Screed rails

Abstract: A method of casting an horizontal area of concrete comprises laying a pattern of screed rails (2,30,48) on a substrate (46) with the rails supported in shoes (8,34,60,68) on the substrate (46) at spaced locations therealong to define at least one casting region in the pattern. Concrete is cast in the region or regions to cover the area. The rails (2,30,48) may be supported above the substrate (46) to form spaces between the rails and the substrate. The rails (2,30,48) may be located in the shoes (8,34,60,68) by means of one or more of spacers, wedges and bolts (12,14,36,40).

Description: This invention relates to the casting of concrete, especially the in situ casting of large areas of concrete. Such casting is useful for example in the formation of warehouse floors, car parks and similar open areas, roadways and paths. Particularly it relates to the use of screed rails which divide such areas into discrete regions, but remain part of the laid area. Large areas of concrete have traditionally been laid in "patchwork" fashion. Adjacent discrete first regions are cast in a first stage against shuttering which is removed after the regions of concrete have at least partially cured. In a second stage, remaining vacant regions are cast in a second stage against and between the first regions to complete the total area of concrete to the cast. The first regions define at least part of the boundaries of the regions in the second stage, so that separate shuttering is not needed within the total area and the cast concrete is substantially continuous. This technique is time-consuming as at least two curing stages must be accommodated. Further, the machinery used for tamping or vibrating the cast but not cured concrete in the first stage must be moved between the discrete first regions. In order to reduce the number of casting stages necessary in the casting of large areas of concrete, methods have been proposed in which the shuttering used becomes a permanent part of the cast layer. Screed rails, usually of pre-cast concrete, are first laid to define a grid of castable regions in all of which concrete can be poured in a single stage. The screed rails provide support for tamping and vibrating machinery which can thus be applied to the whole area cast, again in a single stage. Two such techniques are disclosed in CH-A-545393 and International Patent Publication No. WO81/02600. Another is described in EP-A-0053977 in which screed rails are supported over the substrate on separate supports. The present invention is directed at a technique broadly of the type described above, but using a screed rail which particularly facilitates the laying of reinforcement rods within the cast concrete. In the method of the invention, screed rails are laid in a predetermined pattern or grid on a substrate, with the rails supported on shoes on the substrate at spaced locations therealong to define at least one casting region in the pattern. Each rail comprises beams forming upper and lower edges of the rail and connected by elements which define slots extending between the beams, normally the full distance between the beams. Reinforcement rods may be laid within the pattern or grid, with the rods passing through the slots. Concrete is then cast in the region or regions to cover the area. A screed rail of solid substantially rectangular cross-section is either too thin to function with sufficient stability in the casting site, or too large for easy transportation. It is also desirable to define in the screed rail a keying mechanism for the concrete cast against it, and this is achieved in the known rails by forming the screed rail with a recess between enlarged upper and lower edges. In the present invention a similar mechanism may be provided, either by enlarging the upper edge of the rail or by forming recesses in parallel sides of the rail. The latter design enables a rail of relatively large cross-section to be employed without the rail being so bulky as to incur transportation problems, but providing sufficient stability to be simply laid on the substrate at the casting site. The former design which may also include recesses in parallel sides of the rail, retains the advantage of easy transportation, and to some extent enhances it as a rail can be suspended from its enlarged upper edge, but the relatively thin lower part will not normally provide sufficient stability at the casting site to permit easy laying or resist the lateral pressure of wet concrete cast thereagainst. According to the present invention though, each rail is supported in shoes spaced along the length thereof, the shoes being disposed on the substrate in for example, concrete dabs. The use of shoes in this way is of particular benefit if the substrate is uneven as described below. The shoes may be formed with a simple slot for receiving the rail, and wedges or other devices can be included to lock it in place. This arrangement has a principle advantage in that the substrate can be less even or level than it would need to be had it to support each rail along substantially its entire length, bearing in mind that its upper edge will define the eventual concrete surface. Spacers may be used to increase the height at which a rail is supported by a shoe for fine adjustment if needed. It should be noted of course that leakage of wet concrete through or under a screed rail is usually of relatively small importance when it is being poured on both sides substantially at the same time although undesirable gaps, particularly larger ones, can be filled as required. The shoes are typically formed in cast concrete, but other materials, for example steel, can be used. Pour of concrete to the boundary of an area is also facilitated using the invention. "Half" rails can be used, i.e. with the upper edge enlarged only on one side in the former design above or with recesses only on one side in the latter. "Full" rails can though often be sufficient on their own. Screed rails used in the invention are usually of cast concrete which can be reinforced and/or pre-stressed in conventional manner. Where the concrete area to be laid is to be reinforced, reinforcement rods can be carried through the slots in rails. The nature of the elements defining the slots in rails of the invention may be selected according to the strength required of the beams but for ease of fabrication are preferably wall portions with surfaces which extend diagonally from one side of the rail to the other. The slots are thus defined by relatively thin edge portions which can be easily broken, without substantially weakening the structure of the rail, to force connecting devices or reinforcement itself of larger dimension than or imperfectly aligned with the slots, therethrough. Thus the slots may be relatively narrow or in some instances be totally closed. It will be appreciated that slots of this type may be formed in either of the basic designs referred to above. In some applications of the invention, the rails can be formed with spacing elements some distance apart. This further reduces their bulk, thereby facilitating handling and transportation, but also results in the creation of wide slots. In this case, such slots can be closed by webs joining the elements, typically at one side of the rail, but equally effectively in one or more planes more centrally of the rail cross-section. Connecting devices or reinforcement can be forced through the webs with relative ease at chosen locations, and the disposition of the devices or reinforcement is therefore less pre-determined. Reinforcement of the webs can be used if desired to minimize fracture thereof around connection devices or reinforcement as it is forced through. Webs of up to 10 mms thickness are contemplated, 3 to 6 mms being preferred. Screed rails according to the invention are particularly suited to battery casting. The parallel sides can be cast against formers which are bendable about axes perpendicular to the longitudinal direction of the rail, enabling a plurality of rails to be cast in a block which can be stored and if desired, transported as such, prior to full cure. Cured rails can be removed seriatim from a block as needed. The provision of recesses in concrete rails of the invention as described above also serves to enhance the keying of poured concrete to the rail, and an irregular surface can be provided on at least the sides of the rail to this end. Such irregularity may take the form of one or more ribs on the surfaces, extending vertically, horizontally or at any chosen angles. Such ribs may be continuous or discontinuous. Other forms of irregularity may be adopted, such as spaced projections or recesses, alternative or additional to the provision of ribs. The nature of the surface irregularity chosen will to some extent at least be determined in relation to the casting method used for the rail, and an intended application. The invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a perspective view showing an end portion of a screed rail for use in a method of the invention; Figures 2 and 3 are elevation and sectional plan views taken respectively on the lines I-I and II-II of Figure 1; Figure 4 is a plan view of the screed rail of Figure 1 with connecting devices or reinforcement passing therethrough; Figures 5 and 6 are views similar to that of Figure 3 showing sectional plan views of alternative screed rails suitable for use in methods of the invention; Figure 7 is a sectional view of the rail of Figure 6, illustrating a casting technique for the rail; Figure 8 is an elevation showing screed rails according to Figures 1 to 3 in place on a substrate; and Figure 9 is an end view of adjacent screed rails in place. Figures 1 to 3 illustrate a screed rail 48 comprising upper and lower beans 50 and 52 connected by portions 54. The portions 54 are better shown in Figure 3 as diagonal walls alternately inclined with respect to the longitudinal axis of the rail to define slots 56 at either side of the rail extending between the beams 50 and 52. The structure shown is strong, stable with or without the use of shoes, spacers and wedges as described below, depending on the intended use and the overall thickness of the rail, and not unduly bulky in view of the large voids formed between the walls 54. As shown in Figure 4, connecting rods, reinforcing rods or the like (58) can pass through the slots 56, and it will be appreciated that rods of larger dimension than the slots 56 can be forced through by chipping the edge of the slots 56 without substantially affecting the strength of the rail 48 as a whole. It will be appreciated that the slots 56 may therefore be very narrow, or even closed. As described below, the slots may be closed by a thin web of concrete through which connecting devices or reinforcement may be forced, whereby the possibility of leakage of poured concrete through the rail can be substantially eliminated. The overall rectangular cross-section of the rail renders stacking and transportation very easy. The rails shown in Figures 5 and 6 are of broadly similar construction to that of Figure 1, differing primarily in the nature of the spacing elements. In the rail of Figure 5 elements 70 of hexagonal cross-section are used, with edges of adjacent elements connected by a web 72. Regular hexagonal sections may be used, in which case the webs 72 are in a substantially central plane of the rail. Alternatively, irregular cross-sections may be adopted to locate the webs 72 towards one or other side of the rail. The webs 72 may also be disposed alternately towards opposite sides of the rail, or oriented obliquely across the rail by suitable selection of the spacing element cross-section. Figure 6 shows a rail cross-section in which the section of the spacing elements 74 is an isosceles trapezium. Webs 76 connect the bases of adjacent elements 74 along one side of the rail to form a continuous surface on that side and a series of recesses 78 on the other. This design has particular advantages in the manufacture of the rail as is apparent from Figure 7 which shows the rail being cast in a tray 80. The tray has spaced projections 82 which form the recesses 78, and the webs 76 define a substantially flat upper surface. Shortly after casting, the mould can be inverted and the tray 80 removed, leaving the rail to cure while freely supported on the web surface, and enabling the tray to be used again with minimum delay. As shown in Figure 8 the rail 48 of Figures 1 to 4, or as modified in Figures 5 to 7, can also be mounted on shoes 60 and concrete dabs 62. The shoes are shown disposed at the ends, forming a coupling between successive rails, although further intermediate shoes and/or dabs may be used as required to prevent sagging or other deformation before or during the pouring of the concrete thereagainst. Levelling of the rails is accomplished primarily by the amount of concrete used in the dabs 62 and if necessary, further vertical adjustment is made using spacers or wedges. Because the height of the rails is established only at the dabs 62, the substrate 46 therebetween does not require accurate levelling itself. Once in place, the rails may be further secured by the use of additional concrete around the dabs 62 to hold the rails to the shoes 60. Figure 9 shows laid rails 48 in an end view, rail 48' being laid against a wall 64. An internal expansion joint 66 is shown to accommodate movement of the cast area, either during or after curing of the concrete. Two rails 48 are shown spaced from the wall 64, disposed in an enlarged shoe 68 and also separated by an expansion joint 66 to provide the same flexibility within the cast area. The construction which is the basis of the rails of Figures 1, 5 and 6 can be modified to have other than parallel sides for specific application. For example vertically inclined walls can provide increased stability with a narrower upper beam while still being easy to stack safely, contiguous rails being inverted. All the rails described herein are suitable for battery casting with suitably shaped formers, and can be reinforced or prestressed by conventional means. In a typical method according to the invention of laying a concrete area using screed rails, the rails are first located substantially as described with reference to Figure 8 to define discrete regions separated by the rails. It will be understood that the rails will be placed at appropriate angles to each other (normally perpendicular) to separate the regions and define the area to be laid. All the regions can then be filled with concrete in one pouring stage, and tamped or vibrated using machinery which traverses the area supported on the rails. Once tamped, the concrete can be left to cure, and the related equipment removed to another site. The rails become part of the concrete structure, being intimately incorporated by means of bonding with the concrete by the respective mechanisms described herein. Rails for use according to the invention are usually provided in a variety of lengths; e.g. 3, 7 and 12 metres, 4 or 5 metres being a suitable standard length. Their height will normally be 50 to 200 mm, and their maximum width in the range 50 to 100 mm. The dimensions will of course vary, and the intended application may dictate certain criteria with respect to strength and dimensions, the former possibly imposing a need for reinforcement of some kind.

Claims: A method of casting an horizontal area of concrete comprising laying screed rails (48) in a predetermined pattern on a substrate (46) with the rails (48) supported in shoes (60,68) on the substrate at spaced locations therealong to define at least one casting region in the pattern; and casting concrete in said at least one region to cover the area, CHARACTERISED IN THAT each rail (48) comprises beams forming upper and lower edges of the rail and connected by elements (54,70,74) which define slots (56) extending between the beams. A method according to Claim 1 CHARACTERISED IN THAT reinforcement rods (58) are laid in said at least one region, which rods pass through the slots (56) in the screed rails. A method according to Claim 1 or Claim 2 CHARACTERISED IN THAT the rails (48) are supported above the substrate (46) to form spaces between the rails and the substrate. A method according to any preceding Claim CHARACTERISED IN THAT the shoes (60,68) are disposed in concrete dabs (62) on the substrate (46). A method according to any preceding Claim CHARACTERISED IN THAT each shoe (60,68) is separate from the rails and has a slot for receiving a rail (48). A method according to Claim 4 CHARACTERISED IN THAT the rails are located in the shoes by one of wedges, spacers and bolts.

Inventors: CLAPSON JOHN DAVID, CLAPSON, JOHN DAVID
Applicants: SQUARE GRIP LTD, SQUARE GRIP LIMITED
Application year: 1985
Main classification: E04G21
IPC codes: E01C23, E01C9, E04F21, E04G21