GB2493173A - Manufacture of hollow concrete panels - Google Patents

Abstract

A method of manufacturing pre-stressed hollow core concrete panels comprises pouring wet concrete into a pre-stress bed 2 comprising: retaining walls 10,11,12,13 surrounding the panel mould and tubes 30 suspended between two substantially parallel retaining walls 12, 13 and retained in place by apertures in said walls, vibrating said wet concrete, and withdrawing said tubes 30. The tubes 30 may be withdrawn before the concrete is set, and may have an arch-like upper profile to facilitate this without the concrete collapsing. The tubes may also be drawn into a further pre-stress bed 3, to allow manufacture of a further panel. The tubes may be withdrawn by means of a winch (41, Figure 4)

Description

PRE-CAST CONCRETE SECTIONS.

BACKGROUND

a. Field of the Invention

This invention relates to the manufacture of hollow core prestressed concrete panels (known as hollowcore).

Holes or bores formed through the panels reduce the weight, therefore allowing the product to span longer distances as well as using less material in production and reducing transport costs.

Hollowcore concrete is one of the biggest concrete products at present, certainly in the UK. It is used in virtually all new buildings, for example blocks of flats, commercial buildings, and the like. Use of hollowcore has replaced the use of timber joists in most buildings.

b. Related Art Hollowcore has been in use in buildings for at least 25 years.

Two known production process for manufacturing hollowcore include extruding' or slipforming' semi-dry concrete.

The concrete is squeezed though a set of dies which creates the outer shape and then small augers or pistons form the holes inside the panel Hollowcore is produced on prestress beds up to l5Ometres long and then cut into lengths. It has to be made to order as each piece can be a different length.

It is usually manufactured in 1200mm widths and is suitable for use in all types of housing as well as in the complete range of commercial and public sector bufldings.

System advantages of hollowcore including the following: * Clear, unpropped spans up to 13.Om * Can be used on masonry, steel or concrete structures * Fast to instali and provides an immediate working piatform * Once concreted together, units can provide diaphragm action without structural topping * Enhanced structural performance is achieved by using a composite structural topping * Excellent sound and fire resistant properties However the current methods of manufacturing hollwocore suffer from some serious disadvantages.

Firstly, the wear and tear on the machine extruding or slipforming the concrete panel using a semi-dry mix is considerable and can contribute as much as a third of the entire cost of production.

Therefore it is desirable to form hollowcore using a wet rather than semi-dry concrete mixture. Known processes which have been devised include creating a core using polystyrene cylinders or by using inflated cylinders in the production process which are deflated and withdrawn once the concrete has set. Both of these techniques suffer from the disadvantage that the cylinders need to be held down whilst the concrete sets otherwise they float to the surface. Adding bars or the like to the prestress beds to hold down such cylinders increases the cost of manufacture considerably and by as much as 50%.

Another problem is that by the very nature of the extrusion or slip-forming process the panels are created in one long section and need to be cut after manufacture.

This operation again adds significantly to the cost.

A third problem is that using this method of manufacture the panels that are produced do not have a particularly good finish due to the drag experienced during the manufacture process. Therefore, the panels often need to be refinished by hand once in situ.

Finally, it is not commercially viable to carry out slipforming or extrusion processes using flint aggregate which is commonly available in many parts of the UK because the flint aggregate is so tough the above problems are magnified to an extent that the process becomes untenable.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of manufacturing prestressed hollow core concrete panels comprising: pouring wet concrete into a prestress bed comprising: retaining walls surrounding the panel mould and tubes suspended between two substantially parallel retaining walls and retained in place by apertures in said walls; vibrating said wet concrete; and withdrawing said tubes.

Preferably the prestress bed comprises a sequence of sections and the step of withdrawing said tubes comprises withdrawing said tubes from a first section through to a second section and suspending said tubes between two substantially parallel retaining walls in a second section.

Withdrawing the tubes is carried out by attaching an end of each tube to a winch and operating the winch.

It is an advantage if the tubes have an upper portion which is substantially arch shaped to facilitate withdrawal of the tubes before the concrete is set and whilst it is still wet.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only with reference to the accompanying drawings in which Figure 1 is a perspective view of first portion of a prestress concrete bed for use in the present invention; Figure 2 is a side view of a prestress concrete bed for use in the present invention; Figure 3 is a top view of a of a prestress concrete bed for use in the present invention; Figure 4 is a perspective view of a second portion of a prestress concrete bed for use in the present invention; and Figure 5 shows example tubular cross sections which may be advantageously used in the invention.

DETAILED DESCRIPTION

A prestress concrete bed 1 is typically tens of metres long. Usually partitions are placed at intervals along the length to create sections of the desired length. A prestress concrete bed 1 has retaining walls forming a mould comprising longitudinal side walls 10, 11 and crosswise partition walls 12, 13, 14, 15. In the embodiment shown and illustrated further in Figures 2 and 3, the bed is forty two metres long and is separated into seven x six metre sections. Neighbouring partition walls 13, 14 between two separate sections 2, 3 are typically separated from each other by about 10cm by steel spacers.

Pretensioned steel wires 20 extend the full length of the bed 1. In known prestress concrete beds wet concrete is poured into separate sections 2, 3 etc formed by the retaining walls and then vibrated to compact the concrete. The concrete is then left to set. Once the concrete is set the pretensioned wires 20 are cut between neighbouring partition walls 13, 14 and the individual sections are released.

In the prestress bed of the present invention as well as having apertures 21 through which the steel wires 20 pass, the partition walls 12, 13, 14, 15 have further apertures 22 through which steel tubes 30 may be suspended. Only two tubes are shown in Figure 1, but in operation there would be up to eight tubes extending through the eight apertures 22 in the embodiment iilustrated.

Tubes 30 are suspended in a first section 2 formed between partitions 12, 13 and walls 10, 11. The tubes 30 are slightly longer than the section to be constructed and are thus held in place vertically by the apertures 22 in the partitions 12, 13.

Concrete is poured into the first section 2 and vibrated in the usual way.

The tubes only need to be slightly longer than the longest section to be constructed, and will usually be significantly shorter than the full length of the bed, but longer tubes can be used in shorter sections if necessary.

Referring now to Figures 2 and 3, the tubes 30 are each connected by a respective thin wire 40 to a winch 41.

Once the concrete has been vibrated in the first section 2 the tubes are pulled by the winch 41 through the apertures in the partition walls and parallel to the longitudinal walls, until they are suspended in the next section 3.

It is not necessary to wait until the concrete has set to withdraw the tubes, as long as the upper portion of the tube is circular, oval or similarly arch shaped then once the concrete has been vibrated the shape holds itself in place and the tube can be withdrawn immediately. Figure 5 illustrates possible tube cross sections The essential feature of the shape is that it the concrete will be self supporting whilst still wet once the tube is withdrawn. The arch may be formed from several short straight sections for example as illustrated in Figure Sc.

Once the tubes are in place in the next section 2, concreted is pour into that section, vibrated and the process repeated.

Figure 4 illustrates two sections 7, 8 of the prestress bed 1 once all of the sections have been tilled with concrete. Note tor clarity the pretensioned wires 20 are not shown in Figure 4.

Once the final section has been filled and the concrete vibrated the tubes are withdrawn completely and the concrete allowed to set.

The sections 2, 3, .. 7, 8 are then separated from one another by cutting the pretensioned wires. No turther cutting of the concrete is required and the tinish on the panels is good enough such that further hand tinishing is not necessary.

Furthermore there is no wear and tear on any machinery, and thus the process can be carried out using flint aggregate.

It will be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately, or in any suitable combination.

It is to be recognised that various alterations, modifications, and/or additions may be introduced into the constructions and arrangements of parts described above without departing from the scope of the present invention as defined in the appended claims.

Claims (1)

1. <claim-text>CLAIMS1. A method of manufacturing prestressed hollow core concrete panels comprising: pouring wet concrete into a prestress bed comprising: retaining walls surrounding the panel mould and tubes suspended between two substantially parallel retaining walls the tubes being retained in place by apertures in said walls; vibrating said wet concrete; and withdrawing said tubes.</claim-text> <claim-text>2. A method according to claim 1, in which said prestress bed comprises a sequence of sections and in which the step of withdrawing said tubes comprises withdrawing said tubes from a first section until they are suspended between two substantially parallel retaining walls in a second section.</claim-text> <claim-text>3. A method according to claim 1 or claim 2 in which said step of withdrawing said tubes comprises attaching the tubes to a winch and operating said winch.</claim-text> <claim-text>4. A method according to any one of the preceding claims in which said tubes have an upper portion which is substantially arch shaped.</claim-text>