent X-ray analysis after cutting out the central portion of the specimen reaching the age of 4 × 4 × 1 cm, drying at 300 ° C. and finely pulverizing the whole amount. For reference, the compressive strength on the 1st day was also measured and shown.

<Materials used> Cement: Ordinary Portland cement manufactured by Denki Kagaku Kogyo Co., Ltd. Sand: Natural sand, river sand produced by Himekawa in Niigata Prefecture Water reducing agent: Denka FT, manufactured by Denki Kagaku Co., Ltd.
-500 "Water: Drinking water Aluminum hydroxide: For industrial use by Sumitomo Chemical Co., Ltd., white fine free-flowing powder, Blaine value 870 cm ² / g.

As is clear from Table-1, when the Blaine value of aluminum hydroxide is less than 3,500 cm ² / g, it does not react and no effect of preventing permeation of chlorine ions is recognized, but 3,500 cm ² / g
When it is above, the effect will be recognized, 4,000 cm ² / g
From the above, the effect becomes remarkable, and it is understood that the smaller the aluminum hydroxide, the more effective.

Also, the more the added amount, the better the penetration of chlorine is stopped.

Example 2 The mortar of 1-day age prepared in Experiment Nos. 1-1 to 1-8 was crushed by a brown crusher, and 50 g under a 250 μ sieve was immersed in a 3% Na ₂ SO ₄ aqueous solution 1 for 72 hours, After repeating filtration and washing with water, it was dried at 200 ° C., pulverized, and the amount of adsorbed sulfate ion was determined by fluorescent X-ray analysis.
The sulfate ion in the cement was obtained by subtracting the blank of the sample under 250 μ before immersion.
Table 2 shows the results.

As is clear from Table 2, when the Blaine value of aluminum hydroxide is 3,500 cm ² / g or more, the adsorption amount of sulfate ions increases, and as the Blaine value increases, the adsorption amount of sulfate ions increases.

This is because aluminum hydroxide has a Blaine value of 3,500c.
When it is m ² / g or more, it shows that even if the sulfate ion permeates, it has an action of stopping further permeation, and suggests the sulfate resistance.

Example 3 Cement 800 was prepared by using sand and silica having particle sizes shown in Table-3.
Parts by weight, 1,800 parts by weight of sand and silica and 1N NaOH aqueous solution 4
Alkali-aggregate reaction test was carried out by changing the Blaine value of aluminum hydroxide and the addition amount to cement in the same manner as in Example 1, using 00 parts by weight of mortar.

The test piece is a 4 x 4 x 16 cm triple mold, and mortar is molded so that gauge plugs for measuring length change can be embedded at both ends, and cured for 24 hours in a room at 20 ° C ± 3 and RH 80% or more. Then, remove the mold, and set the base length according to JIS A 1129.
Cured in a thermo-hygrostat at ℃ ± 2, RH 95% or more, and 3 months, 6 months
The amount of swelling was measured. The results are shown in Table-4.

As is clear from Table 4, when the Blaine value of aluminum hydroxide is less than 3,500 cm ² / g, there is almost no effect of suppressing expansion, and when it is 3,500 cm ² / g or more, the smaller the expansion, the more expansion is suppressed.

Further, it can be seen that the expansion can be suppressed by increasing the addition amount of aluminum hydroxide.

The R ₂ O content in the cement was 0.5%.

In addition, aluminum hydroxide was added to 100 parts by weight of cement, and was added to the mortar as an outer proportion.

Silica stone was opalaceous silica from Iwo Jima, and NaOH was a special grade reagent.

Example 4 Each unit amount of cement, water, sand, crushed stone and water reducing agent
450, 144, 820, 1,014 and 6.75 (kg / m ³ ) with Gmax of 15m
m, s / a is 45%, air content is 2.0%, and slump value is 8 ± 2 cm, as shown in Table-5, aluminum hydroxide and expansive material are used together, and the concrete supply of Φ10 × 20 cm is used. I made a sample.

In the same curing method as in Example 1, a specimen that had been demolded the next day (curing 1) and a specimen that had been cured at room temperature for the next day without steam curing, and then standard cured for 28 days in the form ( Curing 2) was immersed in a 3% NaCl aqueous solution, taken out at a material age of 3 months, the central part of the test piece was cut into Φ10 × 2 cm, and the permeation amount of chlorine ions was determined in the same manner as in Example 1. The results are also shown in Table-5.

<Materials used> Aluminum hydroxide: Blaine value 7,000 cm ² / g Expansion material: Onoda Cement Co., Ltd. product name “Onoda Expan” <Effects of the Invention> When the cement admixture of the present invention is used, it rapidly reacts even under normal temperature and atmospheric pressure steam curing conditions, various durability is improved, and the larger the Blaine value, the more the addition amount is. The greater the number, the more effective.

Further, the cement admixture of the present invention not only improves the above-mentioned various durability, but also fixes sulfate ions and calcium in mortar and concrete, and is therefore effective in preventing efflorescence.

Claims (1)

[Claims] 1. A cement admixture containing aluminum hydroxide as a main component and having a Blaine value of 3,500 cm ² / g or more.