GB2255117A

GB2255117A - Building block

Info

Publication number: GB2255117A
Application number: GB9208644A
Authority: GB
Inventors: R F Tattersall; R Clifton
Original assignee: Hepworth Building Products Ltd
Current assignee: Hepworth Building Products Ltd
Priority date: 1991-04-22
Filing date: 1992-04-22
Publication date: 1992-10-28
Anticipated expiration: 2012-04-22
Also published as: GB9108592D0; GB9208644D0; GB2255117B

Abstract

A building block 2 comprises a perforated body 4 of which 50-70% of the cross sectional area is perforated and the overall compressive strength of the block is at least 2.8 N/mm<2>. A plurality of perforations 8 disposed immediately adjacent its surface reduce the transmission of moisture into the block 2. A building block 2 comprises a channel 8 or channels 8 located just beneath the surface of the block. At least a wall of channel 8 is formed by a web 10 which can be removed to expose the channel 8. Service pipes or cables can be located within the channel, once it has been exposed. The block is made by adding combustible material eg. sawdust, to the block mixture, which leaves voids in the block structure after firing. The combustible material represents at least 38% of the pre-fired volume of the mixture. Regions 6 may be filled with heat insulating material, eg. expanded polystyrene. <IMAGE>

Description

BUILDING BLOCK The present invention relates to a building block. The invention relates particularly but not exclusively to a building block for use in the inner leaf of a cavity wall.

Conventional blocks for use in the inner leaves of cavity walls may be divided into two main categories.

The first category consists of blocks made from lightweight aerated concrete. These blocks are solid and in general have a relatively low thermal conductivity; however many also have a relatively low compressive strength.

The second category consists of concrete-based blocks made from mixtures of cement and various types of aggregate. These blocks suffer a higher thermal conductivity than the first category of blocks but may have any of a range of compressive strengths. They are in general solid, but some are perforated and the perforations are filled with an ins ul ant having a very low thermal conductivity. However, although the filled perforations reduce conductivity of the block, the compressive strength of the block is inversely proportional to amount of perforation.

When such conventional blocks are used, the insulative qualities of an inner leaf can, therefore, only be improved at the expense of a reduction in compressive strength, and vice versa. The blocks do not, in themselves, provide high compressive strength and low conductivity at the same time.

Furthermore, both known types of block have a construction which tends to generate two further problems. Firstly, the blocks are heavy due to the materials used. Secondly, water tends to easily penetrate the blocks, and this leads to an increase in thermal conductivity.

The present invention sets out to provide a relatively light block which has a relatively low thermal conductivity but also has a relatively high compressive strength. Furthermore the invention sets out to provide a block which has a relatively high resistance to water penetration.

According to a first aspect of the invention there is provided a building block comprising a perforated body; wherein a relatively high proportion of the cross sectional area of the said block is perforated and the overall compressive strength of the said block is relatively high for such a highly perforated block.

In a preferred embodiment of the first aspect of the invention the block body is made of clay and the cross sectional area of the perforation of the said block is not less than 50%, preferably not less than 58%, preferably not more than 65% or 70% of the total cross sectional area of the said block, and the overall compressive strength of the said block is at least 2. 8 2 N/mm2. Preferably, the overall compressive strength 2 of the block is 7 N/mm2 or more.

In a preferred embodiment, a portion, preferably in the range of 75% to 80%, of the perforation of the block is formed by columns which are filled with a material having a thermal conductivity in the range of preferably not more than 0.035, 0.025 - 0.040 W/mR, and the overall thermal conductivity of the block is in the range of 0.055 - 0.085 W/mR. Preferably the filled columns are in an inner or central region of the thickness of the block.

According to a second aspect of the invention there is provided a method of manufacturing a building block comprising the steps of: (i) mixing clay with sawdust or some other combustible substance to form an admixture of which said sawdust or other combustible substance represents at least 30% of the volume; (ii) firing a mass formed from the admixture of step (i) in such a manner that the said sawdust or other combustible material undergoes a combustive process to leave pockets in the said clay.

In a preferred embodiment the resultant fired material has a bulk density in the range of 1450 - 1650 kg/m.

According to a third aspect of the invention there is provided a building block comprising a plurality of perforations disposed immediately adjacent the surface thereof, the said perforations being so arranged that they serve to substantially reduce the transmission of moisture into the body of the said block.

When constructing a cavity wall, it is often necessary to provide service pipes and cables. When fitted, the pipes and cables project from the surface of the blocks. This is often undesirable. Using the above conventional blocks, the only way in which this particular problem can be overcome is by locating the pipes or cables within the bodies of the blocks. This requires time-consuming work because it is necessary to provide suitable recesses in the blocks. Furthermore, such recesses can interfere with any insulant-filled perforations which might be disposed in a block.

The present invention sets out to provide a building block which can readily accommodate pipes, service cables and the like without substantially affecting any insulating portions of the block.

According to a fourth aspect of the invention there is provided a building block comprising at least one enclosed channel disposed in a surface portion of the said block, at least one wall of said channel being formed by a web portion, which web portion forms an outer surface of the said block and can be selectively removed to expose the said channel.

In a preferred embodiment of the invention, the block comprises a plurality of channels, and the degree of perforation of the cross-section of the block provided by the said channels is in the range of 20% to 25% of the total perforation of the cross-section of the block.

The invention will now be further described by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a building block embodying several aspects of the invention; and Figure 2 is a plan view of the building block shown in Figure 1.

The main structure of the building block 2 shown in Figures 1 and 2 is generally defined by a clay body 4.

The body consists of outer webbing 10, which defines two parallel end faces 16 and two parallel side faces 18 of the block; and inner webbing 12, which defines a number of channels 8 and columns 6 within the block. The columns 6 and the channels 8 are specific types of perforation, which will be described in more detail below.

All of the webbing extends from a top face 14 of the block 2 to a bottom face 20 of the building block 2.

The columns 6 and channels 8 defined by the webbing are all parallel and extend from the top face 14 to the bottom face 20. A cross-section, taken parallel to the top face and anywhere between the top face and the bottom face, will therefore be identical to the top face.

The thickness of the webbing is such that it defines 40% of the area of the cross section, with the remaining 60% being made up by the perforations, namely the columns 6 and channels 8 taken together.

The columns 6 serve to reduce the thermal conductivity of the block and are filled with expanded polystyrene, which has a conductivity in the range of 0. 025-0. 035 W/m K The channels 8 serve three purposes. Firstly, they provide means for housing cables, service pipes and the like within the body of the block; secondly, they reduce the volume of the block through which water can possibly travel, thus reducing the overall permeability of the block. Any water absorbed by the block must therefore take a relatively long path through the webbing.

Thirdly, like the columns 6 they serve to reduce the overall thermal conductivity of the block.

In order to serve these three purposes effectively the channels are located in surface portions of the block, immediately behind that outer webbing which forms the side faces 18. Each channel has four walls, and one of these walls is provided by a respective portion of the outer webbing. In order to house a pipe, for example, within a block, a suitable portion of the outer webbing is first removed, which leaves the channel(s) lying directly beneath exposed. The pipe can then be accommodated within the channel(s) so as not to project from the surface of the block.

A number of parallel grooves 22 are disposed in the surface of the block. Each groove is disposed along a line midway between junctions of a portion of inner webbing with the outer webbing. Because a groove is located in the centre of the portion of outer webbing covering each respective channel, the grooves help a workman to locate the position of the channels, which are hidden beneath the surface of the block until the appropriate part of the outer webbing is broken open.

Furthermore, the grooves serve to provide fracture lines for facilitating the removal of selected parts of the outer webbing to expose a channel or channels.

The geometrical arrangement of the inner webs and the perforations affords strength, whilst ensuring that any absorbed water must take a particularly devious path to penetrate the innermost regions of the block. This geometrical arrangement will now be described in more detail.

The top face of the block, shown in plan in figure 2, is generally rectangular, with its perimiter being described by the outer webbing 10, which is of generally constant thickness. The outer surface of the block is interrupted by the grooves 22, which are located at regular intervals around the perimeter of the block.

Grooves on opposed faces of the block correspond in position.

The inner webbing 12 extends inwardly and perpendicularly of the inner surface of the outer webbing 10. The inner webbing 12 is defined by twenty one inner web portions.

Three longitudinal inner web portions extend from the inner surface of the outer webbing 10 at one end face 16 of the block 2, to the inner surface of the outer webbing 10 at the other end face 16 of the block 2.

These three longitudinal inner web portions extend parallel to the side faces 18 of the block, and divide the perforations in the block into four discrete rows.

One of the longitudinal web portions is central and extends equidstantly between the two side faces 18, the remaining two longitudinal inner web portions are transversely offset and are positioned between the central lonitudinal inner web portion and a respective side face 18, and are each approximately twice as far from the central longitudinal inner web portion as from the respective side face 18. The rows of perforations between the central longitudinal inner web portion and each of the offset longitudinal inner web portions form the columns 6. The rows of perforations between the side faces and the offset longitudinal inner web portions form the channels 8.

Nine transverse inner web portions extend inwardly from the inner surface of the outer webbing 10 at each side of the block, and thus define the boundaries between adjacent perforations within any particular one of the two rows nearest that side from which they extend. All of the transverse web portions extend at least as far as the offset longitudinal web portion which is closest to the side from which they extend. Alternate transverse web portions extending from a particular side extend beyond the closest offset longitudinal web portion to the central longitudinal web portion. Transverse inner web portions extending from opposite faces of the block do not meet at a mutual node with the central longitudinal inner web, but are longitudinally offset with respect to each other. Thus, heat being conducted by the inner webbing from one side face to the other must take a zig-zag route.Furthermore, because the channels 8 are all disposed adjacent the side faces 18 of the block, water can only be absorbed by means of the inner webbing.

It will be seen from figure 2 that the arrangement is such that the longitudinal width of the channels is half that of the perforations.

The manufacture of the block will now be described.

Firstly, clay is extracted from a quarry and ground to a desired maximum particle size. The clay is then mixed with sawdust. In the case of the present block 2 the sawdust forms 40% of the mixture. The mixture is then mixed with water, and air is removed from the mixture.

The resulting mixture is then extruded to form block bodies. Once a block body 4 has been thus formed, it is dried and fired in a conventional manner. During this process, the sawdust undergoes combustion and leaves air pockets in the block body. After the block body 4 has been fired, a measured quantity of partially expanded polystyrene beads are placed in the columns 6. Steam is then injected to the columns, which has the effect of curing the polystyrene into a solid mass.

The volume of sawdust added to the clay prior to firing causes the fired clay body to be very light and have a low overall thermal conductivity. Because air is removed from the mixture during mixing, it is possible to accurately control the air content of the fired block by varying the proportion of sawdust added. This, in combination with the structure and relative proportions of the webs and the filled perforations and the channels, means that the filled fired block can be made to have a resultant effective thermal conductivity of between 0.08-0.09 W/mOK. The compressive strength of the fired filled block is at least 7N/m2.

Furthermore, due to the position of the channels within the block body, water cannot penetrate the block through the side faces 18 of the block, but can only penetrate the block body by means of the webs.

In one example, a cavity wall comprises a water brick leaf, an air gap of 50mm, an inner block leaf, and a layer of plaster of 13mm thickness. The inner block leaf is constructed of blocks according to the invention and having a thickness, from side face to side face, of 2 125mm. The wall has a U - value of 0. 45 W/m2K.

Many modifications of the present invention, of which the foregoing embodiment is merely an example, will suggest themselves to the skilled reader upon making reference to the foregoing description. In particular, the expanded polystyrene could be replaced by a suitable alternative ins ul ant such as foamed polyurethane or urea formaldehyde. Furthermore, many other arrangements of the channels and perforations could be successfully used.

Claims

Claims.

1. A building block comprising a perforated body comprising upper and lower faces, front and rear faces and two respective side faces, wherein from 50% to 70% of the cross sectional area of the body is perforated and the overall compressive strength of the block is at least 2. 8 N/mm2.

2. A building block according to claim 1, wherein 58% or more of the cross sectional area of the block body is perforated.

3. A building block according to claim 1, wherein 65% or less of the cross sectional area of the block body is perforated.

4. A building block according to any preceding claim, wherein the overall compressive strength of the block is 2 7 N/mm2 or more.

5. A building block according to any preceding claim, wherein from 75% to 80% of the perforation of the block is formed by channels filled with insulating material, the said channels extending from the upper face of the block to the lower face of the block.

6. A building block according to claim 5, wherein the said channels are filled with a material having a thermal conductivity from 0.025 W/m K to 0.04 W/m-R.

7. A building block according to any preceding claim, wherein the body of the block has an overall thermal conductivity form 0.055 W/m*R to 0.085 W/mK.

8. A building block according to any preceding claim, wherein the block body is made from clay.

9. A building block according to any one of claims 5 to 8, wherein the said channels are located in a region separated from the front and rear faces of the block body.

10. A building block comprising a block body comprising front and rear faces, upper and lower faces and two respective side faces, wherein the body comprises a plurality of internal perforations disposed immediately adjacent a front, rear or side face thereof, the said perforations being so arranged that they serve to substantially reduce the transmission of moisture into the body of the said block via the said face.

11. A building block according to claim 10, wherein the said perforations are defined by a plurality of elongate channels.

12. A building block comprising at least one enclosed channel disposed in a surface portion of the said block, at least one wall of the said channel being formed by a web portion, which web portion forms at least part of an outer surface of the said block and can be removed to expose the said channel.

13. A building block according to claim 12, comprising a row of discrete enclosed channels located in a surface portion of the said block, at least one wall of each channel being formed by a web portion, which web portion forms part of an outer surface of the said block, the said web portions being selectively removable to expose one or more of the said channels, thereby providing one or more recessed portions in the surface portion of the said block.

14. A building block according to claim 12 or 13 wherein the said outer surface comprises one or more grooves, the or each groove being located in the outer surface of a respective one or more of the said web portions, for facilitating removal of the said web portion or portions, in order to expose a respective one or more of the said channels located therebehind.

15. A building block substantially as herein described with reference to the accompanying drawings.

16. A method of manufacturing a building block comprising the steps of: (i) mixing clay with sawdust or some other combustible substance to form an admixture of which the said sawdust or other combustible substance represents at least 30% of the volume; and (ii) firing a mass formed from the admixture of step (i) in such a manner that the said sawdust or other combustible material undergoes a combustive process to leave pockets in the said clay.

17. A building block manufactured in accordance with the method of claim 16, in which the fired material has a bulk density of from 1450 kg/m to 1650 kg/m.

18. A method of manufacturing a building block substantially as herein described.