JP2001262834A - Surface layer stabilizing method for floor concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface finishing method which can enhance and stabilize the surface strength of flat-placed concrete with high slump. SOLUTION: After the flat-placed concrete with high slump is placed and leveled, it is left at rest over 90 minutes or more, and then dehydration and deairing of the concrete is carried out from the surface thereof via a filtering mat by means of a vacuum pump. Then, the surface of the concrete is evenly finished with a trowel or the like. Alternatively, immediately after the dehydration and deairing by means of the vacuum pump, a water-retaining curing agent is sprayed, and then the surface of the concrete is evenly finished with the trowel or the like. Alternatively, after the dehydration and deairing by means of the vacuum pump, the surface is evenly finished with the trowel or the like, and then the water-retaining curing agent is sprayed within three days after the finishing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for increasing the strength of a surface layer of flat concrete applied to floors, roads, secondary products and the like and stabilizing the surface layer strength. The term "high slump concrete" as used in the present invention covers soft concrete with a slump value of 15 cm or more.

[0002]

2. Description of the Related Art In the case of 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 compression of the surface layer is reduced. The strength is lower than inside. In addition, in concrete casting by pumping at the site, the time difference until loading by a mixer truck,
Inappropriate treatment of the washing water of the mixer truck, unit water volume due to illegal water addition at the site, unevenness of slump, water pool due to unevenness in leveling work, etc., cause unevenness in the surface layer strength of hardened concrete, Wear, dusting,
It is a factor that greatly affects durability performance and the like such as cracks. It also causes blistering and peeling of the synthetic resin material that is painted or adhered as a finishing material.

[0003] In high slump concrete usually cast for floors, the breathing phenomenon is an unavoidable problem as long as it occurs as a reaction to the aggregate settlement phenomenon. Add water reducing agent, fluidizing agent, etc.
Although the water / cement ratio is reduced as much as possible, the problem of insufficient surface strength and unevenness has not been solved since the breathing phenomenon cannot be used as a service.

A vacuum concrete method for removing excess water from concrete is known. This method is characterized in that low slump concrete is dewatered from the concrete surface for a long time immediately after casting. However, high slump concrete cast on building floors has a problem that even if it is dehydrated for a long time immediately after casting, the inside is soft and finishing work cannot be performed. The range of application is limited to low slump hardened concrete such as concrete.

[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. It is difficult to reduce it to a certain amount or less because it is necessary to ensure workability. In addition, the problem of the variation in the concrete cast at the site cannot be solved.

In the method of reducing the water / cement ratio, there is a possibility that another problem of increasing the unit cement amount and increasing drying shrinkage to obtain the same workability may be caused.

In either method, surplus water collects on the surface layer due to the effect of the breathing phenomenon, and the water / cement ratio of the surface layer increases, so that the density of the surface layer decreases and the strength of the surface layer is essentially low. The problem is not 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.

In particular, flat cast concrete has a wide surface with respect to its thickness, so that side pressure is not applied and excess water cannot be discharged through gaps in the formwork as in the case of a wall surface. In addition, there was a variation in the surface strength in combination with the variation in the concrete to be cast, and there was a problem in durability performance.

The inventor of the present invention has 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 a concrete surface layer using vacuum pressure, and spraying and finishing a room temperature hardened emulsion. However, it was found that removing excess water increased the strength of the surface layer and reduced drying shrinkage.

As a result of intensive studies on this problem,
The present invention has led to the invention of a finishing method which increases the strength of the concrete surface layer, significantly reduces the variation in the surface layer strength due to the time from mixing and the effect of water on site, and stabilizes the surface layer strength.

[0012]

In order to solve the above-mentioned problems, this finishing method is to provide at least 90 minutes of standing time after concrete casting, compaction and leveling are completed. Features.

The dehydration and deaeration work using vacuum pressure varies depending on the slump of concrete, the outside temperature, and the like. Therefore, in the work under hot concrete and direct sunlight in summer,
The setting of concrete becomes faster, and conversely, the setting reaction of cement is delayed at low temperatures in winter. Therefore, it is necessary to adjust the work start time in consideration of the situation. Generally, on the building floor, it is necessary for the worker to work on the cast concrete, so take a time to allow the breathing water to sufficiently float. Provide at least 90 minutes of resting time, at least during the spring and fall seasons.

After a lapse of a predetermined time, dehydration and deaeration are performed by a vacuum pump from the upper surface of the concrete casting through a filter mat, and excess water and entrapped air are dehydrated and deaerated.

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.

The time required for the dewatering / deaeration operation is such that surplus water floats on the surface of the concrete due to the breathing phenomenon, so that 70% of the total drainage is drained in 10 minutes after the start of vacuum dehydration / deaeration. Therefore, it may be less than 10 minutes per place.

Dewatering and degassing are performed from the concrete casting surface, and then the surface is finished using a trowel, a gold iron, or the like. Immediately after the completion of the dehydration and deaeration work, a water retaining curing agent is sprayed, the cement and the water retaining curing agent are mixed in a trowell, and the surface layer can be made into resin mortar before finishing.

Alternatively, dewatering and deaeration can be performed on the concrete casting surface, followed by surface finishing using a disk trowell, a gold iron, or the like, and after finishing, the surface can be sprayed with a water retentive curing agent. In this case, the time for spraying the water-retaining curing agent is within three days from immediately after finishing. If the dry state continues for 3 days or more, the hydration reaction of the cement in the surface layer does not proceed, and the surface layer strength becomes insufficient, and at the same time, problems such as cracks are likely to occur.

Of the water-retaining curing agents used in the present invention, the room-temperature-curable synthetic resin emulsions that can be formed into a film at room temperature, such as acryl, acrylic copolymer, SBR, vinylidene chloride, epoxy, and EVA, are preferably used. Room temperature curable synthetic resin emulsions can also be used by coloring with an inorganic pigment. The synthetic resin emulsion may be sprayed immediately after the vacuum dehydration and deaeration work is completed, or may be used within three days after the concrete finishing work is completed. The synthetic resin emulsion is sprayed in an amount of 10 g to 150 g per 1 m ² as a solid content. 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 / deaeration work, it sticks to a trowel or the like, causing remarkable difficulty in the finishing work and hindering the finished appearance. In the method of spraying after finishing, there is no particular limitation on the spraying amount, but it is uneconomical in cost.

Among the water-retaining curing agents used in the present invention, the water-soluble polymer includes methylcellulose, hydroxyethylcellulose, poval and the like, and modified ones thereof, and is used as a single aqueous solution or as a protective colloid of a synthetic resin emulsion. .

Among the water-retaining curing agents used in the present invention, the water-soluble inorganic salts are required to have the property of solidifying and drying in concrete to fill voids, and thus sodium silicate, magnesium silicofluoride and the like are preferably used. These are sprayed and used within three days after the concrete finishing operation is completed.

Among the water-retaining curing agents used in the present invention, the solvent-based resin solution may be urethane, acrylic, epoxy, siloxane, or a modified one thereof, and is sprayed within three days after the concrete finishing operation. Used as

[0023]

According to the concrete finishing method of the present invention, the dewatering and deaeration filtration mat used is made of a cloth filter material that allows water and air to pass therethrough but does not substantially pass cement particles. Only the surplus water and entrained air are sucked without losing the cement component of the concrete surface layer, the water / cement ratio of the surface layer is reduced, and air bubbles of the concrete surface layer structure can be removed to make the concrete denser.

The dewatering and degassing by the vacuum action makes the water / cement ratio of the concrete surface layer constant irrespective of the type of concrete, the air bubbles are remarkably reduced and the density is increased. As a result, the variation in the surface strength resulting from the variation in the water content in the concrete caused by the addition of the concrete poured on the site is significantly reduced.

The filter mat does not substantially pass through the cement particles, so that the concrete mix does not change at all. Only surplus water and salts and air bubbles dissolved in the surplus water can be efficiently discharged.

The dewatering and deaeration time is as follows: the excess water concentrated on the surface layer is discharged in a short time because the breathing water is sufficiently floated and then brought into a vacuum state. The existing vacuum method and the amount of drainage do not change.

[0027] The effect of the water retention curing agent does not change even if it is sprayed immediately after the completion of vacuum dehydration and degassing to finish the surface, or if it is sprayed after completing the surface finishing after vacuum dehydration and degassing. Synthetic resin emulsions and water-soluble polymers are sprayed immediately after vacuum dehydration and deaeration, and then when finishing concrete, resin mortar is applied to the surface layer. When sprayed after finishing concrete, a polymer film is formed on the surface. Therefore, any of the methods suppresses evaporation of water and gives the same water retention effect. In addition to this, a more stable surface layer strength can be obtained by adding a sealing curing by a sheet or the like and a watering curing.

A description will be given below based on an embodiment.

[Comparative Example 1] The compounding strengths shown in Table 1 are 20, 30, and 40 Mp.
a, Concrete with a slump of 18 cm and a coarse aggregate maximum size of 15 mm was kneaded and cast into a 60 × 40 × 24 (height) cm formwork. No processing). The concrete specimen was covered with a wet cloth and subjected to wet curing to prevent surface drying.

[0029]

[Table 1]

[0030]

Comparative Example 2 Concrete having the same composition as in Comparative Example 1 was poured into a mold having the same size, and after 30 minutes, vacuum dewatering was carried out through a vacuum mat made of polypropylene woven fabric as a filter layer and not passing cement particles. After performing the deaeration treatment for 15 minutes, the surface was dehydrated and became firm and tight, but about 5 cm
The concrete having the following depth was in a very soft state as in the state immediately after casting, and when the surface was pressed with a wooden iron and a gold iron, unevenness was generated and could not be finished.

[0031]

Example 1 Concrete having the same composition as in Comparative Example 1 was poured into a mold having the same size, and a standing time of 120 minutes was provided. Subsequently, a vacuum pressure dehydration / deaeration treatment was performed for 5 minutes through a vacuum mat that uses a polypropylene woven fabric as a filtration layer and does not allow cement particles to pass through. After the treatment, the inside of the concrete was sufficiently hard and the finishing work was easy, and it was finished smoothly with a wooden iron and a gold iron. The concrete specimen was covered with a wet cloth and subjected to wet curing to prevent surface drying. Comparative Example 1 and Example 1 were compared by the following test method. First, the concrete was sliced into 4 parts in the depth direction into 5cm thickness from the surface (the first layer from the bottom layer, the surface layer was the fourth layer), and the compressive strength of each was measured 28 days old, and the results in Table 2 were obtained. I got Next, regarding the surface layer strength of the concrete, the surface rebound hardness was measured using a Schmidt Mammamer P type on days 3 and 7 and an N type on days 7 and 28, and the results in Table 3 were obtained. Regarding the strength of the very surface of concrete, the scratch width was measured with a scratch tester (Mie University system), and the results shown in Table 4 were obtained. The surface rebound hardness is a method of evaluating the hardness (compression strength) of the surface layer, and a scratch tester is a method of evaluating the hardness of the surface. In the four-part compressive strength, the fourth layer (surface layer) has an order of measured values in the order of the concrete mixing strength regardless of the presence or absence of the vacuum dehydration / deaeration treatment. Regarding the rebound hardness, untreated concrete has an order of compounding strength and rebound hardness, but those that have been dewatered and deaerated under vacuum have significantly improved surface rebound hardness, and both P-type and N-type have a level of rebound. Was almost constant regardless of the concrete mixing strength. In the case of the scratch width in the scratch test, even when the material age is 28 days, the order of the scratch width is observed according to the mixing strength when no treatment is performed. It became the same scratch width.

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

[Embodiment 2] In actual four different RC construction sites, A and B are constructed by a conventional machine iron and gold iron finishing method (untreated), and C and D are concrete casting 120 Minutes later, a vacuum pressure dehydration deaeration treatment is performed for 5 minutes through a vacuum mat that does not allow cement particles to pass through using a polypropylene woven fabric as a filtration layer, and immediately thereafter, an acrylic emulsion-based water-retaining curing agent (BF coat, JC 60 g / m ² as a resin solid content
It was scattered and finished with a machine iron and a gold iron. Neither of them has a special wet curing. After the concrete at each site was hardened, the surface rebound hardness was measured with a Schmidt Hammer N type. The type of ready-mixed concrete used, the age at the time of measurement and the measurement results are as shown in Table 5. Measurement points are 12 points in a range of 1 × 10 m on the upper surface of the slab, and 5 points separated by 3 cm or more at each point are measured at a total of 60 points. The rebound hardness was converted into an estimated strength according to the Society of Materials Science (unit: Mpa.).
The average value of the untreated concrete is lower than the compounding strength, but changes in proportion to the compounding strength. so,
The coefficients of variation were 5.13% and 8.99%. After 2 hours, the sample subjected to vacuum dehydration and deaeration had a dispersion of measured values of 5.3 and 6.6 Mpa. The coefficient of variation was significantly improved and stabilized at 1.45% and 1.11%.

[0036]

[Table 5]

[0037]

As is clear from the above description, flat cast concrete is allowed to stand still for 90 minutes or more after casting, and excess water and entrapment is applied within a short time of 10 minutes or less using vacuum pressure from the upper surface. The concrete surface layer stabilization method of dewatering and degassing foam can improve the strength level and greatly reduce the variation in surface layer strength due to the variation in cast concrete. Furthermore, the hydration reaction of cement is promoted by finishing with the use of the water-retaining curing agent, whereby the drying shrinkage of concrete can be reduced and cracks can be reduced. In the case of floor concrete, it is not possible to predict which parts will be subjected to load or wear during transportation, etc., so if the strength level of the surface layer is improved and the surface strength is stabilized without variation,
The durability of the floor will be significantly improved. In an actual building construction site, a great deal of labor and time is required for wet curing, so that sufficient moisture curing is often not performed. In extreme cases, the concrete is exposed to drying immediately after finishing the concrete. In addition, when a floor coating or a sticking floor is applied to the concrete surface, the concrete may be actively dried. However, even under such conditions, the quality of the concrete can be stabilized. Completing the quality improvement and stabilization of the surface layer under such harsh conditions in a short time and at low cost in the process from concrete casting to finishing is a great contribution economically from the viewpoint of the durability of the structure. You can do it.

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Takeshi Yamaguchi 5-1-189-102 Mitsugaoka, Neyagawa-shi, Osaka F-term (reference) 2D051 EA00 2E172 AA05 DB07 EA00

Claims (6)

[Claims] 1. In high slump flat cast concrete,
After the casting is leveled and allowed to stand for 90 minutes or more, the surface of the concrete is dewatered and deaerated by a vacuum pump through a filter mat through a filter mat, and then the surface is finished smoothly with a trowel or the like. Method. 2. In high slump flat cast concrete,
After casting and leveling, after leaving still for 90 minutes or more, the concrete surface is dewatered and degassed by a vacuum pump through a filter mat, immediately sprayed with a water-retaining curing agent, and then smoothed with a trowel or the like. Surface stabilization method characterized by finishing. 3. In high slump flat cast concrete,
After casting and leveling, let it stand for 90 minutes or more, then dewater and deaerate the concrete surface with a vacuum pump through a filter mat, then smooth the surface with a trowel, etc., and finish the water retention within 3 days 2. The method for stabilizing a surface layer according to claim 1, wherein an agent is sprayed. 4. The filter mat according to claim 1, wherein said filter mat is a synthetic resin woven fabric which does not substantially pass cement.
Surface stabilization method. 5. The method for stabilizing a concrete surface layer according to claim 1, wherein the time of vacuum dehydration and deaeration is within 10 minutes per one place. 6. The water-retaining curing material is at least one of a room temperature-curable synthetic resin emulsion, a water-soluble polymer solution, a water-soluble inorganic salt, and a solvent-based resin solution, and 10 to 150 g as a solid content is sprayed. Claim 1 characterized by the fact that
5. Concrete surface finishing method.