JP2002128552A - Agent for reducing grounding resistance and electrically conductive cement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a agent for reducing grounding resistance capable of uniformly dispersing a carbon fiber into a cement hardened body and obtaining high electric conductivity. SOLUTION: The agent for reducing grounding resistance containing a carbon fiber containing a sizing agent and inorganic salts, and an electrically conductive cement containing the agent and cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cement used in a field requiring conductivity, such as a grounding resistance reducing agent and a radio wave absorber.

[0002]

2. Description of the Related Art In order to impart conductivity to cement, conductive powder such as carbon black and conductive fibers such as carbon fiber and steel fiber are added. Among these, carbon fibers are preferably used because the conductivity is improved by adding a small amount thereof (Japanese Patent Publication No. 60-4 / 1985).
No. 5142).

[0003]

However, since carbon fibers are elongated and bulky, they are mixed and mixed in cement.
There is a problem that it is difficult to disperse and it is difficult to obtain a hardened cement in which carbon fibers are uniformly dispersed.

[0004] In view of the above problems, the present invention has been made with the object of obtaining a hardened cement having good conductivity in which carbon fibers are uniformly dispersed.

[0005]

That is, the present invention is a grounding resistance reducing agent containing an inorganic salt and carbon fibers to which a sizing agent is attached. And it is a conductive cement containing the ground resistance reducing agent and cement.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The carbon fiber of the present invention has a sizing agent attached thereto.

The carbon fibers of the present invention include aramid fibers and carbon fibers. Among these, carbon fibers are preferred in terms of conductivity.

As the carbon fiber, coal tar pitch,
Examples thereof include carbon fibers made from petroleum pitch, coal liquefaction, polyacrylonitrile, cellulose, and the like.

[0010] The length of the carbon fiber is not particularly limited, but if the length of the fiber is short, the conductivity may decrease. Conversely, if the length is long, the dispersibility may decrease. Length (hereinafter referred to as fiber length) is 3 to 100 mm
Is preferable, and 5 to 30 mm is more preferable.

[0011] The diameter of the carbon fiber is not particularly limited, but if the diameter of the carbon fiber is large, the dispersibility becomes poor.
The fiber diameter (hereinafter referred to as fiber diameter) is preferably 50 μm or less, since conductivity may be deteriorated.
μm is more preferred.

The sizing agent of the present invention is to be attached to carbon fibers so that the fibers are bundled and bunched into strands. Examples of the method of attaching the sizing agent to the fiber include a method of spraying with a spray, a method of contacting the fiber with a roller, and a method of impregnation.

Examples of the sizing agent include an epoxy resin, a urethane resin, a polycarbonate resin, a butyral resin, and a nylon resin. Of these, epoxy resins are preferred because of their good convergence and high conductivity.

The amount of the sizing agent used is preferably from 0.3 to 1.2 parts by mass, more preferably from 0.7 to 0.9 parts by mass, per 100 parts by mass of the carbon fibers. If the amount is less than 0.3 parts by mass, the fibers will not be bundled, and it may not be possible to expect improvement in conductivity.
If the amount is more than 0 parts by mass, the fiber becomes a paste, and even when mixed with cement, the dispersibility of the fiber is poor, and there is a possibility that improvement in conductivity may not be expected.

The amount of carbon fiber to which the sizing agent is attached is
0.5 to 6 parts by mass, preferably 1 to 4 parts by mass, based on 100 parts by mass of cement. If the amount is less than 0.5 part by mass, improvement in conductivity may not be expected. If the amount exceeds 6 parts by mass, carbon fibers may be in a dumpling shape, and improvement in conductivity may not be expected.

Examples of the inorganic salts of the present invention include sulfates such as alkali metal sulfates such as potassium sulfate and sodium sulfate, calcium sulfate and the like, and alkali metal hydrogen sulfates such as potassium hydrogen sulfate and sodium hydrogen sulfate. Carbonates such as alkali metal carbonates and calcium carbonate such as potassium carbonate and sodium carbonate, carbonates such as alkali metal bicarbonate such as potassium bicarbonate and sodium bicarbonate, and nitrates such as potassium nitrate, sodium nitrate and calcium nitrate , Potassium chloride, sodium chloride, and calcium chloride; and hydroxides such as potassium hydroxide, sodium hydroxide, calcium hydroxide, and aluminum hydroxide. These inorganic salts may be used alone or in combination of two or more. Among these, sulfates are preferred, alkali metal sulfates are more preferred, and potassium sulfate is most preferred, in that carbon fibers have good dispersibility and conductivity is improved.

The amount of the inorganic salt used is preferably 0.5 to 30 parts by mass, more preferably 1 to 10 parts by mass, based on 100 parts by mass of the cement. If the amount is less than 0.5 parts by mass, the carbon fibers do not disperse, and there is a possibility that improvement in conductivity cannot be expected.
If the amount exceeds 0 parts by mass, the inorganic salt may set and harden too quickly to disperse the carbon fibers, so that improvement in conductivity may not be expected.

The cement of the present invention includes Portland cements such as ordinary Portland cement, moderately heated Portland cement, early-strength Portland cement, ultra-high-strength Portland cement, and sulfate-resistant Portland cement, blast furnace cement, silica cement, and the like. Special cements such as mixed cements such as fly ash cements, alumina cements, white cements, ultra-rapid hardening cements, and expanded cements are exemplified.

The conductive cement of the present invention can be prepared by a method in which carbon fiber, inorganic salt, and cement are previously mixed by a mixer, or a method in which carbon fiber, inorganic salt, and cement are used as cement paste, mortar, or concrete. And a method of mixing a grounding resistance reducing agent containing an inorganic salt with a mixing machine. Examples of the mixer include a Nauta mixer, a V blender, a ball mill, a tilting mixer, and a product name "Omni mixer" (manufactured by Chiyoda Giken Kogyo Co., Ltd.). These mixers can uniformly mix.

The conductive cement mixed by the above method may be used as a paste by directly mixing and kneading with water, or the conductive cement and fine aggregate may be mixed and used as mortar. The conductive cement,
Fine aggregate and coarse aggregate may be mixed and used as concrete. In this case, examples of the kneader include general mixers such as a tilting mixer, a mortar mixer, a hand mixer, and a forced mixer.

Further, in order to prevent cracks due to drying shrinkage of the cured product of the conductive cement, a hydrated inert powder such as quartz, silicon carbide, alumina, and talc may be used.

[0022]

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

EXPERIMENTAL EXAMPLE 1 100 parts by mass of cement, 2 parts by mass of carbon fiber with a sizing agent shown in Table 1 in 100 parts by mass of carbon fiber, 2 parts by mass of inorganic salt, and 80 parts by mass of water were trade names " The mixture was mixed for 3 minutes using an "omni mixer" to prepare a cement paste. The obtained cement paste is 4 cm × 4 cm × 16
cm in a mold, temperature 20 ° C, relative humidity 60
% Cured. Then, the resistivity of the cured body 7 days after the casting was measured. Table 1 shows the results.

(Materials used) Cement: ordinary Portland cement, commercially available carbon fiber: fiber length 25 mm, fiber diameter 15 μm sizing agent: epoxy resin, commercially available inorganic salt: potassium sulfate, commercially available product

(Measurement Method) Specific Resistance: When the cement paste started to set, an electrode (copper earth rod) was inserted into the cured product, and the specific resistance was measured for a predetermined period.

[0026]

[Table 1]

Experimental Example 2 0.8 parts in 100 parts by mass of cement and 100 parts by mass of carbon fiber
The procedure was performed in the same manner as in Experimental Example 1 except that the carbon fiber to which the sizing agent was attached in parts by mass was as shown in Table 2, and 2 parts by mass of the inorganic salt was used. Table 2 shows the results.

[0028]

[Table 2]

Experimental Example 3 0.8 parts in 100 parts by mass of cement and 100 parts by mass of carbon fiber
2 parts by mass of carbon fiber to which parts by mass of the sizing agent were attached, and Table 3
Experimental Example 1 except that the inorganic salt in parts by mass shown in
The same was done. Table 3 shows the results.

[0030]

[Table 3]

Experimental Example 4 0.8 parts in 100 parts by mass of cement and 100 parts by mass of carbon fiber
2 parts by mass of the carbon fiber having the sizing agent attached thereto and 2 parts by mass of the inorganic salt were mixed for 3 minutes by an omni mixer. After mixing, 80 parts by mass of water was added and kneaded with a hand mixer for 5 minutes to prepare a cement paste. The obtained cement paste was not in a dumpling state, and the carbon fibers were sufficiently dispersed. Furthermore, 50cm in height, 50c in width
This cement paste was poured into a hole having a height of 70 cm and a height of 70 cm. After 5 minutes, the cement paste hardened and could be backfilled.
At the time when the cement paste started to set, the electrode was placed on the hardened body at two end portions of the hole (indicated by) and at the center portion of the hole.
(Indicated by). Thereafter, the specific resistance for a predetermined period was measured. Further, before pouring the cement paste (hereinafter referred to as “before treatment”), the specific resistance was measured 7 days, 6 months and 1 year after pouring the cement paste. Table 4 shows the results.

[0032]

[Table 4]

[0033]

The following effects are obtained by using the grounding resistance reducing agent of the present invention. (1) Carbon fibers can be uniformly dispersed in a cured cement body. (2) By mixing a small amount of carbon fiber, the cured cement has high conductivity.

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Claims (2)

[Claims] 1. A grounding resistance reducing agent containing an inorganic salt and carbon fibers to which a sizing agent is attached. 2. A conductive cement comprising the ground resistance reducing agent according to claim 1 and cement.