JPH0248409B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing cement products, particularly a method for manufacturing highly dense cement products. [Prior Art] Cement products manufactured from hydraulic cement are required to have high strength, excellent durability, and low water permeability. Such a hardened cement body must have a dense internal structure, and if large voids are present, the above-mentioned physical properties cannot be exhibited. The strength of a hardened cement product is related to macropores with a pore diameter of 15 μm or more or capillary voids with a pore diameter of 15 μm to 0.0075 μm, and it is known that the smaller these voids are, the stronger the hardened product will be. (Practical Concrete Technology, page 2, edited by Mori). Therefore, in order to increase the strength, a method is known in which the water-cement ratio is extremely reduced and compression molding is performed under high pressure. For example, Roy, Gouda, and Bobsowsky pressed cement paste at 7000 kg/cm ² with a compressive strength of 3250.
A hardened product of Kg/cm ² was obtained, and a strength of 4200 Kg/cm ² was obtained by hot pressing at 150° C. and 3500 Kg/cm ² (Ceramics 8, [10], 1973, p. 101). On the other hand, as a method for obtaining a high-strength cement molded body, a small amount of water and an organic polymer thickener for imparting plasticity are added to the cementitious raw material, and the mixture is kneaded to form a plastic clay. Methods of wet compaction of soil by compaction or extrusion methods are also known. For example, in Japanese Patent Application Laid-Open No. 52-53927, a low water ratio cementitious composition to which a thickener has been added is mixed in a planetary kneader,
After making a homogeneous dough by high-shear mixing under atmospheric pressure using a batch-type kneader such as a Pui kneader or a Hobart kneader, the dough is fed into a ram-type extruder, deaerated, and left as is.
A method of slow extrusion molding under a high pressure of 13.8 MN/cm ² has been proposed. In addition, Japanese Patent Application Laid-Open No. 56-9256 discloses that the particle size of the cement raw material is reduced to 20 μm or less,
Add a small amount of water and a thickener, and pass repeatedly between the rolls of a twin-roll mill to mix homogeneously to form a dough. This dough is press-formed, and at this time, the dough releases pressure. A method has been proposed in which the pressure is released after hardening has progressed to the extent that it does not relax during the process. Furthermore, Japanese Patent Application Laid-Open No. 56-84349 proposes a method of making the particle size distribution of cement raw materials multimodal using the above two methods. [Problems to be Solved by the Invention] However, as described above, none of the methods of extremely reducing the water-cement ratio and performing compression molding under ultra-high pressure are impractical. Furthermore, the method described in JP-A No. 52-53927 does not provide a dense and high-strength molded product free of macropores. The reason for this is that the kneaded product of a cementitious composition with a low water-to-cement ratio and a thickener added has very high viscosity and low fluidity. (In this case, as long as a batch kneader is used, even under vacuum, voids will be generated.) Macropores cannot be completely removed. In the methods described in JP-A-56-9256 and JP-A-56-84349, it is said that it is desirable to repeatedly knead in a twin roll mill, but if kneading is performed under atmospheric pressure, air is likely to be drawn in and production There is also the problem of low gender. Furthermore, the method of continuing to apply pressure until it hardens for molding is extremely inefficient. Furthermore, it is necessary to use a cement raw material with a special particle size, which makes the production method impractical. [Means for solving the problem] We have solved the above-mentioned drawbacks and have conducted extensive research into a hardened cement material that is high in strength, high density, durability, and water permeability, and a method for producing it with high productivity. In order to eliminate air bubbles and reduce the amount of capillary in the hardened cement, the water-cement ratio should be lower than the theoretical reaction amount, and in the kneading process, a kneaded product consisting only of solid and liquid phases without voids should be obtained. It was discovered that this is essential, and that for this purpose, kneading should be carried out under vacuum degassing using a continuous screw type kneader. Batch-type kneaders such as kneaders involve air bubbles under normal pressure, and even under vacuum, in the case of such kneaders, the raw material is highly viscous (based on the low water-cement ratio above) and has poor fluidity. Because the temperature is so low, the raw material flows behind the rotating blades of the kneader.
If the filling is not completed, a vacuum space is created there, and furthermore, the rotation of these space vanes creates a narrow vacuum space within the raw material, resulting in the formation of a space as well. (These voids are in a vacuum state during kneading.) On the other hand, in the continuous screw type kneader used in the present invention, the raw materials are sent one after another and the kneaded material is under pressure, so It is considered that the above-mentioned voids are not formed. Thus, the present invention provides a novel cement product in which the pores in the hardened product are extremely dense, with no macropores with a pore diameter of 15 μm or more, and with capillary voids (micropores) of 15 to 0.02 μm being less than 2.5% by volume. A method of kneading a raw material obtained by adding a thickener and water to a hardened cement body and a starting material mainly composed of hydraulic cement powder to form a plastic kneaded product, and molding this into a desired shape. 26-100% of the theoretical reaction amount for hydraulic cement
Provided is a method for producing a cement product, which comprises subjecting a raw material to a vacuum treatment to an absolute pressure of 260 mmHg or more and obtaining a plastic kneaded product using a continuous screw type kneader in that state. This high density cement product has a bending strength of 600
Kg/cm ² , the compressive strength reaches 1700Kg/cm ² , and the permeability coefficient is 2×10 ^-15 m/s, 1/1 that of regular concrete.
00, and because there are few capillary voids, it also exhibits excellent freeze resistance. Hydraulic cement includes plain cement such as ordinary Portland cement and special Portland cement, mixed cement with blast furnace slag, fly ash, etc., or alumina cement,
Examples include gypsum, magnesium carbonate, calcium silicate, etc., and these can be used alone or in combination. Furthermore, fillers such as fine silica powder, charcoal, and serpentine powder may be added to the hydraulic cement as necessary. Blended water is an essential component for curing hydraulic cement, and also plays the role of imparting plasticity to the kneaded composition. Mixed water reacts with cement and produces cement hydrate, but if the water-cement ratio exceeds the necessary and sufficient water content (theoretical water content) for hydraulic cement to produce hydrates, excess water will be generated. water evaporates and forms a capillary void. Therefore, in order to obtain a dense cement hardened body without capillary voids, it is necessary that the blended water be less than the theoretical reaction water amount.
The theoretical amount of reaction water in ordinary Portland cement is thought to be 0.38 in water-cement ratio (Neville, Characteristics of Concrete, p. 26). When the water-cement ratio is 0.38 or less, the hardened cement body in which the hydration reaction has progressed to 100% has a structure consisting of unhydrated cement, cement hydrate, and gel voids, and there are virtually no capillary voids. However, if the water-cement ratio is extremely reduced, the kneaded material becomes too hard and the plasticity necessary for molding cannot be obtained. Therefore, it is necessary that the amount of water blended is 26 to 100% of the theoretical amount of water blended. This blended water amount corresponds to a water-cement ratio of 0.10 to 0.38. As mentioned above, if the water-cement ratio is lower than the theoretical water content, the cement mixture tends to have insufficient plasticity, so it is necessary to add a thickener. The thickener mentioned here is an essential component that imparts plasticity to a non-plastic powder such as cement and enables it to be molded by plastic deformation. The thickener is also called a hydro-deforming agent (Japanese Patent Application No. 7134/1989) or a forming aid (Ceramic Manufacturing Process, Vol. 1, Yoichi Motoki, p. 67). As such a thickener, a water-soluble organic polymer having water-retentive properties such as methyl cellulose, polyacrylamide, polyethylene oxide, polyvinyl alcohol, etc. is used. The amount of thickener added is determined in order to impart the necessary plasticity to the kneaded material, but it is 0.5 to 5 parts per 100 parts of cement.
It is desirable that the To enhance impact resistance, organic fibers, e.g.
Polypropylene fibers, vinylon fibers, cellulose fibers, nylon fibers or inorganic fibers such as asbestos, glass fibers, etc. may be added. Raw material powders such as hydraulic cement, aggregates, thickeners, reinforcing fibers, etc. are dry blended using an omni mixer, a Lodeige mixer, etc., and then a predetermined amount of water is added to form a granular mixture. This mixture is charged into a hopper of a continuous screw type kneader, vacuum degassed, and then sent in that state to a kneading section. Only by this operation can a plastic kneaded material (dough) containing no bubbles or voids, that is, consisting only of two phases, a solid phase and a liquid phase, be obtained. There are vacuum extruders and vacuum kneaders as screw-type kneaders that knead while vacuum degassing.
In all of these, a deaeration zone is provided in the center of the kneader, and the raw materials are not deaerated in advance as in the present invention, so air bubbles, etc., once formed are difficult to disappear, resulting in plasticity. It is unavoidable that the kneaded material contains air bubbles. In general, there are two types of kneading or kneading of viscous substances: batch type and continuous type. Batch-type kneading machines include kneader mixers with Z-shaped or sigma-type rotary blades, Banbury mixers, Muller-type mixers, roll mixers, etc., but kneader mixers and Banbury mixers can mix under normal pressure or vacuum degassing. Bubbles or voids are formed in the product, making it impossible to obtain a dense composition. With a Muller type mixer or a roll mixer, kneading under vacuum degassing is difficult due to its mechanism. On the other hand, no matter which continuous screw type kneader is used, such as a clay kneader, auger machine, pack mill, or co-kneader, if the kneading is carried out under vacuum degassing as described above, no air will be taken in, and no voids will be present. A kneaded product is obtained in which no particles are formed. Figure 1 shows an example of a continuous screw type kneader. In the figure, 1 is the hopper, 2 is the cylinder, and 3 is the hopper.
4 is a cooling jacket, and 5 is a die. The interior of the hopper 1 and the cylinder 2 is vacuum degassed through the intake port 6. Furthermore, the inside of the cylinder 2 can be cooled by a cooling jacket 4. The cement mixture thus supplied to the hopper 1 is kneaded in the cylinder 2 by the screw 3 and then extruded through the die 5 to provide a dense cement mixture free of micropores. During kneading, by vacuum degassing the kneaded material and reducing the pressure to a low pressure of 260 mmHg or less, particularly 60 mmHg or less, a remarkable effect can be achieved compared to the case where vacuum degassing (pressure reduction) is not performed. Since heat is generated when cement and water are kneaded at such a low water-cement ratio as described above, it is desirable that the kneader has a structure that allows cooling. For example, when kneading
Since the temperature rises to about 40℃, it is desirable to cool it to about 20℃. As described above, the continuous screw type kneader has the advantage of being superior in kneading productivity compared to the batch type kneader. In order to continuously operate kneading while vacuum degassing,
For example, it is possible to install two or more hoppers and operate them while switching between them for continuous operation without breaking the vacuum. The plastic kneaded material obtained in this way is press-molded,
It is molded into a desired shape by processing such as injection molding or extrusion molding. At this time, the molding pressure or molding time may be the minimum value that gives plastic deformation to the plastic kneaded material, and a particularly large pressure or holding time is not required.
It is also desirable to perform the molding using a molding machine equipped with a vacuum degassing device. Most preferably, kneading and molding are carried out continuously under vacuum degassing using an apparatus having a structure in which a continuous screw kneading machine and a molding machine are integrated and vacuum degassing is performed. In this way, the plastic kneaded material can be directly molded without being exposed to outside air. The molded product thus obtained is cured at room temperature and in a humid air, and then cured with normal pressure steam or high pressure steam to form a hardened product, thereby producing a final product. Examples will be explained below. [Example] Effect of vacuum degassing during kneading Changes in the density and bubble amount of the kneaded product when the degree of vacuum deaeration during kneading is changed, and furthermore, the extrusion-molded uncured product when this kneaded product is extruded Changes in the density and amount of bubbles were investigated under the following conditions. Raw material composition: Ordinary Portland cement 100 parts by weight Methyl cellulose 4 parts by weight (Hi-Metrose 15000 manufactured by Shin-Etsu Chemical Co., Ltd.) Water 18 parts by weight Kneading Continuous screw kneader (MP- manufactured by Miyazaki Iron Works Co., Ltd.)
100) Vacuum deaeration degree (pressure): 760, 460, 260, 30mmHg Molding: Vacuum extruder (PE-75 manufactured by Honda Iron Works) Molding pressure: 30-35Kg/cm ² Molded objects: Width 120mm, length 2000mm, Thickness: 6 mm The density and the amount of bubbles were measured for the kneaded product and the extruded uncured product obtained under the above conditions. At that time, the density was determined by cutting a pea-sized sample, measuring its weight in air (W ₁ ) and its buoyancy (W ₂ ) in water, and using Archimedes' principle to calculate the density using the formula: ρ ^o = W ₁ /
Calculated using W ₂ . The amount of bubbles is calculated from the above density ρ ^o of the sample and the theoretical density ρ ^c calculated from the composition of the raw materials.
Calculated using the formula: (bubble amount)=1- ^ρo / ^ρc . The theoretical density of this blended raw material was calculated from the blending ratio, assuming that the true density of each raw material was 3.19 g/cm ³ of ordinary Portland cement, 1.3 g/cm ³ of methyl cellulose, and 1.0 g/cm ³ of water. The results are shown in Table 1.

[Table] From the results in Table 1, it can be seen that when the degree of vacuum deaeration is -500 mmHg or higher, the density of the kneading machine material and extruded uncured material increases significantly, and the amount of bubbles contained also increases, compared to the case without vacuum deaeration. A drastic decrease can be seen. In particular, by setting the degree of vacuum deaeration to -730mmHg,
A dense molded body consisting only of solid-liquid and containing no air bubbles is obtained. Next, the extruded uncured product was cured by steam curing at 60° C. for 24 hours, and the void volume distribution of the cured product was examined. The pore size distribution of the cured product has a pore size of 15
Measurement was performed by dividing macropores of ~100 μm and micropores of 0.02-15 μm. Macropores with a pore size of 15 to 100 μm were measured by microscopy according to ASTM C-457. Micropores with a pore diameter of 0.02 to 15 μm were measured by mercury intrusion method. In the mercury intrusion method, when a sample is immersed in mercury and the pressure in the mercury is gradually increased, the mercury gradually infiltrates into smaller pores according to the pressure. This is to calculate the pore size distribution. Figure 2 shows the pore size distribution of the extrusion-molded cured products of Comparative Example 1 and Example 1 measured by the mercury intrusion method, and the curve shows the minimum pore size that allows mercury to penetrate without applying pressure to the mercury. Starting from a certain 15 μm pore, the pressure is gradually increased until mercury enters a 0.02 μm pore. In other words, it represents the cumulative value of the pore volume from 15 μm to 0.02 μm. ing. The results are shown in Table 2.

[Table] From Table 2, the pore size distribution of the extrusion-molded cured product is
It is greatly influenced by the degree of vacuum deaeration during kneading, and when the degree of vacuum deaeration is -500 mmHg or higher, it can be seen that the macropores and micropores are significantly reduced compared to the case without vacuum deaeration. In particular, pressure 30mm
Hg has a dense structure in which there are no macropores of 15 μm or more, and micropores of 15 to 0.02 μm exist at only 1.5% by volume. The physical properties of the extrusion-molded cured product were measured. The air-dry water absorption rate was measured according to the method of JIS A5403. The bending strength was measured by performing a three-point bending fracture test on a sample of 6 thickness x 50 width x 200 length (mm) under conditions of a span of 150 mm and a loading rate of 1 mm/min. The hydraulic conductivity was calculated using Darcy's equation using a U.S. Bureau of Reclamation hydraulic conductivity subtractor. Freeze resistance is 300 according to ASTM C666-71.
I checked the cycle. The results are shown in Table 3.

[Table] From Table 3, it can be seen that when the pressure during kneading is 260 mmHg or more, the physical properties of the extrusion-molded cured product are significantly improved compared to the case where vacuum degassing is not performed. In particular, when the pressure during kneading is 30 mmHg, the extrusion molded cured product
For example, the water absorption rate is 1% or less, and the bending strength is 600.
Kg/cm ² or more, compressive strength is 1700Kg/cm ² or more, hydraulic conductivity is 2×10 ^-15 or less, and freeze resistance is good for 300 cycles, making it far superior to conventional cement products. have Comparison of vacuum kneading performed using a continuous screw type kneader and a batch type kneader Density of kneaded materials when vacuum degassing and kneading operations were performed using a continuous screw type kneader and a batch type kneader The changes in the amount of air bubbles and the density and amount of air bubbles of the extruded uncured product when this kneaded product was extruded were investigated under the following conditions. Raw material distribution: White Portland cement 100 parts by weight Polyacrylamide 3 parts by weight (manufactured by Showa Denko) Vinylon fiber 1 part by weight (manufactured by Unitika Kasei Co., Ltd. 2.4 d x 6 m/m) Water 25 parts by weight Kneading: (1) Continuous screw Type kneader (same as Example 2) Vacuum deaeration degree (pressure): 30 mmHg Others: Same as Example 2 (2) Batch type double-arm type kneader (D3- manufactured by Moriyama Seisakusho)
Type 5) Degree of vacuum deaeration (pressure): 30 mmHg Kneading time: 3 minutes Molding: Same as Example 2 Curing: Same as Example 2 Tests or measurements of physical properties: Same as Example 2 The results are shown in Tables 4 to 5. It is shown in Table 6.

[Table] From the results in Table 4, it is clear that when a batch kneader is used, the kneaded product contains many bubbles even under vacuum degassing. It can be seen that substantially no air bubbles were contained when a kneader was used. A similar tendency is also observed for extrusion-molded cured products formed using this kneaded product.

[Table] Values expressed as %.
According to the results in Table 5, the pore size distribution of the extrusion-molded cured product is greatly affected by the type of kneading machine, and in a batch kneader, even if kneaded under vacuum degassing, macropores of 15 μm or more, However, according to the continuous screw kneader, there are no macropores larger than 15μm, and micropores of 0.02 to 15μm can also be kneaded in batches. It can be seen that the decrease is much greater than in the case of airplanes.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, there is a method for manufacturing cement products with high productivity that is extremely dense, has high strength, is highly durable, has high water permeability, etc., without compression molding under high pressure. is provided. Also, as a result, new cement products having such properties are provided.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a continuous screw extruder, and FIG. 2 is a graph showing pore size distribution curves in Examples.

Claims (1)

[Claims] 1. A method of kneading a raw material obtained by adding a thickener and water to a starting material mainly composed of hydraulic cement powder to form a plastic kneaded material, and molding this into a desired shape, The amount of water is calculated based on the theoretical reaction amount for hydraulic cement.
A method for producing a cement product, which comprises subjecting raw materials having a concentration of 26 to 100% to a pressure of 260 mmHg or less and obtaining a plastic kneaded product using a continuous screw type kneader in that state. 2. The method according to claim 1 for cooling a kneader. 3. The method according to claim 1 or 2, wherein the molding is performed using an injection molding machine, an extrusion molding machine, or a press molding machine.