Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-08-10
2003-08-12
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S675000, C106S676000, C106S679000, C106S681000, C264S333000
Reexamination Certificate
active
06605148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fiber-reinforced cement molded product and a process for its production.
2. Discussion of Background
A mechanism of how freezing damage of a cement molded product occurs is considered, according to “hydraulic pressure theory” by T. C. Powers, that movement of non-frozen water corresponding to the amount of cubical expansion when water freezes into ice generates a hydrostatic pressure due to viscosity resistance, and destroys a structure. In order to prevent freezing damage by this mechanism, a method of introducing a space filled with air in a cement molded product to absorb the generated hydrostatic pressure has been employed. It is known that the effect for preventing freezing damage is high when the amount of the space introduced is large in this method.
As one technique for introducing the space to absorb stress due to the hydrostatic pressure, a method of adding hollow particles may be mentioned (JP-A-08-217561). However, in this method, it is necessary to add a large amount of hollow particles to obtain adequate freezing damage resistance, and there are problems such as decrease in bending strength and decrease in surface smoothness due to aggregation of said hollow particles.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above-mentioned problems of prior art, and it is an object of the preset invention to provide a fiber-reinforced cement molded product which has a high strength and which is excellent in surface smoothness and freezing damage resistance, and a process for its production.
The present invention provides a fiber-reinforced cement molded product which contains from 2 to 15% of hollow particles and from 1 to 40% of an inorganic admixture having pores which open to the surface, and which has a bulk specific gravity of from 0.9 to 1.2.
Here, in the present specification, “%” means percentage by mass and “part” means part by mass, unless otherwise specified. Further, “mean particle diameter” means a median diameter when a particle size distribution is measured, i.e. a mode diameter.
Such a fiber-reinforced cement molded product is excellent in freezing damage resistance, and a product of which has a high strength and a good surface smoothness.
The fiber-reinforced cement molded product of the present invention preferably contains, in addition to the hollow particles and the inorganic admixture having pores which open to the surface, from 5 to 70% in total of cement and/or lime, from 0 to 50% of slag, from 0 to 50% of gypsum, from 20 to 60% of a quartzite powder, from 0 to 20% of microsilica, from 0 to 30% of an inorganic aggregate other than the above components and from 2 to 30% of cellulose fibers.
Further, in the present invention, the hollow particles are preferably inorganic hollow particles having particle diameters of from 20 to 1000 &mgr;m, and the inorganic admixture having pores which open to the surface is preferably a perlite ground powder and/or a cement product ground powder having a bulk specific gravity of from 0.1 to 0.5.
The present invention further provides a process for producing a fiber-reinforced cement molded product, which comprises adding an organic admixture and water to a material mixture containing, as calculated as solid content, from 2 to 15% of hollow particles and from 1 to 40% of an inorganic admixture having pores which open to the surface, followed by mixing to obtain a hydraulic slurry, subjecting said hydraulic slurry to dehydration molding into a predetermined shape to form an intermediate molded product, and subjecting said intermediate molded product into curing.
By employing such a process, a pattern can easily be formed on the surface of said product, and a high strength can be obtained in early stages.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As mentioned above, in the cement molded product, movement of non-frozen water generates a hydrostatic pressure due to viscosity resistance, which becomes a stress to destroy a structure. Namely, the hydrostatic pressure (stress) relates to the degree of resistance during movement of moisture and movement distance (distance to the space for absorption) of moisture. Accordingly, the present inventors have considered to make a structure portion other than the hollow particles have a high water permeability to reduce resistance during moisture movement, in order to reduce addition amount of the hollow particles and in order not to increase the hydrostatic pressure even in a case where the distance to the space for absorption is long.
In the present invention, it is essential that the bulk specific gravity of the fiber-reinforced cement molded product is within a range of from 0.9 to 1.2. If the bulk specific gravity is less than 0.9, the strength of the fiber-reinforced cement molded product tends to decrease, and on the other hand, if the bulk specific gravity exceeds 1.2, the fiber-reinforced cement molded product tends to be hard, and processability tends to be poor.
In the present invention, it is essential that the content of the hollow particles is from 2 to 15%. If the content of the hollow particles is less than 2%, the distance to the space for absorption tends to be long, and movement distance of the non-frozen water tends to be long, whereby the stress can not be reduced, and the freezing damage resistance tends to be poor. If the content of the hollow particles exceeds 15%, the hollow particles are less likely to disperse uniformly in the material, and the surface smoothness tends to decrease due to aggregation, and the strength of the fiber-reinforced cement molded product also tends to decrease.
In the present invention, the purpose of use of the hollow particles is to disperse a space to absorb the stress generated along with freezing of moisture into the material, and to improve freezing damage resistance. Accordingly, it is necessary that the hollow particles themselves do not absorb water and the space in the particles is not filled with moisture, and the hollow particles are required to be completely sealed. As hollow particles which satisfy these conditions, inorganic hollow particles are particularly preferred, and fly ash balloon, glass balloon or volcanic ash balloon may, for example, be mentioned.
The hollow particles are preferably hollow particles having particle diameters of from 20 to 1000 &mgr;m. If the particle diameters of the hollow particles are less than 20 &mgr;m, if the thickness of the shell of the particles is at a level of 10 &mgr;m, the space in the particles disappears, and the particles are not hollow particles but solid particles, and accordingly the freezing damage resistance tends to be poor. Further, even if they are hollow particles, the thickness of the shell of the particles tends to be thin, the strength of the shell tends to decrease, and the particles are likely to be destroyed in a process of producing the fiber-reinforced cement molded product, and accordingly the freezing damage resistance tends to be poor. On the other hand, if the sizes of the hollow particles exceed 1000 &mgr;m, the surface smoothness tends to decrease, such being unfavorable.
In the present invention, it is essential that the content of the inorganic admixture having pores which open to the surface is from 1 to 40%. If the content of the inorganic admixture having pores which open to the surface is less than 1%, no adequate water permeability can be imparted to the structure portion other than the hollow particles, whereby the viscosity resistance tends to increase, and the freezing damage resistance tends to decrease. If the content exceeds 40%, the bulk specific gravity of the fiber-reinforced cement molded product tends to be small, whereby the strength tends to decrease, or the coefficient of water absorption of the fiber-reinforced cement molded product tends to be high, whereby freezing damage resistance tends to decrease.
In the present invention, the inorganic admixture having pores which open to the surface has the follow
Inoue Seiji
Shirakawa Tetsuro
Asahi Glass Company, LImited
Marcantoni Paul
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