JP5188104B2 - How to remove uneven color on concrete surface - Google Patents

Description

  The present invention relates to a method for removing color unevenness on a concrete surface, in particular, color unevenness on a concrete surface due to occurrence of efflorescence.

  Conventionally, there is a problem that efflorescence (white flower) is likely to occur on the concrete surface of a concrete structure, which leads to uneven color and greatly impairs the aesthetic appearance of the concrete surface.

  Eflorescence means "soluble components in hardened mortar and concrete cement (such as lime hydroxide, bitter earth, lime sulfate, lime sulfide, calcium hydroxide, sodium hydroxide, potassium hydroxide). The dissolved solution passes through the interior of the concrete and moves to the surface, and the water evaporates as the surface dries, so that it precipitates on the surface, or reacts with carbon dioxide in the air to dissolve insoluble calcium carbonate, sodium carbonate, It is a “white substance with potassium carbonate deposited on the concrete surface”.

  The following three factors can be given when the generation factors of efflorescence generated on the surface of a conventional concrete structure are roughly classified.

  (1) As surplus water other than the bound water of concrete dries, a solution in which soluble components are dissolved on the surface oozes out and reacts with carbon dioxide gas to become efflorescence. This factor is remarkable in concrete with a large water-cement ratio.

  (2) A solution formed by dissolving the soluble components in cement by water infiltrated into concrete emerges from the concrete cracks, etc., reacts with carbon dioxide, and dries to become efflorescence.

  (3) Condensation occurs on the concrete surface due to a decrease in the outside air temperature, and the condensed water absorbs the inside of the concrete and dissolves soluble components. It comes out of the concrete cracks, etc., and reacts with carbon dioxide to dry. And it becomes efflorescence.

Recently, a concrete structure using so-called ultra-high-strength concrete having a compressive strength of 100 N / mm ² or more has attracted attention due to an increase in demand for ultra-high-rise apartments. This ultra high strength concrete is formed from a material in which pozzolanic reaction particles such as cement, silica fume and fly ash, blast furnace slag, fine aggregate, high performance water reducing agent and water are mixed. Such a material is characterized by using a larger amount of unit cement, unit silica fume, and the like of the material than ordinary concrete materials. When building columns, beams, slabs, etc. that make up a concrete structure with such materials, the concrete material is filled in the formwork, demolded after the specified strength is developed, and then the strength is developed in a short period of time. For this purpose, or in order to obtain a dense and durable concrete hydrate, it is effective to perform heat curing with steam.

  However, when performing high-temperature curing with steam, a solution in which soluble components are dissolved by water vapor is formed near the concrete surface, and at the end of steam curing, the solution in which the soluble components are dissolved reacts with carbon dioxide gas and dried. At the same time, it becomes efflorescence.

  In addition, in ultra-high-strength concrete, silica fume may be mixed in order to improve the strength, but this results in a strong blackish color compared to normal concrete, and white efflorescence is more noticeable. As a result, aesthetics are often impaired.

  There are several conventional solutions to the occurrence of efflorescence described above.

  (1) One of the solutions is a method of mixing an admixture that increases the waterproofness by forming a dense structure of concrete when the concrete is mixed. Although this method can be expected to have some effect on concrete having a relatively large water-cement ratio, it is ineffective on high-strength concrete and ultra-high-strength concrete.

  (2) Another solution is a method in which the concrete surface on which efflorescence is deposited is washed with a hydrochloric acid-based chemical and eliminated by neutralization and decomposition. In this method, since the concrete surface is neutralized with a weak acid, the concrete itself deteriorates in the vicinity of the surface. From the viewpoint of long-term durability of the concrete, this method remains a problem.

  The efflorescence described so far does not fundamentally reduce the mechanical performance and durability of a concrete structure. The only problem is detracting from the aesthetics of the concrete structure. Therefore, if the aesthetic improvement can be achieved, the objective of dealing with the occurrence of efflorescence has been achieved.

  In addition, as a conventional disclosure technique related to a method of removing efflorescence, as shown in Patent Document 1, the surface of contaminated concrete is irradiated with a low-power laser to completely remove efflorescence, and then organic or inorganic contamination is performed. There is also a technique in which a purifying material is sprayed and the like is melted by high-power laser irradiation. Furthermore, as shown in Patent Document 2, there is also a technology related to aerosolized cement and organic polymer used for partial repair paints and touch-up paints for inorganic cement bases widely used outside. is there.

JP-A-7-269130 JP 2005-162999 A

  The conventional solutions for the occurrence of efflorescence have the above-mentioned problems inherent to each, and the technique of Patent Document 1 described above is economical and practical because concrete surface treatment is performed in various steps. hard. Moreover, since the coating material of patent document 2 is not cement milk, it is necessary to thicken a coating film, Furthermore, since the extra time for aerosolization is required, material cost becomes expensive. In addition, the aerosolized cement spray coating material has a problem that the working environment is deteriorated because it is scattered in the air as dust when sprayed. As mentioned above, since the occurrence of efflorescence is only detrimental to the aesthetics, the aesthetic damage on the concrete surface can be done in a simpler way, more economically, and under normal working conditions. The development of a method that can prevent this is desired.

  The present invention has been made in view of the above problems, and color unevenness is caused by efflorescence generated on the concrete surface of a concrete structure or a concrete member such as a girder, column, beam, or slab constituting the concrete structure. An object of the present invention is to provide a method for removing color unevenness on a concrete surface, which can prevent the appearance of a structure from being damaged by a simple method.

  In order to achieve the above object, the method for removing uneven color on a concrete surface according to the present invention is either a first white cement from which iron in a cement component is removed or a second white cement made of cement and titanium oxide. One is mixed with water to produce white cement milk, and the white cement milk is adhered to the surface of the concrete structure after demolding.

  Cement is generally composed mainly of calcium, silica, alumina, and iron. By removing iron in this component, a white cement can be produced (first white cement).

  Moreover, a white cement can also be produced | generated by mixing about 3-15 weight% of cement with titanium oxide in the normal cement containing an iron component (2nd white cement).

  One of the white cements described above is mixed with 45 to 65% by weight of white cement to produce white cement milk.

  The method for removing uneven color on the concrete surface of the present invention is to form a white cement film made of an inorganic compound similar to concrete by adhering this white cement milk to the concrete surface of the concrete structure after demolding. . That is, it is not a technical idea of removing the efflorescence itself, but is a method that removes (eliminates) the uneven color of the concrete surface that may be caused by this while allowing the occurrence of efflorescence.

  The thickness of the white cement film described above is extremely thin, for example, about 30 to 100 μm, and since it is an inorganic compound similar to the concrete forming the concrete structure, it can be integrated with the surface of the concrete structure and is white due to shrinkage. There is no problem of cracks in the cement film. Furthermore, since it is an inorganic compound like concrete, there is no possibility of deterioration due to ultraviolet rays or the like, and it has long-term durability like a concrete structure. Therefore, there is no maintenance cost for the white cement film. Note that it is preferable to use an ultrafine cement having an average particle size of about 4 μm as the cement because the white cement film is uniform.

  In addition, as described above, white cement milk is generated and applied to the surface of the concrete structure after demolding, so that the construction cost is low, and even when the construction area is large, it is a short time. Construction can be carried out.

  Further, in the method for removing color unevenness on the concrete surface according to the present invention, the method of attaching the white cement milk is one of a method of spraying or a method of application, and after the white cement milk is attached to the concrete surface. The concrete surface is heat-cured.

  Here, the method by application | coating can be performed with a brush, a roller, etc.

  In addition, since cement milk may sag when adhering to the surface of concrete structures, organic polymers such as styrene butadiene based polymer dispersions can be mixed with white cement to improve adhesion performance. .

  In the present embodiment, after the white cement milk is attached to the concrete surface, the concrete surface is heat-cured with steam or the like. By this heat-curing, the cement milk adhering to the surface and the original concrete structure The unhydrated cement component on the surface can be integrated with each other to complete the hydration reaction. Therefore, the cement milk adhering to the concrete surface is integrated with the unhydrated cement on the surface of the concrete structure, and a stable white hydrate film can be formed. Since this stable film is an inorganic hydrate, it does not deteriorate due to ultraviolet rays or the like, and the film does not peel off due to shrinkage.

  When the concrete structure (surface) is steam-cured, as described above, the solution containing soluble components that cause efflorescence reacts with the carbon surface at the same time as steam curing, and this causes the efflorescence to react with drying. Precipitate on the surface. However, in the method according to the present invention, since the white cement film is on the ground, the white color of the generated efflorescence becomes inconspicuous, and as a result, the appearance of the concrete surface is not impaired.

  As a method similar to the present invention, there is a method of applying a white paint. In the case of painting with paint materials, it is impossible to prevent deterioration due to ultraviolet rays over a long period of time because the materials used are organic compounds, and it is necessary to repaint the paint approximately every 5 years. Not right. Also, since the paint is made by dissolving the pigment with a solvent, the solvent gradually evaporates after the coating, the paint itself contracts and cracks the coating film, which impairs the aesthetic appearance. Furthermore, when paint is applied in a state where moisture is present inside or on the concrete, the concrete surface is completely sealed, and the moisture inside and on the concrete becomes steam as the temperature rises, and this precipitates. As a result, a moisture layer that does not escape is formed at the interface between the concrete and the paint coating, and the paint layer is in a blistering state that bulges outward, causing a difficult repair state.

  On the other hand, according to the method of the present invention, as described above, since the cement film, which is an inorganic compound, is integrated with the surface of the concrete structure, there is no deterioration over time due to ultraviolet rays, so that maintenance costs are not generated.

  In addition, the white cement film is integrated with the surface of the concrete structure, and the moisture inside and on the surface is consumed by the hydration reaction of the cement. Such a problem cannot occur.

Furthermore, in the method for removing uneven color on the concrete surface according to the present invention, the concrete forming the concrete structure is made of a material in which cement, fine aggregate, high-performance water reducing agent, water, and pozzolanic reaction particles are mixed, It is characterized by being ultra high strength concrete having a compressive strength of at least 100 N / mm ² .

  Concrete structures made of ultra-high-strength concrete targeted by the method of the present invention include all concrete structures including precast segments and girders of bridges, columns, beams, slabs, and tunnel liner segments. Is done.

  Here, examples of the pozzolanic reaction particles include silica fume, fly ash, and blast furnace slag.

  As described above, the material for ultra-high-strength concrete uses a larger amount of material unit cement, unit silica fume, etc. than ordinary concrete material, and fills the formwork with the concrete material, It is effective to perform heat curing with steam in order to remove the mold after the predetermined strength development and then develop the strength in a short period of time, or to obtain a dense and durable concrete hydrate. .

  In such high-strength concrete structures or precast segments, girders, columns, beams, slabs, etc. that make up this structure, efflorescence is caused by the water that has penetrated into the interior of ordinary concrete structures after use. Unlike occurring, it occurs only after steam curing. It is impossible to avoid the occurrence of this efflorescence itself.

  Therefore, by forming the white cement film according to the present invention before steam curing, even if efflorescence occurs on the surface of the ultra-high-strength concrete structure, the color unevenness due to the efflorescence is effectively prevented without impairing the aesthetic appearance. Can be removed.

  As can be understood from the above description, according to the method for removing uneven color on the concrete surface of the present invention, the surface of the concrete structure resulting from the efflorescence in an inexpensive and extremely simple manner while allowing the occurrence of efflorescence. The color unevenness can be effectively removed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining a method for removing uneven color according to the present invention, and shows a girder in which white cement milk is applied to the surface after demolding to form a white cement film. FIG. 2a is a front view photograph of a girder coated with white cement milk containing white cement containing 7.5% by weight of titanium oxide as a component on the surface, and FIG. It is the front view photograph of the girder which applied the white cement milk which made the white cement mixed with weight% the ingredient on the surface. FIG. 3 is a front view photograph of a girder divided into two regions. One region has white cement milk on the surface containing white cement composed of 7.5% by weight of titanium oxide in the cement. The coated area, and the other area is a non-measure area. In the illustrated embodiment, a girder made of ultra-high-strength concrete is taken up as a target concrete structure. However, the concrete structure may be a girder, column, slab, or the like in any other form. Of course, it may be formed of a general concrete material.

  FIG. 1 is a schematic diagram for explaining a method for removing color unevenness generated on the surface of a concrete structure by efflorescence.

  First, an ultrahigh strength concrete material is filled in a mold having a predetermined shape (not shown). Here, the concrete material is a material in which cement, fine aggregate, high-performance water reducing agent, water, and pozzolanic reaction particles such as silica fume are mixed.

  Next, the mold is removed after waiting for a predetermined strength to be produced.

  Immediately after demolding, white cement milk is sprayed on the left and right wide surfaces of this girder 1. This white cement milk is produced by mixing water with either a white cement from which iron in the cement component has been removed or a white cement made of cement and titanium oxide.

  By spraying the white cement milk, as shown in FIG. 1, the girder 10 in which the white cement films 2 and 2 are formed on the left and right surfaces is manufactured. Here, the film thickness of the white cement film 2 is as extremely thin as about 30 to 100 μm.

  In addition to the spraying, there is a method of applying white cement milk to the surface of the girders, for example, a method using a brush or a roller. However, the spraying method is more economical.

  After the white cement film 2 is formed, the process proceeds to a steam curing process. For example, the girders 10 shown in FIG. 1 are transferred into a high-temperature steam pot (not shown) and steam-cured in a high-temperature atmosphere. In addition, a method may be used in which the steam gaze is not used, the girder is surrounded by a heat insulating sheet, steam is supplied, and steam curing is performed.

  By manufacturing the girders in the above process, carbon dioxide gas reacts with a solution that dissolves soluble components that cause efflorescence on the concrete surface at the same time as steam curing, and this causes efflorescence to precipitate on the surface as it dries. To do. However, according to the above method, the white color of the efflorescence generated due to the white cement film 2 on the ground becomes inconspicuous, and as a result, the color unevenness generated on the concrete surface is removed, and a girder excellent in aesthetic appearance is manufactured. Can do.

  The inventors actually manufactured the girders according to the method of the present invention, changed the mixing ratio of titanium oxide to produce white cement milk, and compared the white cement film formed with each cement milk. (Contrast observation 1). Furthermore, the presence or absence of color unevenness in the place where the white cement film was formed and the place where it was not formed was confirmed (contrast observation 2).

  First, in contrast observation 1, two types of white cement were prepared: white cement containing 7.5% by weight of titanium oxide and white cement containing 12% by weight of titanium oxide. The white cement milk produced by mixing with the glass was sprayed on the surface of the spar, and the state of uneven color on the surface of the spar after steam curing was observed and compared. Here, the spraying method was performed by spraying in the horizontal direction after spraying in the vertical direction.

  2a shows the case of white cement mixed with 7.5% by weight of titanium oxide, and FIG. 2b shows the case of white cement mixed with 12% by weight of titanium oxide.

  FIG. 2a is a front view photograph of the girder 20. In FIG. 2a, 21 indicates a white cement film. From FIG. 2 a, almost no color unevenness due to efflorescence was observed on the surface on which the white cement film 21 was formed.

  On the other hand, FIG. In FIG. 2b, 31 indicates a white cement film. Also in FIG. 2b, there was almost no uneven color due to efflorescence in the white cement film 31, but from the aesthetics of the surface, the white cement film 21 in FIG. 2a was more uniform and excellent in aesthetics. .

  Next, the result of the contrast observation 2 will be described based on FIG. The figure shows a front view of a girder divided into two areas. One area (the right area in the figure) is made of white cement containing 7.5% by weight of titanium oxide in the cement. This is a region where white cement milk as a component is applied to the surface, and the other region (the left region in the figure) is a non-measured region. It was clear that color unevenness due to efflorescence was not confirmed on the surface on which the white cement film 21 on the right side was formed, whereas color unevenness due to efflorescence was significant on the left non-coated surface 22.

  According to the color unevenness removal method of the present invention described above, the following effects can be obtained.

  (1) Since the white cement film is an inorganic compound similar to the concrete forming the concrete structure, there is no possibility of deterioration due to ultraviolet rays, and long-term durability is equivalent to that of the concrete structure. Maintenance costs are not incurred.

  (2) Since the hydration reaction is completely completed by steam curing, the white cement film does not shrink and dry over a long period of time, and since the film thickness is extremely thin, the film does not crack. .

  (3) Although it is impossible to prevent the occurrence of efflorescence when steam curing ultra-high strength concrete, by forming a white cement film on the concrete structure surface before steam curing, Even if efflorescence occurs, it does not lead to a loss of aesthetics.

  (4) In the blending of ultra high strength concrete, the color of the concrete becomes blacker than that of normal concrete by mixing silica fume. Therefore, the uneven color due to the efflorescence is easily noticeable due to the steam curing, resulting in aesthetic damage. On the other hand, by forming the white cement coating on the surface of the concrete structure by the method for removing color unevenness according to the present invention, it is possible to eliminate aesthetic damage while allowing the occurrence of efflorescence.

  (5) Since the uneven color removal method according to the present invention is an economical and simple method, the uneven color removal work on the surface of the concrete structure in the future, especially the uneven color removal on the surface of the ultra-high-strength concrete structure. Suitable for construction.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

It is a schematic diagram for explaining the method for removing uneven color according to the present invention, and shows a girder in which white cement milk is applied to the surface after demolding to form a white cement film. (A) is a front view photograph of a girder coated with white cement milk containing white cement containing 7.5% by weight of titanium oxide in cement as a component, and (b) is titanium oxide with respect to cement. It is the front view photograph of the girder which applied the white cement milk which made the white cement which mixed 12weight% of the ingredient into the surface. It is a front view photograph of a girder divided into two regions, and one region is a region in which white cement milk containing white cement composed of 7.5% by weight of titanium oxide mixed with cement is applied to the surface. The other area is a non-measure area.

Explanation of symbols

1, 10, 20, 30 ... girders, 2, 21, 31 ... white cement coating, 22 ... non-coating surface

Claims (3)

  Mixing water with either the first white cement from which iron in the cement component is removed or the second white cement made of cement and titanium oxide to produce white cement milk, demolded concrete A method for removing uneven color on a concrete surface, characterized in that the white cement milk is adhered to the surface of a structure.   The method for adhering the white cement milk is one of a method by spraying or a method by application, and after the white cement milk is adhered to the concrete surface, the concrete surface is heat-cured. Item 4. The method for removing uneven color on the concrete surface according to Item 1. The concrete forming the concrete structure is an ultra-high-strength concrete having a compressive strength of at least 100 N / mm ^{2 made} of a material in which cement, fine aggregate, high-performance water reducing agent, water, and pozzolanic reactive particles are mixed. The method according to claim 1 or 2, wherein there is uneven color removal on the concrete surface.

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