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Title:
A PRECAST CONCRETE SLAB WITH INTERCONNECTED ELEMENTS AND METHOD FOR MAKING THE SAME
Document Type and Number:
WIPO Patent Application WO/2003/052208
Kind Code:
A1
Abstract:
A slab, with elements connected by a flexible joint, having an improved resistance to degradation by freezing and thawing, while being adapted to support heavy axial loads coming from the top and that is able to flex under pressure coming from the bottom of the slab. The slab comprises a plurality of interconnected plate-shaped elements laying side by side. Each of the plate-shaped elements have at least one side wall forming a pair of adjacent side walls with a side wall of an adjacent plate-shaped element. The slab also comprises at least one flexible joint, each flexible joint connecting one of the pair of adjacent side walls respectively. The flexible joint comprises an upper section of each of the side walls of the pair, in contact relationship with each other, a bottom section of each of the side walls of the pair, spaced apart from each other, and defining a gap between the side walls of the pair; and a flexible connecting rod extending across the gap and connecting the bottom section of the side walls together. A method for manufacturing such a slab using an upside down molding technique is also disclosed.

Inventors:
JALBERT GAETAN (CA)
Application Number:
PCT/CA2002/001957
Publication Date:
June 26, 2003
Filing Date:
December 17, 2002
Export Citation:
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Assignee:
FLEXOSOL INC (CA)
JALBERT GAETAN (CA)
International Classes:
B28B23/00; E01C5/06; E04F15/02; E04F15/08; E04F15/14; (IPC1-7): E01C5/06; B28B7/00; B28B19/00; E04F15/02; E04F15/10; E04F15/14
Foreign References:
GB220787A1924-08-28
US5937602A1999-08-17
GB2169327A1986-07-09
US4620401A1986-11-04
US5588775A1996-12-31
US3471987A1969-10-14
Attorney, Agent or Firm:
Robic (CDP Capital Center 1001, Victoria Square, Bloc E - 8th Floo, Montreal Quebec H2Z 2B7, CA)
Download PDF:
Claims:
WHAT IS CLAIMED IS :
1. A slab for covering a ground surface comprising: a plurality of interconnected plateshaped elements, each of said plateshaped elements having at least one side wall forming a pair of adjacent side walls with a side wall of an adjacent plateshaped element ; and at least one flexible joint, each connecting one of said pair of adjacent side walls respectively, said at least one flexible joint comprising: an upper section of each of said side walls of the pair, in contact relationship with each other; a bottom section of each of said side walls of the pair, spaced apart from each other, and defining a gap between said side walls of the pair; and a flexible connecting rod extending across the gap and connecting the bottom section of said side walls together.
2. The slab according to claim 1, wherein said upper section of each of said side walls of the pair comprises a top section spaced apart from each other, and defining a groove between said pair of adjacent side walls.
3. The slab according to claim 2, wherein the groove is Vshaped.
4. The slab according to claim 2, wherein the groove is Ushaped.
5. The slab according to any one of claims 1 to 4, wherein said flexible connecting rod extends horizontally across the gap.
6. The slab according to any one of claims 1 to 5, wherein said flexible connecting rod comprises two opposite end portions, each end portion being respectively embedded into said bottom section of the adjacent side walls.
7. The slab according to any one of claims 1 to 6, wherein said plateshaped elements are made of concrete or cementbased grout.
8. The slab according to any one of claims 1 to 7, wherein said flexible connecting rod is made of fiber glass.
9. The slab according to any one of claims 1 to 8, wherein the bottom section of each of said side walls of the pair is bevelled for defining an upside down Vlike shaped gap between said side walls of the pair.
10. The slab according to any one of claims 1 to 9, wherein the slab is precast.
11. The slab according to any one of claims 1 to 10, wherein said at least one flexible joint comprises more than one of said connecting rod extending across the gap spaced apart from each other.
12. The slab according to any one of claims 1 to 11, wherein each of said plate shaped elements has a characteristic geometric form selected from the group consisting of circles, polygons and ellipses.
13. The slab according to claim 12, wherein the plateshaped elements have similar or different geometric forms.
14. A method for making a slab as defined in any one of claims 1 to 13, comprising the steps of: a) setting a form on a planar surface, the form comprising : . a base wall for forming the top surface of the plateshaped elements; . a plurality of side walls for forming a peripheral side wall of the slab ; and . a removable molding structure for forming said at least one flexible joint, said molding structure comprising: at least one elongated rigid member for extending horizontally above said base wall, said at least one elongated member having a body shaped and sized for forming said bottom section of said at least one flexible joint, said body having a flexible slotted hole shaped and sized for removably inserting therein one of said connecting rod; and supporting means for supporting said at least one elongated member above the base wall for defining a gap between said at least one elongated member and said base wall, thereby allowing to form the upper section of said at least one flexible joint; b) inserting a rod in said slotted hole of the body of each of said at least one elongated member; c) pouring a hardenable filling material into the form; d) hardening the filling material; and e) removing said molding structure and side walls of the form, thereby obtaining the slab in an upside down position.
15. The method according to claim 14, wherein said upper section of each of said side walls of the pair comprises a top section spaced apart from each other, and defining a groove between said pair of adjacent side walls, and wherein the form further comprises at least one elongated projecting ridge extending on said base wall in an alignment relationship with the body of said at least one elongated member of said molding structure for forming said groove.
16. The method according to any one of claims 14 to 15, wherein said supporting means comprises a plurality of supporting arms extending outwardly and lying on the side walls of the form.
17. The method according to any one of claims 14 to 16, wherein the body of said at least one elongated element of said molding structure is triangularshaped for forming an upside down Vlike shaped gap between said side walls of said pair of adjacent side walls.
18. The method according to any one of claims 14 to 17, wherein the form further comprises a rubber sheet disposable over said base wall for facilitating a removal of the slab from the mold.
Description:
A PRECAST CONCRETE SLAB WITH INTERCONNECTED ELEMENTS AND METHOD FOR MAKING THE SAME FIELD OF THE INVENTION This invention relates generally to ground coverings, more particularly it concerns a ground covering with improved resistance to degradation by freezing and thawing and/or to degradation by any other natural movings of the ground. It also concerns a slab for covering a ground surface able to resist to heavy axial load coming from the top and that will flex under pressure coming from the bottom of the ground covering, and to a method for manufacturing such a slab.

BACKGROUND OF THE INVENTION A number of different devices and methods currently exist for making material makeup placed over and onto existing floor surfaces, as means for enhancing the wearability and the look of both indoor and outdoor surfaces.

Devices for making paving with sophisticated ornamental forms are disclosed in US patent No. 2,867, 886. Such devices consist of molds which are removed when the concrete is dry.

In another conventional method, large surfaces to be treated are covered with a single concrete plate and an ornamental effect is obtained with molds which are placed on the surface of the humid concrete and which are then removed when the concrete is dry. Such a method is described in US patent No. 5,406, 763.

Also known are floor surfaces which are adapted to heavy traffic. Such surfaces are described in US patents Nos. 1,841, 819,3, 148,482, 3,344, 570 and 4,932, 182. The expected result is obtained by addition of a reinforcing rigid framework. An alternative solution is proposed in US patent No. 1,539, 988 with the

device constituted of moulded elements wherein the elements are simultaneously rigidly anchored on a rigid support and wherein each block is flexibly anchored to every adjacent block.

None of the known methods or devices described above provides ground covering elements which are suitable for countries like Canada or the northern part of the United States where extreme freezing and thawing forces are applied to such protective and decorative covers or for places like California where earthquakes frequently occur.

A ground cover which is placed outdoor in a country like those mentioned above is submitted to extreme forces generated by the repetitive freezing and thawing of the natural supporting material. This phenomena results first in the optical degradation of the surface of the cover. Then, cracks appear as a first sign of degradation of the internal structure. After appearance of the cracks, the degradation of the cover accelerates and splitting of the cover may even occur. Even with known sophisticated methods and apparatus, such as covers with a reinforced rigid metallic structure, the degradation ineluctably takes place in a relatively short period of time after the cover has been installed onto the surface to be covered. Moreover, a similar degradation phenomena may be generated by other significant natural movings of the ground, like those generated by earthquakes.

To overcome the disadvantages of the ground covers discussed above, US patent No. 5,937, 602, by the same inventor, proposes a ground cover and a method for manufacturing such a ground cover that can be used as a protective and decorative ground covering and has an improved resistance to degradation caused by freezing and thawing or caused by any other natural motion of the ground. The ground cover has a plurality of molds, each having a bottom wall and side walls. The molds have their bottom walls lying flat onto the ground and are positioned with their side walls in close adjacent relationship with respect to each other so as to fully cover the ground. Connectors of given flexibility extend through the side walls of pairs of adjacent molds in order to connect the molds to each other. A filling material is

poured and hardened into the molds and acts then as a covering. Once installed, the ground cover forms a network of molds filled up with the hardened material that can easily be adapted to floor surfaces of different shapes. This improved resistance to degradation can be explained by the fact that the cover according to the invention is constituted of a plurality of units that are connected together but each has the ability to slightly move up and down with respect to the adjacent units. However, this particular manufacturing method is limited to the cast in place technique where the filling material is poured and hardened on the site of the installation.

Also known in the prior art, there is US patent Re. 26,733 (which is a reissuing of US patent No. 3,375, 763) which discloses an elastomeric expansion joint for use between two adjacent sections of concrete for compensating for the thermal expansion and contraction of the sections of concrete. This expansion joint is provided with a plurality of rigid plates embedded in the elastomeric body of the joint, preferably horizontally, and adapted to render the joint relatively stiff in the vertical direction. This joint is therefore able to support a heavy axial load coming from the top of the ground covering but does not allow any flexion in the vertical direction.

US patent No. 3,471, 987 discloses, as for it, a device for positioning, spacing and supporting an elongated member from a reference surface. This device is adapted to support and space a reinforcing bar from the ground surface or a form surface during the pouring of concrete around the reinforcing bar which remains permanently within the concrete.

US patent No. 5,870, 869 describes a yielding tie bar which transfers load stress across a joint between adjacent concrete slabs, and accommodates internal movement of the slabs to reduce cracking. A combination of adjacent slabs have a cracking strength and comprise a plurality of such tie bars. A yieldable strip made of yieldable metal is welded to the bar and mounted near each end of the bar perpendicular to the bar axis. The strip has a predetermined yield strength which is sufficient to restrain slab movement in a direction which opens the joint, and which is yielding in the metal thereof to an extent that will prevent substantial cracking of

the slabs.

Other examples of prior art ground coverings and expansion joints are given in the following US patents: 1,058, 908; 1,060, 919; 1,254, 853; 1,769, 828; 2,111, 114; 2,224, 148; 3,068, 763; 3,114, 221; 3,136, 022; 3,418, 899; 3,440, 934; 4,346, 542; 4,736, 558; 4,953, 340; 5,598, 682; 5,615, 971 and 5,956, 912.

The prior ground covering of the applicant disclosed in US patent No.

5,937, 602 has thus shown to be well adapted to resist to many natural degradations.

Unfortunately, it does not satisfactory take up the problem of heavy axial loads coming from the top or from the bottom of the ground covering.

Thus, there is still a need for a ground covering adapted to resist to degradation by freezing and thawings and/or to degradation by any other natural movings of the ground while being adapted to resist to a heavy axial load coming from the top and that will flex under a pressure coming from the bottom of the ground covering.

SUMMARY OF THE INVENTION An object of the present invention is to provide a slab for making a ground covering which satisfies the above-mentioned need.

Accordingly, the present invention is directed to a slab comprising a plurality of interconnected plate-shaped elements, each of the plate-shaped elements having at least one side wall forming a pair of adjacent side walls with a side wall of an adjacent plate-shaped element. The slab also comprises at least one flexible joint, each connecting one of the pair of adjacent side walls respectively. The flexible joint comprises an upper section of each of the side walls of the pair, in contact relationship with each other, a bottom section of each of the side walls of the pair, spaced apart from each other, and defining a gap between the side walls of the pair;

and a flexible connecting rod extending across the gap and connecting the bottom section of the side walls together.

Preferably, the upper section of each of the side walls of the pair comprises a top section spaced apart from each other, and defining a groove between the pair of adjacent side walls.

Thus, thanks to its upper section, the flexible joint is able to resist to heavy axial loads coming from the top of the slab while its bottom section allows a movement of each plate-shaped element with respect to each others. More particularly, the connecting rod of the flexible joint is able to flex under a pressure coming from the bottom, and this will generate upwards movements of the plate- shaped elements connected through this flexible joint.

Another object of the present invention is to provide a method for manufacturing a slab as disclosed hereinabove by precast wet or dry technique.

Accordingly, the method comprises the steps of: a) setting a form on a planar surface, the form comprising : . a base wall for forming the top surface of the plate-shaped elements ; . a plurality of side walls for forming a peripheral side wall of the slab ; and . a removable molding structure for forming the at least one flexible joint, the molding structure comprising: -at least one elongated rigid member for extending horizontally above the base wall, the at least one elongated member having a body shaped and sized for forming the bottom section of the at least one flexible joint, the body having a flexible slotted hole shaped and sized for removably inserting therein one of the connecting rod; and

- supporting means for supporting the at least one elongated member above the base wall for defining a gap between the at least one elongated member and the base wall, thereby allowing to form the upper section of the at least one flexible joint; b) inserting a rod in the slotted hole of the body of each of the at least one elongated member; c) pouring a hardenable filling material into the form; d) hardening the filling material ; and e) removing the molding structure and side walls of the form, thereby obtaining the slab in an upside down position.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the invention will become apparent upon reading the detailed description and upon referring to the drawings in which : Figure 1 is a perspective top view illustrating a slab according to a first preferred embodiment of the present invention.

Figure 2 is a perspective top view illustrating a slab according to a second preferred embodiment of the present invention, and showing the flexibility of the same.

Figure 3a is a cross-sectional view along line 111-111 of Figure 1 of a control joint connecting two plate-shaped elements of a slab according to a preferred embodiment of the present invention, the plate-shaped elements being subjected to a top load.

Figure 3b is a partial view of the view shown in Figure 3a.

Figure 4 is the same view as in figure 3a showing the slab being subjected to a bottom pressure.

Figure 5 is a perspective top view illustrating a form suitable for manufacturing the slab shown in Figure 1.

Figure 6 is a perspective view of a portion of a form suitable for manufacturing the slabs shown in figures 1 or 2.

Figure 7 is a perspective top view illustrating the form of Figure 5 wherein a hardenable filling material has been poured.

Figure 8 is a perspective top view illustrating the form of Figure 7 wherein the filling material has been hardened and the molding structure removed.

Figure 9 is a perspective bottom view of the slab of Figure 1.

While the invention will be described in conjunction with an example embodiment, it will be understood that it is not intended to limit the scope of the invention to such embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the appended claims.

DESCRIPTION OF PREFERRED EMBODIMENTS In the following description, similar features in the drawings have been given similar reference numerals and in order to weight down the figures, some elements are not referred to in some figures if they were already identified in a precedent figure.

Figure 1 shows a first preferred embodiment of a slab 1 according to the present invention while Figure 2 shows a second preferred embodiment. In both

cases, the slab 1 comprises a plurality of plate-shaped elements 3 (hereinafter referred to as elements) disposed side by side on the ground, all being interconnected together by means of a flexible joint able to resist to heavy axial load coming from the top and that will flex under pressure coming from the bottom of the ground covering, as will be explained in more details further below. The slabs 1 are preferably precast slabs that are mass-produced in a plant and shipped as such to the construction site.

It is worth mentioning that to cover a large surface, several slabs 1 may be interconnected together, using one of the known techniques in the art, for reproducing a floating surface of any dimension.

The elements 3, which may be of any geometric form, comprise a plurality of side walls 5 defining the perimeter thereof. Each element 3 is adjacent to at least one other element 3 through one of its side walls 5. For example, the slab 1 illustrated in Figure 1 consists of thirteen elements 3 of different geometric forms. The central element, which is circular, is adjacent to eight polygonal elements 3 also adjacent to four square elements, all interconnected together, as can be better seen in Figure 9.

The flexible joint 7 which interconnects the different elements 3 of a slab 1 will be described in more details by referring to figures 3a, 3b and 4. As can be appreciated, each of the elements 3 has at least one of its side walls 5 which forms a pair 6 of adjacent side walls with a side wall 5 of an adjacent element 3, which side wall 5 divides into a bottom section 11, an upper section 9 and a top section 27.

Referring now to Figures 3a, 3b and 4, the flexible joint 7 is formed of the upper sections 9 of the side walls 5, which are in contact relationship with each other, and of the bottom sections 11 of the pair 6, which are spaced apart from each other, thereby defining a gap 13 between the side walls 5 of the pair 6. The flexible joint 7 also comprises a flexible connecting rod 15 extending across the gap 13 and connecting the bottom sections 11 of the side walls 5 together.

The elements 3 are advantageously obtained from a molding method, wherein a hardenable filling material is poured into a predetermined form. The elements 3 are preferably made of concrete or cement-based grout, and they can be either obtained by wet cast or dry cast. A preferred realisation of such a method will be described further below.

Referring again to Figures 3a and 4, the flexible connecting rod 15 of the flexible joint 7 preferably extends horizontally across the gap 13, and even more preferably, through the upper portion of the gap 13. Of course, the flexible connecting rod 15 could extend slightly angularly across the gap 13 without departing from the scope of the present invention. Preferably, the two opposite end portions 17 of each flexible connecting rod 15 are respectively embedded into the concrete elements 3 for giving the convenient strengthening to the assembly. The flexible connecting rods 15 are advantageously made of fiber glass which can be a pultruded fiber glass for providing an even greater strength and flexibility to the slab 1. Also, to facilitate their anchoring into the concrete, the connecting rods 15 may be provided with anchoring corrugations 31. For example, the connecting rod discloses in US patent No. 4,620, 401 may advantageously be used for providing the appropriate strength and flexibility. Optionally, the flexible joint 7 may comprise more than one of such connecting rod 15 extending across the gap and spaced apart from each other for enhancing the resistance of the flexible joint 7.

Referring now to Figures 1 and 3a, the slab 1 may be provided with a plurality of grooves 21 on its top side 23 which would thus reproduce an aesthetic mosaic of any shape and design. More particularly, for defining a groove 21 between a pair 6 of adjacent side walls 5 of two adjacent elements 3, the top sections 27 of the side walls 5 are spaced apart from each other. The groove 21 may be V-shaped, U- shaped or may have any other desired form. As explained below, the groove 21 is an optional element of the present invention but allows an intentional weakness into the hardenable filling material, thereby allowing a self control of the natural fracture of the upper section 9 into an aesthetic shape.

Referring again to Figures 1 and 2, each of the elements 3 of the slab 1 has a characteristic geometric form selected from the group consisting of polygons with straight or curved segments, circles and ellipses. So, the slab 1 may comprise elements 3 of similar shape and elements of different shape for enhancing the look thereof.

It is worth mentioning that in another preferred embodiment of the invention, which is not illustrated, all the elements 3 of the slab 1 are rectangular for forming a rectangular slab 1. In this case the elements 3 are thus disposed side by side for forming aligned rows of elements. Instead of having separate flexible connecting rods 15 connecting two adjacent elements together, a single connecting rod may be used to connect all, elements belonging to a same row. In this way, the single connecting rod extends through the pairs 6 of adjacent side walls 5 of all the elements belonging to the same row. Of course, this technique could also be used to connect elements of a different shape, like hexagonal elements for example. An hybrid slab which would be provided with both separate connecting rods and single connecting rods could also be envisaged.

Referring now to Figures 3a and 4, the presence of the gap 13, which is free of filling material, between two adjacent elements 3, allows movements of the elements 3 without any damage to the slab such as the formation of cracks, and give therefore a great resistance to the slab to degradation caused by repeated freezing and thawing of the ground. Preferably, the gap 13 has an upside down V-like shape.

For defining such a gap 13, the bottom section 11 of each of the side walls 5 of the pair is bevelled. Naturally, any other suitable shape may be envisaged for the gap 13.

As can be seen in Figures 2 and 4, the complete slab 1 is able to flex under a pressure coming from the bottom side 25 of the slab 1, which may be produced by an earthquake, a subsidence of the ground, or any other natural movings of the ground. In fact, the connecting rod 15 works as a flexible axle in absorbing any

deformation generated by the ground, and render the slab 1 able to support any moving of the ground without be subjected to degradation.

As can be seen in Figure 3a, the slab 1 is able to support a heavy axial load coming from the top side 23 without any flexion, thanks to the upper section 9 of each of the side walls 5 of the pair 6 in contact relationship with each other, and that are able to accept and support a compression of the filling material.

Just after the forming of such a slab, the upper section 9 of the side walls 5 forming the joints 7 are in integral relationship with each other. According to the construction of the slab 1, this common concrete portion will naturally crack during manipulation or under ground pressure.

A theoretical analysis of the mechanical behaviour of the slab 1 as described above has been made for determining the best characteristics the slab should have to offer the greatest performance. In this analysis, different load cases based on different field of applications such as pedestrian traffic, residential or commercial parking or surfaces exposed to heavy vehicles have been studied. Thus, calculations have been made for the harshest concentrated load, which is a 54kN load pressing down on a surface of 40 cm x 40 cm, that is the load applied by two twin-wheels of a heavy truck. A numerical modelling of the structural behaviour of a flexible joint 7 of a slab 1 having outside dimensions of 1200 mm x 1200 mm and being subjected to an axial load of 54 kN has been made for obtaining the best model. This modelling has thus suggested several recommendations to follow concerning the thickness of the slab and the shape of the groove for example according to the type of supporting conditions at the level of the ground. First, the use of a groove 21 between two adjacent side walls 5 allows a reduction of the compression constraint applied to the upper portion of the flexible joint 7 when an axial load is applied on the top surface 23 of the slab 1. Moreover, the fact that the groove 21 is V-shaped instead of U- shaped still decreases of about 50 percent this compression constraint. Second, for the case of a slab 1 lying flat on the ground, a minimal thickness of 80 mm is optimal when the slab 1 is provided with a V-shape groove 21. And last, for optimising the

stability of the flexible joint 7 of the slab 1 lying flat on an homogenous ground, two connecting rods 15 having a length of 200 mm and a diameter of 9.5 mm are preferable. The spacing between these two connecting rods 15 is preferably 30 cm.

Therefore, in the best mode of realisation, the elements 3 are made of concrete or cement-based grout and have a thickness of about 90 mm. The flexible connecting rods 15 have a length of 200 mm, a nominal diameter of about 9.5 mm and a longitudinal axis extending horizontally across the gap 13 about 30 mm above the bottom wall of the elements 3. The slab 1 is provided with \ {-shaped grooves 21 having a depth of about 10 mm and an opening of about 6 mm. The upper portion of each of the side wall 5 of the pair 6 have a thickness of about 40 mm. Of course numerous changes could be made to this best mode of realisation without departing from the scope of the present invention. More specifically, the thickness of the elements, the length of the connecting rod, its nominal diameter and the longitudinal axis given above refer only to the best mode or realisation and can thus be different in another embodiment of the invention.

Referring now to Figure 5, there is shown a form 50 used in an upside down molding method for the manufacturing of a slab 1 as described above for an outside or an inside use.

In accordance with a preferred mode of realisation, the form 50 comprises a base wall 51 for forming the top surface 23 of the elements 3, a plurality of side walls 53 for forming a peripheral side wall of the slab 1; and a removable molding structure 55 for forming the gap 13 and to locate the connecting rod 15 of each flexible joint 7. The molding structure 55 comprises at least one elongated rigid member 57 for extending horizontally above the base wall 51. Referring now also to Figure 6, the elongated member 57 has a body 59 shaped and sized for forming the bottom section 11 of the flexible joint 7. The body 59 has a flexible slotted hole 61 shaped and sized for removably inserting therein one of the connecting rod 15. Supporting means are provided for supporting the elongated members 57 above the base wall 51 for defining gaps to be filled between the elongated members 57 and the base

wall 51, thereby allowing to form the upper section 9 of the flexible joints 7.

The supporting means preferably comprises a plurality of supporting arms 63 extending outwardly and lying on the side walls 53 of the form 50 for supporting the elongated member 57 above the base wall 51. The supporting arms 63 have two opposite end portions; the first end portion is attached to an elongated member 57 while the second end portion is laid onto the peripheral side wall of the form 50. In the embodiment illustrated, the second end portion of each supporting arms 63 is secured to a framing member 67 devised to surround the peripheral side wall of the form and to strengthen the molding structure 55. The framing member 67 may be made of assembled steel tubes. In this case, the first and second end portions of the supporting arms 63 are welded respectively to the elongated element 57 and to the framing member. Of course the supporting means described above is an exemplary embodiment and is not directed to limit the scope of the invention. Any other convenient supporting means allowing to support the elongated member 57 above the base wall 51 is believed to be within the limits of the present invention.

In the embodiment illustrated in figure 6, the body 59 of the elongated member 57 is preferably made of rubber and triangular-shaped for forming an upside down V-like shaped gap 13 between the side walls of the pair 6 of adjacent side walls 5. The elongated member 57 is preferably made of steel for giving the appropriate rigidity to the molding structure 55. The slotted hole 61 of the molding structure 55 must be a flexible slotted hole for allowing a release of the connecting rod 15 during the removal of the molding structure 55. As a preferred embodiment, rubber is molded around the elongated member 57 for defining the body 59 thereof and consequently, defining the flexible slotted hole 61. Moreover, the elongated member 57 may be provided with a plurality of anchoring holes (not shown) for securing the rubber body 59 to the steel elongated member 57. During the molding of the rubber around the elongated member, some rubber will seep and dry in the anchoring holes, thus providing a stronger anchoring of the rubber on the steel, as well known in the art.

Referring again to Figure 5, the illustrated form 50 is a square form but any other convenient shape could be provided, depending on the surface to be covered or the desired ornamental design which one wants to reproduce. The bottom wall 51 can be a fully distinct part of the form 50 but it also could be the ground on which the side walls 53 of the form 50 are disposed. However, in a preferred embodiment which is illustrated in Figures 5 and 6, the bottom wall 51 of the form is a fully distinct part. Moreover, the form 50 may advantageously comprise a rubber sheet disposable over the base wall 51 for facilitating a removal of the slab 1 from the form 50. The side walls 53 of the form 50 may also be provided with rubber elements which are attached to their inner surfaces for facilitating even more the removal of the slab from the form 50.

Still referring to Figures 5 and 6, the form 50 may advantageously comprise at least one elongated projecting ridge 65 extending on the base wall 51 in an alignment relationship with the body 59 of the at least one elongated member 57 of the molding structure 55 for forming the groove 21 on the top surface 23 of the slab 1. The elongated projecting'ridge 65 may have any suitable shape, for example, a U-shape or a V-shape.

The method for manufacturing the slab comprises the steps of: a) setting the form 50 on a planar surface; b) inserting a rod 15 in the slotted hole 61 of the body 59 of each of the elongated members 57, as shown in Figure 6; c) pouring a hardenable filling material into the form, as shown in Figure 7; d) hardening the filling material (Figure 7); and e) removing the molding structure 55, as shown in Figure 8, and side walls 53 of the form 50, thereby obtaining the slab in an upside down position, as shown in Figure 9.

Figure 7 shows such a form 50 wherein a hardenable filling material has been poured. After the hardening of the filling material, the molding structure 55 is

removed, as can be seen on Figure 8. The side walls 53 are then also removed for obtaining the slab in an upside down position, as illustrated in Figure 9.

The method described above uses a precast wet technique, but it should be understood that a dry technique could also be used. Moreover, the preferred method described here uses an upside down moulding method but it should be noted that a method wherein the slab is right side up may also conveniently be used.

It is worth mentioning that the dimensions given throughout the description may vary slightly, for example from plus or minus 10 to 20 percent, without departing from the scope of the invention.

Although preferred embodiments of the present invention have been described in detail herein and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention.