KR100328539B1 - Heat emitting cement mortar or concrete composition, heating element and preparation method thereof - Google Patents

Abstract

PURPOSE: A heat emitting cement mortar or concrete composition, a heating element and its preparation method are provided, to obtain a cement heating element having a suitable electrical resistance without using expensive carbon fiber or a large amount of graphite as a conducting material and a water-reducing agent. CONSTITUTION: The heat emitting cement mortar or concrete composition comprises the powder comprising 100 parts by weight of Portland cement and 35-90 parts by weight of crystalline graphite; and 10-35 wt% of water based on the total weight of the powder. Preferably the graphite is amorphous graphite, has a particle size of 0.5 mm or less and/or has a purity of 70-90%. The heating element is prepared by pressure compression molding the composition with a pressure 10-80 kg/cm2 or vibration compression molding the composition with a frequency of 10-30 Hz and a pressure of 5-10 kg/cm2.

Description

Pyrogenic cement mortar or concrete composition, heating element and method of manufacturing the same

The present invention relates to a pyrogenic cement mortar or concrete composition for compression or extrusion, a cement heating element using the same, and a method of manufacturing the same. Specifically, a pyrogenic cement mortar or concrete composition suitable for compression or extrusion molding obtained by adding a certain proportion of graphite and water to hydraulic cement, and a method for producing a cement heating element by pressure compression molding, vibration compression molding or extrusion molding the composition. And it relates to a cement heating element produced by the method.

Cement mortar or concrete combines strength and durability and has long been used as a building material. However, with the changes of the times and the development of technology, various kinds of concrete products are required for new purposes. Currently, concrete, ready mixed concrete, prepacked concrete, prestressed ) Concrete, lightweight concrete, foamed concrete, soil concrete, electrically conductive concrete, etc. have been developed, produced and marketed, and their application fields are gradually expanding.

In general, cement mortar or concrete is known as an insulator because the electrical resistance is higher than 10 ⁸ Ω cm. As described above, attempts have been made to make conductive cement mortar or concrete by mixing a conductive material with a non-conductive cement mortar or concrete to lower electrical resistance. For example, Japanese Patent Application Laid-Open No. 61-l7845l The publication discloses conductive concrete in which conductive regenerated cellulose fibers are mixed, and Japanese Patent Laid-Open No. 63-2l5542 discloses conductive fiber-reinforced concrete in which reinforcing fibers, aggregates, synthetic resins or rubbers are mixed in addition to conductive fibers.

As an example of using carbon fiber as a conductive material, Japanese Laid-Open Patent Publication No. 64-10583 discloses conductive concrete obtained by using and mixing twisted carbon fibers in combination with conductive fine powder carbon such as graphite or carbon black. Japanese Unexamined Patent Publication No. 64-l4l37 discloses conductive concrete containing curved carbon fibers, and Japanese Patent Laid-Open Publication No. 64-72947 discloses conductive concrete containing carbon fibers and alkali metal carbonates or hydrogen carbonate salts. have. Japanese Unexamined Patent Application Publication No. 3-l74342 discloses a conductive inorganic cured body in which carbon whisker is mixed as a conductive material.

However, the above-mentioned conductive concretes are conductive concretes suitable for use as a ground resistance reducing agent, a radio wave absorber or an antistatic building material, and have not been used as a building material for heating.

Regarding heating applications, Korean Patent Publication No. 96-7495 discloses a conductive cement composite suitable for use as a finishing or panel for heating, but in this method a cement containing graphite powder of 0.1-0.l5 in weight ratio is used. The conductive cement composite material is obtained by adding carbon fiber 0.005-0.45, extrusion aid 0.005-0.02, and water 0.3-0.4 to a binder. On the other hand, Korean Patent Publication No. 96-37598 discloses 100-400 parts by weight of at least one selected from earthy graphite, impression graphite and artificial graphite as conductive material with respect to 100 parts by weight of binder and naphthalene-based, melamine-based or lignin-based flow. A conductive mortar and concrete composition is disclosed, in which 0.5-0.2 parts by weight of fire is added.

However, as described above, it can be seen that most conventional techniques for conductive concrete use carbon fiber as the conductive material, which is not only expensive but also poor in compatibility with cement and uniform. The disadvantage is that it is difficult to obtain one concrete composition. In addition, in the case of Korean Patent Publication No. 96-37598, although graphite is used only as a conductive material without using carbon fiber, a large amount of graphite should be used in an amount of 100 to 400 parts by weight based on 100 parts by weight of cement. In order to improve the miscibility of graphite with cement, a fluidizing agent is required.

The final molded product obtained by molding the exothermic cement mortar or concrete composition is preferably as low as possible porosity and evenly distributed pores. It is the water content that affects the pores of the final molded body. When manufacturing a conventional cement mortar or concrete composition, a large amount of water is used. When a large amount of water is used, the porosity of the final molded article is large and the distribution of pores becomes uneven. Therefore, in order to reduce such a problem caused by the use of a large amount of water, there was a disadvantage in that an additional reducing agent was used.

The object of the present invention is to produce a cement heating element having a suitable electrical resistance as a heating element, without using expensive carbon fiber or a large amount of graphite as a conductive material, and without using a water reducing agent, unlike the prior art. To provide a suitable pyrogenic cement mortar or concrete composition.

Still another object of the present invention is to provide a method for producing a cement heating element having low porosity, uniform porosity, and excellent strength and durability from the composition.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a photograph of a fracture surface (A) and a polishing surface (B) of a pyrogenic cement mortar or concrete composition heating element of the present invention produced by pressure compression molding.

Fig. 2 is a photograph of the fracture surface A and the polishing surface B of the exothermic cement mortar or concrete composition heating element produced by the extrusion molding method.

The present inventors compress or extrude a pyrogenic cement mortar or concrete composition made by adding 10 to 35% by weight of water to a raw material powder containing 100 parts by weight of hydraulic cement and 35 to 90 parts by weight of graphite. The present invention has been completed based on the fact that molding can yield cement mortar or concrete heating elements.

Hereinafter, the present invention will be described in detail.

The composition of the present invention is a pyrogenic cement for compression or extrusion molding made by adding 10 to 35% by weight of water to a raw material powder containing 100 parts by weight of hydraulic cement and 35 to 90 core parts of graphite. Mortar or concrete composition.

The hydraulic cement used in the present invention refers to a single cement and a mixed cement, and the single cement includes hydraulic lime, Rooman cement, natural cement, Portland cement, alumina cement, and the like. Fly ash cement, masonry cement, expandable cement, colored cement, and the like. The hydraulic cement serves as a binder for providing strength and durability to the cement heating element obtained by molding the composition of the present invention.

The cement used in the manufacture of hydraulic cement mortar and loncrete heating elements as binders has an abnormal condensation or even a little condensation, which increases the amount of compounding and causes initial cracking, thereby affecting the strength of the heating element mortar or concrete composition heating element. Get mad. That is, since the change in the quality of the cement due to moisture and weathering affects the strength of the exothermic cement mortar or the concrete composition heating element, the cement stored in a waterproof, moisture-proof and unaffected by sunlight and ventilation is used.

The composition of the present invention contains 35 to 90 parts by weight of graphite with respect to 100 parts by weight of cement, which serves to reduce electrical resistance of hydraulic cement mortar or concrete, which is a nonconductor, to impart conductivity. Graphite used in the composition of the present invention must be added to the hydraulic cement in a range not only uniformly mixed with the hydraulic cement, but also adjusted to a range that does not significantly affect the strength and exothermic properties. Since the composition of the present invention is molded into a heating element through a compression or extrusion method, there is an advantage that good conductivity can be obtained even if a small amount of expensive graphite is used as compared with the conventional molding method. In the above composition of the present invention, when the blending ratio of graphite is less than 35 parts by weight, the strength of the heating element after molding is increased, but the conductivity is extremely lowered. The case does not require high conductivity and the strength is greatly reduced, making it unsuitable for the production of heating element products.

Graphite used in the composition of the present invention includes earthy graphite, impression graphite or artificial graphite. In the case of earth graphite, it is 60-90 weight part, Preferably it is 70-80 weight part, and in the case of impression or artificial graphite, it is 35-60 weight part, Preferably it is 40-50 weight part.

The graphite used in the present invention is preferably a powder finely ground to a particle size of 0.5 mm or less. If the particle size of the graphite is large, since it is added unevenly to the hydraulic cement, there is a disadvantage that the exothermic temperature is different depending on the position in the cement heating element obtained by molding. In addition, when the coarsely pulverized graphite powder is used to increase the strength of the cement heating element, the specific surface area may be drastically reduced, and thus, it may be impossible to provide a passage through which electricity can pass through the cement heating element, resulting in poor heat generation characteristics. .

In addition, the graphite used in the present invention is known to vary in purity depending on the region to be produced and the method of producing artificial graphite. Since the purity change of graphite also affects the exothermic properties and manufacturing cost of hydraulic cement mortar and concrete heating element, the purity of graphite used must be adjusted. For this purpose, the purity of the graphite used in the present invention is preferably 70-99.9%, and the purity of the earth-based graphite is 70-90%, and the graphite is 95-99.9%.

In the composition of the present invention, a small amount of water is used in an amount of 10 to 35% by weight based on the raw material powder, which serves to exert strength and durability of the cement and to uniformly mix the raw material powder. Water used in the present invention is clean water without any particular taste, color, turbidity, etc., and does not contain harmful components that adversely affect the quality of the molded cement heating element. When the mixing ratio of water is less than 10% by weight, cement and graphite are not mixed well, and thus, it is not possible to obtain a uniform cement mortar or concrete composition, and the workability and the minimum amount of water required for hydration of cement are lowered. And, if it exceeds 35% by weight there is a disadvantage that a lot of pores after molding is reduced the electrical conductivity. The preferred mixing ratio of water depends on the molding method, the pressure compression molding method is 10-20% by weight based on the raw material powder, the vibration compression molding method is 15-25% by weight, and the extrusion molding method is 25-35% by weight.

The composition of the present invention may further contain additives such as binders, antifoams, reinforcing agents, lubricating release agents and the like, in addition to cement, graphite and water, which additives facilitate the production of cement heating elements. Specifically, the binder may be polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic emulsion, starch, etc., and the antifoaming agent may be a polyether, silicone compound amide, silicone compound metal soap compound. Lubricant release agents include wax emulsions, stearic acid emulsions and higher fatty acid esters. As a reinforcing agent to increase the strength of the cement heating element obtained by molding, glass fiber, glass fiber net or polypropylene fiber is suitable. Glass fiber of 10-25 mm size is suitable, and glass fiber net is 3/8 -2 inch mesh fiberglass mesh is suitable.

Hereinafter, the method of manufacturing a cement heating element using the composition of this invention is demonstrated. These shaping | molding methods are demonstrated concretely as follows.

First, the compression compression molding method is the most numerous and the most commercially available molding method. The cement paste is formed by using an adhesive method of manually molding cement paste, a punch press, a ram press, or the like. The hydraulic press method for compressing in the air is the most used. The pressure compression molding method used in the present invention corresponds to a wet hydraulic press method. In the pressure compression molding method of the present invention, 10-20 wt% of water is added to the raw material powder to which graphite is added to the cement, and then uniformly mixed with water, and the resulting cement paste is filled into a mold to apply a molding pressure of 10-80 kg / cm2. do. In demolding, in order to prevent the surface of the molded body from becoming equal, it is demolded for several minutes, for example, for 1 minute. The mold of the present invention, the inner wall of the mold should be highly polished to prevent deformation caused by the press molding pressure, and the chrome-carbon steel mold is heat-treated to use a material having a Rockwell hardness of C _55-92 value do.

The vibration compression molding method is a molding method for pressurizing while applying vibration by installing an air hammer, a hydraulic hammer, and an eccentric vibrator in the upper or lower mold. Variables affecting uniform filling of vibration compression molding include frequency, amplitude, and acceleration load. In the present invention, a molding machine equipped with an electric vibrator having a frequency of 10 to 30 Hz and an amplitude of at most 5 mm is preferably used. The vibratory compression molding method has an advantage that the cement heating element can be manufactured at a lower molding pressure than the pressure compression molding method because the raw powder can be vibrated at the low molding pressure to close the raw material powder compared to the pressure compression molding method. The vibration compression molding machine used in the present invention is a method of pressurizing the upper mold while applying vibration by vibrator of the upper mold side, and cement paste obtained after uniformly mixing water by adding 15 to 25% by weight to the raw material powder. To a mold and pressurized for 1 to 5 minutes at a low molding pressure, such as 5-10 kg / cm 2 depending on the size of the molded body.

The extrusion method is a method of pressing and pushing into a hole of a suitable shape to obtain a molded body of various shapes, it is a molding method commonly used to produce a building tile or clay refractory. Types of the extruder include a piston type extrusion machine and an auger type extrusion machine, and industrially an auger type extrusion machine is mainly used. The extruder used in the present invention is an auger type extruder, and the opening ratio (introduction area / discharge area) of the extrusion die is preferably 1-4. If the aperture ratio is less than 1, the pressure is too low to be molded, and if the aperture ratio exceeds 4, cracks may occur due to excessive pressure, which is undesirable. The extrusion pressure may be increased or decreased depending on the shape of the discharge portion. As the extrusion aid, PVA, methyl cellulose, carboxy cellulose binder may be used to express strength of the molded article, and propylene glycol, glycerin, etc. may be used to obtain reversibility and plasticity. In order to impart lubricity between particles, paraffins, esters, vegetable oils and the like may be used as lubricants. In the extrusion method of the present invention, water is added in an amount of 25 to 35% by weight based on the raw material powder, uniformly mixed, and then molded.

In the present invention, the composition of the present invention suitable for compression or extrusion molding is mixed and then subjected to pressure extrusion, vibration compression molding or extrusion molding to obtain a cement heating element having good conductivity and low porosity. The cement heating element obtained by the molding method of the present invention has a specific resistance of 0.5-80 Ω cm and a compressive strength of 100 kg / cm 2 or more. The cement heating element of the present invention obtained by the pressure compression molding method has a specific resistance of 0.5 to 50 Ω cm, and the cement heating element of the present invention obtained by the vibration compression or extrusion molding method has a specific resistance of 20 to 80 Ω cm.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the technical scope of these examples.

<Example 1>

Finely ground earth graphite having a purity of 80% was obtained to obtain earth graphite having a particle size of 0.5 mm or less. After adding 70 parts by weight of the obtained earth graphite to 100 parts by weight of Portland cement, the mixture was put in a plastic bag and shaken for 1 to 3 minutes to mix well. Raw powder was obtained. 15 wt% of water was added to the raw material powder and mixed to obtain the exothermic cement mortar or concrete composition of the present invention. Here, the mixing process used mixers, mixing vessels and paddles complying with the provisions of 2.1, 2.2 and 2.3 of "Mechanical Mixing Method of Hydraulic Cement Dough and Mortar" as defined in KS L 5109.

The mixing method was performed as follows.

First, the raw material powder was mixed into a plastic bag, shaken, and the first mixed raw material powder was transferred to the mixing container, and water was added in a weight ratio to the raw material powder by 15%. After the mixing vessel containing the raw material powder was attached to the mixer, the mixer was started and mixed at the first speed for 60 seconds. The mixer was stopped for 15 seconds, and the raw powder adhering to the mixing vessel was scraped and collected again. Mix for 30 seconds into the second speed. After the mixing, the raw material powder adhering to the mixing paddle and the mixing vessel was scraped off.

<Example 2>

The earth graphite was finely ground to obtain earth graphite having a particle size of 0.5 mm or less. 80 parts by weight of the obtained earth graphite and 1 part by weight of methyl cellulose were added to 100 parts by weight of Portland cement, which was then placed in a plastic bag and shaken for 1 to 3 minutes to obtain a well mixed raw powder. To this raw material powder, 33% by weight of water was added and mixed to obtain the exothermic cement mortar or concrete composition of the present invention. Here, an omni mixer was used when water was added to the raw material powder and mixed.

<Example 3>

The composition obtained in Example 1 was placed in a molding machine equipped with an electric vibrator having an amplitude of up to 5 mm and a frequency of 30 Hz, followed by vibration pressure molding by applying molding pressure at 5 kg / cm 2, immediately demolding and atmospheric curing. The cement heating element of the present invention was obtained.

After the copper electrode was crimped | bonded by the screw by the both ends of the obtained heating body, the copper electrode was closely adhered to the heating body, and electrical resistance was measured by the 4-probe method using the Milio ohmmeter (Hewlett packard model 4338B). The cement paste mixed by the mixing process of Example 1 was measured in accordance with the method specified in KS L 5105 "Test method for compressive strength of hydraulic cement mortar" except for the specimen preparation method.

The specific resistance of the gal and the cement heating element obtained in this example was 31.2 Ω cm, and the compressive strength was 145 kg / cm 2 for 7 days.

<Example 4>

After filling the composition of the present invention prepared in Example 1 with a manual hydraulic molding machine produced at 50 x 50 mm in width and length, the molding pressure is slowly raised to 10 kg / cm 2, and the pressure generated inside the molding specimen is uniform. Pressurized compression molding was maintained for 1 minute at the molding pressure to be distributed. The molded specimens were demolded immediately after molding to cure the atmosphere, thereby obtaining a cement heating element of the present invention.

The specific resistance and the compressive strength were measured in the same manner as described in Example 3. As a result, the resistivity of the cement heating element obtained in this example was 23.8 Ω cm, and the compressive strength was 7 days and 124 kg / cm 2.

Example 5

The cement heating element of the present invention was obtained in the same manner as in Example 4 except that the molding pressure was applied to 40 kg / cm 2.

The specific resistance and the compressive strength were measured in the same manner as described in Example 3. As a result, the specific resistance of the cement heating element obtained in this example was 4.16 Ω cm, and the compressive strength was 7 days at 183 kg / cm 2.

A photograph of the fracture surface and the polished surface of the heating element obtained in this example is shown in FIG. As shown in Figure 1, there is no pores and it can be seen that the graphite added as a conductive material is in close contact with the hydraulic cement.

<Example 6>

The cement heating element of the present invention was obtained in the same manner as in Example 5, except that 15 wt% of water was added to the raw material powder to which 100 parts by weight of portpane cement and 90 parts by weight of earthy graphite were added.

The specific resistance and the compressive strength were measured in the same manner as described in Example 3. As a result, the specific resistance of the cement heating element obtained in this example was 1.83 Ω cm, and the compressive strength was 7 days at 179 kg / cm 2.

<Example 7>

The cement heating element of the present invention was obtained in the same manner as in Example 4 except that the molding pressure was applied to 80 kg / cm 2.

The specific resistance and the compressive strength were measured in the same manner as described in Example 3. As a result, the specific resistance of the cement heating body obtained in this example was 2.54 Ω cm, and the compressive strength was 7 days at 223 kg / cm 2.

<Example 8>

The composition of the present invention prepared in Example 2 was placed in an auger-type extrusion machine, and the opening ratio (introduction area / discharge area) of the extruder die was extruded to 4 to be molded into a pipe shape having a diameter of 20 mm. The molded specimen was air cured to obtain a cement heating agent of the present invention.

Resistivity and compressive strength were measured in the same manner as described in Example 3, except that specimens having a size of 2 cm in diameter and 3 cm in height were used. As a result, the resistivity of the electrical resistance heating cement heating element obtained in this example was 39 Ω cm, and the compressive strength was about 127 kg / cm 2. A photograph of the fracture surface and the polished surface of the heating element obtained in this example is shown in FIG. 2. As shown in FIG. 2, no pores exist and graphite added as a conductive material is well adhered to the hydraulic cement.

As can be seen from the above, according to the present invention, it is suitable as a heating element through extrusion or compression molding, without using expensive carbon fiber or a large amount of graphite as a conductive material, and without using any admixture such as a water reducing agent. A pyrogenic cement mortar or concrete composition suitable for producing a cement heating element having a degree of electrical resistance can be obtained.

In addition, by vibrating compression molding, pressure compression molding or extrusion molding the composition of the present invention, as shown in Figures 1 and 2, it is possible to obtain a cement heating element having a low porosity, uniform pores, and excellent strength and durability.

Cement heating elements obtained by the composition of the present invention is ① heating-related heating elements, such as residential buildings and accommodations, heating systems and devices, ② heat storage electric water heater, kitchen range, electric stove, radiator, water heater, heating pipe, electric iron, warmer Industrial heating-related heating elements such as heating elements, heating systems and devices, ③ drying chambers for drying cigarettes and peppers, electric stoves for making bricks and tiles, heating elements for glass fiber manufacturing, various liquid heaters, heating devices for photographic equipment, industrial heating pipes, etc. Heating elements related to heat generation, heating systems and devices, ④ heating elements for road traffic, heating systems and heat generation such as airport runways, icing eliminators in docks around ship ports, ramps for underground parking garages, roads in snowy areas, and heat generators for train rails Appliance, ⑤ car garage, rural house, plastic house It can be applied to building heating elements, heating system and heating equipment such as heating system, freezing plate of refrigerator floor for fish storage warehouse, heating plate for roof, electric slab for bathroom, heating element for winter farm, etc. It can also be used for prevention and electromagnetic shielding.

Claims (11)

An exothermic cement mortar for compression or extrusion molding, comprising adding 10 to 35% by weight of water to a raw material powder containing 100 parts by weight of Portland cement and 35 to 90 parts by weight of soil or impression graphite. Or concrete composition. The composition of claim 1 wherein the graphite is earthy graphite. The composition of claim 2 wherein the particle size of the graphite is 0.5 mm or less. The composition of claim 2 wherein the graphite has a purity of 70-90%. The composition of claim 1, further comprising at least one additive selected from the group consisting of a binder, an antifoaming agent, a reinforcing agent, and a lubricating release agent. To a raw powder containing 100 parts by weight of Portland cement and 35 to 90 parts by weight of soil or impression graphite, exothermic cement mortar or concrete composition comprising the addition of 10-20% by weight of water to the total weight of the raw material powder A method for producing a cement heating element comprising press-molding at a molding pressure of a filling seeker of 10-80 Kg / cm 2. To a raw powder containing 100 parts by weight of Portland cement and 35 to 90 cores of soil or impression graphite, a pyrogenic cement mortar or concrete composition comprising the addition of 15 to 25% by weight of water to the total weight of the raw material powder is subjected to a frequency of 10 A method for producing a cement heating element comprising vibration compression molding at 30 Hz and molding pressure of 5-10 Kg / cm 2. Extruded exothermic cement mortar or concrete composition comprising 100 parts by weight of Portland cement and 25 to 35 parts by weight of water based on the total weight of the raw material powder to 35 to 90 parts by weight of soil or impression graphite. A method for producing a cement heating element comprising extrusion molding the die opening ratio (introduction area / discharge area) as 1-4. Cement heating element having a specific resistance of 0.5 to 50 Ω cm prepared by the method of claim 6. Cement heating element having a specific resistance of 20 to 80 Ω cm prepared by the method of claim 7. Cement heating element having a specific resistance of 20 to 80 Ω cm prepared by the method of claim 8.

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