JPS6291455A - Cement product and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a cement product and a method for producing the same, particularly a highly dense cement product and a method for producing the same.

[Conventional technology]

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 hardened cement is determined by macrobore with a pore diameter of 1.5 μm or more or with a pore diameter of 15 μm.
It is related to capillary voids of 70.0075 μm, and it is known that the smaller these voids are, the better the hardening and strength of the body will be (Practical, Concrete Technology, page 02, scan line).

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 used cement paste for 7
Compressive strength 32 by strong pressing at 000 kg/ct
A cured product of 50 kg/ct was obtained at 150°C135
00kg/4200kg by own hot press
/ cJ strength (ceramics 8, (
]0'l, 1973.1 old page).

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 to impart plasticity are added to the cementitious raw material, and the mixture is mixed to form a plastic clay. A method of wet molding clay by compression or extrusion is also known. For example, in JP-A-52-53927, a low water ratio cementitious composition to which a thickener has been added is mixed under atmospheric pressure with a batch kneader such as a planetary kneader, a buoy kneader, or a Hobart kneader. After high shear mixing to make a homogeneous clay (F), put it into a ram extruder, deaerate it and leave it at 13.8
A method of slow extrusion molding under high pressure of MN/- has been proposed. In addition, JP-A No. 56-9256 discloses that the particle size of the cement raw material is set to 20 μm or less, a small amount of water and a thickener are added, and the mixture is homogeneously mixed by repeatedly passing between the rolls of a twin roll mill. A method has been proposed in which the clay is press-molded and the pressure is released after the clay has hardened to such an extent that it does not loosen when the pressure is released.

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.

[Problem that the invention seeks to solve]

However, as mentioned above, by making the water-cement ratio extremely small,
Any method of compression molding under ultra-high pressure is impractical.

Furthermore, the method described in Japanese Patent Application Laid-Open No. 5253927-υ cannot produce a dense and high-strength molded article free of macropores. The reason for this is that the kneaded product of cementitious monolithic acid with a low water-to-cement ratio and a thickener added has very high viscosity and low fluidity, so when kneaded with a batch kneader,
This is because air is mixed in under atmospheric pressure and macropores cannot be completely removed (in this case, as long as a batch kneader is used even under vacuum, voids will be formed).

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 problems]

As a result of intensive research into a hardened cement material that eliminates the above drawbacks, has high strength, high density, durability, and water permeability, and a method for manufacturing it with high productivity, we have eliminated air bubbles in the hardened cement material. In order to reduce the amount of capillary, the water-cement ratio should be lower than the theoretical reaction amount, and in the kneading process,
It was discovered that it is important to obtain a kneaded product consisting of only a solid phase and a liquid phase without voids, and that for this purpose, kneading should be carried out using a continuous screw kneader under vacuum degassing.

Hatch-type kneaders such as kneaders involve air bubbles under normal pressure, and even under vacuum, in the case of such kneaders,
Because the raw material has high viscosity (based on the low water-cement ratio mentioned above) and very low fluidity, the raw material flows behind the rotating blades of the kneader and cannot be completely filled, creating a vacuum space. Moreover, the rotation of these spaces results in the creation of narrow vacuum voids within the raw material, which also results in the formation of voids. (This void is in a vacuum state during kneading) On the other hand, the continuous screw type temperature
a. It is thought that the above-mentioned voids are not formed in the kneaded material because the raw materials are sent one after another in the machine and the kneaded material is under pressure.

Thus, the present invention provides a novel cement product in which the pores in the hardened product are free of macropores with a pore diameter of 15 μm or more and contain capillary voids (micropores) with a diameter of 15 to 0.02 μm at 2.5% by volume or less. A method of kneading an extremely dense hardened cement product and 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. In this case, the amount of water is 26 to 26, which is the theoretical reaction amount for hydraulic cement.
A method for producing a cement product is provided, which comprises subjecting a raw material made to 100% to a reduced pressure of -500 mmHg or less and obtaining a plastic kneaded product using a continuous screw kneader in that state.

This high-density cement product has a bending strength of 600 kg/
cJ, the compressive strength reaches 1700 kg/ant, and the hydraulic conductivity is 2 show.

Hydraulic cements include plain cements such as ordinary port 1 to land cement, special portland cement, mixed cements mixed with blast furnace slag, fly ash, etc., or alumina cement, gypsum, magnesium carbonate, calcium silicate. 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 considered 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 to be blended is 26 to 100% of the theoretical amount of water to be blended. The amount of water mixed is 0.10 to 0.
Corresponds to a water-cement ratio of 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. Thickeners are also known as hydro-deforming agents (Japanese Patent Application No. 7134-1983) or forming aids (Ceramic Manufacturing Process, Vol. 1, written by Hiroshi Motoki, 6).
(page 7). 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 the thickener added is determined in order to impart the necessary plasticity to the kneaded material, and is preferably about 0.5 to 5 parts per 100 parts of cement. In order to reinforce impact resistance, organic fibers such as 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, and reinforcing fibers are tri-blended using an omni mixer, Loedige mixer, etc., and then a predetermined amount of water is added to form a granular mixture. This mixture is put into a hopper of a continuous screw 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, the same phase and the liquid phase, be obtained. There are vacuum extruders and vacuum clay kneaders as screw-type kneaders that knead while vacuum degassing, but both of these have a degassing zone in the center of the kneader.
Since the raw material is not degassed in advance as in the present invention, air bubbles, etc. once formed are difficult to disappear, and as a result, it is inevitable that the plastic kneading mixture contains air bubbles.

Generally, there are two types of kneading sections for viscous substances: batch-type kneading units and continuous-type kneading units. . Batch-type kneading machines include kneader mixers, Hanhari mixers, Muller type mixers, roll mixers, etc. that have two-figure or sigma-type rotary blades, but kneader mixers and Hanhari mixers can be used for vacuum degassing even under normal pressure. Even if the kneaded mixture is mixed, bubbles or voids are generated in the kneaded material, and a dense composition cannot be obtained. 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 one of the continuous screw type warm-up machines such as a clay kneader, auger machine, bag mill, or co-kneader is used, if the kneading is carried out under vacuum degassing as described above, no air will be taken in, and no voids will be formed. A kneaded product is obtained in which no particles are formed.

Figure 1 shows an example of a continuous screw kneader. In the same figure, ■ is a hopper, 2 is a cylinder, 3 is a screw,
4 is a cooling jacket, and 5 is a die. The inside of the hopper 1 and the cylinder 2 are vacuum degassed through the intake port 6. In addition, 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 by the die 5.
to provide a dense cement mixture with no micropores.

During kneading, the kneaded material is brought to a vacuum deaeration level of -500 mm Hg or higher, especially -700 mm Hg or higher, by Kokichi.
A significant effect is achieved compared to the case without vacuum degassing.

Since heat is generated when cement and water are kneaded at a low water-cement ratio as described in -1-, it is desirable that the kneader has a structure that allows cooling. For example, during kneading, the temperature rises to about 40°C, so it is desirable to cool it to about 20"C.

As described above, the continuous screw type kneader has the advantage of being superior in kneading ():L productivity compared to the batch type kneader.

In order to perform continuous kneading without vacuum degassing, it is possible, for example, to install two or more hoppers and operate them while switching between them to perform continuous operation without breaking the vacuum.

The plastic kneaded material thus obtained is molded into a desired shape by processing such as press molding, injection molding, and 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.

After the molded product thus obtained is cured at room temperature and in a humid air,
Curing with normal pressure steam or high pressure steam is performed to harden the product and make it into a final product. Examples will be explained below.

〔Example〕

[Shoulder] 1Y'' Soaking - Changes in the density and bubble volume of the kneaded product when the degree of vacuum deaeration during kneading is changed, and also 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 l-100 parts by weight Methyl cellulose 4 parts by weight (HiJ manufactured by Shin-Etsu Chemical Co., Ltd.
) Kano 215000) Water 1
8 parts by weight Kneading: Continuous screw kneader (Miyazaki Iron Works I!!! Liver-10
0) Vacuum deaeration degree: 0, -300, -500, -730+
+m11g Molding: Vacuum extruder (I'E-75 manufactured by Honda Iron Works) Molding pressure: 3
0 to 35 kg/cJ molded product: Width: 120 mm, length: 2000 mm, 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 calculated by cutting a pea-sized sample, measuring its weight in air (Wl) and its buoyancy (W2) in water, and using Archimedes' principle using the formula: ρ' = W, /W2. The amount of bubbles is calculated from the above density ρ0 of the sample and the theoretical density ρ0 calculated from the composition of the raw materials, using the formula: (Bubble amount) - 1 - ρ
Calculated using 0/ρ0. The theoretical density of this blended raw material is
The true density of each raw material is 3.19g of ordinary Portland cement.
/cJ, methylcellulose 1.3g/c+d, water, O
It was calculated from the blending ratio as g/cn.

The results are shown in Table 1.

From the results in Table 1, it can be seen that when the degree of vacuum deaeration is -500mmt1g or less, the density of the kneaded material and the extruded uncured material becomes significantly larger, and the amount of air bubbles contained also becomes significantly larger than when no vacuum deaeration is performed. This is seen to decrease. In particular, by setting the degree of vacuum degassing to -730 mmHg, a dense molded body consisting only of solid-liquid and containing no air bubbles can be obtained.

Next, the extruded uncured product was cured at 60° C. for 124 hours with Fuji air curing, and the distribution of void volume of the cured product was examined. The pore size distribution of the cured product is 15 to 100 μm.
The measurement was carried out by dividing into macropores of 0.02 to 15 μm and micropores of 0.02 to 15 μm. Macropores with a pore size of 15-100 μm were measured by microscopy according to STM C-457. Microbore diameters 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. The amount of mercury that enters a pore with a pore size of 0.02 μm by starting from a certain 15 μm pore and gradually increasing the pressure, that is, the cumulative value of the pore volume from a pore size of 15 μm to 0.02 μm. It represents.

The results are shown in Table 2.

Table 2 Note) The volume percentage of the bore is the value with the volume of the cured body as 100%.

From Table 2, the pore size distribution of the extrusion-molded cured product is greatly influenced by the degree of vacuum deaeration during kneading.
When the temperature exceeds mmHg, it can be seen that the macropores and micropores are greatly reduced compared to the case without vacuum degassing. In particular, at a deaeration degree of -730IIIHg, 15
Macropores larger than μm are zero, and 15 to 0.02
It is a dense Mi weave with only 1.5% by volume of μm microbore.

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 A 5403. The bending strength was measured by performing a three-point bending fracture test on a sample of 6 thickness x 50 medium x 200 length under conditions of a span of 1501 and a loading rate of 1+n/min. The permeability coefficient was calculated from Darcy's equation using a U.S. Bureau of Reclamation hydraulic permeability tester. Freeze resistance was tested up to 300 cycles according to 8STM C666-71.

The results are shown in Table 3.

Below is a list of blank spaces. (1) From Table 3, the degree of vacuum deaeration during kneading is -500m m 1
At 1 g or more, it can be seen that the physical properties of the extrusion-molded cured product are significantly improved compared to the case without vacuum degassing.

In particular, when the degree of vacuum deaeration during kneading is 1730mm11g,
For example, the extrusion molded cured product has a water absorption rate of 1% or less, a bending strength of 600 kg/Cl+ or more, a compressive strength of 1700 kg/d or more, and a water permeability coefficient of 2X10-15.
As shown below, it has good freeze resistance after 300 cycles, and has much superior physical properties compared to conventional cement products.

Changes in the density and air bubbles of the kneaded product when the vacuum degassing and kneading operation was performed with a continuous screw kneader and a batch kneader, and the extruded uncured product when this kneaded product was extruded. Differences in density and amount of bubbles 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 kneader (same as Example 2) Degree of vacuum deaeration: -730 mmHg Others: Same as Example 2 (2) Batch type double-arm kneader (D3 manufactured by Moriyama Seisakusho) -5 type) Degree of vacuum deaeration: -730 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 Table 4~ Shown in Table 6.

Table 4 The results in Table 4 show that when a batch kneader is used, the kneaded product contains many bubbles even under vacuum degassing; however, when a continuous screw kneader is used It can be seen that substantially no air bubbles are contained when using a machine. A similar tendency is also observed for extrusion-molded cured products formed using this kneaded product.

Table 5 (margin below) Note) The volume percentage of pores is the value based on the volume of the cured body as 100%.

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, the pore size distribution of the extrusion-molded cured product is 15 μm or less. Macropores - Contains many micropores of 10.02 to 15 μm, resulting in incomplete degassing. However, according to a continuous screw kneader, there are no macropores of 15 μm or more, and 0.02 to 15 μm. It can be seen that the micropores in the kneader are also significantly reduced compared to the case of the batch kneader.

Table 6 shows that even when kneading is performed under vacuum deaeration, when a batch kneader is used, the physical properties are inferior to when a continuous screw kneader is used. Can be seen.

This difference in physical property values can be seen from the bubble content of the uncured products and the pore size distribution of the cured products shown in Tables 4 and 5.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, cement products that are extremely dense, have high strength, and are rich in durability, water permeability, etc. can be manufactured with high productivity without compression molding under high pressure. A method is provided.

Also, as a result, new cement products having such properties are provided.

[Brief explanation of drawings]

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 cement product characterized in that substantially no pores have a pore diameter of 15 μm or more, and 2.5% by volume or less of pores have a pore diameter of 0.02 μm or more and less than 15 μm. . 2. In a method of kneading a starting material mainly composed of hydraulic cement powder with a thickener and water added to form a plastic kneaded material and molding it into a desired shape, the amount of water is 26-1 of the theoretical reaction amount for hard cement
1. A method for producing a cement product, which comprises subjecting a raw material made to 0.00% to a reduced pressure of -500 mmHg or less and obtaining a plastic kneaded product in that state using a continuous screw kneader. 3. The method according to claim 1, in which the kneading machine is cooled. 4. The method according to claim 2 or 3, wherein the molding is performed using an injection molding machine, an extrusion molding machine, or a press molding machine.