EP2760653B1 - Method for producing components having a high-quality concrete edge zone and concrete surface - Google Patents

Description

Technical area:

The invention relates to a method for applying an agent on the formwork surface of a concrete formwork for the production of concrete components with a high-quality concrete edge zone.

State of the art:

Concrete is ubiquitous as a building material in the construction of buildings and civil engineering. Due to the possibility of incorporating the concrete in a flowable consistency into a formwork of any shape and allowing it to harden, it is possible to give the components almost any shape and size. There has therefore been no lack of efforts to use concrete not only for components with a constructive purpose, but also to use as a means of producing visually appealing structures.

In this context, the concrete surface as a visible surface is of overriding importance. Their optical quality depends primarily on the color uniformity, the surface texture and the porosity. Influencing factors on these factors are, in addition to the concrete recipe and the processing of the concrete, above all the formwork and the release agent used. These significantly influence the concrete structure in the concrete edge zone and thus not only the strength, but also the optical quality of the concrete surface.

Concrete basically consists of three components, namely a hydraulic binder, mineral aggregates and water. With regard to the quality of the concrete, the water-cement value plays a key role. If the concrete has too little water, the hydration can not be complete. Is more Water present as necessary for hydration, so the excess mixing water leads to increased pore formation and strength losses.

The quality of the concrete edge zone is essentially determined by the interaction of the concrete, the formwork and the release agent. In the concrete edge zone, the concrete has less aggregate, while the proportion of cement paste is increased. When using a non-absorbent formwork, such as a formwork made of steel or plastic, the excess mixing water can not diffuse into the formwork. In the concrete edge zone, therefore, an increased water content and thus increased water-cement value. This leads to a lower concrete strength and an increased pore content in this area with a tendency to sedimentation. When using absorbent formwork such as wood or cardboard, water is extracted from the concrete edge zone and the water-cement value is lowered. By adhering the concrete to the formwork, there is the risk during demoulding that the closed concrete surface is broken up into partial areas, which can only be partially remedied by time-consuming refurbishment work.

Powdered, water-insoluble hydrophilic polymers are for example from EP 1 329 435 A1 and the publication of Mechtcherine V. et al. "Internal curing by superabsorbent polymers (SAP) - VOLUME CHANGES OF HARDENING CONCRETE: TESTING AND MINI-GATION: INTERNATIONAL RILEM CONFERENCE; LYNGBY, DENMARK, AUGUST 20-23, 2006. PROCEEDINGS, August 20, 2006, (2006-08-20) pages 87-96 ,

The GB 976 133 A discloses a method for producing a concrete component by placing concrete in a formwork on which surface of the formwork facing the concrete is applied a means of a paper carrier layer coated with a hydrogel forming agent. The hydrogel-forming agent / polymer is a mixture of starch and carboxymethyl cellulose or sodium alginate.

The US 3,941,864 A describes a method for producing a concrete component by introducing concrete into a formwork on which the concrete facing surface of Forming a dispersion of fine silica fume (hydrogel) and a curable organosilicon compound is applied.

The publications " Form concrete - formwork web from Betomax / Formwork bed for a high surface quality Formtex - Formwork non-woven mat from Betomax ", BFT International, Bauverlag, Gütersloh, DE, Vol. 69, No. 9, 1 January 2003 ( 2003-01-01), page 84 and Springenschmid R. et al: "Shutterings to improve the concrete edge area", BFT International, Bauverlag, Gütersloh, DE, Vol. 56, No. 11, 1 November 1990 (1990-11-01), pages 78-82 reveal formwork inserts to improve the concrete area and thus to reduce the porosity. However, other means are used there.

Presentation of the invention:

Against this background, the object of the present invention is to provide an alternative method for improving the quality of the concrete in the edge zone as well as on the component surface.

This object is achieved by a method having the features of patent claim 1.

Advantageous embodiments will be apparent from the dependent claims.

The invention is based on the idea of creating an optimal framework for the hydration of the concrete by an automatic regulation of the water-cement value and thus to improve the quality of the concrete edge zone. This is achieved according to the invention with the aid of a means which has as an essential component at least one hydrogel, which is applied flat on the concrete facing side of a formwork.

For the purposes of the invention, the term "hydrogel" is understood to mean water-insoluble polymers which are present as a three-dimensional network. These polymers also include so-called superabsorbents. In water, these polymers swell under retention of shape until an equilibrium state is reached. The networking takes place predominantly via covalent linkages of the polymers, but is also possible via electrostatic, hydrophobic or dipole / dipole interactions between individual segments of Poylmerketten. The necessary hydrophilicity of the polymers comes, inter alia, from hydroxyl, carboxylate, sulfonate or amide groups. By appropriate selection, the properties of the hydrogel can be adjusted. The invention also encompasses synthetic hydrogels which are based, for example, on polyacrylic acids, polyacrylates, polycarboxyllates, polyvinylpyrrolidone or polyvinyl alcohol. Due to its ability to store water, hydrogel and thus the agent is able to absorb excess mixing water in the concrete with volume increase. The agent forms a full-surface dense film on the scarf surface. Should additional water be needed at a later date for complete hydration in the concrete rim zone, the hydrogel will be able to return stored water to the concrete.
Because of these properties, the agent used in the process proves to be advantageous in two respects. On the one hand, the water content in the concrete edge zone is regulated and thus the local water-cement value. This partially replaces a post-treatment of the concrete and also leads to an improvement in the quality of the concrete and reduction of porosity. It forms a smooth, closed and dense surface without the risk of sanding fine concrete particles.
At the same time, the film which forms causes a separating effect between concrete and formwork, which prevents adhesion of the concrete to the shell surface in the course of hardening. The result is a concrete surface with uniform texture without significant visible pores. Reworking due to adhering concrete is completely eliminated. The agent therefore also equals a release agent.

The hydrogel has powdery consistency before it comes in contact with the concrete. The application to a horizontal or vertical scarf surface is then advantageously by spraying, rolling or rubbing with a sponge, Flaps or the like, wherein by selecting the appropriate surface density of the order, the absorption capacity can be adjusted. For the purposes of the invention, a preferred surface coverage of the hydrogel provides 1 g / m ² to 10 g / m ² .

The fixation of the hydrogel on the scarf surface is done according to a preferred embodiment of the invention by means of a carrier layer which is applied to the scarf surface and adheres there. The support layer can cure after application of the hydrogel, whereby a particularly good and permanent fixation of the hydrogel takes place. This alternative is preferred in scarf areas for single use, since the hardened carrier layer does not have to be removed from the scarf surface. However, the support layer may also be formed by a viscous material, for example a polyol which immobilizes the hydrogel with its adhesive surface. Especially with scarf areas for repeated use, this alternative proves to be advantageous because the carrier layer can be easily removed from the scarf surface.

An advantageous embodiment of the invention also provides to arrange the carrier layer on a film or form itself as a film. The film can then be applied as a disposable film on the formwork inside, where it comes into contact with the fresh concrete. For attachment, the film may be self-adhesive on its back. The film also serves as protection for the formwork, which can be used again without further preparation for re-use in this way. Since the film is intended for single use, this embodiment is equally suitable for both hardenable carrier layers and viscous carrier layers. The film is preferably made of PVC, polyethylene or polyurethane.

Suitable materials for a carrier layer according to the invention are, for example, clearcoats, resins, pressure-sensitive adhesives, polyurethanes and formaldehyde oils which are sprayed on in a liquid or viscous state. StyrolButadien, which is applied as an aqueous solution on the scarf surface is also suitable as a carrier layer. After evaporation of the aqueous portion, an adhesive layer for receiving the hydrogel remains. A further embodiment provides for the use of an aqueous silicate solution as a carrier layer, for example based on biopolymers or Water glass, which additionally has a positive effect on the quality of the concrete surface in terms of a closed and dense structure. The powdery hydrogel adheres to the surface of such carrier layers, where it absorbs mixing water in the region of the edge zone after introduction of the fresh concrete.

Another embodiment of the invention provides to embed the hydrogel in a matrix and apply both components together as a kind of dispersion on the scarf surface, which can also be done by spraying. The weight-related mixing ratio of hydrogel to matrix is preferably in a range of 0.01 to 2.5. Suitable materials for this purpose consist of resin, pressure-sensitive adhesive, polyol, formaldehyde oil or an aqueous styrene-butadiene solution.

In an advantageous embodiment of the invention, the carrier layer or the matrix has hydrophobic properties. For this purpose, the carrier layer or the matrix may consist of a hydrophobic material or have hydrophobic constituents or a hydrophobic layer, for example of a hydrophobic polyol or acrylate. Before concreting, the hydrophobic properties ensure that the hydrogel does not prematurely absorb moisture and swell. During concreting, the concrete surface also obtains hydrophobic properties by crosslinking with the agent according to the invention, so that optionally a subsequent hydrophobic surface treatment of the component is no longer necessary, for example for protection against impurities, graffiti and the like.

Both the support layer embodiment and the matrix embodiment may additionally be provided with a protective layer which protects the hydrogel from moisture to prevent swelling prior to concreting. As a protective layer, for example, hydrophobic agents or conventional concrete release agents are. The concrete pressure acting on the protective layer during concreting exposes the hydrogel and results in the desired absorption of water.

Since the hydrogel applied to the formwork surface is not readily perceptible to the naked eye due to its inconspicuous coloration and the relatively low surface density of the application, in an advantageous embodiment of the invention the hydrogel is removed from the surface Application to the scarf surface mixed with color pigments. Suitable color pigments are the pigments or carbon black particles known for the coloration of concrete. The mixture of hydrogel and color pigments is well perceived after the order on the scarf surface, so that a complete and uniform application of the composition according to the invention is easy to monitor. The mixture of hydrogel and color pigments can be applied as described above to a carrier layer or incorporated into a matrix. Since some color pigments themselves have adhesive properties, the mixture can also be applied directly to the formwork surface, for example by rubbing in.

Brief description of the drawings:

The invention will now be described with reference to two illustrated in the drawings embodiments.

Fig. 1

einen Teilquerschnitt durch eine Schalung, bei der ein Hydrogel unter Zwischenschaltung einer Trägerschicht auf die Schalung aufgebracht ist und

Fig. 2

einen Teilquerschnitt durch eine Schalung, bei der ein in eine Matrix eingebettetes Hydrogel auf die Schalung aufgebracht ist.

It shows

Fig. 1

a partial cross section through a formwork, in which a hydrogel is applied with the interposition of a carrier layer on the formwork and

Fig. 2

a partial cross-section through a formwork, in which a embedded in a matrix hydrogel is applied to the formwork.

Ways to carry out the invention and commercial usability:

In Fig. 1 one sees the area of a formwork skin 2 facing the concrete 1, the formwork surface of which is designated by the reference numeral 3. A viscous carrier layer 4 adheres to the formwork surface 3. Particles of a pulverulent hydrogel 5, which adheres to the carrier layer 4 as a result of adhesion occurring, can be seen on the outside of the carrier layer 4. Optionally, the hydrogel 5 may be covered with a protective layer 6, which is merely indicated by dashed lines.

In the Fig. 2 illustrated embodiment of the invention also shows the concrete side part of a formwork 2 with scarf 3. On the scarf surface 3, a matrix 7 is applied, in which particles of a hydrogel 5 are embedded. Again, the matrix may be 7 may be covered with a hydrogel 5 of a protective layer 6 according to the under Fig. 1 described embodiment.

Claims (12)

1. Method for producing a concrete component having a high-quality concrete edge region by introducing concrete (1) into a shuttering (2), characterised in that an agent is applied to the surface (3) of the shuttering (2) facing the concrete (1), which agent comprises a water-insoluble hydrophilic polymer (5) having a powdery consistency.
2. Method according to claim 1, characterised in that the water-insoluble hydrophilic polymer (5) is based on starch, cellulose, carboxymethyl cellulose, polyacrylic acid, polyacrylate, polyacrylamide, polyvinylpyrrolidone, potassium polyacrylate, polyvinyl alcohol, sodium polyacrylate or polycarboxylates.
3. Method according to claim 1, characterised in that a backing layer (4) is initially applied to the shuttering surface (3) and the water-insoluble hydrophilic polymer (5) is applied to the backing layer (4).
4. Method according to claim 3, characterised in that the backing layer (4) is made of a clear lacquer, resin, pressure-sensitive adhesive, polyol, polyurethane, shuttering oil, an aqueous styrene-butadiene solution or an aqueous silicate solution.
5. Method according to claim 3, characterised in that the backing layer (4) consists of a hardening material, for example polyurethane.
6. Method according to claim 3, characterised in the backing layer (4) consists of a permanently viscous material, for example polyol.
7. Method according to claim 3, characterised in that the backing layer (4) is made of a film or is arranged on a film that is applied, preferably glued, to the concrete shuttering (2).
8. Method according to claim 7, characterised in that the film comprises at least one layer made of PVC, polyethylene or polyurethane or is made of one of these materials.
9. Method according to claim 1, characterised in that the water-insoluble hydrophilic polymer (5) is mixed with a liquid or viscous matrix (7) and is applied to the shuttering surface (3) together with the matrix (7).
10. Method according to claim 9, characterised in that matrix (7) is made of a resin, pressure-sensitive adhesive, polyol, shuttering oil or an aqueous styrene-butadiene solution.
11. Method according to any of claims 3 to 10, characterised in that the backing layer (4) or the matrix (7) has hydrophobic properties.
12. Method according to any of claims 1 to 11, characterised in that the agent comprises a protective layer (6) on the surface facing the concrete (1).

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