Abstract:
The invention relates to an artificial stone floor element with a basic shape that corresponds to the combination of a plurality of square basic elements, especially to an angular floor element. The floor element includes projections and recesses along its peripheral sides of the basic element when seen from the centre of the respective top face of the basic element is substantially point-symmetric with respect to its mid-point. The floor element in further embodiments includes a profile that consists of three projections and three recesses.

Description:
This application is a Divisional of U.S. patent application Ser. No. 10/633,663 filed on Aug. 5, 2003, which is a continuation of PCT Application Number PCT/EP01/11151 filed on Sep. 26, 2001, which claims priority from German application number 101 05 055.0 filed on Feb. 5, 2001; which are all incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates, according to a first aspect, to a ground covering element of artificial stone material, having a basic shape corresponding to a unification of several square basic elements, in particular an angular ground covering element, the ground covering element comprising projections and recesses all around its circumference, all circumferential basic element sides—as seen from the center of the respective basic element upper side—having substantially the same profile which is substantially point-symmetric with respect its halving point. 
   2. Description of the Prior Art 
   Basic elements of this kind, also angular ground covering elements, are known. So far, the design of the profile has been based more or less on intuition. 
   It is an object of the invention to purposefully design the profile in order to obtain a good compromise between inter-engagement effect in case of not completely perfect mutual orientation of adjacent ground covering elements and strength of the inter-engagement between adjacent ground covering elements. 
   SUMMARY OF THE INVENTION 
   To meet this object, the aforementioned ground covering element is characterized in that this profile consists of three projections and three recesses. It will be elucidated in more detail further below that this number will result in an optimum compromise in the sense of the underlying object mentioned. 
   The afore-mentioned “artificial stone material” in most cases is concrete. As a further preferred possibility, brick-like materials should be mentioned. In general, there are also all materials conceivable having embedded therein additives or fillers in binders (e.g. also plastics) hardening as a function of time, in particular polymer concrete. The word “substantially” was used with consideration, since in most cases, the profile is not equal on all circumferential basic element sides in the strict sense and since the point symmetry is not realized in the strict sense in most cases. Ground covering elements of artificial stone material are manufactured with such large manufacturing tolerances that this is of itself sufficient to prevent the manufacture of exactly identical profiles and exact point symmetry. In addition thereto, it happens quite often that minor changes in dimension are purposefully made on specific locations of the ground covering element, e.g. for taking into account e.g. a slanted corner or a retraction of a circumferential portion in order to create free space for a laying gap, so that the term “substantially” makes sense under this aspect. Finally, it may be reasonable to make e.g. the projections slightly narrower (as measured in the direction of extension of the basic element side) than the recesses, which are complementary in engagement, in order to thus provide a laying gap between adjacently laid ground covering elements. Quite analogous aspects are applicable as regards the use of the term “substantially” in the following description and in the entirety of the claims. 
   One could also say, in other words, that the profiles at the circumferential basic element sides of the ground covering element are designed such that a particular profile considered may be placed adjacent a substantially identical profile after rotation by 180° so as to provide complementary inter-engagement. 
   The claims as well as the description of the present patent specification, at numerous locations thereof, make statements on geometric relationships, e.g. “square basic element”, “angular ground covering element”, “projection”, “recess”, “profile”, “wide”, “trapezoidal”. All of these statements relate to a representation of the ground covering element in a plan view, i.e. a view from above onto the useful or upper side of the respective ground covering element, as if the same were laid on a base, unless otherwise expressly stated at the particular location. The ground covering element according to the invention preferably is a ground covering element provided to make ground coverings for “outdoor use” or for laying areas in the outside. A particularly preferred field of use of the ground covering element according to the invention is for traffic areas, in particular such areas outdoors, e.g. areas for motor vehicle traffic, areas for bicycle traffic, areas for pedestrian traffic. Particularly typical and preferred are squares, yards, drives, paths, roads, pedestrian areas, loading areas, terraces, parking areas for vehicles, filling stations, commercial traffic areas, industrial traffic areas, factory yards, container sites. 
   Preferably, the projections and recesses are trapezoidal, which can be manufactured easily and is favorable for the shear strength of the projections. As an alternative it is preferred that the projections and recesses are confined each by a line rounded at least in part, e.g. semi-circular with rounded transition to the left and to the right. It is to be noted generally that the geometric design of the projections and recesses offers a large variety of possibilities. 
   Preferably, the middle projection and the middle recess each are considerably wider than the other projections and recesses, respectively. In this regard, at least 1.5 times as wide is particularly preferred, at least 1.8 times as wide is still further preferred, and at least 2.0 times as wide is even further preferred. It will become clearer by more detailed statements further below why this difference in dimensions will result in a still further improved compromise in the sense of the solution of the object. 
   Preferably, the ground covering element is provided with spacer projections on its circumference, with these spacer projections being left disregarded in the consideration of the geometric relationships discussed in the claims. However, it is pointed out that there are also designs in which the geometric relationships mentioned in the claims are maintained despite the spacer projections. Due to the spacer projections, ground covering elements are obtained that can be laid in particularly expedient manner with the laying gap width remaining the same (as measured transversely of the general direction of extension of the circumferential basic element side). 
   According to a second aspect, the invention relates to a ground covering element of artificial stone material, having a basic shape corresponding to a unification of several square basic elements, in particular an angular ground covering element, the ground covering element comprising projections and recesses all around the circumference and comprising retractions on the circumference which result in efficient water passage openings in a group of the adjacently laid ground covering elements, 
   characterized in that the projections and recesses in their entirety are defined by one profile each for each circumferential basic element side, there being provided 
   (a) on zero to all circumferential basic element sides, substantially a first profile each, having—as seen from the center of the particular basic element upper side—a first end neighboring projection, a second end neighboring projection and an end distance projection there-between; 
   (b) on zero to part of the circumferential basic element sides, substantially a second profile each, having—as seen from the of the particular basic element upper side—a first end neighboring projection and a second end neighboring projection; 
   (c) and on zero to part of the circumferential basic element sides, substantially a third profile each, having—as seen from the center of the particular basic element upper side—an end distance projection and an end neighboring projection; 
   (d) wherein, for laying a group of the ground covering elements adjacent each other, 
   a first profile, if provided, can be applied to a first profile, if provided, of a neighboring ground covering element; or can be applied to a second profile, if provided, of a neighboring ground covering element; or can be applied to a third profile, if provided, of a neighboring ground covering element; 
   a second profile, if provided, can be applied to a second profile, if provided, of a neighboring ground covering element; or can be applied to a third profile, if provided, of a neighboring ground covering element, 
   and a third profile, if provided, can be applied to a third profile, if provided, of a neighboring ground covering element. 
   Ground covering elements of this type according to the invention, in the state laid adjacent each other, thus lead to ground coverings in which efficient water passage openings are present in a very considerable part of the ground covering element circumferences. However, due to this, the ground covering elements mostly lose the feature “the profile is substantially point-symmetric with respect to its halving point”. 
   All statements made so far in the description, of course with the exception of statements that are contradictory to the second aspect of the invention, apply analogously also for ground covering elements according to the second aspect of the invention, inclusive of the preferred developments thereof. 
   It is emphasized that the terms “first end neighboring projection” and “second end neighboring projection” do not mean that the projection concerned begins immediately at an end of the respective circumferential basic element side. There may be a distance provided. Rather, what is to be expressed is that the respective projection is positioned not very far from the respective end and in particular that there is no additional projection present between the end neighboring projection and the end proper. The first end does not necessarily have to be the left-hand end of a particular profile, but may optionally be the left-hand end or the right-hand end of the particular profile. 
   As in case of the ground covering element according to the first aspect of the invention, the projections and recesses preferably are trapezoidal, and as an alternative are preferably confined by a line that is rounded at least in part. The statements made further above are applicable here as well. 
   Preferably, the retractions are trapezoidal, as an alternative preferably confined at least in part by a rounded line. The statements made hereinbefore in connection with the shape of the projections and recesses apply analogously for the retractions as well. 
   The embodiments described herein provide further details of the first, second and third profiles. 
   With respect to the first profile and/or the second profile and/or the third profile, the retraction in each thereof is preferably at least 33% of the width of the respective circumferential basic element side, more preferably at least 40% of the width, still more preferably at least 50% of the width. In the second profile, it is easier to obtain a maximum possible width of the retraction than in case of the first and third profiles. 
   Preferably, the particular retraction at least in part is retracted or taken back further towards the interior of the ground covering element than the recesses or recesses of the particular basic element side. The wider the respective retraction and the “deeper” the retraction is taken back, the higher the percentage of the sum of the cross-sectional areas of the water penetration passages in relation to the size of the covering in total. 
   The present disclosure further defines preferred combinations of first profiles, second profiles and third profiles on the circumference of the ground covering element. More detailed information in this regard will be given by the embodiments further below. 
   As regards the ground covering element according to the first aspect of the invention, it is indeed preferred that the first projection, the first recess, the third projection and the third recess all have substantially the same width (as measured in the direction of the circumferential basic element side). However, it is possible as well to provide just the first projection and the third recess with substantially the same width and to provide just the first recess and the third projection with substantially the same width (which, however, is narrower or wider than the width of the afore-mentioned “pair”). 
   As with the ground covering element according to the first aspect of the invention, the ground covering element according to the second aspect of the invention preferably may have spacer projections and/or at least one dummy gap. 
   According to a third aspect, the invention relates to a set of ground covering elements, containing a ground covering element according to the first aspect of the invention (first ground covering element) and a ground covering element according to the second aspect of the invention (second ground covering element) wherein, for laying a first ground covering element and a second ground covering element adjacent each other, the basic side profile of the first ground covering element can be laid adjacent a first profile or a second profile or a third profile of an adjacent second ground covering element. 
   The invention thus provides a set of ground covering elements, in which first ground covering elements and second ground covering elements can be laid adjacent each other in an arbitrary mutual orientation. This property comes to bear in particularly advantageous manner either at the boundary between a first part of a covering laid with first ground covering elements and a second part of the covering laid with second ground covering elements or—which is possible without any problem—in a covering with a regular alternation between a first ground covering element and a second ground covering element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and preferred developments of the invention will be described in more detail hereinafter by way of embodiments shown in the drawings in which 
       FIG. 1  shows an angular ground covering element; 
       FIG. 2   a  to  2   d  each show the abutment portion of two adjacent ground covering elements in a fragmentary view; 
       FIG. 3  shows a second embodiment of a ground covering element that is modified over that of  FIG. 1 , with partial regions being broken away; 
       FIG. 4  shows a portion of a circumference of a ground covering element; 
       FIG. 5  shows a portion of a circumference of a ground covering element; 
       FIG. 6  shows a portion of a circumference of a ground covering element; 
       FIG. 7  shows an angular ground covering element according to a third embodiment; 
       FIG. 8  shows a fourth embodiment of a ground covering element that is modified over that of  FIG. 7 , with partial regions being broken away; 
       FIG. 9  shows an angular ground covering elements according to a fifth embodiment; 
       FIG. 10  shows a sixth embodiment of a ground covering element that is modified over that of  FIG. 7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   All of the drawing figures are plan views. 
     FIG. 1  shows an angular ground covering element  2 . In the following, the term “covering element” will be used throughout in the following instead of “ground covering element” for reasons of brevity. All covering elements shown preferably consist of concrete. 
   The configuration of the covering element  2  is conceivable easiest if one first speaks of a “basic shape”. In case of the covering element  2  of  FIG. 1 , this basic shape is constituted by the unification of three square basic elements  4 ,  6 ,  8 . The junction lines  10  of the three basic elements  4 ,  6 ,  8  are illustrated in broken lines  10 . Basic element  4  thus has three circumferential basic element sides  12 , basic element  6  has two circumferential basic element sides  12 , and basic element  8  has three circumferential basic element sides  12 . In basic element  8 , the three circumferential basic element sides  12  are illustrated in broken lines. When looking at the combination of these three circumferential basic element sides and the junction line  10  belonging to basic element  8 , the basic element square will become apparent immediately. 
   Basic element  8  shall be considered in more detail in the following: 
   On each of the three circumferential basic element sides  12 , there is provided a profile  14  composed of projections  16  and recesses  18 . The respective circumferential basic element side  12  at the same time represents a neutral line with respect to which the projections  16  are projecting outwardly and with respect to which the recesses  18  are receding inwardly. 
   To begin with, the in  FIG. 1  upper, in total horizontally extending profile  14  of basic element  8  shall be considered. Starting from the left-hand end of the basis element side  12  considered, the profile  14  begins with a projection  16   a , followed by a recess  18   a , then a projection  16   b , thereafter a recess  18   b , then a projection  16   c  and thereafter a recess  18   c  extending up to the right-hand end of basic element side  12 . All projections  16   a  to c and all recesses  18   a  to c are of trapezoidal shape, i.e. they begin with a slightly wider base on the straight basic element side  12  and taper towards the free end and towards the base, respectively. The projections  16  and recesses  18  follow each other without a gap. The projections  16   a  and  16   c  closer to the ends of basic element side  12  (in other embodiments described hereinafter, reference will be made to “end neighboring projection”) and the recesses  18   a  and  18   c  closer to the ends of basic element side  12  all have substantially the same mutual width (measured on the basic element side  12 =neutral line). The projection  16   b  remoter from the ends of basic element side  12  as well as the recess  18   b  remoter from the ends of basic element side  12  have the same mutual width and each are about twice as wide as any of the projections  16   a  and  16   c  and any of the recesses  18   a  and  18   c , respectively. The terms “substantially” and “about” have been used purposefully, since—for reasons to be elucidated in more detail further below—the measurement relationships mentioned are not to be understood as being exactly so. For example, projection  16   a  indeed is somewhat wider than projection  16   c . On the other hand, recess  18   c  indeed is somewhat wider than recess  18   a ; moreover, the corner of covering element  2  is slanted with a small taper at the right-hand end of recess  18   c . Finally, it is pointed out that in case of concrete products, like the covering element  2  illustrated, indications of measurements and measurement relationships are not to be understood as being exact anyway due to the tolerances of the manufacturing mold and due to the material providing no particularly smooth areas. A particularly relevant aspect resulting in a variation in width among projections  16  and recesses  18  is the fact that on the circumferential sides of covering element  2 , where a neighboring covering element is adjoining when several covering elements  2  are laid adjacent each other, a laying gap e.g. of a width of 3 to 5 mm is maintained, whereas there is no laying gap on junction line  10 . To provide for certain compensation in this respect, the more or less mathematical initial design of the profile  14  with respect to the width of the projections  16  and the recesses  18  and with respect to the positioning of the projections  16  and recesses  18  is slightly modified. 
   The profile  14  in consideration is substantially point-symmetric with respect to its halving point  20 , i.e. when the left-hand profile half is rotated by 180° in the drawing plane of  FIG. 1 , it is identical with the right-hand profile half. The term “substantially” was inserted for the reasons analogous to those set forth hereinbefore. 
   It is emphasized that the profile  14  described could also be formed “inversely”, i.e. folded by 180° about a halving line located in the drawing plane, i.e. left-hand end and right-hand end are interchanged. Profile  14  then would begin with a first recess on the left-hand side. 
   The afore-mentioned widths of the projections  16  and recesses  18  are measured on the neutral line  12 . This is as a rule the most appropriate place of the covering element  2  according to the invention. 
   It is pointed out that the trapezoidal shape of the projections  16  and recesses  18  constitutes just one of numerous embodiments possible. Instead of this, one could choose e.g. a rectangular shape (which however is more difficult to produce) or a farther projecting or farther receding shape e.g. in the form of a low triangle. The profile  14 , as seen from the center  22  of the particular basic element, is the same on each of the three circumferential basic element sides  12 , i.e. when the upper profile  14  considered first is rotated clockwise by 90° about the center  22 , it merges substantially with the in  FIG. 1  right-hand profile  14  extending in its entirety in vertical direction, and when the upper profile  14  is rotated by 180° about the center  22 , it merges substantially with the in  FIG. 1  lower profile  14  of the particular basic element  8 , extending in its entirety in horizontal direction. As regards the use of the term “substantially”, it is referred to the statements made hereinbefore. Due to the afore-mentioned point symmetry of each profile  14  with regard to the halving point  20 , the lower profile  14  is substantially a parallel shift of the upper profile  14 . 
   All statements made hereinbefore with respect to the profiles  14  apply analogously to the basic elements  4  and  6 , with the basic element  6  of course having only two circumferential basic element sides and thus only two profiles  14  extending so to speak perpendicularly with respect to each other. 
   The geometry of the profiles  14  described allows adjacent covering elements to be placed adjacent the covering element  2  illustrated in  FIG. 1 , either in the same orientation or in an orientation rotated by 90° (clockwise or anticlockwise) or an orientation rotated by 180°. The profiles  14  of adjacent covering elements  2  always fit together in complementary manner (with some “air” there-between); there is mutual engagement or anchoring of the adjacent covering elements  2  in addition to the mutual anchoring of adjacent covering elements in the laid state that is obtained by the angular configuration of the covering element  2  illustrated. 
   It is pointed out that covering elements  2  according to the invention indeed are supposed to have a basic shape corresponding to a unification of several square basic elements, but that the number of the basic elements and the orientation of the unification can be chosen. For example, it would be possible to unify e.g. three basic elements  4 ,  6 ,  8  (or also two basic elements or four basic elements) in a straight series, or to provide an L-shaped covering element  2  by addition of a further basic element on the right-hand side of basic element  8 , or to provide a T-shaped covering element  2  by addition of a further basic element to the upper side of the middle basic element  6 , or to provide a cruciform covering element  2  by addition of a further basic element to the upper side of the middle basic element  6  and addition of a further basic element to the left-hand side of the middle basic element  6 , etc. 
   It is expressly emphasized that the invention, as an alternative, also provides a ground covering element whose basic shape consists of one square basic element only, but otherwise has the cogent features described in the present patent specification and optionally further preferred features. 
   It is illustrated by way of  FIGS. 2   a  to  d  why the number of “three projections” and “three recesses” according to the invention provides for especially good results. Each of the partial figures a to d schematically illustrates a profile  14  of a circumferential basic element side  12 . In  FIG. 2   a , the basic element side is divided into eight projections  16  and eight recesses  18  which all have the same mutual width. In partial  FIG. 2   b , the basic element side is divided into three projections  16  and three recesses  18  which all have the same mutual width. In partial  FIG. 2   c , the basic element side is divided into two projections  16  and two recesses  18  which all have the same mutual width. The alternative with just one projection and one recess is not illustrated as it results in incomplete inter-engagement between two covering elements. 
   Each of the basic element sides  12  of the two adjacent covering elements  2   a  and  2   b  do not extend parallel to each other (as desired for perfect laying), but extend at an angle  24  with respect to each other, with angle  24  being the same in all partial  FIGS. 2   a  to  d.    
   If two adjacent covering elements  2   a  and  2   b  are arranged beside each other with a misalignment in the sense of the angle  24  mentioned, which may occur due to inaccurate laying work or by displacement of individual covering elements  2  by traffic loads in the laid state,  FIG. 2   a  still maintains a residual inter-engagement by the last projection  16  at the right-hand end of basic element side  12  of the one covering element  2   a  and a recess  18  at the corresponding end of the basic element side  12  of the other covering element  2   b . In case of the covering elements  2   a  and  2   b  of  FIG. 2   b , the left hand trapezoidal side of the rightmost projection  16   c  of covering element  2   a  and the left-hand trapezoidal side of the rightmost recess  18   c  of covering element  2   b  have migrated a certain distance to the left, but in this situation there is just left a residual inter-engagement between this projection  16   c  and this recess  18   c  (although with lesser depth of positive engagement). In case of the covering elements  2   a  and  2   b  according to  FIG. 2   c , there is no residual inter-engagement left in this situation. The conclusion to be drawn therefrom is that the residual inter-engagement effect in case of angular misalignment between adjacent covering elements is the better the larger the number of projections and recesses over a given length of a basic element side. 
   A further aspect is the strength or load-bearing capacity of the inter-engagement between two adjacently laid covering elements  2   a  and  2   b  in the correctly laid state, i.e. with mutually parallel basic element sides  12  with so little spacing from each other as corresponds to the usual laying gap. In this respect, the shear strength, i.e. the covering elements  2   a  and  2   b  have forces of opposite directions applied thereto in the direction parallel to the basic element sides  12 , decreases with increasing number of projections  16  and recesses  18  on a given length of the basic element side  12 . On the one hand, the overall shear area summed up from the individual projections  16  becomes ever smaller with increasing number of projections (since the laying gap sections between the oblique trapezoidal sides do not contribute in the overall shear area and since a loss in overall shear area is caused in that, on a larger number of projections, the cross-sectional area of shear is not located in the root of the projection, but in the projection portion that is tapered in comparison therewith). On the other hand, there is the effect that, with a larger number of projections, it is by far not the entire number of projections that provides a supporting effect against shearing, but less than half thereof in accordance with experience. The aspect of shear strength thus speaks for making the number of projections and recesses as small as possible for a given length of the basic element side. 
   On consideration of these aspects, the inventors thus have arrived at the conclusion that the number of three projections and three recesses represents the optimum compromise between residual inter-engagement effect in case of angular misalignment and high shear strength. 
   This compromise is still further enhanced when the pairs of projection  16   a  and recess  18   a  and projection  16   c  and recess  18   c  closer to the respective ends of the basic element side are of lesser width than the pair of projection  16   b  and recess  18   b  arranged there-between, cf.  FIG. 2   d.    
   The embodiment of a covering element  2  according to  FIG. 3  differs from the embodiment according to  FIG. 1  in that straight dummy gaps  26  extend at those locations where the junction lines  10  were illustrated in  FIG. 1 . Dummy gaps are gaps extending from the upper side downwardly into covering element  2  up to a specific depth of e.g. 5 mm only. The dummy gaps  26  provide for an optical subdivision of covering element  2  into three partial covering elements which, apart from the profiles  14 , correspond to the three basic elements  4 ,  6 ,  8 . As measured transversely of their direction of extension, the dummy gaps  26  have a width corresponding substantially to the height of the projections  16 , as measured from the bottom of the recesses  18  and, in addition, the afore-mentioned laying gap width (the latter being measured transversely to the general direction of extension of profile  14 ). It is possible not only with the embodiment according to  FIG. 3 , but with all embodiments that the upper sides of the projections  16  are slightly lowered with respect to the remaining upper side of covering element  2 , e.g. by 4 to 8 mm. The consequence hereof is that the inter-engagement between two adjacent profiles  14  is optically less apparent in the laid covering of several covering elements  2 . The dummy gaps  26  so to speak represent an optical continuation of the groove formed by the two adjacent profiles  14  and the laying gap there-between. 
   Moreover,  FIG. 3  illustrates the possibility of providing spacer projections  28  distributed over the circumference of the covering element  2 . In the illustrated embodiment, the spacer projections  28  are of semi-circular cross-section each and are provided on the—as seen from the center  22  of the respective basic element upper side—leftmost projection  16  of the corresponding profile  14  each. In  FIG. 3 , the size of the spacer projections  28  is shown in enlarged form as compared to their natural size in order to make the spacer projections clearly visible at all. The spacer projections  28  facilitate laying of the covering elements  2 , since the adjacent covering element  2  to be laid next can be placed simply in physical contact between the spacer projections  28  of the already laid covering element  2  and the spacer projections  28  of the new covering element  2  to be laid. In this manner, a laying gap of uniform width is created. It is emphasized that the spacer projections may be selectively of other cross-sectional geometry and be located on other locations than those shown in  FIG. 3 . It is preferred that the spacer projections begin only a certain distance below the covering element upper side and extend from there to the very bottom side of the covering element  2 . The spacer projections  28  are formed integrally with the remainder of the covering element  2  of concrete. 
     FIG. 3  finally illustrates the possibility of confining the projections  16  and the recesses  18  by a rounded line each (rounded throughout or rounded in portions and straight in portions). 
   It is emphasized furthermore that the features “dummy gaps  26 ” and “spacer projections  28 ” need not necessarily be realized in combination, but that it is possible to provide covering elements  2  with at least one dummy gap  26  and/or with spacer projections  28 . It is possible to provide just one dummy gap  26  or more than two dummy gaps  26 , e.g. to optically subdivide the unification of the basic elements  6  and  8  into three parts by means of two dummy gaps  26 . It is possible, furthermore, to provide one or more non-linear dummy gaps, extending e.g. in conformity with the path of profile  14 . 
     FIGS. 4 to 6  illustrate profiles  14   a ,  14   b ,  14   c  that are modified with respect to profile  14  of  FIG. 1 . Here too, the neutral line  12  is shown in each of the figures. The distance from the respective left-hand end to the respective right-hand end corresponds to that of a basic element side in  FIG. 1 . 
   The profile illustrated in  FIG. 4  is a profile of the type referred to as “first profile  14   a ” in the present text. In comparison with the profile  14  of  FIG. 1  (e.g., considering the “horizontal” profile  14  to the upper right in  FIG. 1 ), the second projection  16   b  is rendered narrower to such an extent that it has a width (as measured in the direction of the neutral line  12 ) corresponding to the width of third projection  16   c . Between the thus formed second projection  16   b  and the third projection  16   c , there is located a retraction  30 . Retraction  30  is further retracted towards the interior of covering element  2  than the bottom of recess  18   a  and the bottom of recess  18   c . Retraction  30  in total is of trapezoidal shape. In the introductory part of the specification, first projection  16   a  is designated “first end neighboring projection” (as it is located in the neighborhood of the first end of the profile), second projection  16   b  is designated “end distance projection” (as, in comparison with the other projections, it is arranged at a larger distance from the ends of the profile), and third projection  16   c  is designated “second end neighboring projection” (as it is located in the neighborhood of another end of the profile). 
   The profile illustrated in  FIG. 5  is a profile of the type referred to as “second profile  14   b ” in the present text. In comparison with the profile  14  of  FIG. 1  (e.g. considering the “horizontal” profile  14  to the upper right in  FIG. 1 ), the second projection is omitted completely so that of the projections only the first end neighboring projection  16   a  and the second end neighboring projection  16   c  are left. Between these projections  16   a  and  16   b , there is located a retraction  30  (which thus replaces first recess  18   a , second projection  16   b  and second recess  18   b ) which, as in case of  FIG. 4 , is retracted further towards the interior of covering element  2  than the bottom of recess  18   c.    
   The profile illustrated in  FIG. 6  is a profile of the type referred to as “third profile  14   c ” in the present text. In comparison with the profile  14  of  FIG. 1  (e.g. considering the “horizontal” profile  14  to the upper right in  FIG. 1 ), the first projection  16  is omitted and substituted by a corresponding broadening of the first recess  18   a . The second projection  16   b  of  FIG. 1  is rendered narrower to the same extent as in case of profile  14   a  in  FIG. 4 . The retraction  30  in  FIG. 5  also corresponds to the retraction  30  in  FIG. 4 . In the description, projection  16   b  is designated “end distance projection” (since, in the light of the just outlined history of origin, it corresponds to the end distance projection  16   b  in  FIG. 4  and although there is no further projection between it and the left-hand end of the profile  14   c ). It is emphasized that the profiles  14   a ,  14   b ,  14   c  as an alternative may also be designed such that they are folded by 180° about their halving axis located in the drawing plane, so that they would each begin with recess  18   c  at the left-hand end. 
   In the first profile  14   a  of  FIG. 4 , the projections  16   a ,  16   b ,  16   c  all have substantially the same width (as measured in the direction of the neutral line  12 ); the recesses  18   a  and  18   c  also have substantially the same mutual width and substantially the same width as the projections (as measured in the direction of neutral line  12 ). As regards the reasons for using the term “substantially”, these have already been pointed out hereinbefore in connection with  FIG. 1 . In particular, one can see in  FIG. 4  that the first end neighboring projection  16   a  in reality is somewhat wider than the projections  16   b  and  16   c . It is expressly pointed out that the end distance projection  16   b  could very well be wider towards the right than is illustrated, without this interfering with the inter-engagement with a neighboring covering element  2  to be discussed in more detail further below. 
   As regards the second profile  14   b  of  FIG. 5 , the two projections  16   a  and  16   c  and the recess  18   c  all have substantially the same width. 
   In the third profile  14   c  of  FIG. 6 , the projections  16   b  and  16   c  and the recess  18   c  are substantially of the same width; the recess  18   a  is substantially twice as wide as in  FIG. 1 . Here, too, the end distance projection  16   b  indeed could be wider towards the right without this interfering with the inter-engagement. 
   A comparison of  FIGS. 4 ,  5 ,  6  directly reveals that the first profile  14   a  (of course upon rotation thereof by 180°) could be laid selectively adjacent an additional first profile  14   a  or a second profile  14   b  or a third profile  14   c . The second profile  14   b , too, can be laid selectively adjacent a first profile  14   a , a second profile  14   b  and a third profile  14   c . The third profile  14   c  also is adapted to be selectively laid adjacent a first profile  14   a  or a second profile  14   b  or a third profile  14   c . This becomes clear also from the history of origin of profiles  14   a ,  14   b ,  14   c  since, as compared to the profile  14  of  FIG. 1 , projections have been cut off completely or in part, while however no essential changes have been made, with the exception of the retractions  30 . It is recognizable furthermore that, with respect to the retractions  30  (in so far as they are not reduced in a small part by projections  16  of the neighboring covering element  2  engaging therein), there are left elongate openings in the covering of a plurality of adjacently laid covering elements  2 . These openings represent efficient water passage openings through which water precipitated may flow off into the bed underneath the covering, so that it need not be discharged into a discharge channel system. The depth of the retractions  30  with respect to the neutral line  12  determine—in addition to the width of the retractions  30 , though this cannot be chosen very freely—the percentage of the water passage openings in the total covering. The purpose of the described change from the profile  14  of  FIG. 1  to the profiles of  FIGS. 4 to 6  consisted in providing covering elements  2  which in the laid state form water penetration passages in the covering. 
   If a second profile  14   b  is laid in inter-engagement with a second profile  14   b , an inter-engagement is established that provides for positive locking in just one of two possible directions. The same holds if a third profile  14   c  is laid in inter-engagement with a third profile  14   c . However, if a first profile  14   a  is laid in inter-engagement with a first profile  14   a , positive locking in the two directions possible is achieved (since projection  16   c  engages in recess  18   a  framed on both sides by projections). The same holds for inter-engagement between a first profile  14   a  and a second profile  14   b  as well as for inter-engagement between a first profile  14   a  and a third profile  14   c . Also with inter-engagement of a second profile  14   b  and a third profile  14   d , there is a positive locking effect achieved in the two directions possible, i.e. towards the left and towards the right in  FIGS. 4 ,  5 ,  6 . The result of this is that covering elements  2  having only second profiles  14   b  all around their circumference and covering elements  2  having only third profiles  14   c  all around their circumference are not particularly advantageous under the aspect of inter-engagement on each circumferential basic element side. However, this aspect is not of extremely large significance especially with angular covering elements  2  as shown in  FIG. 1 , since the overall configuration of the covering element  2  already results in effective mutual anchoring of the covering elements  2  in the covering. 
   Good inter-engagement and/or good anchoring due to the covering element configuration is advantageous not only for the laid state but also for holding together of covering elements manufactured together on a plate of the manufacturing machine, when these are machine-laid using a gripper. 
   It has already been pointed out hereinbefore that it is basically possible to make covering elements  2  for providing coverings with efficient water passage openings which, at the circumference thereof, have either only first profiles  14   a  or only second profiles  14   b  (better, however, with at least one exception) or only third profiles  14   c  (better, however, with at least one exception) or an arbitrary combination of profiles  14   a ,  14   b ,  14   c.    
     FIG. 7  illustrates an embodiment of a water passage opening covering element  2  which has no first profile  14   a , but five second profiles  14   b  and three third profiles  14   c . As regards the locations of such second profiles  14   b  and such third profiles  14   c , it is expressly referred to  FIG. 7 . 
     FIG. 8  illustrates schematically (i.e. without explicit indication of the profiles) a modification in which four second profiles  14   b  and four third profiles  14   c  are provided, with these being distributed moreover in different manner along the circumferential basic element sides  12 . As regards the distribution thereof over the circumferential basic element sides  12 , it is expressly referred to  FIG. 8 . 
     FIG. 9  shows an embodiment having two first profiles  14   a , five second profiles  14   b  and a third profile  14   c . As regards the individual circumferential basic element sides with the individual profiles, it is expressly referred to  FIG. 9 . The transition from the embodiment of  FIG. 7  to the embodiment of  FIG. 9  is conceivable such that two third profiles  14   c  have been replaced by two first profiles  14   a.    
   Analogous with  FIG. 3 ,  FIG. 10  shows an embodiment in which the additional features “dummy gaps  26 ”, “spacer projections  26 ” and “rounded projections  16 ” or “rounded recesses  18 ” or “rounded retraction  30 ”, respectively, can be seen. Here too, the detailed statements made hereinbefore in relation to  FIG. 3  hold in particular with respect to the non-existing cogent requirement of providing several of these features in combination.