JP2550093B2 - Conductive cement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a cement used in a field requiring conductivity such as a ground resistance reducing agent and a radio wave absorber.

[Conventional technology and its problems]

To impart conductivity to the cement, conductive powder such as carbon black or conductive fibers such as carbon fibers or steel fibers are added to the cement.

Of these, carbon fibers are preferable because addition of a small amount improves conductivity, but since they are long and bulky, it is difficult to mix and disperse them in cement, and therefore carbon fibers are uniformly dispersed. Moreover, there is a drawback that it is difficult to obtain a hardened cement (Japanese Patent Publication No. 60-45142).

The present invention has been made in view of the above-mentioned drawbacks, and has been made with the object of obtaining a hardened cement having good conductivity in which carbon fibers are uniformly dispersed.

[Means for solving problems]

The present invention is a conductive cement comprising a cement composition containing at least one selected from carbon fiber and an alkali metal carbonate or hydrogen carbonate.

 Hereinafter, the present invention will be described in detail.

The length and the diameter of the carbon fiber in the present invention are not particularly limited, but the conductivity decreases when the length of the fiber becomes shorter, and conversely when the length becomes longer, the dispersibility tends to decrease. The length is preferably 3 to 100 mm. Further, when the fiber diameter becomes large, the dispersion density becomes coarse with the same amount of addition,
The fiber diameter is preferably 50 μm or less because it becomes difficult to uniformly conduct electricity and it is necessary to add a large amount.

The alkali metal carbonate or hydrogen carbonate means lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc., and the above alkali metal carbonate or hydrogen carbonate alone. You may use, and may use 2 or more types.

The cement composition is a mixture of ordinary Portland cement, medium heat Portland cement, early strength Portland cement, ultra early strength Portland cement or Portland cement such as sulfate resistant Portland cement, blast furnace cement, silica cement or fly ash cement. Special cements such as cement, alumina cement, white cement, ultra-rapid cement or expansive cement, or those containing hydraulic substances such as gypsum dihydrate and gypsum hemihydrate as main components.

In order to obtain a conductive cement, carbon fibers, carbonates or hydrogen carbonates of alkali metals and cement compositions are mixed in advance with various mixers, or simultaneously mixed when used as cement paste, mortar or concrete. You may.

The mixing ratio is preferably 6% by weight or less for carbon fiber and 30% by weight or less for alkali metal carbonate or hydrogen carbonate with respect to the cement composition.

If carbon fibers are added in a proportion exceeding 6% by weight, the fibers become dumpling-like, and no improvement in conductivity can be expected. Alkali metal carbonates or hydrogen carbonates have a coagulation / hardening accelerating action, so if they are added in a proportion exceeding 30% by weight, they will coagulate immediately after pouring water and the dispersibility of the fibers will be poor.

As a mixer, for example, a Nauter Kimiser, a V blender, a ball mill, a tilting drum mixer, a product name "Omni Mixer" manufactured by Chiyoda Giken Kogyo Co., Ltd., or the like can be used for uniform mixing.

When using the conductive cement mixed by the above method, it may be kneaded with water as it is and used as a paste, or the conductive cement and fine aggregate may be mixed and used as a mortar. Alternatively, the conductive cement, the fine aggregate and the coarse aggregate may be mixed and used as concrete.

In this case, the kneading machine may be a general one such as a tilting mixer, a mortar mixer, a hand mixer or a forced mixer.

Further, for the purpose of preventing cracks and the like due to drying shrinkage of the hardened cement, it is possible to add quartz, calcium carbonate, silicon carbide, alumina, talc or the like as a hydrated inert powder.

〔Example〕

 Hereinafter, the present invention will be specifically described with reference to examples.

Example 1 Ordinary Portland cement (manufactured by Andes Cement)
To 100 parts by weight, 2 parts by weight of a carbon fiber having a fiber length of 25 mm and a fiber diameter of 15 μm (made by Kureha Chemical Industry Co., Ltd.) and 2 parts by weight of sodium hydrogencarbonate (made by Toyo Soda Co., Ltd.) are mixed and mixed for 3 minutes by an omni mixer. did.

To this, 80 parts by weight of water was added and kneaded with a hand mixer for 5 minutes. The paste was not dumped and the fibers were well dispersed.

In order to use this paste as a grounding resistance reducing agent,
When a hole 50 x 50 cm in height and 70 cm in height was dug in advance and poured into the place where the copper earth rod was embedded, it hardened after 5 minutes and could be backfilled.

Table 1 shows the measurement results of the specific resistance before treatment, after 7 days, after 6 months and after 1 year.

As shown in Table 1, the specific resistance of the cured product was improved and 1
No change was observed after the mosquito year.

Example 2 100 parts by weight of ordinary Portland cement and 2 fiber lengths
2 parts by weight of carbon fiber having a fiber diameter of 15 μm and 5 parts by weight and 1 part by weight of potassium carbonate (manufactured by Nippon Soda Co., Ltd.) were added and mixed for 5 minutes by a V blender. 80 parts by weight of water was added thereto and kneaded with a mortar mixer for 5 minutes.

For comparison, calcium carbonate (Nitto Koka Co., Ltd.), sodium silicate (Tokuyama Soda Co., Ltd.), and potassium hydroxide (Asahi Glass Co., Ltd.) were used in place of potassium carbonate, which is an alkali metal carbonate, for comparison. The same test was carried out when was used.

The one to which potassium carbonate was added did not form a dumpling and the fibers were sufficiently dispersed, but in the case of no addition,
When calcium carbonate, sodium silicate, and potassium hydroxide were used, the fibers became entangled with each other and became dango-like.

Place these pastes in a 4x4x16cm mold and heat
Seven days after the casting at 20 ° C. and a relative humidity of 60%, the specific resistance of the cured product was measured.

When calcium carbonate, sodium silicate, and potassium hydroxide were used instead of potassium carbonate, when potassium carbonate was not added, and when potassium carbonate was not added,
When 6 parts by weight of carbon fiber was added to 100 parts by weight of cement, the specific resistance of the cured product was not improved in any case.

Example 3 In Example 2, 2 parts by weight of a mixture of sodium carbonate (manufactured by Toyo Soda Co., Ltd.) and sodium hydrogen carbonate (manufactured by Toyo Soda Co., Ltd.) in a weight ratio of 1: 1 was added in place of potassium carbonate. The test was conducted and Table 3 was obtained.

[Effect of the Invention] By using the conductive cement of the present invention, there are the following effects.

(1) Carbon fibers can be uniformly dispersed in a hardened cement.

(2) By mixing a small amount of carbon fiber, the hardened cement product can obtain high conductivity.

Claims (1)

(57) [Claims] 1. A conductive cement comprising a cement composition containing carbon fiber and one or more selected from carbonates or hydrogencarbonates of alkali metals.