GB2243179A

GB2243179A - Screed rail

Info

Publication number: GB2243179A
Application number: GB9108428A
Authority: GB
Inventors: Ernest Bruce Robert Thomson
Original assignee: PERMABAN
Current assignee: PERMABAN
Priority date: 1990-04-21
Filing date: 1991-04-19
Publication date: 1991-10-23
Also published as: GB9108428D0; GB9008977D0; CA2040553A1

Abstract

A screed rail (1) has a keying formation, for example a groove (4) in the upwardly-facing surface of its bottom flange (2), to enable positive keying between the flange (2) and the concrete cast against the rail in use. The rail (1) may be laid using laying means comprising a stool (6) which is intended to rest on a substrate and has an engagement portion (7) for receiving the bottom flange (2) with the keying groove (4), and a locking wedge (8) engageable between the keying groove (4) and the engagement portion (7) of the stool (6) to lock the rail (1) in position in the stool (6). The rail may also include an oppositely-directed second bottom flange (2). <IMAGE>

Description

SCREED RAIL The present invention relates to screed rails and is more particularly concerned with so-called leave-in-place screed rails.

A leave-in-place screed rail is a type of lost formwork for use in the casting of concrete slabs for floors or paving, for example, in warehouses and car parks. Such screed rails are used to define the edges of successive slabs during casting and are left in place as integral parts of the finished paving or floor, forming joints between adjacent slabs. Leave-in-place screed rails are described, for example, in the document "PERMABAN Leave-in-Place Screed Rails" published by Permaban (UK) Ltd., Mill Close, Lee Mill Industrial Estate, Ivybridge, Devon (1983).

In general terms, a screed rail can be seen to include a longitudinal bottom flange intended to rest on the substrate directly or with the interposition of so-called stools or of dabs or mounds of concrete on which the rail is bedded, and an upstanding web portion perpendicular to the bottom flange. Screed rails may be produced as a 11full" rail in which the web portion projects from the centre of the bottom flange, giving the rail a general inverted-T-section in the position of use, or as an asymmetric or "half" rail with a generally L-shaped cross-section in which the web portion is upstanding from one edge of a bottom flange narrower than that of a "full" rail.

Certain problems have been inherent in the use of leave-in-place screed rails available until now. If a joint between two slabs is formed by such a screed rail, the concrete will generally tend to shrink away from the side of rail against which the later, fresher slab was cast because the bond between the concrete and the rail is weaker on that side of the rail than on the other side. Cracks may open up on both sides of the rail, however, due to variations in the standard of concreting and of installation of the rail itself, causing the rail to loosen and ultimately to break if subject to the passage of wheeled loads. The use of a "half" rail may help to reduce the tendency for cracks to form but is more difficult to lay than a "full" rail because it tends to tilt sideways.In any event, it has been found that considerable skill is required on the part of the installer to achieve the accurate levelling of the screed rails necessary for some floors because of the difficulty of bedding the rails firmly on dabs or mounds of wet concrete.

The present invention aims to overcome these problems.

According to a first aspect, therefore, the present invention provides a screed rail for use in the casting of concrete, including a longitudinal bottom flange provided with a keying formation which extends along a surface of the flange intended to face upwardly or downwardly in use so as to enable positive keying between the flange and the concrete cast against the rail.

The keying formation is preferably constituted by a continuous groove or ridge extending along the entire length of the flange but it may be in the form of a series of discrete elongate recesses or projections spaced along the flange.

In the case of a "full" rail, the bottom flange may be provided with a keying formation on each side of the web portion. Such a rail may have a keying formation on only one side of the web portion, however, in which case the rail would usually be laid with the keying formation on the side against which the concrete is to be poured first so that a firm bond is achieved between the concrete and the rail on that side.

A second aspect of the present invention provides means for laying a screed rail according to the first aspect of the invention, comprising a stool which is intended to rest on the substrate and has an engagement portion adapted to receive the bottom flange with the keying formation in a position such that the flange is clear of the substrate, and a wedge engageable between the keying formation and the engagement portion of the stool to lock the rail in position in the stool.

The laying means may also include shims of varying thickness for insertion between the bottom flange and the stool to adjust the level of the rail relative to the substrate. The shims may themselves be wedge-shaped.

Some embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figures l(a)-l(d) show four prior-art screed rails in cross-section; and Figures 2, 3, 4 and 5 are cross-sectional views of four embodiments of a screed rail and of laying means therefor, according to the present invention.

With reference to the drawings, a screed rail, generally indicated 1 in all the Figures, can be seen to include a longitudinal bottom flange 2 intended to rest directly or indirectly on a substrate and an upstanding web portion 3 perpendicular to the flange 2.

The edge of the web portion 3 opposite the flange 2, which constitutes the upper edge of the rail 1 in use, may be enlarged to form an upper flange but in any event defines a flat surface corresponding to the surface of the concrete slab which will be cast against the rail 1 in use.

A screed rail may be a "full" rail, as shown in Figures 1 (a) and 1 (b), having an inverted-T-shape in cross-section with the web portion 3 projecting from the centre of the bottom flange 2, or a "half" rail, as shown in Figures 1(c) and l(d) and in Figures 2 to 5, in which the web portion 3 is upstanding from one edge of a bottom flange 2 narrower than that of a "full" rail.

According to the present invention, the bottom flange 2 of the screed rail 1 is provided with a keying formation which extends along a surface of the flange intended to face upwardly or downwardly in use. The keying formation may be in the form of a groove 4, as shown in Figures 2 and 4, or in the form of a ridge 5, as shown in Figures 3 and 5. In the embodiments illustrated, the grooves 4 and ridges 5 are continuous, extending along the entire length of the flange 2.

Although the screed rail of the invention as described and illustrated with reference to Figures 2 to 5 is in the form of a "half" rail, it may equally well be in the form of a "full" rail such as, for example, those illustrated in Figures l(a) and l(b).

In use, when the wet concrete is poured against the rail 1, it flows into the groove 4 or over the ridge 5 and sets to afford a strong mechanical connection or positive keying between the rail 1 and the concrete.

This resists the tendency of the concrete to shrink away from the rail.

When the rail 1 forms a joint between two successive slabs, for example, in a floor, it is laid so that the keying groove 4 or projection 5 is on the side against which the first slab will be cast.

The present invention also provides means for laying a screed rail 1 whose bottom flange 2 has a keying formation 4, 5 as described above. These means include a stool 6 which is intended to rest on the substrate and has an engagement portion 7 adapted to receive the bottom flange 2 with the keying formation 4, 5 in a position such that the flange, and hence the enitre rail, is held clear of the substrate by a certain distance, enabling concrete to flow under the rail if necessary. In the embodiment illustrated, the stool 6 is generally C-shaped in a cross-section and the engagement portion 7 is defined by the recess of the C.

A locking wedge 8 is engageable between the keying formation 4, 5 and the engagement portion 7 of the stool 6 to lock the rail 1 in position in the stool 6.

As illustrated, the part of the engagement portion 7 engageable by the wedge 8 may have a groove 9 in correspondence with the keying groove 4 or projection 5 so as to accommodate a wedge 8 of appropriate profile.

This groove 9 is not essential, however, if there is sufficient clearance between the flange 2 and the engagement portion 7 of the stool.

A set of shims 10 of different thicknesses is also provided so that a shim 10 of appropriate thickness can be inserted between the bottom flange 2 and the stool 6 to adjust the level of the rail 1 relative to the substrate, if necessary. The shims 10 may themselves be wedge-shaped.

The use of a rail with a keying groove 4 or projection 5 and two or more stools 6 with respective locking wedges 8 enables the rail to be laid easily and to be held securely in line and level so that it will withstand the forces exerted by the wet concrete during casting.

The screed rail 1 of the invention is normally of precast concrete whilst the stools 6 may also be of concrete, as illustrated, or of moulded plastics material. In the embodiments shown, the wedges 8 and the shims 10 are of metal but they may be made from wood, plastics or even concrete, as appropriate.

Although not specifically described herein, the present invention extends to a screed rail with a bottom flange having keying formations on its surfaces which face upwardly and downwardly in use.

Claims

1. A screed rail for use in the casting of concrete, including a longitudinal bottom flange intended to rest directly or indirectly on a substrate and having surfaces which face upwardly and downwardly in use, and an upstanding web portion perpendicular to the bottom flange, wherein at least one of said surfaces of the bottom flange has a keying formation which extends along the surface to enable positive keying between the flange and the concrete cast against the rail in use.

2. A screed rail according to Claim 1, wherein the keying formation is constituted by a continuous groove or ridge extending along the entire length of the flange.

3. A screed rail according to Claim 1 or Claim 2, of the type in which the web portion projects from the centre of the bottom flange, wherein the bottom flange has a keying formation on each side of the web portion.

4. A screed rail according to Claim 1 or Claim 2, of the type in which the web portion projects from the centre of the bottom flange, wherein the bottom flange has a keying formation on only one side of the web portion.

5. Means for laying a screed rail including a bottom flange with surfaces which face upwardly and downwardly in use and at least one of which has a keying formation extending therealong to enable positive keying between the flange and concrete cast against the rail in use, and an upstanding web portion perpendicular to the bottom flange, the laying means comprising a stool which is intended to rest on a substrate and has an engagement portion adapted to receive the bottom flange with the keying formation in a position such that the flange is clear of the substrate, and a wedge engageable between the keying formation and the engagement portion of the stool to lock the rail in position in the stool.

6. Laying means according to Claim 5, wherein the stool is generally C-shaped and the engagement portion is defined by the recess of the C.

7. Laying means according to Claim 5 or Claim 6, wherein the part of the engagement portion of the stool engageable by the wedge has a groove in correspondence with the keying formation of the bottom flange of the rail to accommodate the wedge.

8. Laying means according to Claim 5, Claim 6 or Claim 7 including shims of different thicknesses for insertion between the bottom flange of the rail and the stool to adjust the level of the rail relative to the substrate.

9. A screed rail substantially as herein described with reference to and as shown in Figure 2, Figure 3, Figure 4 or Figure 5 of the accompanying drawings.

10. Means for laying a screed rail, substantially as herein described with reference to and as shown in Figure 2, Figure 3, Figure 4 or Figure 5 of the accompanying drawings.