GB2379679A

GB2379679A - Building block with arcuate - cornered cavities

Info

Publication number: GB2379679A
Application number: GB0221458A
Authority: GB
Inventors: John Fifield
Original assignee: Forticrete Ltd
Current assignee: Forticrete Ltd
Priority date: 2001-09-14
Filing date: 2002-09-16
Publication date: 2003-03-19
Also published as: GB0122298D0; GB0221458D0

Abstract

A cementitious building block has at least one cavity 16 defined by walls having opposite arcuate corners 22, and at least one cavity wall 18,19, has a thickness which is greater between than at corners 22. As shown, wall 20 may be arcuate, but it could be flattened near mid point 23 (Fig 6, not shown) or be constituted by two angularly disposed walls meeting at point 23 (Fig 7, not shown), or end wall 7 could be shaped like wall 18 (Fig 8, not shown).

Description

CEMENTITIOUS PRODUCTS This invention relates to cementitious building block products, more particularly but not exclusively for use in, and for, the building, construction and civil and structural engineering industries.

Cementitious products, such as masonry, paving, paving flags, paviours, flagstones, blocks, bricks, tiles, slates, posts, lintels, sills, slabs and panels and claddings and linings for walls, ceilings, roofs and floors have been made for many years by pressing or moulding processes. Hereinafter such pressing or moulding processes will be generically referred to for convenience as"pressing". Cementitious products are typically made of a cementitious mix of water, cement, sand, aggregate, filler, etc. , with or without a colouring pigment. Instead of pigment, the aggregate itself may provide colour to the cementitious product.

A typical pressing process involves the use of what is commonly known as a static block making machine. Pallets made from metal or wood or plastics are fed by a conveying means into the block making machine which comprises a mould, a cementitious mix (concrete) filling means, one or more compacting devices, optional vibration devices, a stripping device, and an outgoing conveying means.

The pallet, which forms the profile of one side of the block, is located under the mould in the machine.

The mould comprises one or more side walls each defining a side of the desired block, and preferably the compacting and stripping device forms the final side of the block. Once the pallet has been located, the mould is lowered on to the pallet and held in frictional contact to define a mould cavity comprising the upper surface of the pallet, and the surfaces of the side walls of the mould.

The mould cavity is then filled with a cementitious mix (concrete) of the desired composition optionally using vibration or other levelling means to achieve a desired profile of concrete. A compacting head, which preferably will also be used for stripping, is then lowered on to the upper surface of the concrete in the mould cavity and the concrete is compacted by the force exerted by the compacting head, such force being direct pressure and/or vibration.

The compacting forces are stopped and the mould is then raised from the pallet with both the pallet and the compacting head, now acting as a stripping device, being held in stationary alignment. When the mould has been raised clear of the green concrete block the compacting/stripping head is also raised clear of the green concrete. The formed green block of cementitious mixture (concrete) is then conveyed out of the block making machine on the pallet on which it was formed.

The formed green concrete block on its pallet is conveyed into an area where it is allowed to cure to a hardened state. Having cured to a sufficiently hardened strength the block is then conveyed on the pallet to a depalleting station. The depallated block is then optionally transported to another secondary processing area where it is subjected to the action of secondary processing apparatus such as a grinder, shotblasting machine, bush hammer, chain flailer or the like and thence into an area where it is packaged for delivery. In some cases the depalleted blocks are put into yard storage for a period of time before returning to a secondary processing area The pallet is conveyed back into the block making machine and the making cycle restarts.

Concrete building blocks made in this way may be either solid as shown by the building block A in Figure 1 of the accompanying drawings, or may have cavities 6 as shown by the building block B in Figures 2 and 3 of the accompanying drawings. The building block B of Figures 2 and 3 is of similar external dimensions to the block A of Figure I and the cavities 6 have a shape that is the accepted norm with the cavities having, or being defined by, walls that are of substantially uniform thickness.

These cavities 6 may pass through the entire block B such that top and bottom faces 4,5 are both open or the cavities 6 may only penetrate partially into the block B such that the top face 4 is open and the bottom face 5 closed or vice versa.

Building blocks having cavity walls of non-uniform thickness are also known in the prior art. GB 162726 discloses a building block which possesses a cavity of double undercut type (see Figure 2), whereby two oppositely facing cavity walls reach their maximum thickness at around their midlength forming angular protrusions into the cavity.

Hollow building blocks are also known from EP 0276447, which discloses a hollow clay building block formed by extrusion having an indentation on one or more exterior sides which serves as a gripping aid.

Applicant has found that there are problems associated with concrete building blocks such as B having cavities 6 and in particular that they suffer from high levels of damage when subjected to secondary processing such as grinding, shotblasting, bush hammering, chain flailing and the like when compared with solid blocks. Furthermore when installed in a wall and subjected to intermittent wetting and drying, blocks B with cavities 6 have a tendency to both wet and dry non uniformly giving temporarily a patchy appearance. The building block disclosed in GB 162726 also lacks strength, since the comers of its central cavity are angular in character and, as such, provide natural break points which are prone to fracture lines.

With a view to overcoming these problems applicant has experimented with changing the shape of the cavities within the blocks.

Accordingly and from one aspect, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls, characterised in that the walls have oppositely facing arcuate comers and in that at least one cavity wall has a thickness that is greater between, than at, the oppositely facing arcuate comers of that wall.

Expressed in another way, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls, characterised in that at least one cavity wall is of non-uniform thickness and increases to a maximum thickness at around the mid-length of that wall.

From another aspect, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls having oppositely facing ends, characterised in that at least one cavity wall has a thickness that is greater between, than at, the oppositely facing ends of that wall.

From a still further aspect, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls having oppositely facing ends, characterised in that the distance of the mid point between the ends of the at least one cavity wall and one face of the block presented by that wall is greater than the distance between the ends of that cavity wall and the said one face of the block.

Expressed in yet anther way, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls having oppositely facing ends, characterised in that at least one cavity wall has a thickness at its mid point that is greater than wall thickness at its oppositely facing ends.

By means of the invention it has been possible to prevent or at least significantly reduce the damage caused by secondary processing, together with the occurrence of fractures at cavity wall corners, and, surprisingly, to reduce the visual patchiness of the blocks during intermittent wetting and drying.

Accordingly, the present invention also comprehends a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls, characterised in that at least one cavity wall is of non-uniform thickness such that visual patchiness of the blocks during intermittent wetting and drying is at least substantially reduced.

From a still further aspect, the present invention resides in a building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls, characterised in that at least one cavity wall is of non-uniform thickness such that the likelihood of any damage being caused by secondary processing is at least substantially reduced.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which :- Figure I is a perspective view of a known solid concrete building block ; Figure 2 is a perspective view of a known concrete building block having cavities with a shape that is the accepted norm ; Figure 3 is a top plan view of the building block of Figure 2; Figure 4 is a perspective view of a concrete building block according to one embodiment of the present invention and having cavities with one shape; Figure 5 is a top plan view of the building block of Figure 4; Figure 6 is a top plan view of a concrete building block according to another embodiment of the invention and having cavities with an alternative shape to that shown in Figures 4 and 5; Figure 7 is a top plan view of a concrete building block according to a further embodiment of the invention and having cavities with another alternative shape to that shown in Figures 5 and 6; and Figure 8 is a top plan view of a concrete building block according to a still further embodiment of the invention and having cavities with a shape that benefits both the front and side faces of the block.

Referring to Figure 1 of the drawings, the solid block A has a front face 1, a rear face 2, side faces 3, a top face 4, and a bottom face 5. The distance between the front and rear faces 1,2 is normally in excess of 90mm and is therefore sufficiently strong to withstand the forces applied by secondary processing means such as grinding, shotblasting, bush hammering, chain flailing and the like. The block being of substantially uniform consistency is not subject to the uneven wetting and drying in situ that leads to a patchy visual appearance.

The block B shown in Figures 2 and 3 of the drawings also has a front face 1, a rear face 2, side faces 3, a top face 4, and a bottom face 5. As previously mentioned, this block B also has cavities 6. The inclusion of the cavities 6 creates connecting webs or walls 7 between the front face I and the rear face 2 of the block and face shells or walls 8 and 9 between the front face 1 and the cavities 6 and the rear face 2 and the cavities 6. It is the norm that the cavities in these building blocks B are substantially rectangular in plan view with front and rear straight faces 10 and side straight faces 11 and with the connecting comers or ends 12 rounded to improve the ease of production. This design determines that the thickness of the face shells 8 and 9 between the face I of the block B and a cavity 6 in the region of the comers 12 of the cavity 6 and the mid point 13 of the face 10 of the cavity is approximately equal. Expressed in another way, the cavity walls are of substantially uniform thickness. What applicant has found is that when subjected to secondary processing means such as grinding, shotblasting, bush hammering, chain flailing and the like there is a tendency for the block B to rupture in the region of the face shell 8 or 9 and approximately at the mid point 13 of the said face shell. Furthermore applicant has noticed that when subjected to intermittent wetting and drying in situ the area of the exposed front face 1 in contact with the connecting webs 7 tend to behave dissimilarly to the areas in contact with the face shells 8 and this causes a patchy visual appearance until the block B is either fully wet or completely dry. The faults with this block design can be reduced by thickening all of the face shell areas 8 but this decreases the reduction in weight that was the original purpose of having the cavities.

Turning now to Figures 4 and 5, a building block C has cavities 16 that are of similar volume to that of the cavities 6 shown in Figures 2 and 3. However, the shape of each of the cavities 16 is different from that of cavities 6 in that the front and rear sides 20 are no longer straight but are of inwardly shaped or directed form and in that the connecting comers 22 are no longer angular but are arcuate in shape. The inwardly shaped form is such that the distance between the arcuate comer 22 of the cavity 16 and the front face 1 of the block in figures 4 and 5 is less than the distance between the comer 12 of the cavity 6 and the front face 1 of the block in figures 2 and 3 and at the same time the distance between the mid point 23 of the front face 20 of the cavity 16 and the front face 1 of the block in Figures 4 and 5 is

greater than the distance between the mid point 13 of the front face 10 of the cavity 6 and the front face 1 of the block in Figures 2 and 3. By adopting this design of cavity, applicant has found that the damage caused by secondary processing means such as grinding, shotblasting, bush hammering, chain flailing and the like is significantly reduced or eliminated, as are the fracture lines normally associated with cavity comers. More surprisingly, applicant has found that the patchiness caused by intermittent wetting and drying in situ is also significantly reduced.

The shape of the front and rear sides 20 of the cavity 16 shown in Figure 5 are of arcurate (convex) form but other configurations are possible within the scope of the invention. By way of example Figures 6 and 7 show two further examples of the front and rear sides 20 of the cavities 16 wherein each are still of inwardly shaped form in blocks D and E respectively, with both cavities 16 possessing arcuate comers 22.

The invention has been described with reference to solving problems of the front and rear faces of blocks containing cavities but is not limited to these faces only. Figure 8 shows a block F designed to be used at either an end or corner detail wherein the side face 3 is visible in situ. In this case the end face 3 will also need to withstand secondary processing means such as grinding, shotblasting, bush hammering, chain flailing and the like and is provided with an inwardly facing cavity with side 31, comers 32 and mid point 33. Again, block F is strengthened by having arcuate comers 22.

The invention has been described with a block design containing two cavities but is equally applicable to blocks with either a single cavity or more than two cavities. Applicants have discovered that the patchiness due to intermittent wetting and drying can be virtually eliminated by the inclusion of between four and eight cavities according to the invention in a single block.

Claims

CLAIMS 1. A building block that is made from a cementitious material such as concrete and which has at least one cavity defined by walls, characterised in that the walls have oppositely facing arcuate comers and in that at least one cavity wall has a thickness that is greater between, than at, the oppositely facing arcuate comers of that wall.
2. A building block as claimed in claim 1, characterised in that the at least one cavity wall is of arcuate shape.
3. A building block substantially as hereinbefore described with reference to Figures
4 and
5 of the accompanying drawings 4. A building block substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings 5. A building block substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.
6. A building block substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.