METHOD FOR PRODUCING A FORMWORKED COLOURED CONCRETE STRUCTURE AND A CONCRETE STRUCTURE PRODUCED IN ACCORDANCE WITH SAID METHOD

Abstract: The present invention relates to a method for producing a formworked, coloured concrete structure, whereby a form is set up, and that form removal is effected when sufficient curing of the concrete structure has taken place. The invention also relates to a concrete structure produced in accordance with said method. When producing coloured concrete structures it is a common technique that concrete, coloured throughout, is used for the entire concrete structure. This is costly since coloured concrete is more expensive than uncoloured concrete and besides the casting properties of the concrete is affected negatively. The present invention is characterized in that a layer of shotcrete, coloured throughout, is applied on the inner side of the form, and that subsequently further concrete is supplied to the form, said further concrete adhering to the shotcrete.

Description: METHOD FOR PRODUCING A FORMWORKED COLOURED CONCRETE STRUCTURE AND A CONCRETE STRUCTURE PRODUCED IN ACCORDANCE WITH SAID METHOD Technical Field of the Invention The present invention relates to a method for producing a formworked coloured concrete structure, whereby a form being set up, and that form removal is effected when sufficient curing of the concrete structure has taken place. The invention also relates to a formworked coloured concrete structure . Prior Art A common technique m the marketplace to produce coloured concrete structures, e.g. bridges and pre-fabricated elements, is to colour the whole of the concrete mass throughout . This involves high expenses and also brings about technical problems. Concrete coloured throughout is often subjected to deteriorated properties as regards casting compared to uncoloured concrete. The colouring pigment, usually in the shape of a fine powder, causes the fine material content to increase in the concrete . The concrete mass then becomes semi-fluid and is subjected to deteriorated fluid properties, i.e. it becomes more difficult to displace the concrete inside the form. This brings about difficulties as regards proper filling of the form and enclosure of the reinforcement . To a certain degree the problem may be reduced by having fine material washed away from the aggregate. However, such a method is expensive and brings about further demands as regards the producing process. It is also difficult to maintain an unchanged chromatic colour m connection with the production of large quantities of concrete that is coloured throughout, i.e. several batches of concrete. An extremely careful cleaning of the batching plant is also necessary before it is again possible to produce uncoloured concrete . A method for producing a concrete article having a coating is previously known from SE-B-378 783. The used technique involves the production of the form, or part of the form, in expanded polystyrene and when the concrete has cured in the form an organic solvent is supplied to the expanded polystyrene and then a solution from expanded polystyrene in the organic solvent is run off leaving the surface of the concrete covered by the solution. When the solvent evaporates the polystyrene creates an attractive glaze on the surface of the concrete . Objects and Features of the Invention The primary object of the present invention is to define a method for producing coloured formworked concrete structures, only a surface layer of the concrete structure being coloured throughout, said surface layer having an extremely high strength. A further object of the method according to the present invention is to achieve an extremely good adhesion between the surface layer that is coloured throughout and the rest of the concrete structure. Still an object of the method according to the present invention is that the surface configuration of a concrete structure produced in accordance with the method according to the present invention achieves a surface configuration that corresponds to the surface configuration of conventional uncoloured concrete structure . The objects of the invention are realised by means of a method and a concrete structure that has been given the features of the appending claims. Preferred embodiments of the invention are defined in the dependent claims. Description of a Preferred Embodiment of the Invention When a concrete structure according to the invention is to be produced a form for said concrete structure is initially set up, i.e. formwork if effected. When the formwork is ready a surface layer of shotcrete is applied on the inner side of the form, said shotcrete being coloured throughout . By shotcrete should in this connection be understood a concrete consisting of cement and fine aggregate, i.e. sand having a grain size of usually 0-8 mm and water. The shotcrete may be unreinforced or reinforced, the reinforcement normally being fibres of a suitable material, said fibres being mixed into the shotcrete. Different chemical additives may also be supplied to the shotcrete in order to affect its properties. The application of the shotcrete is normally carried out in a conventional way by means of a conventional equipment, e.g. a spray nozzle through which pressurised fresh concrete is brought to pass. Within the scope of invention it is feasible that the shotcrete is applied in a way other than the conventional. The surface layer of shotcrete that is applied on the inner side of the form preferably has a thickness of 15-30 mm. There is normally no problems in making the shotcrete to adhere to the inner side of the form, regardless if the inner side of the form constitutes for instance unplaned wood, so-called tongued and grooved board, plywood or sheet metal. In this connection the possibility to attach dies on the inner inside of the form, in order to achieve the desired surface configuration, should also be mentioned. To through-colour the shotcrete does normally involve no problems since the mixture of a colouring pigment normally is carried out in the same way as when colouring pigment is supplied to conventional concrete. In this connection it should be pointed out that the negative effect that the mixture of colouring pigment has upon the casting properties of concrete, see above under "Prior Art", is not the same for shotcrete since the application of shotcrete if effected under pressure and the concrete is thrown against the form. Within the scope of the invention it is also feasible that the mixture of the colouring pigment in the shotcrete is effected in the way that is described in SE-B-397 940, i.e. that the shotcrete and the colouring pigment are applied by means of separate nozzles that are concentric relative to each other. When the shotcrete has cured to a certain degree reinforcement of the form, inside of the surface layer, is effected, if such reinforcement constitutes a part of the concrete structure. Otherwise this operation is cancelled. If reinforcement is effected it is important that the surface layer of shotcrete is allowed to cure during necessary long time in order to make the surface layer able to withstand the stresses that arise in connection with the reinforcing. If shotcrete for instance is applied on the bottom of the form the adherent surface layer normally must withstand the stresses that arise when the people in charge of the reinforcement walk upon said surface layer. When a sufficient curing of the shotcrete has been effected and possible reinforcement has been effected further concrete is supplied, normally conventional uncoloured concrete, i.e. the form is filled with said conventional concrete . By the term concrete it should be understood in this connection a mass consisting of cement, aggregate (crushed rock and gravel), water and suitable additives. The mass is mixed to a consistency that makes the mass castable, i.e. fluid characteristics, handling stability and so on are important parameters of the concrete . In this connection it should be noted that the inwardly facing surface of the shotcrete is rough/coarse since it is not subjected to any treatment but is allowed to cure with the surface configuration that is achieved in connection with application of the shotcrete. The positive effect of this is that the conventional uncoloured concrete properly adheres to the rough/course surface of the shotcrete when said conventional uncoloured concrete is supplied to the form. When the conventional uncoloured concrete has been supplied to the form and reached the desired level it is allowed to cure, whereby a through-hardened concrete structure is achieved where the core consists of conventional uncoloured concrete and the surface layer consists of shotcrete that is coloured throughout. In this connection it should be pointed out that shotcrete generally has a lower water-cement ratio than conventional concrete that is used for casting. The water- cement ratio defines in principle the water content of the concrete, whereby a low water-cement ratio corresponds to a low water content. It is a well known fact in connection with concrete structures that low water content provides a strong concrete. The fact that the concrete structure according to the present invention is provided with a surface layer of shotcrete is thus beneficial since said surface layer has an even higher strength than the conventional concrete forming part of the structure. In other connections, if a method according to the invention for instance is applied when producing prefabricated wall elements in a factory where the surface layer of shotcrete is not subjected to any stresses worth mentioned, it may be sufficient with a substantially shorter curing time for said surface layer of shotcrete. It is also feasible that the remaining concrete is supplied before the shotcrete has cured, this increasing the adhesion between the shotcrete and the remaining concrete. Since the shotcrete at its outer side contacts the inner side of the form the form removal produces an external surface having a corresponding configuration as if concrete coloured throughout had been used for the entire concrete structure. According to the present invention only a surface layer of the concrete structure is coloured throughout and hence it is realised that essential cost savings are achieved by means of the present invention compared to conventional technique, i.e. that the entire concrete structure is coloured throughout . The additional cost to provide a coloured concrete structure is reduced by at least 50% when applying the present invention. Generally, the invention is applicable on a number of different concrete structures where a surface layer that is coloured throughout is desired. In exemplifying but not restricting purpose m-situ cast concrete structures as well has pre-fabricated concrete structures may be mentioned. Different feasible application areas are for instance bridges, retaining walls, wall elements. Of course, the invention may also be applied only on a part of or parts of a concrete structure. Thus, the invention may be freely varied within the scope of the appending claims.

Claims: Claims 1. Method for producing a formworked coloured concrete structure, whereby a form is set up, and that form removal is effected wnen sufficient curing of the concrete structure has taken place, c h a r a c t e r i z e d m that a layer of shotcrete, coloured throughout, is applied on the inner side of the form, and that subsequently further concrete is supplied to the form, said further concrete adhering to the shotcrete. 2. Method according to claim 1, c h a r a c t e r i z e d m that the further concrete is supplied to the form when the shotcrete has cured to a sufficient degree. 3. Method according to claim 1 or 2 , c h a r a c t e r i z e d m that the further concrete constitutes uncoloured standard concrete. 4. Method according to claim 2 or 3 , c h a r a c t e r i z e d in that reinforcement is effected when the shotcrete layer has cured to a sufficient degree and before further concrete is supplied to the form. 5. Method according to any of the claims 1-4, c h a r a c t e r i z e d in that the further concrete is vibrated when it has been supplied to the form. 6. Formworked coloured concrete structure, c h a r a c t e r i z e d in that it comprises a surface layer of shotcrete, coloured throughout, that during production of said concrete structure said layer of sotcrete is applied on the inner side of the form, and that the further concrete of said concrete structure adheres to the surface layer of shotcrete. 7. Concrete structure according to claim 6, c h a r a c t e r i z e d m that the surface layer of shotcrete is unreinforced or reinforced. 8. Concrete structure according to claim 6 or 7 , c h a r a c t e r i z e d in that the further concrete constitutes uncoloured standard concrete. 9. Concrete structure according to any of the claims 6-8, c h a r a c t e r i z e d in that the further concrete is unreinforced or reinforced. 10. Concrete structure according to any of the claims 6-9, c h a r a c t e r i z e d in that the surface layer of shotcrete has a thickness of 15-30 mm.

Inventors: MELLSTROEM GOERAN, MELLSTROEM, GOERAN
Applicants: MELLSTROEM GOERAN, MELLSTROEM, GOERAN
Application year: 1999
Main classification: B28B11
IPC codes: B28B1