EP2253760A1

EP2253760A1 - A system of at least two flat prefabricated concrete elements

Info

Publication number: EP2253760A1
Application number: EP10162429A
Authority: EP
Inventors: Johannes Peter Wilhelmus Bongers
Original assignee: ModieSlab vof
Current assignee: ModieSlab vof
Priority date: 2009-05-18
Filing date: 2010-05-10
Publication date: 2010-11-24
Also published as: NL2002901C2

Abstract

A system of at least two flat prefabricated concrete elements, which can be interconnected in a plane near their facing short ends so as to form a pavement, the short end of each concrete element being provided with a recess, and a dowel extending from one recess into the other recess in the connected condition of the concrete elements for transferring forces exerted on the concrete elements between said elements, characterised in that a wall of the recess in the short end of the one concrete element is at least partially lined with a flexible material, and in that a wall of the recess in the short end of the other concrete element is at least partially roughened so as to allow horizontal movements and/or rotations of the adjacent concrete elements relative to each other, substantially without stresses, via the dowel.

Description

The invention relates to a system of at least two flat prefabricated concrete elements, which can be interconnected in a plane near their facing short ends so as to form a pavement, the short end of each concrete element being provided with a recess, and a dowel extending from one recess into the other recess in the connected condition of the concrete elements for transferring forces exerted on the concrete elements between said elements.
The invention also relates to a separate concrete element as defined in said system. The invention further relates to a method for forming a pavement, using at least two of said concrete elements.
It is noted that within the framework of the invention the term "pavement" is understood to comprise any pavement having ample load bearing capacity which is subjected to uneven and/or variable loads, for example by traffic, and/or which is subject to temperature variations, such as, for example, but not exclusively, roads, sidewalks, bus lanes and tramway tracks, squares and the like.
It is further noted that within the framework of the invention the term "concrete element" is in particular, but not exclusively, understood to mean a concrete slab. The term "flat concrete slab" is to be understood to include a warped concrete slab.
Such a system is known from Dutch patent No. 1 029 373 (Pressplate). In the system that is known therefrom, the prefabricated concrete elements are positioned relative to each other in situ, such that a wide joint is formed between their facing short ends. Into said joint a liquid joining substance is poured, which, after curing, functions as a dowel at the location of said recesses.
A drawback of the system known from the aforesaid Dutch patent is that the dowel is not suitable for efficiently transferring transverse forces between the concrete elements. Another drawback is that the known system does not allow vertical and horizontal movements of adjacent concrete elements relative to each other. A drawback of the fact that horizontal movements under the influence of loads exerted by traffic and weather conditions are not allowed is that the concrete elements can be loaded to such an extent in practice that the concrete elements may crack locally. It is the object of the invention to obviate the drawbacks of the prior art, that is, to provide a system of at least two flat prefabricated concrete elements, wherein the concrete elements are easy to install and to remove and wherein the transfer of vertical forces being exerted perpendicularly to the aforesaid plane both to the one concrete element and to the other concrete element can take place in an efficient manner via the dowel. It is in particular the object of the invention to enable horizontal movements and/or rotations of adjacent concrete elements relative to each other substantially without stresses.
In order to accomplish that object, a system of the kind described in the introduction is according to the invention characterised in that a wall of the recess in the short end of the one concrete element is at least partially lined with a flexible material, and in that a wall of the recess in the short end of the other concrete element is at least partially roughened so as to allow horizontal movements and/or rotations of the adjacent concrete elements relative to each other, substantially without stresses, via the dowel. The flexible material has the advantage that transverse forces can be efficiently transferred from one concrete element to another and/or that wrenching forces are prevented. An advantage of roughening is that if the dowel between the two concrete elements is formed by pouring and/or injecting and curing cement-bound dowel material, the dowel will bond well to the wall of the recess of the other concrete element, also in the case of possible shrinkage of the material, whilst the cement-bound material, on the contrary, does not bond well to the wall of the recess of the one concrete element provided with a flexible material, so that the connection between the concrete elements will not be a rigid connnection. In other words, the invention provides a non-rigid connection between the one concrete element and the dowel and a rigid connection between the other concrete element and the dowel.
In a preferred embodiment of a system according to the invention, the recesses have a polygon-shaped section with a substantially horizontal lower surface and/or upper surface, for example a rectangular or square cross-section. In another preferred variant, a slot-shaped cross-section is used. More in particular, an upper wall and a lower wall of the recess in the short end of the other concrete element are roughened, whilst an upper wall and a lower wall of the recess in the short end of the one concrete element are lined with the flexible and/or elastically deformable material. The flexible and/or elastically deformable material is preferably an elastomer, more preferably rubber. Minor rotations of the concrete elements relative to each other caused by shrinkage and expansion gradients (under the influence of temperature effects and/or uneven concrete shrinkage and/or loads exerted by aircraft and/or vehicles, for example, and/or goods stored thereon) are thus allowed, whilst loads applied to the slabs can be efficiently transferred from the one concrete element to the other concrete element by the dowel via transverse force transmission.
In another preferred embodiment of a system according to the invention, a rear wall of the recess in the short end of the one concrete element is lined with a material which is compressible under the influence of forces exerted on the concrete elements and/or under the influence of horizontal movements of the abutting concrete elements relative to each other. The compressible material is for example a closed-cell foam tape and/or expanded polystyrene (EPS). More in particular, the surface of the short end of at least one of the concrete elements outside the recess in question is lined with a compressible material. As already said before, horizontal movements of two abutting concrete elements relative to each other caused by shrinkage and expansion under the influence of temperature effects and/or by concrete shrinkage thus become possible. In particular, in the case of a poured and/or injected dowel the compressible material in the joint ensures that the cement-bound material being poured will not leak out when the cement-bound material is being poured for forming the dowel.
In another preferred embodiment of a system according to the invention, at least one concrete element comprises at least one channel near its short end, which channel extends from an upper surface of the concrete element into the recess of the short end, said channel being designed for transporting dowel material therethrough for forming the dowel in the recesses. Preferably, two channels to a recess are located on a short side, one channel being designed for transporting dowel material therethrough and the other channel being designed to function as a vent. The channel that extends downwards into the recess can therefore be efficiently used for filling the recesses with a cement-bound material and/or for venting purposes, with a dowel joint being formed between the two concrete elements after the cement-bound material has cured. When the two concrete elements are placed in abutment with each other, the cement-bound material is poured or injected through one channel of the other concrete element for forming the dowel in the recesses, whilst the other channel of the other concrete element is used as a vent. In another embodiment, each concrete element is provided with a channel to a recess, wherein the cement-bound material is poured or injected through the channel in the other concrete element for forming the dowel in the recesses and the channel of the one concrete element is used as a vent. Since the concrete elements are positioned in close abutment with each other, i.e. leaving only a narrow gap therebetween, and/or because the joint is provided with the compressible material, hardly any, if any, cement-bound material will leak out, whilst the dowel can nevertheless be formed in a very controlled manner.
As already said before, the invention also relates to a concrete element, in particular a concrete slab, as defined in a system according to the invention. Such a concrete element is therefore characterised in that the short end of the concrete element is provided with a recess, whilst a wall of the recess in the short end of the concrete element is at least partially lined with a flexible material or is at least partially roughened.
The invention also relates to a method for forming a pavement wherein at least two flat prefabricated concrete elements are supplied, wherein a recess is formed at the short end of each concrete element, which concrete elements are interconnected in a plane near their facing short ends, and wherein a dowel is provided, which dowel extends from one recess into the other recess in the connected condition of the concrete elements for transferring forces exerted on the concrete elements between said elements. Such a method is according to the invention characterised in that a wall of the recess in the short end of the one concrete element is at least partially lined with a flexible material and that a wall of the recess in the short end of the other concrete element is at least partially roughened so as to allow horizontal movements and/or rotations of the adjacent concrete elements relative to each other, substantially without stresses, via the dowel.
Preferably, at least one channel, preferably two channels, is (are) provided in at least one concrete element near the short end thereof, which channel(s) extend(s) from an upper surface of the concrete element into the recess of the short end, wherein dowel material is supplied through the one channel of the other concrete element for forming the dowel in the recesses, and wherein the other channel of the one and/or the other concrete element is used as a vent.
It is noted that according to the invention a non-reinforced dowel of cement-bound material is used, for example cement-bound grouting mortar. In other words, the dowel consists of curable - but liquid upon application - jointing material which (after curing) extends from one recess into the other for transferring forces exerted on the concrete elements between said elements.
The invention will now be explained in more detail with reference to figures illustrated in the drawing, in which:

Figure 1 is a schematic top plan view of a prefab concrete slab according to a preferred variant of the invention; and
Figure 2 is a cross-sectional view of the prefab concrete slab of figure 1; and
Figure 3 is a cross-sectional view of two adjacent prefab concrete slabs according to figure 1; and
Figure 4 is a cross-sectional view of two adjacent and interconnected prefab concrete slabs according to figure 1; and
Figure 5 is a cross-sectional view of two adjacent and interconnected slabs according to figure 1, without flexible and/or elastically deformable strips.

In figures 1 and 2 there is shown a prefab concrete slab 1 provided with two horizontal recesses 2, 3 and two vertical channels 4, which are in communication with the recess 2. Instead of using two vertical channels 4 being in communication with the recess 2, is also possible to use one channel which is in communication with the recess 2 and one channel which is in communication with the recess 3. The recess 2 on a first side of the concrete slab 1 has rough horizontal upper and lower surfaces 5, which surfaces 5 have been roughened, for example by subjecting them to a blasting treatment. Horizontal upper and lower surfaces 6 of the recess 3 on a second short side of the concrete slab are provided with two thin strips 7 of a flexible and/or elastically deformable material, and the rear surface of the recess 3 is provided with a material 8 which is compressible under the influence of forces exerted on the concrete elements and/or in the case of horizontal movements of the adjacent concrete elements. The surface of the second short side of the concrete slab 1 located outside the recess 3 is also provided with the compressible material. Preferably, the flexible and/or elastically deformable material of the strips 7 is an elastomer, more preferably rubber, and the compressible material of the subsequent joints 8,9 consists of closed-cell foam tape and/or expanded polystyrene foam (EPS).
By placing two or more concrete slabs adjacent to each other and interconnecting said slabs a pavement can be formed which is suitable for heavy loads, for example from aircraft and/or vehicles and/or goods stored thereon. In figure 3 two prefab concrete slabs 1A and 1B are placed adjacent to each other on a ground surface 10. The first concrete slab 1A is provided with the recess 3 with the thin strips 7 and the compressible material 8, and the surface of the second short side (the first short side is not shown) of the concrete slab 1A located outside the recess 3 is provided with a compressible material 9. The second concrete slab 1B is provided with the recess 2 with the rough surfaces 5. The two concrete slabs 1A and 1B can be interconnected after being placed by pouring or injecting a cement-bound material into one of the two channels 4, which material will cure after being poured or injected, with the other channel 4 functioning as a vent. The material used for this purpose is preferably a low-shrinkage cement-bound mortar, which bonds well to the rough surfaces 5 of the second concrete slab 1B, also in case of shrinkage, whilst the low-shrinkage cement-bound mortar does not bond well to the flexible and/or elastically deformable material of the first concrete slab 1A, so that the connection between the two concrete slabs is not a rigid connection. Another advantage of the cement-bound connection between the two concrete slabs is that the connection can be simply sawn through when a concrete slab is damaged, after which the damaged concrete slab and the remnants of dowel material can be removed. A new concrete slab can then be placed adjacent to the other concrete slab and be connected to the other concrete slab by pouring or injecting the material to be poured.
Figure 4 shows two concrete slabs 1A and 1B placed adjacent to each other on a ground surface 10 after the mortar has been poured or injected into the channel 4, the cured mortar forming a (dowel) connection 11 in the recesses 2,3, thereby interconnecting the two concrete slabs 1A and 1B. Because the concrete slab 1A is provided with compressible materials 8,9, horizontal movements caused by shrinkage and expansion of the concrete slabs 1A and 1B under the influence of temperature effects and/or uneven concrete shrinkage are compensated thereby. Because the upper and the lower surface of the recess 3 are provided with flexible and/or elastically deformable strips 7, also rotation caused by shrinkage and expansion gradients of the concrete slabs 1A and 1B under the influence of temperature effects or uneven concrete shrinkage and/or of loads exerted by aircraft and/or vehicles and/or goods stored thereon is compensated, whilst furthermore an efficient, two-sided transfer of transverse forces can take place. This is indicated by means of the arrows V in figure 4. A load is applied to the first concrete slab 1A, resulting in a downward force V₁, which force is transferred to the second concrete slab 1B via an upward force V₂. Likewise, an effective transfer of the transverse forces will take place from the second concrete slab 1B to the first concrete slab 1A when a load is applied to the second concrete slab 1B. From figure 4B it is apparent that horizontal movements of the concrete slabs 1A and 1B are possible also in the case of a rotating concrete slab 1A.
Figure 5 shows that the transfer of transverse forces between the concrete slabs 1A and 1B takes place less efficiently when no flexible and/or elastically deformable strips 7 are used. The downward force V₁ acting on the first concrete slab 1A is not fully transferred to the second concrete slab 1B in this case, because wrenching forces V₃ and V₄ develop, with the effective transfer of transverse forces equalling V_eff = V₁ - V₃ = V₂ - V₄.
The dimensions of the recesses 2,3 of the concrete slab 1 are carefully selected so as to realise an optimum transfer of transverse forces while using the smallest possible dowel. The dimensions of the recesses 2,3 may be 30 mm for the upper and lower surfaces 5,6, for example, with a height of 50 mm for the rear wall of the recess 2,3 in the case of a concrete slab being 4500 mm in length, 3600 mm in width and 200 mm in height. The joint 8,9 is 10 mm thick, for example.
The concrete slabs depicted in the figures concern a preferred variant of the invention, in which the recess is a polygon-shaped recess (seen in cross-sectional view), with a substantially horizontal upper and lower surface. In an alternative embodiment the recess is a slot-shaped recess, however.
It is noted that the invention is not limited to the embodiment discussed in the foregoing, but that it also extends to other variants that fall within the scope of the appended claims. The skilled person will thus appreciate that several such recesses may be present in the two grooved sides of the concrete slab, or that more sides of the concrete slab may be provided with recesses. It will furthermore be understood that several strips of a flexible and/or elastically deformable material may be provided in the case of a polygon-shaped recess, so that the lateral surfaces will likewise be provided with said strips. It is also possible to use a single strip, which is circumferentially provided on the lateral, upper and lower surfaces. It will further be understood that instead of providing two channels to a recess, it is also possible to form two channels in the compressible material in the joint, which channels can be bored out, if desired, after filling. Furthermore, the compressible material present in the joint may be provided only at a certain level below the recess, so that the joint can be used for filling the recesses with dowel material. Following this, the joint can be sawn through up to the dowel. Furthermore, the channels may be provided from a side or from the underside of the concrete element to extend into the recess.

Claims

A system of at least two flat prefabricated concrete elements, which can be interconnected in a plane near their facing short ends so as to form a pavement, the short end of each concrete element being provided with a recess, and a dowel extending from one recess into the other recess in the connected condition of the concrete elements for transferring forces exerted on the concrete elements between said elements, characterised in that a wall of the recess in the short end of the one concrete element is at least partially lined with a flexible material, and in that a wall of the recess in the short end of the other concrete element is at least partially roughened so as to allow horizontal movements and/or rotations of the adjacent concrete elements relative to each other, substantially without stresses, via the dowel.
A system according to claim 1, wherein the recesses have a polygon-shaped or slot-shaped cross-section with a substantially horizontal lower and upper wall.
A system according to claim 1 or 2, wherein an upper wall and/or a lower wall of the recess in the short end of the one concrete element is (are) lined with the flexible material.
A system according to claim 1, 2 or 3, wherein a rear wall of the recess in the short end of the one concrete element is lined with a material which is compressible under the influence of forces exerted on the concrete elements.
A system according to any one of the preceding claims 1-4, wherein the surface of the short end of at least one of the concrete elements outside the recess in question is lined with a material which is compressible under the influence of forces exerted on the concrete elements.
A system according to claim 1, wherein the compressible material is a closed-cell foam tape and/or expanded polystyrene (EPS).
A system according to any one of the preceding claims 1-6, wherein an upper wall and a lower wall of the recess in the short end of the other concrete element is roughened.
A system according to any one of the preceding claims 1-7, wherein the flexible material is elastically deformable.
A system according to claim 8, wherein the flexible material is an elastomer.
A system according to any one of the preceding claims 1-, wherein at least one concrete element comprises at least one channel near its short end, which channel extends from an upper surface of the concrete element into the recess of the short end, said channel being designed for transporting dowel material therethrough for forming the dowel in the recesses.
A concrete element as defined in a system according to any one of the preceding claims 1-10, wherein the short end of the concrete element is provided with a recess, and wherein a wall of the recess in the short end of the concrete element is at least partially lined with a flexible material or is at least partially roughened.
A method for forming a pavement wherein at least two flat prefabricated concrete elements are supplied, wherein a recess is formed at the short end of each concrete element, which concrete elements are interconnected in a plane near their facing short ends, and wherein a dowel is provided, which dowel extends from one recess into the other recess in the connected condition of the concrete elements for transferring forces exerted on the concrete elements between said elements, characterised in that a wall of the recess in the short end of the one concrete element is at least partially lined with a flexible material and that a wall of the recess in the short end of the other concrete element is at least partially roughened so as to allow horizontal movements and/or rotations of the adjacent concrete elements relative to each other, substantially without stresses, via the dowel.
A method according to claim 12, wherein at least one channel is provided in at least one concrete element near the short end thereof, which channel extends from an upper surface of the concrete element into the recess of the short end, wherein dowel material is supplied through the channel of the concrete element for forming the dowel in the recesses.
A method according to claim 13, wherein two channels are provided in a concrete element near the short end thereof, which channels extends from an upper surface of the concrete element into the recess of the short end, wherein dowel material is supplied through the one channel of the other concrete element for forming the dowel in the recesses, and wherein the other channel of the one and/or the other concrete element is used as a vent.
A method according to claim 13, wherein a channel is provided in each concrete element near the short end thereof, which channel extends from an upper surface of the concrete element into the recess of the short end, wherein dowel material is supplied through the channel of the other concrete element for forming the dowel in the recesses, and wherein the other channel of the one and/or the other concrete element is used as a vent.