FACE MATERIAL AND ITS MANUFACTURING PROCESS

Abstract: The invention relates to a combined facade element (1), consisting of a first layer (2), made of natural stone, and a second layer (3), made of concrete, located against the layer of natural stone. The invention also relates to the method for the manufacture of the element. According to this method, one side of the natural stone slab is sand-blasted to make it convex. The sand-blasted surface is treated with a polymer to reduce its hygroscopicity, whereafter concrete is cast on this side and formed into a slab which is reinforced and allowed to harden. While the concrete shrinks, the prebending of the natural stone slab, produced by sand blasting, returns to its previous shape, and the result is a weather-resistant slab with good strength properties and with an excellent bond between the natural stone and concrete layers.

Description: Face material and its manufacturing process The present invention involves a combined natural stone and concrete slab intended for use as face material in accordance with the caption of Claim 1. This element consists of a face layer of natural stone and of a base layer of concrete which lies against the natural stone layer. Furthermore, the invention involves, in accordance with the caption of Claim 14, the manufacture of the combined natural stone and concrete slabs. According to the process, concrete is cast on one side of the natural stone slab which then provides the casting bed for the concrete and, if required, the concrete is fitted with reinforcement, and is then allowed to set and harden . The invention also involves the way of making natural stone slabs, especially face slabs of natural stone, more water repellent . Until now, marble facades have been made of compact natural stone slabs. The disadvantage of such slabs is that in outdoor conditions they, in a relatively short time, bend and break due to weathering. It is also known how to manufacture combined natural stone and concrete slabs which comprise a first outer layer made of natural stone and a second inner layer of concrete. But the insufficient bond between the two layers has proved to be a great problem with the known combined slabs. The aim of the invention is to provide a remedy for the difficulties relating to the state of the art and to offer a combined natural stone and concrete slab of a whole new type which can be used as face material . The invention is based on the idea that natural stone, for example marble, is cast together with a reinforced concrete slab to form a face element. According to the invention, the natural stone slab is bent, so that the surface upon which the concrete for the concrete slab is cast becomes convex and shows a bending of about 0.1 to 10 mm per metre. Since the cast concrete shrinks during setting and hardening, the natural stone slab straightens out of the firm concrete thereupon, and this takes place during the setting and hardening process. To achieve a sufficient bond between the concrete and the natural stone, the surface of the natural stone must be made water repellent prior to casting, preferably by a treatment with a polymerized resin. It is an advantage if the concrete contains a part of crushed natural stone which is able to bind water. The distinctive and distinguishing features of the combined facade element, according to the invention, are specified in more detail in the respective section under Claim 1. As for the process according to the invention, its distinctive and distinguishing features are specified in the respective section under Claim 14. The distinctive and distinguishing features of the way of increasing the water repel lence of natural stone slabs are specified in the respective section under Claim 23. The invention allows to gain considerable advantages. As mentioned above, the bent natural stone slab straightens out of the concrete during the setting and hardening process, which means that the tension or stress is taken up by the concrete reinforcements. A continuing (undesirable) bending of the natural stone slab is prevented by both the concrete and its reinforcement, which means that such bending in natural stone, for example in marble, that would otherwise cause breaking due to weathering can be avoided. This means that the service life of marble facades can be extended considerably. The bond between the natural stone and the concrete is excellent: tests have shown that the slab breaks in the concrete layer rather than at the junction between the natural stone slab and concrete. The crushed natural stone serves in the concrete as a water reservoir, which means that we achieve a controlled setting of the cast concrete, while water is prevented from escaping out of the natural stone slab, which would weaken the bond. The invention and its advantages are discussed in detail herebelow, starting with the following description of the process, and making reference to the appended drawings, whereby Figure 1 gives a perspective representation of the combined natural stone and concrete slab, according to the invention, where the natural stone consists of marble. Figure 2 gives a front view of the slab. Figure 3 gives a sectional view 1-1. Figure 4 gives a sectional view 2-2. Figure 5 gives a sectional view A-A and B-B. The following reference numbers are used in the figures: 1 combined slab 2 marble layer 3 concrete layer 4 concrete protraction 5 suspension rods 6 suspension bracket 7 reinforcing irons 8 groove 9 fixing iron laid in the groove 10 U-shaped fixing iron 11 screw hole The combined slab (I), shown in perspective in Figure 1, with a front view in Figure 2 and sections in Figures 3 and 4, consists of a natural stone slab (2) and a concrete slab (3), with suspension rods laid in the concrete on both edges of the slab. The concrete protraction (4) covers the fixing irons (9, 10) which strengthen the construction above the suspension rods (5) and on the lower edge of the slab. The fixing irons provide a mechanical fastening of the natural stone, in addition to the contact adhesion between the concrete and the slab which is produced in the casting process. Figure 5 shows in more detail the construction of the slab, with the concrete protraction (4) (section A-A) and the suspension rod (5) (section B-B) . The reinforcement (7) is laid across the middle of the concrete layer (3), to produce a mesh reinforcement which increases the concrete layer's tensile strength in the long direction and in the direction of the breadth. A suitable diametre for the reinforcing irons is from 2 to 6 mm, for example about 4 mm, for a slab with a 10 mm layer of marble and a 30 mm layer of concrete. As seen from Figure 4, double reinforcement can be used to make the construction extra strong. The edge of the natural stone slab (2), along the concrete protraction (4), is provided with a longitudinal groove (8). A U-shaped fixing iron (9) which is cast in under the transverse reinforcing iron is bent twice, so that it first runs over the longitudinal reinforcing iron and then bends in with the end of the U-shaped iron in the groove (8). A second flat U-shaped fixing iron is fitted in the concrete layer with the U-iron's end cast in the concrete protraction (4). Most suitably the fixing iron is made of spring steel. Section B-B shows the fastening of the suspension rod (5) in the concrete layer (3) between the mesh reinforcements (7). The suspension rod is made of flat steel and its end is bent in profile into a Z, so that it first lies against the edge of the concrete slab and reaches towards the wall onto which the slab will be hung, and then forms, parallel with the wall, a firm edge (5 1 ) (see Figure 1). A screw hole is made in the firm edge (5'). The slab (1) is hung up on suspension brackets (6) which can be formed, for example, as shown in Figure 1. In this case the slab is not hung on a massive marble slab but on its old bracket where part of an old protracted rustproof steel has been left to support the back of the concrete layer. The suspension bracket has an edge which is turned up and which grips on the firm edge of the suspension rod. The suspension rod is then pushed into a groove on the edge, so that the edge comes to lie tightly against the bracket. The firm edge can be fastened with a screw to the bracket. To manufacture a slab as mentioned mentioned, we use a natural stone slab which consists of a stone type that is suited for use as face material. Such natural stones are, for example, oxide and hydroxide minerals as well as carbonate minerals. We can mention as suitable natural stones, for example, marble and other calcium and calcium-magnesium-carbonate based minerals (for example limestone), as well as granite, quartz and quartzites, labradorite and other similar silicate based minerals. Preferably we use marble or granite. According to the invention, the natural stone slab is bent approximately 1 to 4 mm per metre. The bending is calculated as the distance from a point in the middle of the slab to an assumed straight line which unites the edges of the slab. Preferably the required bending is achieved by sand blasting the inner surface of the natural stone slab. For sand blasting we use preferably sand which is OK 50 to 90, most suitably OK 70 that contains nickel slag. The pressure reaches in general 5 to 20 kg/cm.2, preferably about 10 to 12 kg/cm2. The slab can also be bent in a different way, for example mechanically by applying pressure on the middle of the slab. As a result of sand blasting, the slab bends so that it bulges out in the middle. Sand blasting removes the soft particles from the marble surface, leaving an uneven surface which affords a large bond area for the cast concrete. The area of the marble slab increases usually by about 50 to 500 per cent. Also granite and quartz slabs bend in this way and their surfaces increase through sand blasting. After sand blasting, the surface is cleaned to remove all dust. To achieve a good bond of the cast concrete, the slab is then treated, so that it will not essentially absorb water from the cast concrete. This can be achieved by saturating the slab with water, so that it will not draw more water from the cast concrete, which would weaken the strength of the bond between the natural stone and the concrete. According to a specially preferable procedure, this is achieved by using a polymer which forms a water repellent surface on the natural stone. The amount of polymer is usually about 0.00001 to 1 per cent, preferably about 0.00005 to 0.1 per cent, especially about 0.0001 to 0.01 per cent of the weight of the natural stone layer. We typically use 1 to 100 g, most suitably about 5 to 50 g of polymer per one square metre of the natural stone. During the application, the polymer is absorbed into the pores and cracks of the natural stone and helps to make also the face surface of the stone more water repellent. This way of increasing the water repellence of the natural stone can also be used generally in all applications of natural stone, i.e. by applying on at least one side of a piece of natural stone a solution of a polymer which is allowed to be absorbed into the pores and cracks of the stone. If necessary, additional cracks can be made in the stone to intensify the process of absorption. Suitable polymers for the above mentioned purposes are synthetic resins which may be used, for example, in the form of latexes or other dispersions. After the treatment, any overflow is removed to prevent the formation of layers of polymer between the natural stone and the concrete, which would also essentially weaken the strength. Suitable preparations are, for example, dispersions containing polymers and copolymers of the following substances: acrylic acid, acrylic acid esters, acrylonitrile, vinyl acetate, butadiene and styrene. These dispersions can be used as such or in combination with suitable natural binders, such as modified starch and carboxy-methyl cellulose. Products which are used as primers before surface coating, surface finishing, painting and construction works are suited for the purpose. When the convex surface is dry, concrete is cast thereupon. The cast concrete, which after setting forms one part of the combined element, contains a hydraulic binder (i.e. a binder that hardens when water is added to it), fillers and suitable additives. The binder can be, for example, Portland cement, rapid cement or slag cement but we prefer to use cement with a high bond strength, such as white cement. The suitable fineness of the cement is up to 100 to 800 m2/g, preferably 200 to 600 m2/g. The fillers for the concrete may be sand, polymeric compounds and fibrous materials. We preferably use sand with a particle size of up to 3 mm. According to a preferred procedure, we use sand of two different particle sizes. In addition to sand, the concrete can also contain fibrous fillers, such as natural and synthetic fibres. As examples we may mention cellulose based fibres, glassfibre, carbon fibres and plastic fibres. In addition to the above mentioned conventional fillers, the concrete will also contain a component that binds water. This component most suitably consists of crushed natural stone with a particle size of about 0.5 to 15 mm, preferably about 2 to 10 mm, especially about 3 to 5 mm. The crushed material can be one of the above mentioned natural stone materials. We usually use crushed marble, limestone, granite or quartz. By saturating the crushed stone with water before or during the casting of the concrete, a water reservoir is formed in the setting concrete, which helps to improve the bond of the concrete. Depending on the cement and fillers used, the concrete may contain known additives, such as fluidizers, accelerators or retardants, pore-forming agents for frost resistance and corrosion protection. On the basis of the above, the concrete layer generally contains 0.1 to 25 weight per cent of hydraulic binder, 0.1 to 25 weight per cent of filler and 0.1 to 99.8 weight per cent of crushed natural stone. Especially the concrete used to cast the concrete layer shall contain the following components: 1 to 5 parts by weight of cement 1 to 10 parts by weight of ordinary mineral filler 1 to 15 parts by weight of crushed natural stone 0.5 to 3 parts by weight of water The amount of water is usually about 0.5 to 0.55 times the quantity of cement and the total amount of filler (including the crushed natural stone) is up to 4 to 6 times the amount of cement . In the process of casting, the concrete layer is most suitably provided with the above mentioned reinforcement, which takes up tensile stresses acting on the slab, as well as with the above mentioned fixing irons and suspension rods. After the casting, the combined slab is allowed to dry and set. The bending of the natural stone layer reverts as the concrete dries and shrinks. The bending stress is carried on to the concrete layer and taken up by the reinforcement. Examples A combined facade element according to the invention was produced of a marble slab, which was about 10 mm thick, with a polished surface and an unpolished surface. First the unpolished side of the marble slab was sand-blasted, so that a bending of about 2 mm per 1 m was formed on the slab and the slab looked like a calotte. The sand-blasted surface was cleaned by removing all dust and a thin coat of synthetic polymerized resin in the form of a water solution (latex) was applied thereupon. The consumption was about 1.5 dl of latex per square metre. An acrylic dispersion was used in this example, marketed under the name of RESCON CP by Resco, Norway. The purpose of the treatment is to make the natural stone layer water repellent. The overflown primer was removed and the surface was allowed to dry thereafter. After the application of the polymerized resin, the marble slab was laid down in a form lined with a plastic sheet, and the treated side was turned up and used as the casting bed for the concrete mixed according to the following formmula: 1.2 kg of white cement 1.8 kg of sand No. 1 0.85 kg of sand No. 2 3.3 kg of crushed marble 0.66 kg of water The mixed concrete was poured onto the marble slab, so that it formed a layer that was about 10 mm thick. Next, the reinforcing irons and the fixing irons were laid in place and another layer of concrete was cast on the reinforcement, which means that the total layer of concrete was about 30 mm thick. The concrete was vibrated. The cast concrete was then covered with a plastic sheet and kept moist for about 2 weeks. When the concrete had dried and shrunk, the bending of the marble slab had reduced by over 50 per cent, and after about 3 months the surface was again quite even. The bond strength of the combined marble and concrete slabs (25 x 35 cm), manufactured according to the above description, have been tested in the Laboratory for Structural Engineering at the Technical Research Centre of Finland (VTT). The slabs contained crushed granite, limestone or quartz. The frost resistance of the slabs as well as the bond strength between the marble layer and the concrete layer were determined in the testing. The tensile strength of the slabs after a freezing/melting process (SFS 5447) was determined according SFS 5445. The first inspection showed that the treatment had not caused any visible damage to the slabs. The tensile strength of the slabs was at least 88 per cent of that of the reference slabs, and was up to 2.8 MPa for slabs containing crushed granite, 2.5 MPa for slabs with limestone and 2.9 MPa for slabs with quartz. Since a facade construction is considered to be frost resistant if after 100 cycles of freezing and melting its strength is not below 2/3 of the reference, it was found that the slabs according to the invention obviously well fulfil the criteria of the standards.

Claims: 8 Patent claims: 1. The combined facade element, consisting of a first layer of natural stone and a second layer of concrete which lies against the layer of natural stone, is distinguished by the distinctive feature that the natural stone layer contains - calculated by the weight of the layer - about 0.0001 to about 1 weight per cent of a polymerized resin and the concrete layer contains crushed natural stone. 2. The facade element according to Claim 1 is distinguished by the distinctive feature that the crushed natural stone consists of crushed marble, granite or quartz, with a particle size of 1 to 10 mm. 3. The facade element according to Claim 1 or 2 is distinguished by the distinctive feature that the concrete layer contains - 0.1 to 25 weight per cent of hydraulic binder - 0.1 to 25 weight per cent of filler, and - 0.1 to 99.8 weight per cent of crushed natural stone. 4. The facade element according to Claim 3 is distinguished by the distinctive feature that the concrete layer is cast with mixed concrete containing - 1 to 5 parts by weight of cement - 1 to 10 parts by weight of ordinary mineral filler - 1 to 15 parts by weight of crushed natural stone - 0.5 to 3 parts by weight of water. 5. The facade element according to Claim 3 or 4 is distinguished by the distinctive feature that the hydraulic binder consists of white cement. 6. The facade element according to any of the above claims is distinguished by the distinctive feature that the polymerized resin consists of a synthetic resin. 7. The facade element according to Claim 6 is distinguished by the distinctive feature that the polymerized resin consists of a polymer or a copolymer of acrylic acid, acrylic acad esters, acrylonitrile, vinyl acetate, butadiene and styrene. 8. The facade element according to Claim 6 or 7 is distinguished by the distinctive feature that the surface of the natural stone against the concrete layer is essentially water repellent. 9. The facade element according to any of the above claims is distinguished by the distinctive feature that the layer of natural stone consists of marble, granite or quartz. 10. The facade element according to any of the above claims is distinguished by the distinctive feature that it shows a bending of less than 1 mm per metre per year. 11. The facade element according to any of the above claims is distinguished by the distinctive feature that the thickness of the natural stone layer is 5 to 20 mm and that of the concrete layer 25 to 50 mm. 12. The facade element according to any of the above claims is distinguished by the distinctive feature that the concrete layer is provided with reinforcement. 13. The facade element according to any of the above claims is distinguished by the distinctive feature that the fixing element is of spring steel which unites the natural stone layer with the concrete layer. 14. The process for the manufacture of a facade element consisting of a face layer of natural stone and a base layer of concrete lying against the natural stone layer, according to which process - concrete is cast on one side of the natural stone slab which then forms the casting bed for concrete, - if required, the concrete is fitted with reinforcement, and - the concrete is allowed to set, is distinguished by the distinctive feature that - before casting the natural stone slab is bent, so that the casting bed for the concrete layer becomes convex. 15. The process according to Claim 14 is distinguished by the distinctive feature that the natural stone slab is bent by sand blasting the side that serves as the casting bed for the concrete layer. 16. The process according to Claim 14 or 15 is distinguished by the distinctive feature that the natural stone slab is bent to achieve a bending of 1 to 4 mm per metre. 17. The process according to any of the above claims is distinguished by the distinctive feature that the inner side of the natural stone slab is made water repellent before casting the concrete layer. 18. The process according to Claim 17 is distinguished by the distinctive feature that the inner side of the natural stone slab is treated with a polymerized resin. 19. The process according to any of the above claims is distinguished by the distinctive feature that the natural stone slab consists of marble or granite. 20. The process according to Claim 17 or 18 is distinguished by the distinctive feature that the concrete used contains a hydraulic binder, fillers as well as crushed natural stone with a particle size of 1 to 10 mm. 21. The process according to Claim 20 is distinguished by the distinctive feature that the crushed natural stone is saturated with water prior to or during the casting of the concrete. 22. The process according to Claims 14 to 21 is distinguished by the distinctive feature that the edges of the natural stone slab are provided with grooves for fitting in the ends of a fixing iron. 23. The way of increasing the water repellence of pieces of natural stone is distinguished by the distinctive feature that the piece of natural stone is treated with a solution-based dispersion of a polymer. 24. The way according to Claim 23 is distinguished by the distinctive feature that the polymer is applied thinly in the form of a water dispersion which is allowed to be absorbed into the pores and cracks of the piece of natural stone.

Inventors: LUNDIN SUNE, LUNDIN, SUNE
Applicants: LUNDIN SUNE, SUNE LUNDIN KB, LUNDIN, SUNE
Application year: 1997
Main classification: B28B19
IPC codes: B28B19, E04C2