JPH11117530A - Finishing method of concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking by increasing surface strength and lowering drying shrinkage by scattering a shrinkage-reducing agent onto a surface and finishing the surface immediately after dehydration and deaeration after placing of concrete, cast flat. SOLUTION: A shrinkage-reducing agent is scattered onto a concrete surface immediately after excess water and rolled-in air are dehydrated and deaerated by a vacuum pump through a filter mat from the top face of a flat-casting concrete after placing of the flat casting concrete, and the surface is finished by a trowel, etc. The surface is finished after dehydration and deaeration, and the shrinkage reducing agent may also be scattered. A synthetic-resin fiber woven fabric, through which cement particles are not passed substantially, is preferable as the filter mat for dehydration and deaeration at that time. An anionic surface-active agent having surface tension of 50 dyne/cm or less in an aqueous solution having a shrinkage reducing ratio of 3%, a common- setting synthetic resin emulsion, a water-soluble high-molecular solution, etc., are preferable as the shrinkage reducing agent. Accordingly, surface strength is increased, and drying shrinkage is lowered and cracking can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel finishing method for improving the strength of the surface layer of flat-cast concrete applied to floors, roads, secondary products and the like, and for preventing drying shrinkage cracks.

[0002]

2. Description of the Related Art In flat-cast concrete, the water / cement ratio of the surface layer increases due to the water floating phenomenon caused by breathing. Therefore, the density of the surface layer after casting is lower than that of the inside, and the compressive strength of the surface layer is reduced. Lower than inside. Further, drying shrinkage cracks are liable to occur, which is not only unsightly in appearance, but also has a great effect on waterproof performance, durability performance and the like.

[0003] In concrete that is usually cast for floors, the breathing phenomenon is an unavoidable problem as long as it occurs as a reaction to the aggregate settlement phenomenon. By adding a water reducing agent and fluidizing agent, etc., the unit water content and the water / cement ratio of the concrete are reduced as much as possible, but there is a limit from the workability at the site, and the problem that the surface strength is lowered is solved. Not.

[0004] Regarding the prevention of cracks in concrete,
The reducing unit water (amount of water per 1 m ^3),
Methods of reducing the water / cement ratio, blending the expansive material partially with cement, and admixing or spraying a shrinkage inhibitor are employed.

[0005]

The method of reducing the unit water amount (the amount of water per 1 m ³ ) is to obtain the fluidity for pumping and the smooth surface accuracy at the site in the concrete which is usually used. At present, it is difficult to reduce the amount to below a certain level because it is necessary to secure liquidity for the purpose.

In the method of reducing the water / cement ratio, in order to obtain the same workability, the unit cement amount increases, and on the contrary, the drying shrinkage tends to increase.

The method of mixing or spraying an anti-shrinkage agent, in which a part of the expansive material is replaced with cement, has a certain effect from the viewpoint of preventing drying shrinkage, but the surplus water is affected by the influence of breathing water. And the water / cement ratio of the surface layer increases, so that the density of the surface layer decreases, and the problem of essentially low strength of the surface layer cannot be solved.

[0008] The amount of water mixed with concrete is excessive compared with the water required for the hydration reaction of cement, and the fact that this water has a large effect on drying shrinkage as surplus water is described in the workability of concrete. Has not been considered so far as unavoidable from the viewpoint of security and labor saving.

[0009] In the case of wall concrete poured into a formwork, there is a period during which the formwork exists, and the initial hydration of the concrete is achieved. However, in the case of flat cast concrete, it is often exposed to single-sided drying immediately after finishing the casting.

[0010] In particular, flat cast concrete has a large surface with respect to its thickness, so that side pressure is not applied and no excess water can be discharged through the gaps of the formwork like wall surfaces. Since it is not treated at the time of finishing, there is a problem that the water / cement ratio becomes large as a result and drying shrinkage cracks easily occur.

The inventor of the present invention proposed in Japanese Patent Application Laid-Open No. Hei 7-305510 a method of dewatering and degassing excess water and entrapped air due to breathing of the concrete surface layer using vacuum pressure, and spraying and finishing a room temperature hardened emulsion. However, it has been found that removing excess water increases the strength of the surface layer portion and reduces drying shrinkage. However, this method also has a limit in reducing drying shrinkage caused by evaporation of water.

As a result of intensive studies on this problem,
The inventors have invented a reliable finishing method which increases the strength of the concrete surface layer and further has a high shrinkage reducing effect.

[0013]

In order to solve the above-mentioned problems, this finishing method is to first dewater and deaerate from the concrete casting upper surface by a vacuum pump through a filter mat to dewater excess water and entrapped air. It is characterized by degassing.

The dehydration / deaeration using vacuum pressure varies depending on the slump of the concrete, the outside temperature, etc., but may be performed immediately after the casting and before the concrete setting is completed. Preferably, it is performed after the rising of the breathing water has reached a resting state.

The filter mat for dehydration and deaeration used in the present invention uses a filter material that does not substantially pass cement particles. It is preferable to use the one disclosed by the present inventors in JP-A-7-305510 because it is efficient and does not change the concrete mixing ratio.

Immediately after dewatering and deaeration of excess water and entrapped air from the concrete casting upper surface by vacuum action, a shrinkage reducing agent is sprayed on the surface of the concrete, and then the surface is finished with a trowel or the like. In this case, the timing of the surface finishing tends to be slightly delayed due to the property of the shrinkage reducing agent, but the finishing workability is rather improved in concrete under direct sunlight or in summer.

Alternatively, surplus water entrained air is deaerated from the concrete casting surface by a vacuum action, and then the concrete surface is finished with a trowel or the like, and after finishing, a shrinkage reducing agent is sprayed on the surface. In this case, the time for spraying the shrinkage-reducing agent and the water-retaining agent is preferably within three days because the initial dry cracks are usually observed in three to seven days.

Among the shrinkage reducing agents used in the present invention, a surfactant having a surface tension of a 3% aqueous solution of 50 dynes / cm or less is used. The lower alcohol alkylene oxide adduct or ether type is used. Nonionic surfactants are preferably used. When the surface tension is 50 dynes / cm or more, the effect of reducing shrinkage due to a decrease in capillary tension in concrete is small, and the effect of suppressing cracking is not recognized. Surface active agents 1 m ² per 30g least 30
0 g or less is sprayed. When the amount of spraying is small, a sufficient amount of shrinkage reducing effect cannot be obtained because the amount of the shrinkage reducing agent does not reach the deep portion of the capillary in the concrete. 300g
The above application amount is not preferable because the rate of enhancement of the surface layer strength obtained by vacuum dehydration and deaeration is greatly reduced.

Among the shrinkage reducing agents used in the present invention, synthetic resin emulsions include acrylic, acrylic copolymer, SB
Those which form and cure at room temperature, such as R, vinylidene chloride, epoxy and EVA, are preferably used. The synthetic resin emulsion has a solid content of 10 g to 150 g per m ² .
Is sprayed. If it is less than 10 g, a water retention effect for preventing water evaporation cannot be obtained. If it is 150 g or more, when spraying immediately after the vacuum dehydration and deaeration work, it sticks to a trowel or the like, which impairs the finishing work and finish appearance. In the method of spraying after finishing, the amount of spraying is not particularly limited in work, but it is uneconomical in cost.

As the water-soluble polymer among the shrinkage reducing agents used in the present invention, methylcellulose, hydroxyethylcellulose, poval and the like and modified ones thereof are used and used as a single aqueous solution or as a protective colloid of a synthetic resin emulsion. .

As the shrinkage reducing agent, the above-mentioned surfactant can be used alone or diluted with water, but it can also be used in combination with a synthetic resin emulsion or a water-soluble polymer. That is, a method in which a surfactant is sprayed and then a synthetic resin emulsion and a water-soluble polymer are sprayed, and a method in which a surfactant, a synthetic resin emulsion and a water-soluble polymer are mixed in advance is sprayed.

As the coloring pigment used in the present invention, a pigment which does not discolor due to cement alkali and has excellent weather resistance is used. Preferably iron oxide, chromium oxide, titanium oxide,
Inorganic pigments such as ultramarine and phthalocyanine organic pigments are used.

[0023]

According to the concrete finishing method of the present invention, the dewatering and degassing filtration mat used is made of a cloth-like filtering material which allows water and air to pass through but does not substantially pass cement particles. It is possible to reduce the water / cement ratio of the surface layer portion by sucking only surplus water and entrained air without losing components.

Excessive water on the concrete surface layer is removed by dehydration and deaeration by the action of vacuum, and compaction by atmospheric pressure is performed, so that dense concrete having high surface strength can be obtained.

Further, the shrinkage reducing agent sprayed after vacuum dehydration and deaeration can efficiently penetrate into the inside of the concrete because the water content of the concrete surface layer is reduced, and the range of reducing the capillary tension reaches the deep part of the concrete.

Since the surfactant penetrates into the concrete and lowers the surface tension of water, the capillary tension in the concrete tissue decreases, and as a result, the drying shrinkage stress due to the capillary tension is reduced. The effect is the same whether the surfactant is sprayed immediately after the completion of vacuum dehydration and degassing to finish the surface, or sprayed after completing the surface finishing after vacuum dehydration and degassing.

When finishing the concrete after spraying the synthetic resin emulsion and water-soluble polymer immediately after the dehydration treatment under vacuum, polymer cement is formed on the surface layer, and when the concrete is finished after finishing the concrete, a polymer film is applied on the surface. In any of the methods, water evaporation is suppressed, and a water retention effect is provided to the same extent.

When a surfactant, a synthetic resin emulsion and a water-soluble polymer are used in combination, the action of lowering the surface tension of the surfactant and the action of water retention and curing by forming a film of the synthetic resin emulsion and the water-soluble polymer are synergistic. To achieve the purpose in one working process. The surface finishing method may be trowel finishing or brushing.

By spraying a shrinkage preventive mixed with a coloring pigment, a color having a high surface strength can be obtained at the time of finishing the concrete, and the concrete is dried, and the strength is developed, and then compared with the case where coloring is performed by a method such as painting. There is no problem of peeling, and it is inexpensive, shortens the construction period, and has a great economic advantage. Hereinafter, description will be made based on embodiments.

[0030]

Comparative Example 1 Fresh concrete (nominal strength 240
kg / cm ² , slump 8cm, coarse aggregate maximum dimension 25m
m, unit water amount 160kg, water / cement ratio 53.3%)
Into a 50 cm x 50 cm 20 cm thick formwork cured with a vinyl sheet to prevent water from leaking from the bottom and formwork seams in a room at 20 ° C and 60% humidity. After finishing the surface, 0.5
Curing was performed for 3 days by blowing a constant m / sec wind from the lateral direction to the entire surface of the concrete, and then the blowing was stopped to continue the curing. As a result, cracks were observed in one day of the material age. At the end of the test, cracks were observed on the entire surface in the form of a non-directional tortoiseshell. When the surface strength was measured using a Schmidt hammer at the age of 28 days, the estimated strength was 262 kg /
cm ² .

[0031]

Comparative Example 2 Concrete having the same conditions as in Comparative Example 1 was used for 20 times.
Placed in a room with a humidity of 80 ° C and 80% humidity, watch the concrete harden and finish the surface with a gold trowel. After 24 hours, sprinkle water on the surface and cover it with a polyethylene sheet, and cure it until the age of 14 days. Remove the polyethylene sheet, transfer to a room at 20 ° C and 60% humidity, and cure for 0.5 days with a constant air flow of 0.5 m / sec from the side to the entire surface of the concrete. After that, stop blowing and continue curing. did. The surface was dried under the same conditions as in Comparative Example 1. On the 18th day of material age, fine cracks were visually observed. After the test was completed, the concrete surface was wetted with water, and extremely fine surface cracks were observed throughout the concrete. When the surface strength was measured with a Schmidt hammer at the end of the visual inspection, the estimated strength was 294 kg / cm ² .

[0032]

Example 1 Concrete was cast under the same conditions as in Comparative Example 1, and after three hours had elapsed after waiting for the emergence of breathing water, dehydration and deaeration were performed using vacuum pressure. The amount of drainage is 500m
l. Immediately after the completion of the dehydration and deaeration treatment, 30 g of “Tetraguard AS20” (manufactured by Sanyo Chemical Industries, Ltd.) was sprayed as a shrinkage-reducing agent, and a gold iron finish was performed while observing the state of curing. Cured by the procedure. result,
No visual cracking occurred up to 28 days of age. When the concrete surface was moistened with water after the test, no cracks were observed. When the surface strength was measured with a Schmidt hammer at the end of the visual inspection, the estimated strength was 340 kg / cm ² .

[0033]

Example 2 Concrete was cast under the same conditions as in Comparative Example 1, and after three hours had passed while waiting for the breathing water to float, vacuum dehydration deaeration treatment was performed. The amount of drainage was 520 ml.
Immediately after the completion of the vacuum dehydration and deaeration, “Tetraguard AS
20 "(manufactured by Sanyo Kasei Kogyo Co., Ltd.) diluted twice with water and an equal amount of a cement mixing emulsion of polyvinyl alcohol protective colloid" Sumikaflex 430 "(manufactured by Sumitomo Chemical Co., Ltd.) to reduce shrinkage. Agent 5
Spray 0g and finish the ironing while watching the curing condition.
Cured in the same atmosphere as in Comparative Example 1. As a result, no visual cracking occurred until the age of 28 days. When the concrete surface was moistened with water after the test, no cracks were observed. At the end of the visual inspection, the surface strength was measured using a Schmidt hammer.
It was 45 kg / cm ² .

[0034]

Example 3 Concrete was poured under the same conditions as in Comparative Example 1, and after three hours had passed after waiting for the breathing water to float, dehydration and deaeration were performed using vacuum pressure. The drainage is 480m
l. Finish the trowel while watching the curing condition,
After completion of the finishing operation, 30 g of "Tetraguard AS20" manufactured by Sanyo Kasei Kogyo Co., Ltd. was sprayed as a shrinkage reducing agent and cured in the same atmosphere as in Comparative Example 1. Result, material age 2
Until the 8th, no visual cracking occurred. When the concrete surface was moistened with water after the test, no cracks were observed. When the surface strength was measured with a Schmitt hammer at the end of the visual inspection, the estimated strength was 358 kg / cm ² .

[0035]

Example 4 Concrete was cast under the same conditions as in the comparative example, and after 3 hours from the release of breathing water, dehydration and deaeration were performed using vacuum pressure. The amount of drainage is 500m
l. Finish the trowel while watching the curing condition,
After finishing work, the shrinkage reducing agent "Tetraguard AS20" (manufactured by Sanyo Kasei Kogyo Co., Ltd.) was diluted twice with water, and the acrylic emulsion "Yodosol A" was used.
60 g of a shrinkage reducing agent containing an equal amount of "D91" (manufactured by NSC Japan) was sprayed, and cured under the same atmosphere as in Comparative Example 1. As a result, no visual cracking occurred until the age of 28 days. No cracks were observed when the concrete surface was wetted with water after the test. When the surface strength was measured with a Schmidt hammer at the end of the visual inspection, the estimated strength was 345 g / cm ² .

[0036]

Example 5 Concrete was poured under the same conditions as in Comparative Example 1, and after three hours had elapsed after waiting for the breathing water to float, dehydration and deaeration were performed using vacuum pressure. 520m drainage
l. "Tetraguard AS20" (manufactured by Sanyo Chemical Industries, Ltd.) diluted twice with water, an acrylic emulsion "Yodozol AD91" (manufactured by NSC Japan) and an iron oxide inorganic pigment "Viferox 130"
M "(manufactured by Bayer) in a ratio of 1: 1: 2 (weight ratio) was sprayed with 100 g of a shrinkage-reducing agent, and was subjected to a gold iron finish while observing the state of curing, followed by curing in the same atmosphere as in Comparative Example 1.
As a result, a bright colored concrete surface appearance was obtained, and no visual cracking occurred until the age of 28 days. No cracks were observed even when the concrete surface was wetted with water after the test. At the end of the visual inspection, surface strength was measured using a Schmidt hammer, and the estimated strength was 347 kg / cm ² .

[0037]

As is apparent from the above description, the method of dewatering and degassing excess water and entrained foam using vacuum pressure from the upper surface of flat cast concrete, and then spraying and finishing the shrinkage reducing agent is performed by casting. It can increase the surface strength of concrete for many buildings and civil engineering that is exposed to drying conditions from the beginning, and can reduce the drying shrinkage of concrete to prevent cracking. If a coloring pigment is blended with the shrinkage reducing agent, concrete having desired color and high surface strength can be quickly and inexpensively finished. Cracking is not only unsightly in appearance, but also promotes neutralization due to carbon dioxide gas, acid rain, etc., causing corrosion of steel bars, water leakage, etc., which greatly affects the durability of the structure. It is said that wet curing is important. At an actual construction site, a great deal of labor and time is required for wet curing, so that sufficient moisture curing is often not performed, and in extreme cases, the concrete is exposed to drying immediately after finishing. Also,
When floor coating or sticking is applied to the concrete surface, the concrete may be actively dried in order to reduce the moisture content of the concrete. It is a great economical contribution that ensuring and improving quality under such severe curing conditions can be completed inexpensively in the concrete pouring and finishing process.

Claims (5)

[Claims] In a flat-cast concrete, after the casting is leveled, a shrinkage-reducing agent is sprayed from the surface of the concrete immediately after dehydration and deaeration by a vacuum pump through a filter mat, followed by surface finishing. A concrete surface finishing method characterized by: 2. The flat cast concrete is characterized in that after casting and leveling, the surface of the concrete is dewatered and deaerated by a vacuum pump through a filter mat through a filter mat, and then a shrinkage reducing agent is sprayed. Concrete surface finishing method. 3. The concrete surface finishing method according to claim 1, wherein the filter mat used for dewatering and deaeration uses a synthetic resin fiber woven fabric that is substantially impermeable to cement particles. 4. A shrinkage reducing agent having a surface tension of 50% of a 3% aqueous solution.
3. The concrete surface finishing method according to claim 1, wherein the method is at least one selected from the group consisting of a nonionic surfactant of dyne / cm or less, a cold-curable synthetic resin emulsion, and a water-soluble polymer solution. 5. The concrete surface finishing method according to claim 1, wherein a color pigment is blended with the shrinkage reducing agent.