JPH06279147A - Lightweight concrete - Google Patents

Abstract

PURPOSE:To provide lightweight concrete having high compressive strength and stable specific gravity, capable of working in the designed thickness, preventing the reduction of the strength and capable of enhancing dry shrinking performance. CONSTITUTION:This lightweight concrete consists of a binder, water, aggregate for structural lightweight concrete and foamed plastic obtd. by foaming plastic by 2-15 times.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to lightweight concrete. More specifically, the present invention relates to a lightweight concrete which has a high compressive strength, can obtain a stable specific gravity, can be constructed according to a design thickness, can prevent a decrease in strength, and can improve drying shrinkage performance.

[0002]

2. Description of the Related Art Conventionally, in order to reduce the weight of a building,
As the aggregate, lightweight concrete using structural lightweight concrete aggregate consisting of natural lightweight aggregate obtained from volcanoes, artificial lightweight aggregate such as expanded clay and expanded shale, and by-product lightweight aggregate such as expanded slag is used. Has been. In addition, aerated concrete made by curing in an autoclave (AL
C) is also used.

[0003] However, lightweight concrete has a specific gravity of 1.4 to 2.0 and is insufficient in weight reduction. There is also a problem that the lightweight aggregate floats up and separates during kneading or driving, which makes it difficult to obtain homogeneous concrete. ALC has a compressive strength of 40 kg / cm.
It cannot be used as a structural material because it is as small as ² and is brittle and easily damaged. Moreover, high temperature and high pressure steam curing in an autoclave is required, and special equipment is required for manufacturing. Furthermore, as a disadvantage of both, since there is a large amount of continuous voids, the water absorption is large, the water permeability is large, water leakage is easy to occur, and freeze-thaw resistance, neutralization etc. durability is also inferior is there.

As a solution to this problem, it has been proposed to reduce the weight of concrete or mortar by using synthetic resin foam beads or crushed products having an expansion ratio of about 30 to 70 (for example, Japanese Patent Publication No. 16454, Japanese Patent Publication No. 63-39536, etc.).

[0005]

However, when the water-cement ratio is reduced in order to increase the strength and durability of concrete, the synthetic resin foam shrinks during kneading at the conventional expansion ratio, It was not possible to obtain a stable specific gravity. In addition, when pouring concrete using a pump, the pump pressure (usually about 10
80 kgf / cm ² ), the synthetic resin foam contracted at the conventional expansion ratio, and in this respect also, stable specific gravity could not be obtained.

Table 1 shows the compressive strength of expanded polystyrene (4%
Strain) is shown, and it can be seen from Table 1 that the pumping pressure of the pump cannot be withstood when the expansion ratio exceeds about 15 times.

[0007]

[Table 1]

When the synthetic resin foam contracted by kneading or pumping is restored before the concrete is cured, a so-called back swelling phenomenon occurs, and the concrete thickness as designed cannot be obtained, and the strength is also high. 20-50%
It had fallen to some extent.

In view of the above circumstances, it is an object of the present invention to provide a lightweight concrete which is capable of preventing instability of specific gravity and concrete thickness and reduction of strength due to the shrinkage and improving drying shrinkage performance. To do.

[0010]

The lightweight concrete of the present invention is a lightweight concrete comprising a binder, water, a structural lightweight concrete aggregate and a synthetic resin foam, and the synthetic resin foam has an expansion ratio of 2 to 2. It is characterized by being 15 times.

[0011]

EXAMPLES In the present invention, it is preferable to use cement as a binder, but gypsum other than cement,
Lime, calcium silicate, gypsum, plaster, adhesive, etc. can be used.

As the cement, ordinary Portland cement, early strength Portland cement, super early strength Portland cement, medium heat Portland cement and other portland cement, mixed cement such as blast furnace cement, silica cement and fly ash cement, and ultra early strength. Cement, expansion cement, cosmetic cement (white cement,
Special cements such as color cement) and alumina cement can be used, and it is preferable to use properly depending on the application.

The synthetic resin foam in the present invention is obtained by foaming polystyrene, polypropylene, polyethylene, acrylonitrile / styrene copolymer, styrene / ethylene copolymer, polyvinylidene chloride, etc., and the expansion ratio is 2 The range is up to 15 times. When the expansion ratio is less than 2, the non-combustibility of the obtained concrete decreases and it becomes difficult to reduce the weight, which is not preferable. On the other hand, when the expansion ratio exceeds 15 times, various problems due to shrinkage start to occur as described above, which is not preferable. The foaming ratio is preferably 5 to 10 from the viewpoints of strength, weight reduction and cost.

The synthetic resin foam is preferably synthetic resin foam beads because the ratio of water binder (water cement ratio) can be reduced by the rolling effect. Beads have better fluidity and are easier to construct than crushed products. Further, the strength is about 20 to 30% higher than that of the crushed product. In the case of crushed products, there are many variations in weighing, making it difficult to obtain stable quality.

In the present specification, the "bead" means a spherical, oval or cylindrical sphere. In addition,
Of these, spherical spheres are most preferable.

The average particle size of the synthetic resin foam beads is 2 mm.
In the following, it is particularly preferably 0.5 to 1.0 mm, which can further improve the fluidity of concrete due to the rolling effect when kneading with the binder and water. As a result, the water binder ratio can be reduced while maintaining good workability. The concrete thus obtained is a highly durable lightweight concrete having small continuous voids, denseness, small shrinkage, low water absorption and water permeability, and excellent freeze-thaw resistance and neutralizing performance. When the average particle size is 2 mm or more, the particles are easily separated due to buoyancy and the strength tends to vary. This separation can be prevented to some extent by using an admixture such as a thickener, but it is not perfect, and the use of the admixture causes a problem that workability becomes poor. In addition, if the aggregate is large, a defective portion is likely to occur, and stress concentration is applied to that portion, so that the concrete strength is 20 to 30.
It will be reduced by about%.

When synthetic resin foam beads are used, the water binder ratio is preferably 45% or less, more preferably 30 to 40%. By doing so, various qualities of concrete, that is, strength characteristics, neutralization characteristics, freeze-thaw resistance, watertightness, etc. can be improved. In addition,
When the water cement ratio is less than 30%, the viscosity is high and the workability becomes poor. Among the synthetic resin foam beads, expanded polystyrene beads are used because it is easy to obtain spherical beads with a small particle size, no toxic gas is emitted during combustion, and the compressive strength is relatively large and the cost is low. Preferably.

Although it is possible to use an inorganic foam in place of the synthetic resin foam, in the case of an inorganic foam, it is easily damaged during kneading or pumping, and especially when the water binder ratio is reduced. This tendency becomes remarkable, and it is difficult to obtain a predetermined density. In order to eliminate this, an inorganic foam with a small expansion ratio (density of about 0.5 g / cm ³
It is necessary to use the above), and it becomes difficult to reduce the weight. In addition, in the case of an inorganic foam, there is a problem that it takes a lot of time to handle, such as a large amount of water absorption, and this water absorption must be corrected during preparation.

The compounding ratio of the synthetic resin foam beads is 10 to 10.
It is 55% by volume, preferably 15 to 35% by volume. If the mixing ratio is less than 10% by volume, there is a problem that the specific gravity of concrete cannot be reduced, the heat insulating property is deteriorated, and nails cannot be driven. On the other hand, if it exceeds 55% by volume, the strength is high. And the flame retardancy (incombustibility) are lowered, and the nail pullout resistance is lowered. The volume% is based on the absolute volume of the synthetic resin foam beads, and voids between particles are not taken into consideration.

The lightweight concrete of the present invention is characterized in that the foaming ratio of the synthetic resin foam is reduced to 2 to 15 times, and that the lightweight concrete aggregate is mixed.

When the structural lightweight concrete aggregate is blended, the shrinkage is constrained by the compressive resistance of the structural lightweight concrete aggregate, and the amount of cement and water that cause shrinkage is reduced per unit volume, so that the drying shrinkage performance is reduced. Is improved. In this case, the dry shrinkage performance can be improved without lowering the compression strength.

The structural lightweight concrete aggregates that can be used include those specified in JIS A 5002. Specifically, artificial lightweight aggregates, natural lightweight aggregates, and by-product lightweight aggregates can be used. And so on. Of these, artificial lightweight aggregates are most preferable because of their low water absorption and high strength. The mixing amount of the artificial lightweight aggregate is not particularly limited in the present invention, but it is preferably 20 to 50% by volume, particularly 30 to 40% by volume of the whole concrete.

In the case of conventional lightweight concrete using structural lightweight concrete aggregate, the specific gravity of mortar composed of cement and fine aggregate is as large as about 2.3, whereas the specific gravity of structural lightweight concrete aggregate is about 2. Since it was as small as 1.0 to 2.0, there was a problem that the coarse aggregate was lifted up by the buoyancy and the material was separated. For this reason, the conventional lightweight concrete using structural lightweight concrete aggregate has a drawback in that there is a variation in strength due to the difference between the upper and lower, but in the present invention, cement and synthetic resin foam corresponding to conventional mortar are used. The specific gravity of the mixture with beads is about 1.0 to 1.5, which is lighter than or almost equal to that of the structural lightweight concrete aggregate, so that the aggregate does not float up and good mixing is achieved. You can get it.

The size of the structural lightweight concrete aggregate is not particularly limited, but it is preferably about 2.5 to 20 mm, particularly about 5 to 10 mm, and the specific gravity is about 1.0 to 2.0, especially 1. It is preferably about 0.3 to 1.8. When the specific gravity is less than 1.0 (0.2 or more), the size is 2.5 to prevent the separation of aggregate.
It is preferably about 5.0 mm.

The lightweight concrete of the present invention comprises a binder, water and synthetic resin foam as well as an adhesive, a fiber, and
Sand, gravel, etc. can be mixed.

Next, the lightweight concrete of the present invention will be explained based on examples, but the present invention is not limited to such examples as a matter of course.

Examples 1 to 2 Polystyrene beads were polymerized while adding a foaming agent (butane) to a styrene monomer, and the selected raw material resin having a small particle size was put into a pre-foaming machine, and a predetermined foaming was performed with steam. Foam to a magnification (Example 1:10 times, Example 2: 5 times),
Polystyrene foam beads (synthetic resin foam beads) were obtained.

The obtained synthetic resin foam beads, ordinary Portland cement, water, asanolite (product name: artificial lightweight aggregate manufactured by Nippon Cement Co., Ltd.) having a specific gravity of 1.5 and a particle size of 5 to 10 mm, and high-performance AE water reduction The agents were kneaded with an omni mixer at the compounding ratio shown in Table 2. As a kneading method, water and a high-performance AE water reducing agent were added to cement and the mixture was kneaded for 1 minute. Then, synthetic resin foam beads and artificial lightweight aggregate were added and further kneaded for 3 minutes. The obtained kneaded product was put in a mold to prepare a test piece (φ100 × 200 mm). After 1 day, the formwork was removed and cured. The curing method was underwater curing.

Regarding the obtained test piece, JIS
The 4-week compressive strength was measured based on the “compressive strength test method for concrete” of A 1108. Also, JIS A112
The dry shrinkage rate at 20 weeks was measured based on the test method for length change of mortar and concrete in 9 of Table 2. The results are shown in Table 2.
Shown in.

[0030]

[Table 2]

Comparative Examples 1 to 3 Test pieces were prepared in the same manner as in Example 1 except that the expansion ratio of the synthetic resin foam and the mixing ratio of concrete were changed as shown in Table 2, and the compression strength was 4 weeks and the compression strength was 20 weeks. The dry shrinkage was measured. The results are shown in Table 2.

[0032]

As described above, the lightweight concrete of the present invention uses the low-foaming synthetic resin foam having a foaming ratio of 2 to 15 times and the structural lightweight concrete aggregate. It is possible to eliminate the instability of the specific gravity and the instability of the design thickness due to the contraction such as the resin foam, and it is possible to prevent the decrease of the compressive strength. Further, the drying shrinkage performance can be improved.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area // (C04B 28/02 16:08 2102-4G 14:02) B 2102-4G

Claims (9)

[Claims] 1. A lightweight concrete comprising a binder, water, a structural lightweight concrete aggregate and a synthetic resin foam, wherein the synthetic resin foam has a foaming ratio of 2 to 15 times. . 2. The lightweight concrete according to claim 1, wherein the expansion ratio is 5 to 10 times. 3. The lightweight concrete according to claim 1, wherein the synthetic resin foam is synthetic resin foam beads. 4. The water binder ratio is 45% or less.
Lightweight concrete as described. 5. The lightweight concrete according to claim 3, wherein the water binder ratio is 30 to 40%. 6. The synthetic resin foam beads have an average particle diameter of 2
The lightweight concrete according to claim 3, 4 or 5, having a size of not more than mm. 7. The lightweight concrete according to claim 3, wherein the synthetic resin foam beads have an average particle diameter of 0.5 to 1.0 mm. 8. The lightweight concrete according to claim 3, 4, 5, 6, or 7, wherein the synthetic resin expanded beads are expanded polystyrene beads. 9. The binder according to claim 1, wherein the binder is cement.
Lightweight concrete according to 2, 3, 4, 5, 6, 7 or 8.