(19)
(11) EP 0 724 941 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
07.08.1996 Bulletin 1996/32

(21) Application number: 96870009.6

(22) Date of filing: 01.02.1996
(51) International Patent Classification (IPC)6B28D 1/18, E01C 5/06
(84) Designated Contracting States:
BE DE FR LU NL

(30) Priority: 01.02.1995 BE 9500075

(71) Applicant: MARMORITH BETONINDUSTRIE
B-3530 Houthalen-Helchteren (BE)

(72) Inventor:
  • Houben, Ewald
    3530 Houthalen-Helchteren (BE)

(74) Representative: Van Reet, Joseph et al
Gevers Patents S.A., Brussels Airport Business Park, Holidaystraat 5
1831 Diegem
1831 Diegem (BE)

   


(54) Process for manufacturing a concrete slab and a slab manufactured in this way


(57) Process for manufacturing a concrete slab (1) and slab obtained in this way having a surface (2) formed by granules of natural stone embedded in a matrix of cement stone. In the process, concrete is prepared at least on the basis of soft granules of natural stone and cement, and this concrete being applied in a mould and enabled to harden in order to form a slab. The surface (2) of the hardened concrete slab (1) is treated by means of a milling cutter so as to cleave grains of said natural stone present therein and to obtain a rough surface (2) which is partially formed by the cleaved surfaces of the grains of natural stone.




Description


[0001] The present invention relates to a process for manufacturing a concrete slab having a surface formed by granules of natural stone embedded in a matrix of cement stone, in which process concrete is prepared at least on the basis of said granules of natural stone and cement, this concrete being applied in a mould and enabled to harden in order to form a slab, and said surface of the hardened concrete slab being made rough.

[0002] From DE-OS-37 16 344, such a concrete slab is known. Upon manufacturing this known concrete slab, there is started with concrete composed of grains of granite, grains of diabase, cement and water. The purpose is to obtain a concrete slab of granite which looks as much as possible like natural slabs of granite. With slabs of granite, it is known that they obtain a silky shine when their surface is made rough. According to DE-OS-37 16 344, a same effect is obtained upon making rough the concrete slabs of granite comprising also grains of diabase. Making rough of the surface of the slabs is performed by so-called "granulating" of the slabs wherein the surface of these slabs is cut by means of a "granulating machine" with several cutters.

[0003] The invention has now however as object to provide a process enabling to manufacture concrete slabs of natural stone with another type of look.

[0004] According to this object, the process according to the invention is characterised in that said concrete is prepared on the basis of granules of a soft natural stone and said surface of the hardened slab being treated by means of a milling cutter so as to cleave grains of said natural stone present therein and to obtain a rough surface which is partially formed by the cleaved surfaces of the grains of natural stone.

[0005] In the process according to the invention, a rough surface is thus obtained which is considerably formed by the natural cleaved surfaces from the grains of natural stone. This is achieved by the combination of the use of soft granules of natural stone and of a milling treatment for making rough the surface.

[0006] In DE-OS-37 16 344 use is on the contrary made of hard granules of natural stone, i.e. of granite with a Mohs hardness from 6 to 7 and of diabase with a Mohs hardness of 6, the grains of which are made rough upon "granulating" the slabs in order to obtain the desired silky shine. Only a limited number of the hard grains of natural stone will be cleaved in this way.

[0007] Milling the surface of concrete slabs is known per se front DE-OS-39 27 601. This German patent application proposes as alternative for "granulating" the concrete slabs to treat the surface thereof with a milling cutter. In this way, an old and weathered outlook would be obtained. An essential aspect of the invention according to DE-OS-39 27 601 consists in the fact that the milling treatment, in contrary with "granulating", can be performed onto a non hardened slab. From DE-OS-39 27 601 it appears thus nowhere that by milling the concrete slabs another surface effect would be obtained than by a "granulating treatment".

[0008] As already indicated hereinabove, such a new effect is obtained according to the invention by the combination of the use of a soft natural stone in combination with the milling treatment.

[0009] Preferably, this natural stone has therefore in the process according to the invention a Mohs hardness of 2 to 5 and in particular a Mohs hardness of 2.5 to 4 and preferably of about 3.

[0010] In an efficient embodiment of the process according to the invention, said concrete is prepared on the basis of granules of natural stone having a granulometry between 0 and 6 mm.

[0011] In this way, a good bound can be obtained between the grains of the granules and the matrix of cement stone causing most of the grains upon the milling treatment to be cleaved instead of to be knocked out, in particular if use is made of a rotary milling cutter. An additional advantage is further that the application of this small granulometry contributes to a larger amount of the surface to be formed by the granules of natural stone which contributes on its turn that formation of moss and soil of the surface of the slabs are avoided.

[0012] Preferably, said concrete is prepared on the basis of granules of natural stone having a sufficient quantity of fine fraction to form said cement stone.

[0013] In this way, the small quantity of cement stone remaining visible can be given the same colour as the granules of natural stone itself. In case of a light natural stone, use is for example made of white cement causing the colour of the natural stone to be maintained.

[0014] The invention relates further also to a concrete slab manufactured by application of the process according to the invention and comprising a roughened surface formed by granules of natural stone embedded in a matrix of cement stone. In the concrete slab according to the invention, the granules of natural stone are formed by a soft natural stone and said surface is a rough milled surface with grains therein of said granules of natural stone which are cleaved as a result of the milling treatment.

[0015] Further details and particularities of the invention will become apparent from the following description of a particular embodiment of the process and the concrete slab manufactured in this way according to the invention. This description is however only given by way of example and is clearly not intended to limit the scope of the invention. The reference numerals used in this description relate to the annexed drawings, wherein :

Figure 1 shows a perspective view on a concrete slab according to the invention;

Figure 2 shows a perspective view on the milling part of a possible rotary milling cutter which can be applied in the process according to the invention, with omission of the milling cutter discs; and

Figure 3 shows on an enlarged scale a shaft of the milling part shown in Figure 2 onto which milling cutter discs are mounted.



[0016] In the process according to the invention for manufacturing a concrete slab 1 with a surface 2 formed by granules of natural stone embedded in a matrix of cement stone, firstly concrete 3 is prepared at least on the basis of the granules of natural stone and cement. This concrete 3 is then applied in a mould and is hardened in order to form a slab. After the concrete 3, also a further layer of concrete 4, made of sand, cement and gravel is however mostly as usual applied in the mould. This layer 4 has for example a thickness of 3 cm while the layer 3 with the granules of natural stone has for example a thickness of 1 to 2 cm.

[0017] Before hardening, the concrete layers 3 and 4 are, as known, vibrated at high frequency and pressed at for example 500 tons.

[0018] According to the invention, the surface 2 of the slab 1 is treated, after hardening, by means of a milling cutter, more specifically in such a manner that a number of grains from the natural stone present therein are cleaved and a rough surface is obtained being partially formed by the cleaved surfaces of the grains of natural stone. By the selection given hereinafter of soft granules of natural stone and by using a milling cutter, natural cleaved surfaces are essentially obtained being practically not disturbed by the working of the milling cutter. In this way, a surface having a natural look is obtained wherein the cleaved surfaces of the grains of natural stone contribute to a special effect. The remaining part of the surface is formed by the cement stone and the uncleaved grains of the granules of natural stone. Since these granules of natural stone are particularly obtained by grinding larger pieces of natural stone, the grains of these granules have already on their own cleaved surfaces. In order to obtain this effect, it is preferable to prepare the concrete 3 on the basis of granules of natural stone having a granulometry between 0 and 6 mm.

[0019] Upon preparing the concrete 3, it is essential that use is made of granules of a soft natural stone, such as the known French natural stone or the Burgundian natural stone such as Comblanchien. Of course, also other varieties of soft natural stone can be applied which deliver the desired rough structure with cleaved surfaces, when they are treated by means of a rotary milling cutter. The Mohs hardness of the used granules of natural stone is efficiently between 2 and 5, in particular between 2.5 and 4 and is preferably about 3.

[0020] The granules of natural stone comprise preferably a sufficient quantity of fine fraction for forming a cement stone wherein the grains of natural stone are embedded. In this way, no sand or other fine granulated material must thus be used for preparing the concrete 3, so that a uniform colour can be given readily to the surface 2, which is already considerably formed by the cleaved surfaces of the granules of natural stone. The concrete 3 is for example prepared from 450 kg white cement P50, 1600 kg Comblanchien ( 0 - 6 mm, hardness 2 to 3 Mohs), 3.7 l Superplasticizer and 250 litre water per m3.

[0021] To obtain the rough surface with cleaved grains of natural stone described hereinabove, a milling cutter 5 is used according to the invention, more particularly a rotary milling cutter.

[0022] In Figure 2, a part of such a rotary milling cutter 5 is shown, more particularly the milling part itself. This milling part has a number of shafts 6, for example six shafts, which are positioned at equal distance of a central geometric rotation axis 7. The shafts 6 are for example fixed at the extremity to two circular discs 8. These discs 8 are beard in the milling machine in a non illustrated manner and can be driven by means of a drive belt 9, for example by an electrical motor.

[0023] As can be seen in Figure 3, a number of milling cutter discs ("flails") 10 are rotatably mounted on each of the shafts 6 in such a manner that the shafts 6 extend through the centre point of these milling cutter discs. The milling cutter discs 10 are provided, at their periphery, with a number of protrusions 11, in particular five protrusions, by means of which the surface of the slab is milled. These protrusions 11 are therefore provided, at their extremities, with a hard cutting element 12, for example from wolfram carbide.

[0024] To keep the milling cutter discs 10 at a certain mutual distance, circular rings 13 are for example applied therebetween. Possibly, additional circular discs 14 can be slid between the discs 8 over the shafts 6 in such a manner that the milling cutter discs 10 on the different shafts 6 are always in line and that therefore a certain groove structure is obtained in the surface 2 of the slab 1. Due to the special construction of the rotary milling cutter 5, this groove structure is not formed by fine ground grooves, but it pertains globally to the rough structure of the granules of natural stone of the surface 2.

[0025] In this respect, it has been found that it is preferable to use a rotary milling cutter 5 as described hereinabove, of which the mutual distance between two neighbouring cutting elements 12 on the milling cutter discs 10 being practically equal to 1/3 to 1/5 of the distance between the shafts 6 and the geometric rotation axis 7. The shafts 6 can further be positioned therefore in particular at 5 to 10 cm from the rotation axis 7 and more particularly at 7 to 8 cm from this rotation axis 7.

[0026] It has been established that a rotational speed of 1500 to 2500 rpm and in particular of about 2000 rpm is preferable in view of obtaining the desired rough structure of granules of natural stone. To obtain an optimal effect, the milling cutter is preferably moved at a speed of about 1 m/min with respect to the slab.

[0027] From the description given hereinabove of some particular embodiments of the process and the concrete slab according to the invention, it will be clear that several modifications can be applied to these embodiments without falling outside the scope of the annexed claims.


Claims

1. A process for manufacturing a concrete slab (1) having a surface (2) formed by granules of natural stone embedded in a matrix of cement stone, in which process concrete is prepared at least on the basis of said granules of natural stone and cement, this concrete being applied in a mould and enabled to harden in order to form a slab, and said surface (2) of the hardened concrete slab (1) being made rough, characterised in that said concrete is prepared on the basis of granules of a soft natural stone and said surface (2) of the hardened slab (1) being treated by means of a milling cutter (5) so as to cleave grains of said natural stone present therein and to obtain a rough surface (2) which is partially formed by the cleaved surfaces of the grains of natural stone.
 
2. A process according to claim 1, characterised in that said natural stone has a Mohs hardness of 2 to 5 and in particular a Mohs hardness of 2.5 to 4 and preferably of about 3.
 
3. A process according to claim 1 or 2, characterised in that said concrete is prepared on the basis of granules of natural stone having a granulometry between 0 and 6 mm.
 
4. A process according to anyone of the claims 1 to 3, characterised in that said concrete is prepared on the basis of granules of natural stone having a sufficient quantity of fine fraction to form said cement stone.
 
5. A process according to anyone of the claims 1 to 4, characterised in that use is made of a rotary milling cutter (5) for treating said surface of the hardened slab.
 
6. A process according to claim 5, characterised in that use is made of a rotary milling cutter (5) having a number of shafts (6) positioned at equal distance of a central geometric axis (7) and rotating around said axis (7) and on each of which a number of milling cutter discs (10) are rotatably mounted, said shafts (6) extending through the centre point of these milling cutter discs (10).
 
7. A process according to claim 6, characterised in that said milling cutter discs (10) are provided around their periphery with a number of protrusions (11), in particular five protrusions (11), by means of which said surface (2) of the hardened slab (1) is milled.
 
8. A process according to claim 7, characterised in that a milling cutter (5) is used of which the distance between the extremities of two neighbouring protrusions (11) being equal to 1/3 to 1/5 of the distance between said shafts (6) and said central geometric axis (7).
 
9. A process according to anyone of the claims 6 to 8, characterised in that a milling cutter (5) is used said shafts (6) of which being positioned at 5 to 10 cm of said central geometric axis (7), and in particular at 7 to 8 cm of this geometric axis (7).
 
10. A process according to anyone of the claims 1 to 9, characterised in that said milling cutter treatment is performed with a rotational speed of 1500 to 2500 rotations per minute and in particular with a rotational speed of about 2000 rotations per minute.
 
11. A concrete slab manufactured by application of the process according to anyone of the claims 1 to 10 and comprising a roughened surface (2) formed by granules of natural stone embedded in a matrix of cement stone, characterised in that the granules of natural stone is formed by a soft natural stone and that said surface (2) is a rough milled surface with grains therein of said granules of natural stone which are cleaved as a result of the milling treatment.
 
12. A concrete slab according to claim 11, characterised in that said natural stone has a Mohs hardness of 2 to 5 and in particular a Mohs hardness of 2.5 to 4 and preferably of about 3.
 




Drawing







Search report