JPH0316943A - Cement admixture - Google Patents

Abstract

PURPOSE:To improve durability of product by using Al(OH)3 having Blaine value larger than a specific value as cement admixture. CONSTITUTION:Mortar mixture composed of cement such as various Portland cement, etc., aggregate and water containing 100 pts.wt. cement calculated as solid is mixed with 0.2-2 pts.wt. high-performance water-reducing admixture and expanding agent, etc. Then, Al(OH)3 having at least 3500cm<2>/g Blaine value is added to resultant mortar mixture in an amount of >=0.5 pt.wt., preferably 1-30 pts.wt. to 100 pts.wt. said cement to form the aimed mortar. The aimed mortar is set in a mold frame and cured with gas of normal pressure at normal temperature to obtain product having improved various durabilities.

Description

[Detailed Description of the Invention] Industrial Application Fields The present invention relates to cement admixtures, and specifically to reducing or preventing alkaline aggregate reactions in mortar and concrete, and improving durability such as salt resistance and sulfate resistance. This article relates to cement admixtures that can achieve this.

In recent years, the amount of alkali in cement has increased due to the depletion of high-quality cement raw materials, changes in cement combustion methods, and changes in combustion fuel to pulverized coal. There was a problem that an alkaline aggregate reaction occurred, coupled with a decline in quality due to depletion.

In addition, the durability of mortar and concrete, such as salt resistance and sulfate resistance, is becoming more important as offshore development progresses, but simply lowering the water/cement ratio and increasing the strength will not significantly improve the durability. The problem was that it was not recognized.

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

Although the reason why blast furnace slag cement reduces or prevents alkaline aggregate reactions is not clear, it has been confirmed in the laboratory that it has a preventive effect. In addition, for durability such as salt resistance and sulfate resistance, the property of AI components in blast furnace slag chemically adsorbing penetrating chlorine ions and sulfate ions is utilized.

The recommended amount of blast furnace slag to be used is 40 parts by weight or more per 100 parts by weight of cement and blast furnace slag in all cases, including suppression of alkaline reactions, salt resistance, and sulfate resistance. The slag blending ratio of blast furnace slag type B cement was generally 30 to 35% by weight, but recently it has been increased to 40 to 55% by weight.

Also, is the fineness (plain value) of the slag used in blast furnace slag cement as rough as around 4,000 cJ/g? However, recently, ultrafine slag with a fineness of around 10,000c+fl/g and a maximum particle size of around 10μ has been used for the purpose of high strength and even higher durability such as salt resistance and prevention of alkali aggregate reaction. It has been proposed to use it (Japanese Patent Laid-Open No. 61-281057, etc.).

However, perhaps because blast furnace slag is produced as a by-product from the reducing atmosphere, when each component is chemically analyzed and converted into oxides, there is a considerable increase in total weight, which is thought to be due to oxygen deficiency. When such blast furnace slag is subjected to an elongation reaction with cement or slaked lime, although the blast furnace slag contains a large amount of AI, it is mostly found in X-ray diffraction as calcium aluminum hydrate. is not detected. However, when chlorine ions and sulfate ions penetrate there, Friedenoll's salt (3CaO-AIzO: + ca
CIz-1011■O) and ettringite (3CaO・
AIzOi・3CaSO. -3211zO) to prevent permeability, but on the other hand, it easily adsorbs carbon dioxide gas and oxygen, which tends to cause deterioration of the hardened material and rusting of reinforcing bars due to neutralization and oxidation. Issues remain regarding long-term durability.

On the other hand, aluminum hydroxide is commercially available for industrial use, and although it looks fine, its plain value is 1.0
It is about 00c+fl/g. If this aluminum hydroxide is used as it is in mortar or concrete, it will not react at all under normal temperature or atmospheric pressure curing conditions, and it will not have the effect of suppressing alkaline aggregate reaction, salt resistance, sulfate resistance, etc. No durability effect was observed at all.

The present invention provides a cement 1 admixture that reduces or prevents alkaline aggregate reactions and improves durability such as salt resistance and sulfate resistance without using conventional blast furnace slag at all.

In order to solve the above problem, the present inventors have conducted intensive studies and found that even aluminum hydroxide, which is usually said to be inert or has little activity, can be used at room temperature or normal temperature if it is used with a specific plain value or higher. The present invention was completed based on the knowledge that it reacts under pressure steam curing conditions, reduces or prevents alkaline aggregate reactions, and improves durability such as salt resistance and sulfate resistance.

Means for solving problems〉 That is,. The present invention is a cement admixture containing aluminum hydroxide as a main component and having a plain value of 3,500 cJ/g or more.

The present invention will be explained in detail below.

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

If the plain value is less than 3,500c+fl/g, the reactivity of aluminum hydroxide is low and there is almost no effect of its use. The finer aluminum hydroxide is, the more effective it is, but industrial crushing and classification techniques have shown that the maximum particle size is 10 to 12μ, and the plain value is 10,
The most preferred is around OOOafl/g, but when economical considerations are also taken into consideration, 4,000 cm/g or more is preferred;
000 to 9,000 cffl/g is more preferable.

The amount of Cement I admixture whose main component is aluminum hydroxide with a plain value of 3,500 afl/g or more is 0.5 parts by weight or more as aluminum hydroxide or more per 100 parts by weight of cement in concrete. It is.

The larger the amount of aluminum hydroxide used, the greater the effect of its use, but if it exceeds 5 parts by weight,
The strength gradually decreases probably due to an increase in the amount of crystalline calcium alumina-1 hydrate, so the amount is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight.

Cement i of the present invention? Cement 1 where F1 Japanese wood is used.
is a mixed cement of various boltland cements such as normal, early strength, super early strength, medium heat, and white, as well as fly ash cement and silica cement.

In addition, various commercially available water reducing agents, AE agents, retarders, accelerators, expansion agents, etc. that are commonly used in the production of mortar and concrete can be used in combination. In particular, it is preferable to use a high-performance water reducer in combination. By lowering the water/cement ratio and increasing the density, it helps reduce or prevent alkaline aggregate reactions and improve durability such as salt resistance and sulfate resistance. do.

A high-performance water reducing agent is a surfactant with a large dispersion ability that does not cause excessive delay in condensation or excessive air entrainment even when added in large amounts, and is a surfactant that does not cause excessive condensation delay or excessive air entrainment even when added in large amounts. These include salts of condensates, high-molecular-weight trignin sulfonates, polycarboxylate salts, etc. as main components.Specifically, for example, Kao Corporation's product name "Mighty 150J", Denki Kagaku Kogyo Co., Ltd.'s product name Examples include rFT-500J and rNL-4000J (trade name) manufactured by Bozoris Bussan.

The amount of high-performance water reducing agent used is not particularly limited, but it is 0.2 to 2 parts by weight of cementite OO in terms of solid content.
Parts by weight are preferred.

In addition, mortar and concrete that use expansive materials,
It is particularly preferable to use the cement admixture of the present invention in combination because the expansion increases the amount of micropores and facilitates the penetration of chloride ions and sulfate ions.

The expansion material is Denka CSA11 manufactured by Denki Kagaku Kogyo ■.
It is broadly classified into ettringite type such as 20 J and lime type such as Onoda Exban manufactured by Onoda Cement ■.

As for the method of adding the cement admixture of the present invention, any of the following methods can be used, such as adding it as a powder when mixing mortar or concrete, dispersing it in mixing water and adding it, or mixing it into cement in advance.

Example The present invention will be explained below with reference to Examples.

Example 1 800 parts by weight of cement, 1 part by weight of sand. Using a mortar formulation of 600 parts by weight, 8 parts by weight of water reducing agent, and 320 parts by weight of water,
The plain value of aluminum hydroxide was varied and the amount added to 100 parts by weight of cement was varied to prepare mortar, and mortar specimens of 4 x 4 x 16 cm were prepared. Approximately 5 hours after the molding, it was capped and heated to 65°C at a rate of 15°C/hr.
The mixture was kept as it was for 4 hours, the steam valve was shut off, and the mixture was allowed to cool naturally in a steam curing tank. The next day, the mold was removed and immersed in a 3% NaCl aqueous solution to quantify the amount of chlorine permeation at each material age. Table 1 shows the results.
Shown below.

Although aluminum hydroxide is for industrial use, it does not contain a large amount of impurities that would affect the amount added, and the total amount of aluminum hydroxide was added by replacing the weight with sand.

The plain value was measured using a specific gravity of aluminum hydroxide of 2.43 (air comparison type hydrometer) and a borosity of 0.50. However, if the powder was too fine to be compressed to the volume of the bed, the porosity was increased so that the powder could be compressed to the volume of the bed.

Furthermore, for the determination of chlorine, the central part of the specimen that had reached the material age was
X4X1cn+ was cut out, dried at 300°C, and the entire amount was pulverized, and subjected to fluorescent X-ray analysis. For reference, the compressive strength at 1 day of age was also measured and listed.

<Materials used> Cement: Ordinary boltland cement made by Denki Kagaku Kogyo ■ Sand: Natural sand, river sand from Himekawa, Niigata Prefecture Water reducer: Made by Denki Kagaku Kogyo ■, product name "Denka FT-500J" Water: Drinking water Aluminum hydroxide: Sumitomo Chemical industry ■ Industrial use, white smooth fine powder, Blaine value 870 cffl/g, as is clear from Table 1, if the plain value of aluminum hydroxide is less than 3,500c+a/g, it will not react and chlorine Although no effect was observed in preventing ion penetration, 3
, 500c+ff/g or more, the effect becomes noticeable at 4,00cIi/g or more, and it can be seen that the finer the aluminum hydroxide, the more effective it is.

Also, the higher the amount added, the better the penetration of chlorine is prevented.

Example 2 Experiment No. The 1-day-old mortar prepared in 1-1 to 1-8 was crushed using a brown crusher, and 50g of the 250μ sieve was added to 1L of 3% NazSOa aqueous solution at 72 °C.
After soaking for an hour, filtering and washing with water, it was dried at 200"C, finely pulverized, and the amount of sulfate ions adsorbed was determined by fluorescent X-ray analysis. A blank was obtained from a sample 250μ below, and the amount was subtracted.The results are shown in Table 2.

Table 2 As is clear from Table 2, when the plain value of aluminum hydroxide is 3.5000 Ill/g or more, the adsorption amount of sulfate ions increases, and the larger the plain value, the greater the adsorption amount of sulfate ions. I understand that.

This means that the plain value of aluminum hydroxide is 3,50
A value of 0 cIfi/g or more indicates that even if sulfate ions penetrate, there is an effect of preventing further penetration, suggesting sulfate resistance.

Example 3 Using sand and silica with the particle sizes shown in Table 3, cement 800
Parts by weight, 1,800 parts by weight of sand and silica, and 1 part by weight
1 Using a mortar formulation of 400 parts by weight of an I2 NaOFl aqueous solution,
As in Example 1, an alkaline aggregate reaction test was conducted by changing the plain value of aluminum ξ hydroxide and the amount added to the cement.

Table 3 (%) The specimen was a triple formwork of 4 x 4 x 16 cm, with mortar shaped so that gauge plugs for length change measurement could be embedded at both ends, and 20°C ± 3, R} 180 After curing for 24 hours in a room with a temperature of 40°C ± 2, R} 195% or more, it was removed from the mold and lengthened according to JIS A 1129 for 3 months and 6 months. The amount of expansion of the wood was measured. The results are shown in Table 4.

13 As is clear from Table 4, if the plain value of aluminum hydroxide is less than 3,500cJ/g, there is almost no effect in suppressing expansion, and if it is 3,500c+fl/g or more, the finer the expansion is suppressed. .

It can also be seen that the larger the amount of aluminum hydroxide added, the more the expansion can be suppressed.

Note that R20 in the cement was 0.5%.

Further, aluminum hydroxide was added in parts by weight relative to the parts by weight of the cement mouth OO, and was added to the mortar in proportion to the weight.

The silica used was opalescent silica from Iwo Jima, and the NaOH used was a special grade reagent.

Example 4 Each unit amount of cement, water, sand, crushed stone and water reducing agent was 4
50, 144.820, 1.014 and 6. 75 (
kg/n+'), Gmax is 15mm, Sea is 4
5%, air content is 2.0%, and slump value is 8 ± 2 cm. As shown in Table 5, a concrete specimen of Φ10 x 20 cm was made using aluminum hydroxide and an expanding agent. did.

A specimen that was removed from the mold the next day using the same curing method as in Example 1 (Curing 1), and a specimen that was cured at room temperature until the next day without steam curing and then left in the mold for standard curing for 28 days (Curing 1)
Curing 2) was immersed in a 3% NaCI aqueous solution, taken out after 3 months of age, and the central part of the specimen was cut to Φ10 x 2 cm, and the amount of chlorine ion penetration was determined in the same manner as in Example 1. The results are also listed in Table-5.

Materials used〉 Aluminum hydroxide: Plain value? ．． 000cffl
/g Expanding agent: Product name "Onoda Expan" manufactured by Onoda Cement ■ 15 16 Table 5 <Effects of the invention> When the cement admixture of the present invention is used, it reacts rapidly even under normal temperature and normal pressure steam curing conditions. , various types of durability are improved, and the greater the plain value and the greater the amount added, the more effective the effect is.

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

The base length when measuring restraint expansion is measured using a dial gauge on a uniaxially restrained steel bar before concrete formation.

Claims (1)

[Claims] (1) A cement admixture whose main component is aluminum hydroxide and whose plain value is 3,500 cm^2/g or more.