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Title:
CORE INSERT AND METHOD OF MANUFACTURING A HOLLOW CORE CONCRETE SLAB
Document Type and Number:
WIPO Patent Application WO/2018/042180
Kind Code:
A1
Abstract:
A core insert (100) for the manufacture of hollow core concrete slabs has a hollow core insert body (202) constructed from a flexible material and having a body end, a plug member (208) increasing in cross section from a minor end to a major end and defining an exterior surface and, a collar (210) increasing in cross section from a minor end to a major end and defining an interior surface, in which the plug member (208) and the collar are tapered and clamp the hollow core insert body (202) under pressure. The plug (208) allows hollow core insert body (202) to be extracted without hindrance through the cast hollow core concrete slab.

Inventors:
DURHAM, John (83 Victoria Street, London SW1H 0HW, SW1H 0HW, GB)
BRIGGS, Warren (Boyle Road, Corby Northamptonshire NN17 5XU, NN17 5XU, GB)
Application Number:
GB2017/052537
Publication Date:
March 08, 2018
Filing Date:
September 01, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HOLLOW CORE INTERNATIONAL LTD (83 Victoria Street, London SW1H 0HW, SW1H 0HW, GB)
International Classes:
B28B7/32; B29C33/50
Foreign References:
US1624704A1927-04-12
DE3240166A11984-05-03
US1715920A1929-06-04
US2086276A1937-07-06
US3361449A1968-01-02
Attorney, Agent or Firm:
VAULT IP LIMITED (Cavendish House, 39 Waterloo Street, Birmingham west midlands B2 5PP, B2 5PP, GB)
Download PDF:
Claims:
Claims

1. A core insert for the manufacture of hollow core concrete slabs, comprising: a hollow core insert body constructed from a flexible material and having a body end; a plug member increasing in cross section from a minor end to a major end and defining an exterior surface; and, a collar increasing in cross section from a minor end to a major end and defining an interior surface; in which the plug member is positioned inside the hollow core insert body, and the collar is positioned outside the hollow core insert body such that the hollow core insert body is clamped between the exterior surface of the plug member and the interior surface of the collar; and, in which the respective minor ends of the plug member and collar are closer to the end of the hollow core insert body than the respective major ends, such that internal fluid pressure inside the hollow core insert body drives the plug member further into engagement with the collar to increase the clamping force on the hollow core insert body. 2. A core insert according to claim 1, in which the interior surface of the collar and the exterior surface of the plug member are tapered.

3. A core insert according to claim 2, in which the surfaces are frustroconical.

4. A core insert according to claim 2 or 3, in which the angle of the taper of the interior surface of the collar and the exterior surface of the plug member are within 1 degree of each other. 5. A core insert according to any of claims 2 to 4, in which the angle of the taper of the interior surface of the collar and the exterior surface of the plug member are in the range 2 to 10 degrees.

6. A core insert according to any preceding claim, in which the interior surface of the collar defines recesses to aid grip on the hollow core insert body.

7. A core insert according to claim 6, in which the recesses are circumferential channels. 8. A core insert according to any preceding claim, in which the plug member defines a plug central axis.

9. A core insert according to claim 8, in which the plug member defines a major end face which is planar and perpendicular to the plug central axis.

10. A core insert according to claim 8 or 9, in which the plug member defines a minor end face which is planar and perpendicular to the plug central axis.

11. A core insert according to any preceding claim, in which the plug member defines a fluid passage therethrough. 12. A core insert according to claim 11, in which the fluid passage comprises an attachment formation for a valve or sealing member.

13. A core insert according to any preceding claim, in which the hollow core insert body has a main axis and an inflated diameter under an inflation pressure in the range of 2 - 5 bar, and in which the maximum dimension of the collar viewed along the main axis is less than the inflated diameter. 14. A core insert according to any preceding claim, in which the collar has a substantially constant thickness.

15. A core insert according to any preceding claim, in which the flexible material is inextensible.

16. A core insert according to claim 15 in which the flexible material is polyurethane.

17. A core insert according to any preceding claim, in which the plug member and / or collar are constructed from a metal, preferably steel.

18. An casting apparatus for manufacture of a hollow core concrete slab, comprising: a casting bed; at least one core insert according to any of claims 1 to 17 therein.

19. A method of manufacturing a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one core insert according to any of claims 1 to 17; placing at least part of the core insert body within the casting volume; pouring concrete into the casting bed to completely submerge the at least part of the core insert body within the casting volume; allowing the concrete to set; removing the core insert.

20. A method of manufacture of a hollow core concrete slab according to claim 19, in which the core insert body is pressurised to an internal pressure of 2 - 5 bar before the concrete is poured into the casting bed.

21. A method of manufacture of a hollow core concrete slab according to claim 20, in which the core insert body is depressurised before removal.

22. A method of manufacture of a hollow core concrete slab according to claim 21, in which the core insert body is depressurised sufficiently to collapse the core insert body before removal.

23. A method of manufacture of a hollow core concrete slab according to claim 22, in which the core insert body is depressurised to a first pressure, and partially re-pressurised to a second pressure before removal.

24. A method of manufacture of a hollow core concrete slab according to any of claims 19 to 23, comprising the step of introducing a liquid between the core insert and the concrete before removal.

25. A method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one inflatable core insert; placing at least part of the core insert within the casting volume; pouring concrete into the casting bed to completely submerge the at least part of the core insert within the casting volume; allowing the concrete to set; introducing a liquid between the core insert and the concrete; removing the core insert.

26. A method of manufacture of a hollow core concrete slab according to claim 25, in which after the concrete has set, the at least one inflatable insert is at least partially deflated to form a void between the core insert and the concrete. 27. A method of manufacture of a hollow core concrete slab according to claim 26, in which the core insert is depressurised to a first pressure, and partially re-pressurised before removal.

28. A method of manufacture of a hollow core concrete slab according to any of claims 25 to 27, comprising the step of coating the core insert in a hydrophobic release agent prior to the concrete being poured.

29. A method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one inflatable core insert; placing at least part of the core insert within the casting volume; pressurising the core insert to a casting pressure; pouring concrete into the casting bed to completely submerge the at least part of the core insert within the casting volume; allowing the concrete to set; depressuring the core insert to a first pressure; partially repressuring the core insert to a second pressure, higher than the first pressure but lower than the casting pressure; removing the core insert.

30. A method of manufacture of a hollow core concrete slab according to claim 25, in which at least part of the core insert extends from the concrete, and in which the first pressure is sufficient to flatten the core insert, and at the second pressure the core insert has reverted to a form permitting removal through the concrete slab.

31. A method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least three inflatable core inserts; placing the core inserts within the casting volume such that the core inserts are spaced-apart; providing a plurality of cross inserts; placing the cross inserts within the casting volume such that the core inserts and cross inserts define a serpentine form; pouring concrete into the casting bed to submerge the core inserts and cross inserts within the casting volume; allowing the concrete to set; removing at least the core inserts to create a serpentine flow path through the slab.

32. A method of manufacture of a hollow core concrete slab according to claim 31, comprising the step of providing a at least one cross insert extending from the edge of the casting volume so as to form an entry / exit fluid path.

33. A method of manufacture of a hollow core concrete slab according to claim 31 or 32, in which the cross inserts are hollow.

34. A method of manufacture of a hollow core concrete slab according to claim 33, in which the interior of the cross inserts are at ambient pressure during pouring and setting.

35. A method of manufacture of a hollow core concrete slab according to any of claims 31 to 34, in which the cross inserts are constructed from cardboard. 36. A method of manufacture of a hollow core concrete slab according to any of claims 31 to 35, comprising the step of removing the cross-inserts after setting.

37. A core insert as described herein, with reference to, or in accordance with, the accompanying drawings.

38. A method of manufacture of a hollow core slab as described herein, with reference to, or in accordance with, the accompanying drawings.

Description:
CORE INSERT AND METHOD OF MANUFACTURING A HOLLOW

CORE CONCRETE SLAB

The present invention is concerned with a method of manufacturing a hollow core concrete slab. More specifically, the present invention is concerned with manufacturing such a slab using removable, inflatable inserts to form the core or cores. Hollow core slabs generally comprise a thick, planar concrete slab in which at least one cavity is formed. The cavity is typically a through-bore. The presence of the cavity provides a reduction in overall mass without a reduction in strength. Such slabs are used as structural elements (typically floors and ceilings) in buildings. The voided percentage of hollow core slabs is typically 40-60% of the total volume (providing a corresponding weight reduction over a solid slab). The slabs are usually pre-stressed with elongate steel members which extend the length of the slab. The steel members are placed under a tensile load (creating a stress) which is released once the concrete has set and bonded thereto.

Hollow core slabs are also used in systems such as TermoDeck (TM) in which the cavities carry a fluid for heat transfer to and from the adjacent room. Such systems often require cross-drilling of the slab to connect adjacent cores, forming a serpentine flow path.

There are several techniques for manufacturing hollow core slabs. These fall into two main categories- extrusion and casting. Extrusion involves the use of an extruder. Extruders are large, expensive machines which require a significant amount of surrounding infrastructure. They are also complex, and therefore require significant maintenance. The method of extrusion is also not suited to providing transverse reinforcements in the slab- known in the art as "shear links". Shear links add significant strength and stiffness to the slab, and are highly desirable.

Casting by pouring concrete is an alternative process which although more labour-intensive than extrusion, is much less dependent upon capital expenditure. Therefore, it can be more useful in situations where high capital expenditure and infrastructure is not appropriate, and where inexpensive labour is available. Casting can better accommodate shear links. One such casting method is disclosed in UK patent application GB2478739, the content of which is incorporated herein where permissible.

In GB2478739, a casting bed is provided, into which a plurality of sleeved, inflatable core inserts are disposed. Self-compacting concrete is poured around the cores. Once the concrete has set, the cores are extracted by pulling the cores and thereby inverting the sleeves. This solution has some drawbacks- firstly the sleeves can become cast into the concrete, making removal difficult. Secondly, the sleeves and extraction mechanism are somewhat complex. A further problem with hollow core casting is that the pressures required inside the inflatable core insert are relatively high (in the order of 4 bar) to resist compression and uplift by the weight of the concrete. Therefore, the integrity and sealing of the core inserts is vital for safety.

It is an aim of the present invention to overcome, or at least mitigate, at least one of the above problems.

According to a first aspect of the present invention there is provided a core insert for the manufacture of hollow core concrete slabs, comprising: a hollow core insert body constructed from a flexible material and having a body end; a plug member increasing in cross section from a minor end to a major end and defining an exterior surface; and, a collar increasing in cross section from a minor end to a major end and defining an interior surface; in which the plug member is positioned inside the hollow core insert body, and the collar is positioned outside the hollow core insert body such that the hollow core insert body is clamped between the exterior surface of the plug member and the interior surface of the collar; and, in which the respective minor ends of the plug member and collar are closer to the body end of the hollow core insert body than the respective major ends, such that internal fluid pressure inside the hollow core insert body drives the plug member further into engagement with the collar to increase the clamping force on the hollow core insert body. This solution advantageously provides a self-tightening apparatus which will not easily become detached from the core insert body.

Preferably, the interior surface of the collar and the exterior surface of the plug member are tapered. More preferably they are tapered and circular in cross section- i.e. frustroconical. This allows for easy manufacture. Preferably the angle of the taper of the interior surface of the collar and the exterior surface of the plug member are with 1 degree of each other. This allows for a high area over which the core insert body is clamped and avoids stress concentrations.

Preferably the angle of the taper of the interior surface of the collar and the exterior surface of the plug member are in the range 2 to 10 degrees. This shallow angle allows the plug member and collar to be quite long, again increasing the surface area of contact and reducing local stress. Preferably the interior surface of the collar defines recesses to aid grip on the hollow core insert body. The recesses may be circumferential channels. This improves grip, and defining them on the collar (rather than the plug) means that they will not allow pressurised fluid to pass more easily.

Preferably, the plug member defines a plug central axis and either a major or minor end face which is planar and perpendicular to the plug central axis.

Preferably, the plug member defines a fluid passage therethrough. This can be used to attach a valve (for pressurisation / depressurisation from a compressor) or sealing member. This allows for sealing and pressurisation without removal of the plug.

Preferably the hollow core insert body has a main axis and an inflated diameter under an inflation pressure in the range of 2 - 5 bar, and in which the maximum dimension of the collar viewed along the main axis is less than the inflated diameter. This facilitates removal of the insert by passing the collar (and plug member) through the hollow core of the cast slab.

Preferably the collar has a substantially constant thickness for ease of manufacture.

Preferably the flexible material is inextensible- more preferably it is constructed from polyurethane or similar.

Preferably the plug member and / or collar are constructed from a metal, preferably steel.

According to the invention there is provided a casting apparatus for manufacture of a hollow core concrete slab, comprising: a casting bed; at least one core insert according to the first aspect therein.

According to the invention there is provided a method of manufacturing a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one core insert according to the first aspect; placing at least part of the core insert body within the casting volume; pouring concrete into the casting bed to completely submerge the at least part of the core insert body within the casting volume; allowing the concrete to set; removing the core insert.

This allows for swift and safe construction of hollow core slabs without the need for extrusion equipment. The cross-section of the core insert body is preferably completely submerged.

Preferably the core insert body is pressurised to an internal pressure of 2 - 5 bar before the concrete is poured into the casting bed. This prevents the flexible core from collapsing under the weight of the concrete.

Preferably the core insert body is depressurised before removal- this at least partially separates the insert from the interior wall of the newly formed concrete slab.

Preferably the core insert body is depressurised sufficiently to collapse the core insert body before removal. This significantly reduces contact area between the concrete and insert, making removal easier.

Preferably the core insert body is depressurised to a first pressure, and partially re-pressurised to a second pressure before removal. This has the effect of loosening / separating the insert from the concrete as much as possible before removal. Full depressurisation can significantly deform the insert, to the extent that any core insert body which is not encased will flatten and become difficult to remove. e-pressurisation allows the core insert body to at least partially resume its inflated shape making removal easier.

Preferably there is provided a step of introducing a liquid (preferably water) between the core insert and the concrete before removal. This acts as a lubricant, facilitating removal. According to a second aspect of the invention there is provided a method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one inflatable core insert; placing at least part of the core insert within the casting volume; pouring concrete into the casting bed to completely submerge the at least part of the core insert within the casting volume; allowing the concrete to set; introducing a liquid between the core insert and the concrete; removing the core insert. Advantageously, the liquid, which is preferably water, lubricates the materials and facilitates removal of the insert, especially for long slabs (over 20m in length).

Preferably, after the concrete has set, the at least one inflatable insert is at least partially deflated to form a void between the core insert and the concrete. This facilitates transport of the liquid to the length of the slab.

Preferably the core insert is depressurised to a first pressure, and partially re-pressurised before removal.

Preferably there is provided the step of coating the core insert in a hydrophobic release agent prior to the concrete being poured. This aids the formation of a water layer to facilitate removal. According to a third aspect of the invention there is provided a method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least one inflatable core insert; placing at least part of the core insert within the casting volume; pressurising the core insert to a casting pressure; pouring concrete into the casting bed to completely submerge the at least part of the core insert within the casting volume; allowing the concrete to set; depressuring the core insert to a first pressure; partially repressuring the core insert to a second pressure, higher than the first pressure but lower than the casting pressure; removing the core insert.

In the event that part of the core insert extends from the concrete (which is almost always the case), the first pressure is sufficient to flatten the core insert, and at the second pressure the core insert has reverted to a form permitting removal through the concrete slab. This allows for the maximum effect of deflation (reducing the "stiction" between the insert and the concrete surface)

According to a further aspect of the invention there is provided a method of manufacture of a hollow core concrete slab comprising the steps of: providing a casting bed defining a casting volume; providing at least three inflatable core inserts; placing the core inserts within the casting volume such that the core inserts are spaced-apart; providing a plurality of cross inserts; placing the cross inserts within the casting volume such that the core inserts and cross inserts define a serpentine form; pouring concrete into the casting bed to submerge the core inserts and cross inserts within the casting volume; allowing the concrete to set; removing at least the core inserts to create a serpentine flow path through the slab.

Preferably the method includes the step of providing a at least one cross insert extending from the edge of the casting volume so as to form an entry / exit fluid path.

Preferably the cross inserts are hollow.

More preferably the cross inserts are at ambient pressure during pouring and setting. The cross inserts may be constructed from cardboard.

Preferably the method comprises the step of removing the cross-inserts after setting.

An example apparatus and method in accordance with the invention will now be described with reference to the accompanying Figures, in which:

Figure la is a plan view of a casting bed for use in the present invention; Figure lb is a side view of the casting bed of Figure la in direction B;

Figure lc is an end view of the casting bed of Figure la in direction C;

Figure 2a is a side view of a core insert in accordance with the present invention;

Figure 2b is a detail view of area B of the core insert of Figure 2a;

Figure 2c is a section view through C-C in Figure 2b; Figure 2d is a sectioned, exploded view of the area B of the core insert of Figure 2a;

Figure 3a is a plan view of the casting bed of Figure la with several core inserts installed therein; Figure 3b is a plan view of the casting bed of Figure 3a filled with concrete; Figure 3c is a section view along line C-C in Figure 3b;

Figure 3d is a detail view of the area D of Figure 3c showing an insert in a partially deflated state;

Figure 4a is a detail plan view of a part a deflated insert; Figure 4b is a detail side view of the part of the insert of Figure 4a;

Figure 5 is a section view of a second casting bed in accordance with the present invention;

Figure 6a is a plan view of a first end of a third casting bed in accordance with the present invention;

Figure 6b is a plan view of the second end of the casting bed of Figure 6a; and,

Figure 6c is a section view through line C-C in Figure 6a. Starting with Figures la to lc, a casting bed 100 is shown in plan. The bed 100 comprises a body 102, a first end shutter 104, a second end shutter 106 and an intermediate shutter arrangement 108.

The body 102 is elongate, prismatic and channel-shaped having a main axis X. The body 102 has a base 110 and two generally vertically extending walls 112, 114 each of which extend along the axis X. The base 110 and walls 112, 114 are constructed from steel (although they could be timber). The end shutters 104, 106 are identical, and as such only the end shutter 106 will be described here. The end shutter 106 comprises a shutter plate 116 whose outer profile conforms to the inner profile of the body 102. Five core insert openings 118a, b, c, d, e are formed through the thickness of the end shutter 106. Four smaller pre-stress bores 128a, b, c, d are formed below and horizontally spaced between the core insert openings 118a, b, c, d. Opposing support flanges 120a, 120b are formed at an upper edge of the end shutter 118. The openings are each lined with a sealing material on their inner edges- for example an elastomeric or similar. When inserted into the body 102 at either end of the body 102, transverse to the axis X, the shutters 104, 106 define a casting volume.

The intermediate shutter arrangement 108 comprises two intermediate shutters 108a, 108b. As with the end shutters 104, 106, each intermediate shutter 108a, 108b comprises a shutter plate 122 whose outer profile conforms to the inner profile of the body 102. Five core insert openings 124a, b, c, d, e are formed through the thickness of each intermediate shutter 108a, 108b. Four smaller pre-stress bores 130a,b ,c, d are formed between the core insert openings 124a, b, c, d, e. Opposing support flanges 126a, 126b are formed at an upper edge of the shutters 108a, b. The openings are each lined with a sealing material on their inner edges- for example an elastomeric or similar. When inserted into the body 102, transverse to the axis X, the shutters 108a, 108b form a barrier within the casting volume. The shutters 108, 108b are also offset by a distance O.

Turning to Figures 2a to 2d, a core insert 200 according to the present invention is shown. The core insert 200 comprises a core insert body 202 having a first end cap assembly 204 and a second end cap assembly 206.

The core insert body 202 is an elongate tube having a main axis Y. It is constructed from a flexible, inextensible, airtight material. In this embodiment, it is constructed from (for example) polyurethane. In an inflated shape under an inflation pressure of 2-5 bar, the tube is circular in cross-section (i.e. cylindrical) having an outer tube diameter Dto, an inner tube diameter Dti and a uniform thickness t. It will be noted that Dto = Dti + 2t.

The first and second end cap assemblies 204, 206 are identical and as such only the first cap assembly 204 will be described here. With reference to Figures 2b to 2d, the first cap assembly 204 comprises a plug member 208, a collar 210 and a pneumatic attachment 212.

The plug member 208 is a solid body having plug central axis PCA. It defines a rotationally symmetrical, frustroconical outer surface 211, a first end face 212 and a second end face 214. Because the plug member 208 is tapered as a frustrocone, the first end face 212 is of a minor diameter Dmi and the second end face of a larger, major diameter Dma. The taper angle is shown as Apt. A central open bore 216 is defined through the plug member 208 between the geometric centres of the end faces 212, 214. The diameter Dma of the major end face 214 of the plug member 208 is the same as, or very slightly smaller than, the inner diameter Dti of the tube member 202.

The collar 210 is collar-shaped, and comprises a thin wall of thickness ct. The wall has a plurality of endless circumferential recesses 213 defined to create an uneven inner surface. The collar 210 is frustroconical in shape extending from a minor first end 218 with inner diameter Dcmii and outer diameter Dcmio to a major second end 220 with inner diameter Dcmai and outer diameter Dcmao. It will be noted that Dcmio = Dcmii + 2ct and Dcmao = Dcmai + 2ct. A taper angle is shown as Act. The major second end outer diameter Dcmao (the largest part of the collar 210) is less than the outer diameter Dto of the core insert body 202 when fully inflated.

The plug member 208 and collar 210 are geometrically related. In particular: · The angles Apt and Act are the same; • The minor diameter Dmi of the plug member 208 is smaller than both the minor and major inner diameters Dcmii and Dcmai of the collar 210 so plug member is fully engageable in the collar 210;

• The major diameter Dma of the plug member 208 is larger than both minor and major inner diameters Dcmii and Dcmai of the collar 210 so that the plug member 208 cannot pass through the collar 210;

• The minor diameter Dmi of the plug member 208 is 2t less than the inner diameter Dcmii of the minor end of the collar 210 (where t is the thickness of the core insert body 202).

To secure the end cap assembly to the core insert body 202, the plug member 208 is first inserted sufficiently far into the end of the core insert body 202 to leave 10 - 20mm of the core insert body 202 protruding from the first end face 212. The collar 210 is then forced over the core insert body 202 to clamp the core insert body 202 between the collar 210 and plug member 208. The collar 210 is pushed onto the core insert body 202 such that the minor end 218 is aligned with the first end face 212 of the plug member 208 as shown in Figure 2c. A combined frictional / mechanical fit is therefore provided between the core insert body 202 and the collar 210. The mechanical aspect of the fit is provided by the recesses 213 into which the core insert body 202 is forced during this process.

The pneumatic attachment 212 is secured to the bore 216 via screw thread to provide a suitable attachment for either a pneumatic plug or pressure / vacuum hose 222 (figure 2b) attached to a vacuum pump (not shown). The end cap assembly operates as follows. When an internal pressure is applied to the interior of the core insert body 202 (via the pneumatic attachment), an internal pressure P rises (Figure 2c). This pressure results in a force applied to the second, major, face 214 of the plug member 208. This force tends to push the plug member 208 out of the core insert body 202, but in doing so it forces the plug member 208 further into engagement with the collar 210 to clamp the core insert body 202. The higher the pressure, the more the core insert body 202 is clamped. Therefore the end cap assembly 204 is self-tightening.

Turning to Figures 3a to 3d, the casting of a hollow core slab is shown in stages.

In Figure 3a, a casting assembly 10 is shown comprising the casting bed 100, five core inserts 200 and four longitudinal reinforcements 201. Each of the core inserts 200 extends parallel to the axis X, and fits in respective bores in the shutters 104, 106, 108a, 108b forming a tight fit against the seals. The core inserts 200 are inflated to 2-5 bar pressure, and the pressure held at that level by sealing the inserts 200. The outer surface of each insert is coated with a wax release agent. The release agent is hydrophobic.

Each of the longitudinal reinforcements 201 is a steel cable, which is fed through the pre-stress bores in each of the shutters. The reinforcements are placed under tension by an appropriate tension generating means (as known in the art, and not discussed here for brevity). It is important that the reinforcements can bind to the concrete, and as such care is taken to avoid contact between the release agent and the reinforcements.

Self-compacting concrete is poured into the casting bed 100 in the volume between the first end shutter 104 and the first intermediate shutter 108a to form a first slab section 12. Similarly, concrete is poured into the casting bed 100 in the volume between the second end shutter 106 and the first intermediate shutter 108b to form a second slab section 14.

Referring to the section view of Figure 3c, once the concrete slab 14 has set, each core insert body 202 is encased in sold concrete, and the inserts 200 need to be removed.

According to the present invention this is achieved in the following manner. Firstly, the pressure inside the core insert body 202 is released to ambient (or pumped out). A vacuum pump is then used to extract further air from the core insert body 202 to reduce the pressure below ambient, i.e. to below 1 bar (15psi). Eventually, this forces the core insert body 202 to flatten, and collapse into a crescent shape as shown in Figure 3d. At this point, the ends of the core insert body 202 which project from the slab 14 are flattened as shown in Figures 4a and 4b (each at 90 degrees to the other). At this point, removal would be impossible because the flattened core insert body 202 is too wide for the concrete core diameter Dto. To facilitate removal, air is permitted to re-enter the core insert 200 (i.e. interior pressure is increased) to allow the ends of the core insert body 202 to expand again. Because it is desirable to reduce the contact area between the core inserts and the cores in the slabs, only enough air is reintroduced to allow the maximum linear dimension of the core insert body 200 outside the slabs to become equal to, or less than, the diameter Dto.

At this point, water may be introduced between the intermediate shutters 108a, 108b. The water passes along the cores formed by the core inserts towards the ends of the slabs 12, 14. Space between the core inserts and slabs created by collapsing the core inserts aids water transport.

The water aids both release of the core inserts from the concrete. As the core inserts are pulled in the direction of axis X, the water aids the release agent to reduce static friction as well as reducing dynamic friction. Removal of the core inserts is thereby made easier. It will be noted that once the concrete has set, the tension-generating means can be released from the reinforcements 201.

Turning to Figure 5, an alternative slab 14' is shown in a casting assembly 10'. A steel shear link 300 is provided, which is placed into the casting bed before the concrete is introduced. The shear link 300 is transverse the reinforcements 201 as is known in the art.

With reference to Figures 6a to 6c, a modification of the manufacturing process will be described. Reference numerals to equivalent features are suffixed ". A casting assembly 10" comprises a casting bed 100".

As well as core inserts 200" having bodies 202", there are provided cross-inserts 400. The cross-inserts 400 are hollow cylindrical members which form a seal against adjacent core inserts 200". They can be arranged to abut the inserts 200" before inflation (when the inserts are flexible and movable) and upon inflation will be held in place by their conformity to the exterior surface of the bodies 202".

The cross-inserts 400 are dimensionally stable, constructed from thick cardboard (or similar material), and remain in place after casting. Once the inserts 200" are removed the cross-inserts form passages between the cores from the top or underside of the slab.

Similar to cross-inserts 400, there are provided entry / exit inserts 402 which are similar in construction and size, but can project from the top or bottom of the slab during casting. These inserts can be removed after casting.

The arrangement shown in Figures 6a and 6b provides a serpentine flow path from one entry / exit insert to the other (on the assumption that the ends of the cores are blocked). This is useful in thermal management systems such as TermoDeck (TM).

Variations fall within the scope of the present invention.

The sides 112, 114 may be movable to facilitate removal of the slab. For example, they may be removably attached or pivoted, for example being held in place during casting by magnets. In this manner, the sides 112, 114 may even taper inwardly.

Water may be introduced before the pressure in the core inserts is released. This provides a pumping effect along the slab when pressure is reduced.