JPH0339032B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a cement molded body, and more particularly, to a method for manufacturing a highly durable cement molded body having a metal oxide coating on its surface. Surface-decorated cement molded products are already known, in which an inorganic paint or glaze is baked onto the surface of a cement molded product, but since cement molded products generally contain water and are hydraulic, they cannot be heated to high temperatures. When this occurs, the moisture contained inside the material evaporates, causing contraction and significantly reducing its mechanical strength. On the other hand, thermal spray coating is generally a method of spraying metal oxides or other ceramic materials in a hot molten state onto the surface of the adherend to bond them. However, when this method is applied to cement molded bodies, the surface of the molded body is heated to high temperatures. Generally, as mentioned above, a large number of microscopic cracks occur in the base of the cement molded product, resulting in an unavoidable decrease in strength. Obtaining cement compacts was seen as difficult. The present invention has been made in order to solve the above-mentioned problems, and it is possible to thermally spray metal oxide onto a cement molded body without causing cracks in the base of the molded body, and to firmly adhere the metal oxide particles to the surface. An object of the present invention is to provide a method for manufacturing a cement molded body with excellent durability. The method for producing a cement molded body of the present invention includes drying at least the surface layer of the cement molded body to a moisture content of 2% or less before the cement molded body is completely hardened.
It is characterized by spraying metal oxide particles onto the surface to form a metal oxide coating, followed by hydration and curing. In the method of the present invention, the cement compact is a cement mixture obtained by mixing a hydraulic inorganic material such as Portland cement or alumina cement with water and, if necessary, aggregate, filler, fiber, etc. It is obtained by molding into the desired shape, and the aggregate is usually sand, lightweight aggregate, siyamoto, etc.
As the filler, slag, clay, fly ash, etc. are used, and as the fiber, asbestos, glass fiber, vinylon fiber, pulp fiber, etc. are used, but the present invention is not limited to these. According to the method of the present invention, the cement molded body to be thermally sprayed must be hardened at least to the extent necessary for the thermal spraying operation, but not completely hardened. Here, "completely hardened" usually means that it has a final strength after 4 weeks of curing, and in the present invention, preferably, the thermally sprayed cement molded product has a strength that is higher than the above 4-week strength. If the strength is 70% or less of that value, this is considered to be before it is completely cured. As described above, if the cement molded body has a strength of 70% or less of the 4-week strength, it is usually possible to thermally spray coat the surface of the molded body with a metal oxide with good adhesion, but it is particularly preferable that the strength is 50% or less. As described above, after adjusting the degree of hardening of the cement molded body, according to the present invention, at least the surface layer on the side to be thermally sprayed is dried so that the moisture content becomes 2% or less. Such drying can be performed, for example, by heating the surface with an infrared heater. Detailed experimental results have shown that, in particular, the sprayed surface should be coated with a moisture content of 2 mm over a thickness of at least 2 mm.
Good results are obtained when drying below %. In the method of the present invention, metal oxides such as alumina, zirconia, etc. are used as the spray material. Glass powder and glaze frit do not adhere well to the surface of cement molded bodies and are not suitable for use. The metal oxide is preferably thermally sprayed by gas plasma spraying or water plasma spraying, which can be thermally sprayed at a high temperature. According to this thermal spraying, metal oxides are
It is heated to over 1000°C and forms a highly adhesive coating on the surface of the cement compact in its molten state. The thickness of the thermal spray coating is usually 10~2000μ, preferably 30~
It is 500μ. If the thickness of the coating is too thin, the effect of the coating will not be sufficient, while if it is too thick, it will be uneconomical and distortion will occur in the sprayed coating, which is not preferable. After spraying the metal oxide onto the surface of the cement molded body in this way, the molded body is hydrated and cured using a normal method, thereby making it possible to obtain a surface-decorated cement molded body with excellent durability. . This hydration regimen, as long as the necessary water is supplied,
The method is not particularly limited, and for example, it may be carried out under pressure in water, steam, or in an autoclave. As described above, although the reason is not clear, the method of the present invention adjusts the degree of hardening of the cement molded body and dries the water content of at least the sprayed side surface to a predetermined value or less. Even when sprayed at high temperature, no cracks occur on the cement molded body base, and the resulting metal oxide coating firmly adheres to the surface of the molded body, making it possible to create surface-coated cement molded bodies with excellent durability. Obtainable. In addition, in the method of the present invention, at least the surface layer on the sprayed side of the cement molded body is dried as described above, and at least the surface layer on the sprayed side is further coated with a good thermal conductor material such as copper powder or carbon fiber. By dispersing it, the high heat that the molded object receives during thermal spraying is diffused, and rapid volume changes in the surface layer are prevented, resulting in a thermally sprayed metal oxide coating with even better adhesion and durability. can be formed. Examples of the present invention are listed below. In each example, the bending strength of the sheet molded product obtained was JIS A.
Measurements were made according to the bending test method for architectural boards according to 1408. Example A Portland cement kneaded material having the composition shown in Table 1 was formed into a sheet with a length and width of 15 cm and a thickness of 6 mm, and the degree of hardening of the sheet and the water content of the surface layer over a thickness of 2 mm on the sprayed side were shown in Table 2. It was adjusted to either H. Here, the degree of hardening is adjusted by interrupting the curing of the molded sheet and comparing its compressive strength with the final strength (4-week strength),

[Table] Next, alumina particles with a particle size of 10 to 50μ are applied to the surface of each sheet using a gas plasma spraying method to a thickness of 100μ.
After that, it was cured for 24 hours in a steam atmosphere at a temperature of 90°C and a humidity of 100%.

【table】

[Table] Also, the water content of the surface layer on the sprayed side is determined by heating and drying the surface on the spraying side with an infrared heater, then taking a 2 mm thick surface layer, heating it at 105℃ for 2 hours, and determining its weight loss. I asked for it. The surface sprayed sheet thus obtained was visually observed for the presence or absence of abnormalities, and its frost damage resistance was evaluated using the ASTM method. In all of the sheets obtained in the examples above, no abnormalities such as cracks were observed in the thermally sprayed coating layers. In addition, all of them had frost damage resistance of 100 cycles or more. On the other hand, as for the comparative example, the 5-I treated product (the cement molded body from the kneaded material of No. 5 in Table 1 was adjusted to have the degree of hardening and surface layer moisture content shown in Condition I of Table 2). The thermal spray coating of the obtained molded product (hereinafter the same shall apply) peeled off, and cracks occurred in the molded product base of the 5-J treated product and the 5-K treated product. Also, 5-I, 5
-J and 5-K treated products have frost damage resistance of 5, respectively.
There were 8 and 8 cycles.

Claims (1)

[Claims] 1. Before the cement molded body is completely cured, at least its surface layer is dried to a moisture content of 2% or less, and after spraying metal oxide particles on the surface to form a metal oxide coating, A method for producing a cement molded body characterized by hydration curing.