GB2564439A

GB2564439A - Moulded blocks for bond beams and the like

Info

Publication number: GB2564439A
Application number: GB1711069.3A
Authority: GB
Inventors: Clear Liam
Original assignee: Wembley Innovation Ltd
Current assignee: Wembley Innovation Ltd
Priority date: 2017-07-10
Filing date: 2017-07-10
Publication date: 2019-01-16
Anticipated expiration: 2037-07-10
Also published as: GB2564439B; GB201711069D0

Abstract

The block 10 has a U-shaped cross-section defining a base 12 at least 160mm wide and a pair of opposed side walls 14, 16, an upper surface of the cross-section sloping inwardly and downwardly from each side wall to a lowest point, where at all positions from a point at most 20mm from the lowest point to the adjacent side wall the slope is at least 31.5 degrees relative to the bottom surface of the base. The upper surface may comprise straight portions sloping to the centre of the block. The straight portions may be joined to each other and the side walls by central and outer smoothly curved portions respectively. Also claimed is a block having a U-shaped cross-section but where the base is up to 160mm wide and the slope of the upper surface at all positions from a point at most 10mm from the lowest point to the adjacent side wall is at least 35 degrees relative to the bottom surface of the base, the base being at least 35mm thick. The block may be concrete and used to form bond beams.

Description

MOULDED BLOCKS FOR BOND BEAMS AND THE LIKE

This invention concerns building blocks moulded from concrete or similar materials, the blocks having an open ended, U-profiled, upwardly open channel extending from one header face to the other. Such blocks can be used to build a course in a blockwork wall, with the U-profiled channels of the individual blocks aligned to form a continuous cavity extending along the course, for receiving a cast-in-situ bond beam. The cavity can also be partly filled or left unfilled and used to carry cables, pipes, trunking and the like; and/or be filled partly or wholly with insulation, or be used for a combination of two or more of the above uses. Still other uses for the cavity are also possible. Optionally one or both end blocks in such a course may comprise a header end wall which closes off the block’s channel and the corresponding end of the bond beam cavity. Whatever their intended uses, for brevity such blocks are referred to in this specification as “bond beam blocks”.

Such building blocks are typically formed using a relatively standard concrete product moulding machine, such as the Columbia CPM (RTM) machines available from Columbia Machine Inc., of Vancouver, Washington, U.S.A. These machines use a multi-cavity mould comprising a base plate or pallet, a frame which forms the mould cavity sides and partitions, and a set of plunger legs and shoes which form the top surfaces/edges of the moulded blocks and help to eject them from the mould. During ejection, the pallet moves downward relative to the frame, so that the still uncured blocks are de-moulded but remain supported on the pallet. The pallet and blocks may then be transferred to a kiln for curing. The mould frame can support a set of mould cores which are suitably shaped for forming any internal cavities required in a given block design. For example, page 28 of Columbia Machine Inc.’s manual, “Recommended Procedure for Mold Assembly” (available from their website as cpm-moldassembly-instructionmanual.pdf) shows an exploded view of the mould frame and plunger assembly for a five block machine, in which each block has two vertical through going cavities formed by a corresponding pair of cores. The resulting hollow blocks are of the type having a centre partition wall extending parallel to their header faces. Moulds used to form bond beam blocks as mentioned above will require a respective single core of generally U-shaped transverse vertical cross-sectional profile, extending from one end of each mould cavity to (or to adjacent,) the other end. The lowermost portion of each core is spaced above the bottom of the mould frame by the thickness of the eventual block base. With the pallet supported in position against the mould frame, the mould cavities are filled with a semi-dry mixture of the uncured concrete by gravity and are then vibrated to compact the mixture within the mould cavities and about the mould cores. The plunger assembly and shoes are then lowered to form the block top edges and then the pallet is lowered, to demould the blocks, as described above.

For standard sized blocks of up to 140 mm in width, this process works reliably to form a high-quality product. However, problems have been encountered when attempting to mould bond beam blocks which are significantly wider than 140 mm, for example standard sized blocks 190 or 215 mm wide. The mould fills from the top and material has to feed down the side walls of the bond beam block and under the core to fill the base region ofthe mould cavity. As blocks become wider the semi-dry concrete material has to travel further horizontally beneath the core and it becomes harder to fully fill and compact material at the base of the block. This leads to the formation of unacceptable voids in or near the inside surface at the base of the bond beam block, and/or to unacceptably long vibrational compaction times and consequentially reduced production rates. Adding a suitable plasticiser to the semi-dry concrete mixture can improve fill and compaction, but makes the sides of the block more flexible, resulting in distortion when de-moulding. There is also a trowelling effect as the dimensionally unstable block leaves the mould frame, leading to unacceptable markings on the face finish.

To achieve good fill and compaction whilst maintaining shape and quality, further improvement of the bond beam block design is required. Accordingly, the present invention provides a building block formable by moulding and comprising a vertical transverse cross-section of U-shaped profile thereby to define a base portion at least 160 mm wide and a pair of opposed side walls; an upper surface of the vertical transverse cross-section sloping inwardly and downwardly from each side wall to a lowest point, and wherein the slope of this upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall is of at least 31.5 degrees relative to the bottom surface at the base of the block. It has been found that blocks having these characteristics can be made to a consistently acceptable quality, sufficiently free of voids and surface blemishes, using the moulding machines and methods described above, without requiring excessive vibratory compaction. Without wishing to be bound by theory, it is thought that where the upper surface of the block at the base of the U-channel slopes at an angle that is significantly smaller than the angle of repose of the semi-dry cement mixture used in block moulding, the flow resistance or non-Newtonian viscosity of the mixture combined with the frictional contact between the mixture and the walls at the base of the mould (including in particular the pallet surface and the bottom surface of the insert) is enough to prevent the mixture from flowing sideways beneath the insert to completely fill the base of the mould. Making the slope of the insert lower surface and corresponding part of the block not significantly less than the angle of repose over the span of these surfaces, up to a critical distance away from their lowermost point, ensures that the mould will fill properly and completely under the vibratory compaction.

Optionally the slope of the vertical transverse cross-section upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall is between 31.5 and 45 degrees relative to the bottom surface at the base of the block. At angles greater than 45 degrees, the outer regions of the block base can become too thick, restricting the free space available in the bond beam cavity; and/or the central part of the block base can become too thin and fragile. The slope of the vertical transverse cross-section upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall may be at least 33 degrees.

The vertical transverse cross-section upper surface may comprise respective straight portions sloping downwardly and inwardly from the side walls towards the centre of the block.

The vertical transverse cross-section upper surface may comprise a central smoothly curved portion joining the two straight portions, and opposed outer smoothly curved portions joining the sloping portions to respective straight portions ofthe inner surfaces of the side walls. The central smoothly curved portion may be arcuate, with a radius of between 5 and 15 mm inclusive, for example 10 mm. The outer smoothly curved portions may be arcuate, with a radius of between 7 and 17 mm inclusive, for example 12 mm. Such smooth curves and radii help to reduce stress concentrations and make the block less vulnerable to cracking and breakage, both during the manufacturing process and in service.

The minimum thickness of the base of the block may be between 30 and 45 mm, for example 36 or 40 mm.

The vertical transverse cross-section’s side walls may comprise a straight inner surface. The minimum thickness of these side walls may be between 30 and 44 mm inclusive, for example 37 mm. The straight inner surface may taper inwardly and downwardly by between 3 and 10 mm, for example by 4 mm, 6 mm or 8 mm.

The block may have a width of between 170 and 235 mm inclusive, for example 190 or 215 mm. The block may have a height of 200 to 230 mm inclusive, for example 215 mm. The block may have a length of 415 to 465 mm inclusive, for example 440 mm.

For bond beam blocks which are 160 mm wide or less, for example 140 or 100 mm, the thickness of the side walls cannot be made large without unduly restricting the width of the channel and hence the width of the bond beam cavity. However, such thin walls are quite fragile. During their manufacture, they can therefore be easily broken as the blocks are transferred between the moulding machine and the curing kiln. There is therefore a need for narrow blocks which have thin side walls, but which are relatively robust, especially prior to curing.

Accordingly, in a second aspect the present invention provides a building block formable by moulding and comprising a vertical transverse cross-section of U-shaped profile thereby to define a base portion up to 160 mm wide, and a pair of opposed side walls; an upper surface of the vertical transverse cross-section sloping inwardly and downwardly from each side wall to a lowest point, and wherein the slope of this upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall is of at least 35 degrees relative to the bottom surface at the base of the block and wherein the minimum thickness of the base of the block is greater than or equal to 35 mm. Blocks with thin side walls and thin bases, unless handled very carefully, tend to break during manufacture: at the junction between the side walls and the base, or along the centreline of the base. Bond beam blocks having the characteristics specified immediately above have been found to be more robust during the manufacturing process. They may be transferred out of the moulding machine and to the drying kiln with reduced breakage rates under the same handling conditions compared to prior bond beam block designs.

Optionally the slope of the vertical transverse cross-section upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall is between 35 and 65 degrees relative to the bottom surface at the base of the block. At angles greater than 65 degrees, the outer regions of the block base can become too thick, restricting the free space available in the bond beam cavity; such that the lower portion of the bond beam may become too thin and fragile. The slope of the vertical transverse cross-section upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall may be 40 or 57 degrees, for example.

The vertical transverse cross-section upper surface may comprise a central smoothly curved portion joining the two straight portions, and opposed outer smoothly curved portions joining the sloping portions to respective straight portions of the inner surfaces of the side walls. The central and outer smoothly curved portions may each be arcuate, with a radius of between 5 and 15 mm inclusive, for example 10 mm. Such smooth curves and radii help to reduce stress concentrations and make the block less vulnerable to cracking and breakage, both during the manufacturing process and in service.

The vertical transverse cross-section’s side walls may comprise a straight inner surface. The minimum thickness of these side walls may be between 20 and 35 mm inclusive, for example 25 or 30 mm. The straight inner surface may taper inwardly and downwardly by between 3 and 10 mm, for example by 4 mm, 6 mm or 8 mm.

The block may have a width of between 85 and 160 mm inclusive, for example 100 or 140 mm. The block may have a height of 200 to 230 mm inclusive, for example 215 mm. The block may have a length of 415 to 465 mm inclusive, for example 440 mm.

The base of the block may be provided with a thinned region forming a knockout which may be removed to form a through-going hole, e.g. for accommodating a stress transfer rod or bracket; the hole being of such a diameter that it is confined to the base of the block without affecting the sides of the block.

For a more complete understanding of the various aspects of the invention and its features, options and advantages, illustrative embodiments are described below by way of non-limiting example and with reference to the drawings in which:

Figures 1, 2 and 3 are respectively a plan view, front or rear view and an end view of a bond beam block forming a first embodiment of the invention, and Figures 4, 5 and 6 correspond to Figures 1, 2, and 3, but show a second embodiment in which a hole or knockout web for a stress transfer rod or bracket is omitted and the block channel is closed at one header face.

The block 10 shown in the drawings has a base 12 and a pair of opposed side walls 14, 16, which together define an open-ended, upwardly open channel 18. In the version shown in Figures 4-6, one end of the channel is closed at a header face by an end wall 20. A series of blocks 10 of the kind shown in Figures 1-3 may therefore be laid in a course header to header, to define a bond beam cavity extending for the length of the course. At one or both ends of the bond beam cavity (particularly where the bond beam cavity terminates at an end of the course), a block 10 as shown in Figures 4-6 may be used to terminate the bond beam cavity. The end wall 20 serves to conceal the end of the bond beam and to contain the bond beam material during casting and while it cures. Alternatively, the bond beam cavity may be terminated by using an adjacent block in the course, having a closed vertical transverse cross-sectional profile, e.g. a complete header face. The blocks 10 may be cut to any suitable length in the usual way, e.g. to achieve a desired bond pattern in combination with adjacent courses, and/or to fitthe dimensions of the structure being built and/or any required penetrations, such as for windows, doors and service apertures. Whether or not the bond beam block has an end wall, it may be provided with a thinned portion in its base, forming a web 21. This can be knocked (broken) out, to form a through-going hole 22 e.g. for receiving a stress transfer rod or bracket used in conjunction with the bond beam, e.g. as shown in W02009/147427. Figures 1-3 show such a hole 22 in the centre of the base 12, although any other suitable position is possible. As another alternative, the web 21 may be omitted altogether, so that a through-going hole is present from the outset, in either version of the block shown in Figures 1-3 or 4-6. As yet another alternative, the base of the block shown in Figures 1-3 may have no hole 22 or web 21 (similar to the continuous base shown in Figures 4-6).

As shown in the drawings, the upper areas of the inner surfaces of the side walls 14 and 16 are substantially planar, and slope gently inwardly in the downward direction, so that the breadth of the channel 18 decreases gradually from a dimension bl at the top, to a dimension b2 at the bottom edge of the side wall inner surface upper areas. This provides sufficient “drift” for easy demoulding of the block 10 during manufacture. These upper areas of the side wall inner surfaces may comprise curved or vertical or faceted surfaces, so long as such surface configurations do not interfere with demoulding. Re-entrant or overhanging portions of the side walls of the channel 18 are even possible, e.g. if a collapsible or longitudinally withdrawable mould core is used. However, a non-overhanging or non-re-entrant transverse cross-sectional profile to the channel 18 allows for a relatively simple mould insert and easy demoulding.

Below the side wall inner surface upper areas, Figures 3 and 6 show that the inner surfaces of the walls 16 and 18 smoothly transition via an outer transition surface, into a substantially planar lower area forming an upper surface of the base 12, which slopes downwardly and inwardly at an angle a to the lower surface of the base 12. The outer transition surface is shown as arcuate, with a radius Ro. The lower edges of the opposing lower areas forming the upper surface of the base 12 are joined via a smoothly curved inner transition surface which forms the lowest point of the channel 18. Figures 3 and 6 show this lower transition surface as arcuate, with a radius Ri. The lower downwardly and inwardly sloping areas need not be planar, as long as in the case of bond beam blocks which are 160 mm or more wide, they have a slope of 31.5 degrees or greater at all positions from a point at most 20 mm away from the lowest point, to the bottom of the upper areas of the inner surfaces of the side walls 14 and 16. Or in the case of bond beam blocks which are less than 160 mm wide, the lower downwardly and inwardly sloping areas need not be planar, so long as they have a slope of at least 35 degrees relative to the bottom surface at the base of the block, at all positions from a point at most 10 mm away from the lowest point, to the bottom of the upper areas of the inner surfaces of the side walls 14 and 16. The inner and outer transition surfaces need not be arcuate, but may have any other suitable curved shape, for example parabolic, hyperbolic, elliptical, sinusoid, involute, etc. Indeed, the entire upper surface of the base 12 may be curved, so long as it meets the required slope conditions. The block channel 18 need not be mirror-symmetrical, although such symmetry is efficient for moulding and mould-filling purposes.

Dimensions of the blocks may be as follows in Table 1, to produce sizes which are standard for building blocks used in the UK. Other standardised sizes (e.g. for North America, Australia, and continental Europe) are also possible within the scope of the presently claimed invention.

Table 1: example standard block dimensions, "n/p" = not present.

Table 1 shows that for 100 mm blocks with a base hole, the more usual hole diameter is reduced from 50 mm to 38.1 mm (examples 7 and 15). This ensures that the hole does not intersect the side walls of the block. The mould insert is usually fabricated from sheet metal. A hole which is circular in horizontal planar projection is formed in its bottom, into which a cylindrical penetrator (e.g. a solid metal rod) is welded. In use, the penetrator depends from the mould insert towards the pallet. The web 21 and hole 22 in the eventual block base is then formed as the semi-dry concrete is vibration-packed around the penetrator. When the penetrator is of large diameter compared to the insert, the hole in the insert cuts into the sides of the insert by a substantial amount. This can cause unacceptable distortion of the sheet metal of the insert as the penetrator is welded into place. The large hole in the corresponding blocks will also cut into the block walls, which may unacceptably weaken them. A smaller hole mitigates these problems, by ensuring that the penetrator weld is largely confined to the base of the insert and the block base hole does not cut into the block sides.

The concrete mixture used to mould the block may comprise lightweight expanded clay aggregate (LECA), although this is not essential, as other aggregates which are suitable or used for moulding concrete products may be used in addition or instead. LECA which is denser than normal may be used in the moulding process, to assist in gravitational/vibrational compaction of the mixture in the mould, without excessively compromising useful properties such as thermal and sound insulation. For example a LECA having a dry density of around 500 Kg/m3 may be used. An acceptable mixture may be formed from the following ingredients and relative quantities by weight (Table 2).

Table 2

Claims

1. A building block formable by moulding and comprising a vertical transverse cross-section of U-shaped profile thereby to define a base portion at least 160 mm wide and a pair of opposed side walls; an upper surface of the vertical transverse cross-section sloping inwardly and downwardly from each side wall to a lowest point, and wherein the slope of this upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall is of at least 31.5 degrees relative to the bottom surface at the base of the block.

2. The building block of claim 1, in which the slope of the vertical transverse cross-section upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall is between 31.5 and 45 degrees relative to the bottom surface at the base of the block.

3. The building block of claim 1 or 2, in which the slope of the vertical transverse cross-section upper surface at all positions from a point at most 20 mm away from the lowest point to the adjacent side wall is at least 33 degrees.

4. The building block of any preceding claim, in which the vertical transverse cross-section upper surface comprises respective straight portions sloping downwardly and inwardly from the side walls towards the centre of the block.

5. The building block of claim 4, in which the vertical transverse cross-section upper surface comprises a central smoothly curved portion joining the respective upper surface straight portions, and opposed outer smoothly curved portions joining the upper surface straight portions to respective straight portions of the inner surfaces of the side walls.

6. The building block of claim 5, in which the central smoothly curved portion is arcuate, with a radius of between 5 and 15 mm inclusive.

7. The building block of claim 5, in which the radius of the central smoothly curved portion is 10 mm.

8. The building block of any preceding claim, in which the outer smoothly curved portions are arcuate, with a radius of between 7 and 17 mm inclusive.

9. The building block of claim 8, in which the outer smoothly curved portions have a radius of 12 mm.

10. The building block of any preceding claim, in which the vertical transverse cross-section’s side walls comprise a straight inner surface.

11. The building block of claim 10, in which the straight inner surface tapers inwardly and downwardly by between 3 and 10 mm.

12. The building block of claim 10, in which the straight inner surface tapers inwardly and downwardly by 4 mm, 6 mm or 8 mm.

13. The building block of any preceding claim, in which the minimum thickness of the vertical transverse cross-section’s side walls is between 30 and 44 mm inclusive.

14. The building block of any preceding claim, in which the block has a width of between 170 and 235 mm inclusive.

15. The building block of claim 14, in which the block has a width of 190 mm or 215 mm.

16. The building block of any preceding claim, in which the block has a height of 200 to 230 mm inclusive.

17. The building block of claim 16, in which the block has a height of 215 mm.

18. The building block of any preceding claim, in which the block has a length of 415 to 465 mm inclusive.

19. The building block of claim 18, in which the block has a length of 440 mm.

20. A building block formable by moulding and comprising a vertical transverse cross-section of U-shaped profile thereby to define a base portion up to 160 mm wide, and a pair of opposed side walls; an upper surface of the vertical transverse cross-section sloping inwardly and downwardly from each side wall to a lowest point, and wherein the slope of this upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall is of at least 35 degrees relative to the bottom surface at the base of the block and wherein the minimum thickness of the base of the block is greater than or equal to 35 mm.

21. The building block of claim 20, in which the slope of the vertical transverse cross-section upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall is between 35 and 65 degrees relative to the bottom surface at the base of the block.

22. The building block of claim 21, in which the slope of the vertical transverse cross-section upper surface at all positions from a point at most 10 mm away from the lowest point to the adjacent side wall is 40 degrees or 57 degrees.

23. The building block of any of claims 20-22, in which the vertical transverse cross-section upper surface comprises respective straight portions sloping downwardly and inwardly from the side walls towards the centre of the block.

24. The building block of claim 23, in which the vertical transverse cross-section upper surface may comprise a central smoothly curved portion joining the two straight portions, and opposed outer smoothly curved portions joining the sloping portions to respective straight portions of the inner surfaces of the side walls.

25. The building block of claim 24, in which the central and outer smoothly curved portions are arcuate, with a radius of between 5 and 15 mm inclusive.

26. The building block of claim 24, in which the radii of the central and outer smoothly curved portions are 10 mm.

27. The building block of any of claims 20-26, in which the vertical transverse cross-section’s side walls comprise a straight inner surface.

28. The building block of claim 27, in which the straight inner surface slopes inwardly and downwardly by between 3 and 10 mm.

29. The building block of claim 20, in which the straight inner surface slopes inwardly and downwardly by 4 mm, 6 mm or 8 mm.

30. The building block of any preceding claim, in which the minimum thickness of the side walls is between 20 mm and 35 mm inclusive.

31. The building block of claim 30, in which the minimum thickness of the side walls is 25 mm or 30 mm.

32. The building block of any of claims 20-31, in which the block has a width of 85 mm up to 160 mm.

33. The building block of claim 32, in which in which the block has a width of 100 mm or 140 mm.

34. The building block of any of claims 20-34, in which the block has a height of 200 to 230 mm inclusive.

35. The building block of claim 34, in which the block has a height of 215 mm.

36. The building block of any of claims 20-35, in which the block has a length of 415 to 465 mm inclusive.

37. The building block of claim 36, in which the block has a length of 440 mm.

38. The building block of any preceding claim, in which the base of the block is provided with a thinned region forming a knockout which may be removed to form through-going hole, the hole being of such a diameter that it is confined to the base of the block without affecting the sides of the block.